JP2010204603A - Projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projector of high light use efficiency with a simple and compact configuration. <P>SOLUTION: The projector includes: a plurality of light source parts for emitting coherent light which is the color lights of mutually different wavelength regions; a CGH 12 which is a diffraction optical element for diffracting the coherent light made incident from the plurality of light source parts and for emitting diffracted light; a parallelizing lens 13 for parallelizing the luminance fluxes of the diffracted light made incident from the diffraction optical element; and a spatial light modulator 14 for modulating the light made incident from the parallelizing lens 13 according to image signals. The diffraction optical element superimposes a plurality of color lights parallelized by the parallelizing lens 13 in the irradiation region of the spatial light modulator 14 by deflecting the luminous flux of at least one of the plurality of color lights from the plurality of light source parts, and the angle change of a main light beam in the diffraction optical element of the color light whose peak wavelength is the shortest among the plurality of color lights is smaller than the angle change of the main light beam in the diffraction optical element of at least one of the plurality of color lights. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a projector, and more particularly to a projector that displays an image using diffracted light by a diffractive optical element.

  A so-called single-plate projector that modulates a plurality of color lights with a single spatial light modulator can make the projector simpler and more compact than a plurality of spatial light modulators provided for each color light. There is an advantage. Conventionally, as one of the single-plate projectors, one that adopts a color display system that distributes each color light to each pixel by causing each color light to enter the spatial light modulator at different incident angles has been proposed ( For example, see Patent Document 1). In a single-plate projector, a technique has been proposed in which each color light is distributed to each pixel using a diffractive optical element (see, for example, Patent Document 2). The diffractive optical element diffracts laser light that is coherent light, thereby shaping and expanding the irradiation region and making the light amount distribution uniform in the irradiation region. By providing the diffractive optical element with a plurality of functions, the projector can be made more compact. As the diffractive optical element, for example, a computer generated hologram (CGH) is used. The advantages of CGH are that it is relatively easy to design, can produce highly accurate shapes, and can easily produce duplicates by transfer.

Japanese Patent Laid-Open No. 4-60538 JP 2007-286110 A

  It is known that the efficiency of obtaining desired diffracted light decreases as the CGH deflects the light so that the angle of the principal ray of the emitted light becomes larger than the principal ray of the incident light. When superimposing a plurality of color lights from the CGH in the irradiation region of one spatial light modulator, a reduction in light utilization efficiency due to deflection of each color light by the CGH becomes a problem. It is an object of the present invention to provide a projector with high light utilization efficiency with a simple and small configuration.

  In order to solve the above-described problems and achieve the object, a projector according to the present invention includes a plurality of light source units that emit coherent light that is colored light in different wavelength ranges, and coherent light that is incident from the plurality of light source units. A diffractive optical element that diffracts and emits diffracted light, a collimating lens that collimates the light beam of diffracted light incident from the diffractive optical element, and spatial light modulation that modulates light incident from the collimating lens according to an image signal And a diffractive optical element that deflects at least one light beam of a plurality of color lights from a plurality of light source units to convert a plurality of color lights collimated by a collimating lens into a spatial light modulation device The angle change of the chief ray in the diffractive optical element of the color light having the shortest peak wavelength among the plurality of color lights is superimposed on the irradiation area of And it is smaller than the angle change of the principal ray in the diffractive optical element.

  A decrease in light utilization efficiency due to deflection in the diffractive optical element becomes more conspicuous as the light has a shorter wavelength. By reducing the chief ray angle change in the diffractive optical element for the color light with the minimum peak wavelength compared to other color lights, the diffraction efficiency decreases due to the angle change in the diffractive optical element for the color light with the minimum peak wavelength. Reduce. By reducing the decrease in diffraction efficiency of the color light having the minimum peak wavelength, the decrease in light utilization efficiency of each color light as a whole is reduced. The projector can have a simple and compact configuration by using a spatial light modulation device that modulates a plurality of color lights and a diffractive optical element. Thereby, a projector with high light utilization efficiency can be obtained with a simple and small configuration.

  As a preferred embodiment of the present invention, it is desirable that the color light having the shortest peak wavelength has the smallest change in the angle of the principal ray in the diffractive optical element among the plurality of color lights. Thereby, the fall of light utilization efficiency can further be reduced.

