WO2023084589A1 - Optical laminate and optical device - Google Patents

Abstract

An optical laminate 10 comprises a polarization grating 11 that diffracts a light beam γ, and a compensation layer 12 that is disposed on the input side of the polarization grating 11 and modulates the polarization orientation angle of the incident light beam γ. When unnecessary light other than plus and minus first-order light is produced even if circularly polarized light is obliquely incident on the polarization grating 11, the generation of the unnecessary light is suppressed by modulating the polarization orientation angle of the incident light beam γ via the compensation layer 12 and letting the incident light beam into the polarization grating 11.

Description

Optical laminate and optical device

The present invention relates to an optical layered body that enhances diffraction efficiency and an optical device provided with the optical layered body.

A polarization grating (PG) selectively diffracts incident light according to its polarization state. The PG described in Patent Document 1 uses a polarization hologram to record its polarization pattern in a photo-alignment film, and orients a liquid crystal composition such as a polymerizable mesogen having birefringence on the photo-alignment film. created. The liquid crystal composition is aligned in a uniaxially cyclically rotated orientation on the alignment plane along the pattern of the photo-alignment film. As a result, when a light beam having circular polarization (also called circularly polarized light) is incident on the PG, depending on the polarization state of the incident light with respect to the periodically oriented structure of the PG, circularly polarized light with the direction of polarization rotation reversed is emitted with high efficiency (i.e. , other components are almost zero), and output in the +1st or −1st order diffraction direction. A geometrical phase hologram element (GPH element) described in Patent Document 2 provides a lens action using an orientation pattern of a liquid crystal composition as a lens profile.
Patent Document 1: Japanese Patent Publication No. 2008-532085 Patent Document 2: Japanese Patent Publication No. 2016-519327

Problem to be solved

When circularly polarized light is obliquely incident on the PG, +1st or -1st order diffracted light having elliptically polarized light is output, and diffracted light other than +1st or -1st order is output as leakage light, resulting in a decrease in efficiency. Invite. In various optical systems, it is common for light to enter an internal optical component in an oblique direction. Especially in an optical system using a lens, the function of the lens is to focus and diffuse the light. Light in an oblique direction tends to be generated from the The decrease in the efficiency of the PG with respect to obliquely incident light as described above leads to a decrease in the efficiency of the optical system using the PG, and the leakage of light causes a decrease in contrast and appearance of a ghost image when used in an optical system for displaying an image, for example. There are issues that arise.

General disclosure

(Item 1)
The optical stack may comprise compensation layers that modulate the polarization azimuth of an incident light beam.
The optical stack may comprise a polarization grating arranged on the output side of the compensation layer to diffract the light beam.
(Item 2)
In the compensation layer, the direction of the polarization azimuth of the light beam that is output from the compensation layer and is incident on the polarization diffraction grating is such that when the light beam having circular polarization is obliquely incident on the polarization diffraction grating, it is output from the polarization diffraction grating. It may be configured to be equal to the direction of the polarization azimuth angle of the elliptically polarized light possessed by the light beam.
(Item 3)
In the compensation layer, the value of the polarization azimuth of the light beam that is output from the compensation layer and is incident on the polarization diffraction grating is such that the value of the polarization azimuth angle of the light beam is equal to that from the polarization diffraction grating when the light beam having circular polarization is obliquely incident on the polarization diffraction grating. It may be configured to be equal to the value of the polarization azimuth angle of the elliptical polarization of the output light beam.
(Item 4)
The compensation layer may further modulate the polarization ellipticity of the light beam.
(Item 5)
In the compensation layer, the polarization ellipticity of the light beam that is output from the compensation layer and is obliquely incident on the polarization diffraction grating is output from the polarization diffraction grating when the light beam having circular polarization is obliquely incident on the polarization diffraction grating. It may be configured to be approximately equal to the ellipticity of the elliptically polarized light possessed by the light beam.
(Item 6)
The polarization grating may diffract the light beam radially inward or outward relative to the optical axis of the light beam.
(Item 7)
The compensation layer may include a plurality of first modulation regions arranged in an annular shape centered on the optical axis.
Each of the plurality of first modulation regions may modulate the polarization azimuth angle of the light beam according to the incident angle and incident azimuth angle of the light beam at a representative position within each region.
(Item 8)
The compensation layer may further modulate the polarization ellipticity of the light beam.
(Item 9)
The compensation layer may have slow axes facing different directions for each of the plurality of first modulation regions.
(Item 10)
The compensation layer may further include a plurality of second modulation regions arranged in an annular shape around the optical axis inside or outside the plurality of first modulation regions.
Each of the plurality of second modulation regions may modulate the polarization azimuth angle of the light beam according to the incident angle and incident azimuth angle of the light beam at the representative position within each region.

(Item 11)
An optical device may comprise the optical laminate according to any one of items 6 to 10.
The optical device may comprise a lens element arranged at the input side or the output side of the polarization grating for refracting the light beam.
(Item 12)
The optical device may further comprise a liquid crystal panel disposed on the input side of the compensation layer or between the compensation layer and the polarization grating for outputting the light beam with its polarization rotation direction inverted or non-inverted.

(Item 13)
An optical device may comprise the optical laminate according to any one of items 1 to 10.
The optical device may comprise a liquid crystal panel disposed on the input side of the compensation layer or between the compensation layer and the polarization grating for outputting the light beam with or without reversing its polarization rotation direction.

It should be noted that the above outline of the invention does not list all the features of the present invention. Subcombinations of these feature groups can also be inventions.

1 shows the overall configuration of an optical layered body according to a first embodiment; 1 shows an exploded configuration of an optical layered body according to a first embodiment; 2 shows the optical diffraction function of a polarization diffraction grating when left-handed circularly polarized light is perpendicularly incident. 2 shows the optical diffraction function of a polarization diffraction grating when left-handed circularly polarized light is obliquely incident. FIG. 4 shows measurement results of polarization characteristics of an output beam when a light beam having left-handed circularly polarized light is incident on a polarization diffraction grating. The optical diffraction function of the polarization diffraction grating when left-handed elliptically polarized light is obliquely incident is shown. 4 shows the measurement results of the polarization characteristics of the output beam when a light beam having left-handed elliptically polarized light is obliquely incident on the polarization diffraction grating. The efficiency when a left-handed circularly polarized light beam is incident on the polarization diffraction grating (see FIG. 2C) and the efficiency when a left-handed elliptically polarized light beam (efficiency optimized light beam) is incident on the polarization diffraction grating ( Fig. 3B). 2 shows the optical diffraction function of a polarization diffraction grating when right-handed circularly polarized light is perpendicularly incident. 2 shows the optical diffraction function of a polarization diffraction grating when right-handed circularly polarized light is obliquely incident. 4 shows the measurement results of the polarization characteristics of an output beam when a right-handed circularly polarized light beam is incident on the polarization diffraction grating. The optical diffraction function of the polarization diffraction grating when right-handed elliptically polarized light is obliquely incident is shown. 4 shows the measurement results of the polarization characteristics of the output beam when a light beam having right-handed elliptically polarized light is obliquely incident on the polarization diffraction grating. The efficiency when a right-handed circularly polarized light beam is incident on the polarization diffraction grating (see FIG. 5C) and the efficiency when a right-handed elliptically polarized light beam (efficiency optimized light beam) is incident on the polarization diffraction grating ( Fig. 6B). 4 shows the measured intensity of the output beam versus the polarization azimuth angle of the input beam input to the polarization grating. 2 shows the optical diffraction efficiency of a polarization grating. 2 shows the optical diffraction function of a polarization diffraction grating when left-handed circularly polarized light is obliquely incident. FIG. 4 shows measurement results of polarization characteristics of an output beam when a light beam having left-handed circularly polarized light is incident on a polarization diffraction grating. The optical diffraction function of the polarization diffraction grating when left-handed elliptically polarized light is obliquely incident is shown. 4 shows the measurement results of the polarization characteristics of the output beam when a light beam having left-handed elliptically polarized light is obliquely incident on the polarization diffraction grating. Comparison of the efficiency when a light beam having left-handed circularly polarized light is incident on the polarization diffraction grating (see FIG. 10B) and the efficiency when a light beam having left-handed circularly polarized light is incident on the polarization diffraction grating (see FIG. 11B) indicates 2 shows the optical diffraction efficiency of a polarization grating. 1 shows the overall configuration of an optical layered body according to a second embodiment; 3 shows the action of the optical layered body and the function of the compensation layer according to the second embodiment. 2 shows the optical diffraction function of a polarization diffraction grating when left-handed circularly polarized light is obliquely incident. The optical diffraction function of the polarization diffraction grating when left-handed elliptically polarized light is obliquely incident is shown. 2 shows the optical diffraction efficiency of a polarization grating. Figure 3 shows the modulation function of the compensation layer; Figure 3 shows the modulation function of the compensation layer; 4 shows the principle of beam diffraction in the optical layered body according to the second embodiment. 4 shows a configuration of a compensation layer according to a modified example; FIG. 11 shows a configuration of a modulation region of a compensation layer according to a modified example; FIG. An example of an optical device including an optical layered body according to a second embodiment is shown. 1 shows an example of an optical device provided with the optical laminates according to the first and second embodiments.

