JP2001311825A - Polarized light separation element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarized light separation element being easily manufactured and having high reliability. SOLUTION: A diffraction optical element (10) is produced by forming a resin layer (7) having a diffraction grating plane (7a) on a surface on a glass substrate (6) and a liquid crystal layer (3) adjacent to the diffraction grating plane (7a) is composed of a nematic or smectic liquid crystal. A counter flat plate (4) is adjacent to the liquid crystal layer (3) in such a way that it interposes the liquid crystal layer (3) between the resin layer (7) and itself and is provided with an alignment layer (4a) to align the liquid crystal on the surface of the liquid crystal layer (3) side. A non-forming region (B2) on which no resin layer (7) is formed exists on the glass substrate (6). The counter flat plate (4) is arranged so as not to be deviated from a forming region (B1) of the resin layer (7) to the non-forming region (B2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization splitting element, and more particularly to a polarization splitting element used in an illumination optical system for illuminating a liquid crystal panel in a liquid crystal projector.

[0002]

2. Description of the Related Art In a spatial light modulator, such as a liquid crystal panel, which displays an image by modulating light of a specific polarization, illumination light other than the specific polarization is absorbed by a polarizer. Becomes In order to solve this problem and improve the light use efficiency, various illumination optical systems that perform polarization conversion by separating polarized light and rotating a plane of polarization (ie, a plane of vibration of an electric vector) have been proposed. For example, JP-A-10-1
In the illumination optical system described in Japanese Patent No. 97827, the illumination light from the lamp is separated into two linearly polarized lights whose polarization planes are orthogonal to each other by a polarization separation element, and one of the separated linearly polarized lights is a half-wave plate. , The planes of polarization of the two linearly polarized lights are made the same. By this polarization conversion, only linearly polarized light with a uniform polarization plane can be made incident on the polarizer, so that there is almost no loss of light quantity due to the polarizer, and illumination with high light use efficiency can be achieved for the spatial light modulator. Become.

[0003]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. Hei 10-1978
The polarized light separating element described in Japanese Patent Publication No. 27 comprises a diffraction grating made of an isotropic transparent body, an optically anisotropic layer made of a birefringent material, and the like. However, since the diffraction grating is an optical component having a fine structure, it is difficult to configure the diffraction grating with a single member and to keep its reliability high. In addition, the diffraction grating is required to be easy to manufacture in consideration of formability.

The present invention has been made in view of such circumstances, and has as its object to provide a highly reliable polarization splitting element that is easy to manufacture.

[0005]

In order to achieve the above object, a polarized light separating element according to a first aspect of the present invention comprises forming a resin layer having a diffraction grating surface having a mold shape transferred on a surface thereof on a glass substrate. A diffractive optical element comprising a liquid crystal having birefringence, and a liquid crystal layer adjacent to the diffraction grating surface, and the liquid crystal layer adjacent to the liquid crystal layer such that the liquid crystal layer is sandwiched between the resin layers, and the liquid crystal is sealed. And a transparent substrate for performing the above operation, wherein the transparent substrate is disposed so as not to protrude from the region where the resin layer is formed.

According to a second aspect of the present invention, in the polarization splitting device according to the first aspect, the diffraction grating surface has a blazed shape and satisfies the following conditional expression and / or conditional expression or: I do. 1.5 <H <6 ... 0.1 <Δn <0.3 ... np ≒ no ... np ≒ ne ... where H: height of diffraction grating (μm), Δn: refractive index difference | np-no |, | np-ne | Where np is the refractive index of the resin layer, no is the refractive index of the liquid crystal layer for ordinary light, and ne is the refractive index of the liquid crystal layer for extraordinary light.

According to a third aspect of the present invention, in the polarization splitting device according to the first or second aspect, the liquid crystal layer has a thickness of 50 μm.
m or less.

A fourth aspect of the present invention is a polarization beam splitting element,
In the structure of the second or third invention, the resin layer is a resin layer having burrs at a peripheral portion higher than the diffraction grating surface.

A composite element according to a fifth aspect of the present invention comprises a diffractive optical element formed by forming a resin layer having a diffraction grating surface on which a mold shape is transferred on a glass substrate on a glass substrate, and a birefringent liquid crystal. And, a liquid crystal layer adjacent to the diffraction grating surface,
A transparent substrate for enclosing liquid crystal adjacent to the liquid crystal layer such that the liquid crystal layer is sandwiched between the resin layer and the transparent substrate. It is characterized by being arranged so as not to protrude.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a polarization splitting element and an illumination optical system embodying the present invention will be described with reference to the drawings. The same or corresponding parts in the embodiments and the like are denoted by the same reference numerals, and redundant description will be appropriately omitted.

