Lighting device

Abstract

Provided is a lighting device in which a dot pattern of each color to be projected on a projection surface can be prevented from appearing dark.　A lighting device (10) comprises a diffraction optical element (50) that receives laser light (Ray2) having a wavelength in the visible range and converts the laser light into a light beam group (Ray3) corresponding to a dot pattern group to be projected on a projection surface (S). The longer the wavelength of the laser light incident on the diffraction optical element, the larger the dot interval of a dot pattern to be projected on the projection surface and the larger the spot size of the dot pattern to be projected on the projection surface.

Description

Lighting device

[0001] This disclosure relates to a lighting device.

[0002] A lighting device (for example, a projector) is known that uses multiple light sources that emit light of different wavelengths, such as RGB light sources, and combines the light emitted from each light source using a dichroic mirror, then diffuses it with a homogenizer, and forms an image using an optical modulation element such as LCOS (Liquid Crystal On Silicon) (see, for example, Non-Patent Document 1).

[0003] In response to this, the present inventors investigated the use of a diffractive optical element that receives laser light in the visible wavelength range and converts the laser light into a group of rays corresponding to a group of dot patterns projected onto a projection surface, thereby forming an image composed of multiple dot patterns.

[0004] Light Edge, a technical information magazine on optical technology, No. 37, "Special Feature: Ushio's New Initiatives, Part 2" [Accessed February 19, 2024], Internet <URL: https: / / www.ushio.co.jp / jp / technology / lightedge / 201206 / 100438.html>

[0005] However, the inventors have found that when forming an image composed of multiple dot patterns using the above-mentioned diffractive optical element, the longer the wavelength of the laser light incident on the diffractive optical element, the smaller the total dot area per unit area of ​​the dot pattern projected onto the projection surface (or the luminous flux per unit area of ​​the dot pattern projected onto the projection surface, i.e., the illuminance), resulting in the dot pattern projected onto the projection surface appearing darker.

[0006] This disclosure was made to solve these problems and aims to provide a lighting device that can prevent the dot patterns of each color projected onto the projection surface from appearing dark.

[0007] The illumination device according to this disclosure includes a diffractive optical element that receives laser light of a visible wavelength and converts the laser light into a group of rays corresponding to a group of dot patterns projected onto a projection surface, wherein the longer the wavelength of the laser light incident on the diffractive optical element, the larger the dot spacing of the dot pattern projected onto the projection surface and the larger the spot size of the dot pattern projected onto the projection surface.

[0008] This configuration makes it possible to create a lighting device that prevents the dot patterns of each color projected onto the projection surface from appearing dark.

[0009] In the above-described lighting device, the longer the wavelength of the laser light incident on the diffractive optical element, the larger the beam diameter of the laser light incident on the diffractive optical element may be.

[0010] Furthermore, in the above-mentioned lighting device, the total area of ​​dots per unit area of ​​each colored dot pattern projected onto the projection surface may be the same for all of them.

[0011] Furthermore, in the above-described lighting device, the luminous flux per unit area of ​​each colored dot pattern projected onto the projection surface may be the same for all of them.

[0012] Furthermore, the above-mentioned lighting device may further include a plurality of laser light sources that emit laser light of different visible wavelengths, and a plurality of lenses provided corresponding to the plurality of laser light sources, wherein each of the plurality of lenses is a collimating lens that converts the laser light emitted by the laser light source corresponding to that lens into parallel light.

[0013] Another illumination device according to this disclosure includes a diffractive optical element that receives laser light in the visible wavelength range and converts the laser light into a group of rays corresponding to a group of dot patterns projected onto a projection surface, wherein the luminous flux per unit area of ​​each colored dot pattern projected onto the projection surface is the same for all of them.

[0014] The above-described lighting device further comprises a plurality of laser light sources that emit laser light of different visible wavelengths, and a control device that controls the brightness of each of the plurality of laser light sources, wherein the control device may control the brightness of the plurality of laser light sources so that the luminous flux per unit area of ​​each colored dot pattern projected onto the projection surface is the same for all of them.

[0015] Another illumination device according to this disclosure includes a diffractive optical element that receives laser light in the visible wavelength range and converts the laser light into a group of rays corresponding to a group of dot patterns projected onto a projection surface, wherein the brightness per unit area of ​​each colored dot pattern projected onto the projection surface is the same for all of them.

[0016] The above-described lighting device further comprises an optical element disposed between the diffractive optical element and the projection surface, wherein the optical element forms an image on the projection surface by blocking at least a portion of the group of light rays converted by the diffractive optical element.

[0017] This disclosure provides a lighting device that can prevent the dot patterns of each color projected onto the projection surface from appearing dark.