The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the invention according to the scope of claims. Also, not all combinations of features described in the embodiments are essential for the solution of the invention.

<<1st Embodiment>>
1A and 1B respectively show the overall configuration and exploded configuration of an optical laminate 10 according to the first embodiment. The optical laminate 10 is an assembly of a plurality of optical elements for diffracting the light beam γ. Here, the optical axis L is defined as the Z-axis direction, the traveling direction of the light beam γ is defined as the +Z direction, and the two axial directions orthogonal to this are the X-axis direction (also referred to as the horizontal direction) and the Y-axis direction (also referred to as the vertical direction). , the −Z side is the front side (also called the input side) and the +Z side is the rear side (also called the output side), and the angle toward the +Z direction with respect to the +Y direction in the YZ plane is the polar angle θ. Also, the angle toward the +Z direction with respect to the +X direction in the XZ plane is defined as a polar angle λ. Furthermore, with the Y axis as a reference, the angle toward the +X direction on the XY plane is defined as an azimuth angle ψ, which defines the elliptical azimuth angle of the elliptical polarization of the light beam γ (see FIG. 2B, etc.).

The optical layered body 10 is a layered body of optical elements for diffracting the light beam γ, and includes a plurality of layers (one layer in this embodiment) of layers 10 corresponding to the diffraction angle of the light beam γ. good.

The compensation layer 12 modulates a circularly polarized light beam γ input from the −Z side, and outputs an elliptically polarized light beam having an appropriate polarization ellipticity (also simply called ellipticity) and polarization azimuth angle ψ. It is a sheet-like or film-like optical element formed as follows.

As will be described later, even if a light beam having circular polarization is obliquely incident on the polarization diffraction grating 11, leakage light (that is, unnecessary light) other than ±first-order light is generated. By modulating the ellipticity and/or polarization azimuth of the elliptically polarized light through the layer 12 and entering the polarizing diffraction grating 11, the occurrence of leakage light can be suppressed.

Note that the compensation layer 12 does not necessarily have to be included in the optical laminate 10 . It may be arranged separately on the incident side of the polarization diffraction grating 11 . The configuration and characteristics of the compensation layer 12 will be described later.

The polarization diffraction grating 11 is an optical element that selectively diffracts the light beam γ input from the -Z side according to its polarization state. The polarization diffraction grating 11 is formed, for example, by orienting a liquid crystal composition such as a polymerizable mesogen having birefringence on a photo-alignment film in which a polarization pattern is recorded using a polarization hologram (see Patent Document 1). ). Here, the liquid crystal composition of the polarizing diffraction grating 11 is aligned clockwise (that is, rotating the birefringence axis) at a constant period in the +X direction when viewed from the output side of the light beam to the input side. Suppose there is Thereby, the diffraction direction of the polarization diffraction grating 11 becomes the X-axis direction. Here, the diffraction order to the +X side is defined as positive, and the diffraction order to the -X side is defined as negative.

The optical diffraction function of the polarization diffraction grating 11 will be detailed later.

In the optical layered body 10, the compensation layer 12 and the polarization diffraction grating 11 are formed directly in front of the polarization diffraction grating 11 via an adhesive layer (not shown) or by a method for manufacturing the compensation layer 12 described later. are integrally laminated.

FIG. 2A shows the optical diffraction function of the polarization diffraction grating 11 when left-handed circularly polarized light is vertically incident. When a left-handed circularly polarized light beam is vertically incident on the polarization diffraction grating 11 from the back side of the drawing, a right-handed circularly polarized light beam whose polarization rotation direction is reversed is highly efficient (that is, other diffraction components are almost zero). It is output in the -1st order diffraction direction.

The left side of FIG. 2B shows the optical diffraction function of the polarization diffraction grating 11 when left-handed circularly polarized light is obliquely incident. The light beam is incident at an angle θ with respect to the normal direction of the polarization diffraction grating 11 . When a left-handed circularly polarized light beam is incident on the polarizing diffraction grating 11 from the back side of the paper at an angle θ, a right-handed elliptical polarized light beam with a negative elliptical azimuth angle (−ψ _θ ) whose polarization rotation direction is reversed is − The light is output in the first-order diffraction direction, and the leaked light is output in the other diffraction directions. Using a polarimeter, we rotated the analyzer to select the polarization of the output beam and measured the intensity of the output beam with a power meter. , the elliptically polarized light has an elliptical azimuth angle (−ψ _θ ) of .

FIG. 2C shows the measurement results of the polarization characteristics of the output beam when a light beam having left-handed circularly polarized light is incident on the polarization diffraction grating 11 . The polarization properties of the output beam were measured using a polarimeter as before. For normal incidence (zero polar angle), a light beam with right-handed circular polarization is output in the −1 order diffraction direction. The intensity is 0 as a ratio to the sum of the intensity of the -1st order diffracted light and other leaked light (+1st order diffracted light, ±2nd order diffracted light, and 0th order light that is output as the incident light goes straight without diffraction). 0.992, and it can be seen that all of the output light beams within the range of the measurement error (±0.002) are −1st order diffracted light output with the direction of polarization rotation of the incident light beam reversed. For oblique incidence (angle of incidence equal to polar angle), a light beam with right-handed elliptical polarization is output in the −1 order diffraction direction. Here, the efficiency is defined as the intensity of the output beam output in the diffraction direction of the target order/the output beam including the leaked light (±1st-order diffracted light, ±2nd-order diffracted light, and incident light that goes straight without diffraction and is output as it is. If the ellipticity of elliptically polarized light is defined as the length of the minor axis/the length of the major axis, the ellipticity decreases as the incident angle (polar angle) increases, and the elliptical azimuth angle decreases from negative to zero and the efficiency decreases.

FIG. 3A shows the optical diffraction function of the polarization diffraction grating 11 when left-handed elliptically polarized light is obliquely incident. When a light beam having a left-handed elliptical polarized light with a negative elliptical azimuth angle (−ψ _θ ) is incident on the polarization diffraction grating 11 from the back side of the paper at an angle θ, the right-handed elliptical polarized light whose polarization rotation direction is reversed has a negative elliptical azimuth angle. A light beam with (−ψ _θ ) is output in the −1 order diffraction direction. However, unlike the example of FIG. 2B, less leakage light is output in other diffraction directions.

