JP5188524B2 - Polarization separation element - Google Patents

Description

  The present invention relates to a polarization beam splitting element that has a plurality of wavelengths or band lights and is used in a relatively wide incident angle range, for example, a photographing optical system, a projection display device (projector), an image processing device, and a semiconductor manufacturing device. It relates to various optical devices such as.

  Conventionally, a polarization separation element using a dielectric multilayer film is known. As shown in FIG. 16, for p-polarized light (18) incident on the multilayer film 17, transmission at the Brewster angle (19) is used, and for s-polarized light (20), reflection due to interference of the multilayer film (21). It is what makes you.

The multilayer film is formed by stacking dielectric layers having different refractive indexes. A layer having a high refractive index nH is an H layer, and a layer having a lower refractive index nL is an L layer. In general, the Brewster angle θ _B between two media having refractive indexes n1 and n2 is given by equation (10). Of the light rays incident at this angle, all p-polarized light components are transmitted.
tan θ _B = n ₂ / n ₁ (10)

In order to configure as a polarization separation element, it is necessary that the relationship between the refractive index and the angle be simultaneously established at the interface of the prism medium and the H layer and the L layer. Therefore, between the refractive index and n _p of the prism medium, the refractive index n _H and n _L of the two dielectric medium to form a thin film, it is necessary to the following relational expression holds.

For the s-polarized light, and the high refractive index medium, using the reflection at the interface resulting from the refractive index difference between the refractive index n _H and n _L of the low refractive index medium, constituting the reflective film by the multilayer interference. By optimizing the thickness of each layer and stacking 20 to 40 layers, it is possible to realize a reflective film for the entire visible light region. With regard to s-polarized light, it is possible to design wide angle characteristics and wavelength characteristics by increasing the number of layers of the film. However, since the transmittance of p-polarized light depends only on the refractive index and angle between the media, Not affected by film thickness. Conversely, as the number of layers is increased, the reflectance for p-polarized light accompanying the deviation from the Brewster angle increases, and the wavelength characteristics and angular characteristics of the transmittance deteriorate.

  On the other hand, as disclosed in Patent Document 1, a polarization separation element is known in which a birefringent adhesive is sandwiched between prisms instead of a dielectric multilayer film. This is based on the difference in refractive index between ordinary and extraordinary rays of a birefringent material. Although the difference in refractive index is small, it can be selectively used at a large incident angle of about 60 °. Polarization separation is realized by totally reflecting the polarized light.

In order for total reflection to occur, the critical angle θ _C needs to be greater than or equal to the critical angle θ _C , but the critical angle θ _C is given by the following equation.

sin θ _C = n ₂ / n ₁ (12)
And a polarization separating element using the form birefringence, by etching the multi-layer film as shown in FIG. 15, those that in a one-dimensional lattice pattern is known. An H layer 15 such as TiO ₂ and an L layer 16 such as SiO ₂ are alternately stacked and etched to form a one-dimensional lattice. The birefringence is formed as a structure in which the period of the one-dimensional grating is shorter than the wavelength.

Such a SWS grating can be handled with an effective refractive index. In the grating as shown in FIG. 10A, when the polarization in the direction parallel to the grating is TE and the polarization in the direction orthogonal to the grating is TM, In general, it is known that the effective refractive index of each polarized light is expressed by the equations (13) and (14) in a one-dimensional grating in which the medium of n ₁ and n ₂ repeats at a ratio of a: b.

このとき、ａ：ｂの比率によらずｎ_ＴＥ＞ｎ_ＴＭである。

At this time, n _TE > n _TM is _satisfied regardless of the ratio of a: b.

