JP2009300547A - Optical unit and projection type liquid crystal display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress returning light which returns from a reflection type polarizing plate to a transmission type liquid crystal panel, to eliminate astigmatism, and to suppress increase of back focus while using the reflection type polarizing plate as an emitting side polarizing plate. <P>SOLUTION: The emitting side polarizing plate comprises, in order from the transmission type liquid crystal panel side, a birefringent diffraction-grating type polarized light splitting element which is arranged orthogonally to an optical axis of an optical path, transmits first polarized light incident from the transmission type liquid crystal panel and also diffracts second polarized light orthogonal to the first polarized light, and the reflection type polarizing plate which is arranged orthogonally to the optical axis, transmits the first polarized light transmitted through the birefringent diffraction-grating type polarized light splitting element and also reflects the second polarized light diffracted by the birefringent diffraction-grating type polarized light splitting element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for providing an optical unit that projects an optical image with light from a light source and a projection-type liquid crystal display device using the optical unit.

  Conventionally, an optical unit that is an optical block that modulates the light intensity of a light source according to a video signal with a light valve and projects an enlarged optical image together with a drive circuit, a power supply circuit, a cooling fan, etc. A projection display device housed in a housing is known.

  In a projection display device, when a transmissive liquid crystal panel (hereinafter simply referred to as a “liquid crystal panel”) is used as a light bubble, the polarization direction is generally different before and after the liquid crystal panel (light incident side and light output side) (for example, An orthogonal polarizer is provided. As the polarizing plate, an absorption polarizing plate made of a uniaxially stretched organic film obtained by uniaxially stretching a polymer film containing, for example, iodine or dye molecules having a low allowable temperature has been conventionally used. Since this absorption-type polarizing plate absorbs unnecessary polarized light and generates heat, it is cooled by a cooling fan together with a liquid crystal panel having a low heat-resistant temperature to improve reliability. However, since the exit side polarizing plate disposed on the light exit side of the liquid crystal panel absorbs most of the light in the case of black display, its heat resistance is a major issue. In particular, recent projectors are required to achieve high brightness and long life while being downsized, and the problem of heat resistance in the output-side polarizing plate is increasing.

  As one means for solving this problem, a technique is known in which a reflection-type polarizing plate is used as the output-side polarizing plate and is inclined at about 45 degrees with respect to the optical axis of the optical path (see, for example, Patent Document 1). . Since the reflective polarizing plate reflects unnecessary polarized light and hardly absorbs light, reliability can be ensured.

  As another means for solving the problem, a hologram polarization separation element (volume phase type diffractive polarization separation element) in which a hologram is formed on a glass substrate that does not absorb unnecessary polarized light and has excellent reliability on the output side polarizing plate. Also known is a technique using (also referred to as Patent Document 2).

Japanese Patent Laid-Open No. 11-295660 JP 11-271533 A

  However, in Patent Document 1, in order to reduce the return light to the liquid crystal panel that causes a photoelectric effect in a TFT (Thin Film Transistor) built in the liquid crystal panel, the reflective polarizing plate is inclined to the optical axis of the optical path. Arranged. For this reason, in the polarized light transmitted through the reflective polarizing plate, astigmatism occurs in the translucent substrate that supports the reflective polarizing element. This astigmatism causes deterioration (for example, blurring) in, for example, an image (image) projected on the screen. Astigmatism is, for example, as shown in FIG. 6 of Patent Document 1, by arranging astigmatism correction glass of a plane parallel plate inclined in a direction twisted by 90 degrees with respect to the inclination of the output side polarizing plate. Can be canceled. However, since the astigmatism correction glass is also tilted in addition to the tilted arrangement of the reflective polarizing plate, the back focus, which is the distance between the rear end of the projection lens and the liquid crystal panel, becomes longer, and the projection There arises a new problem of increasing the size of the lens.

In Patent Document 2, unnecessary polarized light out of light vertically incident on a hologram polarization separation element (volume phase type diffractive polarization separation element) from a liquid crystal panel is converted into an optical axis (parallel to the normal line of the hologram polarization separation element). On the other hand, it is diffracted obliquely by a predetermined angle (for example, when diffracting S-polarized light, the diffraction angle θ _S is 48.2 °), and the diffracted unnecessary polarized light is emitted from the light exit surface (interface with air) of the glass substrate. To prevent unnecessary polarized light from exiting from the light exit side of the hologram polarization separation element. That is, as is clear from FIG. 1 of the same document, it is intended that unnecessary polarized light totally reflected by the emission surface of the glass substrate is emitted from the side surface of the glass substrate. In the example of this document, since the hologram polarization separation element is arranged orthogonal to the optical axis, the back focus can be shortened while reducing the above-mentioned astigmatism.
However, when the glass substrate is thin (for example, about 1 mm), unlike the intent of this patent document, unnecessary polarized light diffracted by the hologram and reflected by the light exit surface of the glass substrate is distant from the original diffraction point. It is thought that it will re-enter the hologram in the vicinity. For example, when the thickness of the glass substrate is 1 mm and S-polarized light is diffracted, in this patent document, the diffraction angle θ _S is 48.2 °, so that it is located only 2.2 mm away from the original diffraction point. It will be incident again. This re-incident unnecessary polarized light is diffracted by the hologram and becomes return light to the liquid crystal panel, which may cause deterioration in image quality. Further, as shown in FIG. 7 of Patent Document 2, in order to improve the contrast, when the exit side polarizing plate has a configuration in which an absorption polarizing plate is added to the hologram polarizing separation element, the hologram polarizing separation element is transmitted. Unnecessary polarized light is absorbed by the absorptive polarizing plate. When performing black display, the emission side polarizing plate must prevent light (unnecessary polarized light) emitted from the liquid crystal panel from being emitted to the light emission side. On the other hand, the projection type display device is required to have high brightness and downsizing, and even the absorption type polarizing plate disposed at the subsequent stage of the hologram polarization separation element generates a considerable amount of heat. Reliability may be deteriorated.

  The present invention has been made in view of the above circumstances, and its purpose is to return light from a reflective polarizer to a liquid crystal panel while using a reflective polarizer instead of an absorbing polarizer as an output-side polarizer. Another object of the present invention is to provide an optical unit that can suppress astigmatism and suppress an increase in back focus, and a projection-type liquid crystal display device using the same.

  In order to solve the above-described problems, in the optical unit according to the present invention, the output-side polarizing plate disposed on the light output side of the transmissive liquid crystal panel is arranged in order from the transmissive liquid crystal panel side with respect to the optical axis of the optical path. A birefringence diffraction grating type polarization separation element that is arranged orthogonally and transmits the first polarized light incident from the transmissive liquid crystal panel and diffracts the second polarized light orthogonal to the first polarized light; The second polarized light, which is arranged perpendicular to the optical axis, transmits the first polarized light transmitted through the birefringent diffraction grating type polarization separation element and is diffracted by the birefringence diffraction grating type polarization separation element. It is comprised with the reflective polarizing plate to reflect. Then, the birefringence diffraction grating type polarization separation element and the reflection type polarizing plate are arranged at a predetermined interval.