<< Polarization Separation Element Having Sheet-like Diffractive Optical Element Layer (FIGS. 1 to 3) >> FIG. 1 is a cross-sectional view of a polarization separation element (1) having a sheet-like diffraction optical element layer (2). Show. This polarization separation element (1) has a surface relief type (thickness modulation type) diffractive optical element layer (2), a liquid crystal layer (3) composed of nematic liquid crystal or smectic liquid crystal, an opposing flat plate (4), and a seal. Agent (5) as a main component. The diffractive optical element layer (2) is made of a transparent sheet made of resin having optically almost isotropic properties, and has a blazed diffraction grating surface (2a).
have. Liquid crystal layer adjacent to this diffraction grating surface (2a)
(3) is a uniaxial optically anisotropic layer having optical anisotropy, and the liquid crystal layer (3) is sandwiched between the liquid crystal layer (3) and the diffractive optical element layer (2). ) And the adjacent flat plate (4)
It is a transparent substrate made of resin or glass. An alignment film (4a) is provided on the liquid crystal layer (3) side of the opposing flat plate (4), and the liquid crystal is homogeneously aligned along the groove direction of the diffraction grating surface (2a) on the alignment film (4a). Rubbing treatment is performed.

The diffractive optical element layer (2) is preferably made of a thermoplastic resin. As the thermoplastic resin, for example, P
A (polyamide), PE (polyethylene), PS (polystyren
e), PVC (polyvinyl chloride), PMMA (polymethy
methacrylate) and amorphous polyolefin-based resins. When a thermoplastic resin is used as a constituent material of the diffractive optical element layer (2), injection molding becomes possible, so that the diffractive optical element layer (2) can be manufactured at low cost. Further, it is desirable that the opposing flat plate (4) and the diffractive optical element layer (2) have substantially the same linear expansion coefficient. If the coefficient of linear expansion is approximately the same,
High reliability because the sealant (5) hardly peels off even if the diffractive optical element layer (2) or the opposing flat plate (4) expands or contracts due to environmental changes (temperature change, etc.) can do. In order to make the linear expansion coefficients substantially the same, it is preferable that the opposing flat plate (4) and the diffractive optical element layer (2) are made of the same material, and both of them are made of resin having optically almost isotropic properties. Is more preferred.

The liquid crystal sealed between the diffractive optical element layer (2) and the opposing flat plate (4) is a birefringent material having optical anisotropy. Different from refractive index. Therefore, the diffraction effect exerted by the diffraction grating surface (2a) located at the boundary with the optically isotropic diffractive optical element layer (2) is also different between ordinary light and extraordinary light. In this polarization separation element (1), each material is selected such that the refractive index for one of ordinary light and extraordinary light is the same as the refractive index of the diffractive optical element layer (2). For example, when the refractive index of the liquid crystal layer (3) and the refractive index of the diffractive optical element layer (2) with respect to ordinary light are the same, ordinary light passes through the diffraction grating surface (2a) without being affected by diffraction, and extraordinary light is transmitted. Is deflected by the diffraction effect on the diffraction grating surface (2a). Conversely, when the refractive index of the liquid crystal layer (3) and the refractive index of the diffractive optical element layer (2) for the extraordinary light are the same, the extraordinary light is not affected by the diffraction effect and the diffraction grating surface (2
a), the ordinary light is deflected by the diffraction effect on the diffraction grating surface (2a).

As described above, the liquid crystal layer (3) is placed on the diffraction grating surface (2a).
, The incident illumination light can be separated into two linearly polarized lights whose polarization planes are orthogonal to each other. Moreover, since the diffraction grating surface (2a) has a blazed shape, high diffraction efficiency can be obtained. If the diffraction efficiency on the diffraction grating surface (2a) is high, the polarization conversion efficiency also increases, so that the light use efficiency can be improved.

