Lighting device and method for changing dot size

Abstract

The present invention provides an illumination device, etc., that can change the size of multiple dot patterns formed using diffractive optical elements. [Solution] The illumination device 10 includes a diffractive optical element 50 that receives a laser beam Ray1 of visible wavelength and converts the laser beam into a group of rays Ray2 corresponding to a group of dot patterns DP projected onto a projection surface S; a first optical element 60 disposed between the diffractive optical element and the projection surface, which forms an image on the projection surface by blocking at least a portion of the group of rays converted by the diffractive optical element; and a beam diameter adjusting means 80 that adjusts the beam diameter of the laser beam incident on the diffractive optical element.

Description

Technical Field

[0001] The present disclosure relates to a lighting device and a dot size changing method.

Background Art

[0002] There is known a lighting device (for example, a projector) that uses a plurality of light sources that emit lights having different wavelengths from each other, such as RGB light sources, combines the lights emitted from each light source by a dichroic mirror, and then diffuses the combined light by a homogenizer to form an image by a light modulation element such as a Liquid Crystal On Silicon (LCOS) (see, for example, Non-Patent Document 1).

[0003] On the other hand, the inventors of the present invention have considered using a diffractive optical element that receives laser light having a wavelength in the visible range and converts the laser light into a group of light rays corresponding to a dot pattern group projected onto a projection surface to form an image composed of a plurality of dot patterns and changing the sizes of the plurality of dot patterns.

Prior Art Documents

Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Non-Patent Document 1, nothing has been considered regarding changing the sizes of a plurality of dot patterns formed using a diffractive optical element.

[0006] This disclosure is made to solve these problems and aims to provide an illumination device and a method for changing the size of multiple dot patterns formed using diffractive optical elements. [Means for solving the problem]

[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; a first optical element disposed between the diffractive optical element and the projection surface, which forms an image on the projection surface by blocking at least a portion of the group of rays converted by the diffractive optical element; and a beam diameter adjusting means for adjusting the beam diameter of the laser light incident on the diffractive optical element.

[0008] This configuration makes it possible to realize an illumination device that can change the size of multiple dot patterns formed using diffractive optical elements.

[0009] In the above-described lighting device, the beam diameter adjustment means may include a second optical element that receives laser light of a visible wavelength and diffuses the laser light, and an actuator that moves the second optical element either on the optical path of the laser light of a visible wavelength or outside the optical path of the laser light of a visible wavelength.

[0010] Furthermore, in the above-described lighting device, the second optical element may be any of the following: a diffractive optical element, a holographic element, or a lens, configured to receive laser light of a visible wavelength and diverge the said laser light.

[0011] Furthermore, in the above-described lighting device, the beam diameter adjustment means may include a variable-focus lens positioned on the optical path of the visible-wavelength laser light, the focal length of which is changed according to control from a control device.

[0012] Furthermore, in the above-described lighting device, the first optical element is a transmissive liquid crystal element including a plurality of cells that can be switched on or off according to control from a control device, and the light rays incident on the cells that are on from the group of light rays may pass through the cells, while the light rays incident on the cells that are off from the group of light rays may not pass through the cells and may block the light.

[0013] Furthermore, in the above-described lighting device, the first optical element may be a physical mask that includes an image composed of an opaque region that does not transmit visible light and a transmissive region that transmits visible light.

[0014] The dot size changing method according to this disclosure involves a first optical element, which is positioned between a diffractive optical element and a projection surface, which 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 the projection surface. The first optical element forms an image on the projection surface by blocking at least a portion of the group of rays converted by the diffractive optical element, and the first optical element changes the size of the dot pattern projected onto the projection surface by adjusting the beam diameter of the laser light incident on the diffractive optical element. [Effects of the Invention]

