JP2005352288A - Optical system for enlarging luminous flux diameter, image combiner and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system for enlarging a luminous flux diameter with which generation of unnecessary light beams is easily suppressed. <P>SOLUTION: An optical system (1) for enlarging a luminous flux diameter is provided with a plurality of partially transmissive reflection surfaces (61 and 62) that are arranged in a mutually serial, parallel and tilted relationship with respect to the optical path of an incident luminous flux, reflect the incident luminous flux for every portion and generate an emitting luminous flux having a larger diameter than the diameter of the incident luminous flux. Each of the plurality of the partially transmissive reflection surfaces (61 and 62) is made of a reflection diffraction optical element which selectively diffracts and reflects the incident luminous flux. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical system for expanding a beam diameter applied to an image display device, a beam expander, a flat panel illumination device, and the like, an image combiner applied to a see-through image display device, and a see-through image display device.

One of see-through type image display devices (eyeglass displays) is one in which the viewing angle and the exit pupil are enlarged (FIG. 50 of Patent Document 1).
In this type of image display device, a half mirror (partial reflection surface) made of a plurality of parallel reflective multilayer films is provided in a substrate that guides a display light beam, and the substrate has a function of expanding the light beam.
Special Table 2003-536102A

By the way, in the item [0054] and below in Patent Document 1, the incident angle of light (necessary light) to be reflected by the half mirror is 27 °, and the incident angle of light (unnecessary light) to be transmitted by the half mirror is 81. An example is disclosed.
However, in principle, it is difficult to provide a half mirror made of a reflective multilayer film with the characteristic of reflecting light with a small incident angle and transmitting light with a large incident angle. Even if it can be made, special materials are required and the film structure becomes extremely complicated.

Therefore, it is necessary to devise a design so that unnecessary light does not enter the observation eye as much as possible, and even so, ghosts due to unnecessary light are still not completely suppressed.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical system for expanding a light beam diameter that can easily suppress generation of unnecessary light.
Another object of the present invention is to provide an image combiner that has a large viewing angle and exit pupil and that can easily suppress ghosting.

  It is another object of the present invention to provide a see-through type image display apparatus that has a large viewing angle and exit pupil and that can easily suppress ghosts.

In carrying out the present invention, the present inventor studied the following.
(Wavelength characteristics of diffraction efficiency)
The wavelength characteristics of the diffraction efficiency of the reflection type hologram element, particularly the volume type and phase type reflection type hologram element, is sharp wavelength selectivity (only the specific wavelength component of the reproduction light incident at a certain incident angle in a specific direction). (Diffracting properties).

The diffraction efficiency varies depending on the emulsion parameters (thickness and refractive index modulation) for recording the interference fringes of the hologram element (see FIG. 18).
For example,
Emulsion thickness: 15 μm, refractive index modulation: 0.03 → maximum diffraction efficiency: about 98%,
Emulsion thickness: 15 μm, refractive index modulation: 0.015 → maximum diffraction efficiency: about 76%
Emulsion thickness: 5 μm, refractive index modulation: 0.03 → maximum diffraction efficiency: about 52%
It becomes. That is, the diffraction efficiency of the hologram element can be controlled by adjusting the emulsion parameters.

(Angle characteristics of diffraction efficiency)
This hologram element has a sharp characteristic with respect to an incident angle (a characteristic of diffracting only light having a specific incident angle out of reproduction light incident at a certain wavelength) (see FIG. 19).
For example,
Emulsion thickness: 15 μm, refractive index modulation: 0.03 → full width at half maximum: about 7.5 °,
Emulsion thickness: 15 μm, refractive index modulation: 0.015 → full width at half maximum: about 4.5 °,
Emulsion thickness: 5 μm, refractive index modulation: 0.03 → full width at half maximum: about 1.1 °,
It becomes. That is, the peak width of the diffraction angle of this hologram element can be controlled by adjusting the emulsion parameters.

Accordingly, it is possible to give the hologram element the characteristic of reflecting light with a small incident angle and transmitting light with a large incident angle.
(Diffraction efficiency and recording and playback conditions)
In the diffraction by the hologram element, the intensity of the diffracted light emitted in the direction according to the Bragg conditional expression is maximized.