In a one-dimensional lattice, when n1 is a dielectric and n2 is air, a filling factor f, which is a ratio to the pitch of the medium, is expressed by Expression (15). In this example, the etching is performed so that the filling factor is about 0.5.
f = a / (a + b) (15)

FIG. 10B is a graph showing a change in effective refractive index with respect to the filling factor f of TiO ₂ in a lattice in which n1 is TiO ₂ and n2 is air. Like FIG. 10 (c) is a graph of the effective refractive index of when the n1 and SiO _2. From this graph, it can be seen that the refractive index difference between the H layer and the L layer is large in the TE direction, and the refractive index difference between the H layer and the L layer is small in the TM direction. When an appropriate prism medium is taken, the Brewster angle condition is satisfied in the TM direction, and p-polarized light can be transmitted. Since the thickness of each layer is independent of the Brewster angle condition, it is possible to form a dielectric multilayer film by optimizing the film thickness of the H layer and the L layer. Thereby, the s-polarized light is reflected, and a function as a polarization separation element can be obtained. This increases the degree of freedom in selecting a medium that satisfies the Brewster angle condition in p-polarized light, compared to a polarization separation element composed of only a dielectric thin film. Therefore, it is possible to increase the reflectance for s-polarized light at the same time. As a result, the polarization separation element covering the entire visible light region can be configured with about 20 layers.

  On the other hand, as disclosed in Patent Document 2 as a manufacturing method of a SWS cross-girder structure, a manufacturing method of a shape in which a one-dimensional lattice layer having a lattice pitch smaller than a used wavelength is stacked in an orthogonal direction has been proposed. The arrangement of photosensitive materials in a periodically laminated structure is realized.

Japanese Patent Registration No. 2958377 JP 2001-209189 A

  However, in the polarization separation element using the dielectric multilayer film, the Brewster angle condition is used for transmission of the p-polarized light, so that the refractive index of the prism glass material or the thin film medium is restricted by the expression (6), It is difficult to take a wide angle characteristic. This is not improved by increasing the number of layers.

  In a polarization separation element in which a polymer material having birefringence is sandwiched between prisms, since the difference in refractive index between the ordinary ray and the extraordinary ray of the polymer material is not large, in order to totally reflect, the incident angle is set to about 60 ° or more. There is a problem that the use of optical systems that can be used is limited. Further, since a polymer material or the like is used as the birefringent element, it is inferior in terms of heat resistance and light resistance.

  A rectangular-polarized laminated polarization separation element using an SWS structure has a complicated structure, increases manufacturing costs, and uses Brewster angle conditions for transmission of p-polarized light. As with the multilayer film, wide angular characteristics cannot be obtained. In particular, as apparent from the grating structure shown in FIG. 15, as the incident angle increases, the difference in refractive index between TE and TM disappears, so that the increase in reflectivity at an incident angle exceeding the Brewster angle increases the dielectric thin film. It is larger than the case of using, and it is obstructed to widen the angle characteristics, and an element having sufficient performance cannot be obtained.

  In addition, Patent Document 2, which is a polarizing element using structural birefringence, shows a method for producing a cross-girder-shaped SWS grating. However, it is assumed that a photonic bandgap structure is formed as a use, and as a polarization separating element. There is no description regarding the specific shape. Moreover, since an organic material having a low refractive index is used as the medium, sufficient structural birefringence cannot be obtained. Some examples shown in Patent Document 2 exhibit some polarization characteristics, but it is impossible to achieve a high extinction ratio at an incident angle of about 45 degrees. Moreover, polarization separation in a wide incident angle range cannot be realized.

  A polarization separation element used for a liquid crystal projector or the like is not suitable for these conventional examples because it requires a wide wavelength range of the entire visible light range and a small FNo for obtaining brightness, that is, a wide angle characteristic.

  In view of these problems, the present invention is suitable for a liquid crystal projector and the like. An object of the present invention is to obtain a polarization separation element having a wide angle characteristic that can be used in the above-mentioned.

In order to solve the above problems, the present invention provides:
Polarization separating layer birefringent layer has a plurality of product layer is a polarization separation element disposed between the optical member,
It has a grating structure with a period shorter than the wavelength of visible light, and has first and second birefringent layers adjacent to each other,
The direction of the grating in the first birefringent layer and the direction of the grating in the second birefringent layer are substantially orthogonal ,
When the polarization component in the direction parallel to the incident plane when light enters the polarization separation layer is p-polarized light, and the polarization component orthogonal to the incident plane is s-polarized light, p-polarized light is transmitted and s-polarized light is reflected. the shall be the feature.