[0015] This disclosure provides an illumination device and a method for changing the size of multiple dot patterns formed using diffractive optical elements. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of the lighting device 10 (showing the second optical element 81 in a state where it has moved onto the optical path of the laser beam Ray 1). [Figure 2] This is a schematic diagram of the lighting device 10 (with the second optical element 81 moved outside the optical path of the laser beam Ray1). [Figure 3] (a) An enlarged view of the diffractive optical element 50 in Figure 1, seen from the direction of arrow AR1, and (b) A cross-sectional view of AA in Figure 3(a). [Figure 4]This is an example of a dot pattern DP group projected onto the projection plane S. [Figure 5] This is a configuration example for moving the second optical element 81 onto the optical path of the laser beam Ray1 (see Fig. 1) or outside the optical path of the laser beam Ray1 (see Fig. 2). [Figure 6] This is a flowchart of an operation example of the illumination device 10. [Figure 7] This is an example of a lens (group) 91, 92 configured to receive a laser beam Ray1 with a wavelength in the visible range and convert it into a diverging light beam (slightly diverging). [Figure 8] This is an example in which a focus variable lens 100 whose focal length is changed according to the control from the control device 70 is disposed on the optical path of a laser beam Ray1 with a wavelength in the visible range instead of the second optical element 81. [Figure 9] This is an example of an illumination device 10A using a plurality of laser light sources 20, a plurality of lenses 30, and a dichroic prism 40. [Figure 10] This is an example of the first optical element 60 (physical mask). [Figure 11] This is an example of an image composed of dot patterns DP (plural) formed on the projection plane S.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, an illumination device 10 (image forming device) according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. The same reference numerals are assigned to corresponding components in each figure, and redundant descriptions are omitted.

[0018] Fig. 1 is a schematic configuration diagram of the illumination device 10 (a state in which the second optical element 81 has moved onto the optical path of the laser beam Ray1). Fig. 2 is a schematic configuration diagram of the illumination device 10 (a state in which the second optical element 81 has moved outside the optical path of the laser beam Ray1).

[0019] As shown in Figure 1, the illumination device 10 includes a laser light source 20 that emits laser light Ray 1 with a visible wavelength, a lens 30, a diffractive optical element 50 (DOE), a first optical element 60 (spatial light modulation element) that forms an image I (image) on the projection surface S by blocking (e.g., reflecting or absorbing) at least a portion of the group of light rays Ray 2 converted by the diffractive optical element 50, a control device 70, and a beam diameter adjustment means 80 that adjusts the beam diameter of the laser light Ray 1 incident on the diffractive optical element 50.

[0020] According to the lighting device 10, as shown in Figures 1 and 2, the beam diameter adjustment means 80 adjusts the beam diameter of the laser light Ray 1 incident on the diffractive optical element 50, thereby changing the size of the dot pattern DP projected onto the projection surface S.

[0021] The laser light source 20 is, for example, a laser light source that emits green laser light. The laser light Ray 1 emitted from the laser light source 20 passes through the lens 30 (collimating lens), is converted into parallel light, and then enters the diffractive optical element 50. The beam diameter of the laser light Ray 1 entering the diffractive optical element 50 is, for example, about 3 mm in diameter. Note that the lens 30 may be omitted.

[0022] Figure 3(a) is an enlarged view of the diffractive optical element 50 in Figure 1, seen from the direction of arrow AR1, and Figure 3(b) is a cross-sectional view AA of Figure 3(a). Note that the cross-sectional view BB of Figure 3(a) is the same as the cross-sectional view AA.

[0023] The diffractive optical element 50 includes a microlens array and receives the laser light Ray1 emitted from the laser light source 20, converting or branching (diffracting) the laser light Ray1 into a group of rays Ray2 corresponding to a group of dot patterns projected onto the projection surface S. That is, the diffractive optical element 50 diffracts and divides the laser light Ray1 incident on it in the up, down, left, and right directions. Note that the laser light Ray1 incident on the diffractive optical element 50 is not limited to parallel light, but may also be divergent light. The group of rays Ray2 becomes a bundle of light beams with multiple directions. Specifically, the group of rays Ray2 becomes substantially parallel light and becomes a beam with multiple different divergence angles. 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. The diffractive optical element 50 is not limited to this configuration, and can have any configuration as long as it receives laser light and converts (diffracts) the laser light into a group of rays corresponding to a group of dot patterns projected onto the projection surface S. For example, it may be a general diffraction grating with a groove structure.

