Projection device

Abstract

The goal is to miniaturize the device while maintaining focus on images that use different colors. [Solution] The projection device comprises a light source unit 31, a diffractive optical element 51, a prism unit 41, a display element 61, and collimator lenses 421 and 422. The light source unit 31 includes laser diodes 31G and 31R that emit light in first and second wavelength bands with different wavelengths. The prism unit 41 includes prisms 411 and 412, respectively, which are provided on the optical paths of the first and second wavelength bands of light. The display element 61 transmits at least a portion of the light diffracted by the diffractive optical element 51 to form an image. The collimator lenses 421 and 422 are arranged between the light source unit 31 and the diffractive optical element 51. The distance between prism 411 and collimator lens 421 is different from the distance between prism 412 and collimator lens 422.

Description

Technical Field

[0001] The present invention relates to a projection apparatus.

Background Art

[0002] Conventionally, a projection apparatus including an LD (Laser Diode) light source and a DOE (Diffractive Optical Element) is known. The projection apparatus forms planar light composed of multiple bright spots by means of multiple orders of diffracted light based on the DOE. The projection apparatus transmits the planar light through a display element such as an LCD (Liquid Crystal Display) and projects a pattern onto a display object.

[0003] There is also known a projection apparatus including LDs for respective colors of R (red), G (green), and B (blue), and collimator lenses and dichroic prisms respectively corresponding to the respective LDs (see Patent Document 1). In the projection apparatus, after the light from each of the RGB LDs is transmitted through each corresponding collimator lens, each color light is reflected by each dichroic prism that reflects light of the corresponding color and transmits light of other colors, so that the light of respective RGB colors are combined to output white light. The projection apparatus projects a starry sky onto a screen surface with the white light via a projection optical system and a reflector assembly.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, in the projection device described in Patent Document 1, the distance between each RGB LD and each collimator lens is the same. Even if this configuration is applied to a projection device equipped with diffractive optical elements, the image will be displayed without the light of each color being in focus due to axial chromatic aberration of multiple colors of light. Axial chromatic aberration is an aberration in which the image formation position shifts forward or backward along the optical axis depending on the color, due to the difference in refractive index of the optical system depending on the color.

[0006] The objective of this invention is to achieve miniaturization while focusing on images that use different colors. [Means for solving the problem]

[0007] To solve the above problems, the projection apparatus of the present invention comprises a light source unit including a first light source that emits light in a first wavelength band and a second light source that emits light in a second wavelength band different from the first wavelength band; a diffractive optical element that diffracts the first wavelength band light and the second wavelength band light emitted from the light source unit; an optical path conversion unit including a first optical path conversion unit provided on the optical path of the first wavelength band light and the optical path of the second wavelength band light between the light source unit and the diffractive optical element, and a second optical path conversion unit provided on the optical path of the second wavelength band light; a mask unit that transmits or reflects at least a portion of the light diffracted by the diffractive optical element to project an image onto a display target surface and form an image; and a lens disposed between the light source unit and the diffractive optical element on the optical paths of the first wavelength band light and the second wavelength band light, wherein the distance between the first optical path conversion unit and the lens is different from the distance between the second optical path conversion unit and the lens. [Effects of the Invention]

[0008] This invention makes it possible to achieve miniaturization while focusing on images that use different colors. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the image projection unit and the object to be displayed in a projection device according to an embodiment of the present invention. [Figure 2]This is a schematic diagram illustrating axial chromatic aberration. [Figure 3] This figure shows the wavelength characteristics of the reflectance of the mirror portion corresponding to the green color. [Figure 4] This figure shows the wavelength characteristics of the reflectance of the mirror portion corresponding to the red color. [Figure 5] This figure shows the wavelength characteristics of the reflectance of the mirror portion corresponding to the blue color. [Figure 6] This is a block diagram showing the functional configuration of a projection device. [Figure 7] This is a flowchart showing the image display process. [Figure 8] This is a diagram showing an image. [Figure 9] This is a diagram showing an image. [Figure 10] This figure shows the image projection unit and the object to be displayed in the projection device in a modified example. [Modes for carrying out the invention]

[0010] Embodiments and modifications of the present invention will be described in detail below with reference to the drawings. However, the scope of the present invention is not limited to the illustrated examples.

