JP5541375B2 - projector - Google Patents

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 modulation device can have a simpler configuration and a smaller size than when a plurality of spatial light modulation devices provided for each color light is used. 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 the laser light, which is coherent light, to shape and enlarge the irradiation area and make the light amount distribution uniform in the irradiation area. 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

  However, when CGH which is a digital hologram is used, granular illuminance unevenness may occur in the irradiation region due to, for example, interference between diffracted lights. Irradiance unevenness in the irradiation region can affect the light amount distribution of the image, and can cause a reduction in image quality. An object of the present invention is to provide a projector capable of obtaining a high-quality image 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 light source unit that emits coherent light, and
A diffractive optical element that diffracts the coherent light incident from the light source unit 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;
Driving means for moving the diffractive optical element,
The diffractive optical element comprises a plurality of hologram structures that differ from each other in granular illuminance unevenness,
The diffracted light having different illumination intensity is temporally superimposed by moving the diffractive optical element by the driving means so that the coherent light sequentially enters the plurality of hologram structures. To do.

  For the diffractive optical element, a plurality of hologram structures are prepared which are designed so that the direction of diffracted light and the shape of the irradiated region are the same and the unevenness of illuminance is different. The diffractive optical element is moved at high speed so that light is incident on each of the hologram structures, and the hologram structure on which the coherent light is incident is temporally changed. By changing temporally the hologram structure on which the coherent light is incident, the diffracted light emitted from each hologram structure is temporally superimposed at the position of the irradiation region. By superimposing the diffracted light with different illuminance unevenness temporally, the uneven illuminance is made inconspicuous and the influence on the light quantity distribution of the image 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. This makes it possible to obtain a high-quality image with a simple and compact projector.

  As a preferred aspect of the present invention, it is desirable that the hologram structure on which the coherent light is incident is continuously changed by driving of the driving means. Thereby, the hologram structure in which each color light enters is temporally changed.

  As a preferred aspect of the present invention, it is desirable that the driving unit rotates the diffractive optical element. As a result, the diffractive optical element can be moved so as to temporally change the hologram structure on which each color light is incident.

  Moreover, as a preferable aspect of the present invention, it is desirable that a color light having a longer peak wavelength among a plurality of color lights is incident on a position away from the center of rotation by the driving unit in the diffractive optical element. The illuminance unevenness due to the digital hologram becomes conspicuous as it becomes uneven at a low frequency as the light has a longer wavelength. By making long-wavelength light enter a position away from the center of rotation, diffracted light from more hologram structures is temporally superimposed. By superimposing the pattern of uneven illuminance more in time, the uneven illuminance can be made inconspicuous with respect to light having a long wavelength where illuminance unevenness easily occurs. Thereby, illumination unevenness can be reduced for the entire image.

  Moreover, as a preferable aspect of the present invention, it is desirable that a single diffractive optical element is provided and a plurality of color lights are incident on the diffractive optical element. By adopting a configuration in which each color light is incident on one diffractive optical element, one driving means for rotating the diffractive optical element can be provided, and the occurrence of mechanical problems can be reduced.

Moreover, as a preferable aspect of the present invention, a plurality of the light source units and a plurality of the diffractive optical elements are included, and the coherent light emitted from one light source unit among the plurality of light source units is the plurality of the light source units. Coherent light that is incident on one of the diffractive optical elements and is emitted from the other light source unit among the plurality of light source units is incident on another diffractive optical element among the plurality of diffractive optical elements. It is desirable. By distributing a plurality of color lights to a plurality of diffractive optical elements, the diameter of the diffractive optical element can be reduced. As a result, the projector can be reduced in size and thickness.

  As a preferred aspect of the present invention, it is desirable that the driving means swings the diffractive optical element. Thereby, the diffractive optical element can be moved so that the incident position of each color light in the diffractive optical element changes.

  In a preferred aspect of the present invention, the driving means includes a first driving means for swinging the diffractive optical element in a first direction, and the diffraction in a second direction substantially perpendicular to the first direction. It is preferable that the first driving unit and the second driving unit swing the diffractive optical element at different periods. This makes it possible to superimpose many illuminance unevenness patterns in time by making light incident on many hologram structures, thereby effectively reducing illuminance unevenness.

1 is a schematic diagram illustrating a schematic configuration of a projector according to Embodiment 1. FIG. It is a plane schematic diagram of a diffractive optical element. FIG. 6 is a schematic diagram illustrating a schematic configuration of a projector according to a second embodiment. FIG. 10 is a schematic diagram illustrating a schematic configuration of a projector according to a third embodiment. It is a perspective view about a part of structure shown in FIG. It is a figure explaining the illumination intensity nonuniformity by a digital hologram.

