JP2005250057A - Projection type video display device, optical unit to be used for the same and structure for separating polarized light - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology suppressing the temperature rise of a polarized light separating element and securing the high picture quality of images in projection type video display technology. <P>SOLUTION: A polarized light separating means has the constitution in which a polarized light separating element is arranged in a medium of which light refractive index is > 1. The polarized light separating element is provided with a polarized light separation surface for polarizing and separating light by diffraction based on grating structure and has the constitution in which an air layer is formed in contact with the polarized light separation surface. A projection type video display device or an optical unit to be used for the display device has the constitution for polarizing and separating light with which a light valve is irradiated and light modulated by the light valve by the polarized light separating means, for synthesizing the colors of polarized and separated light by a color synthesis means, and for enlarging and projecting the color-synthesized light by a projection lens unit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polarization separation technique in a projection-type image display apparatus that irradiates light from a light source side to a light valve such as a liquid crystal panel to form an optical image according to an image signal and project an enlarged image.

  Liquid crystal projectors for business use are becoming widespread. Further, as an alternative to a conventional image display device that projects an image displayed on a cathode ray tube onto a screen, a projection television using a liquid crystal panel has been developed. In particular, home projection televisions are required to have more faithful color reproducibility, high contrast performance, and quick video display performance than commercial liquid crystal projectors.

  In the case of a reflective liquid crystal panel, the liquid crystal layer is reciprocated twice by reflection, so that the thickness of the liquid crystal layer can be reduced to about half that of the transmissive liquid crystal panel. If the thickness of the liquid crystal layer is halved, the response speed is quadrupled, which is advantageous for displaying moving images.

  In the projection type liquid crystal projector apparatus using this reflection type liquid crystal panel, in general, a polarization wave having a predetermined polarization direction having a function of a polarizer and an analyzer is transmitted in front of the reflection type liquid crystal panel, and a polarization direction perpendicular thereto. Polarization separation means for reflecting the polarized wave is arranged. Such a technique is described in, for example, Japanese Patent Application Laid-Open No. 2001-142028 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2003-131212 (Patent Document 2).

  In these patent documents, three sets of reflective liquid crystal panels for red, green, and blue light and polarized light separating means are arranged, and the three-color light is color-combined by a cross dichroic prism.

  As a polarization separation means, a PBS prism (described in Patent Document 1) in which a polarizing beam splitter (hereinafter referred to as PBS), which is a dielectric multilayer film, is formed at the interface between two right-angle prisms, or on a glass substrate. In addition, there is a wire grid type polarization separation element (described in Patent Document 2), which is a grating structure diffraction grating in which a wire grid (metal grating) is formed at a predetermined pitch (formation period) to form a diffraction grating.

JP 2001-142028 A

JP 2003-131212 A

  The PBS prism described in Patent Document 1 has a large extinction ratio with respect to vertically incident light, and is excellent in polarization separation action. However, when oblique light that is not parallel to the surface (main incident surface) formed by the optical axis and the normal of the PBS film surface is incident on the PBS prism, leakage light is generated and the extinction ratio is lowered. As an improvement measure for this, in Patent Document 1, a quarter-wave plate is provided in front of the reflective liquid crystal panel, but the effect is not sufficient, and the contrast may not be increased.

  Further, in the case of the wire grid type polarization separation element described in Patent Document 2, the peak value of the extinction ratio at an incident angle of 45 ° is low, but this is shown in the polarization separation characteristic of FIG. Thus, there is little degradation of the extinction ratio with respect to an angled light ray (oblique light). For this reason, although the contrast performance as the whole light beam is improved, there are concerns about the following about the wire grid type polarization separation element.

  There are two possible methods for disposing the wire grid type polarization separation element on the optical path where the light beam reflected from the reflective liquid crystal panel enters the projection lens. FIG. 12 shows the arrangement method. In the arrangement method of FIG. 12 (1), the incident S-polarized light beam from the illumination optical system is reflected by the wire grid type polarization separation element 17 and enters the reflective liquid crystal panel 214, and is reflected by the reflective liquid crystal panel 214. The outgoing light (reflected light) converted into is transmitted to the projection lens (not shown) through the wire grid type polarization separation element 17 (hereinafter, for convenience, this arrangement is referred to as the reflected light from the reflective liquid crystal panel being wire grid. (This is referred to as “transmission arrangement” because it passes through the polarized light separating element and travels toward the projection lens). In the arrangement method of FIG. 12 (2), the incident light beam of P-polarized light from the illumination optical system passes through the wire grid type polarization separation element 17, enters the reflective liquid crystal panel 217, and is s-polarized light by the reflective liquid crystal panel 217. The outgoing light (reflected light) converted into light is reflected by the wire grid type polarization separation element 17 and travels toward a projection lens (not shown) (hereinafter, for convenience, this arrangement is applied to the reflected light from the reflective liquid crystal panel. This is called “reflection arrangement” because it reflects the wire grid type polarization separation element and travels toward the projection lens).

  When the wire grid type polarization separation element shown in FIG. 12 (2) is arranged in a reflective manner, if the wire grid type polarization separation element is misaligned or the wire grid type polarization separation element is expanded due to heat, the projection performance deteriorates. Then there is a risk. On the other hand, when the wire grid type polarization separation element shown in FIG. 12 (1) is transmissively arranged, transmission through the plate-shaped wire grid type polarization separation element causes astigmatism, and similarly the projection performance deteriorates. There is a risk.