In the polarization separation of the illumination light by the polarization separation element (1), the illumination light may be incident from either of the diffractive optical element layer (2) and the opposing flat plate (4). However,
It is desirable that the optical member located on the exit side with respect to the diffraction grating surface (2a) be appropriately thin. Since the illumination light incident on the polarization separation element (1) is non-polarized light, there is no problem even if the polarization state is disturbed until it reaches the diffraction grating surface (2a). But,
If the polarization state is disturbed in the optical member passing therethrough after the polarization separation on the diffraction grating surface (2a), the polarization separation efficiency is reduced and the desired performance cannot be obtained. The cause of the disorder in the polarization state is the birefringence of the optical member. Even if the optical member is made of an optically isotropic transparent member, the effect of the birefringence increases as the thickness of the member increases, and the possibility that the polarization state is disturbed thereby increases. When the thickness of the optical member is reduced, the influence of the birefringence is reduced, so that it is possible to suppress the disorder of the polarization state. In addition, there is also an advantage that the transmission efficiency of the optical member is increased by making the optical member thin.

From the above viewpoint, it is desirable that the thickness of the optical member located on the exit side with respect to the diffraction grating surface (2a) is 0.1 to 1 mm. In particular, it is desirable that the thickness of the diffractive optical element layer (2) is 0.1 to 1 mm. By using the diffractive optical element layer (2) thus formed into a thin film, even if the separated polarized light is emitted from the diffractive optical element layer (2) side, the polarization state due to the influence of the birefringence is changed. Disturbance can be prevented. Further, when the diffractive optical element layer (2) is formed of a resin, a thinner one is preferable because the molding can be easily performed, and the cost can be reduced. However, if the thickness of the diffractive optical element layer (2) is smaller than 0.1 mm, the mechanical strength is reduced, so that the handling becomes difficult.

The thickness of the diffractive optical element layer (2) will be described in more detail. Optical materials such as optical resin and optical glass are preferably optically isotropic and do not exhibit birefringence, but actually have slight birefringence. The causes of birefringence include stress remaining inside the optical material during molding, mechanical external force applied to the molded body,
Stress generated in the molded article due to a temperature difference due to cooling is exemplified.

The optical path difference caused by the birefringence is given by the following equation:
(FA). Table 1 shows an optical path difference δ (nm) due to birefringence in each optical material when d = 1 (cm). δ = B · σ · d (FA) where δ: optical path difference due to birefringence (nm), B: photoelastic constant (× 10 ⁻¹² / Pa), σ: stress difference generated in the optical material (10 ⁵ Pa), d: thickness (cm) of the optical material.

[0019]

[Table 1]

The two linearly polarized lights separated by the polarization splitting element (1) shown in FIG. 1 have a polarization plane of one linearly polarized light of 90 °.
By being rotated, two linearly polarized lights having the same plane of polarization are obtained. For example, a half-wave plate (26, FIGS. 11 to 13) used in an illumination optical system to be described later is used as a polarization plane rotating unit for rotating the polarization plane. The 波長 wavelength plate is a phase plate that rotates the plane of polarization by 90 ° by giving an optical path difference of 波長 wavelength to one linearly polarized light. Therefore, the optical path difference δ due to birefringence is smaller than half the wavelength of visible light (in the case of e-line,
Sufficiently small value (several% for 273 nm which is half of 6.1 nm)
Otherwise, the function of polarization conversion cannot be sufficiently achieved.

Generally, an optical resin has a birefringence ten times or more that of an optical glass having a small birefringence.
Therefore, when the illumination light from the lamp (20, FIGS. 11 to 13) proceeds from the liquid crystal layer (3) to the resin-made diffractive optical element layer (2), it is polarized and separated at the diffraction grating surface (2a). As each linearly polarized light travels through the resin of the diffractive optical element layer (2), its polarization state is disturbed, and the function of polarization separation is not performed in the first place. The effect of the birefringence of the resin material itself is great, but even with the same resin material, the effect of the birefringence due to the internal stress that necessarily remains during molding is great. For example, in injection molding, a large internal stress remains near the gate (that is, the resin injection port), so that the birefringence at that location increases.

