JP2006145720A - Polarization conversion element, lighting device, and projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization conversion element capable of readily preventing the light of a low polarization degree mingled with unnecessary light from being formed, and a lighting device, and a projector using the same. <P>SOLUTION: A second prism 83 is provided with a scattering side face 83c which is a light diffusion surface formed like ground glass and therefore even if unintended random polarized light L1 enters the scattering side face 83c, the degradation of the polarization degree of linearly polarized light LO can be prevented. Namely, even if the random polarized light L1 enters the scattering side face 83c, the random polarized light L1 is diffused and is hardly made incident on a polarizer separating film 84 and therefore the polarized light is prevented from leaking out of both exit faces 82d, 83d and eventually high polarization conversion efficiency can be achieved. If the front face of the scattering side face 83c is coated with Japanese ink, the direct incidence of the diffused light or scattered light on the polarizer separating film 84 can be prevented and the higher polarization conversion efficiency can be achieved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polarization conversion element that converts, for example, a random polarized light beam into one type of polarized light beam, and an illumination device and projector using the same.

  As a first type of polarization conversion element for a light source device incorporated in a projector, a composite having a structure in which a plurality of columnar prisms having a shape in which a pair of trapezoidal prisms are bonded to each other with a polarization separation film interposed therebetween are arranged and connected There is a prism (see Patent Document 1).

  In addition, as a second type of polarization conversion element, a composite prism having a structure in which a plurality of columnar polarization beam splitters (PBS) having a shape in which a pair of triangular prism columns are bonded to each other with a polarization separation film interposed therebetween are arranged and connected. There are many (see Patent Documents 2, 3, and 4).

Among the second type of polarization conversion elements, in some composite prisms, unintended light is incident on the inevitably formed periodic non-incident surface, and the polarizing plate provided on the incident surface of the liquid crystal light valve is heated to have a lifetime. In order to prevent adverse effects such as shortening the length, a light shielding plate is attached to the non-incident surface (Patent Document 2). In this polarization conversion element, it has been proposed to directly form a light shielding surface, a reflection surface, or a light scattering surface on a non-incident surface instead of the above-described light shielding plate.
Japanese Patent Laid-Open No. 10-321027 WO97 / 5001 Publication JP-A-10-90520 JP 2002-98936 A

  However, in the first type of polarization conversion element, unless the shape accuracy of the incident lens body is increased, light is incident on an unintended inclined surface of the trapezoidal prism, for example, a slight amount of P-polarized light (S-polarized light) A light beam (light having a low degree of polarization) mixed with unnecessary light enters a liquid crystal panel or the like.

  In addition, the first type of polarization conversion element, in principle, can obtain light having a high degree of polarization, but there is a possibility that unnecessary light may increase due to positional deviation when the light shielding plates are bonded together. Even when the light shielding surface or the like is directly formed on the non-incident surface instead of the light shielding plate, it is not easy to ensure the formation accuracy of the light shielding surface or the like. For example, when a mirror is formed on a non-incident surface, vapor deposition is performed on the incident surface of the composite prism using a mask, but the edge position of the mirror becomes inaccurate due to the wraparound of the vapor deposition material.

  Therefore, an object of the present invention is to provide a polarization conversion element that can easily prevent the formation of light with a low degree of polarization mixed with unnecessary light, and an illumination device and a projector using the polarization conversion element.

  In order to solve the above problems, the polarization conversion element according to the present invention includes a plurality of trapezoidal columnar first and second prisms arranged such that the first side surfaces are bonded to each other and the second side surfaces are in contact with each other. And a polarization separation film formed on the first side surface of the first prism, and the polarization directions of the randomly polarized light incident from the third side surface of the first prism are orthogonal to each other by the polarization separation film The first linearly polarized light is separated into the second linearly polarized light, the first linearly polarized light is reflected by the polarization separation film and emitted from the fourth side surface of the first prism, and the second linearly polarized light is polarized and separated. Transmitted through the film and emitted from the third side surface of the second prism, and emerged from the third side surface of the first prism and the second prism emitted from the fourth side surface of the first prism. A polarization conversion element that aligns the polarization direction with the second linearly polarized light. What a fourth aspect of the second prism is a light diffusing surface.