  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 15. 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. Each color light may be collimated by a collimator lens.

  The diffractive optical element 12 diffracts the laser light incident from the color light source units 11R, 11G, and 11B and emits diffracted light. The diffractive optical element 12 shapes a laser beam having a Gaussian intensity distribution into the rectangular shape of the spatial light modulator 15, 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 diffractive optical element 12. The collimating lens 14 collimates the diffracted light beam incident from the diffractive optical element 12. The diffractive optical element 12 and the collimating lens 14 superimpose each color light at the position of the irradiation region of the spatial light modulator 15. The rotation motor 13 is a driving unit that rotates the diffractive optical element 12. The rotary motor 13 changes the incident position of each color light incident on the diffractive optical element 12 by rotating the diffractive optical element 12.

  The spatial light modulator 15 modulates the light incident from the collimating lens 14 according to the image signal. The spatial light modulator 15 is, for example, a transmissive liquid crystal display device. The spatial light modulator 15 has a microlens array (not shown) in which a plurality of microlenses are arranged in parallel. The plurality of microlenses constituting the microlens array are provided at the same pitch as the pixels in the irradiation region of the spatial light modulator 15. The pixels in the irradiation region of the spatial light modulator 15 are configured by sub-pixels for R light, G light, and B light. Each color light incident on the micro lens at different incident angles is condensed on each sub-pixel in the pixel. By providing the microlens array, each color light incident on the microlens can be condensed at different positions, and each color light can be distributed to each subpixel with high accuracy. The projection lens 16 projects the light modulated by the spatial light modulator 15 onto a screen (not shown). The microlens array is not limited to the one attached to the spatial light modulation device 15 and may be different from the spatial light modulation device 15.

  FIG. 2 is a schematic plan view of the diffractive optical element 12. The diffractive optical element 12 is one of surface relief type diffractive optical elements having minute irregularities on the surface. The diffractive optical element 12 has a circular shape around the rotation axis 20 of the rotary motor 13. On the surface of the diffractive optical element 12, a B-light diffraction region 17, a G-light diffraction region 18, and an R-light diffraction region 19 are formed. The B light diffraction region 17, the G light diffraction region 18, and the R light diffraction region 19 are provided concentrically around the rotation axis 20. Of each region, the B light diffraction region 17 is provided in the central portion of the diffractive optical element 12 closest to the rotation axis 20. The diffraction region 19 for R light is provided on the outer edge of the diffractive optical element 12 that is farthest from the rotation axis 20. The G light diffraction region 18 is provided between the B light diffraction region 17 and the R light diffraction region 19.

  A plurality of CGH structures (hologram structures) 21, 22, and 23 are formed in the diffraction regions 17, 18, and 19, respectively. The CGH structures 21, 22, and 23 are provided in parallel in concentric circles around the rotation axis 20 in each of the diffraction regions 17, 18, and 19. Each CGH structure 21, 22, 23 is formed with a plurality of irregularities. In the CGH structures 21, 22, and 23, the surface conditions including the uneven width and the arrangement pattern are optimized.

  The surface condition of the CGH structure 21 formed in the B light diffraction region 17 is optimized for the B light LB. Each CGH structure 21 diffracts the B light LB. Each CGH structure 21 is designed so that the illuminance unevenness is changed between the CGH structures 21 for the B light LB, in addition to the B light LB traveling to the irradiation region of the spatial light modulator 15.

  The surface condition of the CGH structure 22 formed in the G light diffraction region 18 is optimized for the G light LG. Each CGH structure 22 diffracts the G light LG. Each CGH structure 22 is designed so that the illuminance unevenness between the CGH structures 22 changes with respect to the G light LG in addition to the G light LG traveling to the irradiation region of the spatial light modulator 15.

  The surface condition of the CGH structure 23 formed in the R light diffraction region 19 is optimized for the R light LR. Each CGH structure 23 diffracts the R light LR. Each CGH structure 23 is designed such that the illuminance unevenness of the CGH structures 23 varies between the CGH structures 23 for the R light LR, in addition to advancing the R light LR to the irradiation region of the spatial light modulator 15.

  As a design method for optimizing the surface condition of the diffractive optical element 12, a predetermined calculation method (simulation method) such as an iterative Fourier transform is used. The diffractive optical element 12 is manufactured, for example, by using a so-called nanoimprint technique in which a mold (mold) having a desired shape is formed and then the shape of the mold is thermally transferred to a substrate. In addition, the diffractive optical element 12 may be manufactured by another conventionally used method as long as a desired shape can be formed.