  In the above-mentioned Patent Document 2, as shown in FIG. 1, the wire grid type polarization separation element is arranged in a transmission arrangement, and as shown in FIG. 2, astigmatism generated in the transmission arrangement is reduced. In order to achieve this, a polarization separation means is configured by arranging a wire grid type polarization separation element between the inclined surfaces of two right-angle prisms. In this case, astigmatism is reduced because the glass substrate of the wire grid type polarization separation element and the right angle prism have substantially the same refractive index.

  In addition, in such a polarization separation prism (hereinafter referred to as “diffraction prism”) in which a wire grid type polarization separation element is disposed between the inclined surfaces of two right-angle prisms, the optical path length can be shortened. In addition, the back focus of the projection lens can be shortened, that is, the projection lens can be reduced in size, and further, since the spread of the light beam can be reduced, the diffraction prism can also be reduced.

  A translucent container having a rectangular parallelepiped shape is filled with a liquid medium having a refractive index substantially equal to that of the glass substrate of the wire grid type polarization separation element, and the wire grid type polarization separation element is disposed in this medium. The same effect can be obtained.

  However, the wire grid of the wire grid type polarization separation element absorbs about 5 to 10% of the amount of incident light and becomes high temperature. As the temperature rises, birefringence based on thermal stress occurs in the glass substrate which is a light-transmitting substrate, resulting in a decrease in contrast, and the glass substrate undergoes thermal expansion deformation, resulting in a deterioration in projection performance. Therefore, if the wire grid type polarization separation element is disposed in the liquid medium, the temperature rise can be reduced and the same effect as the above-described diffraction prism can be obtained.

  By the way, when the wire grid type polarization separation element is disposed in a medium having a refractive index larger than that of air, such as a diffraction prism, such as glass or ethylene glycol liquid, the wire grid type polarized light is separated. Compared with the case where the separation element is used in the air, the wavelength of light is shortened. Therefore, in order to ensure appropriate polarization separation characteristics, it is necessary to reduce the lattice pitch of the wire grid.

As a manufacturing method of the wire grid type polarization separation element, as described in paragraph 0039 of Patent Document 2 above, an aluminum base film is formed on a glass substrate, a resist pattern is formed by electron beam drawing, A method of forming a metal lattice by depositing aluminum having a predetermined thickness and selectively removing unnecessary aluminum by lift-off is conceivable. Accordingly, the dimensional accuracy depends on the performance of the electron beam drawing apparatus. In the current electron beam drawing apparatus, the minimum drawing line width is about 100 × 10 ⁻⁹ m for a normal resolution and about 30 × 10 ⁻⁹ m for a high resolution.

In the products currently on the market, for example, the wire grid has a line width of 65 × 10 ⁻⁹ m, the lattice spacing is 150 to 200 × 10 ⁻⁹ m, and the thickness of the wire grid glass substrate is 0.7 × 10 ⁻³ m. m to 1.6 × 10 ⁻³ m (manufactured by MOTTEK) and a line width of 43 × 10 ⁻⁹ m in order to obtain an equivalent polarization separation performance in a medium having a refractive index of 1.5. The lattice spacing needs to be about 100 to 130 × 10 ⁻⁹ m. In consideration of dimensional accuracy, this numerical value is difficult to handle even with a high-resolution electron beam drawing apparatus.

  Thus, reducing the grid pitch of the wire grid involves manufacturing difficulties. What is currently marketed is premised on use in air.

  FIGS. 13 and 14 show a case where a wire grid type polarization separation element designed on the assumption of use in the air is disposed in the air, and a mixed liquid of ethylene glycol and glycerin having a refractive index of 1.45 (hereinafter referred to as the following). The polarization separation characteristics when this mixed solution is disposed in a medium “GE55”) are shown. FIG. 13 is an explanatory diagram of the P-polarized light transmittance characteristic, and FIG. 14 is an explanatory diagram of the S-polarized light transmittance characteristic. As is apparent from FIGS. 13 and 14, when a wire grid type polarization separation element designed for use in the air is disposed in the medium of GE55, the transmission amount of P-polarized light, which is transmitted light, is reduced. In addition, the transmission amount of S-polarized light that is reflected light increases. In the above transmission arrangement, when the transmission amount of the P-polarized light is reduced, the transmission amount of the reflected light of the P-polarized light from the reflective liquid crystal panel toward the projection lens is reduced, so that the brightness is reduced. Further, since the transmission amount of S-polarized light to be removed increases, the degree of polarization decreases and the contrast decreases.

  In view of the situation of the prior art, the problem of the present invention is that a polarization separation element that polarizes and separates light by diffraction based on a grating structure, such as the wire grid polarization separation element, is used in a medium having a higher refractive index than air. In such a case, it is possible to suppress the deterioration of the polarization separation property.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a projection image display technique that can solve the above-described problems and can ensure the resolution, brightness, and contrast of an image in a state where the temperature rise of the polarization separation element is suppressed.