  As described above, in the present invention, since the birefringence diffraction grating type polarization separation element and the reflection type polarizing plate that hardly generate heat due to absorption of unnecessary polarized light are used as the outgoing side polarizing plate, the reliability of the outgoing side polarizing plate is improved. Can be improved. In addition, since both the birefringent diffraction grating type polarization separation element and the reflection type polarizing plate are arranged so as to be orthogonal to the optical axis of the optical path, it is not necessary to provide a member for correcting astigmatism, and an increase in back focus is suppressed. be able to. Also, birefringence that transmits the first polarized light incident from the transmissive liquid crystal panel and diffracts the second polarized light orthogonal to the first polarized light between the transmissive liquid crystal panel and the reflective polarizing plate. Since the diffraction grating type polarization separation element is arranged, the second polarized light diffracted by the birefringence diffraction grating type polarization separation element and inclined with respect to the optical axis is reflected by the reflective polarizing plate with respect to the optical axis. Can be reflected diagonally. At this time, since the birefringence diffraction grating type polarization separation element and the reflection type polarizing plate are set at a predetermined interval, the second polarized light reflected by the reflection type polarizing plate is separated from the birefringence diffraction grating type polarization separation. It is possible to prevent the light from entering the element again, and as a result, it is possible to suppress the return light that returns to the transmissive liquid crystal panel. In addition, since the birefringence diffraction grating type polarization separation element is arranged at the front stage and the reflection type polarizing plate is arranged at the rear stage, the extinction ratio can be increased and a high contrast image can be obtained.

  Moreover, the said structure is described below in another expression.

  An optical unit comprising: an illumination optical unit that emits predetermined polarized light; a transmissive liquid crystal panel that modulates and emits the predetermined polarized light into an optical image; and a projection lens that projects the optical image. Birefringence diffraction grating type polarization separation arranged in order from the transmissive liquid crystal panel side, orthogonal to the optical axis of the light transmitted through the transmissive liquid crystal panel, on the light outgoing side of the light transmitted through the transmissive liquid crystal panel An element and a reflective polarizing plate arranged orthogonal to the optical axis are provided.

  An optical unit comprising: an illumination optical unit that emits predetermined polarized light; a transmissive liquid crystal panel that optically modulates the predetermined polarized light into an optical image; and a projection lens that projects the optical image. The light from the transmission type liquid crystal panel is provided so as to pass through the birefringence diffraction grating type polarization separation element and the reflection type polarizing plate in this order, and is orthogonal to the optical axis of light from the transmission type liquid crystal panel The birefringence diffraction grating type polarization separation element and the reflection type polarizing plate are arranged.

  The birefringence diffraction grating polarization separation element transmits the first polarized light incident from the transmissive liquid crystal panel, and the second polarized light orthogonal to the first polarized light. Make the light diffracted.

  Further, in the optical unit, the reflective polarizing plate transmits the first polarized light incident from the transmissive liquid crystal panel, and the second polarized light diffracted by the birefringence diffraction grating type polarization separation element. It is characterized by reflecting light.

  In the optical unit, the birefringence diffraction grating type polarization separation element and the reflective polarizing plate are provided at a predetermined interval.

  In the optical unit, the birefringence diffraction grating type polarization separation element is an inorganic polarization separation element. In the optical unit, the reflective polarizing plate is an inorganic polarizing plate.

  As described above, according to the present invention, an optical unit capable of suppressing return light returning from the output-side polarizing plate to the liquid crystal panel, eliminating astigmatism, and suppressing an increase in back focus, and a projection type liquid crystal using the same A display device can be provided.

  Hereinafter, the best mode of the present invention will be described with reference to the drawings. In each figure, elements having common functions are denoted by the same reference numerals, and those that have been described once will not be described repeatedly.

  The present invention is characterized in that the exit-side polarizing plate provided on the light exit side of the liquid crystal panel is composed of a birefringent diffraction grating type polarization separating element and a reflective polarizing plate arranged in this order.

  First, the optical system of the optical unit according to the present embodiment will be described, and then the detailed configuration of the output side polarizing plate according to the present embodiment will be described.

  FIG. 1 is a schematic configuration diagram of an optical system of an optical unit according to the present embodiment. In FIG. 1, when distinguishing elements arranged in the optical path of each color light, R, G, and B representing the color light are shown after the code, and when there is no need to distinguish, the color light is attached. Omit the letter. In order to clarify the polarization direction, a local right-handed rectangular coordinate system is introduced. That is, with the optical axis 101 as the Z axis, the axis parallel to the paper surface in FIG. 1 is defined as the Y axis within the plane orthogonal to the Z axis, and the axis from the back to the front of the paper surface is defined as the X axis. For convenience, the direction parallel to the X axis is referred to as “X direction”, and the direction parallel to the Y axis is referred to as “Y direction”. For convenience of explanation, polarized light whose polarization direction is the X direction is referred to as “X polarized light”, and polarized light whose polarization direction is the Y direction is referred to as “Y polarized light”.

  In FIG. 1, the optical system of the projection type liquid crystal display device includes an illumination optical system 100, a light separation optical system 130, a relay optical system 140, three field lenses 29 (29R, 29G, 29B), and three transmissions. Liquid crystal panel 60 (60R, 60G, 60B), a light combining prism 200 that is a light combining means, and a projection lens 300 that is a projection means. The liquid crystal panel 60 includes an incident side polarizing plate 50 (50R, 50G, 50B) on the light incident side, and a birefringence diffraction grating type polarization separation element 70 (70R, 70G, 70B) as an output side polarizing plate on the light emitting side. And a reflective inorganic polarizing plate 80 (80R, 80G, 80B). These optical elements are mounted on a base 550 to constitute an optical unit 500. The optical unit 500 includes a driving circuit 570 for driving the liquid crystal panel 60, a cooling fan 580 for cooling the liquid crystal panel 60, and the like. A projection type liquid crystal display device is mounted on a housing (not shown) together with a power source circuit 560 that supplies power to the light source unit 10, the cooling fan 580, the drive circuit 570 and other circuits (not shown) included in the illumination optical system 100. Constitute.

  An illumination optical system 100 that uniformly illuminates a liquid crystal panel 60 that is an image display element includes a light source unit 10 that includes a lamp (also referred to as a light source) 11 that emits substantially white light and a reflector 12 (here, a parabolic reflector); The optical system includes a first array lens 21 and a second array lens 22 that constitute an optical integrator, a polarization conversion element 25, and a condenser lens (also referred to as a superimposing lens) 27. In addition, the light separation optical system 130 that separates substantially white light from the illumination optical system 100 into, for example, three primary color lights, includes two dichroic mirrors 31 and 32 and a reflection mirror 33 that changes the optical path direction. Yes. The relay optical system 140 includes a first relay lens 41 that is a field lens, a second relay lens 42 that is a relay lens, and two reflection mirrors 45 and 46 that change the optical path direction.

  The lamp 11 is a white lamp such as an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp, a mercury xenon lamp, or a halogen lamp. The reflector 12 has a reflecting surface having, for example, a paraboloidal shape disposed so as to cover the lamp 11 from the rear side, and has a circular or polygonal exit opening.

  The light emitted from the lamp 11 is reflected by, for example, a reflector 12 having a paraboloidal reflecting surface, is substantially parallel to the optical axis 101, and a substantially parallel light beam is emitted from the light source unit 10. The light emitted from the light source unit 10 enters the polarization conversion integrator.

  The polarization conversion integrator is an optical integrator that performs uniform illumination including a first array lens 21 and a second array lens 22, and polarization of a polarization beam splitter array that converts light into a linearly polarized light while aligning the polarization direction of the light with a predetermined polarization direction. And a conversion element 25.

  The first array lens 21 includes a plurality of lens cells having a rectangular shape that is substantially similar to a liquid crystal panel when viewed from the illumination optical axis direction. The first array lens 21 receives a plurality of light incident from the light source unit 10. The light is divided into a plurality of light by the lens cell and guided so as to pass through the second array lens 22 and the polarization conversion element 25 efficiently. That is, the first array lens 21 is designed so that the lamp 11 and each lens cell of the second array lens 22 have an optically conjugate relationship.