  According to the present invention, as described above, with respect to the polarization separation element, the polarization having a high extinction ratio in a wide range in both the wavelength characteristic and the incident angle characteristic while having a simple structure in terms of structure and design. There is an effect that a separation element can be realized.

Configuration diagram of polarization separation element corresponding to the first embodiment of the present invention Schematic diagram of a polarization beam splitter corresponding to the first embodiment of the present invention FIG. 2A is a perspective view of a polarization beam splitting element corresponding to the first embodiment of the present invention, FIG. 3B is a perspective view thereof, FIG. 3B is a sectional view of a lattice from direction A, and FIG. FIG. 5A is a perspective view of a polarization beam splitter corresponding to the second embodiment of the present invention, FIG. 5B is a perspective view, FIG. 5B is a lattice sectional view from direction A, and FIG. FIG. 5A is a perspective view, FIG. 5B is a cross-sectional view of a lattice from a direction A, and FIG. 5C is a cross-sectional view of a lattice from a direction B, according to a third embodiment of the present invention. FIG. 5A is a perspective view, FIG. 5B is a sectional view of a grating from a direction A, and FIG. 5C is a sectional view of a grating from a direction B according to a fourth embodiment of the present invention. The block diagram of the polarization splitting element corresponding to 5th Example of this invention Configuration diagram of polarization separation element corresponding to the sixth embodiment of the present invention Configuration diagram in which a polarization separation element corresponding to the seventh embodiment of the present invention is incorporated in a reflection type liquid crystal projector optical system (A) is a figure explaining the model of the effective refractive index of a one-dimensional type | mold SWS grating | lattice, (b) is a graph showing structural birefringence when TiO2 is used for a one-dimensional type | mold SWS grating | lattice, (c) is a one-dimensional type | mold. Graph showing structural birefringence when SiO2 is used for SWS lattice, (d) is a graph showing structural birefringence when ZrO2 is used for one-dimensional SWS lattice. It is a graph showing the polarization splitting characteristic in the visible region by RCWA calculation of the polarization splitting element corresponding to 1st Example of this invention, (a) is the wavelength characteristic of the reflectance of each polarization | polarized-light in incident angle 35.0 degrees. (B) is the wavelength characteristic of the reflectance of each polarized light at an incident angle of 45.0 °, and (c) is the wavelength characteristic of the reflectance of each polarized light at an incident angle of 55.0 °. It is a graph showing the polarization splitting characteristic in the visible light region by RCWA calculation of the polarization splitting element corresponding to 2nd Example of this invention, (a) is the wavelength characteristic of the reflectance of each polarization | polarized-light in incident angle 35.0 degrees. (B) is the wavelength characteristic of the reflectance of each polarized light at an incident angle of 45.0 °, and (c) is the wavelength characteristic of the reflectance of each polarized light at an incident angle of 55.0 °. It is a graph showing the polarization splitting characteristic in the visible light region by RCWA calculation of the polarization splitting element corresponding to 3rd Example of this invention, (a) is the wavelength characteristic of the reflectance of each polarization | polarized-light in incident angle 35.0 degrees. (B) is the wavelength characteristic of the reflectance of each polarized light at an incident angle of 45.0 °, and (c) is the wavelength characteristic of the reflectance of each polarized light at an incident angle of 55.0 °. It is a graph showing the polarization splitting characteristic in the visible light region by RCWA calculation of the polarization splitting element corresponding to 4th Example of this invention, (a) is the wavelength characteristic of the reflectance of each polarization | polarized-light in incident angle 35.0 degrees. (B) is the wavelength characteristic of the reflectance of each polarized light at an incident angle of 45.0 °, and (c) is the wavelength characteristic of the reflectance of each polarized light at an incident angle of 55.0 °. Schematic diagram of a conventional multilayer film etching type polarization separation element Schematic diagram of a conventional multilayer polarization separation element

  In the present invention, in a polarization separation element in which a polarization separation layer having a structure in which a plurality of layers having structural birefringence are stacked is provided between two optical members, the polarization direction showing a high refractive index of the structural birefringence layer However, the problem is overcome by arranging and laminating adjacent layers in a direction substantially orthogonal to each other.