  In the polarization conversion element, in the trapezoidal columnar second prism, the fourth side surface, which is a non-incident surface that should avoid the incidence of light to generate unnecessary light, is a light diffusion surface. Can be prevented from entering the second prism from the fourth side surface and lowering the degree of polarization of the emitted light. That is, unintended light is incident on the fourth side surface of the second prism, and for example, not only S-polarized light but also slight P-polarized light is mixed as unnecessary light from the third side surface of the first and second prisms. Therefore, it is possible to prevent a light beam having a low degree of polarization from being emitted, and as a result, high polarization conversion efficiency can be achieved.

  In a specific aspect or embodiment of the present invention, in the polarization conversion element, the light diffusion surface is formed in a polished glass shape. In this case, the non-polished surface formed during the grinding process or the like of the second prism can be used as it is as the fourth side surface, so that the process for forming the polarization conversion element can be simplified, and the fourth side Only the side surface can be accurately set as the light diffusion surface.

  In another specific embodiment of the present invention, a light-shielding film is formed on the light diffusion surface. In this case, the light incident on the second prism via the fourth side surface can be reliably blocked.

  In another specific aspect of the present invention, the first prism and the second prism have the same refractive index, and in the first and second prisms, the first side surface and the second side surface. Are parallel to each other, and the third side surface and the fourth side surface are inclined in opposite directions and equal in magnitude to the first side surface. In this case, the first prism and the second prism have substantially the same shape, and the unit-junction prism formed by bonding them can be improved in symmetry, so that the polarization conversion element can be easily manufactured with high accuracy. The polarization conversion element obtained is easy to handle.

  In another specific aspect of the invention, the inclination angle formed by the third and fourth side surfaces with respect to the first side surface corresponds to the refractive indexes of the first and second prisms, and When a light beam parallel to the second side surface is incident on the center of the third side surface of the first prism, the polarization component corresponding to the light beam is parallel to the first and second side surfaces from the center of the fourth side surface. It is set to inject. In this case, the optical axes of the incident light beam and the emitted light beam can be matched.

  In another specific aspect of the invention, the first linearly polarized light emitted from the fourth side surface of the first prism and the second linearly polarized light emitted from the third side surface of the second prism In order to align the polarization direction, a wave plate is provided on either the third side surface or the fourth side surface. In this case, the polarization direction can be efficiently switched by the wave plate, and the polarization conversion efficiency can be easily increased.

  An illumination device according to the present invention includes a light source, an integrator optical system that splits a light beam from the light source to form a plurality of light source images, and superimposes the light beams from the plurality of light source images to enter an illumination target. And the above-described polarization conversion element in which light beams from a plurality of light source images are respectively incident on the third side surface of the first prism.

  In the illumination device, since the polarization conversion element described above is used, illumination light having a high degree of polarization can be formed by the high polarization conversion efficiency of the polarization conversion element.

  The projector according to the present invention includes the above-described illumination device, a light separation optical system that separates light from the illumination device into red light, green light, and blue light, and red light, green light, and blue light, respectively. Three light modulation devices for modulation, a color synthesis optical system for synthesizing light modulated by the three light modulation devices, and a projection optical system for projecting light synthesized by the color synthesis optical system are provided.

  Since the projector uses the above-described illumination device, the light modulation device for each color can be illuminated with illumination light having a high degree of polarization, and a good color image can be projected. In addition, when the light modulation device for each color is a liquid crystal light valve for each color, for example, a polarization component that may reduce the contrast of an image is incident on each liquid crystal light valve, or on the incident surface of each liquid crystal light valve. Defects such as heating the provided polarizing plate and shortening the life can be prevented, and a good color image can be projected over a long period of time.

[First Embodiment]
FIG. 1 is a plan view for explaining a polarization conversion element according to the first embodiment of the present invention, and FIG. 2 is a perspective view of the polarization conversion element of FIG. The illustrated polarization conversion element 80 has a structure in which eight columnar unit junction prism bodies 81 are straightly connected in a direction AB perpendicular to the axis, and in a plan view, a hexagonal portion like an abacus is connected. Has the appearance. The unit bonded prism bodies 81 are merely abutted on the side surfaces and are fixed by a holder (not shown). If the unit bonded prism bodies 81 are fixed to each other with an adhesive, they are fixed to each other. No holder is required. When random polarized light LI is incident on each incident side surface 82c of each unit junction prism body 81 constituting such a polarization conversion element 80, linear polarization LO in a specific direction from the entire opposite surface of each unit junction prism body 81, Specifically, only S-polarized light is emitted.