The conditional expression of Bragg in the volume hologram element is expressed by the following expressions (1) and (2), and the intensity of the diffracted light emitted in the direction θ _I satisfying the expressions (1) and (2) is maximized. .
1 / λ _R (sin θ ₀ −sin θ _R ) = 1 / λ _C (sin θ _I −sin θ _C ) (1)
1 / λ _R (cos θ ₀ −cos θ _R ) = 1 / λ _C (cos θ _I −cos θ _C ) (2)
Here, the left side of the expressions (1) and (2) shows the state during recording of the hologram element (FIG. 20A), and the right side shows the state during reproduction of the hologram element (FIG. 20B). Show. However, in the equations (1) and (2),
λ _R : recording wavelength,
θ _{0 is} the incident angle of the object light with respect to the hologram surface,
θ _{R is} the incident angle of the reference beam,
λ _C : reproduction wavelength,
θ _{C is} the incident angle of the reconstructed light with respect to the hologram surface,
θ _I is the exit angle of the diffracted light.

The basis of equation (1) is that “the interval between the interference fringes formed during hologram recording is determined by the incident angles of the object light and the reference light and the recording wavelength” and “at the time of hologram reproduction, It is strengthened when the optical path difference between lights emitted from adjacent stripes is shifted by one wavelength.
Further, the basis of the expression (2) is that these matters are also established between light beams emitted from stripes adjacent in the hologram thickness direction. Incidentally, as the hologram thickness increases, the contribution of equation (2) increases, so the conditions for maximizing the diffraction efficiency become severe.

As is clear from the formulas (1) and (2), it is preferable to make the recording wavelength coincide with the reproduction wavelength in order to easily increase the diffraction efficiency of the hologram element.
(Structure of hologram element)
In the head-mounted image display device, a small and inexpensive LED is suitable for the light source of the image display element. When the image display element is a monochrome image display element, an LED having an emission spectrum composed of a specific color component, and when the image display element is a color image display element, a plurality of specific color components (R color component, G color component, B color component) An LED having an emission spectrum is used.

If the hologram element is applied to the image display apparatus using the latter, the hologram element may be configured to have a three-layer structure that individually responds to each component of the emission spectrum of the LED. Or what is necessary is just to set it as the structure of 1 layer containing the 3 types of microelement which responds to each of those components separately.
Therefore, the present inventor has made the following invention.

  The optical system for enlarging the light beam diameter according to claim 1 is disposed obliquely in a serial and parallel relationship with respect to the optical path of the incident light beam, partially reflecting the incident light beam and having a diameter larger than the incident light beam. An optical system for expanding a light beam diameter, which includes a plurality of partially transmissive reflecting surfaces for generating an emitted light beam, wherein at least one of the plurality of partially transmissive reflecting surfaces is a reflection that selectively diffracts and reflects the incident light beam. It comprises a type diffractive optical element.

  The optical system for enlarging a light beam diameter according to claim 2 is the optical system for enlarging a light beam diameter according to claim 1, wherein each of the plurality of partially transmissive reflecting surfaces is composed of the reflective diffractive optical element, The relationship of the diffraction efficiency with respect to the incident light flux of each of the reflective diffractive optical elements is optimized so that the intensity of light diffracted and reflected by the reflective diffractive optical elements is equalized.

The optical system for enlarging a light beam diameter according to claim 3 is an optical system for enlarging a light beam diameter according to claim 2, wherein each of the plurality of partially transmissive reflecting surfaces is composed of a volume type reflection hologram element, The relationship between the thicknesses of the respective emulsions of the reflection type hologram elements is optimized so that the intensity of light diffracted and reflected by the reflection type hologram elements is equalized.
The optical system for enlarging the light beam diameter according to claim 4 is the optical system for enlarging the light beam diameter according to claim 2 or claim 3, wherein each of the plurality of partially transmitting and reflecting surfaces is a volume type and a phase type. The relationship between the refractive index modulation degrees of the respective reflection type hologram elements is optimized so that the intensity of light diffracted and reflected by these reflection type hologram elements is equalized. To do.

An image combiner according to claim 5 is an optical system for expanding a light beam diameter according to any one of claims 1 to 4 in the substrate transparent to visible light. The optical element is provided in an inclined posture.
According to a sixth aspect of the present invention, there is provided an image display device comprising the image display element and the image combiner according to the fifth aspect.

According to the present invention, an optical system for enlarging a light beam diameter that can easily suppress generation of unnecessary light is realized.
Further, according to the present invention, an image combiner that has a large viewing angle and an exit pupil and that can easily suppress ghost is realized.
In addition, according to the present invention, a see-through type image display device that has a large viewing angle and an exit pupil and can easily suppress a ghost is realized.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described.
The present embodiment is an embodiment of a see-through and head-mounted image display device (eyeglass display).
First, the configuration of the image display apparatus will be described.

