WO2011001641A1

WO2011001641A1 - Optical element

Info

Publication number: WO2011001641A1
Application number: PCT/JP2010/004207
Authority: WO
Inventors: 藤村佳代子; 岡田真
Original assignee: ナルックス株式会社
Priority date: 2009-06-29
Filing date: 2010-06-24
Publication date: 2011-01-06
Also published as: JPWO2011001459A1; JPWO2011001641A1; KR101129902B1; WO2011001459A1; KR20110116258A; JP4491555B1

Abstract

In the disclosed optical element, first belt regions (A regions), with grating protrusions (1103) disposed thereupon with a first period, and second band regions (B regions), which have no grating protrusions, are arranged at a second period on a substrate (1101). The first period is of a size such that light cannot diffract, and the second period is of a size such that light diffracts. Provided on the A and B regions is a first film that has a refraction index higher than that of the material constituting the aforementioned grating protrusions. In the optical element, the polarization state, the first period, the duty ratio of the A regions, the height and the refraction index of the grating protrusions, the refraction index of the first film, and the film thicknesses of the A and B regions are set such that the differences between a first ratio, being the ratio of the amount of first-order diffracted light and the amount of zero-order diffracted light generated by the A and B regions, and a first and a second target value do not exceed prescribed values for light of a first and second wavelength; and such that the greatest height from the substrate surface is less than or equal to the larger of the first and second wavelengths.

Description

[Name of invention determined by ISA based on Rule 37.2] Optical element

The present invention relates to an optical element that diffracts a plurality of types of light in a desired diffraction state.

For example, optical elements that diffract a plurality of types of light in a desired diffraction state, such as light having a wavelength for CD and light having a wavelength for DVD, have been developed. For example, Patent Document 1 discloses an optical element using two types of gratings including a subwavelength grating structure. However, such an optical element has a complicated structure, takes time for manufacturing, and is expensive. Further, it has been difficult to improve the diffraction efficiency of a diffractive optical element that diffracts a plurality of types of light in a desired diffraction state without using a complicated structure.

On the other hand, an optical element has been developed that diffracts one of light of different wavelengths, such as light of a wavelength for CD and light of a wavelength for DVD, and does not diffract the other. As an example, Patent Document 2 discloses an optical element using an optically isotropic material and an optically anisotropic material. However, such an optical element has a problem that the material cost of the optically anisotropic substance is high and a substrate for holding both sides of the diffractive structure is required. Patent Document 3 discloses an optical element that uses a sub-wavelength grating, which is a grating having a period equal to or shorter than the wavelength to be used. An optical element using such a subwavelength grating can be manufactured using, for example, plastic, and thus has an advantage of low material cost. Furthermore, by adjusting the shape of the sub-wavelength grating, it is possible to freely set characteristics including the effective refractive index of the sub-wavelength grating region. However, as will be described in detail later, in order not to diffract the light, it is necessary to make the optical path length difference between the grating convex part and the grating concave part of the sub-wavelength grating an integral multiple of the wavelength of the light passing through, It is necessary to increase the aspect ratio of the sub-wavelength grating, which is the ratio of the grating height to the grating period. Therefore, it is difficult to manufacture an optical element having such a subwavelength grating.

JP 2008-257771 A JP 2005-141849 A JP 2008-257771 A

Therefore, there is a need for an optical element that diffracts a plurality of types of light in a desired diffraction state and has an easy-to-manufacture structure and high diffraction efficiency.

An optical element using a sub-wavelength grating that does not generate diffraction with respect to light in the first polarization state and generates diffraction with respect to light in the second polarization state. There is a need for optical elements that are relatively small in ratio and easy to manufacture.

The optical element according to the first aspect of the present invention includes a first belt-like region in which lattice convex portions are arranged in a first cycle and a second belt-like region in which no lattice convex portions are provided on the substrate in a second cycle. The first period is such that the used light cannot cause diffraction, and the second period is such that the used light can cause diffraction. A first film having a refractive index higher than the refractive index of the material of the grating convex portion is provided on the region and the second belt-shaped region. In the optical element according to this aspect, the first and second wavelength light is a ratio of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light generated by the first and second band-shaped regions. The difference between the ratio and the first and second target values is set to a predetermined value or less, and the height from the substrate surface is set to be equal to or less than the larger one of the first and second wavelengths. A polarization state of light having a wavelength of 2; a first period; a duty ratio that is a ratio of the lattice convex portion to a space of the height of the lattice convex portion of the first band-shaped region; The height, the refractive index of the material of the lattice convex portion, the refractive index of the first film, the thickness of the lattice convex portion of the first strip region, the thickness of the concave portion of the first strip region, and the The film thickness of the second strip region is determined.

According to the optical element of this aspect, the first film having a refractive index higher than the refractive index of the material of the grating convex portions on the first band-shaped region provided with the sub-wavelength grating and the flat second band-shaped region. By providing, an optical element with high diffraction efficiency that can diffract light of the first and second wavelengths to a desired state with a structure that is easy to manufacture can be obtained. Here, a structure that is easy to manufacture is, for example, a manufacturing method that uses plastic injection molding, which impedes the achievement of theoretical optical performance such as mold shape accuracy and mold-to-product transferability. A structure that does not cause any problems.

According to an embodiment of the present invention, the first and second target values are equal.

According to this embodiment, an optical element having high diffraction efficiency that diffracts light of two different wavelengths in the same manner can be obtained.

According to an embodiment of the present invention, a step is provided between the substrate surface of the first belt-like region and the substrate surface of the second belt-like region, and the light of the first and second wavelengths is short. The first ratio of the light having the longer wavelength is configured to be smaller than the first ratio of the light having the longer wavelength.

According to the present embodiment, the first ratio of the light having the shorter wavelength among the light having the first and second wavelengths is configured to be smaller than the first ratio of the light having the longer wavelength. An optical element can be obtained.

According to an embodiment of the present invention, the first and second wavelengths are any of wavelengths for Blu-ray Disc (BD), Digital Versatile Disc (DVD), and Compact Disc (CD).

According to the present embodiment, an optical element having high diffraction efficiency that can be used in a device that is also used as a Blu-ray Disc (BD), a digital versatile disc (DVD), or a compact disc (CD) is obtained. .

The optical element according to the second aspect of the present invention includes a first belt-like region in which lattice convex portions are arranged in a first cycle and a second belt-like region in which no lattice convex portions are provided on the substrate in a second cycle. The first period is such that the used light cannot cause diffraction, and the second period is such that the used light can cause diffraction. A first film having a refractive index higher than the refractive index of the material of the lattice convex portion is provided on the region and the second strip region, and the substrate surface of the first strip region and the substrate of the second strip region A step is provided between the surface. In the optical element according to this aspect, the first to third wavelength light is a ratio between the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light generated by the first and second band-shaped regions. The difference between the ratio and the first to third target values is set to a predetermined value or less, and the height from the substrate surface is set to be equal to or less than the maximum wavelength of the first to third wavelengths. The polarization state of the light of the wavelength, the first period, the duty ratio that is the ratio of the lattice convex portion to the space of the height of the lattice convex portion of the first band-shaped region, the height of the lattice convex portion , The refractive index of the material of the lattice convex portion, the refractive index of the first film, the film thickness of the lattice convex portion of the first strip region, the film thickness of the concave portion of the first strip region, the second The thickness of the belt-like region and the size of the step are determined.

According to the optical element of this aspect, the first film having a refractive index higher than the refractive index of the material of the grating convex portions on the first band-shaped region provided with the sub-wavelength grating and the flat second band-shaped region. Further, by providing a step between the substrate surfaces of the first and second belt-like regions, the diffraction efficiency can diffract the light of the first to third wavelengths into a desired state with a structure that is easy to manufacture. A high optical element can be obtained. Here, a structure that is easy to manufacture is, for example, a manufacturing method that uses plastic injection molding, which impedes the achievement of theoretical optical performance such as mold shape accuracy and mold-to-product transferability. A structure that does not cause any problems.

According to an embodiment of the present invention, the first to third target values are equal.

According to this embodiment, an optical element with high diffraction efficiency that diffracts light of three different wavelengths in the same manner can be obtained.

According to the embodiment of the present invention, the first ratio of the light having the longer wavelength is the first ratio of the light having the shorter wavelength with respect to the light having the two wavelengths among the light having the first to third wavelengths. It is comprised so that it may become smaller than a ratio.

According to the present embodiment, for light of two wavelengths among the light of the first to third wavelengths, the first ratio of light of the shorter wavelength is greater than the first ratio of light of the longer wavelength. An optical element configured to be small can be obtained.

According to the embodiment of the present invention, one of the first to third target values is zero.

According to the present embodiment, it is possible to obtain an optical element that prevents any one of the first to third wavelengths of light from being diffracted as much as possible.

According to an embodiment of the present invention, the first to third wavelengths are any of wavelengths for Blu-ray Disc (BD), Digital Versatile Disc (DVD), and Compact Disc (CD).

According to this embodiment, an optical element with high diffraction efficiency that can be used in a device that is also used for a Blu-ray disc (BD), a digital versatile disc (DVD), and a compact disc (CD) is obtained.

According to an embodiment of the present invention, a second film having a refractive index lower than that of the first film is further provided on the first film.

According to this embodiment, since the first film and the second film function to reduce the reflectance as compared with the case of only the first film, an optical element with higher diffraction efficiency can be obtained.

In the optical element according to the third aspect of the present invention, the first belt-shaped region in which the lattice convex portions are arranged at the first period and the second belt-shaped region in which the lattice convex portions are not provided are arranged on the substrate in the first direction. They are arranged in the second cycle. The first period has such a magnitude that the used light cannot cause diffraction, and the second period has such a magnitude that the used light can cause diffraction. A film having a refractive index higher than the refractive index of the material of the grating convex portion is provided on the first belt-shaped region and the second belt-shaped region, and the light in the first polarization state passing through the substrate surface, The phase difference between the light passing through the first belt-like region and the light passing through the second belt-like region becomes zero and does not cause diffraction, and the second polarization state light passing through the substrate surface is the second polarization state. The height of the grating protrusions of the first period and the first band region is such that the phase difference between the light passing through the first band region and the light passing through the second band region causes diffraction. Duty ratio, which is the ratio of the grid projections to the space, the height of the grid projections, the refractive index of the material of the grid projections, the refractive index of the film, and the grid projections of the first strip region The film thickness of the part, the film thickness of the recess in the first band-like region, and the film thickness of the second band-like region are determined.