  FIG. 3 is a plan view for explaining the structure of the unit bonded prism body 81. As is apparent from the figure, the unit junction prism body 81 includes a trapezoidal columnar first prism 82 and a trapezoidal columnar second prism 83 on the bottom surfaces 82a and 83a side which are the respective first side surfaces. They are joined to each other, and a polarization separation film 84 is provided between the bottom surfaces 82a and 83a.

  Here, the first prism 82 includes a bottom surface 82a that is a first side surface, a top surface 82b that is a second side surface, an incident side surface 82c that is a third side surface, and an exit side surface 82d that is a fourth side surface. With. The second prism 83 also includes a bottom surface 83a that is a first side surface, a top surface 83b that is a second side surface, an exit side surface 83d that is a third side surface, and a scattering side surface 83c that is a fourth side surface. Is provided.

  The bottom surface 82a, the incident side surface 82c, and the exit side surface 82d of the former first prism 82 are flatly polished optical surfaces, and a polarization separation film 84 for separating polarized light is deposited on the bottom surface 82a. In addition, an antireflection film for preventing a reflection loss of incident light or emitted light is deposited on the incident side surface 82c and the exit side surface 82d.

  The bottom surface 83a and the exit side surface 83d of the latter second prism 83 are optical surfaces that are flatly polished. Among these, the exit side surface 83d has antireflection for preventing reflection loss of incident light and exit light. A film is deposited. In addition, a retardation plate 85 is affixed over the entire emission side surface 83d. The retardation plate 85 is made of a wave plate, and when polarized light in a specific direction is incident, the retardation plate 85 can be converted into polarized light in an orthogonal direction. The scattering side surface 83c of the second prism 83 is a light diffusing surface formed in a frosted glass shape, and a ground surface, that is, a non-polished surface formed when the second prism 83 is ground or the like is used as it is. On the surface of the scattering side surface 83c, a black coating that absorbs light can be applied as a light-shielding film.

  When random polarized light LI perpendicular to the axial direction DA of the unit cemented prism 81 and parallel to the bottom surface 82 a is incident on the incident side surface 82 c of the unit cemented prism 81, the random polarized light LI propagates in the first prism 82. , And enters the polarization separation film 84 through the bottom surface 82a. The random polarized light LI incident on the polarization separation film 84 includes a first light beam LO1 composed of the first linearly polarized light (S-polarized component) reflected by the polarization separation film 84 and a first linearly polarized light (P It is branched into a second light beam LO2 made up of a polarization component. The first light beam LO1 reflected by the polarization separation film 84 is emitted to the outside as S-polarized light from the emission side surface 82d, and the second light beam LO2 transmitted through the polarization separation film 84 is incident on the emission side surface 83d through the bottom surface 83a. Then, it is converted into S-polarized light through the phase difference plate 85 and is emitted to the outside.

  At this time, the random polarized light LI that has entered the center CT1 of the incident side surface 82c enters the center CT3 of the exit side surface 82d as the first light beam LO1 through the center CT2 of the bottom surface 82a. That is, the shape of the first prism 82 is such that the optical axis of the random polarized light LI coincides with the optical axis of the first light beam LO1. Thus, in order to make the optical axis on the incident side coincide with the optical axis on the exit side, the length L and the thickness W of the bottom surface 82a of the first prism 82 are appropriately set, and the law of refraction and geometry are adjusted accordingly. Inclination angle θ with respect to bottom surface 82a of both side surfaces 82c and 82d is determined so as to satisfy the general relationship. When the incident-side optical axis and the exit-side optical axis coincide with each other in this way, the S-polarized component reflected by the polarization separation film 84 out of the light incident on each part of the incident side surface 82c is efficiently emitted from the exit side surface 82d. Can be made. As already described, since the second prism 83 has the same shape as the first prism 82, the second light beam LO2 transmitted through the polarization separation film 84 is incident on the center CT3 ′ of the exit side surface 83d, and the first light beam. The light is emitted in a direction parallel to the optical axis of LO1. At this time, the P-polarized component transmitted through the polarization separation film 84 among the light incident on each part of the incident side surface 82c can be efficiently emitted as the S-polarized component from the emission side surface 83d, that is, the phase difference plate 85.

