Wavelength conversion plate, light source device and image projection equipment

Abstract

A wavelength conversion plate includes a conversion region and a reflection region on a substrate surface. The conversion region includes a wavelength conversion member configured to receive excitation light and produce a color different from the excitation light. The reflection region is configured to reflect the excitation light. The reflection region includes a transmissive diffuse surface, a transmissive layer, and a reflective surface. The transmissive diffuse surface is configured to diffuse the excitation light. The transmissive layer is configured to transmit the excitation light. The reflective surface is configured to reflect the excitation light. The transmissive diffuse surface is located at a position separated from the surface of the wavelength conversion member closer to the substrate surface, facing the direction of incident excitation light.

Description

Technical Field

[0001] This invention relates to wavelength conversion plates, light source devices, and image projection equipment. Background Technology

[0002] In recent years, projectors (image projection devices) that project various videos in a magnified manner have been widely used. A projector is a device that focuses light emitted from a light source onto a spatial optical modulation element (image display element), such as a digital mirror device (DMD) or a liquid crystal display element, and displays the emitted light (reflected light) from the spatial optical modulation element, modulated based on a video signal, on a screen as a color video.

[0003] Simultaneously, to project color video, an illumination source for at least three primary colors is required, and it is possible to generate all light sources as laser sources; however, this configuration is not preferred because the luminous efficiency of green and red lasers is lower than that of blue lasers. Therefore, the main method used is to apply blue laser as excitation light to a fluorescent material and generate red and green light from the fluorescence obtained by converting the wavelength of the fluorescent material. In contrast, the excitation light can be used as is to generate blue light, and thus, there are known techniques related to lighting devices that generate blue light and fluorescence in a temporal manner by using a portion of a fluorescent material substrate to which the fluorescent material is applied as part of a reflective area and sequentially interchanging the reflective area and the area where the fluorescent material is arranged.

[0004] Japanese Patent No. 6305009 discloses a technique for arranging a diffuse reflective surface that diffuses and reflects light on the surface of a metal substrate, in which fluorescent material is arranged on the surface of the metal substrate in a fluorescent wheel, and the emission of light from the light source and the excitation light source is controlled synchronously with the position of the diffuse reflective surface of the fluorescent material relative to the irradiation position of the excitation light. Japanese Unexamined Patent Application Publication No. 2017-181602 discloses a technique for arranging a light scattering layer on a substrate, in which micro-scattering material is dispersed in the material.

[0005] However, according to the conventional diffusion structure of the reflective surface set on the wavelength conversion plate, the emission position (the surface of the fluorescent material to which the excitation light is applied when viewed from the direction of the excitation light incident) and the diffusion position (the position of the transmission diffuse surface through which the excitation light first passes when viewed from the side of the excitation light incident) of the fluorescent material are different, making it difficult to optimize the light utilization efficiency of each of the fluorescence and blue light that serve as the excitation source, and making it difficult to improve the utilization efficiency.

[0006] Furthermore, according to conventional techniques, fluorescence travels from the surface of the fluorescent material into its interior, becoming slightly blurred relative to the illumination size of the excitation light applied to the surface, and possessing a larger fluorescence emission size than the illumination size of the excitation light. A difference exists between the fluorescence emission size and the emission size of the excitation light on the transmissive diffuse surface of the excitation light. In other words, according to conventional techniques, the problem lies in the difficulty of simultaneously optimizing the optical system that captures both fluorescence and blue light as the excitation source, thus hindering efficiency improvements.

[0007] The present invention was conceived in view of the above circumstances, and the object of the present invention is to provide a wavelength conversion plate, a light source device, and an image projection device that can improve light utilization efficiency. Summary of the Invention

[0008] According to one aspect of the invention, a wavelength conversion plate includes a conversion region and a reflection region on a substrate surface. The conversion region includes a wavelength conversion member configured to receive excitation light and produce a color different from the excitation light. The reflection region is configured to reflect the excitation light. The reflection region includes a transmissive diffuse surface, a transmissive layer, and a reflective surface. The transmissive diffuse surface is configured to diffuse the excitation light. The transmissive layer is configured to transmit the excitation light. The reflective surface is configured to reflect the excitation light. The transmissive diffuse surface is located at a position separated from the surface of the wavelength conversion member closer to the substrate surface, in the direction of incident excitation light.

[0009] According to one aspect of the invention, the size of the excitation light source can be set to a specific size close to the size of the light emission that diffuses in the conversion region, which serves as a secondary light source on the transmission-diffusing surface when the excitation light is applied. Therefore, the utilization efficiency of light undergoing wavelength conversion in the conversion region and light captured from the excitation light can be improved. Attached Figure Description

[0010] Figure 1 This is a schematic configuration diagram of a projector according to the first embodiment;

[0011] Figure 2A and 2B This is a schematic diagram showing the configuration of the light source unit;

[0012] Figures 3A to 3C This is a diagram illustrating an example configuration of the wavelength conversion element;

[0013] Figures 4A to 4C This is a diagram illustrating an example of reflection in a wavelength conversion element;

[0014] Figure 5 This is a schematic diagram illustrating the diffusion of light in a conventional wavelength conversion element;

[0015] Figure 6 This is a schematic diagram illustrating the diffusion state of light in the wavelength conversion element of this embodiment;

[0016] Figure 7A and 7B This is a diagram showing a cross-section of the modified wavelength conversion element;

[0017] Figure 8 This is an unfolded cross-sectional view of the wavelength conversion element according to the second embodiment;

[0018] Figure 9 This is a diagram showing the range of the incident direction of the excitation light according to the third embodiment; and

[0019] Figure 10 This is a magnified view of the position where the excitation light is irradiated.

[0020] The accompanying drawings are intended to illustrate exemplary embodiments of the invention and should not be construed as limiting its scope. In the various drawings, the same or similar reference numerals denote the same or similar components. Detailed Implementation

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0022] As used herein, the singular forms “one,” “a,” and “the” are intended to also include the plural forms, unless the context clearly indicates otherwise.

[0023] In describing the preferred embodiments shown in the accompanying drawings, specific terminology may be used for clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology chosen so far, and it should be understood that each specific element includes all technical equivalents that have the same function, operate in a similar manner, and achieve similar results.