FIG. 3B shows measurement results of polarization characteristics of an output beam when a light beam having left-handed elliptically polarized light is obliquely incident on the polarization diffraction grating 11 . The polarization properties of the output beam were measured using a polarimeter as before. Here, the input beam ellipse that maximizes the efficiency (the intensity of the output beam output in the -1st order diffraction direction/the intensity of the sum of the output beams) with respect to the incident angle (polar angle θ) of the light beam Polarization ellipticity and polarization azimuth were determined. As the polar angle θ increases, the ellipticity decreases and the elliptical azimuth angle of the elliptical azimuth is shown to be input with an elliptically polarized light having a small negative angle, whereby high efficiency can be maintained. A light beam having elliptical polarization with these ellipticities and polarization azimuths is called an efficiency optimized light beam.

FIG. 4 shows the efficiency when a left-handed circularly polarized light beam is incident on the polarization diffraction grating 11 (see FIG. 2C) and the left-handed elliptically polarized light beam on the polarization diffraction grating 11 (efficiency optimized light beam). A comparison with the efficiency (see FIG. 3B) in the incident case is shown. As the incident angle (polar angle θ) of the light beam increases, the efficiency decreases, that is, the leakage light other than the −1st order diffracted light increases. It can be seen that input of elliptically polarized light having a negative elliptical azimuth angle is more efficient and can reduce leakage light other than the -1st order diffracted light.

Furthermore, comparing the measurement results shown in FIGS. 2C and 3B, the ellipticity and elliptical azimuth angle of the output beam when a light beam having left-handed circularly polarized light is obliquely incident on the polarization diffraction grating 11 (see FIG. 2C) is roughly consistent within the ellipticity and elliptical azimuth of the left-handed elliptical polarization of the efficiency-optimized input beam (see FIG. 3B) and the measurement error (±0.03 for ellipticity and ±3 degrees for polarization azimuth). I know you are doing it. Therefore, when a light beam is obliquely incident on the polarizing diffraction grating 11, the elliptical polarization of the output beam output when a circularly polarized light beam is incident instead of a circularly polarized light beam is input. By inputting a light beam having an elliptically polarized light with an ellipticity and an elliptical azimuth angle that are equal to or substantially equal to the elliptic index and elliptical azimuth angle, it is possible to suppress the occurrence of leaked light and increase the efficiency.

FIG. 5A shows the optical diffraction function of the polarization diffraction grating 11 when right-handed circularly polarized light is vertically incident. When a right-handed circularly polarized light beam is vertically incident on the polarization diffraction grating 11 from the back side of the drawing, a left-handed circularly polarized light beam whose polarization rotation direction is reversed is generated with high efficiency (that is, other diffraction components are almost zero). Output is in the +1st order diffraction direction.

The left side of FIG. 5B shows the optical diffraction function of the polarization diffraction grating 11 when right-handed circularly polarized light is obliquely incident. The light beam is incident at an angle θ with respect to the normal direction of the polarization diffraction grating 11 . When a right-handed circularly polarized light beam is incident on the polarization diffraction grating 11 at an angle θ from the back side of the drawing, a left-handed elliptical polarized light beam with a positive elliptical azimuth angle (+ψ _θ ) whose direction of polarization rotation is reversed is +1st order. , and leakage light is output in the other diffraction directions. Using the same polarimeter as before, we rotated the analyzer to select the polarization of the output beam and measured the intensity of the output beam with a power meter. It can be seen that it has an elliptically polarized light with a positive elliptical azimuth angle (+ψ _θ ).

FIG. 5C shows the measurement results of the polarization characteristics of the output beam when a right-handed circularly polarized light beam is incident on the polarization diffraction grating 11 . The polarization properties of the output beam were measured using a polarimeter as before. For normal incidence (zero polar angle), a light beam with left-handed circular polarization is output in the +1 order diffraction direction. The intensity is 0 as a ratio to the sum of +1st-order diffracted light and other leaked light (-1st-order diffracted light, ±2nd-order diffracted light, and 0th-order light that is output as the incident light goes straight without diffraction). 0.992, and it can be seen that all of the output light beams within the range of the measurement error (±0.002) are +1st order diffracted light that is output after reversing the direction of polarization rotation of the incident light beam. For oblique incidence (angle of incidence equal to polar angle), a light beam with left-handed elliptical polarization is output in the +1 order diffraction direction. It can be seen that as the angle of incidence (polar angle) increases, the ellipticity decreases, the ellipse azimuth angle decreases from the positive direction toward zero, and the efficiency decreases.

FIG. 6A shows the optical diffraction function of the polarization diffraction grating 11 when right-handed elliptically polarized light is obliquely incident. When a right-handed elliptical polarized light beam with a positive elliptical azimuth angle (+ψ _θ ) is incident on the polarization diffraction grating 11 from the back side of the paper at an angle θ, the left-handed elliptical polarized light beam with the reversed polarization rotation direction has a positive elliptical azimuth angle ( +ψ _θ ) is output in the +1 order diffraction direction. However, unlike the example of FIG. 5B, less leakage light is output in other diffraction directions.

FIG. 6B shows the measurement results of the polarization characteristics of the output beam when a light beam having right-handed elliptically polarized light is obliquely incident on the polarization diffraction grating 11 . The polarization properties of the output beam were measured using a polarimeter as before. Here, the elliptical polarization of the input beam that maximizes the efficiency (the intensity of the output beam output in the +1st order diffraction direction/the intensity of the sum of the output beams) with respect to the incident angle (polar angle θ) of the light beam We determined the ellipticity and polarization azimuth of . It can be seen that high efficiency can be maintained by inputting an elliptically polarized light beam having a smaller ellipticity and a smaller positive elliptical azimuth angle as the polar angle θ increases. A light beam having elliptical polarization with these ellipticities and polarization azimuths is called an efficiency optimized light beam.

FIG. 7 shows the efficiency when a right-handed circularly polarized light beam is incident on the polarization diffraction grating 11 (see FIG. 5C) and a right-handed elliptically polarized light beam on the polarization diffraction grating 11 (efficiency optimized light beam). A comparison with the efficiency when incident (see FIG. 6B) is shown. As the incident angle (polar angle θ) of the light beam increases, the efficiency decreases, that is, the leakage light other than the +1st order diffracted light increases. It can be seen that the input of elliptically polarized light having an elliptical azimuth angle of is higher in efficiency and can reduce leakage light other than the +1st order diffracted light.

Furthermore, comparing the measurement results shown in FIGS. 5C and 6B, the ellipticity and the elliptical azimuth of the output beam when the right-handed circularly polarized light beam is obliquely incident on the polarization diffraction grating 11 (see FIG. 5C) is , the ellipticity and elliptical azimuth of the right-handed elliptical polarization of the efficiency-optimized input beam (see FIG. 6B) roughly match within the measurement error (±0.03 for ellipticity and ±3 degrees for polarization azimuth). It can be seen that Therefore, when a light beam is obliquely incident on the polarizing diffraction grating 11, the elliptical polarization of the output beam output when a circularly polarized light beam is incident instead of a circularly polarized light beam is input. By inputting a light beam having an elliptically polarized light with an ellipticity and an elliptical azimuth angle that are equal to or substantially equal to the elliptic index and elliptical azimuth angle, it is possible to suppress the occurrence of leaked light and increase the efficiency.

FIG. 8 shows the measurement result of the intensity of the output beam with respect to the polarization azimuth angle of the input beam input to the polarization diffraction grating 11 . Here, a light beam having right-handed circularly polarized light is input to the polarization diffraction grating 11 through a quarter-wave plate at an incident angle of 30 degrees, and the quarter-wave plate is rotated to obtain the polarization ellipticity of the input beam. And the intensity of the output beam was measured with a power meter while modulating the polarization azimuth. The intensity of the output beam is represented by the efficiency (the intensity of the output beam output in the +1st order diffraction direction/the intensity of the sum of the output beams). Right-handed elliptically polarized light with positive polarization azimuth versus incident right-handed circularly polarized light with negative polarization azimuth and right-handed circularly polarized light with positive polarization azimuth It can be seen that the efficiency is good when . Thus, it can be seen in FIG. 7 that optimized elliptically polarized incidence with positive elliptical azimuth is more efficient than circularly polarized incidence as well as elliptical incidence with negative elliptical azimuth.