  According to the polarization conversion element 80 of the present embodiment described above, in the second prism 83, the scattering side surface 83c, which is a non-incident surface that should avoid the incidence of light rays, is a light diffusion surface formed in a polished glass shape. Even when unintended random polarized light LI is incident on the scattering side surface 83c, it is possible to prevent the degree of polarization of the linearly polarized light LO from decreasing. That is, even when the random polarized light LI is incident on the scattering side surface 83c, the random polarized light LI is diffused and hardly enters the polarization separation film 84, so that the P-polarized light is prevented from leaking from both exit side surfaces 82d and 83d. As a result, high polarization conversion efficiency can be achieved. If the surface of the scattering side surface 83c is sanitized, it is possible to prevent diffused light or scattered light from entering the polarization separation film 84 and achieve higher polarization conversion efficiency.

  Further, in the case of the polarization conversion element 80 of the present embodiment, there is no optical path difference between the first light beam LO1 and the second light beam LO2 emitted from the both emission side surfaces 82d and 83d. The light beam cross-sections coincide with each other, and the illumination efficiency can be improved.

  4 and 5 are views for explaining a method of manufacturing the polarization conversion element 80 shown in FIG. 4A to 4D illustrate the manufacturing process of the first prism 82, and FIGS. 5A to 5C illustrate the manufacturing process of the second prism 83. Is.

  As shown in FIG. 4A, first, a plate-like base material 100 made of a glass plate is prepared, and a prism body 182 having a trapezoidal cross section is cut out. Specifically, the base material 100 is cut along the cut surface CS shown in the figure, and eight prism bodies 182 are taken out, and the cut surfaces and the like of the respective prism bodies 182 are ground to have the desired size and shape. And

  Next, as shown in FIG. 4B, among the surface of the prism body 182, the bottom surface 182a, the side surface 182c, and the side surface 182d are polished to form optical surfaces. Note that the top surface 182b is not polished. However, when the base material 100 of FIG. 4A is optically polished on both sides in advance, the bottom surface 182a is not required to be polished in the step of FIG. 4B, and the top surface 182b is also automatically polished. It becomes.

  Next, as shown in FIG. 4C, all the prism bodies 182 are arranged in the same posture and fixed to a holder (not shown), and a polarization separation film is deposited on the bottom surface 182a by an appropriate film forming apparatus. This polarization separation film is formed of a multilayer film in which dielectric layers having an appropriate thickness and refractive index are stacked.

  Next, as shown in FIG. 4D, the prism bodies 182 are rearranged and fixed to another holder, and an antireflection film is deposited on the side surface 182c by an appropriate film forming apparatus. This antireflection film is formed of a multilayer film in which several dielectric layers having an appropriate thickness and refractive index are stacked.

  Next, the prism bodies 182 are rearranged again, and an antireflection film is vapor-deposited on the side surface 182d by an appropriate film forming apparatus as in the case of FIG. This antireflection film is formed of a multilayer film similarly to that formed on the side surface 182c.

  The eight prism bodies 182 obtained as described above correspond to the first prism 82 shown in FIG. That is, the bottom surface 182a, the top surface 182b, the side surface 182c, and the side surface 182d of the prism body 182 correspond to the bottom surface 82a, the top surface 82b, the incident side surface 82c, and the exit side surface 82d of the first prism 82 shown in FIG. .

  Next, as shown in FIG. 5A, a plate-like base material 100 made of a glass plate is prepared, and a prism body 183 having a trapezoidal cross section is cut out. Specifically, the base material 100 is cut along the cut surface CS shown in the figure, and eight prism bodies 183 are taken out, and the cut surfaces and the like of the respective prism bodies 183 are ground to have the desired size and shape. And

  Next, as shown in FIG. 5B, among the surface of the prism body 183, the bottom surface 183a and the side surface 183d are polished to form optical surfaces. Note that the side surface 183c is not polished. The side surface 183c becomes the scattering side surface 83c as it is. The side surface 183c can be painted before the bottom surface 183a and the side surface 183d are polished. Also, the top surface 182b is not polished. However, when the base material 100 of FIG. 5A is optically polished on both sides in advance, the bottom surface 183a is not required to be polished in the step of FIG. 5B, and the top surface 183b is also automatically polished. It becomes.