[0024] 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 3(a) and 3(b). Figures 3(a) and 3(b) show an example in which the lens 51 is provided on the incident side of the diffractive optical element 50 (the incident side of the laser light Ray 1), 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 of the diffractive optical element 50 (the incident side of the laser light Ray 1 and the exit side of the laser light Ray 1).

[0025] Figure 4 shows an example of a group of dot patterns DP projected onto the projection surface S.

[0026] The dot pattern DP is, for example, circular (see Figure 4), but is not limited to this; it may also be rectangular or of any other shape.

[0027] Furthermore, if the pitch P of the lens 51 (see Figure 3(b)) becomes too small compared to the wavelength λ of the laser light emitted by the laser light source 20, diffraction will be difficult to occur. Therefore, as long as there are enough lenses 51 within the beam angle of the laser light to cause diffraction, 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.

[0028] The pitch P of lens 51 is, for example, 10 μm, and the height H is, for example, 7 μm.

[0029] 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, but other materials such as acrylic and polycarbonate may also be used, as long as they are light-transmitting materials with a refractive index greater than 1.0. On the other hand, the material of the reflective diffractive optical element 50 may be a metallic material.

[0030] As shown in Figure 1, the first optical element 60 is positioned between the diffractive optical element 50 and the projection surface S, and forms an image I (picture) on the projection surface S composed of a dot pattern DP by blocking at least a portion of the Ray 2 light group converted by the diffractive optical element 50. For example, the first optical element 60 is a transmissive liquid crystal element that includes a plurality of cells (pixels) that are individually switched on or off according to control from the control device 70. The plurality of cells are, for example, 256 × 256 cells. For example, the size of one cell is 400 μm × 400 μm.

[0031] Light rays from the Ray group Ray2 that are incident on an ON cell are transmitted through that cell. An image I is formed on the projection surface S by the light rays that have passed through this diffractive optical element 50 (cell). On the other hand, light rays from the Ray group Ray2 that are incident on an OFF cell are not transmitted through that cell and are blocked (reflected or absorbed).

[0032] The size of the dot pattern DP formed on the projection surface S can be changed by adjusting the beam diameter of the laser light Ray1 incident on the diffractive optical element 50 (see Figures 1 and 2). This is achieved by the beam diameter adjustment means 80.

[0033] The beam diameter adjustment means 80 includes, for example, a second optical element 81 that receives a laser beam Ray 1 of visible wavelength and diffuses the laser beam Ray 1, and an actuator 82 that moves (e.g., slides) the second optical element 81 either on the optical path of the laser beam Ray 1 of visible wavelength (see Figure 1) or outside the optical path of the laser beam Ray 1 of visible wavelength (see Figure 2). The actuator 82 moves (positions) the second optical element 81 either on the optical path of the laser beam Ray 1 (see Figure 1) or outside the optical path of the laser beam Ray 1 (see Figure 2) according to control from the control device 70.

[0034] The second optical element 81 is, for example, a diffractive optical element (diffractive grating) configured to receive a laser beam Ray1 with a wavelength in the visible range and convert the laser beam Ray1 into divergent light (diffractive light) that diverges (slightly diverges).

[0035] Therefore, as shown in Figure 1, the actuator 82 moves the second optical element 81 onto the optical path of the laser beam Ray 1 according to the control from the control device 70, thereby increasing the beam diameter of the laser beam Ray 1 incident on the diffractive optical element 50 (for example, a diameter of 6 mm). This also increases the beam diameter of each of the Ray 2 rays converted by the diffractive optical element 50. As a result, the size of the dot pattern DP formed on the projection surface S is changed (enlarged) (see Figure 1). For example, the diameter of the enlarged dot pattern DP is 200 μm.