[0024] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Embodiments of the wavelength conversion plate, the light source device, and the image projection apparatus will be described in detail below with reference to the accompanying drawings.

[0025] First Embodiment

[0026] Figure 1 This is a schematic configuration diagram of the projector 1 according to the first embodiment.

[0027] The projector (image projection device) 1 includes a housing 10, a light source device 20, a light homogenizing element 30, an illumination optical system 40, an image forming element (image display element) 50, a projection optical system 60, a control device 80, and a color wheel 90.

[0028] The housing 10 houses the light source device 20, the light homogenization element 30, the illumination optical system 40, the image forming element 50, the projection optical system 60, the control device 80, and the color wheel 90.

[0029] For example, the light source device 20 emits light having wavelengths corresponding to each RGB color. The light source device 20 includes light source units 20A and 20B, and an optical path combining element 20C as a combining unit. Light source units 20A and 20B have the same configuration and emit luminous flux with a predetermined shape. The internal configuration of light source units 20A and 20B will be described in detail later. The luminous flux emitted from light source units 20A and 20B is deflected by the optical path combining element 20C and enters the incident-side surface of the light homogenizing element 30. In this embodiment, a prism is illustrated as an example of the optical path combining element 20C, but the embodiment is not limited to this example.

[0030] like Figure 1 As shown, the projector 1 causes the light flux emitted from the light source unit 20A and the light source unit 20B in opposite directions and focused to be reflected by two reflective parts ( Figure 1 The optical path combining element 20C reflects and deflects light, and the two reflecting parts form an angle of about 90 degrees, so that the light flux is reflected in the same direction, and the focused light flux is combined in an adjacent or partially overlapping manner and simultaneously input to the light homogenizing element 30.

[0031] Meanwhile, in this embodiment, an example is shown where the light source device 20 includes two light source units 20A and 20B. However, the embodiment is not limited to this example, and more than two light sources, such as four light sources, can be used to synthesize light.

[0032] The light homogenizing element 30 homogenizes the light emitted from the light source device 20 by mixing the light. More specifically, the light homogenizing element 30 diffuses the luminous flux input from the incident side surface within the light homogenizing element 30, while repeatedly reflecting the luminous flux and outputting the luminous flux from the emitting surface. The light homogenizing element 30 internally reflects the luminous flux input from the incident side surface multiple times, forming a uniform surface light source on the output surface. As the light homogenizing element 30, for example, a hollow light tunnel in which four mirrors are combined on the inner surface, or a prism-shaped rod integrator made of a transparent material such as glass or a compound eye lens, can be used. For example, if a light tunnel is used as the light homogenizing element 30, by adopting an aspect ratio approximately the same as that of the image forming element 50, the exit of the light tunnel has the same shape as the shape projected onto the surface of the image forming element 50, thereby effectively illuminating the surface of the image forming element 50 without any waste.

[0033] The illumination optical system 40 illuminates the image forming element 50 approximately uniformly with light homogenized by the light homogenizing element 30. The illumination optical system 40 includes, for example, one or more lenses, one or more reflective surfaces, etc.

[0034] The image forming element 50 includes a light bulb, such as a digital micromirror device (DMD), a transmissive liquid crystal panel, or a reflective liquid crystal panel. The image forming element 50 modulates the light emitted by the illumination optics system 40 (light from the light source optics system of the light source device 20) and forms an image.

[0035] The control device 80 performs switching on the surface of the image forming element 50 in units of pixels by applying illumination light, for example, based on the reflection or transmission of the input image to the image forming element 50, and guides the illumination light to the projection optics system 60.

[0036] The projection optics system 60 projects an image formed by the image forming element 50 onto a screen (projection target screen) 70 in a magnified manner. The projection optics system 60 includes, for example, one or more lenses. The projection optics system 60 has a conjugate relationship such that an image on the surface of the image forming element 50 is formed as a magnified image at a specific location on the desired screen (projection target screen) 70, and thus a spatially modulated image is projected onto the surface of the image forming element 50 in a magnified manner.

[0037] Furthermore, a color wheel 90 is arranged at the light outlet of the light homogenization element 30. The color wheel 90 has the function of switching between color filters in order to extract at least the blue light component, green light component, and red light component. The color wheel 90 enables the wavelength conversion element 26 (see [reference]) used in the light source unit 20A and light source unit 20B to... Figure 2A and 2B The rotation of the color wheel 90 is synchronized with the rotation of the color wheel 90, driving the switching between color filters in a synchronized manner, and displaying images on the surface of the image forming element 50 according to the switching timing, thereby sequentially displaying monochrome images. As described above, the switching time is faster than the eye's response speed, so the image is recognized as a color image.

[0038] Figure 2A and 2B This is a schematic diagram showing the configuration of the light source unit 20A. Meanwhile, the light source unit 20B has the same configuration. Figure 2A The diagram shows the state when blue laser light (the first color light) is generated. Figure 2B The state when fluorescence (second color light) is generated is shown.

[0039] The light source unit 20A (20B) includes a laser light source (excitation light source) 21, a collimating lens 22 arranged according to each light source, a first lens group 23, a dichroic mirror 24, a second lens group 25, a wavelength conversion element 26 serving as a wavelength conversion plate, and a third lens group 27, all of which are arranged sequentially in the light diffusion direction. For example, the components in the light source device 20 other than the laser light source 21 constitute a "light source optical system". In the light source unit 20A (20B), all the above-mentioned units are arranged in the diffusion order of the excitation light emitted from the laser light source 21.

[0040] The laser source 21 includes multiple light sources (light-emitting points). As the laser source 21, a so-called laser diode is used. Figure 2A and 2B The drawing shows six light sources arranged vertically, but in reality, four rows of six light sources are arranged in the orthogonal direction (depth direction) of the drawing, resulting in 6 × 4 = 24 light sources arranged in a two-dimensional manner. Each light source 21 emits light (blue laser) in the blue band with a center wavelength of, for example, 440 nm to 465 nm, as excitation light for the fluorescent material included in the wavelength conversion element 26.