The value δ shown in Table 1 indicates that the thickness d is 1 (c
Although the birefringence at the time of m) is shown, it can be seen that considerably large birefringence occurs near the gate of PMMA, PC, and the like. In order to eliminate the influence, it is effective to reduce the thickness of the optical resin. For example, e-line (wavelength λ = 546.1n
Since the optical path difference δ due to birefringence in PMMA (near the gate) with respect to m) is 50 (nm) at a thickness d = 1 (cm), the influence of birefringence is large. However, if the thickness d is set to about 1/10 of the thickness (mm), the value becomes substantially sufficiently small at about 5 (nm) with respect to the wavelength λ = 546.1 (nm). Is no longer a problem. If the thickness is too small, the mechanical strength cannot be maintained as described above, so a thickness of about 0.1 (mm) is required. As a result, regardless of the material, the diffractive optical element layer
The thickness of (2) is desirably in the range of about 0.1 to 1 (mm), and when the diffractive optical element layer (2) is made of an optical resin, the thickness is in the range of 0.1 to 1 (mm). Is particularly desirable.

It is desirable that the diffraction grating surface (2a) satisfies the following conditional expression and conditional expression or:
By satisfying these conditions, the polarization separation efficiency can be increased. If the lower limit of the conditional expression is exceeded, the height of the diffraction grating with respect to the diffraction grating pitch becomes too large, so that it becomes difficult to cause diffraction for oblique incident light. For this reason, the diffraction efficiency decreases. The same applies when the upper limit of the conditional expression is exceeded. The use of liquid crystal as the birefringent material is effective in simply and inexpensively forming an optically anisotropic layer having birefringence, but there is no known liquid crystal exceeding the upper limit of the conditional expression. If the lower limit of the conditional expression is exceeded, it becomes difficult to form the diffraction grating surface (2a).

1.5 <H <6... 0.1 <Δn <0.3... Np ≒ no... Np ≒ ne where H: height of the diffraction grating (μm), Δn: refractive index difference | np-no |, | np-ne Larger value of |, np: refractive index of diffractive optical element layer (2), no: optically anisotropic layer for ordinary light {here, liquid crystal layer (3)}
Refractive index, ne: optically anisotropic layer for extraordinary light {here, liquid crystal layer
(3)}, the refractive index of

It is desirable that the diffraction grating surface (2a) satisfies the following conditional expression. The conditional expression is
It defines the conditions under which (1) can be made compact on a layout when used in an illumination optical system, and that high polarization separation efficiency can be achieved. If the lower limit of the conditional expression is exceeded, diffraction for obliquely incident light becomes difficult to occur, so that diffraction efficiency is reduced. When the value exceeds the upper limit of the conditional expression, the polarization separation angle becomes small, so that it is necessary to increase the conjugate length, which makes it difficult to make the device compact.

5 <D <15 where D: diffraction grating pitch (μm).

The graph of FIG. 2 shows the wavelength dependence of the transmission efficiency (E0, 0th-order diffracted light) and the diffraction efficiency (E1, + 1st-order diffracted light) in the polarization beam splitter (1). The diffraction grating pitch D of the diffractive optical element layer (2) is 8.5 (μm), the diffraction grating height H is 2.75 (μm), the refractive index np is 1.52, and the diffraction angle of the + 1st-order diffracted light is 3.8 (°).
It is. Further, the refractive indexes no = 1.52 and ne = 1.72 of the liquid crystal layer (3) for ordinary light and extraordinary light (∴Δn = 0.2).

FIG. 3 is a graph showing light of each wavelength of R, G and B.
(R: 633 nm, G: 532 nm, B: 473 nm) Transmission efficiency (E0R, E0G, E0B; zero-order diffracted light) and diffraction efficiency in the polarization separation element (1)
(E1R, E1G, E1B; + 1st order diffracted light) depends on the incident angle. As can be seen from FIG. 3, the transmission efficiency (E0R, E0
G, E0B) is 90% or more, and the diffraction efficiency (E
1R, E1G, E1B) can obtain high efficiency of 50% or more.

<< Polarization Separation Element Having Composite Diffractive Optical Element (FIGS. 4 to 10) >> FIG. 5 shows a cross section of a polarization separation element (11) having a diffractive optical element (10). FIG. 4 is a sectional view showing a step of forming the diffraction grating surface (7a) of the diffractive optical element (10). This polarization separation element (11) is a composite type / surface relief type diffractive optical element (10) formed by forming a resin layer (7) having a diffraction grating surface (7a) on the surface thereof on a glass substrate (6). Have.
The liquid crystal layer (3) adjacent to the diffraction grating surface (7a) is made of a nematic liquid crystal or a smectic liquid crystal. The liquid crystal layer (3) is sandwiched between the liquid crystal layer (3) and the resin layer (7).
The opposing flat plate (4) adjacent to the liquid crystal layer (3) side of the opposing flat plate (4) is a transparent substrate made of resin or glass. An alignment film (4a) that has been rubbed is provided so that the liquid crystal is homogeneously aligned along the groove direction of the surface (7a).