According to this aspect, the film having a refractive index higher than the refractive index of the material of the lattice convex portions is provided on the first belt-like region provided with the lattice convex portions and the second belt-like region not provided with the lattice convex portions. Thus, an optical element using a sub-wavelength grating that does not generate diffraction with respect to light in the first polarization state and generates diffraction with respect to light in the second polarization state. An optical element having a relatively small aspect ratio and easy to manufacture can be obtained.

In the optical element according to the embodiment of the present invention, the wavelength of the light in the first polarization state is different from the wavelength of the light in the second polarization state.

According to the present embodiment, an optical element that diffracts only one of two wavelengths of light can be obtained.

In the optical element according to the embodiment of the present invention, the wavelength of the light in the first polarization state and the wavelength of the light in the second polarization state are the same.

According to the present embodiment, an optical element that diffracts only one of light of one wavelength in two polarization states can be obtained.

In the optical element according to the embodiment of the present invention, the material of the lattice projections is plastic, and the material of the film is a metal oxide.

According to this embodiment, an inexpensive optical element that does not use an expensive material such as an optically anisotropic material can be obtained.

1 is a perspective view of an optical element according to one embodiment of the present invention. FIG. FIG. 2 is a cross-sectional view in the X direction perpendicular to the substrate surface of the optical element shown in FIG. 1. It is a graph which shows the relationship between a phase difference and the diffraction efficiency of the 0th-order light and primary light by a binary grating. It is a graph which shows the relationship of the ratio of phase difference, the diffraction efficiency of 1st-order light, and the diffraction efficiency of 0th-order light. It is a perspective view of the optical element by other embodiment of this invention. It is a perspective view of the optical element by other embodiment of this invention. FIG. 5B is a cross-sectional view of the optical element shown in FIG. 5A in the X direction perpendicular to the substrate surface. FIG. 5B is a cross-sectional view in the X direction perpendicular to the substrate surface of the optical element shown in FIG. 5B. 3 is a flowchart illustrating a method for designing an optical element according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of an optical element according to Example 1. FIG. 6 is a diagram illustrating a configuration of an optical element of Example 2. FIG. 6 is a diagram showing a configuration of an optical element of Comparative Example 1. FIG. 6 is a diagram illustrating a configuration of an optical element according to Example 3. FIG. 6 is a diagram illustrating a configuration of an optical element according to Example 4. FIG. 6 is a diagram illustrating an example of a configuration of an optical system including an optical element of Example 2. FIG. 6 is a diagram illustrating an example of a configuration of an optical system including an optical element of Example 2. FIG. 6 is a diagram illustrating another example of the configuration of an optical system including the optical element of Example 2. FIG. 6 is a diagram illustrating another example of the configuration of an optical system including the optical element of Example 2. FIG. It is a perspective view of the optical element by other embodiment of this invention. FIG. 18 is a cross-sectional view of the optical element shown in FIG. 17 in the X direction perpendicular to the substrate surface. FIG. 6 is a cross-sectional view in the X direction perpendicular to the substrate surface when the thickness of the optical element is different from the lattice height. It is a flowchart which shows the design method of the optical element of this embodiment. For example, it is a cross-sectional view in the X direction perpendicular to the substrate surface of a conventional optical element shown in Patent Document 2. 10 is a perspective view of an optical element according to Example 6. FIG. 10 is a diagram illustrating an example of a configuration of an optical system including an optical element of Example 5. FIG. FIG. 10 is a diagram illustrating another example of the configuration of an optical system including the optical element of Example 5. FIG. 10 is a diagram showing still another example of the configuration of an optical system including the optical element of Example 5.

First Aspect FIG. 1 is a perspective view of an optical element 1100 according to one embodiment of the first aspect of the present invention. A plurality of grid protrusions 1103 extending in the Y direction are arranged in the X direction at a first period in a first band-like region (referred to as A region in the figure) on the substrate 1101. The first period is so small that the light passing through the first band-like region cannot cause diffraction. Hereinafter, a grating composed of grating convex portions arranged at the first period is referred to as a sub-wavelength grating. On the substrate, a second belt-like region (referred to as “B” region in the figure) in which no grid convex portions are arranged is arranged adjacent to the first belt-like region. The first belt-like region and the second belt-like region are repeatedly arranged in the X direction at the second period. A lattice formed by the first strip region and the second strip region is referred to as a macro lattice. For light passing through the substrate, the first belt-like region functions as a convex portion of the macro lattice, and the second belt-like region functions as a concave portion of the macro lattice. The second period is so large that the light passing through the first band region and the second band region can cause diffraction.

FIG. 2 is a cross-sectional view of the optical element shown in FIG. 1 in the X direction perpendicular to the substrate surface. In the A region, a plurality of lattice convex portions 1103 are arranged on the substrate 1101 in the X direction at the first period. In the region B, the lattice convex portions are not arranged. A film 1105, a film 1107, and a film 1109 are provided on the lattice convex portion 1103 in the first belt-shaped region, the substrate 1101 in the lattice concave portion in the first belt-shaped region, and the substrate 1101 in the second belt-shaped region, respectively. . In FIG. 2, in order to simplify the following description, the thickness of the film is made equal to the height h1 of the lattice projection 1103. Actually, the thickness of the film may be different from the height of the grating protrusion 1103.

The space between the substrate surface and the surface at the position of the lattice height h1 parallel to the substrate surface is referred to as S1. In the A region, the lattice convex portions 1103 and the film 1107 exist at a predetermined ratio in S1. In the region B, a film 1109 exists in S1.

The space between the plane parallel to the substrate surface and the height of the grid height h1 and the plane parallel to the substrate plane and the height of the film 1105 on the grid projection 1103 (h1 + h2) is referred to as S2. In the region A, the film 1105 on the lattice projection 1103 and the surrounding medium are present at a predetermined ratio in S2. Here, since the optical element 1100 is placed in the air, the surrounding medium is air. In the region B, air exists in S2.

The refractive indices of light of a certain wavelength λ in S1 of the A region and S1 of the B region are n1A and n1B, respectively, and the refractive indexes of light of that wavelength in the S2 of the A region and S2 of the B region are respectively n2A and Let n2B. Assume that light passes through the A and B regions in a direction perpendicular to the substrate surface. In that case, the phase difference between the light passing through S1 in the A region and the light passing through S1 in the B region is

The phase difference between the light passing through S2 in the A region and the light passing through S2 in the B region

The phase difference between the light passing through S1 and S2 in the A region and the light passing through S1 and S2 in the B region (hereinafter referred to as total phase difference)

Then, the following formula is established.

Here, a predetermined wavelength is a first wavelength, and a wavelength different from the predetermined wavelength is a second wavelength. It is assumed that light of the first and second wavelengths is used for the optical element.

The first wavelength is λ1, the phase difference and the refractive index of the light of the first wavelength are indicated by (1), the second wavelength is λ2, and the phase difference and the refractive index of the light of the second wavelength. This is indicated by (2).

Then, the following expressions are derived from the expressions (1) to (3).

However, i represents 1 or 2,

It is.

Here, in order to set the total phase difference between the first and second wavelengths to a desired value, the total phase difference between the first and second wavelengths can be calculated using the equations (4) and (5).

N1A, n1B, n2A, n2B, h1 and h2 may be determined so that becomes a desired value.

Here, the refractive index n1A of S1 in the A region and the refractive index n2A of S2 in the A region are obtained. In S1 and S2 in the A region, two types of media are arranged in a lattice pattern with a period equal to or less than the wavelength. In general, the effective refractive index of a region in which two types of media are arranged in a lattice pattern with a period equal to or less than the wavelength is represented by n1 and n2, and the ratio of the volume occupied by n2 to the volume of the entire region If (duty ratio) is represented by f, it can be represented by the following equation. Here, for the sake of simplicity, it is assumed that light is incident on the substrate surface perpendicularly.
0th order approximation

Second order approximation

According to the above formula, the refractive index n1A of S1 in the A region is any value between the refractive index of the grating convex 1103 and the refractive index of the film 1107, and the refractive index n2A of S2 in the A region is , Any value between the refractive index of the film 1105 and the refractive index of air.

Therefore, the refractive index n1A of S1 in the A region can be adjusted by changing the first period, the duty ratio, and the grating height in addition to the material of the grating protrusions 1103 and the film 1107. Further, the refractive index n2A of S2 in the region A can be adjusted by changing the first period, the duty ratio, and the thickness of the film 1105 in addition to the material of the film 1105. Further, according to the equations (6) to (9), the refractive index can be greatly changed by changing the polarization state of the light.

In addition, when the layers such as S1 and S2 in the A region or the B region contain N kinds of different materials (N is an integer of 3 or more), the following zero order is used instead of the equations (6) and (7). Use approximate equations.

Here, the relationship between the phase difference and the diffraction efficiency will be described using a binary grating having a duty ratio of 0.5 as an example. The phase difference between the light passing through the grating convex portion of the binary grating and the light passing through the grating concave portion can be expressed by the following equation. Here, λ is the wavelength of light, n is the refractive index of the grating protrusion, 1 is the refractive index of the medium around the grating, and d is the height of the grating protrusion.

FIG. 3 is a graph showing the relationship between the phase difference and the diffraction efficiency of the zero-order light and the first-order light by the binary grating. The horizontal axis of the graph represents the phase difference between the light that has passed through the grating convex portions and the light that has passed through the grating concave portions. The unit is radians. The vertical axis of the graph represents the diffraction efficiency of the 0th order light and the 1st order light. Here, the diffraction efficiency is the ratio of the amount of diffracted light to the amount of incident light. When the phase difference is 0 and 2π radians, the diffraction efficiency of the first-order light is 0, and the diffraction efficiency of the 0th-order light has a maximum value of 1.0. When the phase difference is π radians, the diffraction efficiency of the first-order light is a maximum value of 0.4, and the diffraction efficiency of the zero-order light is zero.

FIG. 4 is a graph showing the relationship between the phase difference and the ratio between the diffraction efficiency of the first-order light and the diffraction efficiency of the zero-order light. Similarly to FIG. 3, the horizontal axis of the graph represents the phase difference between the light that has passed through the grating convex portions and the light that has passed through the grating concave portions. The vertical axis of the graph represents the ratio between the diffraction efficiency of primary light and the diffraction efficiency of zero-order light. The ratio between the diffraction efficiency of the first-order light and the diffraction efficiency of the zero-order light is 0 when the phase difference is 0 radians, increases as the phase difference increases, and becomes 1 when the phase difference is about 2 radians. Become. It is 1 when the phase difference is about 4.3 radians, decreases as the phase difference increases, and becomes 0 when the phase difference is 2π radians.