[0041] The blue laser light (first color light) emitted from each source of laser source 21 is linearly polarized light with a constant polarization state, and is arranged to become S-polarized light relative to the dichroic mirror 24. The blue laser light emitted from each source of laser source 21 is coherent light. Furthermore, the excitation light emitted from each source of laser source 21 is not limited to light in the blue band, and it is desirable that it can excite light with a specific wavelength from the fluorescent material included in the wavelength conversion element 26.

[0042] Although an example of laser source 21 comprising multiple light sources is shown, a single laser source may also be used. Furthermore, light source units arranged in an array on a substrate may be used as laser source 21, but the embodiments are not limited to this example.

[0043] Twenty-four collimating lenses 22 are arranged according to the 24 light sources of the laser source 21. Each collimating lens 22 adjusts the excitation light emitted from each light source of the laser source 21 to obtain parallel light. The number of collimating lenses 22 is sufficient to correspond to the number of light sources of the laser source 21, and can be increased or decreased according to the increase or decrease of the number of light sources of the laser source 21.

[0044] The excitation light emitted from the laser source 21 is adjusted into approximately parallel light by the collimating lenses 22 corresponding to each light source of the laser source 21. The excitation light, adjusted into approximately parallel light, is reduced and converted into a fine light flux by the first lens group 23, and then guided to the dichroic mirror 24.

[0045] The dichroic mirror 24 is a glass plate with a parallel flat plate shape. The incident surface of the dichroic mirror 24 is coated to reflect S-polarized light (first polarization component) in the wavelength band of the excitation light guided from the first lens group 23, and transmit P-polarized light (second polarization component) in the wavelength band of the excitation light guided from the first lens group 23 and fluorescence (second color light) from the wavelength conversion element 26.

[0046] The center of the dichroic mirror 24 is shifted relative to the optical axis of the second lens group 25, so that the excitation light is input at an angle relative to the normal of the wavelength conversion element 26.

[0047] Although a dichroic mirror 24 with a flat plate shape is used in this embodiment, a prism type can also be used. Furthermore, in this embodiment, the dichroic mirror 24 reflects S-polarized light and transmits P-polarized light in the wavelength band of the excitation light; conversely, it can also reflect P-polarized light and transmit S-polarized light in the wavelength band of the excitation light.

[0048] like Figure 2A As shown, the excitation light reflected by the dichroic mirror 24 is guided by the second lens group 25, which serves as a focusing optical system, to the wavelength conversion element 26, and the desired focusing point is formed on the wavelength conversion element 26. In the blue reflective region A3 of the wavelength conversion element 26 (see...) Figures 3A to 3C The excitation light reflected from the mirror 24 is transmitted again through the second lens group 25, passes through the side of the optical axis of the second lens group 25 opposite to the dichroic mirror 24, passes through the third lens group 27, is polarized by the optical path combining element 20C, and enters the light homogenizing element 30. The light homogenizing element 30 homogenizes the incident light.

[0049] In addition, such as Figure 2B As shown, if excitation light is incident on the fluorescent material regions of wavelength conversion element 26 (yellow fluorescent material region A1 and green fluorescent material region A2: see...) Figures 3A to 3C The fluorescent molecule emits fluorescence in a 360-degree radius around itself, the wavelength of which is converted upon receiving excitation light. The fluorescence emitted in the fluorescent material region of the wavelength conversion element 26 includes either a yellow or green component. Additionally, the excitation light reflected by the surface of the substrate 26a (substrate surface) of the wavelength conversion element 26 (see...) Figures 3A to 3C The fluorescence passes through the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) again, and emits fluorescence with a Lambertian distribution on the surface of the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2). The fluorescence emitted in the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) of the wavelength conversion element 26 is transmitted via the optical path combining element 20C (in... Figure 2A and 2B(omitted) is guided to the light homogenizing element 30. More specifically, the fluorescence is adjusted to approximately parallel light by the second lens group 25, refracted by the third lens group 27 to focus near the light homogenizing element 30, deflected by the optical path combining element 20C, and enters the light homogenizing element 30.

[0050] Figures 3A to 3C This is a diagram showing an example configuration of the wavelength conversion element 26.

[0051] Figure 3A This is a plan view of wavelength conversion element 26. (See diagram below.) Figure 3A As shown, the wavelength conversion element 26 according to this embodiment has a disk shape. The wavelength conversion element 26 is a wavelength conversion plate in which three sections, such as a yellow fluorescent material region (first wavelength conversion region) A1 which is a conversion region including a wavelength conversion member (yellow fluorescent material) 26f, a green fluorescent material region (second wavelength conversion region) A2 which is a conversion region including a wavelength conversion member (green fluorescent material) 26g, and a blue reflective region A3 in which light emitted from the laser light source (excitation light source) 21 is reflected (in other words, a non-conversion region in which light received from the laser light source (excitation light source) 21 is emitted without wavelength conversion), are formed in a strip-like manner around the periphery of the disk-shaped plate at a desired angle.

[0052] The yellow fluorescent material region A1 is formed, for example, by yellow fluorescent material 26f, which receives a blue laser as excitation light and emits fluorescence in the yellow wavelength range. The green fluorescent material region A2 is formed, for example, by green fluorescent material 26g, which receives a blue laser as excitation light and emits fluorescence in the green wavelength range.

[0053] In this embodiment, two fluorescent materials are used: a yellow fluorescent material region A1 and a green fluorescent material region A2. However, this embodiment is not limited to this example. For instance, only the yellow fluorescent material region A1 may be used, or a red fluorescent material region may be added.

[0054] Meanwhile, the color wheel 90 includes color filters for extracting desired color components from the fluorescent material. The color wheel 90 extracts necessary components, such as green or red components, from the fluorescence in a time-division manner by sequentially switching between the color filters. To sequentially switch between the color filters as described above, a segment is set for each color filter and rotation is performed by a rotary motor, such that it is sufficient to sequentially switch the desired color filter from one to another.

[0055] Furthermore, the disc-shaped wavelength conversion element 26 is rotated by a drive unit controlled by the control device 80, allowing the yellow fluorescent material region A1, the green fluorescent material region A2, and the blue reflective region A3 to be moved sequentially in a periodic manner. A rotary motor M is typically preferred as the drive unit for this movement mechanism. Moreover, as the drive unit rotates, the wavelength conversion element 26 switches between the yellow fluorescent material region A1, the green fluorescent material region A2, and the blue reflective region A3 at a focusing point where light is applied from the laser source (excitation source) 21, thus emitting light of different wavelengths in a time-division manner.