  Next, as shown in FIG. 5C, all the prism bodies 182 are arranged in the same posture and fixed to a holder (not shown), and an antireflection film is deposited on the side surface 183d by an appropriate film forming apparatus. This antireflection film is formed of a multilayer film in which several dielectric layers having an appropriate thickness and refractive index are stacked.

  The eight prism bodies 183 obtained as described above correspond to the second prism 83 shown in FIG. That is, the bottom surface 183a, the top surface 183b, the side surface 183c, and the side surface 183d of the prism body 183 correspond to the bottom surface 83a, the top surface 83b, the scattering side surface 83c, and the exit side surface 83d of the second prism 83 shown in FIG. .

  Finally, as shown in FIG. 5 (d), the prism body 182 manufactured through the steps shown in FIGS. 4 (a) to 4 (d), that is, the first prism 82, and FIGS. 5 (a) to 4 (c). The prism body 183 manufactured through the process indicated by (2), that is, the second prism 83 is bonded to the bottom surfaces 182a and 183a to form a cemented prism body 181. By attaching a retardation plate to the exit side surface 83d of the cemented prism body 181, a unit cemented prism body 81 as shown in FIG. 3 is completed.

[Second Embodiment]
FIG. 6 is a diagram for explaining a projector according to a second embodiment of the invention. The projector 210 includes a light source device 20 that generates light source light, a uniformizing optical system 30 that uniformizes illumination light from the light source device 20, and illumination light that has passed through the uniformizing optical system 30 in three colors of red, green, and blue. A divided illumination system 40 that separates into colors, a light modulator 50 that is illuminated by illumination light of each color emitted from the divided illumination system 40, and a cross dichroic prism for combining modulated light of each color from the light modulator 50 60 and a projection lens 70 that projects image light that has passed through the cross dichroic prism 60 onto a screen (not shown). Among these, the light source device 20 and the homogenizing optical system 30 are illumination devices that emit uniform linearly polarized light as illumination light.

  Among the projectors 210 shown in the figure, the light source device 20 includes a lamp main body 21 that forms a substantially spot-like light emitting unit, and a parabolic concave mirror 22 that collimates the light source light emitted from the lamp main body 21. Among these, the lamp body 21 is composed of a lamp light source such as a high-pressure mercury lamp, and generates substantially white light source light. Further, the concave mirror 22 reflects the light beam emitted from the lamp body 21 and causes it to enter the uniformizing optical system 30 as a parallel light beam. Instead of the parabolic concave mirror 22, a concave mirror that is not parabolic, such as a spherical surface or an elliptical surface, may be used. When such a concave mirror is used, if a collimating lens is disposed between the concave mirror 22 and the homogenizing optical system 30, it becomes possible to emit a parallel light beam from the light source device 20.

  The homogenizing optical system 30 includes a pair of fly-eye optical systems 31 and 32 that are integrator optical systems, a superimposing lens 33 for superimposing the wavefront split light, and a polarization conversion element 80 that converts the illumination light into a predetermined polarization component. With. The pair of fly-eye optical systems 31 and 32 includes a plurality of element lenses arranged in a matrix. The element lenses divide the illumination light from the light source device 20 and individually collect and divide the illumination light. The polarization conversion element 80 converts the illumination light emitted from the fly-eye optical systems 31 and 32 into one type of polarized light (for example, only S-polarized light component perpendicular to the paper surface of FIG. 6) and supplies it to the next-stage optical system. The superimposing lens 33 appropriately converges the illumination light that has passed through the polarization conversion element 80 as a whole, and enables superimposing illumination on the light modulation device of each color provided in the light modulation unit 50. In other words, the illumination light that has passed through both the fly-eye optical systems 31 and 32 and the superimposing lens 33 passes through a divided illumination system 40 that will be described in detail below. The image forming areas 51b, 51r, and 51g are uniformly superimposed and illuminated.