When forming the diffraction grating surface (7a), first, a UV (ultraviolet ray) curable resin is applied on a core mold (15) shown in FIG. 4, and a glass substrate (6) is placed thereon. After being placed and pressed so that the resin has a predetermined thickness, UV irradiation is performed. When the UV-curable resin is cured, the peripheral portion of the glass substrate (6) is pressed by the ejector (16) and released. By this step, a U-shaped blazed diffraction grating surface (7a)
A resin layer (7) made of a V-curable resin is obtained. Since the resin layer (7) is not formed in the entire area (A) of the glass substrate (6) in contact with the ejector (16) at the time of release, FIG.
As shown in the figure, on the glass substrate (6), there is a formation region (B1) where the resin layer (7) is formed, and a non-formation region (B2) where the resin layer (7) is not formed. Will do.

A sealant (5, FIG. 6) is applied on the resin layer (7) obtained as described above, and the opposed flat plate (4) is fixed.
At this time, the opposing flat plate (4) is arranged so as not to protrude from the region (B1) where the resin layer (7) is formed to the non-formation region (B2). Resin layer
Of the formation area (B1) of (7), the area (D) of the liquid crystal layer (3) is regulated by the sealant (5), and the area (C) of the opposed flat plate (4) is the area (D) and the area (D). B1), and D <C <
The size relationship of B1 <A holds.

In the step of forming the diffraction grating surface (7a), as shown in FIG. 6 (an enlarged view of the Z section in FIG. 5), the resin which has entered the gap between the core mold (15) and the ejector (16) is used. Bali (7
b) is formed at the same time. Burr (7b) height 50 ~ 10
While the thickness is about 0 μm, the thickness of the liquid crystal layer (3) is 30 μm or less, preferably about several μm. The thickness of the liquid crystal layer (3) is usually controlled by a spacer (not shown) of about 5 to 10 μm, but the opposing flat plate (4) is placed on the burr (7b) and tilts or floats on the opposing flat plate (4). When this occurs, the thickness of the liquid crystal layer (3) cannot be controlled. As the liquid crystal layer (3) becomes thicker, the orientation near the middle of the liquid crystal layer (3) becomes more random, and the liquid crystal layer (3) does not function normally as an optically anisotropic layer (for example, it becomes cloudy). Opposite flat plate
If the burrs (7b) are scraped off so that the (4) does not rest on the burrs (7b), the above problem does not occur. However, increasing the number of workings increases the cost. Also, if you remove burrs, the resin layer
(7) Minute scratches may occur, resulting in environmental changes during use.
If the temperature change is severe, the resin layer (7) will be cracked by the fine scratches.

In order to solve the above problem, an opposed flat plate (4)
Are arranged so as not to protrude from the formation region (B1) of the resin layer (7) to the non-formation region (B2). According to this configuration, the burr
Even if there is (7b), the opposing flat plate (4) does not rest on it, so
The thickness of the liquid crystal layer (3) can be controlled by the spacer, and the liquid crystal can be thinly sealed between the resin layer (7) and the opposed flat plate (4). Further, since a post-processing step for removing the burrs (7b) is not required, the cost is not increased, and scratches that cause cracks are not attached to the resin layer (7).
Therefore, easy to manufacture and highly reliable polarization separation element (11)
It can be.

If the burrs (7b) are left without shaving as shown in FIG. 6, the burrs (7b) may be chipped and the resin layer (7) may be cracked. Therefore, in order to prevent chipping of the burr (7b), it is desirable to cover the burr (7b) with the protective agent (8) as shown in FIG. As the protective agent (8), a flexible material such as silicone rubber is suitable. The burr (7b) is connected to the ejector (1
Since it is made of UV-curable resin in contact with 6), resin layer (7)
No burr (7b) is generated at a portion that does not come into contact with the ejector (16) even if the end is not formed. If there is no burr (7b), the protective agent (8) is unnecessary, but in order to supplement the function of the sealant (5), FIG.
As shown in the figure, the end of the resin layer (7) without burrs (7b) is also a protective agent.
It is desirable to cover with (8). Liquid crystal injection port (5a) shown in FIG.
Since there is no contact of the ejector (16) with the glass substrate (6) even at the portion (2), burrs (7b) do not occur even at the end of the resin layer (7). The liquid crystal injection port (5a) may be covered with a sealing agent (9) as shown in FIG. Examples of the sealant (9) include silicone rubber and UV curable resin.