  In order to solve the above-described problems, in the present invention, the polarization separation structure is configured such that a polarization separation element is disposed in a medium having a refractive index of light greater than 1, and the polarization separation element includes a wire. A polarization separation surface that separates light by diffraction based on a lattice structure such as a grid structure is provided, and an air layer is formed in contact with the polarization separation surface. In addition, the light valve is used as a projection type video display device or an optical unit for use in the projection type video display device that performs polarization conversion of light from the light source side and irradiates the light valve to form an optical image corresponding to the video signal and projects the enlarged image. The polarized light and the light modulated by the light valve are polarized and separated by the polarization separation structure, and the polarized and separated light is color-synthesized by color synthesis means, and the color-synthesized light is screened by a projection lens unit. It is set as the structure which expands and projects to.

  According to the present invention, in the projection type image display technology, it is possible to suppress the temperature rise of the polarization separation element unit and at the same time to ensure the high image quality of the image.

  The best mode for carrying out the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the component which has a common function in all the drawings.

  The present invention provides a wire grid and a medium of the wire grid type polarization separation element in order to reduce the deterioration of the polarization separation characteristic caused when the wire grid type polarization separation element is disposed in a medium having a refractive index larger than that of air. It is characterized in that a thin air layer that does not affect the astigmatism is provided between them.

  FIG. 1 is a configuration example of a projection type video display apparatus as an embodiment of the present invention, and shows an example of a liquid crystal projector apparatus using a reflection type liquid crystal panel as a light valve.

  In FIG. 1, 11 is a light source, 12 is a reflector having a parabolic reflecting surface shape, 13 and 14 are first multi-lens arrays and second multi-lens arrays constituting an integrator optical system, respectively, and 15 is a flat plate type comprising a prism array. Polarization conversion means, 16 is a condensing lens, and 10 is an illumination optical system composed of these. 21 and 22 are field lenses, 23 is a relay lens, 18 and 19 are dichroic mirrors, 20 is a color separation unit composed of dichroic mirrors 18 and 19, 24 is a total reflection mirror, and 291 292 and 293 are S-polarized light, respectively. The polarizing plates 301, 302, and 303, which transmit P, are polarization separation means 411, 412, and 413 that are polarization separation structures that perform polarization separation by transmitting P-polarized light and reflecting S-polarized light. Output-side polarizing plates that transmit P-polarized light, 401, 402, 403 are reflective liquid crystal panels as light valves (reflective light valves), and 42, 43 convert P-polarized light and S-polarized light. A two-wavelength phase difference plate, 44 is a cross dichroic prism for color synthesis, and 45 is a projection lens unit that enlarges and projects the color synthesized light onto a screen or the like. A.

  The light emitted from the light source 11 is reflected by a reflector 12 having a parabolic reflection surface shape, and enters a lens array type integrator optical system. The integrator optical system includes a plurality of rectangular lens cells provided in a rectangular frame having a size substantially equal to the exit aperture of the reflector 12, and a first lens array 13 for forming a plurality of secondary light source images; Similarly, a plurality of rectangular lens cells are disposed in the vicinity of the above-described plurality of secondary light source images, and the individual lenses of the first lens array 13 are disposed on the reflective liquid crystal panels 401, 402, and 403. The second lens array 14 forms a cell image. Each light beam divided into a plurality of light beams by the integrator optical system is aligned in a predetermined polarization direction (here, S-polarized light) by the plate-type polarization conversion means 15, and each light beam aligned with the S-polarized light is converted into the condenser lens 16. After being condensed by the field lens 21 and converted into a parallel light (telecentric) by the field lenses 21 and 22, the light is superimposed on the reflective liquid crystal panels 401, 402 and 403 and irradiated. As a result, the reflective liquid crystal panels 401, 402, and 403 are irradiated with uniform light. The light source 11, the integrator optical system, the flat plate polarization conversion means 15, and the condenser lens 16 constitute an illumination optical system.

  The light emitted from the condenser lens 16 is color-separated into RG (red + green) light and B (blue) light by a dichroic mirror 18 disposed at an angle of 45 ° with respect to the optical axis, and the RG light is dichroic mirror. 18, and the B light reflects the dichroic mirror 18. The RG light transmitted through the dichroic mirror 18 is color-separated into R light and G light by the dichroic mirror 19, the R light passes through the dichroic mirror 19 and enters the reflective liquid crystal panel 401, and the G light passes through the dichroic mirror 19. The light is reflected and enters the reflective liquid crystal panel 402. On the other hand, the B light reflected from the dichroic mirror 18 is transmitted through the relay lens 23, and its optical path is bent by 90 ° by the total reflection mirror 24, and the principal ray is made parallel to the optical axis by the field lens 22. Incident at 403. Since the optical path length of the reflective liquid crystal panel 403 is longer than the other two optical paths, the relay lens 23 guides the illumination light flux to the reflective liquid crystal panel 403 longer than the other two optical path lengths.

  Next, polarization separation means 301, 302, 303 (for each color light) arranged in front of the reflection type liquid crystal panels 401, 402, 403 (hereinafter collectively referred to as the reflection type liquid crystal panel 40) for each color light. Hereinafter, these will be collectively referred to as polarization separation means 30).

  The polarization separation means 30 has a configuration in which a polarization separation element is disposed in a medium having a light refractive index greater than 1, and the polarization separation element is configured to emit light by diffraction based on a lattice structure such as a wire grid structure. A structure having a polarization separation surface for separating polarization and having an air layer formed in contact with the polarization separation surface is used. As described above, since the polarization separation element has a degree of polarization that is insufficient as compared with the PBS prism, the incident-side polarizing plates 291 and 292 as auxiliary polarizers (transmitting S-polarized light) on the incident side of the polarization separating means 30. 293 (hereinafter collectively referred to as incident-side polarizing plate 29), and emission-side polarizing plates 411, 412, and 413 (hereinafter collectively referred to as auxiliary analyzers (transmitting P-polarized light)) on the output side. Then, the output side polarizing plate 41 is provided.