  The B light LB emitted from the B light source unit 11 </ b> B is incident on the B light diffraction region 17. The G light LG emitted from the G light source unit 11G enters the G light diffraction region 18. The R light LR emitted from the R light source unit 11 </ b> R enters the R light diffraction region 19. When the rotary motor 13 rotates the diffractive optical element 12, the B light LB sequentially enters the CGH structure 21 arranged in parallel with the B light diffraction region 17. The G light LG sequentially enters the CGH structure 22 arranged in parallel with the G light diffraction region 18. The R light LR sequentially enters the CGH structure 23 arranged in parallel with the R light diffraction region 19.

  In this way, by rotating the diffractive optical element 12, the CGH structure 21 that makes the B light LB incident, the CGH structure 22 that makes the G light LG incident, and the CGH structure 23 that makes the R light LR incident continuously, respectively. Change. Thereby, the CGH structures 21, 22, and 23 on which the color lights LB, LG, and LR are incident are temporally changed. B light LB emitted from the CGH structure 21 in the B light diffraction region 17, G light LG emitted from the CGH structure 22 in the G light diffraction region 18, and R light LR emitted from the CGH structure 23 in the R light diffraction region 19 Are temporally superimposed at the position of the spatial light modulator 15 via the collimating lens 14.

  CGH which is a digital hologram may cause granular illuminance unevenness, for example, when diffracted light interferes with each other. The projector 10 according to the present embodiment superimposes diffracted light with different illuminance unevenness in terms of time, thereby making the illuminance unevenness inconspicuous and reducing the influence on the light amount distribution of the image. The illuminance unevenness due to the digital hologram becomes conspicuous as it becomes uneven at a low frequency as the light has a longer wavelength. For example, as shown in FIG. 6, the unevenness of illuminance of 450 nm B light and the illuminance unevenness of R light of 640 nm cause coarser illuminance unevenness in R light having a long wavelength.

  As shown in FIGS. 1 and 2, the projector 10 according to the present embodiment makes each color light incident on the diffractive optical element 12 in the order of B light LB, G light LG, and R light LR from the side near the rotation center. Let By making the color light having a longer peak wavelength out of each color light enter a position farther from the center of rotation, the color light having a longer peak wavelength causes more patterns of uneven illumination to be temporally superimposed while the diffractive optical element 12 is rotated once. It becomes possible to do. By superimposing a large number of uneven illumination patterns over time, the uneven illumination can be made inconspicuous with respect to long-wavelength color light that tends to cause uneven illumination. This makes it possible to reduce illuminance unevenness for the entire image. The projector 10 can have a simple and small configuration by using the spatial light modulation device 15 that modulates a plurality of color lights and the CGH 12. As described above, there is an effect that the projector 10 has a simple and small configuration, and a high-quality image can be obtained.

  In the projector 10 according to the present embodiment, the incident angle of each color light incident on the spatial light modulator 15 is determined by the distance between the irradiation region and the microlens and the interval between the sub-pixels. Increasing the distance between the irradiation region and the microlens and shortening the interval between the sub-pixels can reduce the incident angle of each color light incident on the microlens. The smaller the incident angle of each color light incident on the microlens, the shorter the interval between each color light incident on the diffractive optical element 12, and the diffractive optical element 12 can be made smaller. As the diffractive optical element 12 can be made smaller, the projector 10 can be made smaller and thinner. Note that, since the aperture ratio of the pixels in the spatial light modulator 15 depends on the interval between the sub-pixels, the interval between the sub-pixels can be appropriately set according to the relationship with the transmittance of the spatial light modulator 15. desirable.

  As a technique for reducing illuminance unevenness due to a digital hologram, a technique of arranging a diffusion plate that diffuses light can also be adopted. For example, if a diffusing plate is provided in the optical path between the diffractive optical element 12 and the collimating lens 14, the parallelism of the light beam from the collimating lens 14 decreases, and the condensing spot by the microlens increases. Become. The enlargement of the condensed spot may cause a decrease in the transmittance of the spatial light modulator 15 or color mixing. On the other hand, since the projector 10 according to the present embodiment can reduce illuminance unevenness while maintaining the parallelism of the light beam from the collimating lens 14, high light utilization efficiency and good color reproducibility can be obtained. There is an advantage. In addition, the projector 10 according to the present embodiment can also obtain an effect of reducing speckle noise caused by the coherence of laser light.