[0018] This is a schematic diagram of the lighting device 10. This is an enlarged view of the diffractive optical element 50 in Figure 1, seen from the direction of arrow AR1. This is a cross-sectional view taken along line IIB-IIB in Figure 2A. This is an example of a group of dot patterns DP projected onto the projection surface S. Red dot pattern DP Ｒ Size D1, dot spacing L Ｒ This is one example. Green dot pattern DP Ｇ Size D2, dot spacing L Ｇ This is an example. This figure illustrates the increase in the dot spacing of the dot pattern DP projected onto the projection surface S. Compared to Figure 4A, the red dot pattern DP projected onto the projection surface S Ｒ This is an example where the spot (light-emitting point) size D1 is increased. This is a schematic diagram of the lighting device 10A, which is a modified example. This is a schematic diagram of the lighting device 10B, which is a modified example 2. This is an example of an optical element 60 (physical mask). This is an example of an image composed of multiple dot patterns DP formed on the projection surface S.

[0019] Hereinafter, an embodiment of the illumination device 10 (image forming apparatus) described in this disclosure will be explained with reference to the attached drawings. In each figure, corresponding components are denoted by the same reference numerals, and redundant explanations are omitted.

[0020] Figure 1 is a schematic diagram of the lighting device 10.

[0021] As shown in Figure 1, the illumination device 10 includes a plurality of laser light sources 20 that emit laser light Ray 1 of different visible wavelengths, a plurality of lenses 30, a dichroic prism 40, a diffractive optical element 50 (DOE), and a control device 70 that controls the brightness of each of the plurality of laser light sources 20.

[0022] The multiple laser light sources 20 include, for example, a laser light source 20R that emits red laser light, a laser light source 20G that emits green laser light, and a laser light source 20B that emits blue laser light. The laser light Ray 1 emitted from each of the multiple laser light sources 20 passes through multiple lenses 30 (collimating lenses) provided corresponding to the multiple laser light sources 20, is converted into parallel light, and then enters the dichroic prism 40.

[0023] The laser beams Ray1 of each color (each wavelength in the visible range) incident on the dichroic prism 40 are directed along the same optical axis AX due to the action of the dichroic prism 40. ４０ The laser beam Ray 2 is emitted from the dichroic prism 40 along the specified direction. The laser beam Ray 2 (parallel light) emitted from the dichroic prism 40 is incident on the diffractive optical element 50. The beam diameter of the laser beam Ray 2 incident on the diffractive optical element 50 is, for example, about 3 mm.

[0024] Figure 2A is an enlarged view of the diffractive optical element 50 in Figure 1, seen from the direction of arrow AR1, and Figure 2B is a cross-sectional view taken along the line IIB-IIB in Figure 2A. Note that the cross-sectional view taken along the line B-B in Figure 2A is the same as the cross-sectional view taken along the line IIB-IIB.

[0025] The diffractive optical element 50 includes a microlens array and receives laser light Ray 1 emitted from each laser light source 20, i.e., laser light Ray 2 of each color (each wavelength in the visible range) emitted from the dichroic prism 40 after passing through the lens 30, and converts or branches (diffracts) the laser light Ray 2 into a group of light rays Ray 3 corresponding to the group of dot patterns projected onto the projection surface S. In other words, the diffractive optical element 50 diffracts and divides the laser light Ray 2 incident on it in the up, down, left, and right directions. The group of light rays Ray 3 becomes a bundle of light beams with multiple directions. As the diffractive optical element 50, for example, the product name "ardisia" from Scivax may be used. Alternatively, as the diffractive optical element 50, for example, the one described in Japanese Patent Publication No. 7061823 may be used. However, the diffractive optical element 50 may have any configuration as long as it receives laser light and converts (diffracts) the laser light into a group of light rays corresponding to the group of dot patterns projected onto the projection surface S. For example, a general diffraction grating with a groove structure may be used.

[0026] The microlens array of the diffractive optical element 50 includes a plurality of lenses 51 arranged two-dimensionally in the XY direction, as shown in Figures 2A and 2B. Figures 2A and 2B show an example in which the lens 51 is provided on the incident side (incident side of the laser beam Ray 2) of the diffractive optical element 50, but it is not limited to this. The lens 51 only needs to be provided on at least one of the incident side and the exit side (incident side of the laser beam Ray 2 and exit side of the laser beam Ray 2) of the diffractive optical element 50.

[0027] Figure 3 shows an example of a dot pattern DP group projected onto the projection surface S.

[0028] The dot pattern DP is, for example, circular (see Figure 3), but is not limited to this; it may also be rectangular or of any other shape.