  In the present invention, among the light rays incident on the polarization separation layer, the polarization component of the reflected light beam and the polarization component of the mainly transmitted light beam are orthogonal to each other, and the two directions are high in the structural birefringence layer. The two directions orthogonal to the polarization direction indicating the refractive index are configured to be substantially equal.

  Of the two optical members, an exit surface from which light transmitted through the polarization separation layer of light incident from an incident surface provided on one optical member exits is provided on the other optical member, and the polarization separation The exit surface from which the reflected light in the layer exits is provided on the same optical member as the incident surface, and the direction of the reflected light is configured at an angle different from that of the incident light.

When the polarization component in the direction parallel to the incident plane when incident light is incident on the polarization separation layer is p-polarized light, and the polarization component in the direction orthogonal to the incident plane is s-polarized light, p-polarized light is transmitted and s-polarized light is reflected. The polarization separation layer has a structure in which a layer having a first structural birefringence and a layer having a second structural birefringence are alternately stacked, and has a first structural birefringence. When the effective refractive indices for the s-polarized light and the p-polarized light of the layer are n1s and n1p, respectively, and the effective refractive indices for the s-polarized light and the p-polarized light of the second structure birefringence are n2s and n2p, respectively, the following conditions are satisfied. It is set as the structure which satisfy | fills Formula.
n1p <n1s (1)
n2p> n2s (2)
| N1s-n2s |> | n1p-n2p | (3)

Further, each of the layers having the structural structure birefringence is composed of a one-dimensional grating composed of at least two media, and the grating has a periodic structure shorter than the wavelength used.
At least one of the two media is a dielectric, and at least the other is air.

It is assumed that at least one of the two media constituting the structural birefringence is a dielectric, at least the other is air, and the refractive index n1 of the dielectric satisfies the following equation.
1.5 <ni (4)
In particular, the dielectric is titanium oxide (TiO ₂ ).

The effective refractive indexes n1p and n2p for p-polarized light of the layer having the first structural birefringence and the layer having the second structural birefringence satisfy the following conditional expression.
0.95 <n1p / n2p <1.2 (5)

  Light enters the polarization separation layer in an angle range including a Brewster angle determined by an effective refractive index with respect to p-polarized light of the layer having the first structural birefringence and the layer having the second structural birefringence. I will do it.

  Further, at least a part of the light beam is incident at an angle larger than a critical angle determined by an effective refractive index with respect to s-polarized light of the first structural birefringence layer and the second structural birefringence layer. I will do it.

The relationship between the thickness d1 of the layer having the first structural birefringence, the thickness d2 of the layer having the second structural birefringence, and the use wavelength λ S on the shortest wavelength side satisfies the following conditional expression. Like that.
(N 1s d 1 · cos θ) / λ S <0.5 (6)
0.2 <d 2 / λ S <1.0 (7)
Where θ is the angle of incidence of the incident light on the polarization separation layer.

Further, the ratios (filling factors) f1 and f2 of the dielectric medium in the lattice pitch of the dielectric in the one-dimensional grating having the structural birefringence satisfy the following conditional expressions. However, f1 and f2 are the filling factors of the layers having the first and second structural birefringence, respectively.
0.15 <f1 <0.9 (8)
0.10 <f2 <0.8 (9)

Furthermore, using the optical member whose absolute value of the photoelastic constant is smaller than 0.1 × 10 ⁻⁸ cm ² / N, this polarization separation element is used to modulate the light flux from the light source section based on the image signal. An effective optical device can be obtained by constructing a projection display device that guides light to the modulating means for projecting and projects the light beam modulated by the modulating means onto a predetermined surface by the projection optical system.