  Each color light (S-polarized light) color-separated by the color separation means 20 goes to the corresponding reflective liquid crystal panel 40, but after the polarization degree of the S-polarized light is increased by the incident side polarizing plate 29, the polarization separation means The polarized light is separated by 30 and only the S-polarized light is reflected and irradiated to the reflective liquid crystal panel 40 substantially perpendicularly. In the reflective liquid crystal panel 40, the irradiated S-polarized light is light intensity modulated in accordance with the video signal for each pixel to form an optical image, and the polarization state is changed and converted to P-polarized light. Each color light reflected from the reflective liquid crystal panel 40 in the state of forming an optical image and converted into P-polarized light is incident on the polarization separating means 30 again. The P-polarized light is polarized and separated by the polarization separation element of the polarization separation means 30 and passes through the polarization separation means 30. The P-polarized light transmitted through the polarization separating means 30 is increased in the degree of polarization by the output-side polarizing plate 41 and is further color-synthesized by the cross dichroic prism 44.

  The reflective liquid crystal panel 40 is driven according to a video signal by a drive circuit (not shown), modulates the light intensity of the incident S-polarized light while changing the polarization direction for each pixel, and generates P-polarized light according to the video signal. An optical image is formed.

  Of the optical images of each color light from the reflective liquid crystal panel 40, the R color light and the B color light are converted into S polarized light by the half-wave retardation plates 42 and 43, and the cross dichroic prism 44 changes the color. A combined color optical image (image) is formed, and the projection lens 45 enlarges and projects it onto a screen or the like. Instead of arranging the ½ wavelength phase difference plates 42 and 43, all color light may be color-combined in the cross dichroic prism 44 as P-polarized light.

  In the configuration of FIG. 1, a series of optical systems from the light source 11 to the projection lens unit 45 forms an optical unit that includes the illumination optical system of the liquid crystal projector device.

  2 to 3 are explanatory diagrams of a first configuration example of the polarization separating means 30. FIG. FIG. 2 is a first structural example diagram of the polarization separating means 30, and FIG. 3 is a ray diagram thereof. In the first configuration example, the polarization separation unit 30 is referred to as a polarization separation unit 30A. As the polarization separation element provided in the medium in the polarization separation means 30A, a wire grid type polarization separation element in which the polarization separation surface in contact with the air layer has a wire grid structure is used.

In FIG. 2, the polarization separation means 30 </ b> A is disposed in the liquid 31, a translucent container 35 made of glass or plastic whose outer shape is a rectangular parallelepiped, a liquid 31 as a medium filled therein, and the liquid 31. And a wire grid type polarization separation element 50. In the wire grid type polarization separation element 50, a translucent substrate 51 having a plate thickness t2 of 0.7 × 10 ⁻³ m and a diffraction grating, that is, a polarization separation surface formed at a predetermined periodic interval are formed thereon. For example, an aluminum wire grid (metal grid) 52, a translucent flat plate 54 that is disposed in parallel to face the translucent substrate 51 and has a plate thickness t1 of 0.7 × 10 ⁻³ m, and translucency The air is airtight in a space surrounded by the side plate 55 covering the peripheral side surface of the conductive substrate 51 and the flat plate 54, and the translucent substrate 51, the flat plate 54 and the side plate 55 arranged in parallel at a predetermined interval. And an air layer 56 formed by being filled. A reflective liquid crystal panel 40 is disposed on one surface (parallel to the XY plane) of the translucent container 35 of the polarized light separating means 30A, and the wire grid type polarized light separating element 50 is changed from the reflective liquid crystal panel 40 to the projection lens. It is inclined by θ ° (45 ° in this case) on the optical path toward Z (in the Z-axis direction). Further, an incident-side polarizing plate 29 is provided on the incident surface 35i of the translucent container 35 of the polarization separating means 30A, and an outgoing-side polarizing plate 41 is provided on the outgoing surface.

  The principal ray L1 incident on the polarization separation means 30A is first incident on the polarization separation means 30A after the polarization degree in a predetermined polarization direction (here, S-polarized light) is increased by the incident-side polarizing plate 29. Of the principal ray L1 whose S polarization degree is increased by the incident side polarization plate 29, the P-polarized light component is transmitted through the polarization separation surface of the wire grid type polarization separation element 50, and the S-polarized light component is reflected by the polarization separation surface. Then, the light enters the reflective liquid crystal panel 40. In the reflective liquid crystal panel 40, the incident light flux of S-polarized light is modulated in light intensity according to the video signal to form an optical image of P-polarized light and reflected in the Z-axis direction. The reflected light of the P-polarized light from the reflective liquid crystal panel 40 passes through the wire grid type polarization separation element 50, is analyzed by the output side polarizing plate 41, and travels toward the projection lens 45.

  The polarizing plates provided on the incident side and the outgoing side of the polarization separation means 30A are for supplementing the polarization separation function of the wire grid type polarization separation element 50. Further, the space between the translucent substrate 51 and the flat plate 54 is filled with air to form an air layer 56. When the thickness of the air layer 56 (hereinafter referred to as “air thickness”) is too thick, when the reflected light from the reflective liquid crystal panel 40 passes through the wire grid type polarization separation element 50, the air layer 56 is not thick. Point aberration occurs. For this reason, it is necessary to set the air thickness to an appropriate value. This point will be described later.