[0011] Embodiments of the present invention will be described with reference to Figures 1 to 9. First, the device configuration of this embodiment will be described with reference to Figures 1 to 6. As shown in Figures 1 and 2, the projection device 1 of this embodiment includes an image projection unit 20, and projects projection light L onto the display object 2 to display (project) various images onto the surface of the display object 2. The display object 2 may be, for example, a screen, the wall, floor or ceiling of a building, or the surface of any object. In this embodiment, the distance from the projection device 1 (image projection unit 20) to the display object 2 is, for example, about 1 m to 10 m, but is not limited thereto. The image projected onto the surface of the display object 2 is not particularly limited, but may be, for example, an image of a guide sign to guide people in the vicinity, or an image to decorate the surface of the display object 2.

[0012] As shown in Figure 1, the image projection unit 20 includes a light source unit 31, a prism unit 41, collimator lenses 421, 422, 423, a diffractive optical element 51, and a display element 61. Also, Figure 1 (and Figures 2 and 9 described later) have a three-dimensional x, y, and z axis. The light source unit 31 includes laser diodes 31G, 31R, 31B and a light source driving circuit. The laser diodes 31G, 31R, and 31B function as the first, second, and third light sources, respectively. Unlike sunlight and lamp light sources which exhibit a very broad wavelength spectrum, the laser diodes 31G, 31R, and 31B produce a spectrum with a very narrow wavelength width. The prism unit 41 functions as an optical path conversion unit. The display element 61 functions as a mask unit. The collimator lenses 421, 422, and 423 function as lenses. The laser diode 31G is a light source that emits G (green) laser light (hereinafter referred to as G light). Laser diode 31R is a light source that emits red (R) laser light (hereinafter referred to as R light). Laser diode 31B is a light source that emits blue (B) laser light (hereinafter referred to as B light). Laser diodes 31G, 31R, and 31B are arranged sequentially in the +x direction so that each emits laser light in the -z direction. That is, laser diodes 31G, 31R, and 31B are arranged so that their respective emission surfaces are located on the same plane. The light source drive circuit of the light source unit 31 controls the laser diodes 31G, 31R, and 31B independently by following the control of the control unit 11 (Figure 6).

[0013] Collimator lenses 421, 422, and 423 are lenses that convert the incident laser light into parallel light and emit it. Collimator lens 421 is positioned on the optical axis of the laser diode 31G and between the laser diode 31G and the prism section 41 (prism 411 described later). The distance in the z-axis direction between the emitter of the laser diode 31G and collimator lens 421 is denoted as distance D1G. Collimator lens 422 is positioned on the optical axis of the laser diode 31R and between the laser diode 31R and the prism section 41 (prism 412 described later). The distance in the z-axis direction between the emitter of the laser diode 31R and collimator lens 422 is denoted as distance D1R. Collimator lens 423 is positioned on the optical axis of the laser diode 31B and between the laser diode 31B and the prism section 41 (prism 413 described later). The distance in the z-axis direction between the emitter of the laser diode 31B and collimator lens 423 is denoted as distance D1B.

[0014] As shown in Figure 2, consider the collimator lens 420 and the R light emission surface 401R, the G light emission surface 401G, and the B light emission surface 401B. On the optical axis in the x-axis direction of the collimator lens 420, the positions corresponding to the focal lengths of the R, G, and B light emission surfaces are in the order of emission surfaces 401R, 401G, and 401B in the +x direction. The difference in these focal lengths is due to axial chromatic aberration of the collimator lens 420. The difference in focal length between the single lens collimator lens 420 and the emission surfaces 401R and 401B is about 2% of the focal length. The cause of axial chromatic aberration is the difference in refraction for each wavelength. Here, the wavelengths of red, green, and blue are 640 nm, 550 nm, and 460 nm, respectively. Therefore, the collimator lenses 421, 422, and 423 are positioned such that distance D1R > distance D1G > distance D1B.

