JP5088707B2 - Laminated wave plate, polarization converter, polarization illumination device, and optical pickup device - Google Patents

Description

  The present invention relates to a laminated wave plate, in particular, a high-order mode laminated wave plate with improved conversion efficiency, a polarization converter using the same, a polarization illumination device b using the polarization converter, and a higher-order mode. The present invention relates to a pickup device using a laminated wave plate.

  Optical wave plates have been used for optical disk devices, liquid crystal displays, liquid crystal projectors, etc., but function as wave plates in the wavelength band of the light used, for example, a half wave plate is used. It is necessary to provide a function such as a phase shift of 180 ° over the wavelength band to be applied. When a half-wave plate is made of a single crystal plate using birefringence of quartz or the like, assuming that the ordinary ray refractive index and extraordinary ray refractive index of the quartz are no and ne, respectively, and the thickness of the quartz plate is t. The phase difference Γ between the ordinary ray and the extraordinary ray when the light of wavelength λ passes through the half-wave plate is given by Γ = 2π / λ × (ne−no) × t, and the phase difference Γ is It depends on the wavelength λ.

  Patent Document 1 discloses a broadband wave plate in which the phase difference is substantially constant in a desired wavelength band. A quarter wavelength plate 40 shown in FIG. 12A is composed of a half wavelength plate 41, an adhesive 42, and a quarter wavelength plate 43. As shown in FIG. 12B, the stretching axis of the half-wave plate 41 is −15 ° with respect to the polarization direction of the linearly polarized light incident on the quarter-wave plate 40, and the stretching axis of the quarter-wave plate 43. Are arranged in the direction of −75 °. In addition, the angle of the said extending | stretching axis | shaft is described by the angle which made the right direction from the y-axis positive in the yz plane. The half-wave plate 41 and the quarter-wave plate 43 are obtained by stretching a polymer film made of polycarbonate. The quarter-wave plate 40 has a wavelength in the visible light range (400 nm to 700 nm). Functioning as an almost perfect quarter-wave plate that does not depend on the above, and the operation of the quarter-wave plate 40 is described using a Poincare sphere.

Further, Patent Document 2 discloses a laminated wave plate in which a plurality of quartz plates are laminated to have a function as a half-wave plate. FIG. 13A is a perspective view showing the configuration of the half-wave plate 44, which is formed by bonding crystal plates 45 and 46 together. FIG. 13B is an exploded perspective view of the half-wave plate 44. Similarly to the crystal plate 45 having a phase difference Γ1 of 190 ° and an optical axis azimuth angle θ1 of 19 ° with respect to a wavelength of 420 nm, similarly to the wavelength of 420 nm. The quartz plate 46 having a phase difference Γ2 of 200 ° and an optical axis azimuth angle θ2 of 64 ° is bonded so that the optical axes 49 and 50 intersect at an angle of 45 °, and the wavelength is 400 nm to 700 nm as a whole. It is disclosed that it is configured to function as a half-wave plate in the high band. As shown in FIG. 13A, when the P-polarized light 47 is incident on the half-wave plate 44, the phase of the outgoing light is shifted by 180 °, so the polarization plane of the incident light is rotated by 90 ° and converted to S-polarized light. It is disclosed that it has a function.
It is disclosed that the relationship between the optical axis azimuth angles θ1 and θ2 is θ2 = θ1 + 45 ° and 0 ° <θ1 <45 °.

The operation of the half-wave plate 44 is explained using a Poincare sphere, but a detailed analysis is made for the respective Mueller matrices A1 and A2 of the quartz plates 45 and 46 and the respective Stokes vectors T indicating the incident and outgoing polarization states. , S, the Stokes vector S is expressed by the following equation.
S = A2 / A1 / T (1)
The phase difference of the half-wave plate 44 can be obtained from the Stokes vector S component.

JP-A-10-68816 JP 2004-170853 A

  However, when a quarter-wave plate described in Patent Document 1 is applied to produce a half-wave plate and used in a liquid crystal projector or the like, there is a problem that yellowing occurs due to the influence of heat. . The half-wave plate described in Patent Document 2 is a single-mode wave plate and needs to be processed so that the phase difference between the two quartz plates is approximately 180 °. When actually manufacturing a quartz plate, it is desirable to set the thickness of the quartz plate to 100 μm or more in consideration of ease of polishing, yield, and the like. However, when a quartz plate having a phase difference of about 180 ° is produced from the difference in refractive index between the ordinary light and extraordinary light of the quartz, the thickness becomes several tens of μm, and the yield is poor and the processing takes time.

  As a means for solving this thickness problem, the crystal plate is cut so that the optical axis of the crystal plate is inclined from the normal direction to the main surface of the crystal plate, thereby reducing the refractive index difference, It is possible to increase the thickness of the plate. Therefore, in Patent Document 2, in consideration of the workability of the thickness of the quartz plate to be used, the cutting angle of the quartz plate is an angle at which the optical axis is 27 ° with respect to the normal direction on the main surface of the quartz plate, It is disclosed that the so-called cut angle is 27 ° Z. However, if the cutting angle of the quartz plate is 27 ° Z, there arises a problem that the change in the phase difference of the half-wave plate with respect to the incident angle becomes large. When a wave plate is used in an optical system of a liquid crystal projector or an optical pickup, the wave plate may be arranged in a path where light converges (diverges) in a conical shape due to the arrangement of the light source and the lens system. In this case, the vicinity of the center of the light beam is perpendicularly incident on the wave plate, but an incident angle is generated at the conical end. For this reason, the use of a half-wave plate with a large variation in phase difference with respect to the incident angle causes a problem of loss of light quantity.