Thus, by changing the phase difference between the light that has passed through the grating convex portion of the binary grating and the light that has passed through the grating concave portion, the ratio between the diffraction efficiency of the first-order light and the diffraction efficiency of the zero-order light can be changed. it can. Similarly, in the optical element 1100, the ratio between the diffraction efficiency of the first-order light and the diffraction efficiency of the zero-order light is changed by changing the phase difference between the light that has passed through the A region and the light that has passed through the B region. Can do.

Second Aspect FIG. 5A is a perspective view of an optical element 2100 according to one embodiment of the second aspect of the present invention. A plurality of grid protrusions 2103 extending in the Y direction are arranged in the X direction in the first direction in a first band-like region (described as A region in the drawing) on the substrate 2101. The first period is so small that the light passing through the first band-like region cannot cause diffraction. On the substrate, a second belt-like region (referred to as “B” region in the figure) in which no grid convex portions are arranged is arranged adjacent to the first belt-like region. The A region and the B region are repeatedly arranged in the X direction at the second period. A lattice formed by the A region and the B region is referred to as a macro lattice. There is a step between the substrate surface in the A region and the substrate surface in the B region, and the substrate surface in the A region is lower than the substrate surface in the B region. That is, the substrate in the A region forms a concave portion of the macro lattice, and the substrate in the B region forms a convex portion of the macro lattice. The second period is so large that the light passing through the first band region and the second band region can cause diffraction.

FIG. 6 is a cross-sectional view of the optical element 2100 shown in FIG. 5A in the X direction perpendicular to the substrate surface. In the A region, a plurality of grating protrusions 2103 are arranged on the substrate 2101 in the X direction at the first period to form a sub-wavelength grating. In the region B, the lattice convex portions are not arranged. A film 2105, a film 2107, and a film 2109 are provided on the lattice convex portion 2103 in the A region, the substrate 2101 in the lattice concave portion in the A region, and the substrate 2111 in the B region, respectively.

The space between the substrate surface in the A region and the surface at the position of the lattice height h1 parallel to the substrate surface is referred to as S1. In the A region, the lattice convex portions 2103 and the film 2107 are present at a predetermined ratio in S1. In the region B, the convex portion 2111 of the substrate exists in S1.

The space between the surface parallel to the substrate surface and the height of the lattice height h1 and the surface parallel to the substrate surface and the height of the film 2105 on the lattice convex portion 2103 (h1 + h2) is referred to as S2. In the region A, the film 2105 on the lattice convex portion 2103 and the surrounding medium are present at a predetermined ratio in S2. Here, since the optical element 2100 is placed in the air, the surrounding medium is air. In the region B, the convex portion 2111 of the substrate exists in S2.

The space between the surface at the height (h1 + h2) parallel to the substrate surface and the surface at the height (h1 + h2 + h3) of the convex portion 2111 of the substrate parallel to the substrate surface is referred to as S3. In the A region, air exists in S3. In the region B, the convex portion 2111 of the substrate exists in S3.

A space between the surface at the height (h1 + h2 + h3) of the convex portion 2111 of the substrate parallel to the substrate surface and the surface at the height (h1 + h2 + h3 + h4) of the film 2109 on the convex portion 2111 of the substrate parallel to the substrate surface. Is referred to as S4. In the A region, air exists in S4. In the region B, the film 2109 exists in S4.

FIG. 5B is a perspective view of an optical element 3100 according to another embodiment of the second aspect of the present invention. In the optical element 3100, a plurality of grating convex portions 3103 extending in the Y direction are arranged in the X direction in the first direction in the first band-like region (A region) on the substrate 3101. The first period is so small that the light passing through the first band-like region cannot cause diffraction. On the substrate, a second belt-like region (B region) in which no grid convex portions are arranged is arranged adjacent to the first belt-like region. The A region and the B region are repeatedly arranged in the X direction at the second period. A lattice formed by the A region and the B region is referred to as a macro lattice. There is a step between the substrate surface in the A region and the substrate surface in the B region, and the substrate surface in the A region is higher than the substrate surface in the B region. That is, the substrate in the region A forms a convex portion of the macro lattice, and the substrate in the region B forms a concave portion of the macro lattice. The second period is so large that the light passing through the A region and the B region can cause diffraction.

FIG. 7 is a cross-sectional view in the X direction perpendicular to the substrate surface of the optical element 3100 shown in FIG. 5B. In the region A, a plurality of grating convex portions 3103 are arranged in the X direction at the first period on the convex portion 3111 of the substrate to form a sub-wavelength grating. In the region B, the lattice convex portions are not arranged. A film 3105, a film 3107, and a film 3109 are provided on the lattice convex portion 3103 in the A region, the substrate 3111 in the lattice concave portion in the A region, and the substrate 3101 in the B region, respectively.

The space between the substrate surface in the region B and the surface at the position of the thickness (height) h1 of the film 3109 parallel to the substrate surface is referred to as S1. In the A region, the convex portion 3111 of the substrate exists in S1. In the region B, the film 3109 exists in S1.

The space between the surface parallel to the substrate surface and at the height h1 and the surface parallel to the substrate surface and the height position (h1 + h2) of the convex portion 3111 of the substrate is referred to as S2. In the region A, the convex portion 3111 of the substrate exists in S2. In the region B, air exists in S2.

A space between a plane parallel to the substrate surface and having a height (h1 + h2) and a plane parallel to the substrate surface and the height of the film 107 of the lattice concave portion or the height of the lattice convex portion 3103 (h1 + h2 + h3) This is called S3. In the region A, the lattice convex portions 3103 and the film 3107 are present at a predetermined ratio in S3. In the region B, air exists in S3.

A space between the plane parallel to the substrate surface and the height (h1 + h2 + h3) of the lattice convex portion 3103 and the plane parallel to the substrate surface and the height of the film 3105 on the lattice convex portion 3103 (h1 + h2 + h3 + h4) is S4. Called. In the region A, the film 3105 and air are present at a predetermined ratio in S4. In the region B, air exists in S4.

In the

optical elements

2100 and 3100, the refractive indexes of light of a certain wavelength λ in S1 of the A region and S1 of the B region are n1A and n1B, respectively, and the refraction of the light of that wavelength in S2 of the A region and S2 of the B region. The refractive index is n2A and n2B, respectively, and the refractive index of light of that wavelength λ in S3 of the A region and S3 of the B region is n3A and n3B, respectively. The refractive indexes of light are n4A and n4B, respectively. Assume that light passes through the A and B regions in a direction perpendicular to the substrate surface. In that case, the phase difference between the light passing through S1 to S4 in the A region and the light passing through S1 to S4 in the B region (hereinafter referred to as total phase difference).

And

Here, the predetermined wavelength is the first wavelength, and the two wavelengths different from the predetermined wavelength are the second and third wavelengths. It is assumed that light having first to third wavelengths is used for the optical element.

Here, the first wavelength is λ1, the phase difference and refractive index of the light of the first wavelength is indicated by (1), the second wavelength is λ2, and the phase difference of the light of the second wavelength is The refractive index is indicated by (2), the third wavelength is λ3, and the phase difference and refractive index of the third wavelength light is indicated by (3).

Then, the following expressions are derived in the same manner as Expressions (4) and (5).

However, i represents any one of 1 to 3,

It is.

Here, in order to set the total phase difference of the first wavelength to a desired value, the total phase difference of the first to third wavelengths is obtained by the equations (10) to (12).

N1A, n1B, n2A, n2B, n3A, n3B, n4A, n4B, h1, h2, h3, and h4 may be determined so that becomes a desired value.

FIG. 8 is a flowchart showing a method for designing an optical element according to the first and second aspects of the present invention. It is assumed that materials such as the grating convex portions and the film of the optical element are predetermined.

In step S1010 of FIG. 8, a second period of the macro lattice is determined. Here, the second period of the macro grating is determined from the following equation so that the first-order diffracted light of the light having a predetermined wavelength generates a desired diffraction angle. Here, the predetermined wavelength may be any one of the first to third (first or second) wavelengths.

n 'sinθ'-n sinθ = Nλ / Λ (13)

n: Refractive index of the incident side medium (refractive index of air)
n ': refractive index of the output side medium (refractive index of air)
θ: incident angle θ ′: diffraction angle N: diffraction order λ: wavelength of incident light Λ: period of diffraction grating (second period)

In this embodiment, when the incident angle is zero, the diffraction angle of the first-order diffracted light is determined by the wavelength of the incident light and the second period.

In step S1020 in FIG. 8, the upper limit of the first period of the sub-wavelength grating is determined. As an example, the upper limit of the first period of the sub-wavelength grating is determined so that diffraction does not occur when Λ in Equation (13) is the first period and the exit-side medium n ′ is the refractive index of the substrate.

In step S1030 of FIG. 8, the duty ratio of the macro lattice is set. As an example, 0.5 is set as the initial value. Here, the duty ratio of the macro grating is the ratio of the width in the X direction of the area where the sub-wavelength grating is not installed (B area) to the period of the macro grating (second period).

In step S1040 of FIG. 8, the area A (sub-wavelength) necessary to obtain the first ratio (the ratio of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light) with respect to the set duty ratio of the macro grating. The phase difference between the light passing through the grating portion) and the light passing through the B region (flat portion) is obtained, and this value is set as the target value of the phase difference.

In step S1050 in FIG. 8, the polarization direction of the light of each wavelength is determined so that the target value of the phase difference of the light of each wavelength can be easily realized.

In step S1060 of FIG. 8, the film thickness, the sub-wavelength grating height, the step, and the duty ratio in the sub-wavelength grating are determined, and according to equations (4) and (5) or equations (10) to (12), for example, The phase difference of light of each wavelength is obtained by a rigorous coupled wave analysis method.

In step S1070 of FIG. 8, it is determined whether or not the difference between the phase difference of the light of each wavelength obtained in step S1060 and the target value of the phase difference is within a predetermined range. If it is within the predetermined range, the process proceeds to step S1080. If not within the predetermined range, the process returns to step S1030.