By analogy with the above results, for incident left-handed elliptically polarized light with positive polarization azimuth, and for incident left-handed circularly polarized light, left-handed elliptically polarized light with negative polarization azimuth It is also expected that efficiency is good when incident Thus, in FIG. 4, optimized elliptically polarized incidence with negative elliptical azimuth is expected to be more efficient than circularly polarized incidence as well as elliptical incidence with positive elliptical azimuth.

FIG. 9 shows the optical diffraction efficiency of the polarization diffraction grating 11. As shown in FIG. The liquid crystal composition of the polarizing diffraction grating 11 is arranged with rotation of the orientation clockwise (that is, rotation of the birefringence axis) at a constant period on the right side of the drawing when viewed from the output side of the light beam to the input side. The light beam is incident on the polarization diffraction grating 11 at an angle θ from the front side of the paper to the back side of the paper with respect to the optical axis L. As shown in FIG. When left-handed circularly polarized light is obliquely incident (1) as described above with reference to FIG. 2B, the light beam is right-handed elliptical polarized light whose direction of polarization rotation is reversed and has a negative elliptical azimuth angle (−ψ _θ ). is output in the −1st order diffraction direction, leakage light is output in the other diffraction directions, and, as previously inferred from the results of FIG. is obliquely incident (2), a right-handed elliptical polarized light beam with a reversed polarization rotation direction and a negative elliptical azimuth angle (−ψ _θ ) is output in the −1st order diffraction direction, and other Efficiency is low because leakage light is output in the diffraction direction. On the other hand, when elliptically polarized light having a negative elliptical azimuth angle (−ψ) is obliquely incident (3) as described above with reference to FIG. A light beam having a negative elliptical azimuth angle (−ψ _θ ) is output in the −1st order diffraction direction, and leakage light in other diffraction directions is reduced, resulting in high efficiency.

In addition, when right-handed circularly polarized light is obliquely incident ( ₆ ) as described above using FIG. A beam is output in the +1st order diffraction direction, leakage light is output in the other diffraction directions, and elliptically polarized light having a negative elliptical azimuth angle (-ψ) as described above with reference to FIG. When light is obliquely incident (5), a left-handed elliptical polarized light beam with a positive elliptical azimuth angle (+ψ _θ ) whose polarization rotation direction is reversed is output in the +1st order diffraction direction, and other diffraction Efficiency is low because leaked light is output in the direction. On the other hand, when elliptically polarized light having a positive elliptical azimuth angle (+ψ) is obliquely incident (4) as described above with reference to FIG. A light beam having an elliptical azimuth angle (+ψ _θ ) of is output in the +1st-order diffraction direction, and leakage light in other diffraction directions is reduced, resulting in high efficiency.

Based on the above considerations, when a light beam is incident on the polarizing diffraction grating 11 at an angle θ with respect to the optical axis L, the compensation layer 12 is such that the incident light beam is the optimized elliptically polarized light shown in FIGS. to be modulated into a light beam having a In other words, the compensation layer 12 is arranged so that the direction of the polarization azimuth angle of the light beam γ output by them (that is, the orientation rotation direction (+X direction) of the light beam γ and the liquid crystal composition of the polarization diffraction grating 11, that is, the polarization diffraction grating 11 The positive direction (+ψ) or negative direction (−ψ) with respect to the Y-axis orthogonal to the diffraction direction (X-axis direction) of the polarization diffraction grating 11, preferably its value (|ψ|) When a circularly polarized light beam .gamma. Furthermore, the compensation layer 12 is such that the polarization ellipticity of the light beam γ output by these is such that the light beam γ output from the polarization diffraction grating 11 when the light beam γ having circular polarization is incident on the polarization diffraction grating 11 is It is preferable that the ellipticity of the elliptically polarized light is equal or substantially equal to the ellipticity of the elliptically polarized light.

FIG. 10A shows the optical diffraction function of the polarization diffraction grating 11 when left-handed circularly polarized light is obliquely incident. The light beam is incident at an angle λ with respect to the normal to the polarization grating 11 . When a left-handed circularly polarized light beam is incident on the polarization diffraction grating 11 from the back side of the paper at an angle λ, a right-handed elliptical polarized light beam with a negative elliptical azimuth angle (−ψ _θ ) whose polarization rotation direction is reversed is − The light is output in the first-order diffraction direction, and the leaked light is output in the other diffraction directions.

FIG. 10B shows the measurement result of the polarization characteristics of the output beam when a light beam having left-handed circularly polarized light is incident on the polarization diffraction grating 11. FIG. The polarization properties of the output beam were measured using a polarimeter as before. For normal incidence (zero polar angle), a light beam with right-handed circular polarization is output in the −1 order diffraction direction. The intensity is 0 as a ratio to the sum of the intensity of the -1st order diffracted light and other leaked light (+1st order diffracted light, ±2nd order diffracted light, and 0th order light that is output as the incident light goes straight without diffraction). 0.989, and it can be seen that all of the output light beams within the range of the measurement error are −1st-order diffracted light that is output after reversing the direction of polarization rotation of the incident light beam. For oblique incidence (angle of incidence equal to polar angle), a light beam with right-handed elliptical polarization is output in the −1 order diffraction direction. Here, it can be seen that as the incident angle (polar angle) increases, the ellipticity decreases, the elliptical azimuth angle shows a negative azimuth angle, and the efficiency decreases.

FIG. 11A shows the optical diffraction function of the polarization diffraction grating 11 when left-handed elliptically polarized light is obliquely incident. When a light beam having a left-handed elliptical polarized light with a negative elliptical azimuth angle (−ψ _θ ) is incident on the polarization diffraction grating 11 from the back side of the paper at an angle λ, the right-handed elliptical polarized light with the reversed polarization rotation direction has a negative elliptical azimuth angle. A light beam with (−ψ _θ ) is output in the −1 order diffraction direction. However, unlike the example of FIG. 10A, less leakage light is output in other diffraction directions.

FIG. 11B shows measurement results of polarization characteristics of an output beam when a light beam having left-handed elliptically polarized light is obliquely incident on the polarization diffraction grating 11 . The polarization properties of the output beam were measured using a polarimeter as before. Here, the ellipticity and polarization azimuth angle of the elliptical polarization of the input beam, which maximizes the efficiency, were determined with respect to the incident angle (polar angle λ) of the light beam. It can be seen that high efficiency can be maintained by inputting an elliptically polarized light beam having a smaller ellipticity and a smaller negative elliptical azimuth angle as the polar angle λ increases. A light beam having elliptical polarization with these ellipticities and polarization azimuths is called an efficiency optimized light beam.

FIG. 12 shows the efficiency when a left-handed circularly polarized light beam is incident on the polarization diffraction grating 11 (see FIG. 10B) and the left-handed elliptically polarized light beam on the polarization diffraction grating 11 (efficiency optimized light beam). A comparison with the efficiency (see FIG. 11B) in the case of incidence is shown. As the incident angle (polar angle λ) of the light beam increases, the efficiency decreases, that is, the leakage light other than the −1st order diffracted light increases. It can be seen that input of elliptically polarized light having a negative elliptical azimuth angle is more efficient and can reduce leakage light other than the -1st order diffracted light.

FIG. 13 shows the optical diffraction efficiency of the polarization diffraction grating 11. As shown in FIG. The liquid crystal composition of the polarizing diffraction grating 11 is arranged with rotation of the orientation clockwise (that is, rotation of the birefringence axis) at a constant period on the right side of the drawing when viewed from the output side of the light beam to the input side. The light beam is incident on the polarization diffraction grating 11 at an angle λ with respect to the optical axis L. As shown in FIG. When left-handed circularly polarized light is obliquely incident (1) as described above with reference to FIG. 10A, a right-handed elliptical polarized light beam with a reversed polarization rotation direction and a negative elliptical azimuth angle (−ψ _θ ) is obtained. is output in the −1st order diffraction direction, and leakage light is output in the other diffraction directions, resulting in low efficiency. On the other hand, when elliptically polarized light having a negative elliptical azimuth angle (-ψ) is obliquely incident (2) as described above with reference to FIG. A light beam having a negative elliptical azimuth angle (−ψ _θ ) is output in the −1st order diffraction direction, and leakage light in other diffraction directions is reduced, resulting in high efficiency.