As shown in FIG. 1, the present image display device includes a transparent substrate 1 transparent to visible light, and a display unit 1 ′. The transparent substrate 1 and the display unit 1 ′ are supported by the mounting mechanism 1 ″ and are mounted on the observer's head.
The mounting mechanism 1 ″ has, for example, the same configuration as a frame of eyeglasses, and includes a temple, a rim, a bridge and the like as shown in FIG.

When the image display device is mounted on the observer's head, the transparent substrate 1 is positioned in front of the observation eye (here, the right eye of the observer). At this time, the display unit 1 ′ is located at a location that does not obstruct the observer's field of view (here, the vicinity of the right head of the observer).
In the following, in this state, the direction of the visual axis (line of sight) when the observing eye is viewing far away from the front is defined as −Z direction, the observer's lower side is defined as + X direction, and the observer's right side is defined as + Y. The image display device is expressed by a right-handed XYZ orthogonal coordinate system (the same applies to FIG. 2). In some cases, the image display device is expressed in a direction (right, left, up, down, etc.) viewed from the observer.

As shown in FIG. 2, the display unit 1 ′ includes a light source 3, an illumination system 4, a monochrome or color image display element 2, a lens 5, and the like. The lens 5 and the transparent substrate 1 in the display unit 1 ′ serve as an image combiner of the image display device.
As the light source 3, the illumination system 4, and the image display element 2 of the display unit 1 ′, for example, an LED, a parabolic mirror, and an LCD are used. As the LCD, a transmissive LCD, a reflective LCD, or the like is applicable (in FIG. 2, a transmissive LCD is used). Further, the light source 3 and the illumination system 4 can be omitted by using a self-luminous type as the image display element 2.

Such a posture of the display unit 1 ′ is a posture in which the lens 5 is directly opposed to the surface 1 a on the observer side of the transparent substrate 1.
The transparent substrate 1 is based on a parallel plate made of an optical material such as glass or plastic. The posture of the transparent substrate 1 is a posture in which the normal line between the viewer-side surface 1a and the external-side surface 1b is parallel to the Z axis.

Inside the transparent substrate 1, a plane mirror 7 and a plurality of (here, two) reflective hologram elements (hereinafter referred to as “HOE”) 61 and 62 are provided.
The flat mirror 7 is made of a metal film having a high reflectance.
As the hologram photosensitive material of HOE61, 62, for example, photopolymer, photoresist, photochromic, photodichroic, silver salt emulsion, dichromated gelatin, dichromated gelatin, plastic, ferroelectric, magneto-optical material, electro-optical material An amorphous semiconductor, a photorefractive material, or the like is used.

Incidentally, the manufacturing method of the HOEs 61 and 62 irradiates the material simultaneously with recording light emitted from two light sources according to a known method.
The position where the plane mirror 7 is formed is a position facing the display unit 1 ′, and its posture is inclined from the left back of the observer to the right front (the normal of the reflecting surface is perpendicular to the X axis, + Z and -Y orientation). Here, an angle θA formed by the plane mirror 7 and the surfaces 1a and 1b of the transparent substrate 1 is set to 25 °.

The location where the HOE 61 is formed is in the vicinity of a position that is a predetermined distance away from the plane mirror 7 and faces the right half of the observation eye, and its posture is inclined from the left front of the observer to the right back (its normal is Posture perpendicular to the X-axis and facing + Z and + Y directions). Here, an angle θB formed by the HOE 61 and the surfaces 1a and 1b of the transparent substrate 1 is 25 °.
The formation location of the HOE 62 is in the vicinity of the position facing the left half of the observation eye, and the posture thereof is the same as that of the HOE 61.

Incidentally, the manufacturing method of the transparent substrate 1 provided with the HOEs 61 and 62 is, for example, as follows. That is, a small piece made of the same material as that of the transparent substrate 1 on which the HOEs 61 and 62 are formed is placed in a mold that forms the transparent substrate 1, and the material of the transparent substrate 1 is melted in the mold. Pour into and harden.
Next, the behavior of light rays in the image display apparatus will be described.

  When the display unit 1 ′ is driven, the light source 3 and the illumination system 4 illuminate the image display element 2. The display light flux of each angle of view emitted from each point on the display surface of the image display element 2 is converted into a parallel light flux (a display light beam that forms a virtual image of the display surface at infinity behind the image display element 2) in the lens 5. Is done. This display light beam is introduced into the transparent substrate 1 from the surface 1a on the viewer side, and enters the flat mirror 7 to be reflected.

  This display light beam is incident on the surface 1a of the transparent substrate 1 within a predetermined incident angle range (50 ° ± α) (α: half the viewing angle) larger than the critical angle, and is totally reflected. This display light beam is further incident at the same angle on the outer surface 1b and is totally reflected. The display light beam is propagated in the direction from the right to the left (−Y direction) of the observer through the inside of the transparent substrate 1 while repeatedly reflecting such total reflection between the surfaces 1a and 1b. , 62 in order.