[0056] Meanwhile, in the light source unit 20A (20B), light absorption or reflection components are arranged on the wheel of the wavelength conversion element 26 or on the component that supports and rotates the wheel, and based on the detection using an optocoupler, the rotation speeds of the two wavelength conversion elements 26 are equal.

[0057] Figure 3B It is along Figure 3B The cross-sectional view taken from line A-A'. (See example.) Figure 3B As shown, the wavelength conversion element 26 includes a transparent plate 26c in the blue reflective region A3. The transparent plate 26c is a transparent plate member on the disk-shaped substrate 26a via a bonding layer 26b. Meanwhile, as described above, the laser source 21 emits light (blue laser) in the blue band with a center wavelength of, for example, 440 nm to 465 nm as excitation light.

[0058] like Figure 3B As shown, the plate 26c forming the blue reflective region A3 includes a transmissive diffuse surface 261 for diffusely transmitting excitation light, a transmissive layer 262 for transmitting excitation light, and a reflective surface 263 for reflecting excitation light. In the plate 26c, one side surface serves as the transmissive diffuse surface 261, and the other side surface facing the transmissive diffuse surface 261 serves as the reflective surface 263. The plate 26c is made of BK7 glass, quartz glass with high thermal conductivity, sapphire, synthetic glass, etc.

[0059] The transmissive diffuse surface 261 of the plate 26c is formed by performing a roughing process on the glass surface. For example, as a roughing process, processing techniques used to obtain frosted glass can be used, such as etching using sandblasting or solvents. Furthermore, the transmissive diffuse surface 261 of the plate 26c can be formed using microprisms or microlenses. Meanwhile, the transmissive diffuse surface in this example represents a surface in which light is not deflected in a particular direction at the interface, but is transmitted, such that the luminous flux travels while diffusing to a certain extent.

[0060] It is sufficient to form the reflective surface 263 of the plate 26c using conventional methods for forming ordinary mirrors. For example, a thin film can be formed using a metal such as aluminum by vapor deposition or sputtering, and then the plate 26c can be formed. Alternatively, a reflective film can be formed on the plate 26c to increase the reflectivity in the wavelength region of the excitation light. Since the reflective film is a thin film, its thickness is negligible. Specifically, the plate 26c can be formed from a dielectric multilayer film, and a mass production method has been established for this purpose.

[0061] like Figure 3B As shown, when the blue laser light passes through the transmissive diffuse surface 261 of the plate 26c, the light flux diffuses at a certain angle relative to the main beam. Figure 3B As shown, the diffused light flux is transmitted through the plate 26c and reaches the reflecting surface 263 facing the transmissive diffuse surface 261. The light flux that has been transmitted through the plate 26c is mirror-reflected by the reflecting surface 263, reaches the incident surface (transmissive diffuse surface 261) again, and is output from the plate 26c, while further diffusing at a specific angle. The plate 26c is configured such that when the light flux is output, the light flux diffuses from the transmissive diffuse surface 261 at a small angle. Preferably, the diffusion angle is a few degrees, which can be in the range of approximately a few degrees to 10 degrees, and can be up to approximately 20 degrees. The blue laser essentially passes through the transmissive diffuse surface 261 of the plate 26c twice. Therefore, the light flux reflected by the reflecting surface 263 of the plate 26c is diffused and output with a diffusion angle of approximately twice that of the transmissive diffuse surface 261. Therefore, it is sufficient to set the diffusion angle of the transmissive diffuse surface 261 of the plate 26c such that the diffusion angle is approximately half of the desired diffusion angle of the reflected light. Therefore, when you want to diffuse light at a desired angle, it is sufficient to set a diffusion angle that is about half of the desired diffusion angle, so that a transmissive diffuse surface 261 can be easily formed.

[0062] Therefore, the blue laser entering the reflective surface 263 of the plate 26c at a specific angle passes through the transmissive diffuse surface 261 twice with a small diffusion angle, thus being optimized so that the light flux diffuses in the desired manner.

[0063] Here, the need for diffusion of the excitation light, which is a blue laser, will be described. To achieve a projector 1 with practical brightness, several thousand lumens of brightness are required. For this, the excitation light needs at least tens of watts (W) of power. A laser source 21 with a blue wavelength range is advantageous as a light source with tens of W of power. A so-called laser diode is used as the laser source 21. However, while laser diodes are efficient light sources capable of achieving high output power, they have high directionality and coherence, which can cause flickering in the projected image, a condition known as speckle. To eliminate this condition, directionality and coherence can be reduced by passing the laser through a diffuser. To reduce speckle as described above, a diffuser plate is typically arranged in the laser's optical path; however, in this embodiment, a transmissive diffuser surface 261 is arranged in the focusing optical path toward the fluorescent material (near the focusing point) to reduce speckle.

[0064] In addition, such as Figure 3B As shown, when viewed along the incident direction of the blue laser, the closest position of the transmissive diffuse surface 261 of the plate 26c is used as the emission position of the blue light source reflected by the reflective surface 263 of the plate 26c, for capture and use by the optical system in subsequent stages.

[0065] Figures 4A to 4C This is a diagram showing an example of reflection in wavelength conversion element 26. Figure 4A This shows the state of the blue laser entering the blue reflection region A3. Figure 4B The diagram illustrates the state of blue laser light being diffused and reflected by the blue reflection region A3, and... Figure 4C The diagram shows the state where a blue laser enters the fluorescent material region (yellow fluorescent material region A1 and green fluorescent material region A2) and emits fluorescence.

[0066] like Figure 4A and Figure 4B As shown, if a blue laser enters the blue reflection region A3 of the wavelength conversion element 26 at an angle, the spot size of the blue laser formed on the transmission diffuse surface 261 (excitation light irradiation region) is diffused by the transmission diffuse surface 261 of the plate 26c and reflected by the reflection surface 263 of the plate 26c. Therefore, the diffused light is diffused, and the light flux that has been reflected by the reflection surface 263 of the plate 26c re-enters the transmission diffuse surface 261 from the rear side, passes through the transmission diffuse surface 261 a second time, and is output on the transmission diffuse surface 261 with a larger focusing point than the first incident point.