  As a preferred embodiment of the present invention, it is desirable that the color light having the shortest peak wavelength has substantially the same incident angle and exit angle of the principal ray in the diffractive optical element. Thereby, the fall of light utilization efficiency can further be reduced.

  Moreover, as a preferable aspect of the present invention, it is desirable that the spatial light modulator is arranged by shifting the center position of the irradiation region from the optical axis of the collimating lens. The spatial light modulator is arranged so that the principal ray of the color light having the shortest peak wavelength is incident on the center position of the irradiation region. Accordingly, it is possible to realize a configuration in which each color light incident at different incident angles is distributed to the sub-pixels by using a microlens array in which the center position of the microlens and the center position of the pixel are substantially matched.

  Moreover, as a preferable aspect of the present invention, the microlens array includes a plurality of microlenses provided at substantially the same pitch as the pixels in the irradiation region, and the microlens array has a two-dimensional direction in which the microlenses are arranged in parallel. It is desirable that the center position of the microlens is shifted from the center position of the pixel. The microlens array is arranged so that the center position of the sub-pixel into which colored light having the shortest peak wavelength is incident and the center position of the microlens are coaxial. Since each light beam of each color can pass near the center of the collimating lens, the collimating lens can be reduced in size, and aberrations caused by the collimating lens can be reduced.

  Moreover, as a preferable aspect of the present invention, the microlens array includes a plurality of microlenses provided at substantially the same pitch as the pixels in the irradiation region, and the microlens array has a two-dimensional direction in which the plurality of microlenses are arranged in parallel. In this case, it is desirable that the center position of the microlens is substantially aligned with the center position of the pixel. Thus, by arranging the spatial light modulator by shifting the center position from the optical axis, it is possible to realize a configuration in which each color light incident at different incident angles is distributed to the sub-pixels.

  As a preferred embodiment of the present invention, it is desirable that the color light having the shortest peak wavelength is blue light. Thereby, in the structure using red light, green light, and blue light, high light use efficiency can be achieved.

1 is a schematic diagram illustrating a schematic configuration of a projector according to Embodiment 1. FIG. It is a perspective view which shows a part of structure shown in FIG. It is a plane schematic diagram of the pixel in a spatial light modulation device. It is a figure explaining the general structure of the conventional single plate type projector. It is a figure which shows the relationship between diffraction efficiency and the difference of the incident angle of a chief ray, and an output angle. FIG. 3 is a diagram illustrating a characteristic part of the projector according to the first embodiment. It is a cross-sectional schematic diagram explaining a response | compatibility with a pixel and a micro lens. FIG. 6 is a diagram illustrating a characteristic part of a projector according to a second embodiment. It is a cross-sectional schematic diagram explaining a response | compatibility with a pixel and a micro lens.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a schematic diagram illustrating a schematic configuration of a projector 10 according to a first embodiment of the invention. The projector 10 is a so-called single-plate projector that modulates three color lights by one spatial light modulator 14. The red (R) light source unit 11R, the green (G) light source unit 11G, and the blue (B) light source unit 11B are light source units that emit laser light that is coherent light, and have different wavelength ranges. The colored light is emitted. The light source unit 11R for R light is a laser light source that emits R light, and includes, for example, a semiconductor laser. The G light source unit 11G is a laser light source that emits G light, and includes, for example, a semiconductor pumped solid state (DPSS) laser. The light source unit 11B for B light is a laser light source that emits B light, and includes, for example, a semiconductor laser.

  The CGH 12, which is a diffractive optical element, diffracts the laser light incident from the color light source units 11R, 11G, and 11B and emits diffracted light. The CGH 12 shapes a laser beam having a Gaussian intensity distribution into the rectangular shape of the spatial light modulator 14 and further uniformizes the light quantity distribution. For example, the projector 10 displays an image by modulating the first-order diffracted light generated by the CGH 12. The collimating lens 13 collimates the diffracted light beam incident from the CGH 12. The CGH 12 and the collimating lens 13 superimpose each color light in the irradiation region of the spatial light modulator 14.

  The spatial light modulator 14 modulates the light incident from the collimating lens 13 according to the image signal. The spatial light modulator 14 is, for example, a transmissive liquid crystal display device. The spatial light modulator 14 has a microlens array (not shown) in which a plurality of microlenses are arranged in parallel. The projection lens 15 projects the light modulated by the spatial light modulator 14 onto a screen (not shown). The microlens array is not limited to the one attached to the spatial light modulator 14 and may be different from the spatial light modulator 14.