Of the display light flux, the light incident on the HOE 61 within a predetermined angle range (25 ° ± α) (the number of total reflections is an odd number) is diffracted and reflected with a predetermined diffraction efficiency, and from the surface 1a of the transparent substrate 1. The light is emitted substantially vertically (the emission angle is 0 ° ± α), and is incident on a region near the observation eye. Display light beams at other angles pass through the HOE 61.
Of the display light flux, the light incident on the HOE 62 within the predetermined angle range (25 ° ± α) (the total number of reflections is an odd number) is diffracted and reflected at another predetermined diffraction efficiency. The light exits from the surface 1a substantially perpendicularly (the exit angle is 0 ° ± α) and enters a region slightly deviated from the region in the vicinity of the observation eye. Display light beams at other angles pass through the HOE 62.

The display light beam diffracted and reflected by the HOE 61 and the display light beam diffracted and reflected by the HOE 62 form an exit pupil of the image display device in the vicinity of the observation eye. If the pupil of the observation eye is arranged in the exit pupil, the observer can observe the virtual image on the display surface of the image display element 2.
Next, characteristics of each part of the image display apparatus will be described.
The wavelength characteristic of the light emission intensity of the light source (here, LED) 3 has a peak at a specific single wavelength when the image display element 2 is a monochrome image display element. When the image display element 2 is a color image display element, the plurality of specific wavelength components (R color component, G color component, B color component) have peaks. Therefore, the display light beam has a single or a plurality of discrete specific wavelength components.

The wavelength characteristics of the diffraction efficiency of the HOEs 61 and 62 have a peak at the specific wavelength component.
Further, the angular characteristics of the diffraction efficiency of the HOEs 61 and 62 have a peak at the center (25 °) of the predetermined angular range described above.
The relationship between the diffraction efficiencies of the HOEs 61 and 62 is set so that the intensity of the display light beam diffracted and reflected by the HOE 61 and the intensity of the display light beam diffracted and reflected by the HOE 62 are equalized.

Next, the effect of the present image display device will be described.
According to the above characteristics of the HOEs 61 and 62, these HOEs 61 and 62 are incident on the display luminous flux necessary for the observation eye to observe the virtual image of the display surface of the image display element 2, that is, in a predetermined angle range (25 ° ± α). The display light beam is diffracted and reflected, and all other light, that is, the display light beam and the external light beam incident at other angles (the light beam traveling from the external side to the observer side of the transparent substrate 1) are transmitted.

Therefore, only the necessary light (the display light beam and the external light beam incident in a predetermined angle range) are incident on the observation eye, and there is no unnecessary light (the display light beam incident at an angle other than the predetermined angle range) that generates a ghost. Not incident. That is, the use of the HOEs 61 and 62 suppresses ghosts.
Further, the design ingenuity for suppressing the ghost is only the optimization of the wavelength characteristics and the angle characteristics of the diffraction efficiency of the HOEs 61 and 62, so that each optical surface (reference numeral 1a,
1b, 5, 7, 61, 62), the degree of freedom of design such as the arrangement relationship and the surface shape is kept high.

Further, since the intensity of the display light flux from the HOEs 61 and 62 toward the observation eye is equalized, the observer can comfortably observe the virtual image on the display surface even if the pupil of the observation eye is displaced within the exit pupil.
Here, if a film having the same characteristics as those of the HOEs 61 and 62 is realized by a dielectric multilayer film, the film structure is complicated with 20 layers or more. In order to deposit such a complex film with high accuracy, the transparent substrate 1 must be formed of a glass substrate. This is because vapor deposition on a plastic substrate is generally composed of a small number of layers of about 5 to 6 layers in order to avoid the influence of radiant heat during vapor deposition due to its heat resistance limit. Therefore, it is difficult to reduce the weight of the image combiner.

However, if it is HOE61,62, the transparent substrate 1 can be comprised with a plastic substrate. For example, in the case of HOE using a photopolymer as a material, the manufacturing process (exposure process) is all a dry process, and the baking temperature is about 120 ° C.
Therefore, in the present embodiment, it is easy to reduce the weight of the transparent substrate 1 and the image display device.