[0015] As shown in Figure 1, the prism section 41 has prisms 411 (first optical path conversion section), 412 (second optical path conversion section), and 413 (third optical path conversion section). Prism 411 has a mirror section 411G formed on the slanted surface of the triangular prism. As shown in Figure 3, the mirror section 411G is a mirror with high reflectivity [%] across the entire wavelength band (at least the green wavelength band) (total internal reflection). The mirror section 411G reflects the G light incident from the laser diode 31G in the +x direction. As shown in Figure 1, the prism 412 has a mirror section 412R formed on the slanted surface of the triangular prism. As shown in Figure 4, the mirror section 412R is a dichroic mirror with high reflectivity [%] in the red wavelength band and low reflectivity [%] in wavelength bands other than red. The mirror portion 412R reflects the R light incident from the laser diode 31R in the +x direction and transmits the G light incident from the prism 411 in the +x direction. As shown in Figure 1, the prism 413 has a mirror portion 413B formed on the slanted surface of the triangular prism. As shown in Figure 5, the mirror portion 413B is a dichroic mirror with a high reflectivity [%] in the blue wavelength band and a low reflectivity [%] in wavelength bands other than blue. The mirror portion 413B reflects the B light incident from the laser diode 31B in the +x direction and transmits the G light and R light incident from the prism 412 in the +x direction. Thus, the distances between the respective emission surfaces of the laser diodes 31G, 31R, and 31B and the mirror sections 411G, 412R, and 413B, which are positioned on the respective optical paths of the laser diodes 31G, 31R, and 31B and corresponding to the respective laser diodes 31G, 31R, and 31B, are approximately the same. Therefore, the distances between the collimator lens 421 and the mirror section 411G, the distance between the collimator lens 422 and the mirror section 412R, and the distance between the collimator lens 423 and the mirror section 413B are all different. In other words, in order from longest to shortest, the distances are between the collimator lens 423 and the mirror section 413B, the distance between the collimator lens 421 and the mirror section 411G, and the distance between the collimator lens 422 and the mirror section 412R.As described above, even if the distances between the respective laser diodes 31G, 31R, 31B of the light source unit 31 and the corresponding collimator lenses 421, 422, 423 are different from each other in arrangement, the distances between the collimator lenses 421, 422, 423 and the corresponding mirror units 411G, 412R, 413B are adjusted. Therefore, the laser diodes 31G, 31R, 31B can be arranged in parallel with each other on substantially the same plane. Accordingly, the size can be reduced compared to a case where the distances between the collimator lenses 421, 422, 423 and the corresponding mirror units 411G, 412R, 413B are substantially the same. Note that the prism unit 41 serving as an optical path converting unit may be configured to be each disposed on a transparent plate.

[0016] Since the prism unit 41 includes prisms 411, 412, 413, no streak is formed at the center of the light that has passed through the mirror units 411G, 412R, 413B. Assume that a quadrangular prism-shaped dichroic prism composed of four triangular prism prism members is used instead of the prism unit 41. When the light emitted from the laser diodes 31G, 31R, 31B is collimated into parallel light by the collimator lenses 421, 422, 423, and one dichroic prism is provided to combine these lights, the mirrors are arranged in an X shape when the dichroic prism is viewed in a plan view. Since the X shape has an intersecting portion, there arises a problem that a streak is formed at the center of the light that has passed through the dichroic prism.

[0017] The diffractive optical element 51 is a diffraction grating (DOE) having a three-dimensional concavo-convex structure formed by combining a plurality of diffraction gratings with different grating periods. The diffractive optical element 51 diffracts incident laser light in accordance with the pitches of the plurality of grating periods, and emits multi-order diffracted light consisting of a dot pattern of a plurality of bright spots where diffracted light in a matrix (grid) pattern interferes and intensifies each other. The diffractive optical element 51 is disposed perpendicular to the optical axis L0. The display element 61 is a transmissive liquid crystal display element disposed perpendicular to the optical axis L0. The display element 61 includes a dot matrix liquid crystal panel (LCD) in which pixels are arranged in a matrix, polarizing plates disposed on both sides so as to sandwich the liquid crystal panel, and a liquid crystal drive circuit that drives the liquid crystal panel. The liquid crystal panel is, for example, a TN (Twisted Nematic) type or STN (Super TN) type liquid crystal panel. Under the control of the control unit 11, the liquid crystal drive circuit applies a drive voltage corresponding to the pixel value of an image to be projected (displayed) to each pixel based on the image data stored in the storage unit 13 (FIG. 6), and controls the alignment state of the liquid crystal layer of each pixel. In accordance with the application of the drive voltage, each pixel is switched between a state (ON state) in which light incident on the pixel transmits through the polarizing plate on the emission side, and a state (OFF state) in which light incident on the pixel is absorbed by the polarizing plate on the emission side. By distributing ON-state pixels based on image data, the display element 61 transmits the image corresponding to the image data, projects the transmitted light onto the display object 2, and displays the image. The display element 61 has a configuration in which all pixels are in a light-absorbing OFF state when no power is supplied (no drive voltage is applied), or a configuration in which all pixels are in a light-transmitting ON state when no power is supplied.