In the polarization beam splitting element (11), the use range through which the illumination light actually passes is the area (D) of the liquid crystal layer (3). The outer peripheral portion of the liquid crystal layer (3) {for example, a portion of the sealant (5) or a portion of the sealant (9) of the liquid crystal injection port (5a) or the like} is used in the use area (D).
It is an unused area other than. Sealant in unused area
(5) If the sealant (9) is made of UV-curable resin, etc., if light hits it during actual use, it absorbs the light and has heat, There is a possibility that the device itself may be deteriorated and the reliability cannot be maintained. Further, the refractive index of the liquid crystal or the resin may change due to the temperature change, and the diffraction efficiency of the diffractive optical element (10) may be reduced. Therefore,
It is desirable to provide a thin mask plate (for example, a metal reflector made of stainless steel or the like) that reflects light so as to prevent the light from shining on the unused area, thereby blocking illumination light from a light source.

As with the polarization beam splitter (1) of FIG. 1, the polarization grating surface (7a) of the polarization beam splitter (11) shown in FIG.
It is desirable to satisfy the conditional expression or {where, np is the refractive index of the resin layer (7). }. Also, the liquid crystal layer
It is desirable that the thickness of (3) is 50 μm or less. Liquid crystal layer
When the thickness of (3) exceeds 50 μm, it becomes difficult to align the liquid crystal with the alignment film (4a), and the alignment near the middle of the liquid crystal layer (3) becomes random, and the desired performance (diffraction) is obtained. Efficiency).

<< Illumination Optical System (FIGS. 11 to 13) >> FIG. 11 shows an optical configuration of an illumination optical system having the above-described polarization splitting element (1 or 11). FIG. 12 shows a cross section (state viewed from the side) of the polarization conversion optical path. This illumination optical system is an illumination optical system for a liquid crystal projector for illuminating a liquid crystal panel (29),
Lamp (20), UV (ultraviolet ray) -I
R (infrared ray) cut filter (21), integrator rod (22), polarization separation element (1 or 11), hologram for color separation (23), condenser lens (24), relay lens
(25), half-wave plate (26), trimming filter (27),
And a field lens (28).

The lamp (20) is a light source (20a) for emitting illumination light.
And an elliptical mirror (20b) that collects illumination light from the light source (20a),
Consists of The illumination light emitted from the lamp (20) is U
It passes through a V-IR cut filter (21). UV-IR
The cut filter (21) may be provided as needed,
If a UV-IR cut filter (21) is arranged between the light source (20a) and the polarization separation element (1 or 11) to block necessary ultraviolet light and infrared light other than visible light, the polarization separation element (1 or
11) Increase the light resistance and heat resistance of the polarization separation element (1 or 11)
Reliability can be improved.

The illumination light having passed through the UV-IR cut filter (21) is incident on a kaleidoscope type integrator rod (22). The integrator rod (22) is a polygonal prism-shaped glass body or a hollow cylindrical body formed by combining a plurality of mirrors. Uniform energy distribution (ie, illuminance distribution). Since the exit end face of the integrator rod (22) is conjugate with the display surface of the liquid crystal panel (29), the display surface of the liquid crystal panel (29) can be efficiently and uniformly illuminated.

The illumination light emitted from the integrator rod (22) enters the polarization splitting element (1 or 11). The polarization separation element (1 or 11) separates the illumination light emitted from the integrator rod (22) into P-polarized light and S-polarized light whose polarization planes are orthogonal to each other. In this polarization separation, the P-polarized light is placed on the diffraction grating surface (2
polarization splitter (1 or 11) without diffraction at a or 7a)
, And the S-polarized light is deflected by diffraction at the diffraction grating surface (2a or 7a). Due to this polarization separation, a shift in the direction perpendicular to the optical axis occurs at the imaging position (that is, the light source image position) between the P-polarized light and the S-polarized light. The P-polarized light and the S-polarized light emitted from the polarization splitting element (1 or 11) are separated by a color separation hologram (23) and output at different angles for each of the RGB colors, and a condenser lens (24). ). Instead of the hologram (23), another type of diffractive optical element (surface relief type or the like), a color wheel, a dichroic mirror or the like may be used to perform color separation.