  Similar to the first array lens 21, the second array lens 22 having a configuration in which a plurality of rectangular lens cells as viewed from the direction of the illumination optical axis are arranged in a matrix form corresponds to each of the constituting lens cells. The shape of the lens cell of the first array lens 21 is projected (mapped) onto the liquid crystal panel 60.

  At this time, the light from the second array lens 22 in the polarization conversion element 25 has a predetermined polarization direction, for example, X-polarized light of linearly polarized light (X direction whose polarization direction is perpendicular to the paper surface in FIG. Directional light). The projected images of the lens cells of the first array lens 21 are superimposed on the liquid crystal panels 60 by the condenser lens 27, the field lenses 29G and 29B, the relay optical system 140, and the field lens 29R, respectively.

  Note that the second array lens 22 and the condensing lens 27 disposed in the vicinity thereof are such that each lens cell of the first array lens 21 and the liquid crystal panel 60 are optically related to each other between an object and an image. (That is, a conjugate relationship), the light beam divided into a plurality by the first array lens 21 is placed on the liquid crystal panel 60 by the second array lens 22 and the condenser lens 27. It is possible to illuminate with a highly uniform illuminance distribution that is projected in a superimposed manner and has no practical problem.

  As described above, the polarization conversion integrator composed of the first array lens 21, the second array lens 22, and the polarization conversion element 25 applies light having a random polarization direction from a lamp (light source) to a predetermined polarization direction. The liquid crystal panel can be uniformly illuminated while being aligned with (here, X-polarized light).

  The light (substantially white light) emitted from the illumination optical system 100 enters the light separation optical system 130. The light separation optical system 130 separates substantially white light from the illumination optical system 100 into three primary colors of light. For example, the first color light B light (blue band light), the second color light G light (green band light), and the third color light R light (red band light) are spectrally separated. To do. Then, the respective light paths of the separated color lights toward the corresponding liquid crystal panels 60 (60R, 60G, 60B) (the first color light B light path, the second color light G light path, and the third color light R light path). To guide the light. That is, for example, the B light is reflected by the dichroic mirror 31 and travels to the corresponding liquid crystal panel 60B (B optical path). The G light and the R light are transmitted through the dichroic mirror 31 and are separated into the G light and the R light by the dichroic mirror 32. Here, the G light is reflected by the dichroic mirror 32 and travels to the corresponding liquid crystal panel 60G (G optical path), and the R light is transmitted through the dichroic mirror 32 and travels to the corresponding liquid crystal panel 60R (R optical path).

  Each optical path of the light separation optical system 130 will be specifically described.

  The B light reflected by the dichroic mirror 31 is reflected by the reflecting mirror 33, passes through the field lens 29B and the incident-side polarizing plate 50B, and enters the liquid crystal panel 60B for B light.

  On the other hand, of the G light and R light transmitted through the dichroic mirror 31, the G light is reflected by the dichroic mirror 32 and enters the G light liquid crystal panel 60G through the field lens 29G and the incident side polarizing plate 50G.

  The R light passes through the dichroic mirror 32 and enters the relay optical system 140. The R light incident on the relay optical system 140 is condensed (converged) in the vicinity of the second relay lens 42 via the reflection mirror 45 by the first relay lens 41 of the field lens, and diverges toward the field lens 29R. . The light then enters the field lens 29R through the reflection mirror 46, is made substantially parallel to the optical axis by the field lens 29R, passes through the incident-side polarizing plate 50R, and enters the liquid crystal panel 60R for R light.

  The liquid crystal panel 60 (60R, 60G, 60B) includes an incident-side polarizing plate 50 (50R, 50G, 50B) on the light incident side, and serves as an output-side polarizing plate on the light emitting side. (70R, 70G, 70B) and a reflective inorganic polarizing plate 80 (80R, 80G, 80B).

  In each liquid crystal panel 60, X-polarized color light incident from the light separation optical system 130 whose degree of polarization is increased by the incident-side polarizing plate 50 (50 </ b> R, 50 </ b> G, 50 </ b> B) whose transmission axis is the X direction is output by the drive circuit 570. When driven, it modulates (light intensity modulation) in accordance with a color video signal (not shown) to form, for example, a Y-polarized optical image of each color light. Each Y-polarized optical image is unnecessary by the birefringence diffraction grating type polarization separation element 70 (70R, 70G, 70B) and the reflective inorganic polarizing plate 80 (80R, 80G, 80B) whose transmission axis is the Y direction. The polarized light component (here, X-polarized light as the second polarized light) is removed, the contrast is increased, and the light enters the light combining prism 200 as the light combining means. At this time, in the B optical path and the R optical path, 1 / 2λ wavelength plates 90B and 90R are provided between the reflective inorganic polarizing plates 80B and 80R and the light combining prism 200, respectively. Therefore, the Y-polarized B light and R light optical images are converted to X-polarized (S-polarized light with respect to the dichroic film surface for color synthesis of the light combining prism 200), and Y-polarized light (the dichroic film of the light combining prism 200). Along with the optical image of G light (P-polarized light with respect to the surface), the light is efficiently combined by the light combining prism 200.

  In the light combining prism 200, a dichroic film (dielectric multilayer film) 210b that reflects B light and a dichroic film (dielectric multilayer film) 210r that reflects R light are approximately X-shaped at the interface of four right-angle prisms ( (Cross shape). And it has the function which synthesize | combines each optical image of 3 color light, and makes it color image light (image light). In the light combining prism, in general, so-called SPS combining in which G light is P-polarized light and R light and B light are S-polarized light is used with respect to the surface of the dichroic film 210 from the viewpoint of improving light utilization efficiency. Of the light from the liquid crystal panel 60, the polarized light transmitted through the birefringence diffraction grating type polarization separation element 70 and the reflective inorganic polarizing plate 80 is Y-polarized light as first polarized light (P-polarized light with respect to the dichroic film surface). Light). Therefore, ½λ wavelength plates 90B and 90R are provided in the B optical path and the R optical path, respectively, so as to be X-polarized light (S-polarized light). Of the three incident surfaces of the light combining prism 200, the B light and R light (S-polarized light with respect to the dichroic film surface) incident on the opposite incident surfaces are crossed by the dichroic film 210b for B light and the R light The G light (P-polarized light with respect to the dichroic film surface) reflected by the dichroic film 210r and incident on the central incident surface travels straight, is photo-combined, and exits from the exit surface. Thereafter, the image is projected onto a screen (not shown) by a projection lens 300 such as a zoom lens.

  The cooling fan 580 is generated, for example, by absorbing a part of the light emitted from the light source unit 10 by the incident side polarizing plate 50, the birefringence diffraction grating type polarization separating element 70, the reflective inorganic polarizing plate 80, the liquid crystal panel 60, and the like. Heat is blown through an air flow (wind) through a cooling duct (not shown) to flow to the incident side polarizing plate 50, the birefringent diffraction grating type polarization separation element 70, the reflective inorganic polarizing plate 80 and the liquid crystal panel 60. A path 585 is formed to cool. In this embodiment, as the output side polarizing plate, an inorganic birefringence diffraction grating type polarization separation element 70 and a reflection type inorganic polarizing plate 80 that generate little heat due to absorption of unnecessary polarized light and have excellent heat resistance and UV resistance are used. (Details will be described later). Therefore, it is possible to suppress the amount of air blown to the birefringent diffraction grating type polarization separation element 70 and the reflection type inorganic polarizing plate 80 and increase the amount of air flow to the incident side polarizing plate 50 and the liquid crystal panel 60 correspondingly. In this way, it is possible to efficiently cool the incident-side polarizing plate 50 and the liquid crystal panel 60 without increasing the capacity of the cooling fan accompanying the increase in luminance.