[0067] In comparison, such as Figure 4CAs shown, if the wavelength conversion element 26 rotates, and blue laser light is input into the fluorescent material region (yellow fluorescent material region A1 and green fluorescent material region A2) of the wavelength conversion element 26 in an oblique direction, this region is affected by the direction along... Figure 3A The cross-section taken from C-C' in the image indicates that blue laser light is used as the excitation light. Simultaneously, fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) are formed on the reflective surface 26d of the substrate 26a in the wavelength conversion element 26. In this case, the surfaces of the fluorescent materials 26f and 26g in the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) emit slightly diffused fluorescence. In this way, the emission size of the excitation light emitted from the blue reflective region A3 on the transmissive diffuse surface 261 is close to or becomes the same as the light source size of the fluorescence diffused in the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2).

[0068] If the configuration described above is not used, diffused light with a reduced spot size of the focusing point is obtained, causing the light to be emitted as if blue light were emitted on the transmissive diffuse surface 261, and the light homogenizing element 30 captures the light with a small emission size and applies it to the panel. In this case, the problem with the lighting optics system designed with priority given to the emission size of the fluorescence is that it is difficult to homogenize the light with a small blue emission size.

[0069] Back Figures 3A to 3C , Figure 3C It is along Figure 3A The developed diagram of the cross section taken along line B-B'. (See figure.) Figure 3C As shown, the blue reflective region A3 includes a transmissive diffuse surface 261, a transmissive layer 262, and a reflective surface 263 for diffuse excitation light.

[0070] The wavelength conversion element 26 is formed by continuously connecting a yellow fluorescent material region A1, a green fluorescent material region A2, and a blue reflective region A3 in a ring. The yellow fluorescent material region A1, the green fluorescent material region A2, and the blue reflective region A3 are adjacent to each other because they are formed continuously in a ring. Specifically, as... Figure 3C As shown, when unfolded along the cross-section B-B' of the arc, the blue reflective region A3 and the yellow fluorescent material region A1 continuously follow the green fluorescent material region A2. By arranging the yellow fluorescent material region A1, the green fluorescent material region A2, and the blue reflective region A3 in a continuous manner as described above, the time spent traversing the boundary between these regions when the focusing point passes through them can be minimized. This configuration reduces optical losses caused by so-called spoke time.

[0071] In addition, such as Figure 3C As shown, the transmissive diffuse surface 261 of the blue reflective region A3 is positioned in the direction of excitation light incidence, separated from the surfaces of the fluorescent materials 26f and 26g constituting the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) on the substrate 26a side. More specifically, in Figure 3C In the example shown, the height of the blue reflective region A3 is higher than the heights of the yellow fluorescent region A1 and the green fluorescent region A2. That is, as seen in the incident direction, the transmissive diffuse surface 261 formed in the blue reflective region A3 is closer to the excitation source than the surfaces of the yellow fluorescent region A1 and the green fluorescent region A2. In other words, the distance between the transmissive diffuse surfaces 261 of the substrate 26a and the plate 26c has a finite value. Also, in this example, "height" refers to the relative positional relationship.

[0072] Typically, the yellow fluorescent material region A1 and the green fluorescent material region A2 of the wavelength conversion element 26 are coated on the surface of the substrate 26a with a limited thickness. Since the yellow fluorescent material region A1 and the green fluorescent material region A2 formed on the substrate 26a have a limited thickness, they inevitably separate from the surface of the substrate 26a.

[0073] Furthermore, this means that when the positional relationship between the surface of the blue reflective region A3 and the substrate 26a is determined, the position of the transmissive diffuse surface 261 of the plate 26c is at a finite distance toward the surface of the wavelength conversion element 26.

[0074] like Figure 3C As shown, in this embodiment, the height of the transmissive diffuse surface 261 of the plate 26c in the blue reflective region A3 is determined such that the following relationship is established, wherein the thickness of each of the yellow fluorescent material region A1 and the green fluorescent material region A2 is represented by k, and the height of the transmissive diffuse surface 261 of the plate 26c from the surface of the substrate 26a in the blue reflective region A3 is represented by h.

[0075] k <h<2k

[0076] Meanwhile, 2k h represents twice the thickness of each of the yellow fluorescent material region A1 and the green fluorescent material region A2.

[0077] Meanwhile, if the height h of the transmissive diffusive surface 261 of the flat plate 26c in the blue reflection region A3 from the surface of the substrate 26a is equal to or greater than twice the thickness of each of the yellow fluorescent material region A1 and the green fluorescent material region A2, an efficiency approximately the same as that obtained when h is zero is obtained, and the effect is reduced. In other words, compared with the conventional technology, in order to improve the efficiency, if the height h of the transmissive diffusive surface 261 of the flat plate 26c in the blue reflection region A3 from the surface of the substrate 26a is set within a specific range such that k < h < 2k, the light utilization efficiency can be significantly improved.

[0078] Meanwhile, ideally, the surfaces of the yellow fluorescent material region A1 and the green fluorescent material region A2 have the same height (the same distance from the second lens group 25) as the transmissive diffusive surface 261 of the flat plate 26c in the blue reflection region A3, that is, h = k. However, since the yellow fluorescent material region A1 and the green fluorescent material region A2 are made of materials different from those of the blue reflection region A3, strictly speaking, a specific step occurs during the manufacturing process of the wavelength conversion element 26. In this embodiment, the acceptable range of this step is defined.

[0079] Due to the diffusion of the blue laser as the excitation light, the transmissive diffusive surface 261 of the flat plate 26c in the blue reflection region A3 serves as a light source as a secondary light source. In contrast, the yellow fluorescent material region A1 and the green fluorescent material region A2 perform wavelength conversion to obtain a wavelength longer than the blue excitation light In other words, for the wavelength that acts on the transmissive diffusive surface 261 of the flat plate 26c and the wavelength that is emitted as fluorescence from the yellow fluorescent material region A1 and the green fluorescent material region A2, the wavelength that acts on the transmissive diffusive surface 261 of the flat plate 26c is shorter, and a certain degree of chromatic aberration appears. Post-focusing can be reduced by using a shorter wavelength, and thus, the condensing efficiency can be improved.