[0029] Incidentally, if the pitch P of the lens 51 (see FIG. 2B) becomes too small compared to the wavelength λ of the laser light emitted from the laser light source 20, it becomes difficult to cause diffraction. Therefore, as long as the lens 51 sufficient to cause diffraction within the light distribution angle of the laser light is included, the pitch P should be sufficiently larger than the wavelength λ of the laser light, for example, 5 times or more, preferably 10 times or more.

[0030] The pitch P of the lens 51 is, for example, 10 μm, and the height H is, for example, 7 μm.

[0031] The diffractive optical element 50 may be a transmissive diffractive optical element (DOE) or a reflective diffractive optical element (DOE). The material of the transmissive diffractive optical element 50 is, for example, polydimethylsiloxane (PDMS) with a refractive index of 1.53. However, as long as it is a material through which light can pass and has a refractive index exceeding 1.0, other materials such as acrylic and polycarbonate may also be used. On the other hand, the material of the reflective diffractive optical element 50 may be a metal material.

[0032] Here, when the beam diameters of the laser lights Ray2 (parallel lights) of each color incident on the diffractive optical element 50 are the same (substantially the same) as each other, the sizes of the dot patterns DP of each color projected on the projection surface S are the same (substantially the same) as each other regardless of the wavelength of the laser light incident on the diffractive optical element 50. For example, when the beam diameters of the red and green laser lights Ray2 (parallel lights) incident on the diffractive optical element 50 are the same (substantially the same) as each other, the size D1 of the red dot pattern DP Ｒ projected on the projection surface S (see FIG. 4A) = the size D2 of the green dot pattern DP Ｇ projected on the projection surface S (see FIG. 4B). FIG. 4A shows an example of the size D1 and dot interval L of the red dot pattern DP Ｒ , and FIG. 4B shows an example of the size D2 and dot interval L of the green dot pattern DP Ｒ . Ｇ Ｇ

[0033] On the other hand, the longer the wavelength of the laser light Ray2 (parallel light) incident on the diffractive optical element 50, the larger the dot pitch of the dot pattern DP projected onto the projection surface S. For example, the red dot pattern DP projected onto the projection surface S when red laser light Ray2 (parallel light) is incident on the diffractive optical element 50 Ｒ The dot pitch L Ｒ (see FIG. 4A) > the green dot pattern DP projected onto the projection surface S when green laser light Ray2 (parallel light) is incident on the diffractive optical element 50 Ｇ The dot pitch L Ｇ (see FIG. 4B). The reason is as follows.

[0034] FIG. 5 is a diagram for explaining that the dot pitch of the dot pattern DP projected onto the projection surface S becomes larger.

[0035] That is, the diffractive optical element 50 (DOE) is an element that generates light of a specific pattern by utilizing the diffraction and interference of light. The simplest diffractive optical element (DOE) has a sawtooth-shaped periodic structure, and the light reflected or transmitted by the diffractive optical element diffracts and spreads, and the intensity at positions that satisfy the interference conditions becomes high, resulting in a dot pattern.

[0036] From the following formula for the interference condition, the longer the wavelength of the light incident on the diffractive optical element, the larger the diffraction angle θm (≧0) (see FIG. 5), and the larger the dot pitch.

[0037] However, θ ｉ (≧0) is the incident angle, θ ｍ (≧0) is the diffraction angle, m is the diffraction order, λ is the wavelength, and d is the grating constant.

[0038] As described above, when the beam diameters of the laser beams Ray2 (parallel light) of each color incident on the diffractive optical element 50 are the same (approximately the same), the size of the dot patterns DP of each color projected onto the projection surface S will be the same (approximately the same) regardless of the wavelength of the laser beam incident on the diffractive optical element 50. On the other hand, the longer the wavelength of the laser beams Ray2 (parallel light) incident on the diffractive optical element 50, the larger the dot spacing of the dot pattern DP projected onto the projection surface S. Therefore, the longer the wavelength of the laser beam incident on the diffractive optical element 50, the lower the density of the dot pattern DP projected onto the projection surface S.

[0039] Therefore, the longer the wavelength of the laser light incident on the diffractive optical element 50, the smaller the total area of ​​dots (light-emitting points) per unit area of ​​the dot pattern DP projected onto the projection surface S (or the luminous flux per unit area of ​​the dot pattern DP projected onto the projection surface S, i.e., the illuminance), and as a result, the dot pattern DP projected onto the projection surface S appears darker. For example, a green dot pattern DP projected onto the projection surface S... Ｇ (See Figure 4B) Red dot pattern DP projected onto projection plane S Ｒ (See Figure 4A) has the drawback of appearing darker.