  Note that the polarization conversion element 80 is the same as the polarization conversion element 80 of the first embodiment shown in FIG. 1, and passes through the first-stage fly-eye optical system 31 so that the position of the next-stage fly-eye optical system 32 or The individual divided lights collected in the vicinity thereof are polarized and converted by the unit junction prism body 81 unit.

  The divided illumination system 40 includes first and second dichroic mirrors 41a and 41b, reflection mirrors 42a, 42b, and 42c, field lenses 43r and 43b, and first to third lenses 45a, 45b, and 45c. Among these, the light separation optical system including the first and second dichroic mirrors 41a and 41b separates the illumination light into three light beams of red light, green light, and blue light. That is, the first dichroic mirror 41a reflects the blue light LB among the three colors of red, blue, and green (R, G, and B) and transmits the green light LG and the red light LR. The second dichroic mirror 41b reflects the red light LR out of the incident green light LG and red light LR and transmits the green light LG.

  In the split illumination system 40, the illumination light emitted from the light source device 20 through the uniformizing optical system 30 first enters the first dichroic mirror 41a. The blue light LB reflected by the first dichroic mirror 41a is guided to the first optical path OP1 and enters the field lens 43b for adjusting the incident angle via the reflection mirror 42a. Further, the red light LR transmitted through the first dichroic mirror 41a and reflected by the second dichroic mirror 41b is guided to the second optical path OP2 and enters the field lens 43r. Further, the green light LG that has passed through the second dichroic mirror 41b is guided to the third optical path OP3, and passes through the first to third lenses 45a, 45b, and 45c via the reflection mirrors 42b and 42c. The relay optical system including these lenses 45a, 45b, and 45c is disposed in the third green optical path OP3 having the longest optical path distance from the light source device 20 to the liquid crystal panels 51b, 51r, and 51g of the respective colors. Yes. This relay optical system transmits the image of the first lens 45a on the incident side almost directly to the third lens 45c on the emission side via the intermediate second lens 45b, thereby diffusing light. This prevents a decrease in light utilization efficiency. In the relay optical system, for example, the intermediate lens 45b is displaced continuously or stepwise along the optical axis, so that the size of the illumination area at the position of the liquid crystal panel 51g, that is, on the image forming area of the liquid crystal panel 51g. The illuminance of the green light LG can be arbitrarily changed. That is, the illuminance of the blue light LB and the red light LR on the image forming areas of the liquid crystal panels 51b and 51r does not change and is constant and substantially equal, whereas the illuminance of the green light LG on the image forming area of the liquid crystal panel 51g is It can be increased or decreased according to the position of the lens 45b. If this is utilized, the white balance of the image synthesized through the liquid crystal panels 51b, 51r, and 51g and projected onto the screen by the projection lens 70 can be appropriately adjusted with respect to the green light LG. Note that the white balance of a projected image has become an important evaluation item as a color temperature, and has recently been given higher priority in terms of enabling the expression of a natural color of a video.

  The light modulator 50 includes three liquid crystal panels 51b, 51r, and 51g on which the three colors of illumination light LB, LR, and LG are incident, and three sets of polarized light disposed so as to sandwich the liquid crystal panels 51b, 51r, and 51g. Filters 52b, 52r, and 52g. Here, for example, the blue light LB liquid crystal panel 51b and the pair of polarizing filters 52b and 52b sandwiching the liquid crystal panel 51b constitute a liquid crystal light valve for two-dimensionally modulating the illumination light. Similarly, the liquid crystal panel 51r for red light LR and the corresponding polarizing filters 52r and 52r also constitute a liquid crystal light valve, and the liquid crystal panel 51g for green light LG and the polarizing filters 52g and 52g also form a liquid crystal light valve. Constitute.