(Example)
FIG. 1 is a configuration diagram of a polarization beam splitting element according to the present invention and Example 1. FIG. Table 1 shows design values representing the configuration of the first embodiment. In FIG. 1, the polarization separation layer (23) is inclined 45 ° with respect to the incident surface (25) of the prism. The incident plane when the light rays (18) and (20) incident perpendicularly to the incident surface (25) are incident on the polarization separation layer (23) and the first one-dimensional grating of the polarization separation layer are orthogonal as shown in FIG. The direction is defined as a lattice direction V. The second one-dimensional grating is arranged parallel to the incident plane as shown in FIG. In the polarization separation layer, the S-polarized light is reflected (21) and is emitted from an exit surface (26) different from the entrance surface (25) in the incident-side prism (25). The P-polarized light is transmitted (22) and emitted from the exit surface (27) on the exit side prism (24).

3A is a diagram viewed from an oblique direction of the lattice, FIG. 3B is a cross-sectional structure diagram of the lattice viewed from a direction A indicated by an arrow 29 in FIG. 2, and FIG. FIG. 3 is a cross-sectional structure diagram of a lattice viewed from a direction B indicated by an arrow 30 in FIG. The first one-dimensional lattice is an H layer (101, 103, 105) in the lattice direction V in which air and dielectric alternate, and the second one-dimensional lattice in the lattice direction P in which air and dielectric alternate It is composed of L layers (102, 104). It is possible to achieve polarization separation with a relatively simple configuration of five layers as a whole. Further, TiO ₂ is used as the dielectric.

The reason why the layers are the H layer and the L layer represents the level of the effective refractive index with respect to the S-polarized light to be reflected. The thickness of the one-dimensional lattice layer in the lattice direction V is 73 to 75 nm, which sufficiently satisfies the conditional expression (6). Conditional expression (6) is for completely achieving S-polarized light reflection. In general, it is known that when a light is incident on a medium having a low refractive index from a medium having a high refractive index, if the incident angle is equal to or larger than the critical angle θ _C , the light is totally transmitted without being transmitted at all. However, at this time, evanescent light oozes out in a very small region near the boundary surface. If there is a next medium in the light arrival region, the light is transmitted. This phenomenon is attenuated total reflection (ATR). A conditional expression for obtaining a high reflectance in a wide angle range and wavelength range using the interference between the light beams of the ATR is (6). When the upper limit of the conditional expression (6) is reached, that is, when the film thickness considering the incident angle is ½ of the wavelength, the reflected light at the ATR interferes with each other and the reflectance is lowered. This decrease in reflectance due to interference occurs every half wavelength when the film thickness is changed. (6) is a conditional expression for preventing this interference from occurring over a wide wavelength range.

  On the other hand, the thickness of the L layer made of a one-dimensional lattice in the lattice direction P is 318 nm, which satisfies the conditional expression (7). Conditional expression (7) is for effectively utilizing reflection by ATR.

  When the film thickness is reduced beyond the lower limit of (7), transmission by ATR increases in the incident angle region above the critical angle, and sufficient reflection cannot be obtained.

  On the other hand, regarding the setting of the upper limit value, the thicker the film thickness, the better from the viewpoint of ATR. However, even if the film thickness is increased, the reflectance becomes asymptotic to total reflection, so that the effect of simply increasing the film thickness cannot be obtained. With this one-dimensional lattice shape, the manufacturing difficulty increases as the film thickness increases. Therefore, it is preferable to set the upper limit of (7).

  In addition, the range of the use angle includes normal reflection below the critical angle, but in the interference there, the optimum result was obtained by setting it below the upper limit of (7).

In Example 1, as shown in design value 1 in Table 1, a prism glass material having a relatively low refractive index of about 1.603 was used. The dielectrics of the H layer, which is a one-dimensional lattice in the lattice direction V, and the L layer, which is a one-dimensional lattice in the lattice direction P, are both TiO ₂ , and a high refractive index material having a refractive index of 2.282 is used for filling. Birefringence is efficiently generated by setting the factors within the ranges of conditional expressions (8) and (9).

  Structural birefringence is given by the aforementioned equations (13) and (14). Here, TE corresponds to a polarization component in a direction parallel to the grating, and TM corresponds to a polarization component in a direction orthogonal to the grating. Regarding the layer of the one-dimensional grating in the grating direction V, the P-polarized light is TM and the S-polarized light is TE. For the one-dimensional lattice layer in the lattice direction P, P-polarized light is TE and S-polarized light is TM.