  As described above, the wire grid type polarization separation element 50 has the air layer 56, so that the grid pitch of the wire grid can be at least the same as the grid pitch used in the air. For this reason, there is no problem that the manufacture of the wire grid type polarization separation element 50 becomes difficult. Further, since the wire grid type polarization separation element 50 is disposed in the liquid 31 in which the refractive index of light is larger than that of air, the optical path length can be shortened, and the back focus of the projection lens is shortened for projection. It becomes possible to reduce the size of the lens. Furthermore, it can cool with the liquid 31, and can improve the deterioration of projection performance and the contrast fall by birefringence.

Since the wire grid type polarization separation element 50 includes the air layer 56, it is necessary to pay attention to total reflection occurring at the boundary between a medium having a large refractive index of light and a medium having a small refractive index. Hereinafter, in order to facilitate the calculation, the refractive indexes of the light of the flat plate 54 and the liquid 31 are substantially the same. For example, when the refractive index of the light of the liquid 31 is 1.5, the angle causing total reflection with the air layer is 41.8 ° (= sin ⁻¹ (1 / 1.5) from Snell's law. ) Not only S-polarized light on the optical axis of the light incident on the wire grid type polarization separating element 50 but also P polarized light to be transmitted by the wire grid type polarization separating element 50 is reflected. When total reflection occurs on the polarization separation surface, the extinction ratio, that is, the contrast may be deteriorated.

  FIG. 3 is a ray diagram of the polarization separating means 30A shown in FIG.

  In FIG. 3, 53 is a polarization separation surface of the wire grid type polarization separation element 50 (surface on which a wire grid structure is provided to separate and separate light), and N is a refractive index of light in the liquid 31 as a medium.

  The luminous flux incident on the reflective liquid crystal panel 40 from the illumination optical system and reflected and incident on the projection lens unit may be a parallel luminous flux parallel to the optical axis or an angular luminous flux. Assuming that a value obtained by converting a light beam having this angle into an F value is F, in FIG. 3, the light beam L2 having the maximum F value angle is not incident on the interface between the liquid medium and the air layer. It is necessary for the surface 35 i to satisfy the relationship of the following formula 2 and to satisfy the relationship of the following formula 3 at the interface with the air layer 56. Is the incident angle of the principal ray L1 on the optical axis at the air layer interface or the translucent flat plates 51 and 54, and is equal to the angle formed by the Z axis and the wire grid type polarization separation element.

sin α = sin [tan ⁻¹ {1 / (2F)}] = N sin β (Expression 2)
Nsin (β + θ) <1 (Equation 3)
The following equation 4 is obtained from the equations 2 and 3.

θ <sin ⁻¹ (1 / N)
−sin ⁻¹ [(1 / N) sin [tan ⁻¹ {1 / (2F)}]] (Expression 4)
However, in Equation 4, θ> 0.

  Therefore, if the refractive index N of the light of the medium is small and the incident light beam L2 satisfies the above formula 4, total reflection does not occur at the interface between the medium and the air layer of the wire grid type polarization separation element. However, when the refractive index N of the light of the medium is large and the above formula 4 is not satisfied, total reflection occurs and the polarization separation function deteriorates. For example, in the case of F = 3 and N = 1.2, the incident angle θ at which total reflection does not occur is a value less than 48.6 ° from Equation 4, and as a result, the wire grid type polarization separation element is 45 °. Even if tilted, total reflection does not occur. However, when F = 3 and N = 1.39, the incident angle θ at which total reflection does not occur is less than 39.2 °, and total reflection occurs when the wire grid type polarization separation element is inclined 45 °. Happens. In the case of chief rays, since the second term on the right side of Equation 4 is eliminated, θ is a value less than 46 °, and the polarization separation means is entirely at the interface between the medium and the air layer of the wire grid type polarization separation element. There is no reflection.

  4 to 5 are explanatory diagrams of a second configuration example of the polarization separating means 30. FIG. FIG. 4 is a diagram showing a second configuration example of the polarization separating means 30, and FIG. 5 is a ray diagram thereof. In the second configuration example, the polarization separation unit 30 is referred to as a polarization separation unit 30B. As the polarization separation element provided in the medium in the polarization separation means 30B, as in the case of the first configuration example, the wire grid type polarization separation element 50 whose polarization separation surface in contact with the air layer has a wire grid structure is used. In the second configuration example, the angle formed by the wire grid type polarization separation element 50 with respect to the Z-axis is made larger than 45 ° by a predetermined angle φ, and the main incident light beam L3 is inclined by 2φ with respect to the Y-axis so as to be totally reflected. This is an example when it is possible to avoid this.

  In FIG. 4, the polarization separation means 30 </ b> B is disposed in the liquid 32, a metal container 36 provided with a translucent window 37 in a portion where light passes, a liquid 32 serving as a medium filled therein, and the liquid 32. The wire grid type polarization separation element 50 is formed. As the liquid 32, for example, GE55 which is a mixed liquid of ethylene glycol and glycerin is used. The refractive index of light of GE55 is 1.45.