  In the light modulation unit 50, the blue light LB guided to the first optical path OP1 enters the image forming area of the liquid crystal panel 51b through the field lens 43b. The red light LR guided to the second optical path OP2 enters the image forming area of the liquid crystal panel 51r via the field lens 43r. The green light LG guided to the third optical path OP3 enters the image forming area of the liquid crystal panel 51g via a relay optical system including lenses 45a, 45b, and 45c. Each of the liquid crystal panels 51b, 51r, and 51g is a non-luminous and transmissive light modulation device for changing the spatial distribution of the polarization direction of incident illumination light, and is incident on each of the liquid crystal panels 51b, 51r, and 51g. The polarization state of each color light LB, LR, LG is adjusted in units of pixels in accordance with drive signals or image signals input as electrical signals to the liquid crystal panels 51b, 51r, 51g. At that time, the polarization filters 52b, 52r, and 52g adjust the polarization direction of the illumination light incident on the liquid crystal panels 51b, 51r, and 51g, and at the same time, emit light from the light emitted from the liquid crystal panels 51b, 51r, and 51g. The modulated light in the polarization direction is extracted.

  The cross dichroic prism 60 is a color synthesizing optical system, and includes a blue light reflecting first dichroic film (specifically a dielectric multilayer film) 61 formed on a plane and a green light reflecting second dichroic film. (Specifically, a dielectric multilayer film) 62 is incorporated in an X-shaped crossing manner. The cross dichroic prism 60 reflects the blue light LB from the liquid crystal panel 51 b by the first dichroic film 61 and emits the red light LR from the liquid crystal panel 51 r through both the dichroic films 61 and 62. The green light LG from the liquid crystal panel 51g is reflected by the second dichroic film 62 and emitted to the left in the traveling direction.

  The image light synthesized by the cross dichroic prism 60 in this way is projected as a color image on a screen (not shown) at an appropriate magnification through a projection lens 70 which is a projection optical system.

  Hereinafter, the operation of the projector 210 according to the present embodiment will be described. The illumination light from the light source device 20 is homogenized through the homogenizing optical system 30 and the polarization direction thereof is aligned, and is then color-divided by the first and second dichroic mirrors 41a and 41b provided in the divided illumination system 40, The light enters the corresponding liquid crystal panels 51b, 51r, 51g as the color lights LB, LR, LG, respectively. Each liquid crystal panel 51b, 51r, 51g is modulated by an image signal from the outside and has a two-dimensional refractive index distribution, and modulates each color light LB, LR, LG in a two-dimensional space in units of pixels. As described above, the color lights LB, LR, LG modulated by the liquid crystal panels 51b, 51r, 51g, that is, the image light, are combined by the cross dichroic prism 60 and then incident on the projection lens 70. The image light incident on the projection lens 70 is projected onto the screen at an appropriate magnification.

  Since the projector 210 uses the polarization conversion element 80 with high polarization conversion efficiency, linearly polarized light with a high degree of polarization can be incident on the split illumination system 40 and the polarization filters 52b, 52r, and 52g. Therefore, heating of the polarizing filters 52b, 52r, 52g, etc. can be prevented, and a high-quality color image can be projected on the screen.

  In addition, this invention is not restricted to said embodiment, In the range which does not deviate from the summary, it can implement in a various aspect, For example, the following deformation | transformation is also possible.

  In the polarization conversion element 80 of the above-described embodiment, the scattering side surface 83c of the second prism 83 of the unit junction prism body 81 constituting this is used as a ground surface or painted on the scattering side surface 83c as a sanitized surface. A mirror can also be deposited on the side surface 83c.

  In the above embodiment, the two fly's eye optical systems 31 and 32 are used to divide the light from the light source device 20 into a plurality of partial light beams. It can be replaced with an integrator. Also in this case, the light beams from the plurality of light source images formed by the rod integrator are respectively incident on the incident side surface 82 c of the unit bonded prism body 81.

  In the above embodiment, an example of a projector using three liquid crystal light valves has been described. However, the present invention is a projector using one, two, or four or more light modulation devices such as liquid crystal light valves. It can also be applied to.

  In the above embodiment, an example in which the present invention is applied to a transmissive projector has been described. However, the present invention can also be applied to a reflective projector. Here, “transmission type” means that a light valve such as a liquid crystal light valve transmits light, and “reflection type” means that the light valve reflects light. Means. In the case of a reflection type projector, the light valve can be constituted only by a liquid crystal panel, and a pair of polarizing plates is unnecessary. In a reflective projector, the cross dichroic prism is used as a color light separating means for separating white light into three colors of red, green, and blue, and the same is obtained by recombining the modulated three colors of light. In some cases, it is also used as color light combining means for emitting light in the direction of. Further, instead of the cross dichroic prism, there may be used a dichroic prism in which a plurality of triangular or square dichroic prisms are combined. The light modulation device is not limited to a liquid crystal light valve, and may be a light modulation device using a micromirror, for example.