  In this embodiment, each color light is made incident on one diffractive optical element 12, so that one driving means for rotating the diffractive optical element 12 can be provided, and the occurrence of mechanical problems can be reduced. Can do. The driving unit may be any unit other than the rotary motor 13 as long as it can continuously rotate the diffractive optical element 12. The driving means is not limited to the one that continuously changes the hologram structure on which the laser light is incident, and may be one that changes stepwise.

  FIG. 3 is a schematic diagram illustrating a schematic configuration of the projector 30 according to the second embodiment of the invention. The projector 30 according to the present embodiment includes two diffractive optical elements 31 and 32. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. The first diffractive optical element 31 diffracts the G light incident from the G light source unit 11G and emits diffracted light. The second diffractive optical element 32 diffracts the R light incident from the R light source unit 11R and the B light incident from the B light source unit 11B, and emits diffracted light. The first rotation motor 33 is a driving unit that rotates the first diffractive optical element 31. The second rotation motor 34 is a driving unit that rotates the second diffractive optical element 32.

  Both the first diffractive optical element 31 and the second diffractive optical element 32 have a circular shape. The circular diameter of the first diffractive optical element 31 is smaller than the circular diameter of the second diffractive optical element 32. On the surface of the first diffractive optical element 31, a G light diffraction region is formed. On the surface of the second diffractive optical element 32, a diffraction region for R light and a diffraction region for B light are formed. The diffraction region for B light is provided in the central portion of the second diffractive optical element 32. The diffraction region for R light is provided at the outer edge portion of the second diffractive optical element 32.

  In the diffraction region for G light of the first diffractive optical element 31, a CGH structure in which the surface condition for G light is optimized is provided. In the diffraction region for R light of the second diffractive optical element 32, a CGH structure in which surface conditions for R light are optimized is provided. In the diffraction region for B light of the second diffractive optical element 32, a CGH structure in which the surface condition for B light is optimized is provided. In the present embodiment, illustration of each diffraction region and CGH structure is omitted.

  The G light emitted from the first diffractive optical element 31, the R light and B light emitted from the second diffractive optical element 32 are both temporally superimposed at the position of the spatial light modulator 15 via the collimating lens 14. The Also in this embodiment, the projector 30 can have a simple and small configuration, and a high-quality image can be obtained. In the present embodiment, the first diffractive optical element 31 and the second diffractive optical element 32 are separated from each other by allocating the G light to the first diffractive optical element 31 and the R light and B light to the second diffractive optical element 32. The diameter can be reduced. Thereby, the projector 30 can be further reduced in size and thickness.

  By making the G light incident on the first diffractive optical element 31 and the R light and B light incident on the second diffractive optical element 32, the first diffractive optical element 31 and the second diffractive optical element 32 are moved as color light having a longer peak wavelength. It is possible to increase the illuminance unevenness pattern that is temporally superimposed during each rotation. Thereby, also in a present Example, illumination intensity nonuniformity can be made not conspicuous about the color light of the long wavelength which is easy to produce illumination intensity nonuniformity. Note that the projector 30 only needs to have two or more diffractive optical elements and allow different colored light to be incident on each of them. The projector 30 may be appropriately modified such as the arrangement of the diffractive optical elements and the combination of the colored lights incident on the diffractive optical elements. You may do it.

  FIG. 4 is a schematic diagram illustrating a schematic configuration of the projector 40 according to the third embodiment of the invention. The projector 40 according to the present embodiment includes a driving unit that swings the diffractive optical element 41. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. The diffractive optical element 41 diffracts the laser light incident from the color light source units 11R, 11G, and 11B and emits diffracted light. The vibration generating unit 42 is a driving unit that swings the diffractive optical element 41. The vibration generating unit 42 changes the incident position of each color light incident on the diffractive optical element 41 by swinging the diffractive optical element 41.

  FIG. 5 is a perspective view of a part of the configuration shown in FIG. The diffractive optical element 41 has a rectangular shape. On the surface of the diffractive optical element 41, an R light diffraction region 43, a G light diffraction region 44, and a B light diffraction region 45 are formed in parallel so as to correspond to the color light source units 11 R, 11 G, and 11 B. ing. Further, the diffractive optical element 41 is fixed to the vibration generating unit 42 by a fixing jig 46.