(Design example of the HOEs 61 and 62 of the first embodiment)
Hereinafter, a design example of the HOEs 61 and 62 of the present embodiment will be described.
It is assumed that a color image display element is used as the image display element 2 and an LED having an emission spectrum composed of an R color component, a G color component, and a B color component is used as the light source 3.
The wavelength characteristic of the light emission intensity of the LED is as shown in FIG. The horizontal axis represents wavelength and the vertical axis represents intensity. The full width at half maximum of each wavelength component of the emission spectrum of this LED is R color component: 23 nm, G color component: 60.8 nm, and B color component: 29 nm.

Further, the HOEs 61 and 62 are volume type and phase type reflection type hologram elements, and a three-layer structure for the G color component, the B color component, and the R color component is adopted for the structure. Moreover, the local coordinate system (x, y, z) shown in the circle frame in FIG. 2 was used for the coordinates for expressing the design data.
The design data of HOE61 is
Recording wavelength: 532 nm, 476 nm, 647 nm
HOE material: Photopolymer G emulsion thickness for color component: 3.7 μm,
Emulsion thickness for B color component: 3.2 μm,
Emulsion thickness for R color component: 4.4 μm,
Refractive index modulation degree: 0.03
Shrinkage after recording: 1.5%,
First light source coordinates (x, y, z) at the time of recording: (0, −0.422618 × 10 ²⁰ , −0.906308 × 10 ²⁰ ),
The coordinates (x, y, z) of the second light source at the time of recording: (0, 0.422618 × 10 ²⁰ , −0.906308 × 10 ²⁰ ).

When reproduction light having the same wavelength as the recording wavelength is incident on the HOE 61 at an incident angle of 25 °, the diffraction efficiency of the R color component, G color component, and B color component is about 30%. That is, about 30% of the display light beam incident on the HOE 61 is diffracted and reflected by the HOE 61 toward the observation eye, and the remaining about 70% goes to the HOE 62.
The design data of HOE62 is
Emulsion thickness for G color component: 5.2 μm,
Emulsion thickness for B color component: 4.6 μm,
Emulsion thickness for R color component: 6.2 μm,
Other than that, it is the same as HOE61.

When reproduction light having the same wavelength as the recording wavelength is incident on the HOE 62 at an incident angle of 25 °, the diffraction efficiency is about 50% for the R color component, the G color component, and the B color component. That is, about 70 × 50% = about 35% of the display light beam incident on the HOE 61 is diffracted and reflected by the HOE 62 in the direction of the observation eye.
When the viewing angle in the Y direction of FIG. 1 in this design example is 20 °, the incident angle range of the display light beam diffracted and reflected by the HOEs 61 and 62 is 25 ° ± 10 °.

  The wavelength characteristics of the diffraction efficiency of the HOE 61 described above are as shown in FIGS. 4 (a), 4 (b), and 4 (c). (A) is a characteristic for the R color component, (b) is a characteristic for the G color component, and (c) is a characteristic for the B color component. In each figure, the point plotted with a circular point is the characteristic with respect to the display beam at the maximum field angle in the -Y direction, and the point plotted with a triangle is the characteristic with respect to the display beam with the center field angle, plotted with a square point. These are characteristics with respect to a display light beam having a maximum angle of view in the + Y direction. In each figure, the wavelength characteristic of the intensity of the display light beam incident on the HOE 61 (= wavelength characteristic of the emission intensity of the LED shown in FIG. 3) is also overlaid.

  The wavelength characteristics of the diffraction efficiency of the HOE 62 are as shown in FIGS. 5 (a), 5 (b), and 5 (c). The notation in FIG. 5 is the same as that in FIG. However, since the display light beam incident on the HOE 62 is transmitted through the HOE 61 having a diffraction efficiency of 30%, the intensity of the display light beam in FIG. 5 is shown in FIG. 4 in consideration of the transmittance (70%). The intensity of the display light beam is multiplied by 0.7.

The intensity (emitted intensity) of the display beam diffracted and reflected by the HOE 61 is represented by the product of the intensity of the display beam shown in FIG. 4 and the diffraction efficiency of the HOE 61, and the intensity of the display beam diffracted and reflected by the HOE 62 is shown in FIG. 5 is represented by the product of the intensity of the display light beam shown in FIG.
FIG. 6 and FIG. 7 show the values obtained by calculating the respective intensities and standardizing both of the maximum values as 1. FIG.

FIG. 6 is a graph for the HOE 61, and FIG. 7 is a graph for the HOE 62. 6 and 7, the horizontal axis represents the field angle and the vertical axis represents the relative intensity. The intensity of the R color component of the display light beam is plotted with a circular point, the intensity of the G color component of the display light beam is plotted with a square point, and the intensity of the B color component of the display light beam is plotted with a triangular point. It is.
As described above, since the diffraction efficiency of the HOE 61 and the diffraction efficiency of the HOE 62 are set to 30% and 50%, respectively, the intensity of the display light beam diffracted and reflected by the HOE 61 and the intensity of the display light beam diffracted and reflected by the HOE 62 are As is clear from a comparison between FIGS. 6 and 7, the difference due to the HOE is small and similar.