  Note that the relay optical system 140 has an R to R optical path length from the light source to the B light liquid crystal panel 60B (B optical path length) and an optical path length from the light source to the G light liquid crystal panel 60G (G optical path length). Since the optical path length (R optical path length) to the optical liquid crystal panel 60R is long, this is for correcting this.

  Here, the relay optical system 140 will be described a little.

  In the vicinity of the first relay lens 41 on the R optical path, a virtual liquid crystal display image (not shown) in which the lens cell images of the first array lens 21 are superimposed is formed by the illumination optical system 100. The purpose of the relay optical system 140 is to relay this virtual liquid crystal display image to the liquid crystal panel 60R for R light. That is, the second relay lens 42 of the relay optical system 140 maps the virtual liquid crystal display image onto the R light liquid crystal panel 60R. That is, the virtual liquid crystal display image and the liquid crystal panel 60R are in a relationship between an object and an image. The first relay lens 41, which is a field lens of the relay optical system 140, secondly transmits the light that has passed through the virtual liquid crystal display image so that the illuminance of the image formed on the liquid crystal panel 60R is uniform everywhere. The light is condensed near the relay lens 42. A plurality of arc images (secondary light source images) formed on the second array lens 22 are formed in the vicinity of the second relay lens 42. That is, the second array lens 22 and the second relay lens 42 are in an object-image relationship.

  Next, the output side polarizing plate according to this embodiment will be described. In this embodiment, a birefringence diffraction grating type polarization separation element and a reflection type polarizing plate that can be disposed perpendicularly to the optical axis with little absorption of unnecessary polarized light and negligible heat generation are used as the output side polarizing plate. The birefringence diffraction grating type polarization separation element used here transmits the predetermined polarized light (linearly polarized light) included in the light incident from the liquid crystal panel substantially parallel to the optical axis as it is, and the other polarized light orthogonal to this ( (Linearly polarized light) is diffracted and tilted (crossed) to the optical axis before being emitted.

First, the reflective polarizing plate will be described. The reflective polarizing plate transmits polarized light in the transmission axis direction as first polarized light, and reflects polarized light in the reflection axis direction as second polarized light orthogonal to the transmission axis. Examples of the reflective polarizing plate include a film multilayer laminated polarizing plate made of an organic material (for example, a reflective polarizing film D-BEF (trade name) manufactured by 3M Co.), and a reflective inorganic polarizing plate made of an inorganic material. Etc. can be used. Here, a reflective inorganic polarizing plate is used in consideration of heat resistance and light resistance. However, the present invention is not limited to this.
The reflective inorganic polarizing plate is a reflective polarizing plate including a fine structure having a period of, for example, about 1/2 of the wavelength of light along a predetermined direction. For example, a wire grid type polarizing plate described in JP-A-2007-33746 or a photonic crystal structure (a fine structure having a periodic structure of refractive index) described in JP-A-2006-337860, for example. There is a polarizing plate provided. These reflective inorganic polarizing plates are manufactured by applying an inorganic material to a large substrate and then cutting it out to a desired size. Therefore, there is an advantage that it is easy to increase in size and is relatively easier to price than polarizing glass. . The reflective inorganic polarizing plate may be collectively referred to as a structural birefringent polarizing plate (see, for example, JP-A-2007-102246).

  FIG. 5 is an explanatory view showing various examples of the reflective inorganic polarizing plate. FIG. 4A is a perspective view of a wire grid type polarizing plate, and FIG. 4B is a perspective view of a polarizing plate having a photonic crystal structure.

  In FIG. 5A, a wire-grid reflective inorganic polarizing plate 80 is formed on a translucent substrate (for example, a glass substrate) 81 in a striped metal thin film (hereinafter referred to as “wire grid”) extending in the X direction. 82) are periodically arranged through the grooves 83, and the period is smaller than the wavelength of light (for example, about a fraction to one tenth of the wavelength of light). When the incident light L800 is incident on the wire-grid reflective inorganic polarizing plate, the X-polarized light L800x whose polarization direction is parallel to the wire grid 82 is reflected to become reflected light L802, and Y in the polarization direction orthogonal to the wire grid 82 is reflected. The polarized light L800y is transmitted to become transmitted light L801. That is, the Y-polarized light L800y in the direction orthogonal to the wire grid 82 is transmitted, and the X-polarized light L800x parallel to the wire grid 82 is reflected. That is, the direction orthogonal to the wire grid 82 is the transmission axis (polarization axis) direction of the wire grid reflective inorganic polarizing plate. An example of this is ProFlux (trade name) of MOXTEK. A direction parallel to the wire grid 82 orthogonal to the transmission axis direction is referred to as a reflection axis direction.

  In FIG. 5B, a reflective inorganic polarizing plate 80 having a photonic crystal structure is a translucent substrate having line / space-shaped grooves formed at a pitch of 1/4 to 1/2 of the wavelength. 81 and an adjustment layer 85 that fills the groove of the translucent substrate 81 and has a triangular wave shape in the short-side direction (Y direction) of the groove and a linear convex portion in the long direction (X direction) of the groove, On the adjustment layer 85, a plurality of high refractive index layers 86 made of a transparent high refractive index medium and a plurality of low refractive index layers 87 made of a transparent low refractive index medium are alternately laminated. The high refractive index layer 86 and the low refractive index layer 87 are formed in a triangular wave shape in the short direction (Y direction) of the groove of the adjustment layer 85 and in a linear convex shape in the long direction (X direction) of the groove, It has a surface with a triangular wave shape in the short direction (Y direction) and a linear shape in the long direction (X direction). As described above, the high refractive index layer 86 having a surface having a triangular wave shape in the short direction (Y direction) and a linear shape in the long direction (X direction) at a pitch sufficiently smaller than the wavelength of light and low refraction. When the incident light L800 is incident on the laminated body of the refractive index layer 87, the X-polarized light L800x having a polarization direction parallel to the longitudinal direction (X direction) of the high refractive index layer 86 and the low refractive index layer 87 has a photonic crystal structure. Reflected without being able to pass through the reflective inorganic polarizing plate 80 provided with. On the other hand, Y-polarized light L800y having a polarization direction parallel to the short direction (Y direction) of the high refractive index layer 86 and the low refractive index layer 87 passes through the reflective inorganic polarizing plate 80 having a photonic crystal structure. be able to. In this way, light having polarization directions orthogonal to each other is separated into two orthogonal polarized lights by the reflective inorganic polarizing plate 80 having a photonic crystal structure.

  Thus, the reflective inorganic polarizing plate transmits polarized light in the transmission axis direction and reflects polarized light orthogonal thereto. Therefore, unlike the absorption-type polarizing plate, it hardly absorbs light, generates a very small amount of heat, and the temperature rise is very small. Further, since the reflective inorganic polarizing plate is composed of an inorganic material, it can be said that the heat resistant temperature is high and the life characteristics are excellent. The reflective inorganic polarizing plate has a polarization separation function that separates incident light into two polarized light beams (transmitted polarized light and reflected polarized light) that are orthogonal to each other, and therefore can also be used as a polarization separation element. Can do.