[0036] On the other hand, as shown in Figure 2, the actuator 82 moves the second optical element 81 out of the optical path of the laser beam Ray 1 according to the control from the control device 70, thereby reducing the beam diameter of the laser beam Ray 1 incident on the diffractive optical element 50. As a result, the beam diameter of each of the Ray 2 rays converted by the diffractive optical element 50 is also reduced. Consequently, the size of the dot pattern DP formed on the projection surface S is changed (reduced) (see Figure 2). For example, the diameter of the dot pattern DP is 100 μm.

[0037] As described above, when the second optical element 81 moves onto the optical path of the laser beam Ray 1 (see Figure 1), that is, when the second optical element 81 is inserted into the optical path of the laser beam Ray 1, the area ratio of the dot pattern DP projected onto the projection surface S increases, and the resolution of the image I formed on the projection surface S increases (projection close to the resolution of the first optical element 60 becomes possible). In this case, the brightness of the dot pattern DP projected onto the projection surface S decreases.

[0038] Conversely, if the second optical element 81 moves outside the optical path of the laser beam Ray 1 (see Figure 2), that is, if the second optical element 81 is removed from the optical path of the laser beam Ray 1, the area ratio of the dot pattern DP projected onto the projection surface S decreases, and the resolution of the image I formed on the projection surface S decreases. In this case, the brightness of the dot pattern DP projected onto the projection surface S increases. Therefore, the recognition rate of the image I formed by the dot pattern DP improves.

[0039] Next, we will describe an example configuration for moving the second optical element 81 either on the optical path of the laser beam Ray 1 (see Figure 1) or outside the optical path of the laser beam Ray 1 (see Figure 2), as described above.

[0040] Figure 5 shows an example configuration for moving the second optical element 81 either on the optical path of the laser beam Ray 1 (see Figure 1) or outside the optical path of the laser beam Ray 1 (see Figure 2).

[0041] As shown in Figure 5, the laser light source 20, the first optical element 60, and the actuator 82 are electrically connected to a laser drive circuit 83, an LCD driver circuit 84, an actuator drive circuit 85, an MCU 86 (microcontroller), a power supply circuit 87, and a control device 88. The laser drive circuit 83, LCD driver circuit 84, actuator drive circuit 85, MCU 86 (microcontroller), power supply circuit 87, and control device 88 are an example of the control device 70.

[0042] Next, we will describe an example of the operation of the lighting device 10.

[0043] Figure 6 is a flowchart showing an example of the operation of the lighting device 10.

[0044] First, when enlarging the dot size (step S10: enlargement), the control device 88 (for example, the projector itself or an information processing device such as a PC) sends a control signal to the DOE light source module unit (MCU86) to enlarge the dot size in response to user operation (step S11).

[0045] Next, the MCU 86, having received the control signal, transmits a control signal to the actuator drive circuit 85 to move the second optical element 81 onto the optical path of the laser beam Ray 1 (step S12).

[0046] Next, based on the control signal, the actuator 82 moves the second optical element 81 onto the optical path of the laser beam Ray 1 (for example, by sliding it) (step S13). That is, the second optical element 81 is inserted into the optical path of the laser beam Ray 1. As a result, the laser beam Ray 1 incident on the diffractive optical element 50 becomes weakly divergent (the beam diameter of the laser beam Ray 1 incident on the diffractive optical element 50 increases), and the size of the dot pattern DP formed on the projection surface S increases. As a result, the brightness of the dot pattern DP formed on the projection surface S decreases, but the uniformity of the brightness of the entire projection surface S (image I formed on the projection surface S) can be increased, thus improving the resolution.