In the expressions (13) and (14), one medium is TiO ₂ and the other is air, and the effective refractive index of each polarization when the filling factor f (ratio of TiO _{2 to} the pitch) f is changed is expressed. The graph is as shown in FIG.

  Regarding P-polarized light, as shown in Table 2, when f = 0.7 in the first one-dimensional grating, the effective refractive index in the TM direction is 1.60, and when f = 0.3 in the second one-dimensional grating. The effective refractive index in the TE direction is 1.57. Since these refractive indexes are close to the refractive index of the prism medium, they show high transmittance without reflection.

Substituting nH = 1.60, n L = 1.57, and n p = 1.603 into equation (11), the Brewster angle becomes θb = about 44.3 °. Therefore, it is the structure which satisfy | fills substantially the conditions of transmission with respect to the light beam centering on an incident angle of 45 degrees.

For one S-polarized light, as shown in Table 2, the effective refractive index in the TE direction is 2.05 in the first one-dimensional grating, and the effective refractive index in the TM direction is 1.16 in the second one-dimensional grating. Substituting n ₁ = 1.603 and n ₂ = 1.16 into equation (12) yields the critical angle θ _C = about 46 °. On the higher incident angle side, total reflection ATR occurs. Even at the low incident angle side, although it is a reflection at the normal dielectric interface, the incident angle is close to the critical angle, and the refractive index difference is large between 2.05 and 1.16, so each interface has a high reflectivity. Is obtained.

  Thus, the effective refractive indexes of the first and second one-dimensional grating layers are close to each other with respect to the P-polarized light, and a large refractive index difference is generated with respect to the S-polarized light. Reflection is realized.

  The relationship between the effective refractive indexes of the first and second one-dimensional grating layers can be efficiently realized by satisfying conditional expressions (1), (2), and (3).

  FIGS. 11A to 11C show the simulation results of the performance by the rigorous coupled-wave analysis (RCWA) of this design value. In the P-polarized light, the transmittance is lowered at a high incident angle.

  With respect to S-polarized light, there is almost no light beam transmitted in a fairly wide incident angle range of 35 to 55 ° except that the performance is deteriorated on the short wavelength side with a low incident angle, and a complete reflectance is achieved.

  Conditional expressions (8) and (9) define the range of f (filling factor), and are mainly conditions for efficiently generating structural birefringence. As shown in the graph of FIG. 10B described above, a large difference in effective refractive index between TE and TM causes a large birefringence. The refractive index difference with respect to f of the medium is 0 when f = 0 and f = 1, and is maximum around f = 0.5. From this, it is possible to efficiently use the effective refractive index by selecting f in the range of conditional expressions (8) and (9).

  Table 3 shows design values of the configuration of Example 2. As in the first embodiment, in FIG. 1, the polarization separation layer (23) is inclined by 45 ° with respect to the incident surface (25) of the prism. The incident plane and the second one-dimensional grating of the polarization separation layer when the light rays (18) and (20) incident perpendicularly to the incidence surface (25) enter the polarization separation layer (23) are parallel as shown in FIG. The grating direction is P, and the first one-dimensional grating is arranged in a grating direction V perpendicular to the incident plane. In the polarization separation layer, the S-polarized light is reflected (21) and is emitted from an exit surface (26) different from the entrance surface (25) in the incident-side prism (25). The P-polarized light is transmitted (22) and emitted from the exit surface (27) on the exit side prism (24).

  4A is a diagram of the configuration of Example 2 viewed from an oblique direction of the lattice, and FIG. 4B is a cross-sectional structure diagram of the lattice viewed from a direction A indicated by an arrow 29 in FIG. 4 (c) is a cross-sectional structural view of the lattice as viewed from the direction B indicated by the arrow 30 in FIG. Each one-dimensional lattice has a structure in which air and TiO 2 are alternately repeated. The second one-dimensional lattice is an L layer (201, 203) in the lattice direction P. The first one-dimensional lattice is an H layer in the lattice direction V. (202). The filling factor of the grating satisfies the conditional expressions (8) and (9), and structural birefringence is generated efficiently, so that polarization separation can be realized with a simple configuration of three layers as a whole. .