[0018] The light emitted from each of the collimator lenses 421, 422, and 423 is collimated light. Therefore, the optical path distances from each of the collimator lenses 421, 422, and 423 to the diffractive optical element 51 may be different from each other for R light, G light, and B light. Since the R light, G light, and B light that have passed through the diffractive optical element 51 and the display element 61 remain collimated light, they are in focus anywhere.

[0019] As shown in Figure 6, the projection device 1 includes a control unit 11, an operation unit 12, a storage unit 13, a communication unit 14, an audio output unit 15, an image projection unit 20, and the like. The image projection unit 20 includes a light source unit 31, an optical system 40, a diffractive optical element 51, a display element 61, and the like. The optical system 40 includes a prism unit 41 and collimator lenses 421, 422, and 423. All parts of the projection device 1, except for the optical system 40 and the diffractive optical element 51, are connected via a bus 16. The projection device 1 may further include other components, such as a display unit that displays status information of the projection device 1.

[0020] The control unit 11 has a CPU (Central Processing Unit) and RAM (Random Access Memory) and controls each part of the projection device 1. The CPU of the control unit 11 reads various programs stored in the memory unit 13, loads them into the RAM, and executes various processes in cooperation with the loaded programs. The RAM is a volatile semiconductor memory that temporarily stores programs and data, and a work area is formed therein. The operation unit 12 has buttons, a remote control and its receiver, and receives various operation inputs from the user and outputs the operation information to the control unit 11.

[0021] The memory unit 13 is a non-volatile memory composed of flash memory or the like, which is readable and writable, and stores various programs and data. In particular, the memory unit 13 stores an image display program for executing the image display processing described later. The memory unit 13 can also store image data and the like received from external devices via the communication unit 14, under the control of the control unit 11. The communication unit 14 is a communication module for wired communication with external devices such as a PC (Personal Computer) using a communication standard such as USB (Universal Serial Bus). The CPU 11 sends and receives information with external devices via the communication unit 14. For example, an external device sends image data to be projected to the projection device 1. The communication unit 14 may also be a communication module for wireless communication with external devices using a communication standard such as wireless LAN (Local Area Network). The audio output unit 15 has an amplifier, a speaker, etc., and, under the control of the control unit 11, performs various audio outputs, for example, based on audio data stored in the memory unit 13.

[0022] Next, the operation of the projection device 1 will be explained with reference to Figures 7 to 9. Image data, including color information for the image to be projected, is stored in the storage unit 13 in advance. The color information is one of red, green, or blue. In the projection device 1, triggered by, for example, an instruction to execute image display processing from the user via the operation unit 12, the control unit 11 executes image display processing based on the image display program stored in the storage unit 13. Here, an example is described in which the image display processing performs image display (projection) but does not produce sound output, but it is not limited to this, and a configuration that includes sound output is also possible.