[0047] On the other hand, when reducing the dot size (step S10: reduction), the control device 88 (for example, the projector itself or an information processing device such as a PC) sends a control signal to the DOE light source module unit (MCU86) to reduce the dot size in response to user operation (step S14).

[0048] Next, the MCU 86, having received the control signal, sends a control signal to the actuator drive circuit 85 to move the second optical element 81 out of the optical path of the laser beam Ray 1 (step S15).

[0049] Next, based on the control signal, the actuator 82 moves the second optical element 81 out of the optical path of the laser beam Ray 1 (for example, by sliding it) (step S16). That is, the second optical element 81 is removed from the optical path of the laser beam Ray 1. As a result, the beam diameter of the laser beam Ray 1 incident on the diffractive optical element 50 becomes smaller (the beam diameter of the laser beam Ray 1 incident on the diffractive optical element 50 becomes smaller), and the size of the dot pattern DP formed on the projection surface S becomes smaller. As a result, the brightness of the dot pattern DP formed on the projection surface S increases, but the resolution decreases because the uniformity of the brightness of the entire projection surface S (image I formed on the projection surface S) decreases.

[0050] The processes in steps S11 to S16 described above are executed each time a user operation is performed to enlarge or reduce the dot size.

[0051] As described above, according to this embodiment, the size of the multiple dot patterns DP formed using the diffractive optical element 50 can be changed.

[0052] Next, I will explain some variations.

[0053] In the above embodiment, an example was described in which a diffractive optical element (diffractive grating) configured to receive a laser beam Ray1 with a visible wavelength and convert the laser beam Ray1 into divergent light (diffractive light) that diverges (slightly diverges) was used as the second optical element 81, but the invention is not limited to this.

[0054] For example, as the second optical element 81, lenses (groups) 91 and 92 (see Figure 7) configured to receive a laser beam Ray 1 with a wavelength in the visible range and convert the laser beam Ray 1 into divergent light that diverges (slightly diverging) may be used. Figure 7 shows an example of lenses (groups) 91 and 92 configured to receive a laser beam Ray 1 with a wavelength in the visible range and convert the laser beam Ray 1 into divergent light that diverges (slightly diverging). Although not shown, a holographic element configured to receive a laser beam Ray 1 with a wavelength in the visible range and convert the laser beam Ray 1 into divergent light that diverges (slightly diverging) may also be used as the second optical element 81.

[0055] Furthermore, in the above embodiment, an example was described in which the beam diameter adjustment means 80 includes a second optical element 81 that receives a laser beam Ray 1 of visible wavelength and diffuses the laser beam Ray 1, and an actuator 82 that moves the second optical element 81 either on the optical path of the laser beam Ray 1 of visible wavelength (see Figure 1) or outside the optical path of the laser beam Ray 1 of visible wavelength (see Figure 2), but the invention is not limited to this example.

[0056] For example, as shown in Figure 8, a tunable lens 100 may be used as the beam diameter adjustment means 80, which is placed on the optical path of the visible wavelength laser light Ray 1 and whose focal length is changed according to control from the control device 70. Figure 8 shows an example in which a tunable lens 100, whose focal length is changed according to control from the control device 70, is placed on the optical path of the visible wavelength laser light Ray 1 instead of the second optical element 81. As the tunable lens 100, for example, a tunable lens from Optotune (https: / / www.optoscience.com / our-vendors / optotune / tech / focus-tunable-lens.html) may be used.

[0057] According to this modified example, the same effects as in the above embodiment can be achieved by changing the focus of the variable-focus lens 100 and adjusting the beam diameter of the laser light Ray 1 incident on the diffractive optical element 50. Furthermore, according to this modified example, since the focus of the variable-focus lens 100 can be continuously changed (i.e., the beam diameter of the laser light Ray 1 incident on the diffractive optical element 50 can be continuously adjusted), the size of the dot pattern DP formed on the projection surface S can be continuously changed.