  FIG. 5 is a ray diagram of the polarization separation means of FIG. In FIG. 5, the incident side polarizing plate 29, the outgoing side polarizing plate 41, etc. are not shown. Further, for convenience of explanation, the refractive indexes of the light of the flat plate 54 and the liquid 32 are substantially the same. As is apparent from FIG. 5, the wire grid type polarization separation element 50 is arranged at a position shifted by an angle φ counterclockwise from a 45 ° tilt position with respect to the Z axis. Therefore, when the S-polarized light reflected by the wire grid type polarization separating element 50 is directed in the negative direction of the Z axis, the reflection angle is 45 ° −φ, and the principal ray L3 is directed to the wire grid type polarization separating element 50. Is also 45 ° -φ. At this time, the angle formed by the principal ray L3 and the Y axis is 2φ. The incident surface 36i of the metal container 36 is inclined by 2φ with respect to the negative direction of the Z axis, and the principal ray L3 incident on the translucent window 37 of the metal container 36 enters the incident surface 36i perpendicularly.

  In the polarization separating means 30B configured in this way, the incident angle of the principal ray L3 to the wire grid type polarization separating element 50 is 45 ° −φ, and therefore a light beam having an angle (a light beam having a converted F value of F). Even if it considers, total reflection in an air layer can be eliminated. Therefore, the S-polarized light of the incident light incident on the polarization separation means 30B is reflected by the wire grid type polarization separation element 50 and incident on the reflective liquid crystal panel 40, and the light intensity is modulated to form an optical image and P The light is reflected from the reflective liquid crystal panel 40 as polarized light. The P-polarized light emitted from the reflective liquid crystal panel 40 is incident on the polarization separation means 30B again, passes through the wire grid polarization separation element 50 in the polarization separation means 30B, and is a color composition cross dichroic prism 44. Emitted to the side. The light color-combined by the cross dichroic prism 44 is further emitted to the projection lens unit 45 side.

Therefore, if θ calculated from the above equation 4 is the critical incident angle θ _m , the angle φ needs to satisfy the following equation 5.

45−θ _m <φ (Expression 5)
For example, if the refractive index N of the light of the medium is 1.45 and F is 3, the critical incident angle θ _m at the air layer interface of the principal ray is 37.1 ° from Equation 4, and from Equation 5, φ is It must be 7.9 ° or more. If φ is 7.9 ° or more, Equation 4 is satisfied, and total reflection does not occur at the air layer interface.

  In the second configuration example, the wire grid type polarization separation element 50 is disposed at an angle φ from a position inclined by 45 ° with respect to the Z axis. However, unlike the PBS prism, the wire grid type polarization separation element 50 is arranged. Since the dependency of the polarization splitting characteristic of the separating element 50 on the incident angle is low, a good polarization splitting characteristic can be obtained as in the case of the first configuration.

  FIG. 6 is an explanatory diagram of a third configuration example of the polarization separation means 30. In the third configuration example, the polarization separation means 30 is referred to as polarization separation means 30C. Also in the polarization separation means 30C, the polarization separation element provided in the medium is a wire grid type polarization separation element in which the polarization separation surface in contact with the air layer has a wire grid structure as in the first and second configuration examples. Is used. In the third configuration example, a wire grid type polarization separation element is disposed between two prisms.

In FIG. 6, the polarization separation means 30 </ b> C includes a right-angle prism 33, a prism 34 opposed to the right-angle prism 33, and a wire grid type polarization separation element 60 disposed between the right-angle prism 33 and the prism 34. The wire grid type polarization separation element 60 includes a translucent substrate 61 having a plate thickness of 0.7 × 10 ⁻³ m and a diffractive action formed on the transparent substrate 61 at predetermined intervals, that is, a polarization separation surface. Air is formed in the space surrounded by the formed wire grid (metal lattice) 62, the side plate 65 covering the peripheral side surface of the translucent substrate 61 and the prism 34, and the translucent substrate 61, the prism 34 and the side plate 65. And an air layer 66 formed to be hermetically filled. A reflective liquid crystal panel 40 is disposed in parallel to _one surface 34 ₁ (parallel to the XY plane) of the prism 34 other than the side surface of the wire grid type polarization separation device 60. On the optical path from the reflective liquid crystal panel 40 to the projection lens 45 (Z-axis direction), as in the case of the second configuration example, the angle φ is shifted counterclockwise from the 45 ° inclined position with respect to the Z-axis. It is arranged at the position. The incident surface 34i of the prism 34 is inclined by an angle 2φ with respect to the negative direction of the Z axis, and the principal ray L5 incident on the polarization separating means 30C is inclined by an angle 2φ with respect to the Y axis. Therefore, the ray diagram of the incident / exit of the polarization separating means 30C is the same as in the case of FIG.

In the polarization separation means of the third configuration example, the medium is glass, for example, BSC7 (trade name) manufactured by HOYA, and the refractive index of light is 1.52, and the liquid medium (for example, refractive index) of the second configuration example is used. Since it is larger than that of 1.45), it is necessary to make the deviation angle φ from the 45 ° inclined position larger than in the case of the liquid medium. For example, if the refractive index N of the glass medium is 1.52 and F is 3, the seafront incident angle θ _m at the air layer interface of the principal ray is 34.9 ° from Equation 4, and the angle φ is From Equation 5, it is necessary to make the angle larger than 45 ° −34.9 ° = 10.1 °, and a larger angle φ than in the case of the liquid medium is necessary.