  FIG. 2 is a perspective view showing a part of the configuration shown in FIG. The projector 10 includes one R light source unit 11R, one B light source unit 11B, and two G light source units 11G. The color light source units 11R, 11G, and 11B are installed so that the chief rays of the emitted light beams are substantially parallel to each other. The color light source units 11R, 11G, and 11B are arranged in a matrix of two rows and two columns in the plane direction perpendicular to the principal ray of the emitted light beam. Note that the principal ray is a ray at the center of the light beam, and is represented by an alternate long and short dash line in each figure.

  The CGH 12 is one of surface relief type diffractive optical elements having minute irregularities on the surface. Each color light from each color light source unit 11R, 11G, 11B is incident on a different area of the incident surface of CGH12. In the CHG 12, the surface conditions including the width of the unevenness and the arrangement pattern are optimized according to the wavelength of the color light for each region where the color light is incident. As a design method for optimizing the surface condition, a predetermined calculation method (simulation method) such as an iterative Fourier transform is used.

  For example, the CGH 12 is manufactured by using a so-called nanoimprint technique in which a mold having a desired shape is formed and then the shape of the mold is thermally transferred to the substrate. In addition, the CHG 12 may be manufactured by another conventionally used method as long as a desired shape can be formed. The CGH 12 may be divided for each color light. The diffractive optical element is not limited to the CGH 12, and other surface relief type diffractive optical elements, volume type diffractive optical elements manufactured by a two-beam interference method, or the like may be used.

  FIG. 3 is a schematic plan view of the pixel 16 in the spatial light modulator 14. In the figure, four of the large number of pixels 16 in the spatial light modulator 14 are shown. The pixel 16 includes one R light sub-pixel 17R, one B light sub-pixel 17B, and two G light sub-pixels 17G. The R light sub-pixel 17R modulates the R light according to the image signal. The G light sub-pixel 17G modulates the G light according to the image signal. The B light sub-pixel 17B modulates the B light according to the image signal. The four sub-pixels 17R, 17G, and 17B constituting one pixel 16 are arranged in a matrix of two rows and two columns on the irradiated surface. The arrangement of the color light source units 11R, 11G, and 11B corresponds to the arrangement of the sub-pixels 17R, 17G, and 17B. Note that the pixel arrangement described in this embodiment is an example, and any conventionally known arrangement may be used. The projector 10 can be appropriately configured according to the pixel arrangement of the spatial light modulator 14.

  FIG. 4 illustrates a general configuration employed by a conventional single-plate projector provided with the CGH 21. Here, the R light from the R light source unit 11R and the B light from the B light source unit 11B are illustrated. In general, each element constituting the optical system of the projector is arranged around the optical axis AX. The optical axis AX is the optical axis of the collimating lens 13. Each color light source unit 11R, 11G, and 11B is disposed around the optical axis AX. The center position C of the irradiation area of the spatial light modulator 14 is a position on the optical axis AX.

  The light beams of the respective colors are incident on the CGH 21 incident surface at substantially symmetrical positions with the optical axis AX as the center. The CGH 21 deflects the light beams of the respective color lights in order to superimpose the respective color lights in the irradiation region centered on the optical axis AX. Both the principal ray LR of the R light and the principal ray LB of the B light are bent toward the optical axis AX side by diffraction at the CGH 21. The principal ray of G light is also bent in the same manner as the principal ray LR of R light and the principal ray LB of B light. The difference between the incident angle and the exit angle of the principal ray in the CGH 21 is the same for each color light.

  FIG. 5 is a graph showing the relationship between the diffraction efficiency of the R light and the B light by the CGH 21 and the difference between the incident angle and the outgoing angle of the principal ray in the CGH 21. The diffraction efficiency is assumed to be the ratio of the first-order diffracted light to the entire light emitted from the CGH 21. For both B light and R light, the diffraction efficiency decreases as the difference between the incident angle and the outgoing angle of the principal ray increases. The decrease in diffraction efficiency becomes more remarkable as the wavelength of light is shorter. Therefore, if each color light is deflected equally by the CGH 21, the utilization efficiency of the B light having a short wavelength with respect to the R light and the G light is significantly reduced.