[0023] As shown in Figure 7, the control unit 11 reads image data including the color information of the image to be displayed from the storage unit 13 in response to an instruction input from the user via the operation unit 12, and sets a temporal light emission pattern of the light source unit 31 corresponding to the color information of the image to be displayed (step S11). The light emission pattern is a continuous emission of red, green, or blue light. The control unit 11 then starts control of the display element 61 to generate an image (mask) of the color corresponding to the image data read in step S11 (step S12). The control unit 11 emits light for a predetermined time from the laser diode 31G, 31R, or 31B of the light source unit 31 corresponding to the light emission pattern being set (step S13). The control unit 11 then determines whether or not to terminate the image display process, for example, by receiving an instruction from the user via the operation unit 12 (step S14). If the image display process is not to be terminated (step S14; NO), the process proceeds to step S13. If the image display process is to be terminated (step S14; YES), the image display process is terminated.

[0024] As shown in Figure 8, Image 70 is described as an example of an image that is displayed (projected). Image 70 is a no-entry sign image projected onto the floor outside the inaccessible entrance of the store "AA Store". Image 70 is a red image of a no-entry sign, and is actually composed of multiple red dots in a dot matrix. For example, the laser diode 31R emits light, which is diffracted by the diffractive optical element 51 into the light of the dot matrix. Then, each diffracted light is transmitted through the image (mask) corresponding to the red no-entry sign generated by the display element 61, and Image 70 is displayed on the object to be displayed. Image 70 is red and is in focus on the object to be displayed.

[0025] As shown in Figure 9, Image 80 is described as an example of an image that is displayed (projected). Image 80 is an image used to guide people towards the entrance, projected onto the floor outside the entrance of the store "AA Store". Image 80 is a green image in the shape of an arrow, and is actually composed of multiple green dots in a dot matrix. For example, the laser diode 31G emits light, which is diffracted by the diffractive optical element 51 into the light of the dot matrix. Then, each diffracted light passes through the green image (mask) generated by the display element 61, and Image 80 is displayed on the display target. Image 80 is green and is in focus on the display target. In this way, Images 70 and 80 are in focus on the display target. In other words, images using different colors (red, green, blue) are in focus on the display target without moving the projection device 1 and its components or the display target.

[0026] As described above, according to this embodiment, the projection device 1 comprises a light source unit 31, a diffractive optical element 51, a prism unit 41, a display element 61, and collimator lenses 421, 422, and 423. The light source unit 31 includes laser diodes 31G, 31R, and 31B that emit light in first, second, and third wavelength bands (G light, R light, and B light) that are different from each other. The diffractive optical element 51 diffracts the first, second, and third wavelength band light emitted from the light source unit 31. The prism unit 41 is provided between the light source unit 31 and the diffractive optical element 51 on the optical path of the first wavelength band light, the optical path of the second wavelength band light, and the optical path of the third wavelength band light, and includes a prism 411 provided on the optical path of the first wavelength band light, a prism 412 provided on the optical path of the second wavelength band light, and a prism 413 provided on the optical path of the third wavelength band light. The display element 61 projects an image onto the display object 2 by transmitting at least a portion of the light diffracted by the diffractive optical element 51 to form an image. The collimator lenses 421, 422, and 423 are positioned between the light source unit 31 and the diffractive optical element 51 on the optical paths of the first, second, and third wavelength bands, respectively. The distances between prism 411 and collimator lens 421, prism 412 and collimator lens 422, and prism 413 and collimator lens 423 are all different. The number of collimator lenses 421, 422, and 423 is the same as the number of laser diodes in the light source unit 31. Therefore, by adjusting the distance between each color prism and the collimator lens, the effect of axial chromatic aberration can be reduced, and the projection device 1 (image projection unit 20) can be miniaturized while focusing images using different colors (green, red, and blue) on the display object 2.

[0027] The second wavelength band light is light with a longer wavelength than the first wavelength band light. The first wavelength band light is light with a longer wavelength than the third wavelength band light. The lens includes a collimator lens 421 positioned on the optical path of the first wavelength band light, a collimator lens 422 positioned on the optical path of the second wavelength band light, and a collimator lens 423 positioned on the optical path of the third wavelength band light. The distance between collimator lens 421 and prism 411 is longer than the distance between collimator lens 422 and prism 412. The distance between collimator lens 423 and prism 413 is longer than the distance between collimator lens 421 and prism 411. Therefore, the effect of axial chromatic aberration is reduced, making it possible to focus images using colors with different wavelengths (green, red, and blue) on the display object 2.