14 shows a quartz plate 45 having a cutting angle of 27 ° Z plate, a phase difference Γ1 of 190 ° with respect to a wavelength of 420 nm and an optical axis azimuth angle θ1 of 19 °, and a phase difference Γ2 of 200 nm with respect to a wavelength of 420 nm. Incidence of a single-mode half-wave plate constructed by bonding a quartz plate 46 having an optical axis azimuth angle θ2 of 64 ° to each other so that the optical axes 49 and 50 intersect at an angle of 45 °. It is the figure which changed the angle | corner with -5 degrees, 0 degrees, and 5 degrees, and showed the conversion efficiency with respect to the wavelength of 350 nm-750 nm.
Here, the conversion efficiency represents the ratio of converting P-polarized light to S-polarized light. When the conversion efficiency is 1, it indicates that all P-polarized light is converted to S-polarized light. Although it is desirable that this conversion efficiency be as high as possible, it is generally said that about 0.93 is necessary. As apparent from FIG. 14, at an incident angle of 5 °, there is a problem that the wavelength is 525 nm or more and the conversion efficiency is 0.9.
An object of the present invention is to provide a high-order mode laminated wave plate that solves the above yellowing, processing yield, incident angle problems, and the like.

The first form according to the present invention is the same as the first wave plate having the phase difference Γ11 with respect to the light having the wavelength λ.
The second wavelength plate of Γ22 is laminated so that the optical axes intersect, and the wavelengths are different from each other.
Converted into linearly polarized light obtained by rotating the plane of polarization of incident linearly polarized light by 90 °
And the second wave plate is configured to emit an in-plane azimuth angle of the first wave plate, θ3,
The in-plane azimuth angle of the wave plate is θ4, and the phase difference of the second wave plate with respect to the wavelength λ1 is Γ21.
1. When the phase difference with respect to the wavelength λ2 (λ1 <λ2) is Γ222, the following equations (12), (1
3) A laminated wave plate configured to satisfy (14), (21), and (22).
Γ11 = 360 ° + 360 ° × 2 × n (12)
Γ22 = 180 ° + 360 ° × n (13)
ΔΓ2 = (Γ222−Γ211) / 2 (14)
cos2θ3 = 1− (1-cosΔΓ2) / 2 {(1-cosmΔΓ2)} (2)
1)
θ4 = 45 ° ± 10 ° (22)
However, n is a natural number starting from 1, m = 2
According to such a laminated wave plate, there is an effect that the thickness of the two wave plates constituting the laminated wave plate can be easily processed by appropriately setting n.
The second embodiment according to the present invention is a laminated wavelength in which n = 4, θ3 = −16 °, or −21 °.
It is a board. With this configuration, blue, green, and red wavelengths used in liquid crystal projectors
Wavelength-conversion efficiency characteristics of laminated wave plates in the 400 nm band, 500 nm band, and 675 nm band
Is effective to be 0.94 or more.
A third embodiment according to the present invention is a laminated wavelength in which n = 5, θ3 = −16 °, or −21 °.
It is a board. By configuring in this way, as a wave plate for a three-wavelength compatible optical pickup
Wavelength-variation of laminated wave plates in the required wavelength bands of 405 nm, 660 nm, and 785 nm
There is an effect that the conversion efficiency characteristic can be made approximately 0.94 or more.
According to a fourth aspect of the present invention, the first main surface is a light incident surface and the second main surface is a light emitting surface.
A plate-like translucent base material, first and second optical thin films provided in the base material, and the base material
A wave plate provided on the second main surface of the first and second optical thin films, wherein the first and second optical thin films are
Inclining relative to the first and second main surfaces, arranged alternately and parallel to each other,
The first optical thin film has a first linear polarization that is orthogonal to each other from light incident from the first main surface side.
Separating the light and the second linearly polarized light to transmit the first linearly polarized light and to convert the second linearly polarized light into
And the second optical thin film reflects the second linearly polarized light reflected by the first optical thin film.
Reflecting and emitting from the second main surface, the wave plate is disposed on the second main surface,
A polarization that converts the first linearly polarized light transmitted through the first optical thin film into a second linearly polarized light and emits it.
An optical conversion element, wherein the wave plate is a laminated wave plate according to any one of the first to third modes
This is a polarization conversion element. As a result, the intensity of linearly polarized light (S-polarized light) emitted from the polarization converter is increased.
The degree can be strengthened.
According to a fifth aspect of the present invention, there is provided the laminated wave plate according to any one of the first to third aspects.
This is a polarized illumination device. Thus, the laminated wave plate according to any one of the first to third embodiments
By constructing an illuminating device using this, the intensity of linearly polarized light (S-polarized light) emitted from the illuminating device
There is an effect that the degree can be strengthened.
According to a sixth aspect of the present invention, a light source and the light emitted from the light source are collected on an optical recording medium.
And a laminated wave plate according to any one of the first to third embodiments.
This is an optical pickup device. In this way, the laminated wavelength of any of the first to third forms
If a three-wavelength optical pickup device is configured using a plate, three conventional wavelength plates are required.
It can be realized with a laminated wave plate.
Also, the laminated wave plate according to any one of the first to third modes and a laser having three wavelengths are emitted.
If an optical pickup device for three wavelengths is configured with a laser diode that
The cost of the optical pickup device can be reduced.
There is an effect that.
Application Example 1 A laminated wave plate according to Application Example 1 of the present invention is affixed so that an optical axis intersects a first wave plate having a phase difference Γ1 and a second wave plate having a phase difference Γ2 with respect to the wavelength λ. In total, 1
A laminated wave plate that functions as a two-wave plate, wherein the in-plane azimuth angle of the first wave plate is θ1, the in-plane azimuth angle of the second wave plate is θ2, and is incident on the laminated wave plate When the angle between the polarization direction of the linearly polarized light and the polarization direction of the linearly polarized light emitted from the laminated wave plate is θ, the following expressions (1) to (3) are satisfied. Laminated wave plate.
Γ1 = 180 ° + 360 ° × n (1) , Γ2 = 180 ° + 360 ° × n (2)
) , Θ2 = θ1 + θ / 2 (3) where n is a natural number starting from 1 .
According to such a laminated wave plate, there is an effect that the thickness of the two wave plates constituting the laminated wave plate can be easily processed by appropriately setting n.

Application Example 2 A laminated wave plate according to Application Example 2 of the present invention has n = 4, θ1 = 22.5 °, θ2
= 67.5 °. With this configuration, blue used in a liquid crystal projector, green wavelength band 400nm band of red, 500 nm band, the wavelength of the laminated wave plate in 675nm band - there is an effect that it conversion efficiency characteristics approximately 1.