In step S1080 of FIG. 8, it is determined whether the maximum height from the substrate surface (referred to as the height of the macro grating) is equal to or less than the maximum wavelength. If it is determined that the wavelength is equal to or less than the maximum wavelength, the process is terminated. If it is not determined that the wavelength is equal to or less than the maximum wavelength, the process returns to step S1030.

Hereinafter, numerical examples of the optical element according to the present invention will be described. Numerical examples were obtained by calculation using a strict coupled wave analysis method.

Example 1
Example 1 corresponds to the embodiment shown in FIG. The first wavelength is 660 nm, and the second wavelength is 785 nm. The target value of the first ratio between the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light of the light of the first and second wavelengths is set to 0.067 ± 0.012. The optical element of Example 1 was designed according to the flowchart of FIG. 8 so that the first ratio of the light of the first and second wavelengths is the target value.

FIG. 9 is a diagram illustrating the configuration of the optical element according to the first embodiment. In this embodiment, a second film is formed on the first film. It is assumed that the refractive index of the first film is larger than the refractive indexes of the grating convex portions and the second film. The refractive index of the second film may be larger or smaller than the refractive index of the grating convex portion. As an example, the lattice convex portion is formed by injection molding a polyolefin-based resin. The first film is obtained by depositing an evaporation material made of thallium oxide (Ta ₃ O ₅ ) on the first film by an evaporation method or a sputtering method. The second film is obtained by further depositing a vapor deposition material made of silicon dioxide (SiO ₂ ) thereon by a vapor deposition method or a sputtering method.

The reason why the second film is provided on the first film is to make the reflection of incident light as small as possible and improve the diffraction efficiency.

Table 1 is a table showing dimensions of each part of the optical element of Example 1. SWS (Sub-Wavelength Structure) indicates a sub-wavelength grating portion, that is, an A region.

Here, the height of the macro lattice of Example 1 (distance from the substrate surface to the upper surface of the second film) is 306 nm as apparent from Table 1 and FIG. 9, and is below the maximum wavelength (785 nm). is there.

Table 2 is a table showing the refractive index of each part of the optical element of Example 1. The light having the first wavelength and the light having the second wavelength are TE waves.

Table 3 shows the effective refractive index at each level shown in FIG. L1 is a portion corresponding to S1 of the embodiment shown in FIG. L2 is a portion corresponding to S2 of the embodiment shown in FIG.

Table 4 is a table showing the diffraction efficiency of the optical element of Example 1. In Table 3, “0th order” and “1st order” indicate the diffraction efficiencies of 0th order diffracted light and 1 hour diffracted light, and “1st order / 0th order” indicates the light quantity of the first order diffracted light and the light quantity of the 0th order diffracted light. “−1st order + 0th order + 1st order” indicates the sum of the diffraction efficiencies of the 0th order diffracted light, the 1st order diffracted light, and the −1st order diffracted light.

Table 5 is a table showing the phase difference between the light passing through the A region and the light passing through the B region.

The duty ratio of the macro lattice was set to 0.6. The target value 0.067 of the first ratio corresponds to the target value 0.810 [radian] of the phase difference when the duty ratio of the macro grating is 0.6.

From Table 3, for the first wavelength, the second ratio, which is the sum of the diffraction efficiencies of the 0th-order diffracted light, the 1st-order diffracted light, and the −1st-order diffracted light, is 0.907. The second ratio for the second wavelength is 0.874.

Here, a binary lattice having the same function as the embodiment (hereinafter referred to as a binary lattice corresponding to the embodiment) is obtained by the following procedure. As a feasible range, the range of the grating height of the binary grating is 0 to 2 μm, the range of the duty ratio is 0.1 to 0.9, and within this range, the range in which the first ratio is a predetermined value for all wavelengths is searched, A shape that is the center of the range (the center of the allowable range with respect to the grid height and the duty ratio) is a representative shape. For example, corresponding to the degree of freedom of the phase difference 2π, there are a plurality of ranges in which the first ratio is a predetermined value for all wavelengths, and the diffraction efficiency is maximized when a plurality of representative shapes are obtained. Choose one.

In the binary grating corresponding to Example 1, the phase difference between the light beams having the first and second wavelengths is 3.432 and 2.868. In addition, for the light of the first and second wavelengths, the second ratio of the binary grating is 0.708 and 0.707.

Thus, the second ratio of the light of each wavelength in the first embodiment can be made higher than the second ratio of the corresponding light of the binary grating. The reason is as follows. In the case of a binary grating, for the first wavelength having a relatively short wavelength, the phase difference is π or more in order to make the ratio between the second wavelength having a relatively long wavelength and the diffraction efficiency equal. In this case, generally, multi-order diffracted light is easily emitted, and the second ratio is lowered accordingly. On the other hand, in the first embodiment, the target value of the phase difference is reduced by appropriately determining n1A, n1B, n2A, n2B, h1 and h2 according to the equations (4) and (5). Can do.

In the present embodiment, since the height of the macro grating is not more than the maximum wavelength, it is difficult to cause manufacturing problems that impede achievement of theoretical optical performance. Therefore, according to the present embodiment, the ratio of the light quantity of the first-order diffracted light and the light quantity of the 0th-order diffracted light of the light of the wavelength for digital versatile disc (DVD) and compact disc (CD) can be made uniform. The sum of the diffraction efficiencies of the folded light, the first-order diffracted light, and the −1st-order diffracted light can be maintained at a high value.

Example 2
Example 2 corresponds to the embodiment shown in FIG. 5A. The first wavelength is 405 nm, the second wavelength is 660 nm, and the third wavelength is 785 nm. The target value of the first ratio between the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light of the light of the first to third wavelengths is set to 0.067 ± 0.012. The optical element of Example 2 was designed so that the first ratio of light having the first to third wavelengths was set as the target value according to the flowchart of FIG.

FIG. 10 is a diagram illustrating a configuration of the optical element according to the second embodiment. In this embodiment, a second film is formed on the first film. It is assumed that the refractive index of the first film is larger than the refractive indexes of the grating convex portions and the second film. The refractive index of the second film may be larger or smaller than the refractive index of the grating convex portion. As an example, the lattice convex portion is formed by injection molding a polyolefin-based resin. The first film is formed by depositing an evaporation material made of thallium oxide (Ta ₃ O ₅ ) on the first film by an evaporation method or a sputtering method. The second film is obtained by further depositing a vapor deposition material made of silicon dioxide (SiO ₂ ) on the second film by a vapor deposition method or a sputtering method.

Table 6 is a table | surface which shows the dimension of each part of the optical element of Example 2. SWS (Sub-Wavelength Structure) indicates a sub-wavelength grating portion, that is, an A region.

Here, the height of the macro grating of Example 2 (distance from the lower substrate surface to the highest upper surface of the second film) is 342 nm as apparent from Table 6 and FIG. (785 nm) or less.

Table 7 is a table | surface which shows the refractive index of each part of the optical element of Example 2. The light of the first wavelength is a TE wave, and the light of the second wavelength and the light of the third wavelength are TM waves.

Table 8 is a diagram showing the effective refractive index at each level shown in FIG. L1 is a portion corresponding to S1 in the embodiment shown in FIG. L2 is a portion corresponding to S2 of the embodiment shown in FIG.

Table 9 is a table showing the diffraction efficiency of the optical element of Example 2. In Table 7, “0th order” and “1st order” indicate the diffraction efficiencies of the 0th order diffracted light and the 1st order diffracted light, and “1st order / 0th order” indicates the light quantity of the 1st order diffracted light and the light quantity of the 0th order diffracted light. “-1st order + 0th order + 1st order” indicates the sum of diffraction efficiencies of 0th order diffracted light, 1st order diffracted light, and −1st order diffracted light.

Table 10 is a table showing the phase difference between the light passing through the A region and the light passing through the B region.

The duty ratio of the macro lattice was set to 0.7. The target value 0.067 of the first ratio corresponds to the target value 0.949 [radian] of the phase difference when the duty ratio of the macro grating is 0.7.

From Table 7, for the first wavelength, the second ratio, which is the sum of the diffraction efficiencies of the 0th-order diffracted light, the 1st-order diffracted light, and the −1st-order diffracted light, is 0.869. The second ratio for the second wavelength is 0.830. The second ratio for the third wavelength is 0.843.

In the corresponding binary grating corresponding to Example 2, the phase difference between the first wavelengths is 4.070, and the phase difference between the second and third wavelengths is 2.218. The second ratio of the binary grating is 0.750, 0.727, and 0.777 for the first to third wavelengths of light.

Thus, the second ratio of the light of each wavelength in Example 2 can be higher than the second ratio of the corresponding light of the binary grating. The reason is as follows. In the case of a binary grating, in order to make the ratios of the second and third wavelengths having a relatively long wavelength and the diffraction efficiency equal for the first wavelength having a relatively short wavelength, the phase difference of the first wavelength is π That's it. In this case, generally, multi-order diffracted light is easily emitted, and the second ratio is lowered accordingly. On the other hand, in Example 2, n1A, n1B, n2A, n2B, n3A, n3B, n4A, n4B, h1, h2, h3, and h4 are appropriately determined according to the equations (10) to (12). Thus, the target value of the phase difference can be reduced.

In the present embodiment, since the height of the macro grating is not more than the maximum wavelength, it is difficult to cause manufacturing problems that impede achievement of theoretical optical performance. Therefore, according to the present embodiment, the ratio of the light quantity of the first-order diffracted light and the light quantity of the zero-order diffracted light of the light of the wavelength for Blu-ray disc (BD), digital versatile disc (DVD), and compact disc (CD) is made uniform. The sum of the diffraction efficiencies of the 0th-order diffracted light, the 1st-order diffracted light, and the −1st-order diffracted light can be maintained at a high value.

Comparative Example 1
Comparative Example 1 corresponds to Example 2 and uses a binary lattice. The first wavelength is 405 nm, the second wavelength is 660 nm, and the third wavelength is 785 nm. The target value of the ratio of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light of the first wavelength light is set to 0.067 ± 012. In Comparative Example 1, the calculation was performed based on the scalar theory.

FIG. 11 is a diagram showing the configuration of the optical element of Comparative Example 1.

Table 11 is a table showing dimensions and the like of each part of the optical element of Example 1.

Table 12 is a table showing the refractive index of each part of the optical element of Comparative Example 1.