Note that the vertical axis in these figures indicates the light intensity, and the color balance actually felt by the observer viewing the virtual image on the display surface is not limited to the light intensity but as shown in FIG. Sensitivity needs to be considered. Considering this specific visibility, the brightness of the G color is relatively increased, and it can be seen that the balance of the R, G, and B colors felt by the observer of the present embodiment is good.
Further, in this design example, as apparent from the above design data, different diffraction efficiencies were imparted by changing the emulsion thicknesses of HOE61 and HOE62. Thereby, each diffraction efficiency was able to be controlled reliably.

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described.
The present embodiment is an embodiment of a see-through and head-mounted image display device (eyeglass display). Here, only differences from the first embodiment will be described.
The differences are as follows.

As shown in FIG. 9, the four HOEs formed in the transparent substrate 1 are HOEs 63, 64, 65, and 66 in the order of incidence of the display light beam. In FIG. 9, elements having the same functions as those shown in FIG.
The four HOEs 63, 64, 65, and 66 are diffracted and reflected by the display light beam having an even number of total reflections.

An angle θA formed by the plane mirror 7 and the surfaces 1a and 1b of the transparent substrate 1 is 35 °.
An angle θB formed by the HOEs 63, 64, 65, 66 and the surfaces 1a, 1b of the transparent substrate 1 is 55 °.
The HOEs 63, 64, 65, and 66 diffract and reflect a display light beam in an incident angle range of 55 ° ± α (α: half value of viewing angle) with a predetermined diffraction efficiency. A display light beam having an incident angle other than that is transmitted.

Such an image display apparatus according to the present embodiment can achieve the same effects as the image display apparatus according to the first embodiment.
(Design example of HOE 63, 64, 65, 66 of the second embodiment)
Hereinafter, design examples of the HOEs 63, 64, 65, and 66 according to the present embodiment will be described.
A color image element is assumed as the image display element 2 and an LED having the same characteristics as the first embodiment is assumed as the light source 3.

The HOEs 63, 64, 64, and 66 are volume type and phase type reflection hologram elements, and the three-layer structure for the G color component, the B color component, and the R color component is adopted for the structure. did. Moreover, the local coordinate system (x, y, z) shown in the circle frame in FIG. 9 was used for the coordinates for expressing the design data.
The design data of HOE63 is
Recording wavelength: 532 nm, 476 nm, 647 nm,
HOE material: photopolymer,
Emulsion thickness: 6.4 μm,
Refractive index modulation degree of emulsion for G color component: 0.015
Refractive index modulation degree of emulsion for B color component: 0.013
Refractive index modulation degree of emulsion for R color component: 0.017,
Shrinkage after recording: 1.5%,
Coordinates (x, y, z) of the first light source at the time of recording: (0, −0.819152 × 10 ²⁰ , −0.573576 × 10 ²⁰ ),
The coordinates (x, y, z) of the second light source during recording are (0, 0.819152 × 10 ²⁰ , −0.573576 × 10 ²⁰ ).

When reproduction light having the same wavelength as the recording wavelength is incident on the HOE 63 at an incident angle of 55 °, the diffraction efficiency is about 20% for the R color component, the G color component, and the B color component. That is, about 20% of the display light beam incident on the HOE 63 is diffracted and reflected by the HOE 63 toward the observation eye, and the remaining about 80% goes to the HOE 64.
The design data of HOE64 is
Refractive index modulation degree of emulsion for G color component: 0.017,
Refractive index modulation degree of emulsion for B color component: 0.015
Refractive index modulation degree of emulsion for R color component: 0.02,
Other than that, it is the same as HOE63.

When reproduction light having the same wavelength as the recording wavelength is incident on the HOE 64 at an incident angle of 55 °, the diffraction efficiency is about 25% for the R color component, the G color component, and the B color component. That is, about 80 × 25% = about 20% of the display light beam incident on the HOE 63 is diffracted and reflected by the HOE 64 toward the observation eye, and about 80 × 75% = about 60% goes to the HOE 65.
The design data for HOE65 is
Refractive index modulation degree of emulsion for G color component: 0.02,
Refractive index modulation degree of emulsion for B color component: 0.018,
Refractive index modulation degree of emulsion for R color component: 0.025,
Other than that, it is the same as HOE63.