  The R-light diffraction region 43 is provided with a CGH structure 23 in which the surface condition of the R light LR is optimized. The GGH diffraction region 44 is provided with the CGH structure 22 in which the surface condition of the G light LG is optimized. The B light diffraction region 45 is provided with the CGH structure 21 in which the surface condition of the B light LB is optimized. The CGH structures 21, 22, and 23 are provided in parallel in the two-dimensional direction in each of the diffraction regions 45, 44, and 43.

  The vibration generating unit 42 includes a first actuator 47 and a second actuator 48. The first actuator 47 and the second actuator 48 are linear vibration actuators that reciprocate in a specific direction using the power of the linear motor and the restoring force of the spring. The linear vibration actuator is small and has a feature that it can obtain a reciprocating motion with high efficiency and high speed. The first actuator 47 functions as a first drive unit that generates vibration in the Y-axis direction that is the first direction. The second actuator 48 functions as a second drive unit that generates vibration in the X-axis direction, which is the second direction. Here, it is assumed that the X axis and the Y axis are axes parallel to the incident surface of the diffractive optical element 41 and perpendicular to each other.

  The first actuator 47 swings the diffractive optical element 41 in the Y-axis direction via the fixing jig 46. The second actuator 48 swings the diffractive optical element 41 in the X-axis direction via the first actuator 47 and the fixing jig 46. When the vibration generating unit 42 swings the diffractive optical element 41, the CGH structure 21 that makes the B light LB incident, the CGH structure 22 that makes the G light LG incident, and the CGH structure 23 that makes the R light LR incident continuously. To change. Thereby, the CGH structures 21, 22, and 23 on which the color lights LB, LG, and LR are incident are temporally changed.

  The first actuator 47 and the second actuator 48 swing the diffractive optical element 41 at different periods. By oscillating the diffractive optical element 41 at different periods in the X-axis direction and the Y-axis direction, light can be incident on many CGH structures 21, 22, and 23 in each of the diffraction regions 43, 44, and 45. Become. By making each color light incident on many CGH structures 21, 22, and 23, it is possible to superimpose many uneven illumination patterns in time, and effectively reduce uneven illumination.

  If the diffractive optical element 41 is swung by the same period of the first actuator 47 and the second actuator 48, the diffractive optical element 41 has the same linear motion or trajectory in the oblique direction with respect to the X axis and the Y axis. Will repeat the circular motion. On the other hand, by driving the first actuator 47 and the second actuator 48 at different periods, the operation of the diffractive optical element 41 can be varied, and light is incident on more CGH structures 21, 22, and 23. It becomes possible.

  Note that the driving means is not limited as long as the diffractive optical element 41 can be continuously swung in the two-dimensional direction, and may be other than the configuration including two linear vibration actuators. 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.

  DESCRIPTION OF SYMBOLS 10 Projector, 11R R light source part, 11G G light source part, 11B B light source part, 12 Diffractive optical element, 13 Rotation motor, 14 Parallelizing lens, 15 Spatial light modulation device, 16 Projection lens, 17B Diffraction region for light, diffraction region for 18 G light, diffraction region for 19 R light, 20 rotation axis, 21, 22, 23 CGH structure, 30 projector, 31 first diffractive optical element, 32 second diffractive optical element, 33 th 1 rotation motor, 34 2nd rotation motor, 40 projector, 41 diffractive optical element, 42 vibration generator, 43 R light diffraction area, 44 G light diffraction area, 45 B light diffraction area, 46 fixing jig, 47 1st actuator, 48 2nd actuator

Claims (5)

A light source that emits coherent light;
A diffractive optical element that diffracts the coherent light incident from the light source unit 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;
Driving means for moving the diffractive optical element,
The diffractive optical element comprises a plurality of hologram structures that differ from each other in granular illuminance unevenness,
The diffracted light having different illumination intensity is temporally superimposed by moving the diffractive optical element by the driving means so that the coherent light sequentially enters the plurality of hologram structures. Projector. The projector according to claim 1, wherein the driving unit rotates the diffractive optical element. A plurality of the light source units, and a plurality of the diffractive optical elements,
Coherent light emitted from one of the plurality of light source units is incident on one diffractive optical element of the plurality of diffractive optical elements,
The projector according to claim 2, wherein coherent light emitted from another light source unit among the plurality of light source units is incident on another diffractive optical element among the plurality of diffractive optical elements. The projector according to claim 1, wherein the driving unit swings the diffractive optical element. The driving means includes first driving means for swinging the diffractive optical element in a first direction, and second driving means for swinging the diffractive optical element in a second direction intersecting the first direction. Have
The projector according to claim 4, wherein the first driving unit and the second driving unit swing the diffractive optical element at different periods.

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