The illumination light passing through the condenser lens (24) enters the relay lens (25). Two relay lenses
(25) relays the illumination light so that the exit end face of the integrator rod (22) and the display surface of the liquid crystal panel (29) become conjugate. In the vicinity of the stop position of the relay lens (25) (may be near the conjugate position of the stop), a half-wave plate (26) is arranged as a polarization plane rotating means so that only S-polarized light is incident. . In the vicinity of the stop position of the relay lens (25), since the S-polarized light and the P-polarized light form an image at positions shifted from each other, only the S-polarized light can be made incident on the half-wave plate (26). The half-wave plate (26) rotates the plane of polarization of the S-polarized light by approximately 90 ° so that the polarization states of the light emitted from the relay lens (25) are aligned. The rotation of the plane of polarization converts the S-polarized light into P-polarized light, and as a result, all the illumination light becomes P-polarized light. By using the half-wave plate (26) as the polarization plane rotating means, the polarization plane can be rotated at low cost.

The illumination light adjusted to the P-polarized light passes through a trimming filter (27) for increasing color purity and a condensing field lens (28), in addition to the condenser lens (24), and then becomes spatial light. The liquid crystal panel (29) as a modulation element is illuminated. Since the polarizer (not shown) of the liquid crystal panel (29) is arranged so as to transmit the P-polarized light, there is almost no loss of light quantity due to the polarizer, and illumination with high light use efficiency for the liquid crystal panel (29) is provided. Achievable. Also, the RGB illumination light enters the liquid crystal panel (29) at different angles from each other, and
Microlens array located on the illumination light incident side of (29)
Since pixels corresponding to RGB are illuminated by (not shown), full-color display on a single plate becomes possible. In addition, liquid crystal panel
If light enters the microlens array of (29) at different angles for each color, full-color display is possible, so instead of performing color separation with the hologram (23), color separation is performed on three dichroic surfaces. Even so, similar illumination is possible.

Since the polarization beam splitting element (1 or 11) has a small dependence on the incident angle (see FIG. 3), the polarization beam splitting can be performed with high efficiency even for light having a large angle of incidence. Therefore,
Since the light use efficiency can be improved by high-efficiency polarization conversion, the liquid crystal panel (29) can be brightly illuminated. Further, in combination with the half-wave plate (26), inexpensive polarization conversion can be achieved. On the other hand, a polarization splitting means having a large incident angle dependence, such as a PBS (polarizing beam splitter), has poor matching with an integrator rod (22) which emits illumination light at a large angle. Therefore, PBS and integrator rod (2
In combination with 2), it is difficult to perform polarization separation with high efficiency. If the polarization separation efficiency is low, the polarization conversion efficiency is also low, so that it is impossible to improve the light use efficiency.

In a single-panel display device using a reflective liquid crystal panel capable of high-speed driving, in order to secure brightness,
Polarization conversion is particularly needed. In addition, the display device uses a color sequential method (R,
(A method of sequentially switching G and B), a condensing portion such as an exit of the integrator rod (22) is required for disposing the color wheel. An integrator rod (22) and a polarization separation element (1 or 1) as shown in FIG.
According to the combination with 1), it is possible to secure brightness while having a compact configuration and to adopt a color sequential system. On the other hand, when a lens array type integrator is used, it is difficult to configure the light condensing unit, and this leads to an increase in the size of the entire illumination optical system.

FIG. 13 shows an optical configuration of an illumination optical system for performing polarization conversion different from that shown in FIG. 12, in a cross section (as viewed from the side) of a polarization conversion optical path. This illumination optical system has a large polarization separation angle by the polarization separation element (1 or 11) {that is, a large diffraction angle by the diffraction grating surface (2a or 7a)}, and a half-wave plate (26) The configuration is the same as that of the illumination optical system of FIG. 12 except that is disposed. Therefore, the cross section of the color separation optical path of this illumination optical system (the state viewed from the upper surface side) is the same as FIG. If the diffraction angle due to the diffraction grating surface (2a or 7a) is increased by reducing the diffraction grating pitch, the S-polarized light will be deflected at a large polarization separation angle as a whole, so that the degree of freedom of the arrangement of each part of the illumination optical system is reduced. Can be improved.