Based on the above considerations, when a light beam is incident on the polarization diffraction grating 11 at an angle λ with respect to the optical axis L, the compensation layer 12 is such that the incident light beam is the optimized elliptically polarized light (incident angle is shaped to be modulated into a light beam having a smaller ellipticity and a smaller negative elliptical azimuth with increasing .

The compensation layer 12 can be manufactured as follows. First, an alignment agent is applied onto a supporting substrate such as glass or film (in the case of the present embodiment, it may be the front surface of the polarization diffraction grating 11), and dried to form an alignment film. As the alignment agent, for example, an azobenzene-containing polymer material manufactured by DIC Corporation, a polymer material having a photodimerization site such as a cinnamoyl group and a chalcone group manufactured by Nissan Chemical Industries, Ltd. is used. Next, by exposing the alignment film with a light beam having linear polarization (in particular, an ultraviolet beam), the direction parallel or orthogonal to the polarization direction is recorded as the alignment direction of the liquid crystal molecules. In the first embodiment, the orientation direction is set to be uniaxial (Y-axis direction). This direction defines the slow axis. Finally, the alignment film is coated with a photopolymerizable liquid crystal composition to form a liquid crystal film. The liquid crystal molecules contained in the composition are aligned in the alignment direction recorded on the alignment film. Furthermore, you may stick a film on a liquid crystal film.

In the compensation layer manufactured as described above, desired light modulation characteristics are expressed by determining design parameters such as the alignment direction, type and refractive index of the liquid crystal composition, and the film thickness of the liquid crystal film. In the compensation layer 12, the light beam passing through the compensation layer 12 is at the incident angle (polar angle) of the light beam having left-handed circularly polarized light shown in FIG. In particular, the alignment direction of the liquid crystal composition and the thickness of the liquid crystal film are determined so that the corresponding ellipticity and elliptical azimuth angle are modulated. These design parameters can be determined using simulation software such as LCD Master (Shintech Co., Ltd.). As a result, the compensation layer 12 modulates an incident light beam with left-handed circularly polarized light into a light beam with left-handed circularly polarized light with optimized ellipticity and negative elliptical azimuth angle (−ψ).

As the compensation layer 12, a film having birefringence such as polycarbonate, cyclic olefin copolymer (COC), polyester (PET), etc. may be used as long as it can have the above-described polarizing properties.

In the optical laminate 10 according to the first embodiment, the compensation layer 12 is formed so as to modulate the input light beam γ having circular polarization and output the light beam having elliptically polarized light. A light beam γ having linear or elliptical polarization may be modulated to output a light beam having elliptical polarization resulting in an efficiency optimized light beam. Also, when a light beam γ having an appropriate elliptical polarization is input, it may be configured to modulate only the elliptical azimuth angle ψ.

The case where the light beam λ obliquely incident on the optical layered body 10 of the first embodiment is inclined by the polar angle θ or the polar angle λ with respect to the optical axis L has been described. The same applies when the light is obliquely incident at a polar angle of -λ. In such a case, in the above description, the diffraction direction of the output beam of the polarization diffraction grating 11 does not change (whether it is diffracted to +1st order or -1st order is determined by the polarization rotation direction of the incident light beam γ), and The polarization azimuth angle ψ of the elliptical polarization of the output beam is also expected to remain unchanged (when the periodically oriented liquid crystal composition of the polarization grating is incident at a polar angle θ when viewed from the light beam λ and − This is because the inclination of the liquid crystal composition is the same for the case of incidence at θ, and for the case of incidence at the polar angle λ and -λ). Therefore, since the function of the compensation layer 12 is expected to be the same, the function of the optical laminate 10 in the case of oblique incidence with respect to the optical axis L by a polar angle of -θ or -λ will be described in detail. do not. Assuming that the polarization azimuth (and/or ellipticity) of the output beam when the light beam γ is incident on the polarization diffraction grating 11 at a polar angle of −θ or −λ is different from that when the light beam is incident at a polar angle of θ or λ. However, the design of the compensating layer is possible by separately performing the measurements and calculations previously described.

All the measurements described above were performed using the polarization diffraction grating 11 with a pitch of 11 μm between the arrangement patterns of the liquid crystal composition. When using polarization gratings with different pitches, measurements may be performed for each pitch to adjust the conditions of the efficiency-optimized light beam before designing the compensation layer.

<<Second embodiment>>
FIG. 14 shows the configuration of an optical layered body 20 according to the second embodiment. The optical layered body 20 is an assembly of a plurality of optical elements for converging or diffusing the light beam γ, and includes a polarizing diffraction grating 21 and a compensation layer 22 .

FIG. 15 shows the action of the optical layered body and the function of the compensation layer according to the second embodiment. Here, the direction parallel to the optical axis L of the light beam γ (the traveling direction of the light beam γ) is defined as the Z-axis direction (+Z direction), and the optical axis L is used as a reference in a plane (RC plane) perpendicular to the Z-axis direction (+Z direction). The radial direction (this outward direction) is defined as the R direction (+R direction), the direction orthogonal to the Z axis direction and the R direction is defined as the C direction, and the -Z side is the front side (also called the input side) and the +Z side is the The rear side (also referred to as the output side) is defined as the polar angle λ, which is the angle toward the −R direction with respect to the +Z direction in the RZ plane. Also, with the C axis as a reference, the angle toward the +R direction on the RC plane is defined as the azimuth angle ψ, which defines the elliptical azimuth angle of the elliptical polarization of the light beam γ (see FIG. 16, etc.).

The polarization diffraction grating 21 is an optical element that selectively focuses and diffuses the light beam γ input from the -Z side with respect to the optical axis L according to its polarization state. The polarization diffraction grating 21 is, for example, a geometric phase hologram formed by orienting a liquid crystal composition such as a polymerizable mesogen having birefringence on a photo-alignment film in which a polarization pattern is recorded using a polarization hologram. It is an element (GPH element) (see Patent Document 2). Here, the liquid crystal composition of the polarizing diffraction grating 21 rotates its orientation clockwise (that is, are arranged by rotating the birefringence axis). As a result, the diffraction direction of the polarization diffraction grating 21 becomes the R direction, and the incident light is diffracted inward (-R direction) or outward (+R direction) in the R direction with the optical axis L as the reference while changing the polarization direction. By doing so, a lens action (focusing or diffusing action) is exerted to output ±1st-order diffracted light. Here, the diffraction order to the +R side is defined as positive, and the diffraction order to the -R side is defined as negative.

When non-polarized light is incident on the GPH element, the left-handed circularly polarized light beam is diffused and output, and the right-handed circularly polarized light beam is converged and output. In this case, the luminous flux is diffused and output while the polarization direction is inverted to left-handed circularly polarized light, and when left-handed circularly polarized light is incident, the luminous flux is focused and output while being inverted to right-handed circularly polarized light. A GPH element is used to compensate for the wavelength dispersion of the refraction angle for the light beam γ and the associated chromatic aberration.

The polarization diffraction grating 21 is arranged so as to be orthogonal to the optical axis L. The light beam γ enters the polarization diffraction grating 21 from the front side in a direction converging on one point on the optical axis L. Therefore, the light beam γ enters the polarizing diffraction grating 21 perpendicularly on the optical axis L, but enters a position away from the optical axis L in the radial direction at a finite angle (polar angle λ). The optical diffraction function of the polarization diffraction grating 21 will be detailed later.