  Since the wire grid type polarization separation element of the polarization separation means described above includes an air layer, it is necessary to suppress the influence of astigmatism generated in the air layer. In order to suppress the influence of the astigmatism, it is effective to reduce the thickness of the air layer.

  7 to 9, the relationship between the air layer thickness (air thickness) and the light beam size (spot size) in the case where the wire grid type polarization separation element provided with the air layer is disposed in the medium is obtained by simulation. It is a graph which shows a result. FIG. 10 shows the simulation conditions.

As shown in FIG. 10A, a spot image on a 0.8-inch WIDE reflective liquid crystal panel 40 is projected onto a 45-inch screen 90 by a projection lens unit 45 having a magnification of about 56 times. The spot size ratio is obtained at each point A to F and averaged. The standard of the spot size is that the thickness of the air layer is 0.01 × 10 ⁻³ m, and as shown in FIG. 10B, the wire grid type polarization separation element 50 (60 in the medium of the polarization separation means 30 ′. ) Is a spot size when arranged so as to be perpendicular to the optical axis. Based on this, the spot size ratio is obtained for each air thickness. As shown in FIG. 10C, the spot size for each air thickness is such that the incident angle of the principal ray is 35 ° in the wire grid type polarization separation element 50 (60) in the medium of the polarization separation means 30. Sloped and determined. Then, at each air thickness, the shape of the two surfaces of the aspheric lens constituting the projection lens unit 45 and the distance d from the medium of the polarization separating means 30 to the first lens of the projection lens unit 45 are changed, Optimize to find the spot size.

  FIG. 7 shows a case of a liquid medium of polarization separating means having a light refractive index N of 1.3, and FIG. 8 shows a case of a liquid medium having a light refractive index N of 1.45 (for example, GE55). Are spot size ratios in the case of a medium (for example, glass BK7) having a refractive index of light of 1.52.

In FIG. 7, when the thickness of the air layer is about 0.1 to 0.15 × 10 ⁻³ m, the spot size ratio is minimized, and in FIG. 8, the thickness of the air layer is about 0.01. The spot size ratio is minimized when the ^{distance is} around × 10 ⁻³ m. As shown in FIG. 11, the air layer 56 having a refractive index lower than that of the medium is located between the light-transmitting substrate 51 and the light-transmitting flat plate 54 having a refractive index higher than that of the medium. Since the direction of the air layer is opposite to that of the light transmitting substrate 51 and the flat plate 54, it is considered that the lateral aberration is offset and the spot size is minimized at a predetermined air layer thickness. That is, when there are parallel flat plates with a higher refractive index than the medium on both sides of the air layer (the translucent substrate is also a parallel flat plate), the thickness of the parallel flat plate and the refraction of the light of the parallel flat plate and the medium There is an appropriate air thickness that can minimize astigmatism corresponding to the rate difference, and it is desirable to set the air thickness to an appropriate value.

On the other hand, in FIG. 9, since the refractive index of the translucent substrate 51 and the translucent flat plate 54 is equal to that of the medium, and astigmatism occurs only in the air layer, the thickness of the air layer is reduced. Astigmatism will be reduced. When the light-transmitting substrate 51 and the light-transmitting flat plate 54 having a light refractive index higher than that of the medium are used, as in the case of FIG. 7 and FIG. There is an appropriate air thickness that can minimize astigmatism corresponding to the refractive index difference between the light of the flat plate and the medium, and it is desirable to set the air thickness to an appropriate value. However, if the thickness of the air layer is made too thin, an interference effect occurs, so that it is at least about 3 / 2λ (red λr = 700 × 10 ⁻⁹ m) which is 1 × 10 ⁻⁶ m (micron) or more. desirable.

  According to the embodiment of the present invention, when the polarization separation element that separates light by diffraction based on the lattice structure such as the wire grid type polarization separation element is used in a medium in which the refractive index of light is larger than air. However, it is possible to suppress the deterioration of the polarization separation property. For this reason, in the projection type image display apparatus, it is possible to ensure image resolution, as well as brightness and contrast, while suppressing astigmatism while suppressing the temperature rise of the polarization separation element.

  In the above embodiment, the wire grid type polarization separation element is used as the polarization separation means. However, the present invention is not limited to this. For example, the light diffraction is performed on the translucent substrate at a predetermined period. For example, a configuration using a polarization separation element having a polarization separation surface formed with projections and depressions may be used. The light valve is not limited to a reflective light valve, and may be a transmissive light valve. The light valve may be other than a liquid crystal panel.

1 is a configuration example diagram of a projection type video display apparatus as an embodiment of the present invention. It is a 1st structural example figure of the polarization separation means used for the projection type video display apparatus of FIG. FIG. 3 is a ray diagram of the polarization separation means of FIG. 2. It is a 2nd structural example figure of the polarization separation means used for the projection type video display apparatus of FIG. FIG. 5 is a ray diagram of the polarization separation unit of FIG. 4. It is a 3rd structural example figure of the polarization separation means used for the projection type video display apparatus of FIG. It is a figure of the simulation result about the influence of the air layer of a polarization separation means. It is a figure of the simulation result about the influence of the air layer of a polarization separation means. It is a figure of the simulation result about the influence of the air layer of a polarization separation means. It is a figure which shows the simulation conditions of astigmatism. It is explanatory drawing of the astigmatism of the air layer in a polarization separation means. It is explanatory drawing of the arrangement | positioning method of a wire grid type | mold polarization separation element. It is explanatory drawing of the transmittance | permeability characteristic of P polarized light of a wire grid type | mold polarization separation element. It is explanatory drawing of the transmittance | permeability characteristic of S polarized light of a wire grid type | mold polarization separation element.