  FIG. 6 illustrates characteristic portions of the projector 10 according to the present embodiment. Here, the R light from the R light source unit 11R and the B light from the B light source unit 11B are illustrated. Each color light source unit 11R, 11G, and 11B is disposed around the optical axis AX. Both the principal ray LB of B light incident on the CGH 12 and the principal ray LB of B light emitted from the CGH 12 are substantially perpendicular to the incident surface of the CGH 12 and substantially parallel to the optical axis AX. In the B light, the incident angle and the exit angle of the principal ray in the CHG 12 are substantially the same. The incident angle and the outgoing angle of the principal ray are both angles formed by the optical axis AX and the principal ray. In the present embodiment, the incident angle and the outgoing angle of the principal ray LB of B light are both zero.

  On the other hand, the CHG 12 superimposes each color light collimated by the collimating lens 13 in the irradiation region of the spatial light modulator 14 by deflecting the light beam for the R light and the G light. For example, when each color light source unit 11R, 11G, and 11B is arranged as shown in FIG. 2, the G light source unit arranged in the upper side of the drawing with respect to the B light source unit 11B in the drawing. The principal ray of G light from 11G changes the angle toward the lower side of the drawing. The principal ray of the G light from the G light source unit 11G arranged at the left side of the paper surface with respect to the B light source unit 11B changes the angle toward the right side of the paper surface. The principal ray of the R light from the R light source unit 11R disposed at the upper left position of the B light source unit 11B changes its angle toward the lower right side of the page. The principal rays of the respective color lights intersect at a position shifted from the optical axis AX to the principal ray side of the B light. The spatial light modulator 14 is arranged with the center position C coincident with the position where the chief rays of the respective color lights intersect. As described above, the spatial light modulator 14 is arranged with the center position C shifted from the optical axis AX.

  FIG. 7 is a schematic cross-sectional view illustrating the correspondence between the pixel 16 and the microlens 18. The plurality of microlenses 18 constituting the microlens array are provided at the same pitch as the pixels 16 in the irradiation region of the spatial light modulator 14. The plurality of microlenses 18 are arranged in an array in a two-dimensional direction perpendicular to the optical axis AX. In addition, as indicated by a two-dot chain line in the figure, the center position of the microlens 18 and the center position of the pixel 16 coincide in a plane perpendicular to the optical axis AX. Since each color light is incident on the microlens 18 at a different incident angle for each color light, it is condensed on the sub-pixels 17R, 17G, and 17B at different positions for each color light. The projector 10 can realize a configuration in which each color light incident at different incident angles is distributed to the sub-pixels 17R, 17G, and 17B by arranging the spatial light modulator 14 by shifting the center position C from the optical axis AX. Also, by providing the microlens array, each color light incident on the microlens 18 can be condensed at different positions, and each color light can be distributed to each subpixel with high accuracy.

  The projector 10 can have a simple and small configuration by using the spatial light modulation device 14 that modulates each color light and the CGH 12. Further, with regard to the B light having the shortest peak wavelength among the R light, G light, and B light, the B light with the most remarkable decrease in diffraction efficiency due to the angle change at the CGH 21 is eliminated by eliminating the change in the chief ray angle at the CGH 12. About the reduction of diffraction efficiency. By reducing the decrease in the diffraction efficiency of the B light, the decrease in the light utilization efficiency of each color light as a whole is reduced. Thereby, there exists an effect that it can be made high light utilization efficiency with a simple and small structure.

  The projector 10 is not limited to the case where the principal ray LB of B light is parallel to the optical axis AX between the B light source unit 11 </ b> B and the collimating lens 13. It is sufficient that the incident angle and the emission angle of the principal ray LB of B light in the CGH 12 are substantially the same, and the principal ray LB of B light may be non-parallel to the optical axis AX. Further, the projector 10 is not limited to the case where the incident angle and the emission angle of the principal ray of B light in the CGH 12 are the same. The projector 10 only needs to change the angle change of the principal ray LB of the B light in the CGH 12 with respect to the angle change of the principal ray LR of the R light and the principal ray of the G light. Further, the projector 10 only needs to have an angle change of the principal ray LB of the B light in the CGH 12 smaller than an angle change of at least one CGH 12 of the principal ray LR of the R light and the principal ray of the G light. As a result, it is possible to obtain an effect of reducing a decrease in light utilization efficiency as a whole for each color light.