The compensation layer 22 is disposed on the input side of the polarization diffraction grating 21 and modulates the circularly polarized light beam γ input from the −Z side to produce an elliptically polarized light beam with appropriate ellipticity and polarization azimuth angle ψ. It is a sheet-like or film-like optical element configured to output a beam. The compensation layer 22 is arranged perpendicular to the optical axis L by being laminated on the front surface of the polarization diffraction grating 21 . However, the compensation layer 22 may be arranged on the front side of the polarization diffraction grating 21, may be arranged apart from the polarization diffraction grating 21, or may be arranged with another element sandwiched therebetween. good.

As will be described later, the light beam γ having circular polarization converges on the optical axis L and enters the polarization diffraction grating 21 at a finite angle λ. ) is generated, the incident light beam is modulated in the ellipticity and/or the polarization azimuth angle of the elliptical polarized light through the compensation layer 22 and enters the polarization diffraction grating 21, thereby suppressing the occurrence of leakage light. can be suppressed. The configuration and characteristics of the compensation layer 22 will be described later.

FIG. 16 shows the optical diffraction function of the polarization diffraction grating 21 when left-handed circularly polarized light is obliquely incident. The light beam γ enters the polarizing diffraction grating 21 through the compensation layer 22 in a direction converging at one point on the optical axis L, as described above. Therefore, in the localized region of the polarization diffraction grating 21 where part of the light beam γ enters, the liquid crystal composition 21a of the polarization diffraction grating 21 rotates clockwise in a uniaxial direction (in this example, the right direction in the drawing) at a constant cycle. and a part of the light beam γ forms an azimuth angle ψ (equal to the orientation rotation direction 21b of the liquid crystal composition, which is 90 degrees in this example) and a polar angle λ at the center (or representative position) of the local region. incident on the In this way, when the light beam γ having left-handed circularly polarized light is incident on the polarization diffraction grating 21 from the back side of the drawing at an angle λ, it is right-handed elliptical polarized light whose direction of polarization rotation is reversed and has a negative elliptical azimuth angle (−ψ _θ ). A light beam is output in the −1st-order diffraction direction (−R direction), and leakage light is output in the other diffraction directions.

The configuration of FIG. 16 is the same as that of FIG. 10A, except that the +Y direction in FIG. 10A is changed to the +C direction in FIG. 16, and the +X direction in FIG. 10A is changed to the +R direction in FIG. Therefore, when a light beam having left-handed circularly polarized light is incident on the polarization diffraction grating 21, the polarization characteristics of the output beam are as shown in FIG. 10B. That is, in the case of normal incidence (zero polar angle), a light beam having right-handed circularly polarized light is output in the −1st order diffraction direction. The intensity is 0 as a ratio to the sum of the intensity of the -1st order diffracted light and other leaked light (+1st order diffracted light, ±2nd order diffracted light, and 0th order light that is output as the incident light goes straight without diffraction). 0.989, and it can be seen that all of the output light beams within the range of the measurement error are −1st-order diffracted light that is output after reversing the direction of polarization rotation of the incident light beam. For oblique incidence (angle of incidence equal to polar angle), a light beam with right-handed elliptical polarization is output in the −1 order diffraction direction. Here, it can be seen that as the incident angle (polar angle) increases, the ellipticity decreases, the elliptical azimuth angle shows a negative azimuth angle, and the efficiency decreases.

FIG. 17 shows the optical diffraction function of the polarization diffraction grating 21 when left-handed elliptically polarized light is obliquely incident. A light beam having a left-handed elliptical polarized light with a negative elliptical azimuth angle (−ψ _θ ) passes through the polarization diffraction grating 21 at an azimuth angle ψ (equal to the direction 21b of the orientation rotation of the liquid crystal composition 21a, which is 90 degrees in this example). ) and an angle λ, a right-handed elliptical polarized light beam with a reversed polarization rotation direction and a negative elliptical azimuth angle (−ψ _θ ) is output in the −1st order diffraction direction. However, unlike the example of FIG. 16, less leakage light is output in other diffraction directions.

The configuration of FIG. 17 is the same as that of FIG. 11A, except that the +Y direction in FIG. 11A is changed to the +C direction in FIG. 17, and the +X direction in FIG. 11A is changed to the +R direction in FIG. Therefore, when a light beam having left-handed elliptically polarized light is obliquely incident on the polarization diffraction grating 21, the polarization characteristics of the output beam are as shown in FIG. 11B. That is, as the polar angle λ increases, the ellipticity decreases and the elliptical azimuth angle of the ellipse is input with elliptically polarized light having a small negative angle, whereby high efficiency can be maintained. A light beam having elliptical polarization with these ellipticities and polarization azimuths is called an efficiency optimized light beam.

The efficiency when a left-handed circularly polarized light beam is incident on the polarization diffraction grating 21 (see FIG. 10B) and the efficiency when a left-handed elliptically polarized light beam is incident on the polarization diffraction grating 21 (efficiency optimized light beam). Comparison with efficiency (see FIG. 11B) is the same as in FIG. As the incident angle (polar angle λ) of the light beam increases, the efficiency decreases, that is, the leakage light other than the −1st order diffracted light increases. Efficiency is higher when elliptically polarized light having a negative elliptical azimuth angle is input, and leakage light other than the -1st order diffracted light can be reduced.

FIG. 18 shows the optical diffraction efficiency of the polarization diffraction grating 21. As shown in FIG. The liquid crystal composition 21a of the polarizing diffraction grating 21 rotates its orientation clockwise (that is, rotates the birefringence axis) in the +R direction (to the right of the drawing in this example) at a constant cycle when viewed from the output side of the light beam to the input side. ), that is, the orientation rotation direction 21b is to the right in the drawing. A light beam is incident on the polarizing diffraction grating 21 with an angle λ in the −R direction (to the left in the drawing in this example). When left-handed circularly polarized light is obliquely incident (1) as described _above using FIG. is output in the −1st order diffraction direction, and leakage light is output in the other diffraction directions, resulting in low efficiency. On the other hand, when elliptically polarized light having a negative elliptical azimuth angle (−ψ) is obliquely incident (2) as described above with reference to FIG. A light beam having a negative elliptical azimuth angle (−ψ _θ ) is output in the −1st order diffraction direction, and leakage light in other diffraction directions is reduced, resulting in high efficiency.

Based on the above considerations, the compensation layer 22 is suitable for light with an incident light beam having the optimized elliptical polarization shown in FIG. formed to be modulated into a beam.

The configuration of the compensation layer 22 is shown in FIG. 19A. The compensation layer 22 is formed by dividing a plurality of modulation regions arranged in an annular shape around the optical axis L, that is, by dividing the annular region into a plurality of equal parts in the circumferential direction (eight equal parts as an example in this embodiment). It includes eight modulation regions 22a-22h. For each of the modulation regions 22a to 22h, the incident angle (polar angle) λ and incident azimuth angle ψ of the light beam at a representative position such as the center of each region or its vicinity (90 degrees and 45 degrees, 0 degrees, -45 degrees, -90 degrees, -135 degrees, 180 degrees, and 135 degrees). If the azimuth angle ψ of the incident light beam is used as a reference, the modulation areas 22a to 22h correspond to the orientation rotation direction 21b of the liquid crystal composition 21a in each area. can be uniformly designed for the incident angle (polar angle) λ of the light beam. Therefore, the configuration of the modulation area 22a will be described as a representative of the modulation areas 22a to 22h.

FIG. 19B shows the modulation function of the compensation layer 22 in the modulation region 22a. When a light beam having left-handed circularly polarized light is inclined in the −R direction (leftward in the drawing) and enters the modulation region 22a, the compensation layer 22 directs the light beam to the large incident angle (polar angle) shown in FIG. 11B. is configured to modulate the ellipticity and elliptical azimuth angle to have less ellipticity and less negative elliptical azimuth angle (−ψ) with respect to and output at the same angle as the incident angle.