Table 13 is a table showing the diffraction efficiency of the optical element of Comparative Example 1. In Table 11, “1st order / 0th order” indicates the ratio of the light amount of the 1st order diffracted light and the light amount of 0th order diffracted light, and “−1st order + 0th order + 1 order” indicates 0th order diffracted light, 1st order diffracted light, − The sum of the diffraction efficiencies of the first-order diffracted light is shown. The second ratio of light with a wavelength of 405 nm in Comparative Example 1 is about 14 percent lower than the second ratio of light with a wavelength of 405 nm in Example 2 shown in Table 7.

Table 14 is a table | surface which shows the phase difference of a grating | lattice convex part and a grating | lattice recessed part. Here, the first-order / 0th-order diffraction efficiency ratio generated at a phase difference of 4.070 radians of light having a wavelength of 405 nm is equivalent to the first-order / 0th-order diffraction efficiency ratio generated at a phase difference of 2.213 radians. This is because the curve of the 1st / 0th diffraction efficiency ratio in FIG. 4 has a symmetrical shape with respect to the phase difference π radians, and the following equation is established.

According to this comparative example, the ratio of the light quantity of the first-order diffracted light and the light quantity of the 0th-order diffracted light of the light of the wavelength for Blu-ray disc (BD), digital versatile disc (DVD), and compact disc (CD) can be made uniform. However, the sum of the diffraction efficiencies of the 0th-order diffracted light, the 1st-order diffracted light, and the −1st-order diffracted light is smaller than the value in Example 2.

Example 3
Example 3 corresponds to the embodiment shown in FIG. 5B. The first wavelength is 405 nm, the second wavelength is 660 nm, and the third wavelength is 785 nm. The target value of the first ratio (the ratio of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light) of the light of the first wavelength is set to 0.067 ± 0.015. The target value of the first ratio of the light of the second wavelength is set to 0 (0.042 or less). The target value of the first ratio of the light of the third wavelength is 0.154 ± 0.015. The optical element of Example 3 was designed according to the flowchart of FIG. 8 so that the first ratio of the light of the first to third wavelengths is the target value.

FIG. 12A is a diagram illustrating a configuration of an optical element according to Example 3. In this embodiment, a film is formed on the A region composed of the sub-wavelength grating and the B region composed of the flat portion. The refractive index of the film is assumed to be larger than the refractive index of the grating convex portion. As an example, the lattice convex portion is formed by injection molding a polyolefin-based resin. The film is formed by depositing an evaporation material made of thallium oxide (Ta ₃ O ₅ ) on the film by an evaporation method or a sputtering method.

Table 15 is a table | surface which shows the dimension of each part of the optical element of Example 3. FIG. SWS (Sub-Wavelength Structure) indicates a sub-wavelength grating portion, that is, an A region.

Here, the height of the macro grating of Example 3 (distance from the lower substrate surface to the highest upper surface of the film) is 390 nm, as is apparent from Table 15 and FIG. 12A, and the maximum wavelength (785 nm). It is as follows.

Table 16 is a table | surface which shows the refractive index of each part of the optical element of Example 3. The light of the first wavelength and the light of the second wavelength are TM waves, and the light of the third wavelength is a TE wave.

Table 17 shows the effective refractive index at each level shown in FIG. L3 is a portion corresponding to S3 in the embodiment shown in FIG. L4 is a portion corresponding to S4 of the embodiment shown in FIG.

Table 18 is a table showing the diffraction efficiency of the optical element of Example 3. In Table 15, “0th order” and “1st order” indicate the diffraction efficiencies of the 0th order diffracted light and 1 hour diffracted light, and “1st order / 0th order” indicates the light quantity of the 1st order diffracted light and the light quantity of the 0th order diffracted light. “−1st order + 0th order + 1st order” indicates the sum of the diffraction efficiencies of the 0th order diffracted light, the 1st order diffracted light, and the −1st order diffracted light.

Table 19 is a table showing the phase difference between the light passing through the A region and the light passing through the B region.

The duty ratio of the macro lattice was set to 0.5. The target value 0.067 of the first ratio corresponds to the target value 0.771 [radian] of the phase difference when the duty ratio of the macro grating is 0.5.

From Table 15, for the first wavelength, the second ratio, which is the sum of the diffraction efficiencies of the 0th-order diffracted light, the 1st-order diffracted light, and the −1st-order diffracted light, is 0.805. The second ratio for the second wavelength is 0.890. The second ratio for the third wavelength is 0.812.

In the binary grating corresponding to Example 3, the phase difference is 20.515, 12.148, and 10.150 for the first to third wavelengths of light. In addition, for light of the first to third wavelengths, the second ratio of the binary grating is 0.811, 0.985, and 0.697.

Here, the grating height of the binary grating corresponding to Example 3 is 2520 nm, which is more than three times the maximum wavelength (785 nm). Such gratings have manufacturing problems that hinder achievement of theoretical optical performance. The manufacturing problems include, for example, mold shape accuracy and mold-to-product transferability in a manufacturing method using plastic injection molding. In other words, even if such a high grating height is manufactured, the above theoretical optical performance cannot be achieved due to the above manufacturing problems.

On the other hand, since the height of the macro grating is less than or equal to the maximum wavelength in Example 3, problems in manufacturing are unlikely to occur, and theoretical optical performance can be achieved. Therefore, according to the present embodiment, the ratio of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light of the light of the wavelength for Blu-ray disc (BD), digital versatile disc (DVD), and compact disc (CD). The second ratio can be set to a completely different value, and the sum of the diffraction efficiencies of the 0th-order diffracted light, the 1st-order diffracted light, and the −1st-order diffracted light can be maintained at a high value.

Example 4
Example 4 uses a grid similar to the embodiment shown in FIG. 5A. In Example 4, the first wavelength is 660 nm and the second wavelength is 785 nm. The target values of the first ratios of the light amounts of the first and second wavelengths of the first-order diffracted light and zero-order diffracted light are 0 (0.042 or less) and 0.067 ± 0.015, respectively. To do. The optical element of Example 4 was designed according to the flowchart of FIG. 8 so that the first ratio of the light of the first and second wavelengths is the target value.

FIG. 12B is a diagram illustrating the configuration of the optical element of Example 4. In this embodiment, a second film is formed on the first film. It is assumed that the refractive index of the first film is larger than the refractive indexes of the grating convex portions and the second film. The refractive index of the second film may be larger or smaller than the refractive index of the grating convex portion. As an example, the lattice convex portion is formed by injection molding a polyolefin-based resin. The first film is formed by depositing an evaporation material made of thallium oxide (Ta ₃ O ₅ ) on the first film by an evaporation method or a sputtering method. The second film is obtained by further depositing a vapor deposition material made of silicon dioxide (SiO ₂ ) on the second film by a vapor deposition method or a sputtering method.

Table 20 is a table | surface which shows the dimension of each part of the optical element of Example 1. FIG. SWS (Sub-Wavelength Structure) indicates a sub-wavelength grating portion, that is, an A region.

Here, the height of the macro grating of Example 4 (distance from the lower substrate surface to the highest upper surface of the film) is 440 nm, as is clear from Table 20 and FIG. 12B, and the maximum wavelength (785 nm). It is as follows.

Table 21 is a table | surface which shows the refractive index of each part of the optical element of Example 4. The light of the first wavelength is a TE wave, and the light of the second wavelength is a TM wave.

Table 22 is a diagram showing the effective refractive index at each level shown in FIG. 12B. L1 is a portion corresponding to S1 in the embodiment shown in FIG. L2 is a portion corresponding to S2 of the embodiment shown in FIG.

Table 23 shows the diffraction efficiency of the optical element of Example 4. In Table 20, “0th order” and “1st order” indicate the diffraction efficiencies of the 0th order diffracted light and 1 hour diffracted light, and “1st order / 0th order” indicates the light quantity of the 1st order diffracted light and the light quantity of the 0th order diffracted light. “−1st order + 0th order + 1st order” indicates the sum of the diffraction efficiencies of the 0th order diffracted light, the 1st order diffracted light, and the −1st order diffracted light.

Table 24 is a table showing the phase difference between the light passing through the A region and the light passing through the B region.

Table 25 is a table showing the phase difference and the second ratio between the light passing through the A region and the light passing through the B region for the first and second wavelengths in the binary grating corresponding to the fourth embodiment. .

Here, the grating height of the binary grating corresponding to Example 4 is 1250 nm, which is 1.5 times or more of the maximum wavelength (785 nm). Such gratings have manufacturing problems that hinder achievement of theoretical optical performance. The manufacturing problems include, for example, mold shape accuracy and mold-to-product transferability in a manufacturing method using plastic injection molding. In other words, even if such a high grating height is manufactured, the above theoretical optical performance cannot be achieved due to the above manufacturing problems.

On the other hand, since the height of the macro grating is less than or equal to the maximum wavelength in Example 4, a problem in manufacturing hardly occurs, and a value close to the theoretical optical performance can be achieved. Therefore, according to the present embodiment, the first ratio of the light of the wavelength for digital versatile disc (DVD) (the ratio of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light) is set for the compact disc (CD). It can be made smaller than the first ratio of the light of the wavelengths, and the sum of the diffraction efficiencies of the 0th-order diffracted light, the 1st-order diffracted light, and the −1st-order diffracted light of both wavelengths can be maintained at a high value.

Configuration Example of Optical System Including Optical Element of Example 2 FIGS. 13 and 14 are diagrams illustrating an example of the configuration of an optical system including the optical element 2100 of Example 2. FIG. The optical system is a pickup optical system that reads information recorded on the disk 1219 with light of three wavelengths. FIG. 13 shows a light path from the light source to the disk 1219, and FIG. 14 shows a light path after being reflected by the disk 1219.

The optical system includes a laser light source 1201, half-

wave plates

1203 and 1205, an optical element 3100, a polarizing filter 1207, a beam splitter 1209 such as a half mirror, a quarter-wave plate 1211, a collimator lens 1213, a mirror 1215, and an objective lens 1217. A condenser lens 1221 and a light receiving element 1223.