Application Example 3 A laminated wave plate according to Application Example 3 of the present invention has n = 5, θ1 = 22.5 °, θ2
= 67.5 °. By being configured in this way, the wavelength-conversion efficiency characteristic of the laminated wave plate can be made almost 1 in the wavelength bands 405 nm band, 660 nm band, and 785 nm band required as a wave plate for a three-wavelength compatible optical pickup. is there.

Application Example 4 In the laminated wave plate according to Application Example 4 of the present invention , the optical axis intersects the first wave plate having the phase difference Γ11 and the second wave plate having the phase difference Γ22 with respect to the wavelength λ. A laminated wave plate that functions as a half-wave plate as a whole, the in-plane azimuth angle of the first wave plate is θ3, and the in-plane azimuth angle of the second wave plate is θ4. When the phase difference with respect to the wavelength λ1 of the second wave plate is Γ211 and the phase difference with respect to the wavelength λ2 (λ1 <λ2) is Γ222,
Γ1l = 360 ° + 360 ° × 2 × n, Γ22 = 180 ° + 360 ° × n, cos 2θ3
= 1- (1-cosΔΓ2) / 2 (1-cos2ΔΓ2), θ4 = 45 ° ± 10 °, where n is a natural number starting from 1, ΔΓ2 = (Γ222−Γ211) / 2. According to such a laminated wave plate, by appropriately setting the orders nl and n2,
There is an effect that the thickness of the two wave plates constituting the laminated wave plate can be easily processed.

Application Example 5 In the laminated wave plate according to Application Example 5 of the present invention , n = 4, θ3 = −16 °, or −21 °. With this configuration, the wavelength of the laminated half-wave plate in the blue, green, and red wavelength bands 400 nm, 500 nm, and 675 nm used in the liquid crystal projector is −
There is an effect that the conversion efficiency characteristic can be 0.94 or more.

Application Example 6 The laminated wave plate according to Application Example 6 of the present invention was set to n = 5, θ3 = −16 °, or −21 °. With this configuration, a wavelength band 405nm band required as a wavelength plate for three-wavelength handling optical pickup, 660 nm band, the wavelength of the laminated wave plate in 785nm band - that the conversion efficiency characteristic may be 0.94 or more effective.
Application Example 7 A polarization converter according to Application Example 7 of the present invention is a polarization beam splitter array P.
The Henkode morphism surface and characterized in that the configuration Paste the above laminated wave plate.
As described above, by configuring the polarization converter using the laminated wave plate, there is an effect that the intensity of the linearly polarized light (S-polarized light) emitted from the polarization converter can be increased.

Application Example 8 A polarized light illumination device according to Application Example 8 of the present invention includes the laminated wave plate according to any one of Application Examples 1 to 6 of the present invention . As described above, by configuring the illuminating device using the laminated wave plates of Application Examples 1 to 6 of the present invention, there is an effect that the intensity of linearly polarized light (S-polarized light) emitted from the illuminating device can be increased.

Application Example 9 The optical pickup device according to Application Example 9 of the present invention is applied in Application Examples 1 to 6 of the present invention.
Any one of the laminated wave plates is configured. Thus, any one of the application examples 1 to 6 of the present invention
When a three-wavelength compatible optical pickup device is configured using the laminated wave plates, it is possible to realize a half-wave plate, which has been conventionally required, with a single laminated wave plate.
In addition, if an optical pickup device corresponding to three wavelengths is configured by the laminated wave plate according to any one of the application examples 1 to 6 of the present invention and a laser diode that emits a laser having three wavelengths, optical components can be greatly reduced. Thus, the cost of the optical pickup device can be reduced.

(A) is the schematic perspective view which showed the structure of the lamination | stacking 1/2 wavelength plate of the higher order mode which concerns on this invention, (b) is a disassembled perspective view. (A) is a perspective view of the Poincare sphere for explaining the present invention, (b) is a perspective view of the Poincare sphere to the S1S2 plane. The wavelength-conversion efficiency characteristic figure of the lamination | stacking 1/2 wavelength plate which concerns on this invention. The wavelength-conversion efficiency characteristic view of the other laminated 1/2 wavelength plate which concerns on this invention. The exploded perspective view of the lamination half wave plate of the 2nd example. (A) is the wavelength-conversion efficiency characteristic figure of the lamination | stacking 1/2 wavelength plate of 2nd Example, (b) is the wavelength-conversion efficiency characteristic figure after optimization. (A) is the wavelength-conversion efficiency characteristic figure of the other lamination | stacking 1/2 wavelength plate of a 2nd Example, (b) is the wavelength-conversion efficiency characteristic figure after optimization. (A) is a perspective view of the Poincare sphere for explaining the present invention, (b) is a perspective view of the Poincare sphere to the S1S3 plane, and (c) is a perspective view of the Poincare sphere to the S2S3 plane. Schematic which shows the structure of the polarization converter which concerns on this invention. Schematic which shows the structure of the polarization illumination apparatus which concerns on this invention. (A) is a block diagram of an optical pickup device according to the present invention, (b) is a block diagram of another optical pickup device according to the present invention. (A) is a perspective view which shows the structure of the conventional quarter wavelength plate, (b) is a figure which shows the extending | stretching axis direction of each wavelength plate. (A) is the schematic perspective view which showed the structure of the conventional single mode lamination | stacking 1/2 wavelength plate, (b) is a disassembled perspective view. The wavelength-conversion efficiency characteristic view of the conventional single mode laminated half-wave plate.