[0040] Next, we will describe two configuration examples 1 and 2 for solving the above problem. <Configuration Example 1> In Configuration Example 1, the longer the wavelength of the laser light incident on the diffractive optical element 50, the larger the spot (emission point) size of the dot pattern DP projected onto the projection surface S is made so that the total area of ​​dots (emission points) per unit area of ​​each colored dot pattern DP projected onto the projection surface S is the same (approximately the same) as each other. For example, as shown in Figure 6, the red dot pattern DP projected onto the projection surface S Ｒ The spot (light point) size D1 is increased, and the red dot pattern DP Ｒ Spot size D1 > Green dot pattern DP Ｇ The spot size is D2. Figure 6 shows the red dot pattern DP projected onto the projection surface S, compared to Figure 4A. ＲThis is an example of increasing the spot (light-emitting point) size D1. This is achieved by using a lens 30 (collimating lens) with an appropriate focal length. In other words, the spot size of the dot pattern DP projected onto the projection surface S can be made relatively larger by using a lens 30 with a relatively long focal length. Therefore, by using a lens 30 (collimating lens) with an appropriate focal length, the total area of ​​dots (light-emitting points) per unit area of ​​each colored dot pattern DP projected onto the projection surface S can be made the same (approximately the same). Furthermore, the curvature of the curved surface of the lens 30 can be made relatively larger to relatively enhance the diffuseness.

[0041] As described above, in Configuration Example 1, regardless of the wavelength of the laser light incident on the diffractive optical element 50, the total area of ​​dots (emission points) per unit area of ​​each colored dot pattern DP projected onto the projection surface S is the same (approximately the same) for all of them.

[0042] Therefore, in Configuration Example 1, even if the wavelength of the laser light incident on the diffractive optical element 50 becomes longer, for example, even if the green laser light source 20G and the red laser light source 20R are lit in that order, it is possible to prevent the dot patterns DP of each color projected onto the projection surface S from appearing dark.

[0043] In Configuration Example 1, the beam diameters of each color of laser light incident on the diffractive optical element 50 are different from each other. That is, the longer the wavelength of the laser light incident on the diffractive optical element 50, the larger the beam diameter of the laser light incident on the diffractive optical element 50. For example, the beam diameter of the red laser light Ray2 incident on the diffractive optical element 50 > the beam diameter of the green laser light Ray2 incident on the diffractive optical element 50 > the beam diameter of the blue laser light Ray2 incident on the diffractive optical element 50. <Configuration Example 2> In Configuration Example 2, the brightness of the laser light sources 20 (20R, 20G, 20B) is controlled so that the luminous flux per unit area, i.e., the illuminance, of each colored dot pattern DP projected onto the projection surface S is the same (approximately the same) from each other. In other words, the output of the laser light sources 20 should be increased as the wavelength of the laser light sources 20 increases, so that they become relatively brighter. For example, the brightness of laser light source 20R > the brightness of laser light source 20G > the brightness of laser light source 20G. This is achieved by the control device 70. In this case, the total area of ​​dots (light-emitting points) per unit area of ​​each colored dot pattern DP projected onto the projection surface S may be the same (approximately the same) or may be different from each other.

[0044] As described above, in Configuration Example 2, regardless of the wavelength of the laser light incident on the diffractive optical element 50, the luminous flux per unit area of ​​each colored dot pattern DP projected onto the projection surface S, i.e., the illuminance, is the same (approximately the same) for all of them.

[0045] Therefore, in the configuration example 2, even if the wavelength of the laser light incident on the diffractive optical element 50 becomes longer, for example, even if the green laser light source 20G and the red laser light source 20R are lit in that order, it is possible to prevent the dot patterns DP of each color projected onto the projection surface S from appearing dark.

[0046] In the second configuration example, the beam diameters of the laser light of each color incident on the diffractive optical element 50 may be the same or different from each other.

[0047] As described above, according to this embodiment, it is possible to prevent the dot patterns DP of each color projected onto the projection surface S from appearing dark.

[0048] Next, I will explain some variations.

[0049] Figure 7 is a schematic diagram of the lighting device 10A, which is a modified example 1.

[0050] In the above embodiment, an example was described in which multiple combinations of laser light sources 20 and lenses 30 are used, and one diffractive optical element 50 is used, but the embodiment is not limited to this. For example, as shown in Figure 7, multiple combinations of laser light sources 20, lenses 30, and diffractive optical elements 50 may be used. In this case, the dichroic prism 40 may be omitted.

[0051] Figure 8 is a schematic diagram of the lighting device 10B, which is a modified example 2.