In FIG. 13, a laser light source 1201 is a light source of light having three wavelengths of 405 nm, 660 nm, and 785 nm. Here, a wavelength of 405 nm, a wavelength of 785 nm, and a wavelength of 660 nm are defined as a first wavelength to a third wavelength, respectively. The laser light source 1201 selectively emits light having a first wavelength to a third wavelength. It is assumed that all the light with the first to third wavelengths is TE-polarized light. The half-wave plate 1203 is configured to convert the light of the second wavelength and the third wavelength from TE polarized light to TM polarized light and transmit the light of the first wavelength as TE polarized light. The optical element 2100 is, for example, as shown in the second embodiment, and the ratio of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light is set to 0.067 ± 0.012 with respect to light of three wavelengths. It is configured. The half-wave plate 1205 converts the light of the second wavelength and the third wavelength (0th order diffracted light and ± 1st order diffracted light) from TM polarized light to TE polarized light, and the first wavelength light remains TE polarized light. It is configured to transmit. The polarization filter 1207 is configured to remove noise by blocking light other than TE polarized light. The beam splitter 1209 reflects light of any wavelength that is TE-polarized light (0th order diffracted light and ± 1st order diffracted light). The quarter-wave plate 1211 makes light of any wavelength that is TE-polarized light (zero-order diffracted light and ± first-order diffracted light) circularly polarized light. Light of any wavelength (0th order diffracted light and ± 1st order diffracted light) is converted into parallel light by the collimator lens 1213, reflected by the mirror 1215, and then condensed on the disk 1219 by the objective lens 1217. Here, the 0th-order diffracted light and the ± 1st-order diffracted light are condensed at different positions on the disk 1219, respectively. The 0th-order diffracted light is mainly used for reading data recorded on the disk 1219, and the ± 1st-order diffracted light is used for position control of the lens system with respect to the disk 1219.

In FIG. 14, light of any wavelength (0th order diffracted light and ± 1st order diffracted light) reflected by the disk 1219 is transmitted through the objective lens 1217, the mirror 1215, and the collimator lens 1213, and then by the quarter wavelength plate 1211. Converted to TM polarized light. The beam splitter 1209 transmits light of any wavelength that is TM polarized light (0th order diffracted light and ± 1st order diffracted light). Light of any wavelength (0th order diffracted light and ± 1st order diffracted light) that is TM-polarized light is collected on the condensing surface of the three light receiving elements 1223 for 0th order diffracted light and ± 1st order diffracted light by the condenser lens 1221. Lighted. Note that when the TE-polarized light is partially reflected by the beam splitter 1209 in the return path, this light is blocked by the polarizing filter 1207.

15 and 16 are diagrams showing another example of the configuration of the optical system including the optical element 2100 of the second embodiment. The optical system is a pickup optical system that reads information recorded on the disk 1319 with light of three wavelengths. FIG. 15 shows a light path from the light source to the disk 1319, and FIG. 16 shows a light path after being reflected by the disk 1319.

The optical system includes a laser light source 1301, half-

wave plates

1303 and 1305, an optical element 2100, a polarizing filter 1307, a beam splitter 1309 such as a half mirror, a quarter-wave plate 1311, a collimator lens 1313, a mirror 1315, and an objective lens 1317. , A condenser lens 1321 and a light receiving element 1323.

Except for the beam splitter 1309, each optical element functions in the same manner as in the optical system of FIGS. The beam splitter 1309 is configured to transmit light of any wavelength on the forward path and reflect light of any wavelength on the return path.

Third Aspect FIG. 17 is a perspective view of an optical element 100 according to one embodiment of the third aspect of the present invention. A plurality of grid protrusions 103 extending in the Y direction are arranged in the X direction in the first direction in a first band-like region (referred to as the first region in the figure) on the substrate 101. The first period is so small that the light passing through the first band-like region cannot cause diffraction. On the substrate, a second belt-like region (described as the second region in the drawing) in which no grid convex portions are arranged is arranged adjacent to the first belt-like region. The first belt-like region and the second belt-like region are repeatedly arranged in the X direction at the second period. For light passing through the substrate, the first belt-like region functions as a lattice convex portion, and the second belt-like region functions as a lattice concave portion. The second period is so large that the light passing through the first band region and the second band region can cause diffraction.

18 is a cross-sectional view in the X direction perpendicular to the substrate surface of the optical element shown in FIG. In the first belt-like region, a plurality of grid protrusions 103 are arranged on the substrate 101 in the X direction at the first period. In the second band-shaped region, the lattice convex portions are not arranged. A film 105, a film 107, and a film 109 are provided on the lattice convex portion 103 of the first belt-shaped region, the substrate 101 of the lattice concave portion of the first belt-shaped region, and the substrate 101 of the second belt-shaped region, respectively. . In FIG. 18, in order to simplify the following description, the thickness of the film is made equal to the height 103 of the lattice convex portion. Actually, as shown in FIG. 19, the thickness of the film may be different from the height of the grating protrusion 103.

In the first belt-like region, the space between the substrate surface and the surface at the lattice height parallel to the substrate surface is referred to as L1. In L1, the lattice convex portion 103 and the film 107 are present at a predetermined ratio.

In the first band-like region, a space between a plane parallel to the substrate surface and at a lattice height and a plane parallel to the substrate surface and at a height position of the film 105 on the lattice projection 103 is referred to as U1. . In U1, the film 105 on the lattice convex portion 103 and the surrounding medium are present at a predetermined ratio. Here, since the optical element 100 is placed in the air, the surrounding medium is air.

In the second band-like region, the space between the substrate surface and the surface at the lattice height parallel to the substrate surface is referred to as L2. A film 109 exists in L2.

In the second band-like region, the space between the plane at the lattice height parallel to the substrate surface and the plane at the height of the film 105 on the lattice protrusion 103 parallel to the substrate surface is referred to as U2. . Air exists in U2.

Here, in order to simplify the explanation, it is assumed that the height of the film 105 on the lattice convex portion 103 is also equal to the height of the lattice convex portion 103. Let this height be h. Therefore, the thicknesses (heights) of L1, U1, L2, and U2 are all h.

Next, the refractive indexes n _L1 , n _U1 , n _L2 and n _U2 of _L1 , _U1 , _L2 and _U2 will be considered. Since only the film 109 exists in _L2 , _nL2 is the refractive index of the film. Since only air exists in _U2 , _nU2 is the refractive index of air.

Like L1 and U1, the effective refractive index of a region in which two types of media are arranged in a lattice pattern with a period equal to or shorter than the wavelength is expressed by n1 and n2, and n2 with respect to the volume of the entire region. When the volume ratio (duty ratio) occupied by is represented by f, it can be represented by the following equation. Here, for the sake of simplicity, it is assumed that light is incident on the substrate surface perpendicularly.
0th order approximation

Second order approximation

According to the above equation, the refractive index n _L1 of _L1 is any value between the refractive index of the grating convex 103 and the refractive index of the film 107, and the refractive index n _U1 of _U1 is Any value between the refractive index and the refractive index of air.

Here, the optical path length d1 when light passes through U1 and L1 in the direction perpendicular to the substrate surface can be expressed by the following equation.
d1 = h (n _U1 + n _L1 ) (14)
Further, the optical path length d2 when light passes through U2 and L2 in the direction perpendicular to the substrate surface can be expressed by the following equation.
d2 = h (n _U2 + n _L2 ) (15)

From the equations (5) and (6), if the following equation is satisfied, the optical path length of the light passing through U1 and L1 is the same as the optical path length of the light passing through U2 and L2, so the first Diffraction is not caused by the grating formed by the strip region and the second strip region.
n _U1 + n _L1 = n _U2 + n _L2 (16)

Here, the material of the film and the grating convex portion is selected so that the refractive index of the film is higher than the refractive index of the grating convex portion 103. Then, the following relationship is established.
n _U1 > n _U2 (17)
n _L1 <n _L2 (18)

That is, the refractive index of the upper layer U1 of the first band region is larger than the refractive index of the upper layer U2 of the second band region, and the refractive index of the lower layer UL1 of the first band region is the second band shape. It is smaller than the refractive index of the lower layer UL2 of the region. Therefore, Expression (7) can be easily realized by appropriately selecting the material of the film and the lattice convex portion and adjusting the duty ratio of the first band-shaped region.

FIG. 20 is a flowchart showing a method for designing the optical element of the present embodiment.

In step S010 in FIG. 20, a second cycle is determined. Here, the second period is determined from the following equation so that the light in the second polarization state generates a desired diffraction angle.

n 'sinθ'-n sinθ = Nλ / Λ (13)

n: Refractive index of the incident side medium (refractive index of air)
n ': refractive index of the output side medium (refractive index of air)
θ: incident angle θ ′: diffraction angle N: diffraction order λ: wavelength of incident light Λ: period of diffraction grating (second period)

In the present embodiment, when the incident angle is zero, the diffraction angle is determined only by the second period.

In step S020 in FIG. 20, the upper limit of the first cycle is determined. As an example, the upper limit of the first period is determined to be less than 1/20 of the second period.

In step S030 of FIG. 20, the first period, the duty ratio, the height of the grating convex portions, and the film thickness are adjusted so that the expression (16) is satisfied for the light in the first polarization state.

Here, when the material of the film is applied without distinguishing the first belt-like region and the second belt-like region, the lattice convex portions of the first belt-like region, the lattice concave portions of the first belt-like region, and the second In the case where a difference occurs in the film thickness of the belt-shaped region, the relationship between the coating amount of the film material and the film thickness of each part is measured in advance, and the design can be performed using the relationship. By designing in this way, for example, a complicated manufacturing process such as adjusting the coating amount of the film material so as to equalize the film thickness of each portion is not necessary.

In Step S040 of FIG. 20, is the expression (16) satisfied, that is, whether the phase difference (optical path length difference) of the light passing through the first belt-like region and the second belt-like region is not more than a predetermined value? Judgment is made. If expression (16) is satisfied, the process ends. If expression (16) is not satisfied, the process returns to step S040.

FIG. 21 is a cross-sectional view in the X direction perpendicular to the substrate surface of a conventional optical element disclosed in Patent Document 2, for example. The X direction is a direction perpendicular to the direction in which the lattice convex portions extend on the substrate surface. In the lattice region, a plurality of lattice convex portions 103 are arranged on the substrate 101 in the X direction with a predetermined period. The predetermined period is such a magnitude that the used light cannot be diffracted by the grating. In the flat region, the lattice convex portions are not arranged.

Here, the optical path length dg when light passes through the grating region in the direction perpendicular to the substrate surface can be expressed by the following equation.
dg = hg · ng (19)
Here, hg is the grating height, and ng is the effective refractive index of the grating region obtained from the equation (3) or the equation (4).