  As shown in Table 4, the conditional expressions (6) and (7) are satisfied.

  FIGS. 12A to 12C show performance simulation results of RCWA calculation of this design value. At a low incident angle, the reflection of S-polarized light deteriorates and transmits in the entire wavelength range, but the reflectance is sufficient at 45 ° and 55 °. Further, regarding the transmittance of P-polarized light, the transmittance is sufficient in the entire angle range and the entire wavelength range, and good performance is exhibited.

  Similarly, Table 5 shows design values of Example 3, and FIGS. 5A, 5B, and 5C show cross-sectional shapes.

  As shown in Table 6, the conditional expressions (6) and (7) are satisfied.

  FIG. 13 shows a simulation result of performance by RCWA calculation.

  It has a five-layer structure of HLHLH, and the reflectance of short wavelength on the low incident angle side of S-polarized light has deteriorated, but the transmittance of P-polarized light has improved, realizing good performance as a whole. ing.

  Table 7 shows design values of Example 4, and FIG. 6A, FIG. 6B, and FIG.

  As shown in Table 8, the conditional expressions (6) and (7) are satisfied.

  FIG. 14 shows a performance simulation result by RCWA calculation.

Although it has a five-layer structure of HLHLH, ZrO2 is used for the dielectric of the second one-dimensional lattice showing the L layer. When f = 0.3, birefringence equivalent to TiO ₂ is obtained. Although the transmittance of P-polarized light falls at low incident angles and high incident angles, the reflectance of S-polarized light shows good performance at all incident angles and all wavelength ranges.

  FIG. 7 is a configuration diagram of a polarization beam splitting element prism according to a fifth embodiment of the present invention. The polarization separation element of Examples 1 to 4 is sandwiched between prisms inclined in a diamond shape. Incident light from the left side of the figure enters perpendicularly to the prism surface and enters the polarization separation element at an angle larger than 45 °. As for the total reflection, the larger the incident angle, the more advantageous. However, the incident angle can be changed by 5 ° by inclining the prism into the rhombus by about 10 °.

  FIG. 8 is a block diagram of the polarization splitting element prism according to the sixth embodiment of the present invention. In this example, the polarization separating element of the first to fourth embodiments is sandwiched by a flat medium substantially equivalent to a prism and further sandwiched by a triangular prism. Productivity is improved by separating the prisms that require shape performance such as angle, size, and surface accuracy by using a flat glass sandwiched polarization separation element that requires fine processing. .

  FIG. 9 shows a reflective image modulation apparatus using the polarization splitting element of the present invention which is the seventh embodiment of the present invention. In the figure, 1 is a light source composed of a high-pressure mercury lamp, 2 is a reflector for emitting light from the light source 1 in a predetermined direction, and 3 is an integrator for forming an illumination area having uniform illumination intensity. It is composed of eye lenses 3a and 3b, 4 is a polarization conversion element that aligns non-polarized light in a predetermined polarization direction, 5 is a condenser lens that collects illumination light, 6 is a mirror, and 7 is illumination light. A field lens that makes telecentric light, 8 is a dichroic mirror that transmits light in the green wavelength region, and 9a1, 9b1, and 9c1 are polarization separation elements of Examples 1 to 4, respectively, that reflect S-polarized light and transmit P-polarized light. 9a, 9b, and 9c have polarization separating elements 9a1, 9b1, and 9c1, respectively, and 10a and 10b have predetermined wavelengths, respectively. The color-selective phase difference plates 11r, 11g, and 11b that convert (rotate) the polarization direction of the light in the region by 90 ° reflect the incident illumination light, respectively, and modulate it according to the image signal to form image light. The liquid crystal display elements 12r, 12g, and 12b are quarter retardation plates, and 14 is a projection lens system. When the polarization separation elements according to the first to fourth embodiments are arranged as described above, a reflection type liquid crystal projector having a very high contrast obtained in the entire optical system can be realized because of excellent incident angle characteristics and wavelength characteristics.