When reproduction light having the same wavelength as the recording wavelength is incident on the HOE 65 at an incident angle of 55 °, the diffraction efficiency is about 33% for the R color component, the G color component, and the B color component. That is, about 60 × 33% = about 20% of the display light beam incident on the HOE 63 is diffracted and reflected in the direction of the observation eye by the HOE 65, and about 60 × 67% = about 40% goes to the HOE 66.
The design data of HOE66 is
Refractive index modulation degree of emulsion for G color component: 0.03
Refractive index modulation degree of emulsion for B color component: 0.026,
Refractive index modulation degree of emulsion for R color component: 0.035,
Other than that, it is the same as HOE63.

When reproduction light having the same wavelength as the recording wavelength is incident on the HOE 66 at an incident angle of 55 °, the diffraction efficiency is about 50% for the R color component, the G color component, and the B color component. That is, about 40 × 50% = about 20% of the display light beam incident on the HOE 63 is diffracted and reflected by the HOE 66 in the direction of the observation eye.
Here, when the viewing angle in the Y direction of FIG. 9 in this design example is 20 °, the incident angle range of the display light beam diffracted and reflected by the HOEs 63, 64, 65, and 66 is 55 ° ± 10 °.

  The wavelength characteristics of the diffraction efficiency of the HOE 63 described above, the wavelength characteristics of the diffraction efficiency of the HOE 64, the wavelength characteristics of the diffraction efficiency of the HOE 65, and the wavelength characteristics of the diffraction efficiency of the HOE 66 are as shown in FIG. 10, FIG. 11, FIG. It is. The notation in FIG. 10, FIG. 11, FIG. 12, and FIG. 13 is the same as that in FIG. In each figure, the wavelength characteristic of the intensity of the display light beam incident on each HOE is also overlaid.

  However, since the display light beam incident on the HOE 64 is transmitted through the HOE 63 having a diffraction efficiency of 20%, taking into account its transmittance (80%), the intensity of the display light beam in FIG. The intensity of the display light beam is multiplied by 0.8. Similarly, the intensity of the display light beam in FIG. 12 and the intensity of the display light beam in FIG. 13 are values that take into account the transmittance of the HOE that passes through to that point.

  The intensity of the display light beam diffracted and reflected by the HOE 63 is expressed by the product of the intensity of the display light beam shown in FIG. 10 and the diffraction efficiency of the HOE 63. The intensity of the display light beam diffracted and reflected by the HOE 64 is shown in FIG. The intensity of the display light beam that is diffracted and reflected by the HOE 65 is expressed by the product of the intensity of the display light beam and the diffraction efficiency of the HOE 64, and is expressed by the product of the intensity of the display light beam and the diffraction efficiency of the HOE 65 shown in FIG. The intensity of the display light beam diffracted and reflected is represented by the product of the intensity of the display light beam and the diffraction efficiency of the HOE 66 shown in FIG.

FIG. 14, FIG. 15, FIG. 16, and FIG. 17 are obtained by calculating these intensities and normalizing all the maximum values as 1. 14, 15, 16, and 17 are the same as those in FIGS. 6 and 7.
As described above, since the diffraction efficiencies of the HOEs 63, 64, 65, and 66 are set to 20%, 25%, 33%, and 50%, respectively, the intensity of the display light beam that is diffracted and reflected by the HOEs 63, 64, 65, and 66 is As is apparent from a comparison of FIGS. 14, 15, 16, and 17, the differences due to HOE are small and similar.

Note that the vertical axis in these figures indicates the light intensity, and the color balance actually felt by the observer viewing the virtual image on the display surface is the ratio shown in FIG. 8 in addition to the light intensity. It is necessary to consider visibility. Considering this specific visibility, the brightness of the G color is relatively increased, and it can be seen that the balance of the R, G, and B colors felt by the observer of the present embodiment is good.
In this design example, as apparent from the above design data, different diffraction efficiencies were imparted to the emulsions of HOE 63, 64, 65 and 66 by changing the refractive index modulation. Thereby, each diffraction efficiency was able to be controlled reliably.

[Others]
In each of the embodiments described above, in order to control the diffraction efficiency of the HOE, only one of the thickness of the HOE emulsion and the degree of refractive index modulation is adjusted, but both may be adjusted.
Moreover, in each embodiment mentioned above, although the number of HOE provided in the transparent substrate 1 is 2 or 4, you may make it into another number.

  Moreover, in each embodiment mentioned above, the optical path of the display light beam which advances from the observer's right side to the left side inside the transparent substrate 1 is a polygonal line shape (using internal reflection) (FIG. 2). However, the present invention can also be applied to an image display device (an image display device that does not use internal reflection) that is linear. However, even with the transparent substrate 1 having the same thickness, the display light beam having a larger diameter can be guided when the optical path is made into a polygonal line. It is preferable in that both securing and realization can be realized.