[0080] For example, the transmissive diffusive surface 261 of the flat plate 26c in the blue reflection region A3 is located at a height of about 0.3 millimeters (mm) (300 micrometers (μm)) from the surface of the substrate 26a, and each of the yellow fluorescent material region A1 and the green fluorescent material region A2 has a thickness of about 0.2 mm (200 micrometers).

[0081] The effects of this embodiment will be described below.

[0082] Figure 5 is a schematic diagram showing the state in which light travels in a conventional wavelength conversion element, Figure 6 is a schematic diagram showing the state in which light travels in the wavelength conversion element 26 of this embodiment.

[0083] Initially, it is desired that the surfaces of the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) and the entrance (e.g., optical tunnel) of the light homogenization element 30 have an optical conjugate relationship. In other words, the spacing with the focusing element, including the second lens group 25 and the third lens group 27, is determined and set such that the focusing point of the excitation light on the surfaces of the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) is minimized.

[0084] Fluorescence with a specific size corresponding to the focal spot size is generated; therefore, the size of the fluorescence source depends on the position of the wavelength conversion element 26. In other words, to effectively utilize the fluorescence, it is desirable to reduce the focal spot size. Therefore, the wavelength conversion element 26 is arranged such that the excitation light forms the smallest possible focal spot via the optical system. Typically, the focal spot size of the excitation light is about a few millimeters, and in some cases, it is 1 millimeter or less.

[0085] like Figure 5 As shown, in conventional technology, the thickness of the fluorescent material layer separating the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) from the light-concentrating element, which includes the second lens group 25 and the third lens group 27, is as follows. Figure 5 As shown, when excitation light is applied to the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) and fluorescence is emitted, the emission point of the fluorescence is designated as the object point (position A). The light emitted from the object point (position A) is focused by the second lens group 25 and then by the third lens group 27 near the entrance of the light homogenizing element 30. In other words, the surfaces of the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) and the entrance of the light homogenizing element 30 are arranged to have an optical conjugate relationship.

[0086] like Figure 5 As shown, if the conventional wavelength conversion element rotates and the excitation light is reflected by the diffuse surface, the diffuse surface has a specific positional relationship (position B), thereby separating from the focusing element comprising the second lens group 25 and the third lens group 27. Figure 5 As shown, in this state, the position that obtains a conjugate relationship with position B is located in front of the entrance of the light homogenizing element 30. In this state, the blue laser light, bent and reflected by the diffuse surface, reaches the entrance of the light homogenizing element 30 as a diffused light flux, resulting in some light not captured by the light homogenizing element 30, which leads to a reduction in light utilization efficiency.

[0087] In comparison, such as Figure 6As shown, if the wavelength conversion element 26 of this embodiment is used, the surface position of the fluorescent material region (yellow fluorescent material region A1 and green fluorescent material region A2) and the position of the transmission and diffusion surface 261 of the plate 26c in the blue reflection region A3 are roughly aligned, so that the optical conjugate position can be aligned at the entrance of the light homogenization element 30, the optimal positional relationship between fluorescence and blue light can be maintained, and optical loss can be reduced.

[0088] In this manner, according to this embodiment, the transmissive diffuse surface 261 of the blue reflective region A3 is located at a higher position than the rear surface of the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) that serve as wavelength conversion components. This allows the light source size of the excitation light to be set to a specific size close to the luminescent size diffused in the conversion region, which serves as a secondary light source on the transmissive diffuse surface 261 when the excitation light is applied. Therefore, the same utilization efficiency can be achieved between the light undergoing wavelength conversion in the conversion region and the light captured from the excitation light.

[0089] Furthermore, the transmissive diffuse surface 261 of the blue reflective region A3 is positioned separately from the surfaces of the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) in the direction of excitation light incidence, allowing the transmissive diffuse surface 261 to be positioned closer to the surfaces of the fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2). Therefore, the wavelength-converted light and the reflected light from the excitation light can be effectively used as illumination light. More specifically, the blue light, as the excitation light, is diffused by the transmissive diffuse surface 261, and the transmissive diffuse surface 261 serves as a light source as a secondary light source. In contrast, the wavelength of fluorescence is converted to a longer wavelength than the blue excitation light. In other words, for the wavelength that functions in the transmissive diffuse surface 261 and the wavelength that functions as fluorescence, the wavelength that functions in the transmissive diffuse surface 261 is shorter, resulting in chromatic aberration. Backfocusing can be reduced by using a shorter wavelength, thus improving focusing efficiency.

[0090] In other words, according to the projector 1 of this embodiment, the blue light from the laser diode light source is output and used as blue light as is, but the blue light passes through the transmissive diffuse surface 261 of the blue reflective region A3 twice, which ensures uniformity and reduces the speckle of the laser, and a high-quality projected image can be obtained.

[0091] Meanwhile, in this embodiment, assuming that the thickness of each of the yellow fluorescent material region A1 and the green fluorescent material region A2 is represented by k, and the height of the transmission diffuse surface 261 of the plate 26c in the blue reflective region A3 from the surface of the substrate 26a is h, the height of the transmission diffuse surface 261 of the plate 26c in the blue reflective region A3 is determined such that the following relationship is obtained.

[0092] k <h<2k

[0093] However, the embodiments are not limited to this example, and the height can be set such that 0 < h < 2k. In conventional technology, the transmissive diffuse surface 261 is separated from the surface of the fluorescent material layer by the thickness of the fluorescent material layer when viewed from the condenser lens. That is, a position where h = 0 is used. Compared to this state, if the transmissive diffuse surface 261 is located closer to the condenser lens, that is, if the height is set such that h > 0, the focus can be adjusted at a position closer to the fluorescent surface, and the light utilization efficiency of the illumination device that uses wavelength-converted (fluorescent) light and excitation light as blue light can be improved.

[0094] Furthermore, the transmissive diffuse surface 261 of the plate 26c in the blue reflective region A3 can also be located at the same position as the surfaces of the yellow fluorescent material region A1 and the green fluorescent material region A2 when viewed from the direction of excitation light incidence. In other words, assuming that the thickness of each of the yellow fluorescent material region A1 and the green fluorescent material region A2 is represented by k, and the height of the transmissive diffuse surface 261 of the plate 26c in the blue reflective region A3 from the surface of the substrate 26a is represented by h, the height of the transmissive diffuse surface 261 of the plate 26c in the blue reflective region A3 can be determined such that the following relationship is obtained.