Embodiments according to the present invention will be described below in detail with reference to the drawings. FIG. 1A is a perspective view showing a configuration of a high-order mode laminated half-wave plate (hereinafter referred to as a laminated half-wave plate) 1, which includes a first wave plate 2 using crystal, The second wave plate 3 and the second wave plate 3 are bonded so that their optical axes intersect with each other, and the second wave plate 3 functions as a half-wave plate as a whole. FIG. 1B is an exploded perspective view of the half-wave plate 1 where the optical axis azimuth angle of the first wave plate 2 is θ1, and the optical axis azimuth angle of the second wave plate 3 is θ2. The phase difference of the first wave plate 2 with respect to a predetermined wavelength λ, for example, 400 nm is Γ1, the phase difference of the second wave plate 3 is Γ2, and
Γ1 = 180 ° + 360 ° × n (2)
Γ2 = 180 ° + 360 ° × n (3)
The thicknesses of the first and second wave plates 2 and 3 are set so as to satisfy the above. Here, n is the order of the higher order mode, and is a natural number starting from 1.

When a high-order mode wave plate is used for the first and second wave plates 2 and 3 and the half-wave plate 1 is configured as a whole, the phase difference is 180 ° over the entire wavelength band of wavelengths from 350 nm to 750 nm. It is difficult to do.
Therefore, in order to set the phase difference to 180 ° in a desired plurality of wavelength bands, the higher-order mode orders n1 of the first and second wavelength plates 2 and 3 which are the configuration parameters of the laminated half-wave plate 1 are used. , N2, and various phase differences Γ1, Γ2 at respective predetermined wavelengths and respective optical axis azimuth angles θ1, θ2 are variously calculated to calculate a Stokes vector of the emitted light from the laminated half-wave plate 1, A method for obtaining the phase difference, conversion efficiency, etc. was adopted.

  First, a calculation method for finding an example of the laminated half-wave plate according to the present invention will be briefly described. The polarization state after the linearly polarized light passes through the two wave plates can be expressed using a Mueller matrix or a Johns matrix.

E = R ₂ · R ₁ · I (4)

Here, I is a vector representing the polarization state of incident light, and E is a vector representing the polarization state of outgoing light. R ₁ is a Mueller matrix of the first wave plate 2 in the laminated half-wave plate 1, and R ₂ is a Mueller matrix of the second wave plate 3, which are represented by the following equations, respectively.

The higher order mode orders n of the first and second wave plates 2 and 3 are determined, the respective phase differences Γ1 and Γ2, and the optical axis azimuth angles θ1 and θ2 are set. The matrices R ₁ and R ₂ are obtained. When the polarization state I of the incident light is set, the polarization state E of the emitted light can be calculated from the equation (4).
The case where a Mueller matrix is used as the matrix will be described. The polarization state E of the emitted light is expressed by the following equation.

The matrix elements S ₀₁ , S ₁₁ , S ₂₁ and S ₃₁ of E are called Stokes parameters and represent the polarization state. Using this Stokes parameter, the phase difference Γ of the wave plate is expressed as follows.

  In this way, the phase difference can be calculated using Expression (8).

  As shown in FIG. 1, the laminated half-wave plate 1 according to the present invention has a function of rotating the polarization plane of linearly polarized light by a predetermined angle θ. For example, linearly polarized light 4 having a vertical vibration surface is input as input light, transmitted through the laminated half-wave plate 1, and the polarization surface is rotated by θ = 90 ° (phase modulation) to have a horizontal vibration surface. Consider a case where light is emitted as linearly polarized light 5 using the Poincare sphere shown in FIG. Considering the Poincare sphere, this phase modulation (90 ° rotation) is to modulate from the incident polarization state P0 to P2, and the necessary phase difference is 180 °. However, when modulation is performed from P0 to Pa and from P0 to Pb, the phase difference is also 180 °. That is, when the evaluation is performed using the phase difference, it cannot be determined whether the light is modulated to a necessary polarization state. P2 on the Poincare sphere (on the equator) and points of different Pa and Pb are directions of the plane of polarization. In order to detect this, the polarization state can be accurately determined by calculating the product of the matrix E representing the polarization state of the outgoing light and the matrix P of the polarizer and using the obtained light quantity as an evaluation value. . This is defined as conversion efficiency.

  Specifically, the polarization axis in the 90 ° direction is determined from the Stokes parameter of the matrix T obtained by setting the transmission axis of the matrix P of the polarizer to 90 ° and the product of the matrix P and the matrix E representing the outgoing light polarization state. The light quantity of the component can be calculated. The product of the matrix E representing the outgoing light polarization state and the polarizer matrix P is as follows.

  T = P ・ E (9)

  Here, the matrix T represents the conversion efficiency, and is represented by the following equation when represented by the Stokes parameter of the element.

Here, the Stokes parameter S ₀₂ of the vector T represents the amount of light. If the amount of incident light is set to 1, S ₀₂ becomes the conversion efficiency. Both the phase difference and the conversion efficiency can be obtained from the matrix E representing the polarization state after passing through the laminated half-wave plate.

  Using the above conversion efficiency as an evaluation criterion, the higher-order mode orders n of the first and second wave plates 2 and 3 which are various parameters of the laminated half-wave plate, and the predetermined wavelength (for example, wavelength 400 nm), respectively. The phase differences Γ1 and Γ2 and the respective optical axis azimuth angles θ1 and θ2 were variously changed, and simulation was performed using a computer. The simulation was repeated and the above parameters were selected when the conversion efficiency was good in a desired plurality of wavelength bands. If the higher-order mode order n is too large, the wavelength bandwidth with a conversion efficiency close to 1 is narrowed, making it difficult to use as a laminated half-wave plate, so the above parameters were selected including the ease of manufacturing. The results will be described below.

  The cutting angles of the first and second wave plates 2 and 3 of the laminated half-wave plate 1 shown in FIG. 1 are each 90 ° Z (the normal direction on the main surface of the quartz plate and the optical axis (z axis). When the crossing angle is 90 °, the order n of the higher order mode is 4, and the wavelength λ is 400 nm, the phase difference Γ1 of the first wave plate and the optical axis azimuth angle θ1 are 1620 ° (= 180 ° + 360 °), respectively. × 4) When the phase difference Γ2 of the second wave plate and the optical axis azimuth angle θ2 are set to 1620 ° (= 180 ° + 360 ° × 4) and 67.5 °, respectively, the laminate 1 As a result of obtaining the conversion efficiency of the / 2 wavelength plate 1 by simulation, a good wavelength-conversion efficiency was obtained. FIG. 3 is a diagram showing the conversion efficiency of the laminated half-wave plate 1 for wavelengths from 350 nm to 750 nm.