[0058] In the above embodiment, an example using one laser light source 20 was described, but it is not limited to this. For example, as shown in Figure 9, multiple laser light sources 20 may be used. Figure 9 is an example of an illumination device 10A using multiple laser light sources 20, multiple lenses 30, and a dichroic prism 40.

[0059] 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.

[0060] 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 Ray1 (parallel light) emitted from the dichroic prism 40 is incident on the diffractive optical element 50. The beam diameter of the laser beam Ray1 incident on the diffractive optical element 50 is, for example, about 3 mm.

[0061] This modified version can also achieve the same effects as the above embodiment.

[0062] Furthermore, in the above embodiment, an example was described in which a transmissive liquid crystal element including a plurality of cells (pixels) that can be switched on or off according to control from the control device 70 is used as the first optical element 60, but the invention is not limited to this.

[0063] For example, as the first optical element 60, a physical mask (including a dichroic aperture or a polarizing aperture) may be used, which includes an image composed of an opaque region that does not transmit visible light (ray group Ray2) and a transmissive region that transmits visible light. Figure 10 shows an example of the first optical element 60 (physical mask). In Figure 10, 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 10, the hatched region HT1 represents a transmissive region that transmits visible light. By using a physical mask as the first optical element 60, an image composed of multiple dot patterns DP can be formed (projected) onto the projection surface S. Figure 11 shows an example of an image composed of multiple dot patterns DP formed on the projection surface S.

[0064] Furthermore, the first optical element 60 may be a transmissive liquid crystal element containing multiple cells (pixels) whose transmittance is switched in steps according to control from the control device 70, regardless of whether they are in an ON or OFF state. In this way, it becomes possible to create a multi-gradation image I projected onto the projection surface S.

[0065] 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.

[0066] 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. [Explanation of Symbols]

[0067] 10, 10A…Lighting device 20 (20R, 20G, 20B)... Laser light source 30... Lens 40… Dichroic prism 50…Diffractive optical elements 51... Lens 60…First optical element 70...Control device 80... Beam diameter adjustment means 81...Second optical element 82… Actuator 83…Laser drive circuit 84...LCD driver circuit 85…Actuator drive circuit 87…Power circuit 88...Control device 100... Variable focus lens DP... Dot Pattern I... Statue Ray1…Laser light Ray2…ray group S…Projection surface

Claims

1. 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, A first optical element is disposed between the diffractive optical element and the projection surface, and 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. A lighting device comprising a beam diameter adjustment means for adjusting the beam diameter of the laser light incident on the diffractive optical element.

2. The beam diameter adjustment means is A second optical element receives laser light in the visible wavelength range and diffuses the said laser light, The lighting device according to claim 1, further comprising an actuator for moving the second optical element either on the optical path of the visible wavelength laser light or outside the optical path of the visible wavelength laser light.

3. The illumination device according to claim 2, wherein the second optical element is a diffractive optical element, a holographic element, or a lens configured to receive laser light of a visible wavelength and diverge the laser light.

4. The illumination device according to claim 1, wherein the beam diameter adjustment means includes a variable focus lens positioned on the optical path of the visible wavelength laser light, the focal length of which is changed according to control from a control device.

5. The first optical element is a transmissive liquid crystal element that includes a plurality of cells which are switched on or off according to control from a control device. Of the group of light rays, the light ray incident on the cell that is in the ON state passes through the cell, The lighting device according to claim 1, wherein the light rays from the group of light rays that are incident on the cell in the off state do not pass through the cell and are shielded.

6. The illumination device according to claim 1, wherein the first optical element is a physical mask including an image composed of an opaque region that does not transmit visible light and a transmissive region that transmits visible light.

7. A dot size changing method is provided in which a first optical element, positioned between a diffractive optical element and a projection surface, 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 the projection surface, and the first optical element forms an image on the projection surface by blocking at least a portion of the group of rays converted by the diffractive optical element, thereby changing the size of the dot pattern projected onto the projection surface by adjusting the beam diameter of the laser light incident on the diffractive optical element.

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