  However, when the reflective inorganic polarizing plate 80 is disposed on the light emitting side of the liquid crystal panel so as to be orthogonal to the optical axis, unnecessary polarized light reflected by the reflective inorganic polarizing plate 80 returns to the liquid crystal panel 60, and the liquid crystal panel 60 This causes a photoelectric effect in a TFT (not shown) incorporated in the TFT, resulting in image quality degradation. Therefore, in this embodiment, for example, a birefringence diffraction grating type polarization separation element 70 which is a diffraction polarization separation element is disposed between the liquid crystal panel 60 and the reflective inorganic polarizing plate 80. Although details will be described later with reference to FIG. 6, the birefringence diffraction grating type polarization separation element 70 diffracts unnecessary polarized light so as to be inclined with respect to the optical axis. Therefore, the unnecessary polarized light inclined with respect to the optical axis is reflected obliquely with respect to the optical axis by the reflective inorganic polarizing plate 80 and does not return to the liquid crystal panel 60, so that it is possible to eliminate image quality deterioration.

Next, a birefringence diffraction grating type polarization separation element will be described. There are organic and inorganic birefringence diffraction grating type polarization separation elements, but here, as with reflective polarizing plates, here, in consideration of heat resistance and light resistance, inorganic birefringence diffraction grating type A polarization separation element is used. However, the present invention is not limited to this.
FIG. 2 is a partial cross-sectional view schematically showing one configuration of the birefringence diffraction grating type polarization separation element according to the present embodiment, and is a cross-sectional view in the YZ plane parallel to the long side of the liquid crystal panel. FIG. 3 is an enlarged cross-sectional view showing a main part of the birefringent diffraction grating type polarization separation element of FIG. 2 partially enlarged. FIG. 4 is an explanatory diagram for explaining a process of forming a birefringence diffraction grating type polarization separation element. In FIG. 3, since the polarization direction of the X-polarized light is perpendicular to the drawing sheet, it is assumed that the X-polarized light is displayed as “X surrounded by a circle” for simplicity of illustration.

As shown in FIGS. 2 and 3, the birefringent diffraction grating type polarization separation element 70 includes a glass substrate 72 as a translucent substrate and a grating 73a extending in the X direction on the glass substrate 72 with a period d in the Y direction. And a birefringent film (also referred to as an anisotropic film) 73 in which an uneven unidirectional periodic structure is formed, and an isotropic overcoat layer 74 covering the birefringent film 73. Yes. Note that h is the height of the grating 73a.
Here, it is assumed that the light L60 from the liquid crystal panel 60 enters the birefringence diffraction grating type polarization separation element 70 substantially perpendicularly along the optical axis 101 of the optical path in the Z-axis direction. The light L60 is an X-polarized light (S-polarized light) L60x as a second polarized light whose polarization direction is parallel to the extending direction (that is, the X direction) of the grating 73a in a plane orthogonal to the Z axis, and the polarization direction. Is composed of Y-polarized light (P-polarized light) L60y as the first polarized light in the direction orthogonal to the extending direction of the grating 73a (that is, the Y direction).

When the light L60 is incident on the birefringent diffraction grating type polarization separation element 70, the birefringence diffraction grating type polarization separation element 70, when satisfying the conditions described later, as shown in FIG. The Y-polarized light L60y, which is the first polarized light in the direction orthogonal to the extending direction of the grating 73a, goes straight as it is as the zero-order light. Further, the X-polarized light L60x, which is the second polarized light whose polarization direction is parallel to the extending direction of the grating 73a, is diffracted in the direction perpendicular to the extending direction of the grating 73a (that is, the Y direction) as ± first-order light. The light is emitted while being inclined with respect to the axis (θs in FIG. 2 is a diffraction angle of X-polarized light). In other words, the birefringence diffraction grating type polarization separation element 70 is configured such that the incident light L60 is X-polarized light L60x that is diffracted light that is emitted obliquely with respect to the optical axis, and Y-polarized light L60y that is straightly transmitted light as it is. To separate. The direction orthogonal to the grating 73 a can be said to be the transmission axis direction of the birefringent diffraction grating type polarization separation element 70.
Next, conditions for the birefringence diffraction grating type polarization separation element 70 to diffract the X-polarized light L60x will be described.
The refractive index with respect to X-polarized light L60x grating 73a of the birefringent film 73 n _x, the refractive index n _y for the Y-polarized light L60y, the isotropic refractive index of the overcoat layer 74 and n _1, the optical path A, The optical path length difference Δ with respect to B is expressed by the following equation for each polarized light.
(Equation 1)
Y-polarized _{light: Δy = (n y -n 1} ) h
(Equation 2)
X-polarized light: Δx = (n _x −n ₁ ) h
Accordingly, the condition for the Y-polarized light L60y to travel straight and the X-polarized light L60x to be diffracted needs to satisfy the following equation.
(Equation 3)
Δy = mλ
(Equation 4)
Δx = (m ± 1/2) λ
Here, λ is the wavelength of light, and m is an order integer.
Here, the equation (3) is such that the optical path difference in the Y-polarized light L60y is an integral multiple of the wavelength λ, the Y-polarized light passing through the optical path A and the Y-polarized light passing through the optical path B are intensified by interference, and 0 after passing through the grating. It is a condition that goes straight as the next light. The equation (4) is a condition that the optical path difference in the X-polarized light L60x is shifted by an odd multiple of a half wavelength and cancels each other, so that the straight light (zero-order light component) disappears and all becomes diffracted light. That is, the linear component cancels out due to interference, and the X-polarized light becomes diffracted light. Therefore, when the 0th-order and 1st-order polarization separation is performed, it is necessary to satisfy the expressions (3) and (4) in order to increase the polarization separation degree. However, practically, even if the expressions 3 and 4 are not strictly satisfied, the refractive indexes n _y and n _x of the birefringent film 73 are set so that the conditions in the vicinity of the expressions 3 and 4 are _satisfied . The refractive index n ₁ of the overcoat layer 4, the height h of the birefringent film 73, and the order m are set.

Next, one manufacturing method of the birefringent diffraction grating type polarization separation element 70 will be described with reference to FIG. First, as shown in FIG. 4A, a birefringent film 73 is formed on a glass substrate 72 by, for example, a known oblique vapor deposition method. Examples of the material of the birefringent film 73 include a dielectric material made of an inorganic substance that can be formed by an oblique deposition method, such as Ta ₂ O ₅ and SiO ₂ . However, the present invention is not limited to these, and various materials can be used as long as they are inorganic materials capable of providing birefringence (optical anisotropy) by oblique vapor deposition. The oblique deposition method is an evaporation method in which an inorganic material such as a metal oxide is deposited from an oblique direction with respect to a substrate. The vapor deposition film formed by this method has a fibrous columnar structure inclined with respect to the substrate, that is, an anisotropic structure, and has a refractive index for linearly polarized light in a direction orthogonal to the refractive index for linearly polarized light in the inclined direction. There is a difference between The deposited film thus formed is birefringent. As an apparatus used for this method, a normal vacuum apparatus such as a vacuum evaporation apparatus by electron beam heating can be used, and the evaporation operation is performed by installing the substrate in an inclined position in the apparatus. Such vapor deposition methods are described in, for example, APPLIED OPTICS, Vol.28, NO.13, p.2466-2482 (1989), Surface Technology, Vol.46, No.7, 1995, p. ”And the like are described in detail, and further description is omitted.