  The conversion efficiency when the incident angle to the laminated half-wave plate 1 is 0 ° is indicated by a solid line, and the conversion efficiency when the incident angle is −5 ° and + 5 ° are marked with diamonds and triangles, respectively. Although they are displayed, they are almost overlapping curves. Since the wavelengths of blue, green, and red used in the liquid crystal projector are 400 nm band, 500 nm band, and 675 nm band, respectively, it has been found that the conversion efficiency of the laminated half-wave plate 1 with the above parameters is almost 1.

  Further, the cutting angles of the first and second wave plates 2 and 3 of the laminated half-wave plate 1 are each 90 ° Z (intersection angle between the normal direction on the main surface of the crystal plate and the optical axis (z axis)) Is 90 °), the order n of the higher-order mode is 5, and the wavelength λ is 400 nm, the phase difference Γ1 of the first wave plate and the optical axis azimuth angle θ1 are 1980 ° (= 180 ° + 360 ° × 5), respectively. ) Good conversion efficiency when the phase difference Γ2 of the second wave plate and the optical axis azimuth angle θ2 are set to 1980 ° (= 180 ° + 360 ° × 5) and 67.5 °, respectively. was gotten. FIG. 4 is a diagram showing the conversion efficiency of the laminated half-wave plate 1 for wavelengths from 350 nm to 750 nm. The conversion efficiency when the incident angle to the laminated half-wave plate 1 is 0 ° is indicated by a solid line, and the conversion efficiency when it is set to −5 ° and + 5 ° is indicated by diamonds and triangles. However, the curves are almost overlapping. In the case of the laminated half-wave plate 1 using the above parameters, the conversion efficiency may be almost 1 at wavelengths of 405 nm band, 660 nm band, and 785 nm band required as a wave plate for a three-wavelength compatible optical pickup. I understood.

  Here, the relationship between the optical axis azimuth θ1 of the first wave plate 2 and the optical axis azimuth θ2 of the second wave plate 3 will be described using the Poincare sphere shown in FIG. FIG. 2A is a diagram for explaining the transition of the trajectory on the Poincare sphere of linearly polarized light incident on the half-wave plate 1. When light rays are incident as linearly polarized light 4 whose polarization direction is perpendicular to the equator from a predetermined position P0 on the equator, the first wave plate 2 rotates 180 ° about the optical axis R1 and P1 (equator) The linearly polarized light 5 is rotated by 180 ° about the optical axis R2 by the second wave plate 3 and reaches P2 (on the equator) and rotated by θ = 90 ° with respect to the linearly polarized light 4. It can be seen that the light is emitted from the half-wave plate 1.

Next, the relationship between θ1 and θ2 will be examined with reference to FIG.
FIG. 2B is a view (projected on the S1S2 plane) of the locus of the polarization state of the light beam incident on the half-wave plate 1 in the Poincare sphere shown in FIG. Show. The relationship between the optical axis azimuth angle θ1 of the first wave plate 2, the optical axis azimuth angle θ2 of the second wave plate 3, and the rotation angle θ of the linearly polarized light 5 (emitted light) with respect to the linearly polarized light 4 (incident light) is On the Poincare sphere, it can be represented as shown in FIG.
A triangle OP0P1 connecting the points O, P0, and P1 is an isosceles triangle having the point O as an apex, and the optical axis R1 is a bisector of the triangle OP0P1, and the angle and side OP1 formed by the side OP0 and the optical axis R1 And the optical axis R1 is 2θ1. A triangle OP1P2 connecting the points O, P1, and P2 is an isosceles triangle having the point O as an apex, and the optical axis R2 is a bisector of the triangle OP1P2. Here, the angle α formed by the side OP1 and the optical axis R2 and the angle α formed by the side OP2 and the optical axis R2 are obtained as follows.
2θ = 2 × 2θ1 + 2α
α = θ-2θ1
Therefore, the angle 2θ2 formed by the side OP0 and the optical axis R2 can be expressed as follows.
2θ2 = α + 2 × 2θ1 = θ-2θ1 + 2 × 2θ1 = θ + 2θ1
Therefore, θ2 is
θ2 = θ1 + θ / 2 (11)
It can be expressed as.

Next, FIG. 5 is an exploded perspective view of a high-order mode laminated half-wave plate (hereinafter referred to as a laminated half-wave plate) 1 ′ according to the second embodiment of the present invention. A structure in which the wave plate 2 ′ and the second wave plate 3 ′ are bonded so that their optical axes intersect with each other is provided, and functions as a half-wave plate as a whole. The higher order modes of the first and second wave plates 2 ′ and 3 ′ are n1 and n2, and the phase differences of the first and second wave plates 2 ′ and 3 ′ are Γ11, Γ22, and the optical axis. The azimuth angles are θ3 and θ4, respectively. The wavelength λ that determines the phase difference is 400 nm, and the order n is a natural number starting from 1. The configuration conditions of the laminated half-wave plate 1 ′ of the second example were set as follows:
Γ11 = 360 ° + 360 ° × 2 × n (12)
Γ22 = 180 ° + 360 ° × n (13)

  The parameters n, Γ11, Γ22, θ3, and θ4 constituting the first and second wave plates 2 ′ and 3 ′ are set so as to satisfy the expressions (12) and (13), and the laminated half wavelength A plate 1 'is constructed. A simulation was performed by changing the above parameters, and a combination of parameters having good conversion efficiency was obtained. As a result, the cutting angles of the first and second wave plates 2 ′ and 3 ′ are each 90 ° Z (the intersecting angle between the normal direction on the main surface of the quartz plate and the optical axis (z axis) is 90 °), When the order n of the higher-order mode is 4 and the wavelength λ is 400 nm, the phase differences Γ11 and Γ22 of the third and fourth wave plates 2 ′ and 3 ′ are 3240 ° (= 360 ° + 360 ° × 2 × 4), respectively. When the optical axis azimuth angles θ3 and θ4 are −16 ° and 45 °, 1620 ° (= 180 ° + 360 ° × 4), the wavelength-conversion efficiency characteristics are good.