  The projector includes a front projector that projects an image from the direction of observing the projection surface and a rear projector that projects an image from the side opposite to the direction of observing the projection surface. The projector configuration shown in FIG. Is applicable to both.

It is a perspective view explaining the polarization conversion element concerning a 1st embodiment. It is a perspective view explaining the polarization conversion element concerning a 1st embodiment. It is a top view of the unit junction prism body which comprises the polarization converting element shown in FIG. (A)-(d) is a figure explaining the production process of the 1st prism. (A)-(c) is a figure explaining the preparation process of a 2nd prism, (d) is a figure explaining joining of a 1st prism and a 2nd prism. It is a figure explaining the structure of the projector which concerns on 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 210 ... Projector, 20 ... Light source device, 30 ... Uniformation optical system 31, 32 ... Fly eye optical system, 40 ... Divided illumination system, 41a, 41b ... Dichroic mirror, 50 ... Light modulation part, 51b, 51r, 51g ... Liquid crystal panel 60 ... Cross dichroic prism 61 ... First dichroic film 62 ... Second dichroic film 70 ... Projection lens 80 ... Polarization conversion element 81 ... Unit junction prism body 82 ... First prism 83 ... First 2 prisms, 83c ... scattering side surface, 84 ... polarization separation film, 85 ... phase difference plate, LB, LR, LG ... each color light

Claims (8)

A plurality of trapezoidal columnar first and second prisms arranged such that the first side faces are bonded together and the second side faces each other;
A polarization separation film formed on the first side surface of the first prism,
Random polarized light incident from the third side surface of the first prism is separated into first linearly polarized light and second linearly polarized light whose polarization directions are orthogonal to each other by the polarization separation film,
The first linearly polarized light is reflected by the polarization separation film and is emitted from the fourth side surface of the first prism, and the second linearly polarized light is transmitted through the polarization separation film and is transmitted from the second prism. The first linearly polarized light emitted from the third side surface and emitted from the fourth side surface of the first prism and the second straight line emitted from the third side surface of the second prism A polarization conversion element that aligns the polarization direction with polarized light,
The polarization conversion element, wherein the fourth side surface of the second prism is a light diffusion surface.   The polarization conversion element according to claim 1, wherein the light diffusion surface is formed in a polished glass shape.   The polarization conversion element according to claim 2, wherein a light-shielding film is formed on the light diffusion surface.   The first prism and the second prism have the same refractive index, and in the first and second prisms, the first side surface and the second side surface are parallel to each other, and the first prism and the second prism are parallel to each other. The side surface of 3 and the fourth side surface form an inclination angle that is opposite in direction and equal in magnitude with respect to the first side surface. Polarization conversion element.   The inclination angle formed by the third and fourth side surfaces with respect to the first side surface corresponds to the refractive indexes of the first and second prisms, and is a light beam parallel to the first and second side surfaces. Is incident on the center of the third side surface of the first prism, the polarization component corresponding to the light beam is emitted from the center of the fourth side surface in parallel to the first and second side surfaces. The polarization conversion element according to claim 4, wherein the polarization conversion element is set as follows.   To align the polarization directions of the first linearly polarized light emitted from the fourth side surface of the first prism and the second linearly polarized light emitted from the third side surface of the second prism. 6. The polarization conversion element according to claim 1, wherein a wave plate is provided on any one of the third side surface and the fourth side surface. 7. A light source;
An integrator optical system that divides a light beam from the light source to form a plurality of light source images, and superimposes the light beams from the plurality of light source images to enter an illumination target;
An illumination device comprising: the polarization conversion element according to claim 1, wherein light beams from the plurality of light source images are incident on a third side surface of the first prism, respectively. The lighting device according to claim 7;
A light separation optical system for separating light from the illumination device into red light, green light, and blue light;
Three light modulation devices for modulating the red light, green light, and blue light, respectively;
A color synthesis optical system for synthesizing light modulated by the three light modulation devices;
A projector comprising: a projection optical system that projects light synthesized by the color synthesis optical system.

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