Next, as shown in FIG. 4B, a photoresist 76 is coated on the birefringent film 73. Then, a periodic pattern is exposed on the photoresist 76. In this case, contact exposure using a mask or projection exposure may be used. In addition, electron beam exposure or interference exposure using laser light may be used. After the exposure, the photoresist is developed to obtain a periodic lattice pattern by the photoresist 76 as shown in FIG. Next, as shown in FIG. 9D, the birefringent film 73 is etched using the photoresist 76 as an etching mask. As an etching method, known dry etching or wet etching can be used. Next, as shown in FIG. 4E, the photoresist 76 is removed by ashing with a solvent or plasma. Then, as shown in FIG. 4 (f), a dielectric (for example, SiO ₂ , SiON, etc.) is vacuum-deposited or sputtered on the birefringent film 73 having a periodic lattice structure, and isotropic overstrike. A coat layer 74 is formed.

  Next, the detailed structure of the output side polarizing plate according to this embodiment will be described. The configuration of the exit side polarizing plate is the same for all of the R optical path, the G optical path, and the B optical path. Here, the configuration of the exit side polarizing plate of the G optical path is representatively described.

  6A and 6B are diagrams for explaining the configuration of the output side polarizing plate according to the present embodiment, FIG. 6A is a perspective view of the output side polarizing plate in the G optical path, and FIG. 6B is an output side polarizing plate in the G optical path. It is the top view seen from the X direction. In FIG. 6, the direction parallel to the long side of the liquid crystal panel is defined as the Y direction, and the direction parallel to the short side of the liquid crystal panel is defined as the X direction. Further, the extending direction of the grating of the birefringent diffraction grating type polarization beam splitter is defined as the X direction. In FIG. 6B, since the polarization direction of the X-polarized light is perpendicular to the drawing sheet, the X-polarized light is displayed as “X surrounded by a circle” to simplify the illustration.

  As shown in FIG. 6, in this embodiment, the exit-side polarizing plate is arranged in order on the light exit side of the liquid crystal panel 60G and has the same transmission axis (that is, transmits Y-polarized light). It consists of a grating-type polarization separation element 70G and a reflective inorganic polarizing plate 80G. The birefringent diffraction grating type polarization separation element 70G and the reflection type inorganic polarizing plate 80G are arranged so as to be orthogonal to the optical axis of the optical path at a predetermined interval T. Therefore, unlike Patent Document 1, the back focus can be shortened. Of the light emitted from the liquid crystal panel 60G, the transmitted light (here Y-polarized light) transmitted through the birefringence diffraction grating type polarization separation element 70G and the reflection type inorganic polarizing plate 80G is birefringence diffraction grating type polarization separation. Since the surfaces of the element 70G and the reflective inorganic polarizing plate 80G are transmitted substantially perpendicularly, astigmatism does not occur.

In FIG. 6, it is assumed that light LG60 including Y-polarized light LG60y and X-polarized light LG60x orthogonal to each other from the liquid crystal panel 60G is incident on the output-side polarizing plate having the above configuration.
Of the light LG60 incident on the birefringence diffraction grating type polarization separation element 70G, Y polarization light (first polarization light) LG60y whose polarization direction is P-polarization light whose transmission direction is the transmission axis direction is birefringence diffraction grating type polarization separation element. The light passes through 70G, passes through the reflective inorganic polarizing plate 80G, and enters the light combining prism 200.
On the other hand, X-polarized light (second polarized light) LG60x, which is S-polarized light orthogonal to the transmission axis direction, is orthogonal to the extending direction (X direction) of the grating 73a in the birefringence diffraction grating type polarization separation element 70G. The light is diffracted in the direction (Y direction) and becomes an oblique light of ± first-order light inclined to the optical axis, and is incident on the reflective inorganic polarizing plate 80G. Since the polarization direction of the X-polarized light LG60x is the reflection axis direction (X direction) of the reflective inorganic polarizing plate 80G, the X-polarized light LG60x is reflected obliquely by the reflective inorganic polarizing plate 80G on the side opposite to the optical axis side (outside). The reflected obliquely polarized X-polarized light LG60x is directed to the birefringent diffraction grating type polarization separation element 70G. The birefringence diffraction grating type polarization separation element 70G and the reflective inorganic polarizing plate 80G are, for example, a predetermined satisfying the following equation: Are separated by a distance T. Where θs is the diffraction angle of X-polarized light (here, S-polarized light), and M is the length of the long side of the liquid crystal panel.

従って、大部分は複屈折回折格子型偏光分離素子７０Ｇには再入射せず、複屈折回折格子型偏光分離素子７０Ｇの側端部の外側を通り、光学ユニット内部で吸収されることになる。すなわち、反射型無機偏光板８０Ｇで反射されたＸ偏光光ＬＧ６０ｘが液晶パネル６０Ｇに戻ることがないので、画質劣化を招く懸念はない。
これに対して、特許文献２のホログラム偏光分離素子は、ホログラムで回折された不要偏光光をホログラムの基板であるガラス基板の光出射面で全反射させている。そのため、本実施例とは異なり、回折面（ホログラム）と反射面（ガラス基板の光出射面）との間の距離が十分確保されてない場合、つまり、ガラス基板の厚さが薄い場合、回折された後ガラス基板の光出射側で全反射された回折光は、元の回折ポイントから距離的に近い位置近傍のホログラム領域に再入射することになる。従って、従来技術では、再入射光による液晶パネルへの戻り光が生じることになり、画質を劣化させる懸念がある。

Therefore, most of the light does not re-enter the birefringent diffraction grating type polarization separation element 70G, passes through the outside of the side end portion of the birefringence diffraction grating type polarization separation element 70G, and is absorbed inside the optical unit. That is, since the X-polarized light LG60x reflected by the reflective inorganic polarizing plate 80G does not return to the liquid crystal panel 60G, there is no concern of image quality deterioration.
On the other hand, the hologram polarization separation element of Patent Document 2 totally reflects the unnecessary polarized light diffracted by the hologram on the light exit surface of the glass substrate which is the hologram substrate. Therefore, unlike this embodiment, when the distance between the diffraction surface (hologram) and the reflection surface (light emission surface of the glass substrate) is not sufficiently secured, that is, when the glass substrate is thin, Then, the diffracted light totally reflected on the light emitting side of the glass substrate is incident again on the hologram region in the vicinity of the position close to the original diffraction point. Therefore, in the prior art, return light to the liquid crystal panel due to re-incident light is generated, and there is a concern that the image quality is deteriorated.

  As described above, in this embodiment, the birefringence diffraction grating type polarization separation element and the reflection type polarizing plate that hardly generate heat due to absorption of unnecessary polarized light are used as the output side polarizing plate. Reliability can be improved. In particular, if an inorganic type is used for the birefringent diffraction grating type polarization separation element and the reflective polarizing plate, the reliability can be further improved. In addition, the birefringence diffraction grating type polarization separation element 70 (70R, 70G, 70B) and the reflective inorganic polarizing plate 80 (80R, 80G, 80B) are arranged so as to be orthogonal to the optical axis of the optical path. Therefore, astigmatism can be suppressed while suppressing an increase in back focus. In addition, since the birefringent diffraction grating type polarization separation element 70 and the reflective inorganic polarizing plate are sequentially arranged at predetermined intervals along the optical path, the polarized light diffracted by the birefringence diffraction grating type polarization separation element 70 Even if light is reflected by the reflective inorganic polarizing plate, return light to the liquid crystal panel 60 can be suppressed. Accordingly, malfunctions of the TFTs incorporated in the liquid crystal panel can be reduced, so that deterioration in image quality of the liquid crystal panel can be suppressed. In addition, since unnecessary polarized light is removed by the two polarizing plates, the extinction ratio can be increased and a high-contrast image can be obtained. In addition, since both the output side polarizing plates are inorganic polarizing plates, a decrease in reliability due to temperature rise can be suppressed. Thus, the amount of air sent from the cooling fan 580 to the polarizing glass 70 and the reflective inorganic polarizing plate 80 can be suppressed, and the amount of air sent to the incident side polarizing plate 50 and the liquid crystal panel 60 can be increased accordingly.