[0028] The prism section 41 guides the first wavelength band light, the second wavelength band light, and the third wavelength band light into the same optical path. The second wavelength band light is light with a longer wavelength than the first wavelength band light. The first wavelength band light is light with a longer wavelength than the third wavelength band light. The distance between the laser diode 31R and the collimator lens 422 is longer than the distance between the laser diode 31G and the collimator lens 421. The distance between the laser diode 31G and the collimator lens 421 is longer than the distance between the laser diode 31B and the collimator lens 423. Therefore, the emission surfaces of the laser diodes 31G, 31R, and 31B can be arranged on the same plane.

[0029] The emission surfaces of the laser diodes 31G, 31R, and 31B are arranged to be approximately on the same plane. This allows for miniaturization of the projection device 1 (image projection unit 20). The number of collimator lenses 421, 422, and 423 is the same as the number of laser diodes 31G, 31R, and 31B. The prism unit 41 is positioned in the optical path between the collimator lenses 421, 422, and 423 and the diffractive optical element 51. This allows the laser diodes 31G, 31B, and 31G of the light source unit 31 to be arranged on the same line, simplifying the configuration of the light source unit 31.

[0030] Next, a modified example of the above embodiment will be described with reference to Figure 10. The device configuration of this modified example is such that the image projection unit 20 of the projection device 1 in the above embodiment is changed to the image projection unit 20a shown in Figure 10. For this reason, the parts of the projection device 1 that differ from the above embodiment will be mainly described, and the description of the similar parts will be omitted.

[0031] The image projection unit 20a includes a light source unit 31, a prism unit 41, a collimator lens 43, a diffractive optical element 51, and a display element 61. In the light source unit 31, laser diodes 31R, 31G, and 31B are arranged sequentially in the -z direction. The distance in the z-axis direction between the emission end of laser diode 31R and the emission end of laser diode 31B is denoted as distance D2R. The distance in the z-axis direction between the emission end of laser diode 31G and the emission end of laser diode 31B is denoted as distance D2G. The collimator lens 43 is a lens that converts the incident laser light into parallel light and emits it. The collimator lens 43 is positioned on the optical axis of the emitted light from the prism unit 41, between the prism unit 41 (prism 413) and the diffractive optical element 51. The collimator lens 43 converts the laser light incident from the prism unit 41 (prism 413) into parallel light and emits it in the +x direction to the diffractive optical element 51.

[0032] The laser diodes 31G, 31R, and 31B are positioned to achieve a focal length that reduces axial chromatic aberration. Specifically, the distance D2R is set to D2G. The laser light incident on the collimator lens 43 via the prism section 41 from the laser diodes 31G, 31R, and 31B becomes parallel light of equal width. Therefore, the R, G, and B light after passing through the diffractive optical element 51 and the display element 61 remains parallel light, and can be focused anywhere.

[0033] As described above, according to this modified configuration, the projection device 1 is equipped with one collimator lens 43. The prism section 41 is positioned in the optical path between the light source section 31 and the collimator lens 43. Therefore, it achieves the same effects as the above embodiment, and since there is only one collimator lens 43, the configuration of the projection device 1 (image projection section 20a) can be simplified.

[0034] The above description of the embodiment is merely an example of a projection device according to the present invention and is not limited thereto. For example, in the above embodiment, the light source unit 31 is configured to have laser diodes that emit red, green, and blue light, but is not limited thereto. The light source unit 31 may be configured to have at least one laser diode that emits light of colors other than RGB.

[0035] Furthermore, although the above embodiment describes a configuration in which the projection device 1 emits light from one of the GRB laser diodes of the light source unit 31 at a predetermined timing, it is not limited to this. The projection device 1 may be configured to emit light from at least two laser diodes of the light source unit 31 simultaneously. For example, two laser diodes may be provided for each color of the GRB, and the corresponding two laser diodes may emit light at the emission timing of each color. This makes the projected light from the projection device 1 brighter. In this case, a collimator lens corresponding to each laser diode is required. That is, the number of laser diodes and the number of collimator lenses are the same. Alternatively, the projection device 1 may be configured to emit light from at least two laser diodes of the light source unit 31 with different wavelengths in a time-sequential emission pattern. The field sequential method is a method of mixing the emitted light in time by switching the emission of laser light of different wavelengths in a short time.