[0095] k = h

[0096] The distance (back focal length) to the second lens group 25 used to capture fluorescence and diffuse light is very small. In contrast, if the wavelength conversion element 26 is rotated, the surface of the second lens group 25 moves at a high speed above the wavelength conversion element 26 while maintaining a tiny gap. Therefore, by eliminating the step on the wavelength conversion element 26, wind noise or physical obstacles can be prevented.

[0097] However, this does not mean that the transmissive diffuse surface 261 can be separated from the substrate 26a without restriction. If there is an ideal focal position, it is typically designed to be optimized at that ideal focal position as part of a general optical design for robustness. For example, in conventional techniques, if the position is optimized on the fluorescent surface, even at a distance of +k (corresponding to the thickness of the yellow fluorescent region A1 and the green fluorescent region A2) when viewed from the condenser lens, a certain efficiency in capturing reflected light by the transmissive diffuse surface 261 is ensured. Without special design, even if the focal point is moved forward by -k in the opposite direction, it is generally possible to obtain performance that is approximately the same as that at the original position at a distance of +k (characterized by the target being normal regarding focal deviation). Utilizing the technical concept of the present invention, efficiency can be further improved, at least compared to conventional techniques, simply by setting the transmissive diffuse surface 261 to be within Δk (less than ±k) of the fluorescent surface, without requiring special design features. Therefore, by setting the height of the transmission diffuse surface 261 such that 0 < h < 2k, the height of the transmission diffuse surface 261 relative to the fluorescent surface is within ±k, thereby improving efficiency compared to the position where h = 0.

[0098] Revise

[0099] One modification will be described below.

[0100] Figure 7A and 7B This is a diagram showing a cross-section of the modified wavelength conversion element 26. Figure 7A This is a cross-sectional view of the blue reflective area A3. Figure 7B It is a cross-sectional view of the fluorescent material region (yellow fluorescent material region A1 and green fluorescent material region A2).

[0101] like Figure 7A and 7B As shown, the modified wavelength conversion element 26 includes a circular or arc-shaped groove 26e along the outer periphery of the substrate 26a. In the wavelength conversion element 26, a yellow fluorescent material region A1, a green fluorescent material region A2, and a blue reflective region A3 are formed in the groove 26e formed in the substrate 26a. Figure 7A and 7B As shown, the bottom surface of the groove 26e, which is in contact with the yellow fluorescent material region A1, the green fluorescent material region A2, and the blue reflective region A3, serves as the surface of the substrate 26a, and the transmissive diffuse surface 261 of the plate 26c is positioned at a limited distance from the bottom surface of the groove 26e.

[0102] Second Embodiment

[0103] The second embodiment will now be described.

[0104] The second embodiment differs from the first embodiment in that light transmitted through the plate 26c in the blue reflective region A3 is reflected by the surface of the substrate 26a in the wavelength conversion element 26. In the following description of the second embodiment, explanations of components identical to those in the first embodiment are omitted, and the differences from the first embodiment will be described.

[0105] Figure 8 This is a cross-sectional view of the wavelength conversion element 26 according to the second embodiment. Figure 3B In the diagram, only the diffuse state of the outermost surface is shown; however, as... Figure 8 As shown, in the actual behavior of light, in the blue reflective region A3, the main beam of light from the transmissive diffuse surface 261 of the plate 26c diffuses at a diffuse angle, is reflected by the reflective surface 263 of the plate 26c, and is further diffused as it travels through the transmissive diffuse surface 261 in the opposite direction.

[0106] Therefore, as Figure 8 As shown, in the wavelength conversion element 26 according to this embodiment, the surface of the plate 26c is used as a transmissive diffuse surface 261, the other surface facing the transmissive diffuse surface 261 is formed as a transparent surface, and light is reflected by the surface of the substrate 26a. The plate 26c is attached to the surface of the substrate 26a, which serves as a reflective surface 26d, via a bonding layer 26b having a transparent surface opposite to the transmissive diffuse surface 261.

[0107] In wavelength conversion element 26, fluorescent material regions (yellow fluorescent material region A1 and green fluorescent material region A2) are formed on the reflective surface 26d of substrate 26a, allowing the reflective surface 26d to be formed continuously as a reflective surface for excitation light (blue light). In other words, it is not necessary to arrange a reflective layer in the plate 26c, thereby enabling the wavelength conversion element 26 to be constructed at low cost.

[0108] Meanwhile, to achieve practical illumination output power, a blue laser source typically needs to have an output power of tens of W. Tens of W of point light passes through the transmissive and diffuse surface 261 of the plate 26c in a concentrated manner; therefore, the plate 26c needs to have a certain degree of heat resistance. Thus, it is sufficient for the plate 26c to be thermally connected to at least one component with high thermal conductivity (e.g., metal). In other words, by connecting the plate 26c to the substrate 26a via the bonding layer 26b, heat generated by radiation can be dissipated, thereby providing a highly reliable wavelength conversion element 26.

[0109] Meanwhile, in each embodiment, the wavelength conversion element 26, which serves as a wavelength conversion plate, is arranged in the projector (image projection device) 1. However, the embodiments are not limited to this example, and the wavelength conversion element 26 can be widely applied to devices that obtain a white appearance by temporarily mixing fluorescent and blue excitation light sources. For example, the wavelength conversion element 26, as a wavelength conversion plate, can be applied to lighting devices, such as searchlights or spotlights.

[0110] Third Embodiment

[0111] The third embodiment will now be described.

[0112] The third embodiment differs from the first and second embodiments in that it defines the range of the incident direction of the excitation light. In the following description of the third embodiment, explanations of components identical to those in the first and second embodiments are omitted, and the differences from the first and second embodiments will be described.

[0113] If the excitation light is input along the direction of rotation (movement direction) of the conversion region (yellow fluorescent material region (first wavelength conversion region) A1, green fluorescent material region (second wavelength conversion region) A2) and the reflection region (blue reflection region A3), there is a problem of beam diffusion in the movement direction. To address this, in this embodiment, the excitation light emitted from the laser source 21 is input in the range of 45° to 135° relative to the movement direction (rotation direction) of the wavelength conversion element 26.