  In this embodiment, the contrast is improved by arranging the birefringent diffraction grating type polarization separation element 70 at the front stage and the reflection type inorganic polarizing plate 80 at the rear stage perpendicular to the optical axis of the optical path. . On the other hand, in the prior art, a configuration is known in which an absorption polarizing plate made of an organic film is disposed after the reflective polarizing plate inclined to the optical axis of the optical path (for example, FIG. 7 of Patent Document 1). . However, when an organic absorption type polarizing plate is used as the output side polarizing plate, in addition to the problem of temperature rise due to light absorption in the case of black display, the absorption type polarizing plate used in the B optical path is UV light (Ultraviolet Ray). The yellowing of the organic member of the absorptive polarizing plate due to) also becomes a problem. The yellowing of the organic member due to UV light can be slowed by generating cooling air by blowing cooling air with a cooling fan, for example, to lower the temperature. However, after a long time, yellowing always occurs even if the temperature is low. That is, in the case of white display, there is no problem with the temperature rise due to light absorption of the absorption type polarizing plate, but yellowing of the organic member due to the passage of UV light becomes a problem, and its UV resistance is also a major issue. .

  However, in this example, since an inorganic polarizing plate is used as the output side polarizing plate, the UV resistance is also excellent.

In the first embodiment, the X-polarized light is diffracted in the YZ plane parallel to the long side of the liquid crystal panel 60 using the birefringence diffraction grating type polarization separation element 70 in which the grating extended in the X direction is periodically arranged in the Y direction. I did it. However, the present invention is not limited to this. X-polarized light may be diffracted in the ZX plane parallel to the short side of the liquid crystal panel 60 using the birefringence diffraction grating type polarization separation element 70A in which the grating extended in the Y direction is periodically arranged in the X direction. . The output side polarizing plate according to the second embodiment using such a birefringent diffraction grating type polarization separation element 70A will be described.
FIG. 7 is a partial cross-sectional view schematically showing one configuration of the birefringent diffraction grating type polarization separation element according to the second embodiment, and is a cross-sectional view in the ZX plane parallel to the short side of the liquid crystal panel. In FIG. 7, since the polarization direction of the Y-polarized light is perpendicular to the drawing sheet, the Y-polarized light is displayed as “Y surrounded by a circle” for simplicity of illustration.

As shown in FIG. 7, the birefringent diffraction grating type polarization separation element 70A of the present embodiment has a glass substrate 72A as a translucent substrate and a grating 73Aa extending in the Y direction on the glass substrate 72A having a period in the X direction. It is composed of a birefringent film 73A that is repeatedly arranged at d _A and has a unidirectional periodic structure of irregularities, and an isotropic overcoat layer 74A that covers the birefringent film 73A. Note that h _A is the height of the grating 73Aa.

  Here, it is assumed that light L61 from the liquid crystal panel 60 is incident on the birefringence diffraction grating type polarization separation element 70A substantially in the Z-axis direction along the optical axis 101 of the optical path. In the plane perpendicular to the Z axis, the light L61 is a Y-polarized light L61y whose polarization direction is parallel to the extending direction of the grating 73Aa (ie, the Y direction) and a direction whose polarization direction is orthogonal to the extending direction of the grating 73Aa (ie, , X direction) X-polarized light L61x.

  When the light L61 is incident on the birefringence diffraction grating type polarization separation element 70A, the birefringence diffraction grating type polarization separation element 70A, when satisfying the conditions described later, as shown in FIG. The Y-polarized light L61y parallel to the extending direction of the grating 73Aa goes straight as it is as zero-order light. In addition, the X-polarized light L61x whose polarization direction is orthogonal to the extending direction of the grating 73Aa is diffracted as ± primary light in the direction orthogonal to the extending direction of the grating 73Aa (ie, the X direction) and tilted with respect to the optical axis. To emit. That is, the birefringent diffraction grating type polarization separation element 70A includes the incident light L61 as X-polarized light L61x, which is diffracted light that is emitted obliquely with respect to the optical axis, and Y-polarized light L61y, which is straightly transmitted light. To separate. The direction parallel to the grating 73Aa can be said to be the transmission axis direction of the birefringent diffraction grating type polarization separation element 70A.

  Next, conditions for the birefringent diffraction grating type polarization separation element 70A to diffract the X-polarized light L61x will be described.

When the refractive index of the grating 73Aa of the birefringent film 73A with respect to the X-polarized light L61x is n _Ax , the refractive index with respect to the Y-polarized light L61y is n _Ay , and the refractive index of the isotropic overcoat layer 74A is n _A1 , the optical path A, The optical path length difference Δ with respect to B is expressed by the following equation for each polarized light.
(Equation 6)
Y-polarized light: Δy = (n _Ay −n _A1 ) h _A
(Equation 7)
X-polarized light: Δx = (n _Ax −n _A1 ) h _A
Therefore, the condition for the Y-polarized light L61y to travel straight and the X-polarized light L61x to be diffracted needs to satisfy the following equation.
(Equation 8)
Δy = mλ
(Equation 9)
Δx = (m ± 1/2) λ
Here, λ is the wavelength of light, and m is an order integer.
Here, in the equation (8), the optical path difference in the Y-polarized light L61y is an integral multiple of the wavelength λ, the Y-polarized light passing through the optical path A and the Y-polarized light passing through the optical path B are intensified by interference, and 0 after passing through the grating. It is a condition that goes straight as the next light. The equation (9) is a condition in which the optical path difference in the X-polarized light L61x is shifted by an odd multiple of a half wavelength and cancels each other, so that straight light (zero-order light component) disappears and all becomes diffracted light. That is, the linear component cancels out due to interference, and the X-polarized light becomes diffracted light. Therefore, when the 0th-order and 1st-order polarization separation is performed, it is necessary to satisfy the equations (8) and (9) in order to increase the polarization separation degree. However, in practice, the refractive indexes n _Ay and n _Ax of the birefringent film 73A are set so as to satisfy the conditions in the vicinity of the formulas 8 and 9, even if the formulas 8 and 9 are not strictly satisfied. The refractive index n _A1 of the overcoat layer 4, the height h _A of the birefringent film 73A, and the order m are set.

Next, regarding the action of the exit side polarizing plate according to the second embodiment in which the reflective inorganic polarizing plate 80 is combined with the birefringence diffraction grating type polarization separation element 70A described above, the output of the G optical path is representatively similar to the first embodiment. This will be described using the configuration of the side polarizing plate.
FIG. 8 is a diagram for explaining the operation of the output side polarizing plate according to the present embodiment, and is a plan view of the output side polarizing plate in the G optical path as viewed from the Y direction. In FIG. 8, since the Y-polarized light is perpendicular to the drawing sheet, the Y-polarized light is displayed as “Y surrounded by a circle” for the sake of simplicity. In addition, the liquid crystal panel has a short side and a long side in order to obtain a predetermined aspect ratio. Here, the direction parallel to the long side of the liquid crystal panel is defined as the Y direction, and the direction parallel to the short side of the liquid crystal panel is defined as the X direction. And

As shown in FIG. 8, in this embodiment, the output side polarizing plate is arranged in order on the light output side of the liquid crystal panel 60G and has the same transmission axis (that is, transmits Y-polarized light). It consists of a grating-type polarization separation element 70AG and a reflective inorganic polarizing plate 80G. Birefringence diffraction grating type polarized light separating element 70AG a reflective inorganic polarization plate 80G is arranged so as to be perpendicular to the optical axis of the optical path at predetermined intervals T _A.