  FIG. 8 illustrates a characteristic part of the projector according to the second embodiment of the invention. This embodiment is characterized in that the spatial light modulator 14 is arranged so that the center position C is on the optical axis AX. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. The principal ray LB of the B light substantially coincides with the optical axis AX. The light source unit 11B for B light is disposed on the optical axis AX. The chief rays of each color light intersect at the center position C of the spatial light modulator 14.

  FIG. 9 is a schematic cross-sectional view illustrating the correspondence between the pixel 16 and the microlens 18. As indicated by a two-dot chain line in the figure, the center position of the microlens 18 and the center position of the B light sub-pixel 17B coincide with each other in a plane perpendicular to the optical axis AX. In this embodiment, the microlens array is arranged by shifting the center position of the microlens 18 from the center position of the pixel 16 to the position of the sub-pixel 17B for B light in the two-dimensional direction in which the plurality of microlenses 18 are arranged in parallel. Has been.

  By making the center position of the microlens 18 coincide with the center position of the B light sub-pixel 17B, the B light traveling substantially parallel to the optical axis AX is condensed by the B light sub-pixel 17B. Further, the R light and the G light are incident on the microlens 18 at different incident angles, and are condensed on the sub-pixels 17R and 17G, respectively. Also in the case of the present embodiment, the projector can have a simple and small configuration and high light utilization efficiency.

  According to the present embodiment, it is possible to allow each color light beam to pass through the central portion of the collimating lens 13, and thus the collimating lens 13 can be reduced in size. Further, the collimating lens 13 can use only a portion where the spherical aberration can be reduced. Thereby, even when an inexpensive spherical lens is applied as the collimating lens 13, the aberration caused by the collimating lens 13 can be reduced.

  The projector may be either a front projection type projector or a rear projector. A front projection type projector is a projector for viewing an image by projecting light on a screen and observing light reflected on the screen. The rear projector is a projector that appreciates an image by supplying light to one surface of the screen and observing light emitted from the other surface of the screen.

  10 projector, 11R R light source unit, 11G G light source unit, 11B B light source unit, 12 CGH, 13 collimating lens, 14 spatial light modulator, 15 projection lens, 16 pixels, 17R R light sub Pixel, 17B G light sub-pixel, 17GB light sub-pixel, 18 microlens, 21 CGH, AX optical axis, C center position, LR, LB principal ray

Claims (7)

A plurality of light source units that emit coherent light that is colored light in different wavelength ranges;
A diffractive optical element that diffracts the coherent light incident from the plurality of light source units and emits diffracted light;
A collimating lens that collimates the light beam of the diffracted light incident from the diffractive optical element;
A spatial light modulator that modulates light incident from the collimating lens according to an image signal,
The diffractive optical element irradiates the spatial light modulator with the plurality of color lights collimated by the collimating lens by deflecting at least one light beam of the plurality of color lights from the plurality of light source units. Superimpose in the area,
The change in chief ray angle in the diffractive optical element of the color light having the shortest peak wavelength among the plurality of color lights is the change in the chief ray angle in the diffractive optical element of at least one of the plurality of color lights. A projector characterized by being smaller.   2. The projector according to claim 1, wherein the color light having the shortest peak wavelength has the smallest change in chief ray angle in the diffractive optical element among the plurality of color lights.   3. The projector according to claim 1, wherein the color light having the shortest peak wavelength has substantially the same incident angle and emission angle of the principal ray in the diffractive optical element.   The projector according to claim 1, wherein the spatial light modulation device is arranged by shifting a center position of the irradiation region from an optical axis of the collimating lens. Having a microlens array comprising a plurality of microlenses provided at substantially the same pitch as the pixels in the irradiation region;
5. The microlens array according to claim 1, wherein a center position of the microlens is shifted from a center position of the pixel in a two-dimensional direction in which the plurality of microlenses are arranged in parallel. The projector according to any one of the above. Having a microlens array comprising a plurality of microlenses provided at substantially the same pitch as the pixels in the irradiation region;
5. The microlens array is arranged such that a center position of the microlens is substantially coincident with a center position of the pixel in a two-dimensional direction in which the plurality of microlenses are arranged in parallel. The projector according to any one of the above.   The projector according to claim 1, wherein the color light having the shortest peak wavelength is blue light.

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