  The above-described embodiment is an embodiment of a see-through type image display device (eyeglass display). However, the optical system for expanding a light beam according to the present invention is a non-see-through type image display device (head mounted display), beam expansion. The present invention may be applied to a fixture, a flat panel lighting device, or the like.

It is an external view of a see-through type image display device (eyeglass display). It is sectional drawing in the YZ plane of the optical system part of the image display apparatus of 1st Embodiment. It is a figure which shows the wavelength characteristic of the emitted light intensity of LED. It is a figure which shows the wavelength characteristic of the diffraction efficiency of HOE61, and the incident intensity of the display light beam to HOE61. It is a figure which shows the wavelength characteristic of the diffraction efficiency of HOE62, and the incident intensity of the display light beam to HOE62. It is a figure which shows the emission intensity | strength (viewing angle characteristic) of the display light beam from HOE61. It is a figure which shows the emission intensity | strength (viewing angle characteristic) of the display light beam from HOE62. It is a graph which shows a specific visibility curve. It is sectional drawing in the YZ plane of the optical system part of the image display apparatus of 2nd Embodiment. It is a figure which shows the wavelength characteristic of the diffraction efficiency of HOE63, and the incident intensity of the display light beam to HOE63. It is a figure which shows the wavelength characteristic of the diffraction efficiency of HOE64, and the incident intensity of the display light beam to HOE64. It is a figure which shows the wavelength characteristic of the diffraction efficiency of HOE65, and the incident intensity of the display light beam to HOE65. It is a figure which shows the wavelength characteristic of the diffraction efficiency of HOE66, and the incident intensity of the display light beam to HOE66. It is a figure which shows the emission intensity | strength (viewing angle characteristic) of the display light beam from HOE63. It is a figure which shows the emission intensity | strength (viewing angle characteristic) of the display light beam from HOE64. It is a figure which shows the emission intensity | strength (view angle characteristic) of the display light beam from HOE65. It is a figure which shows the emission intensity | strength (viewing angle characteristic) of the display light beam from HOE66. It is a figure which shows the relationship between the parameter of the emulsion of a hologram element, and diffraction efficiency. It is a figure which shows the relationship between the incident angle of the reproducing light of a hologram element, and diffraction efficiency. (A) is a figure at the time of recording of a hologram element, (b) is a figure which shows the state at the time of reproduction | regeneration of a hologram element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 1 'Display unit 1 "Mounting mechanism 2 Image display element 5 Lens 3 Light source 4 Illumination system 7 Planar mirror 61, 62, 63, 64, 65, 66 Reflection type hologram element (HOE)

Claims (6)

Provided with a plurality of partially transmissive reflecting surfaces that are arranged obliquely in series and in parallel with each other with respect to the optical path of the incident light beam and that partially reflect the incident light beam and generate an emitted light beam having a diameter larger than that of the incident light beam An optical system for expanding the beam diameter,
At least one of the plurality of partially transmissive reflecting surfaces is
An optical system for expanding a light beam diameter, comprising a reflective diffractive optical element that selectively diffracts and reflects the incident light beam. The optical system for expanding a light beam diameter according to claim 1,
Each of the plurality of partially transmissive reflecting surfaces is
The reflective diffractive optical element,
The relationship of the diffraction efficiency with respect to the incident light flux of each of the reflective diffractive optical elements is:
An optical system for expanding a light beam diameter, characterized in that the intensity of light diffracted and reflected by these reflective diffractive optical elements is equalized. The optical system for expanding a light beam diameter according to claim 2, wherein each of the plurality of partially transmissive reflecting surfaces is:
It consists of a volume type reflection hologram element,
The relationship of the emulsion thickness of each of the reflection type hologram elements is as follows:
An optical system for expanding a light beam diameter, characterized in that the intensity of light diffracted and reflected by the reflection hologram elements is optimized. In the optical system for expanding the light beam diameter according to claim 2 or claim 3,
Each of the plurality of partially transmissive reflecting surfaces is
It consists of a volume type and phase type reflection hologram element,
The relationship between the refractive index modulation degrees of the reflection hologram elements is as follows:
An optical system for expanding a light beam diameter, characterized in that the intensity of light diffracted and reflected by the reflection hologram elements is optimized. The optical system for expanding the beam diameter according to any one of claims 1 to 4 is provided in a substrate transparent to visible light so that the plurality of reflective diffractive optical elements are inclined. An image combiner characterized by that. An image display element;
An image display device comprising the image combiner according to claim 5.

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