Each modulation region 22a-22h of the compensation layer 22 can be manufactured in the same manner as the compensation layer 12 described above. Desired light modulation characteristics are developed by determining design parameters such as the alignment direction, type and refractive index of the liquid crystal composition, and the film thickness of the liquid crystal film. For example, the modulation region 22a is shown in FIG. The alignment direction of the liquid crystal composition is determined in the direction corresponding to the optimized elliptical azimuth angle (−ψ) corresponding to the incident angle (polar angle) of the light beam shown. The remaining modulation regions 22b to 22h similarly define the orientation direction of the liquid crystal composition in the direction corresponding to the optimized elliptical azimuth angle (−ψ) with reference to the C direction with respect to the center of each region. As a result, the slow axis in each region is determined, and each modulation region 22a to 22h has a slow axis pointing in a different direction for each region. As a result, the compensation layer 22 modulates an incident light beam having left-handed circular polarization into a light beam having left-handed elliptical polarization with a negative elliptical azimuth angle (−ψ). Further, the light beams passing through the modulation regions 22a to 22h are modulated to the optimum ellipticity corresponding to the incident angle (polar angle) of the light beams shown in FIG. 11B. In particular, the film thickness of the liquid crystal film is determined according to the refractive index. These design parameters can be determined using simulation software such as LCD Master (Shintech Co., Ltd.). Thereby, the phase difference that the light beam receives in each region is determined, and each modulation region 22a to 22h has a common phase difference.

FIG. 20 shows the principle of beam diffraction in the optical layered body 20 according to the second embodiment together with the principle of beam diffraction in the polarization diffraction grating 21 of the comparative example.

In the comparative example, a light beam with left-handed circularly polarized light hits the polarization grating 21 (the region corresponding to the modulation region 22a in FIG. 15) at an azimuth angle ψ=90 degrees (i.e., rightward in the drawing) and an incident angle λ. 22, a light beam having right-handed elliptically polarized light with a negative elliptical azimuth angle (−ψ _θ ) is output from the polarizing diffraction grating 21 in the −1st order diffraction direction. Here, the diffraction of the light beam by the polarizing diffraction grating 21 is in the state (1) shown in FIG. 18, and the efficiency is low because leakage light occurs in directions other than the diffraction direction of the target order.

In an embodiment, when a light beam with left-handed circular polarization enters the optical stack 20 at an azimuth angle ψ=90 degrees (i.e., to the right in the drawing) and an incident angle λ, it first enters the compensation layer 22 and forms a negative elliptical A light beam having a left-handed elliptical polarization of azimuth (−ψ _θ ) is output at the same angle λ which enters the polarization grating 21 and from the polarization grating 21 a clockwise elliptical polarized light of negative elliptical azimuth (−ψ _θ ). A light beam having elliptical polarization is output in the -1 order diffraction direction. Here, the diffraction of the light beam by the polarizing diffraction grating 21 is in the state (2) shown in FIG. 18, and the efficiency is high because the leakage light in directions other than the diffraction direction of the target order is small.

The beam diffraction principle of the optical laminate 20 through the remaining modulation regions 22b to 22h is based on the rotational orientation direction 21b of the liquid crystal composition 21a in each region as long as the light beam is focused on one point on the optical axis L. Since the azimuth angle ψ and the incident angle (polar angle) λ of the light beam with respect to are the same, the principle of beam diffraction of the optical stack 20 via the modulation region 22a also holds true. Therefore, in the entire optical layered body 20, the efficiency is high because the generation of light leaking in directions other than the diffraction direction of the target order is small.

In addition, in the compensation layer 22 according to the present embodiment, the incident angle λ of the light beam is small in the regions inside the modulation regions 22a to 22h, and the occurrence of light leakage is small, so the modulation regions need not be provided. However, instead of this, the modulation area may also be provided in the inner area. Further, since the light amount of the light beam is small in the regions outside the modulation regions 22a to 22h, no modulation regions need to be provided. However, instead of this, the modulation area may also be provided in the outer area. That is, a plurality of modulation regions may be provided in the R direction.

FIG. 21 shows the configuration of a compensation layer 22' according to a modification. The compensation layer 22′ has a plurality of modulation regions arranged in an annular shape centered on the optical axis L inside (or may be outside) the plurality of modulation regions 22a to 22h, that is, a ring-shaped region. It further includes eight additional modulation regions formed by dividing into multiple equal parts in the direction (eight equal parts as before). Each of these additional modulation regions modulates the ellipticity and polarization azimuth of the light beam in accordance with the angle of incidence and azimuth of incidence of the light beam at a representative location within each region. Here, the modulation regions 22a to 22h and the additional modulation regions have the same angular range (that is _, the azimuth angle ψ of the incident light beam). ) and the additional modulation region _22a2 located inside it will be described. Other additional modulation regions can be designed similarly to modulation region _22a2 .

FIG. 22 shows the configuration of modulation regions 22a ₁ and 22a ₂ of a compensation layer 22' according to a modification. Each of the modulation regions 22a ₁ and 22a ₂ modulates the ellipticity and polarization azimuth angle of the light beam according to the incident angles (polar angles) λ ₁ and λ ₂ of the light beam at representative positions such as the center of each region or the vicinity thereof. modulate. Here, as an example, it is assumed that the incident angle (polar angle) λ ₁ of the light beam to the modulation region 22a ₁ is 40 degrees. For this, the ellipticity of the efficiency-optimized light beam is 0.865, and the polarization azimuth angle is -54.9 degrees. Requires 1.61 degrees. Therefore, in the modulation region 22a, the alignment direction of the liquid crystal composition is determined with reference to the C direction so as to obtain the desired slow axis direction, and the thickness of the liquid crystal film and the like are determined so as to obtain the desired phase difference. It is also assumed that the incident angle (polar angle) λ ₂ of the light beam to the modulation region 22a ₂ is 30 degrees. For this, the ellipticity of the efficiency-optimized light beam is 0.910, and the polarization azimuth angle is -60.1 degrees. 0.90 degrees is required. Therefore, in the modulation region _22a2 , the alignment direction of the liquid crystal composition is determined so as to obtain the slow axis in the desired direction with reference to the C direction, and the thickness of the liquid crystal film and the like are determined so as to obtain the desired phase difference. . These design parameters can be determined using simulation software such as LCD Master (Shintech Co., Ltd.). As a result, the modulating region 22a ₁ and the additional modulating region 22a ₂ of the compensation layer 22 direct an incident light beam with left-handed circular polarization to the optimum ellipticity and negative elliptical azimuth angle ( −φ) into a light beam with left-handed elliptical polarization. The same is true for other modulation regions and other additional modulation regions.

In this embodiment, the measurement results of FIG. 11B were used as the conditions for the efficiency-optimized light beams incident on the polarization diffraction grating at the polar angles λ ₁ and λ ₂ . When the pitch (11 μm in this example) is different, the measurement corresponding to FIG. The compensation layer may be designed after adjusting the conditions of the efficiency-optimized light beam. Also, in order to deal with incident light with an angle larger than λ ₁ and incident light with an angle smaller than λ ₂ , the outside of the modulation region 22a ₁ (peripheral side of 22') and the inside of the modulation region 22a ₂ (22' center side) may have a plurality of modulation regions.

In this embodiment, an example of the direction (polar angle λ) in which the light beam γ converges with respect to the optical axis L is shown, but conversely, the direction in which the light beam γ diverges with respect to the optical axis L (polar angle − λ) may be incident on the polarization diffraction grating 21 . As described in the first embodiment, the function of the compensation layer 12 is the same whether the light beam γ obliquely incident on the polarization diffraction grating 11 is at a polar angle λ or −λ with respect to the optical axis L. expected to become Therefore, since the same is expected for the compensation layer 22 of the present embodiment, the function of the optical layered body 20 when incident in the direction of divergence (polar angle -λ) with respect to the optical axis L will not be described in detail. Even if the polarization azimuth (and/or ellipticity) of the output beam when the light beam γ is incident on the polarization grating 21 at the polar angle −λ is different from when it is incident at the polar angle λ, the design of the compensation layer is , by separately performing the measurements and calculations previously described.