  FIG. 6A is a diagram showing the conversion efficiency characteristics of the laminated half-wave plate 1 'for wavelengths from 350 nm to 750 nm. The conversion efficiency of the laminated half-wave plate 1 ′ when the incident angle is 0 ° is indicated by a solid line, and the conversion efficiency when the incident angle is −5 ° and + 5 ° are marked with rhombuses and triangles, respectively. Although they are displayed, they are almost overlapping curves. Since the blue, green, and red wavelengths used in the liquid crystal projector are 400 nm band, 500 nm band, and 675 nm band, respectively, the conversion efficiency of the laminated half-wave plate 1 ′ in each wavelength band may be 0.94 or more. found. Furthermore, when optimization was attempted with respect to θ3 and θ4, the wavelength-conversion efficiency characteristics as shown in FIG. 6B are 400 nm band and 500 nm as compared to the wavelength-conversion efficiency characteristics shown in FIG. The bandwidth of the band and the 675 nm band could be expanded respectively. The values of the optical axis azimuth angles after the optimization are θ3 = −21 ° and θ4 = 37.5 °.

FIG. 7 shows another example of parameters in the second embodiment. The cutting angles of the first and second wave plates 2 ′ and 3 ′ are 90 ° Z, the order n of the higher mode is 5, and the wavelength λ. The phase differences Γ11 and Γ22 of the third and fourth wave plates 2 ′ and 3 ′ are set to 3960 ° and 1980 °, and the optical axis azimuth angles θ3 and θ4 are set to −16 ° and 45 °, respectively. In some cases, the conversion efficiency was good.
FIG. 7A is a diagram showing the conversion efficiency of the laminated half-wave plate 1 ′ for wavelengths from 350 nm to 750 nm. The conversion efficiency when the incident angle to the laminated half-wave plate 1 ′ is 0 ° is indicated by a solid line, and the conversion efficiency when it is set to −5 ° and + 5 ° is indicated by diamonds and triangles. There are almost overlapping curves. In this example, the conversion efficiency of 0.93 required for the half-wave plate was cleared in the 405 nm band, 660 nm band, and 785 nm band for the three-wavelength optical pickup, and a value of 0.94 or more was obtained. . Furthermore, when optimization was attempted for θ3 and θ4, the wavelength-conversion efficiency characteristics as shown in FIG. 7B were 405 nm band, 660 nm as compared to the wavelength-conversion efficiency characteristics shown in FIG. The bandwidths of the band and the 785 nm band could be expanded respectively. The values of the optical axis azimuth angles after the optimization are θ3 = −21 ° and θ4 = 37.5 °.

  Here, the optical action of the first wave plate 2 'and the second wave plate 3' constituting the laminated half-wave plate 1 'shown in FIG. 5 will be described with reference to FIG. FIG. 8A is a diagram for explaining the transition of the trajectory of the linearly polarized light 4 incident on the laminated half-wave plate 1 ′ on the Poincare sphere. FIG. 8B is a view of the locus of the polarization state of the light beam incident on the laminated half-wave plate 1 ′ in the Poincare sphere shown in FIG. 8A as seen from the S2 axis direction (projected on the S1S3 plane). ). FIG. 8C is a view of the locus of the polarization state seen from the S1 axis direction in order to explain the function of the first wave plate 2 ′ of the laminated half-wave plate 1 ′ according to the present invention (S2S3). The figure projected on the plane). In FIGS. 8B and 8C, when the light beam of the linearly polarized light 4 enters the predetermined position P0 on the equator of the Poincare sphere, it is rotated 360 ° around the optical axis R1 by the first wave plate 2 ′. It reaches P1 (P0 = P1), and further rotates by 180 ° about the optical axis R2 by the second wave plate 3 ′, and reaches P2 (equator), thereby exiting the laminated half-wave plate 1 ′. It can be seen that the light beam to be emitted becomes the linearly polarized light 5 rotated by θ = 90 ° with respect to the linearly polarized light 4 (incident light) and is emitted from the laminated half-wave plate 1 ′.

Here, when the phase difference Γ22 of the second wave plate 3 ′ causes a phase change of ΔΓ2 due to the change of the wavelength of the incident light, this phase change ΔΓ2 is expressed by the phase change ΔΓ1 due to the wavelength of the first wave plate 2 ′. If cancelled, the wavelength dependence of the laminated half-wave plate 1 'can be suppressed and function as a half-wave plate in a plurality of wavelength bands.
Further, the phase change ΔΓ2 due to the wavelength of the second wave plate 3 ′ has a constant value determined by the wavelength dispersion of the substrate material, and the phase change ΔΓ1 due to the wavelength of the first wave plate 2 ′ is the first value. The size can be varied by adjusting the in-plane azimuth angle θ3 of the wave plate 2 ′.
Therefore, a relational expression between the first wave plate 2 ′ and the second wave plate 3 ′ is derived below.
When the wavelength of the incident light changes between the reference wavelength (design wavelength) λ0 and the wavelengths λ1 to λ2 (λ1 <λ2), the first wavelength plate 2 ′ and the second wavelength plate 3 are caused by the wavelength dependency of the wavelength plate. The phase difference of 'varies from Γ11 and Γ22, respectively.
In addition, in the phase difference of the second wave plate,
When defined as Γ211: phase difference at wavelength λ1, Γ222: phase difference at wavelength λ2, the phase change ΔΓ2 due to the wavelength of the second wave plate 3 ′ satisfies the following equation.
ΔΓ2 = (Γ222−Γ211) / 2 (14)