Since the effective refractive index of the grating region is larger than the refractive index of air, the optical path length of light passing through the grating region obtained from the equation (19) is always greater than the optical path length of light passing through the flat region corresponding to the grating region. growing. Therefore, in order to prevent diffraction from being generated by the grating formed by the grating region and the flat region, the following expression must be satisfied so that the phase difference between the grating region and the flat region is an integral multiple of 2π. There is.
(2π / λ) · hg · ng = (2π / λ) · hg · na + (2π · m) / λ
(20)
Here, na is the refractive index of air, λ is the wavelength of light used, and m is an arbitrary integer. By rearranging the equation (20), the following equation is obtained.
hg = m / (ng−na) (21)

That is, the grating height needs to take a value equal to or larger than the reciprocal of the difference between the refractive index of the grating convex portion and the refractive index of air. As will be described later with respect to the embodiments, when plastic that is easily processed is used for the grating convex portion, the aspect ratio, which is the ratio of the grating height to the grating period, becomes large, and it becomes difficult to manufacture the sub-wavelength grating.

In the above description, the case where the grating of the conventional optical element does not include a film has been described, but the same applies to the case where the grating of the conventional optical element includes a film.

Examples of the present invention will be described below.

Example 5
The fifth embodiment has the configuration shown in FIG. 17, and the direction in which the lattice protrusions 103 are arranged is the X direction, which is the same as the direction in which the first belt-like region and the second belt-like region are arranged. . This embodiment includes the X-direction cross section shown in FIG. In other words, the thickness of the film is equal to the height of the grid protrusion 103.

Table 26 is a table | surface which shows the specification of the optical element of a present Example.

In Table 26, the unit of length is micrometers. The number on the left side of the refractive index column indicates the refractive index of light having a wavelength of 660 nanometers, and the number on the right side indicates the refractive index of light having a wavelength of 785 nanometers. In the present embodiment, the above-described two-wavelength light is used.

The optical element of this example is manufactured by the following method. The lattice projection is formed by injection molding a polyolefin-based resin, and an evaporation material made of thallium oxide (Ta ₃ O ₅ ) is deposited thereon by an evaporation method or a sputtering method.

Table 27 is a table showing the refractive indexes and layer thicknesses of L1, U1, L2, and U2 of light having a wavelength of 785 nanometers. In this embodiment, light having a wavelength of 785 nanometers enters the optical element 100 as TM polarized light. Here, it is assumed that the TM-polarized surface is perpendicular to the substrate surface and is in the X direction, and the TE-polarized surface is perpendicular to the substrate surface and is in the Y direction.

From equations (14) and (15), the optical path length d1 when light passes through U1 and L1 in the direction perpendicular to the substrate surface and the optical path length d2 when light passes through U2 and L2 in the direction perpendicular to the substrate surface. Is calculated, the following formula is obtained.
d1 = 0.3158
d2 = 0.3191
Therefore, the optical path length difference is 0.0033 micrometers. The phase difference is 0.026 radians (1.50 degrees), which is almost zero, and the optical element of this example allows light of 785 nanometer wavelength (TM polarized light) to pass through without being diffracted.

Table 28 is a table showing the refractive indices and layer thicknesses of L1, U1, L2, and U2 of light having a wavelength of 660 nanometers. In this embodiment, light having a wavelength of 660 nanometers enters the optical element 100 as TE polarized light.

From equations (14) and (15), the optical path length d1 when light passes through U1 and L1 in the direction perpendicular to the substrate surface and the optical path length d2 when light passes through U2 and L2 in the direction perpendicular to the substrate surface. Is calculated, the following formula is obtained.
d1 = 0.3891
d2 = 0.3201
Therefore, the optical path length difference is 0.069 micrometers. The phase difference is 0.657 radians (37.6 degrees), and the optical element of this embodiment diffracts light having a wavelength of 660 nanometers (TE polarized light).

Table 29 is a table | surface which shows the state of the diffraction by the optical element of a present Example.

In Table 29, “ratio” indicates the ratio of the first-order diffracted light amount to the zero-order diffracted light amount. The other numerical values indicate the ratio of the amount of diffracted light to the amount of incident light. “Total” indicates the total of the 0th-order diffracted light amount, the 1st-order diffracted light amount, and the −1st-order diffracted light amount. In this embodiment, the “ratio” is set to the above numerical value based on the required specification. First-order diffracted light and −1st-order diffracted light hardly occur with respect to light having a wavelength of 785 nanometers (TM polarized light).

As described above, the optical element of the present embodiment does not diffract the light in the first polarization state (light having a wavelength of 785 nanometers (TM polarization)), and the light in the second polarization state (light having a wavelength of 660 nanometers). (TE polarized light)) is diffracted.

Example 6
FIG. 22 is a perspective view of the optical element according to the second embodiment. As shown in FIG. 22, in Example 2, the direction in which the lattice protrusions 103 are arranged is the Y direction, and is orthogonal to the direction in which the first and second belt regions are arranged (X direction). To do. The cross section in the Y direction of the first band-like region of the present example is the same as the cross section of the first band-like region of FIG. In the first embodiment, as shown in FIG. 18, the arrangement direction of the lattice projections 103 coincides with the arrangement direction of the first belt-like region and the second belt-like region. On the other hand, in the second embodiment, the arrangement direction of the lattice projections 103 is orthogonal to the arrangement directions of the first belt-like region and the second belt-like region. In the present embodiment, the thickness of the film is equal to the height of the lattice projection 103.

Table 30 is a table | surface which shows the specification of the optical element of a present Example.

In Table 30, the unit of length is micrometer. The number on the left side of the refractive index column indicates the refractive index of light having a wavelength of 660 nanometers, and the number on the right side indicates the refractive index of light having a wavelength of 785 nanometers. In the present embodiment, the above-described two-wavelength light is used.

Table 31 is a table showing the refractive indexes and layer thicknesses of L1, U1, L2, and U2 of light having a wavelength of 660 nanometers. In this embodiment, light having a wavelength of 660 nanometers enters the optical element 100 as TE polarized light. Here, it is assumed that the TM-polarized surface is perpendicular to the substrate surface and is in the X direction, and the TE-polarized surface is perpendicular to the substrate surface and is in the Y direction.

From equations (14) and (15), the optical path length d1 when light passes through U1 and L1 in the direction perpendicular to the substrate surface and the optical path length d2 when light passes through U2 and L2 in the direction perpendicular to the substrate surface. Is calculated, the following formula is obtained.
d1 = 0.4322
d2 = 0.4320
Therefore, the optical path length difference is almost zero, and the optical element of this embodiment allows light having a wavelength of 660 nanometers (TE polarized light) to pass through without being diffracted.

Table 32 is a table showing the refractive indexes and layer thicknesses of L1, U1, L2, and U2 of light having a wavelength of 785 nanometers. In this embodiment, light having a wavelength of 785 nanometers enters the optical element 100 as TM polarized light.

From equations (14) and (15), the optical path length d1 when light passes through U1 and L1 in the direction perpendicular to the substrate surface and the optical path length d2 when light passes through U2 and L2 in the direction perpendicular to the substrate surface. Is calculated, the following formula is obtained.
d1 = 0.05045
d2 = 0.4235
Therefore, the optical path length difference is 0.081 micrometers. The phase difference is 0.648 radians (37.2 degrees), and the optical element of this embodiment diffracts light having a wavelength of 785 nanometers (TM polarization).

Table 33 is a table | surface which shows the state of the diffraction by the optical element of a present Example.

In Table 33, “ratio” indicates the ratio of the first-order diffracted light amount to the zero-order diffracted light amount. The other numerical values indicate the ratio of the amount of diffracted light to the amount of incident light. “Total” indicates the total of the 0th-order diffracted light amount, the 1st-order diffracted light amount, and the −1st-order diffracted light amount. In this embodiment, the “ratio” is set to the above numerical value based on the required specification. First-order diffracted light and −1st-order diffracted light hardly occur with respect to light having a wavelength of 660 nanometers (TE polarized light).

As described above, the optical element of the present embodiment does not diffract the light in the first polarization state (light having a wavelength of 660 nanometers (TE-polarized light)), and the light in the second polarization state (light having a wavelength of 785 nanometers). (TM polarized light)) is diffracted.

Other Embodiments In the optical elements of Examples 4 and 5, a one-dimensional grating is arranged in the first band-like region. As another embodiment, a two-dimensional grating may be arranged with a first period of a size that does not cause diffraction of light used in the first belt-like region. In general, the duty ratio of the grating in the first belt-shaped region is the ratio of the lattice convex portion to the space of the height of the lattice convex portion in the first belt-shaped region.

Comparative Example 2
Comparative Example 2 includes a cross section in the X direction shown in FIG.

In the optical element of Comparative Example 2, the lattice region and the flat region are repeatedly arranged in the X direction at the second period on the surface of the substrate. In the first belt-like region, the lattice convex portions 103 extending in the Y direction are arranged in the X direction at the first period.

The specification of the lattice is determined so as to satisfy the formula (13) for light having a wavelength of 785 nanometers (TM polarization).

Table 34 is a table | surface which shows the specification of the grating | lattice of the grating | lattice area | region of the optical element of a comparative example.

As a result, light having a wavelength of 785 nanometers (TM polarized light) is not diffracted by the grating region and the flat region.

In Comparative Example 2, the second period is 22.7 micrometers.

Table 35 is a table | surface which shows the state of the diffraction by the optical element of a present Example.

Comparison between Example 5 and Comparative Example 2 In Example 5 and Comparative Example 2, the specifications are determined so that the ratio of the first-order diffracted light amount to the zero-order diffracted light amount is the same.

The grating height of Example 4 is 0.097 micrometers, and the aspect ratio of the sub-wavelength grating is 0.334. In contrast, the grating height of the comparative example is 3.487 micrometers, and the aspect ratio of the sub-wavelength grating is 9.057. As described above, the aspect ratio of the sub-wavelength grating of the example is 0.037 times (about 1/27) the aspect ratio of the sub-wavelength grating of the comparative example, so that the optical element can be manufactured very easily.

Example of Configuration of Optical System Including Optical Element of Example 5 FIG. 23 is a diagram illustrating an example of the configuration of an optical system including the optical element of Example 5. The optical system is a pickup optical system that reads information recorded on the disk 219 with light of two wavelengths.

The optical system includes a laser light source 201, half-

wave plates

203 and 205, an optical element 100, a polarizing filter 207, a beam splitter 209 such as a half mirror, a quarter-wave plate 211, a collimator lens 213, a mirror 215, and an objective lens 217. , A condenser lens 221 and a light receiving element 223.