[0046]

As described above, according to the present invention, since the transparent substrate is appropriately arranged with respect to the diffractive optical element composed of the glass substrate and the resin layer, the manufacturing is easy and the reliability is low. A high polarization separation element can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a polarization splitting element having a sheet-like diffractive optical element layer.

FIG. 2 is a graph showing the wavelength dependence of transmission efficiency and diffraction efficiency in the polarization separation element of FIG.

FIG. 3 is a graph showing the dependence of transmission efficiency and diffraction efficiency on the incident angle in the polarization beam splitter of FIG. 1;

FIG. 4 is a sectional view showing a step of forming a diffraction grating surface of the composite diffractive optical element.

FIG. 5 is a cross-sectional view showing a polarization splitting element constituted by the diffractive optical element of FIG.

FIG. 6 is an enlarged view showing a part (Z part) of the polarization beam splitter of FIG. 5;

FIG. 7 is an enlarged view showing a state in which a resin layer end (portion with a burr) of the polarization separation element of FIG. 5 is covered with a protective agent.

FIG. 8 is an enlarged view showing a state in which an end portion (a portion without burrs) of the resin layer of the polarization separation element of FIG. 5 is covered with a protective agent.

FIG. 9 is an enlarged view showing a liquid crystal injection port of the polarization beam splitter of FIG. 5;

FIG. 10 is an enlarged view showing a state where a liquid crystal injection port portion of the polarization separation element of FIG. 5 is covered with a sealant.

FIG. 11 is a diagram illustrating an optical configuration of an illumination optical system including a polarization separation element in a cross section of a color separation optical path.

FIG. 12 is a diagram illustrating an optical configuration of an illumination optical system including a polarization separation element in a cross section of a polarization conversion optical path.

FIG. 13 is a diagram illustrating an optical configuration of an illumination optical system that performs polarization conversion different from that in FIG. 12 by a cross section of a polarization conversion optical path.

[Explanation of symbols]

 1… Polarization separation element 2… Diffractive optical element layer 2a… Diffraction grating surface 3… Liquid crystal layer (optically anisotropic layer) 4… Optical flat plate (transparent substrate) 4a… Alignment film 6… Glass substrate 7… Resin layer 7a… diffraction grating surface 10… diffraction optical element 11… polarization separation element 20… lamp 20a… light source 21… UV-IR cut filter 22… integrator rod 25… relay lens… (Rotation means) 29… liquid crystal panel B1… resin layer formation area B2… resin layer non-formation area

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 AA03 AA40 AA43 AA45 AA50 AA63 BA05 BA06 BA42 BB62 2H088 EA48 GA02 GA04 HA16 HA24 HA28 MA06 2H091 FA07Z FA19Z FA26Z FA41Z FB02 FB04 FC19 GA06 JA01 LA16 MA06

Claims (5)

[Claims] 1. A diffractive optical element comprising a glass substrate having a resin layer having a diffraction grating surface on which a mold shape is transferred, and a liquid crystal having birefringence. An adjacent liquid crystal layer, a transparent substrate for enclosing liquid crystal, which is adjacent to the liquid crystal layer so as to sandwich the liquid crystal layer between the resin layer, and wherein the transparent substrate is A polarized light separating element which is arranged so as not to protrude from a region where a resin layer is formed. 2. The polarization separation element according to claim 1, wherein the diffraction grating surface has a blazed shape and satisfies the following conditional expression and / or conditional expression: 1.5 <H <6... 0.1 <Δn <0.3 np ≒ no np ≒ ne where H: height of diffraction grating (μm), Δn: refractive index difference | np-no |, | np-ne | : Refractive index of the resin layer, no: refractive index of the liquid crystal layer for ordinary light, ne: refractive index of the liquid crystal layer for extraordinary light. 3. The polarization separation element according to claim 1, wherein the thickness of the liquid crystal layer is 50 μm or less. 4. The polarization separation element according to claim 1, wherein the resin layer is a resin layer having burrs at a peripheral portion higher than a diffraction grating surface. 5. A diffractive optical element formed by forming a resin layer having a diffraction grating surface on which a mold shape is transferred on a surface on a glass substrate; and a birefringent liquid crystal. An adjacent liquid crystal layer, and a transparent substrate for enclosing liquid crystal, which is adjacent to the liquid crystal layer so as to sandwich the liquid crystal layer between the resin layer, and wherein the transparent substrate is A composite element, wherein the composite element is arranged so as not to protrude from a region where a resin layer is formed.