In FIG. 8B, it is assumed that the coordinate P0 (P1) on the Poincare sphere is changed to P1 ″ due to the phase change ΔΓ2 generated in the second wave plate 3 ′, and this distance P0 → P1 ″ is approximated. Is represented by a straight line x2, ΔΓ2 and x2 satisfy the relationship of the following expression (1).
(X2) ² = 2k ² -2k ² cos ΔΓ2 (15)
However, k shows the radius of a Poincare sphere.
Next, similarly, in FIG. 8C, it is assumed that the coordinate P0 (P1) on the Poincare sphere is changed to P1 ′ by the phase change ΔΓ1 generated in the first wave plate 2 ′, and this P0 → P1 ′. Is approximately represented by a straight line x1, ΔΓ1 and x1 satisfy the relationship of the following expression (16).
(X1) ² = 2r ² -2r ² cos ΔΓ1 (16)
However, r is a radius when rotating Γ11 with R1 as the rotation axis.
Further, r can be expressed by the following equation (17) using the in-plane azimuth angle θ3 of the first wave plate 2 ′.
r ² = 2k ² -2k ² cos 2θ3 (17)

Further, when Expression (17) is substituted into Expression (16), Expression (18) is obtained.
(X1) ² = 4k ² (1-cos 2θ3) (1-cos ΔΓ1) (18)
Therefore, in order for the phase changes of the first wave plate 2 ′ and the second wave plate 3 ′ to cancel each other, it is necessary that x1≈x2, and from the equations (15) and (18) ( x1) ² = (x2) ² 2
The relationship k ² −2k ² cos ΔΓ ² = 4 k ² (1−cos 2θ3) (1−cos ΔΓ1) is established.
Therefore, when k is normalized and collected, Expression (19) is obtained.
cos2θ3 = 1− (1-cosΔΓ2) / { 2 (1-cosΔΓ1) } (19
)
Next, when the first wave plate 2 ′ and the second wave plate 3 ′ are made of the same dispersion substrate material, and Γ11 / Γ22 = m, Expression (20) is obtained.
ΔΓ1 = mΔΓ2 (20)
Therefore, when equation (20) is substituted into equation (19), equation (21) is obtained.
cos2θ3 = 1− (1-cosΔΓ2) / { 2 (1-cosmΔΓ2) } (2
1)
Equation (21) is obtained by the phase change ΔΓ2 caused by the second wave plate 3 ′.
It is shown that the in-plane azimuth angle θ3 is determined.

Next, specific parameters of the first wave plate 2 ′ and the second wave plate 3 ′ constituting the laminated half-wave plate 1 ′ are calculated using the above-described calculation formula.
As a specific example, parameters are calculated for a laminated half-wave plate that functions as a half-wave plate in a plurality of wavelength bands in a wavelength band of 350 nm to 850 nm.
For example, the phase difference Γ11 = 3240 ° (= 360 ° + 360 ° × 2 × 4) of the first wave plate 2 ′, and the phase difference Γ = 1620 ° (= 180 ° + 360 ° × 4) of the second wave plate 3 Then,
m = Γ1 / Γ2 = 2
It becomes.
Next, as for θ4, the value of θ4 is set to 45 ° in order to emit the linearly polarized light incident on the second wave plate 3 ′ as linearly polarized light rotated by 90 °. In order to optimize the solution, the variable range is set to ± 10 °,
θ4 = 45 ° ± 10 ° (22)
It was.

  FIG. 9 is a block diagram showing an embodiment of the polarization converter according to the present invention. The polarization beam splitter array (polarization separation element) 10 has a laminated 1 / A polarization converter is formed by attaching the two-wavelength plate 11. As is well known, the configuration of the polarizing beam splitter array 10 is formed by joining a plurality of parallelepiped transparent members formed using optical glass or the like as shown in FIG. A plurality of parallelogram-shaped prisms are bonded to each other, and the polarization separating portion 13 is formed on one inclined surface of the bonded prism, and the reflection film 14 is formed on the other inclined surface. The action of the polarization converter is that when light (random light) 12 enters the incident surface of the polarization beam splitter array 10, among the random light, P-polarized light is transmitted through the polarization separation unit 13, and the exit surface of the polarization beam splitter array 10. Is converted to S-polarized light by the laminated half-wave plate 11 attached to the light and emitted. On the other hand, the S-polarized light in the random light is reflected by the polarization separation unit 13 and further reflected by the reflection film 14 to be emitted from the polarization converter. The feature of the polarization converter of the present invention is that it has high conversion efficiency from P-polarized light to S-polarized light and can produce strong polarized light.

  FIG. 10 is a block diagram showing an embodiment of the polarization illumination device according to the present invention, which includes a light emitting light source 15, a lens array 18, and the laminated half-wave plate 19 of the present invention described above. Yes. The light-emitting light source 15 includes a lamp 16 such as an ultra-high pressure mercury lamp or a xenon lamp and a reflecting mirror 17, for example, a parabolic reflecting mirror, and light emitted from the lamp 16 is substantially parallel to the optical axis of the parabolic reflecting mirror 17. It becomes light. The light emitted from the lamp 16 is natural light (random light), and can be represented by the sum of two orthogonal linearly polarized light (P-polarized light and S-polarized light) having the same intensity. When the random light is transmitted through the laminated half-wave plate 19, it is a polarized light illumination device that is converted into only S-polarized light.

  FIG. 11A is a block diagram showing an embodiment of the three-wavelength compatible optical pickup 20 according to the present invention. A laser diode (hereinafter referred to as LD) 21 that emits laser light having a wavelength of 785 nm corresponding to CD, an LD 22 that emits laser light having a wavelength of 660 nm corresponding to DVD, and linearly polarized light emitted from the LD 21. And a dichroic prism 23 that transmits linearly polarized laser light emitted by the LD 22 and a BD (Blu-ray disc using a 405 nm band blue-violet laser, and a blue represented by HD-DVD). LD 24 that emits laser light having a wavelength of 405 nm corresponding to a laser disk, and wavelength separation that reflects linearly polarized laser light emitted from the LD 24 and reflects and transmits the laser light transmitted through the dichroic prism 23. Element 25 and the position of the laser beam reflected and transmitted by the wavelength separation element 25. A half-wave plate 26 that emits light after being converted by 180 °, a mirror 27 that reflects and transmits laser light emitted from the half-wave plate 26 at a predetermined ratio, and a laser that passes through the mirror 27 A front monitor (FM) 28 for monitoring the light, a collimating lens 29 for converting the laser light reflected by the mirror 27 into parallel light, and a quarter-wave plate 30 for converting linearly polarized light transmitted through the collimating lens 29 into circularly polarized light The condensing lens 33 that condenses the laser light on the pit 32 formed on the optical disc 31, the laser light reflected by the pit 32, the condensing lens 33, the quarter-wave plate 30, and the collimating lens 29 And a photodetecting element PD34 that detects via the mirror 27. In the optical pickup, a half-wave plate is used for the purpose of changing the relative angle between the far field pattern and the polarization plane.