Explanation of symbols

10: Illumination optical system,
11 ... Light source,
12 ... Reflector,
13, 14 ... multi lens array,
15 ... Flat plate polarization conversion means,
16 ... Condensing lens,
21, 22 ... Field lens,
23 ... Relay lens,
18, 19 ... Dichroic mirror,
20 ... color separation means,
24 ... Total reflection mirror,
29, 291, 292, 293 ... incident side polarizing plate,
30, 301, 302, 303, 30A, 30B, 30C ... polarization separation means,
31, 32 ... Liquid,
33 ... right angle prism,
34 ... Prism,
35 ... translucent container,
36 ... Metal container,
41, 411, 412, 413... Exit side polarizing plate,
40, 401, 402, 403 ... reflective liquid crystal panel,
42, 43 ... 1/2 wavelength phase difference plate,
44. Cross dichroic prism,
45. Projection lens unit,
50, 60 ... wire grid type polarization separation element,
51, 61 ... translucent substrate,
56, 66 ... Air layer.

Claims (10)

A projection-type image display device that converts light from a light source side into polarized light, irradiates a light valve, forms an optical image according to a video signal, and projects an enlarged image.
A polarization separation surface for polarizing and separating light by diffraction based on a grating structure is formed in a medium through an air layer, and polarization separation is performed to separate the light irradiated to the light valve and the light modulated by the light valve. Means,
Color synthesizing means for color synthesizing the polarized and separated light;
A projection lens unit for enlarging and projecting the color-synthesized light, and
A drive circuit for driving the light valve;
A projection-type image display device characterized by comprising a configuration. A projection-type image display device that irradiates an image display element with light from a light source side, forms an optical image according to an image signal, and projects an enlarged image,
A polarization conversion means for aligning the polarization direction of light from the light source side to form P-polarized light or S-polarized light;
Separating means for separating the polarization-converted polarized light into R, G and B color lights;
A light valve that is irradiated with polarized light of each of the separated color lights and modulates the polarized light based on a video signal;
A polarization separation surface for polarizing and separating light by diffraction based on a grating structure is formed in a medium through an air layer, and polarization separation is performed to separate the light irradiated to the light valve and the light modulated by the light valve. Means,
Color synthesizing means for color synthesizing the polarized and separated light;
A projection lens unit for enlarging and projecting the color-synthesized light, and
A drive circuit for driving the light valve;
A projection-type image display device characterized by comprising a configuration.   3. The projection type image display device according to claim 1, wherein the polarized light separating means has a configuration in which the medium is a light transmissive liquid and the polarized light separating surface is formed on a light transmissive flat plate. .   4. The projection type image display device according to claim 1, wherein the light valve is a reflection type light valve. The F value of light modulated by the light valve and passing through the projection lens unit is F, the refractive index of light of the medium is N, the air layer of the polarization separation means of the principal ray emitted from the light valve, or When the incident angle to the light-transmitting flat plate forming the air layer is θ, the θ is
0 <θ <sin ⁻¹ (1 / N)
−sin ⁻¹ [(1 / N) sin [tan ⁻¹ {1 / (2F)}]] (Expression 1)
The projection-type image display device according to claim 1 or 2, wherein the projection-type image display device is in the range. An optical unit for a projection-type image display device that performs polarization conversion of light from a light source side, irradiates a light valve, forms an optical image according to a video signal, and projects an enlarged image.
A polarization separation surface for polarizing and separating light by diffraction based on a grating structure is formed in a medium through an air layer, and polarization separation is performed to separate the light irradiated to the light valve and the light modulated by the light valve. Means,
Color synthesizing means for color synthesizing the polarized and separated light;
A projection lens unit for enlarging and projecting the color-synthesized light, and
An optical unit characterized by comprising a structure. An optical unit for a projection-type image display device that irradiates an image display element with light from a light source side, forms an optical image according to an image signal, and projects an enlarged image.
A polarization conversion means for aligning the polarization direction of light from the light source side to form P-polarized light or S-polarized light;
Separating means for separating the polarization-converted polarized light into R, G and B color lights;
A light valve that is irradiated with polarized light of each of the separated color lights and modulates the polarized light based on a video signal;
Polarized light separating and polarizing the light by polarization based on the grating structure is formed in the medium through the air layer, and polarized light that separates the light irradiated to the light valve and the polarized light modulated by the light valve. Separating means;
Color synthesizing means for color synthesizing the polarized and separated light;
A projection lens unit for enlarging and projecting the color-synthesized light, and
An optical unit characterized by comprising a structure.   The optical unit according to claim 6 or 7, wherein the polarized light separating means is such that the medium is a light-transmitting liquid. A polarization separation structure that separates polarized light from incident light,
A structure for polarization separation, characterized in that a polarization separation surface for polarizing and separating light by diffraction based on a grating structure is formed in a medium via an air layer. The structure for polarization separation according to claim 9, wherein the medium is a light transmissive liquid, and the polarization separation surface is formed on a light transmissive flat plate.

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