[0036] Furthermore, although the above embodiment described a display element 61 that can switch each pixel of the liquid crystal panel between two grayscale states (on and off), it is not limited to this. The display element may also be able to switch each pixel between three or more grayscale states (for example, 256 grayscale states). That is, the orientation state and transmittance of the liquid crystal of each pixel of the liquid crystal panel may be switchable between three or more steps (for example, 256 steps). In this case, the image data should be such that the pixel value of each pixel can take the value of the number of display grayscale levels of the liquid crystal panel.

[0037] Furthermore, although a liquid crystal display element having a liquid crystal panel was described as the display element 61 in the above embodiment, the invention is not limited thereto. The display element may also be a reflective display element such as a DMD (Digital Micromirror Device) that projects an image by reflecting diffracted light from a diffracting optical element. A DMD has a plurality of micro-mirrors arranged in an array, and by switching the tilt angle of each micro-mirror according to the image data, it forms projected light having the image of the object to be projected onto using the reflected light from the plurality of micro-mirrors.

[0038] While embodiments of the present invention have been described, the scope of the present invention is not limited to the embodiments described above, but includes the scope of the invention as described in the claims and its equivalents. [Explanation of Symbols]

[0039] 1 Projection device, 31 Light source unit, 31R, 31G, 31B Laser diode, 41 Prism unit, 51 Diffractive optical element, 61 Display element, 421, 422, 423, 43 Collimator lens

Claims

1. A light source unit including a first light source that emits light in a first wavelength band and a second light source that emits light in a second wavelength band different from the first wavelength band, A diffractive optical element that diffracts the first wavelength band light and the second wavelength band light emitted from the light source unit, A light source and a diffractive optical element are provided on the optical path of the first wavelength band light and the optical path of the second wavelength band light, An optical path conversion unit including a first optical path conversion unit provided on the optical path of the first wavelength band light, and a second optical path conversion unit provided on the optical path of the second wavelength band light, A mask portion that projects an image onto a display surface by transmitting or reflecting at least a portion of the light diffracted by the diffractive optical element to form an image, The system comprises a lens disposed between the light source and the diffractive optical element in the optical paths of the first wavelength band light and the second wavelength band light, A projection device in which the distance between the first optical path conversion unit and the lens is different from the distance between the second optical path conversion unit and the lens.

2. The second wavelength band light is light with a longer wavelength than the first wavelength band light. The lens includes a first lens positioned on the optical path of the first wavelength band light and a second lens positioned on the optical path of the second wavelength band light. The projection apparatus according to claim 1, wherein the distance between the first lens and the first optical path conversion unit is longer than the distance between the second lens and the second optical path conversion unit.

3. The optical path conversion unit guides the first wavelength band light and the second wavelength band light into the same optical path. The second wavelength band light is light with a longer wavelength than the first wavelength band light. The projection apparatus according to claim 1, wherein the distance between the second light source and the lens is longer than the distance between the first light source and the lens.

4. The projection apparatus according to claim 1, wherein the emission surface of the first light source and the emission surface of the second light source are arranged to be substantially on the same plane.

5. The projection apparatus according to claim 1, wherein the lens is a collimator lens.

6. The projection apparatus according to claim 5, wherein the number of collimator lenses is one, or the same number as the number of light sources in the light source unit.

7. The wavelength of the first wavelength band light corresponds to green, The wavelength of the second wavelength band of light corresponds to red, The light source unit includes a third light source that emits light in the third wavelength band corresponding to the blue wavelength, The optical path conversion unit guides the first wavelength band light, the second wavelength band light, and the third wavelength band light into the same optical path. The projection apparatus according to claim 1, wherein the distance between the first light source and the lens is longer than the distance between the third light source and the lens.

8. The projection apparatus according to claim 1, wherein, when the number of lenses is one, the optical path conversion unit is arranged in the optical path between the light source unit and the lens.

9. The projection apparatus according to claim 4, wherein the optical path conversion unit is arranged between the lens and the diffractive optical element in the optical path when the number of lenses is the same as the number of light sources.

Images