  As described above, by configuring the three-wavelength compatible optical pickup device using the laminated half-wave plate of the present invention, the conventional configuration requires three half-wave plates. By using the laminated half-wave plate, there is an effect that a three-wavelength compatible optical pickup device can be configured with only one laminated half-wave plate.

  Furthermore, by using the recently developed three-wavelength laser diode and the laminated half-wave plate of the present invention, a new three-wavelength compatible optical pickup device can be constructed. The same reference numerals are used for the same optical devices as those in FIG. FIG. 11B is a block diagram showing an embodiment of another three-wavelength compatible optical pickup 35 according to the present invention. A composite LD 36 including LDs 36a, 36b, and 36c that emit wavelengths of 785 nm band, 660 nm band, and 405 nm band corresponding to CD, DVD, and BD, respectively, and any of the 785 nm band, 660 nm band, and 405 nm band that the composite LD 36 emits A laminated half-wave plate 26 that emits the phase of the single laser beam by 180 °, and a mirror 27 that reflects and transmits the laser beam emitted from the laminated half-wave plate 26 at a predetermined ratio. A front monitor (FM) 28 for monitoring the laser light transmitted through the mirror 27, a collimating lens 29 for converting the laser light reflected by the mirror 27 into parallel light, and the linearly polarized light transmitted through the collimating lens 29 is converted into circularly polarized light. A quarter-wave plate 30, a condensing lens 33 that condenses the laser light on the pits 32 formed on the optical disk 31, and a pin The laser light reflected by preparative 32, and the condenser lens 33, a 1/4-wave plate 30, constituted by a collimator lens 29, a mirror 27, a light detecting element PD34 detects via.

  As described above, by constructing a three-wavelength optical pickup device using the laminated half-wave plate of the present invention, it becomes possible to significantly reduce optical components and greatly reduce the manufacturing cost of the optical pickup device. There is an effect that can be done.

  1, 1 ', 19, 24 ... laminated half-wave plate, 2, 2', 3, 3 '... wave plate, 4, 5 linearly polarized light, 6, 6', 7, 7 '... optical axis, [theta] 1, θ2, θ3, θ4: azimuth angle of optical axis, 10: polarization converter, 11: beam splitter array, 12: optical axis, 13: polarization separation unit, 14: reflection film, 15: light source, 16: lamp, 17 Reflector, 18 ... Lens array, 20, 35 ... Optical pickup device, 21, 22, 24, 36a, 36b, 36c ... Laser diode (LD), 23 ... Dichroic prism, 25 ... Wavelength separation element, 26 ... Stack 1 / 2 wavelength plate, 27 ... mirror, 28 ... front monitor, 29 ... collimating lens, 30 ... 1/4 wavelength plate, 33 ... condensing lens, 34 ... photodetecting element (PD), 36 ... composite laser diode (LD) .

Claims (6)

  A first wave plate having a phase difference of Γ11 and a second wave plate having a phase difference of Γ22 for each light having a wavelength of λ.
Laminated so that the optical axes intersect,
  Rotate the plane of polarization of incident linearly polarized light by 90 ° at multiple wavelengths with different wavelengths.
A laminated wave plate that emits light after being converted into linearly polarized light,
  An in-plane azimuth angle of the first wave plate is θ3,
  The in-plane azimuth angle of the second wave plate is θ4,
  The phase difference of the second wave plate with respect to wavelength λ1 is set to Γ211 and wavelength λ2 (λ1 <λ2).
When the phase difference to be
  The following expressions (12), (13), (14), (21), and (22) are satisfied.
A laminated wave plate characterized by that.
Γ11 = 360 ° + 360 ° × 2 × n (12)
Γ22 = 180 ° + 360 ° × n (13)
ΔΓ2 = (Γ222−Γ211) / 2 (14)
cos2θ3 = 1− (1-cosΔΓ2) / 2 {(1-cosmΔΓ2)} (2)
1)
θ4 = 45 ° ± 10 ° (22)
However, n is a natural number starting from 1, m = 2   In claim 1,
n = 4,
θ3 = −16 ° or −21 °
A laminated wave plate, wherein   In claim 1,
n = 5,
θ3 = −16 ° or −21 °
A laminated wave plate, wherein   A plate-like translucent substrate having the first main surface as a light incident surface and the second main surface as a light output surface;
  First and second optical thin films provided in the base material, and provided on the second main surface of the base material
A wave plate,
  The first and second optical thin films are alternately inclined with respect to the first and second main surfaces.
And arranged parallel to each other at intervals,
  The first optical thin film is a first straight line orthogonal to the light incident from the first main surface side.
Separated into polarized light and second linearly polarized light to transmit the first linearly polarized light and second linearly polarized light
Reflect
  The second optical thin film reflects the second linearly polarized light reflected by the first optical thin film.
Emanating from the second main surface,
  The first wave plate disposed on the second main surface and transmitted through the first optical thin film.
A polarization converter that converts linearly polarized light into a second linearly polarized light and emits it;
  The said wave plate is a laminated phase difference plate as described in any one of Claim 1 thru | or 3.
A polarization converter characterized by comprising:   A laminated wave plate according to any one of claims 1 to 3 is provided.
Polarized illumination device.   A light source;
  An objective lens for condensing the light emitted from the light source onto an optical recording medium;
  A photodetector for detecting light reflected by the optical recording medium;
An optical pickup device comprising:
  The product according to any one of claims 1 to 3 in an optical path from the light source to the objective lens.
An optical pickup device comprising a layer wave plate.

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