FIG. 23 shows an example of an optical device 30 including the optical layered body 20 according to the second embodiment. The optical device 30 is a device equipped with a triple-pass optical module capable of adjusting the position of the enlarged virtual image according to the diopter of the user. It includes a diffractive optical element 32 arranged on the eyebox 39 side (left side of the drawing), a lens 33 having a half-mirror surface on the display side, and a filter 34 including a reflective polarizing plate, and at least the lens 33 (half-mirror surface). It has an optical system that magnifies the image by The optical device 30 uses a moving device (not shown) to drive the lens 33 with respect to the filter 34 along the optical axis L, thereby folding back the optical path twice between the filter 34 and the lens 33 included in the optical system. By enlarging the image with the lens 33 (half-mirror surface), it is possible to adjust the position of the enlarged virtual image according to the diopter of the user. In the optical device 30 having such a configuration, the diffraction optical element 32 includes the optical layered body 20 (GPH element constituting the polarization diffraction grating 21) according to the second embodiment, so that the image light output from the display 31 is It is possible to compensate for the wavelength dispersion of the refraction angle with respect to 31a and the accompanying chromatic aberration, and to suppress the occurrence of leaked light 31b in directions other than the diffraction direction of the target order, that is, ghost light.

The optical layered body 20 (GPH element constituting the polarization diffraction grating 21) according to the second embodiment is further placed in the filter 34, between the lens 33 and the filter 34, or between the filter 34 and the eyebox 39. It may also include chromatic aberration correction. In such a case, the lens 33 would be arranged on the input side of the polarization grating 21 thereof.

The optical layered body 20 according to the second embodiment includes a compensation layer 22 that modulates the polarization ellipticity and polarization azimuth of an incident light beam, and a polarization layer that is disposed on the output side of the compensation layer 22 and diffracts the light beam. and a diffraction grating 21 . Here, the polarization diffraction grating 21 diffracts the light beam inwardly or outwardly in the radial direction with the optical axis L as a reference. According to this, the compensation layer 22 modulates the polarization ellipticity and the polarization azimuth angle of the light beam, so that the leakage light in the diffraction direction of the target order, for example, the inward direction other than the first order, is small, that is, ghost light. It is possible to provide the optical layered body 20 with less occurrence of .

Although the optical layered body 20 according to the second embodiment is configured to receive a left-handed circularly polarized light beam, it is configured to receive a right-handed circularly polarized light beam instead. You may In such a case, the direction of polarization is reversed with respect to the direction of orientation rotation of the liquid crystal composition constituting the polarization diffraction grating 21, and thus the direction of diffraction changes. is self-explanatory.

FIG. 24 shows an example of an optical device 40 including the optical layered body 10 or the optical layered body 20 according to the first and second embodiments. The optical device 40 includes a polarization diffraction grating 11 , a compensation layer 12 (or a polarization diffraction grating 21 or compensation layer 22 ), and a liquid crystal panel 41 . The liquid crystal panel 41 inverts or non-inverts the polarization rotation direction of the incident light and outputs the light toward the compensation layer 12 (or the compensation layer 22) and the polarization diffraction grating 11 (or the polarization diffraction grating 21). Since the polarization diffraction grating 11 (or the polarization diffraction grating 21) changes its diffraction direction depending on the rotation direction of the incident circularly polarized light, the liquid crystal panel 41 functions as an active diffraction grating that switches the diffraction direction by inverting or not inverting the polarization rotation direction. do. The optical device 40 may further include a lens element arranged on the input side or the output side of the polarization diffraction grating 11 to refract the light beam.

In the optical device 40, the liquid crystal panel 41 is arranged on the incident side of the compensation layer 12 (or the compensation layer 22). and the compensation layer 12 (or the compensation layer 22).

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the scope of the claims that forms with such modifications or improvements can also be included in the technical scope of the present invention.

The execution order of each process such as actions, procedures, steps, and stages in devices, systems, programs, and methods shown in claims, specifications, and drawings is etc., and it should be noted that they can be implemented in any order unless the output of a previous process is used in a later process. Regarding the operation flow in the claims, specification, and drawings, even if explanations are made using "first," "next," etc. for the sake of convenience, it means that it is essential to carry out in this order. isn't it.

DESCRIPTION OF SYMBOLS 10... Optical laminated body 11... Polarization diffraction grating 12... Compensation layer 20... Optical laminate 21... Polarization diffraction grating 21a... Liquid crystal composition 21b... Rotational orientation direction 22, 22'... Compensation layer, 22a 22h...modulation area, _22a1 , _22a2 ...modulation area, 30...optical device, 31...display, 32...diffractive optical element, 33...lens, 34...filter, 39...eye box, 40...optical device, 41 : liquid crystal panel, L: optical axis, γ: light beam.

Claims (13)

1. a compensation layer that modulates the azimuthal polarization of an incident light beam;
   a polarization grating disposed on the output side of the compensation layer for diffracting the light beam;
   An optical stack comprising:
2. In the compensation layer, the direction of the polarization azimuth of the light beam that is output from the compensation layer and is incident on the polarization diffraction grating is such that the direction of the polarization azimuth angle of the light beam is the same as the polarized light beam when the light beam having circular polarization is obliquely incident on the polarization diffraction grating. 2. The optical layered product according to claim 1, which is configured to be equal to the polarization azimuth angle of the elliptically polarized light beam output from the diffraction grating.
3. In the compensation layer, the value of the polarization azimuth of the light beam that is output from the compensation layer and is incident on the polarization diffraction grating is such that when the light beam having circular polarization is obliquely incident on the polarization diffraction grating, 3. The optical stack according to claim 2, configured to be equal to the value of the polarization azimuth angle of the elliptically polarized light beam output from the polarization diffraction grating.
4. The optical laminate according to any one of claims 1 to 3, wherein the compensation layer further modulates the polarization ellipticity of the light beam.
5. In the compensation layer, the polarization ellipticity of the light beam that is output from the compensation layer and is obliquely incident on the polarization diffraction grating is such that the polarization ellipticity of the light beam obliquely enters the polarization diffraction grating. 5. The optical layered product according to claim 4, which is configured to be approximately equal to the ellipticity of the elliptically polarized light of the light beam output from the diffraction grating.
6. The optical laminate according to claim 1, wherein the polarization diffraction grating diffracts the light beam inwardly or outwardly in a radial direction with respect to the optical axis of the light beam.
7. The compensation layer includes a plurality of first modulation regions annularly arranged around the optical axis,
   7. The optical stack of claim 6, wherein each of the plurality of first modulation regions modulates the polarization azimuth of the light beam according to the incident angle and incident azimuth of the light beam at a representative position within each region. body.
8. The optical laminate according to claim 7, wherein the compensation layer further modulates the polarization ellipticity of the light beam.
9. The optical laminate according to claim 7 or 8, wherein the compensation layer has slow axes oriented in different directions for each of the plurality of first modulation regions.
10. The compensation layer further includes a plurality of second modulation regions arranged in an annular shape around the optical axis inside or outside the plurality of first modulation regions,
    10. Any one of claims 7 to 9, wherein each of the plurality of second modulation regions modulates the polarization azimuth angle of the light beam according to the incident angle and incident azimuth angle of the light beam at a representative position within each region. 1. The optical laminate according to item 1.
11. an optical laminate according to any one of claims 6 to 10;
    a lens element disposed on the input side or the output side of the polarization diffraction grating for refracting the light beam;
    An optical device comprising
12. 12. The liquid crystal panel according to claim 11, further comprising a liquid crystal panel disposed on the input side of the compensation layer or between the compensation layer and the polarization diffraction grating for outputting the light beam with its polarization rotation direction inverted or non-inverted. Optical device as described.
13. an optical laminate according to any one of claims 1 to 10;
    a liquid crystal panel disposed on the input side of the compensation layer or between the compensation layer and the polarization diffraction grating for outputting the light beam with its polarization rotation direction inverted or non-inverted;
    An optical device comprising

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