[0114] Figure 9 This is a schematic diagram showing the range of incident directions of the excitation light according to the third embodiment. Figure 9 The dashed arrow P shown is the tangent to the wavelength conversion element 26 used for driving (rotation direction). The incident direction of the excitation light emitted from the laser source 21 is relative to the direction along... Figure 9 The direction of the tangent shown falls within the range of 45° to 135° (it can be from above or below).

[0115] Figure 10 This is a magnified view of the irradiation position of the excitation light. The excitation light emitted from laser source 21 is incident on the laser beam... Figure 10 The range formed by the two arrows Q shown is (45° to 135°). Figure 10 The ellipse shown represents the focal point of the excitation light. For example... Figure 10 As shown, the spot light diffuses in a direction perpendicular to the direction of movement of the conversion regions (yellow fluorescent material region (first wavelength conversion region) A1, green fluorescent material region (second wavelength conversion region) A2).

[0116] The following describes a situation in which, for example... Figure 10As shown, the excitation light emitted from laser source 21 is input in a direction ranging from 0° to 45° or from 135° to 180°. In this case, the focusing point of the excitation light is an ellipse with a major axis in the incident direction, and in the direction of beam diffusion, diffusion increases and color mixing or light utilization efficiency decreases. The light diffusion is similar to that described above. Figures 3A to 3C , Figures 4A to 4C It occurs in the same way as described above.

[0117] In this manner, according to this embodiment, the light beam diffuses within the conversion regions (yellow fluorescent material region (first wavelength conversion region) A1, green fluorescent material region (second wavelength conversion region) A2); however, since the incident direction of the excitation light in the reflection region is defined as an angle equal to or greater than 45 degrees and equal to or less than 135 degrees, diffusion at the boundary between the reflection region and the conversion region can be minimized. In particular, if the incident direction of the excitation light relative to the reflection region is set to approximately 90 degrees, diffusion in the direction of movement is minimized, thereby reducing diffusion in the spoke portion and achieving a highly efficient illumination optics system.

[0118] Meanwhile, preferred embodiments of the present invention have been described in each of the embodiments described above, but the present invention is not limited to the details of the embodiments.

[0119] In particular, the specific shapes and values ​​of each part shown in each embodiment as described above are merely examples for implementing embodiments of the invention, and the technical scope of the invention need not be interpreted in a limiting manner.

[0120] As described above, the present invention is not limited to the details of each of the embodiments described above, and may be appropriately modified without departing from the spirit of the invention.

[0121] The above embodiments are illustrative and do not limit the invention. Therefore, many additional modifications and variations are possible based on the above teachings. For example, at least one element of the different illustrative and exemplary embodiments herein may be combined with or substituted for each other within the scope of this disclosure. Furthermore, the characteristics of the components in the embodiments, such as quantity, position, and shape, are not limited to the described embodiments and may be preferably set. Therefore, it should be understood that within the scope of this application, the disclosure of this invention may be practiced in ways other than those specifically described herein.

Claims

1. A wavelength conversion panel comprising: a conversion region on a substrate surface, the conversion region including a wavelength conversion member configured to receive excitation light and generate a color different from that of the excitation light; and a reflection region on the substrate surface configured to reflect the excitation light, wherein the reflection region includes: a transmissive diffusing surface configured to diffuse the excitation light; a transmissive layer configured to transmit the excitation light; and a reflective surface configured to reflect the excitation light, and the transmissive diffusing surface is located at a position apart from a surface of the wavelength conversion member closer to the substrate surface in a direction in which the excitation light is incident, wherein the reflection region includes a transparent flat plate member, the transmissive diffusing surface is on a first surface of the transparent flat plate member, and a second surface of the transparent flat plate member facing the transmissive diffusing surface is in contact with the substrate surface or is thermally connected to the substrate surface via a bonding layer. the position of the transmissive diffusing surface is determined so as to satisfy the following condition:

2. The wavelength conversion plate of claim 1, wherein, k < h < 2k where k represents a thickness of the wavelength conversion member and h represents a distance between the substrate surface and the transmissive diffusing surface. the position of the transmissive diffusing surface is determined so as to satisfy the following relationship:

3. The wavelength conversion plate of claim 1, wherein, 0 < h < 2k where k represents a thickness of the wavelength conversion member and h represents a distance between the substrate surface and the transmissive diffusing surface. the position of the transmissive diffusing surface is determined so as to satisfy the following relationship:

4. The wavelength conversion plate of claim 1, wherein, k = h where k represents a thickness of the wavelength conversion member and h represents a distance between the substrate surface and the transmissive diffusing surface. the second surface of the transparent flat plate member facing the transmissive diffusing surface is configured to reflect the excitation light.

5. The wavelength conversion plate of claim 1, wherein, the second surface of the transparent flat plate member facing the transmissive diffusing surface is configured to transmit the excitation light.

6. The wavelength conversion plate of claim 1, wherein, 7.A light source apparatus comprising: the wavelength conversion panel according to any one of claims 1 to 6; a light source configured to emit excitation light; and a condensing optical system configured to condense the excitation light onto the wavelength conversion panel. 8.The light source apparatus according to claim 7, wherein the excitation light emitted by the light source is blue light, and the wavelength conversion panel is configured to receive the blue light and convert a wavelength of the blue light into a wavelength including at least a green light component and a red light component. 9.The light source apparatus according to claim 7 or 8, wherein the wavelength conversion panel is configured to be moved by a moving mechanism, and a direction in which the excitation light is incident on the conversion region and the reflection region is at an angle equal to or greater than 45 degrees and equal to or smaller than 135 degrees with respect to a moving direction of the wavelength conversion panel. the direction in which the excitation light is incident on the conversion region and the reflection region is at an angle of about 90 degrees with respect to the moving direction of the wavelength conversion panel.

10. The light source apparatus according to claim 9, wherein 11.An image projection apparatus comprising: the light source apparatus according to any one of claims 7 to 10; a light uniformizing element configured to uniformize light emitted from the light source apparatus and output the uniformized light; an image display element configured to modulate the light from the light uniformizing element to form an image; and a projection optical system configured to project the image formed by the image display element. ​ A projection optical system configured to magnify the image and project the magnified image on a projection target screen.

Images