The laser light source 201 is a light source of two wavelengths, a wavelength of 660 nm and a wavelength of 785 nm. Here, the wavelength 785 nm and the wavelength 660 nm are defined as a first wavelength and a second wavelength, respectively. It is assumed that both the first wavelength light and the second wavelength light emitted from the laser light source 201 are TE polarized light. The half-wave plate 203 converts the first wavelength light from the TE polarized light to the TM polarized light, and transmits the second wavelength light as the TE polarized light. The optical element 100 is, for example, as shown in the first embodiment, and transmits the first wavelength light without diffracting it, and diffracts the second wavelength light. The optical element 100 transmits the first wavelength light as it is to the position of the optical element 100 and diffracts the second wavelength light, and transmits the second wavelength light as it is, and diffracts the first wavelength light. An optical element may be provided. The half-wave plate 205 transmits light having the first wavelength as TM polarized light, and converts light having the second wavelength from TE polarized light to TM polarized light. The polarizing filter 207 removes noise by blocking light other than TM polarized light. The beam splitter 209 reflects light having the first wavelength and the second wavelength, which is TM-polarized light. The quarter-wave plate 211 converts the light having the first wavelength and the second wavelength, which are TM polarized light, into circularly polarized light. The lights having the first wavelength and the second wavelength are converted into parallel light by the collimator lens 213, reflected by the mirror 215, and then condensed on the disk 219 by the objective lens 217. Here, since only the light of the second wavelength is diffracted, the condensing position of the light of the first wavelength and the condensing position of the light of the second wavelength can be configured differently. The light having the first wavelength and the second wavelength reflected by the disk 219 passes through the objective lens 217, the mirror 215, and the collimator lens 213, and is then converted into TE change by the quarter wavelength plate 211. The beam splitter 209 transmits light of the first wavelength and the second wavelength that are TE polarized light. The light having the first wavelength and the second wavelength, which are TE polarized light, is collected on the light collection surface of the light receiving element 223 by the condenser lens 221. Note that, when the TE-polarized light is partially reflected by the beam splitter 209 in the return path, this light is blocked by the polarization filter 207.

In the above example, the half-wave plate 203 converts the first wavelength light from the TE polarized light to the TM polarized light, transmits the second wavelength light as the TE polarized light, and the half-wave plate 205. Is configured to transmit light having the first wavelength as TM polarized light and convert light having the second wavelength from TE polarized light to TM polarized light. Alternatively, the half-wave plate 203 converts the first wavelength light from TE polarized light to TM polarized light and transmits the second wavelength light as TE polarized light. The first wavelength light may be converted from TM polarized light to TE polarized light, and the second wavelength light may be transmitted as TE polarized light. In this case, the polarization filter 207 transmits light having the first wavelength and the second wavelength, which are TE polarized light, and blocks light having the first wavelength and the second wavelength, which are TM polarized light. The beam splitter 209 reflects the light of the first wavelength and the second wavelength, which are TE-polarized light, in the forward path, and transmits the light of the first wavelength and the second wavelength, which are TM-polarized light, in the return path. Constitute.

FIG. 24 is a diagram showing another example of the configuration of an optical system including an optical element according to an embodiment of the present invention. The optical system is a pickup optical system that reads information recorded on the disk 319 with light of two wavelengths.

The optical system includes a laser light source 301, half-

wave plates

303 and 305, an optical element 100, a polarizing filter 307, a beam splitter 309 such as a half mirror, a quarter-wave plate 311, a collimator lens 313, a mirror 315, and an objective lens 317. , A condenser lens 321 and a light receiving element 323.

Except for the beam splitter 309, the function of each optical element functions in the same manner as in the optical system of FIG. The beam splitter 209 is configured to transmit light of the first wavelength and the second wavelength in the forward path and reflect light of the first wavelength and the second wavelength in the return path.

FIG. 25 is a diagram showing still another example of the configuration of an optical system including an optical element according to an embodiment of the present invention. The optical system is a pickup optical system that reads information recorded on the disk 419 with light of one wavelength.

The optical system includes a laser light source 401, an optical element 100, a polarizing filter 407, a beam splitter 409 such as a half mirror, a quarter wavelength plate 411, a collimator lens 413, a mirror 415, an objective lens 417, a condenser lens 421, and a light receiving element 423. including.

The laser light source 401 is, for example, a light source of one wavelength having a wavelength of 408 nm. The optical element 100 is configured to diffract TE polarized light and transmit TM polarized light without diffracting, for example, for light of one wavelength. In this case, the duty ratio, the height of the grating protrusion, the refractive index of the material of the grating protrusion, the refractive index of the film, and the thickness of the film so that TM polarized light of the above wavelength satisfies the equation (16) Etc. As shown in the equations (3) and (4), since the refractive index of the TE-polarized light and the refractive index of the TM-polarized light are different, when the TM-polarized light satisfies the equation (16), the TE-polarized light Of the light does not satisfy Expression (16), and diffraction occurs. The diffracted TE-polarized light passes through the polarization filter 407, is reflected by the beam splitter 409, and reaches the disk 419 via the quarter-wave plate 411, the collimating lens 413, the mirror 415, and the objective lens 417. The light reflected by the disk 419 reaches the light receiving element 423 via the objective lens 417, the mirror 415, the collimating lens 413, the quarter wavelength plate 411, the beam splitter 409 and the condenser lens 421. On the other hand, the TM polarized light transmitted through the optical element 100 as it is is shielded by the polarizing filter 407. At this time, since TM polarized light does not change its traveling direction due to diffraction, it is perpendicularly incident on the polarizing filter 407 and effectively shielded from light.

Claims

On the substrate, the first belt-like region in which the lattice convex portions are arranged in the first cycle and the second belt-like region in which the lattice convex portions are not provided are arranged in the second cycle, and the first cycle is used. The second period is a size that allows the light to be used to generate diffraction, and the grating convexity is formed on the first and second band regions. Providing a first film having a refractive index higher than the refractive index of the material of the portion;
For the light of the first and second wavelengths, the first ratio and the first and second ratios, which are the ratios of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light generated by the first and second band-like regions. Of the light having the first and second wavelengths so that the maximum height from the substrate surface is equal to or smaller than the larger one of the first and second wavelengths. Polarization state, first period, duty ratio that is the ratio of the grid convex portion to the space of the height of the grid convex portion of the first band-like region, the height of the grid convex portion, the grid convexity The refractive index of the material of the portion, the refractive index of the first film, the film thickness of the lattice convex portion of the first strip region, the film thickness of the concave portion of the first strip region, and the thickness of the second strip region An optical element with a fixed film thickness.
The optical element according to claim 1, wherein the first and second target values are equal.
A step is provided between the substrate surface of the first belt-like region and the substrate surface of the second belt-like region, and the first of the light having the shorter wavelength among the light of the first and second wavelengths. The optical element according to claim 1, wherein the optical element is configured to be smaller than a first ratio of light having a longer wavelength.
The optical element according to any one of claims 1 to 3, wherein the first and second wavelengths are any of wavelengths for a Blu-ray disc (BD), a digital versatile disc (DVD), and a compact disc (CD).
On the substrate, the first belt-like region in which the lattice convex portions are arranged in the first cycle and the second belt-like region in which the lattice convex portions are not provided are arranged in the second cycle, and the first cycle is used. The second period is a size that allows the light to be used to generate diffraction, and the grating convexity is formed on the first and second band regions. Providing a first film having a refractive index higher than the refractive index of the material of the part, and providing a step between the substrate surface of the first strip region and the substrate surface of the second strip region,
For the light of the first to third wavelengths, the first ratio and the first to third ratios, which are the ratios of the light amount of the first-order diffracted light and the light amount of the zero-order diffracted light generated by the first and second band-like regions. The polarization state of the light of the first to third wavelengths is set so that the difference from the target value is equal to or less than a predetermined value and the maximum height from the substrate surface is equal to or less than the maximum wavelength of the first to third wavelengths. , The first period, the duty ratio that is the ratio of the grid convex portion to the space of the height of the grid convex portion of the first band-shaped region, the height of the grid convex portion, the height of the grid convex portion, The refractive index of the material, the refractive index of the first film, the film thickness of the lattice convex part of the first band-shaped area, the film thickness of the concave part of the first band-shaped area, the film thickness of the second band-shaped area And an optical element that defines the size of the step.
The optical element according to claim 5, wherein the first to third target values are equal.
Of the first to third wavelengths of light, two wavelengths of light are configured such that the first ratio of light of the shorter wavelength is smaller than the first ratio of light of the longer wavelength. The optical element according to claim 5.
6. The optical element according to claim 5, wherein one of the first to third target values is zero.
The optical element according to any one of claims 5 to 8, wherein the first to third wavelengths are any one of wavelengths for a Blu-ray disc (BD), a digital versatile disc (DVD), and a compact disc (CD).
The optical element according to claim 1, further comprising a second film having a refractive index lower than that of the first film on the first film.
On the substrate, the first belt-like region in which the lattice convex portions are arranged in the first cycle and the second belt-like region in which the lattice convex portions are not provided are arranged in the second cycle, and the first cycle is used. The second period is a magnitude that allows the used light to be diffracted, and the second period is on the first and second strip regions. A film having a refractive index higher than the refractive index of the material of the grating convex portion is provided, and among the light in the first polarization state that passes through the substrate surface, the light that passes through the first band-like region and the second The phase difference between the light passing through the belt-like region becomes zero and diffraction does not occur, and the light passing through the first belt-like region and the second belt-like region out of the second polarization state light passing through the substrate surface The first period, the height of the grating convex portion of the first band-like region so that the phase difference of the light passing through The duty ratio, which is the ratio of the grating protrusions to the space, the height of the grating protrusions, the refractive index of the material of the grating protrusions, the refractive index of the film, and the grating of the first strip region An optical element in which a film thickness of a convex part, a film thickness of a concave part of the first belt-like region, and a film thickness of the second belt-like region are determined.
The optical element according to claim 11, wherein the wavelength of the light in the first polarization state is different from the wavelength of the light in the second polarization state.
The optical element according to claim 11, wherein the wavelength of the light in the first polarization state is the same as the wavelength of the light in the second polarization state.
The optical element according to any one of claims 1 to 13, wherein a material of the lattice convex portion is plastic, and a material of the film is a metal oxide.