[0052] As shown in Figure 8, an optical element 60 may be placed between the diffractive optical element 50 and the projection surface S to block (for example, reflect or absorb) at least a portion of the Ray 3 light group converted by the diffractive optical element 50, thereby forming an image on the projection surface S.

[0053] For example, the optical element 60 may be a physical mask that includes an image (for example, the arrow image shown in Figure 9) composed of an opaque region that does not transmit visible light (ray group Ray 3) and a transmissive region that transmits visible light. Figure 9 is an example of an optical element 60 (physical mask). In Figure 9, the arrow region A1 represents an opaque region that does not transmit visible light. This opaque region is a filter region that reflects or absorbs visible light. On the other hand, in Figure 9, the hatched region HT1 represents a transmissive region that transmits visible light. By using a physical mask as the optical element 60, an image composed of multiple dot patterns DP can be formed (projected) onto the projection surface S. Figure 10 is an example of an image composed of multiple dot patterns DP formed on the projection surface S.

[0054] The optical element 60 may be any optical element capable of forming an arbitrary image (for example, the arrow image shown in Figure 9) projected onto the projection surface S according to control from the control device, such as a transmissive liquid crystal element, a reflective liquid crystal element, or a DMD (Digital Mirror Device) including a group of micromirrors. By using this optical element as the optical element 60, any image (see, for example, Figure 10) composed of multiple dot patterns DP can be formed (projected) onto the projection surface S.

[0055] All the numerical values ​​shown in the above embodiments are examples only, and it goes without saying that other appropriate numerical values ​​can be used.

[0056] The embodiments described above are in all respects merely illustrative. The description of the embodiments above should not be construed as limiting the disclosure. The disclosure can be implemented in a variety of other ways without departing from its spirit or main features.

[0057] This application claims priority based on Japanese Patent Application No. 2024-180443, filed on 16 October 2024, and incorporates all of its disclosures herein.

[0058] 10, 10A, 10B... Illumination device 20 (20B, 20G, 20R)... Laser light source 30... Lens 40... Dichroic prism 50... Diffractive optical element 51... Lens 60... Optical element 70... Control device A1... Arrow area DP (DP Ｇ DP Ｒ )...Dot pattern HT1...Hatching area L Ｇ , L Ｒ ...dot spacing P...pitch Ray1, Ray2...laser beam Ray3...ray group S...projection plane θm...diffraction angle

Claims

1. An illumination device comprising a diffractive optical element that receives laser light of visible wavelength and converts the laser light into a group of rays corresponding to a group of dot patterns projected onto a projection surface, wherein the longer the wavelength of the laser light incident on the diffractive optical element, the larger the dot spacing of the dot pattern projected onto the projection surface and the larger the spot size of the dot pattern projected onto the projection surface.

2. The illumination device according to claim 1, wherein the longer the wavelength of the laser light incident on the diffractive optical element, the larger the beam diameter of the laser light incident on the diffractive optical element.

3. The lighting device according to claim 1, wherein the total area of ​​dots per unit area of ​​each colored dot pattern projected onto the projection surface is the same for all of them.

4. The lighting device according to claim 1, wherein the luminous flux per unit area of ​​each colored dot pattern projected onto the projection surface is the same for all of them.

5. The illumination device according to claim 1, further comprising: a plurality of laser light sources that emit laser light of different visible wavelengths; and a plurality of lenses provided corresponding to the plurality of laser light sources, wherein each of the plurality of lenses is a collimating lens that converts the laser light emitted by the laser light source corresponding to the lens into parallel light.

6. An illumination device comprising a diffractive optical element that receives laser light of visible wavelength and converts the laser light into a group of rays corresponding to a group of dot patterns projected onto a projection surface, wherein the luminous flux per unit area of ​​each colored dot pattern projected onto the projection surface is the same for all of them.

7. The illumination device according to claim 6, further comprising: a plurality of laser light sources that emit laser light of different visible wavelengths; and a control device that controls the brightness of each of the plurality of laser light sources, wherein the control device controls the brightness of the plurality of laser light sources so that the luminous flux per unit area of ​​each colored dot pattern projected onto the projection surface is the same for all of them.

8. An illumination device comprising a diffractive optical element that receives laser light of visible wavelength and converts the laser light into a group of rays corresponding to a group of dot patterns projected onto a projection surface, wherein the brightness per unit area of ​​each colored dot pattern projected onto the projection surface is the same for all others.

9. The illumination device according to any one of claims 1, 6, or 8, further comprising an optical element disposed between the diffractive optical element and the projection surface, wherein the optical element forms an image on the projection surface by blocking at least a portion of the group of light rays converted by the diffractive optical element.

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