  It is assumed that the light LG61 including the Y-polarized light LG61y and the X-polarized light LG61x perpendicular to the liquid crystal panel 60G enters the output-side polarizing plate having such a configuration.

Then, among the light LG61 incident on the birefringent diffraction grating type polarization separation element 70AG, the Y-polarized light LG61y whose polarization direction is P-polarized light in the transmission axis direction that is the extending direction (Y direction) of the grating 73Aa is birefringent. The light passes through the diffraction grating type polarization separation element 70AG, passes through the reflective inorganic polarizing plate 80G, and enters the light combining prism 200.
On the other hand, the X-polarized light LG61x that is S-polarized light orthogonal to the transmission axis direction is diffracted in the direction (X direction) orthogonal to the extending direction (Y direction) of the grating 73Aa by the birefringence diffraction grating type polarization separation element 70AG. As a result, the light becomes oblique light of ± primary light that is inclined with respect to the optical axis, and enters the reflective inorganic polarizing plate 80G. Since the polarization direction of the X-polarized light LG61x is the reflection axis direction (X direction) of the reflective inorganic polarizing plate 80G, the X-polarized light LG61x is reflected obliquely by the reflective inorganic polarizing plate 80G on the side opposite to the optical axis side (outside). X-polarized LG61x of the reflected oblique light is directed to the birefringent diffraction grating type polarized light separating element 70AG, separated by a predetermined distance T _A is a birefringent diffraction grating type polarized light separating element 70AG a reflective inorganic polarization plate 80G Therefore, the light does not re-enter the birefringence diffraction grating type polarization separation element 70AG, passes through the outside of the side end portion of the birefringence diffraction grating type polarization separation element 70AG, and is absorbed inside the optical unit. Therefore, since the liquid crystal panel 60G is not returned, there is no fear of image quality deterioration.

As described above, in the birefringent diffraction grating type polarization separation element 70AG according to the present embodiment, the X-polarized light L61x is diffracted by the ZX plane parallel to the short side of the liquid crystal panel 60G. Therefore, if the diffraction angles by the birefringent diffraction grating type polarization separation element are substantially the same in the first embodiment and the second embodiment, the X-polarized light L61x diffracted by the birefringence diffraction grating type polarization separation element 70AG is reflected by a reflection type inorganic material. Predetermined between the birefringence diffraction grating type polarization separation element 70AG and the reflection type inorganic polarization plate 80G, which is necessary for passing through the outside of the side end portion of the birefringence diffraction grating type polarization separation element 70AG after being reflected by the polarization plate 80G. This distance T _A can be made shorter than the distance T of the first embodiment. That is, according to the present embodiment, there is an effect that the back focus between the projection lens 300 and the liquid crystal panel 60 can be made shorter than that of the first embodiment.
In the embodiments described above, the output side polarizing plate has been described as being specialized for the inorganic type, but the present invention is not limited to this. The birefringence diffraction grating type polarization separation element and the reflection type polarizing plate absorb little light, and heat generated by light absorption can be ignored. Accordingly, it is possible to use an organic type.

1 is a schematic configuration diagram of an optical system of an optical unit according to Embodiment 1. FIG. 2 is a partial cross-sectional view schematically showing one configuration of a birefringence diffraction grating type polarization separation element according to Embodiment 1. FIG. The principal part enlarged view of the birefringence diffraction grating type | mold polarization separation element shown in FIG. Explanatory drawing explaining the formation process of a birefringence diffraction grating type | mold polarization separation element. FIG. 3 is an explanatory diagram showing various examples of a reflective inorganic polarizing plate according to Example 1. FIG. 3 is a diagram illustrating a configuration of an output side polarizing plate according to the first embodiment. FIG. 6 is a partial cross-sectional view schematically showing one configuration of a birefringence diffraction grating type polarization separation element according to Example 2. FIG. 6 is a diagram for explaining the operation of the exit-side polarizing plate according to Example 2.

Explanation of symbols

10: light source unit, 11: lamp, 12: reflector, 21: first array lens, 22: second array lens, 25: polarization conversion element, 27: condenser lens, 29: field lens, 31, 32: Dichroic mirror, 33: reflection mirror, 41: first relay lens, 42: second relay lens, 45, 46: reflection mirror, 50: incident side polarizing plate, 60: liquid crystal panel, 70: birefringence diffraction grating type polarization separation Element: 72: Glass substrate, 73: Birefringent film, 73a: Grating, 74: Overcoat layer, 76: Photoresist, 80: Reflective inorganic polarizing plate, 81: Translucent substrate, 82: Wire grid, 83: Groove, 85: Adjustment layer, 86: High refractive index layer, 87: Low refractive index layer, 90: 1 / 2λ wavelength plate, 100: Illumination optical system, 101: Optical axis, 130: Light separation optical system, 140 Relay optical system, 200: photosynthetic prism, 210: dichroic film, 300: projection lens, 500: optical unit, 550: substrate, 560: power supply circuit, 570: drive circuit, 580: cooling fan, 585: flow path, L60 , L61: light, L800: incident light, L801: transmitted light, L802: reflected light.

Claims (8)

An illumination optical unit that emits predetermined polarized light;
A transmissive liquid crystal panel that modulates and emits the predetermined polarized light into an optical image;
In an optical unit comprising a projection lens that projects the optical image,
Birefringence diffraction grating type polarized light arranged on the light emission side of the light transmitted through the transmissive liquid crystal panel, in order from the transmissive liquid crystal panel side, perpendicular to the optical axis of the light transmitted through the transmissive liquid crystal panel. A separation element;
A reflective polarizing plate arranged perpendicular to the optical axis;
An optical unit comprising: An illumination optical unit that emits predetermined polarized light;
A transmissive liquid crystal panel that modulates and emits the predetermined polarized light into an optical image;
In an optical unit comprising a projection lens that projects the optical image,
Provided so that light from the transmissive liquid crystal panel is transmitted in the order of a birefringence diffraction grating type polarization separation element, a reflective polarizing plate,
An optical unit, wherein the birefringence diffraction grating type polarization separation element and the reflection type polarizing plate are arranged so as to be orthogonal to an optical axis of light from the transmissive liquid crystal panel side. The optical unit according to claim 1 or 2,
The birefringence diffraction grating type polarization separation element transmits the first polarized light incident from the transmissive liquid crystal panel and diffracts the second polarized light orthogonal to the first polarized light. An optical unit. The optical unit according to claim 1 or 2,
The reflective polarizing plate transmits the first polarized light incident from the transmissive liquid crystal panel, and reflects the second polarized light diffracted by the birefringence diffraction grating type polarization separation element. An optical unit. The optical unit according to claim 1 or 2,
The optical unit, wherein the birefringent diffraction grating type polarization separation element and the reflective polarizing plate are provided at a predetermined interval. The optical unit according to claim 1 or 2,
The optical unit, wherein the birefringent diffraction grating type polarization separation element is an inorganic polarization separation element. The optical unit according to claim 1 or 2,
The optical unit, wherein the reflective polarizing plate is an inorganic polarizing plate. An optical unit according to any one of claims 1 to 7,
A drive circuit for driving the transmissive liquid crystal panel of the optical unit;
A projection type liquid crystal display device comprising: a cooling fan for cooling the optical unit.

Images