DESCRIPTION OF SYMBOLS 1 Light source which consists of high pressure mercury lamps etc. 2 Reflector 3 Integrator 3a, 3b Fly eye lens 4 Polarization conversion element 5 Condenser lens 6 Mirror 7 Field lens 8 Dichroic mirror 9a1, 9b1, 9c1 Polarization separation film 9a, 9b, 9c Polarization separation film 9a1 , 9b1, 9c1 Polarizing beam splitters 10a, 10b Color selective phase difference plates 11r, 11g, 11b Reflective liquid crystal display elements 12r, 12g, 12b 1/4 phase difference plates 14 Projection lens system 15 H layer (first one-dimensional lattice)
16 L layer (second one-dimensional lattice)
17 Multi-layer film 18 P-polarized incident light 19 P-polarized transmitted light 20 S-polarized incident light 21 S-polarized reflected light 22 Incident-side prism 23 Polarization separation element 24 Emission-side prism 25 Incident surface 26 S-polarized reflected light exit surface 27 P-polarized light transmitted Light exit surface 28 Incident plane 29 Arrow indicating lattice section observation direction A 30 Arrow indicating lattice section observation direction B 101 to 105 First to fifth layers 201 to 205 from the incident side of the first embodiment 201 to 205 Second embodiment First to third layers 301 to 304 from the incident side of the first layer to fifth layers 401 to 403 from the incident side of the third embodiment 401 to 403 First to fifth layers of the fourth embodiment from the incident side

Claims (11)

Polarization separating layer birefringent layer has a plurality of product layer is a polarization separation element disposed between the optical member comprises a lattice structure having a period shorter than the wavelength of visible light, a first adjacent to each other, the second A birefringent layer of
The direction of the grating in the first birefringent layer and the direction of the grating in the second birefringent layer are substantially orthogonal ,
When the polarization component in the direction parallel to the incident plane when light enters the polarization separation layer is p-polarized light, and the polarization component orthogonal to the incident plane is s-polarized light, p-polarized light is transmitted and s-polarized light is reflected. polarization separating element according to claim. 2. The polarization separation element according to claim 1, wherein two directions orthogonal to each other as a grating direction in the first and second birefringent layers are substantially equal to the two directions of the p-polarized light and the s-polarized light. . When the effective refractive indexes for the s-polarized light and the p-polarized light of the first birefringent layer are n1s and n1p, respectively, and the effective refractive indexes for the s-polarized light and the p-polarized light of the second birefringent layer are n2s and n2p, respectively.
n1p <n1s
n2p> n2s
| N1s-n2s |> | n1p-n2p |
0.81 ≦ | n1s−n2s | ≦ 1.08
The polarization separation element according to claim 1, wherein: Before SL birefringent layer, the polarization separating element according to any one of claims 1 to 3, wherein that you consisting of at least two media. Polarization separating element according to claim 4 one of the two medium, characterized in that the dielectric, the other one is air. When the refractive index of the dielectric is ni ,
1.5 <ni
The polarization separation element according to claim 5, wherein: The polarized light separating element according to claim 5 , wherein the dielectric is titanium oxide (TiO 2). N1s an effective refractive index with respect to s-polarized light of said first birefringent layer, the first thickness of the birefringent layer d1, the second thickness of the birefringent layer d2, the shortest have the wavelength of visible light Is λS , and the incident angle of light to the polarization separation layer is θ,
(N1sd1 · cos θ) / λS <0.5
0.2 <d2 / λS <1.0
The polarization separation element according to claim 1, wherein: When f1 and f2 are filling factors indicating the ratio of the dielectric to the lattice pitch of the first and second birefringent layers ,
0.15 <f1 <0.9
0.10 <f2 <0. 3
The polarization separation element according to any one of claims 5 to 8, wherein: The polarized light according to any one of claims 1 to 9, wherein the polarization separation layer is a layer in which the first birefringent layer and the second birefringent layer are alternately stacked. Separating element. It has the polarization separation element according to any one of claims 1 to 10 ,
The light beam from the light source unit through said polarization separation element to the modulation means for modulating based on an image signal guided, characterized that you projected onto a predetermined surface by a projection optical system the light beam modulated by the modulation means Projection display device.

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