Diffusion plate and optical device

Abstract

This diffusion plate comprises: a substrate having a first main surface and a second main surface opposite to the first main surface; and a lens array constituted of a plurality of lenses formed on the first main surface of the substrate, the lens array letting a light beam be diffused and transmitted therethrough. The plurality of lenses are arranged in a rectangular lattice shape. The light beam on the first main surface of the substrate has a circular or elliptical shape. Expressions (1A), (1B), (2A), and (2B) in the specification are established.

Description

Diffuser and optical device

[0001] The present disclosure relates to a diffuser plate and an optical device.

[0002] A diffuser plate diffuses and transmits light. A diffuser plate can be obtained, for example, by sandblasting one side of a substrate. In this case, the intensity distribution of the light after diffusing and transmitting through the diffuser plate becomes a Gaussian distribution. Diffuser plates with lens arrays have been developed so that the intensity distribution becomes a top-hat distribution instead of a Gaussian distribution.

[0003] A lens array is a regular arrangement of multiple lenses. The lens array can make the intensity distribution of light rays after diffusing and transmitting through a diffuser into a top-hat distribution. A top-hat distribution is also called a flat-top distribution. The intensity distribution of light rays before diffusing and transmitting through a diffuser is, for example, a Gaussian distribution.

[0004] The intensity distribution of the light beam before being diffused and transmitted through the diffuser plate is not limited to a Gaussian distribution, but may be, for example, a super-Gaussian distribution. A super-Gaussian distribution has broader tails than a Gaussian distribution. Furthermore, the intensity distribution of the light beam before being diffused and transmitted through the diffuser plate does not have to be symmetrical with respect to the optical axis, and may have different distributions in the X-axis and Y-axis directions, which will be described later.

[0005] The characteristics of a top-hat distribution are evaluated, for example, by uniformity and cutoff performance. Uniformity is evaluated, for example, by the variation in the intensity of the light beam when the diffusion angle of the light beam is within a predetermined range. The smaller the variation, the better the uniformity. Cutoff performance is evaluated, for example, by the gradient when the diffusion angle of the light beam exceeds the predetermined range and the intensity of the light beam decreases. The steeper the gradient, the better the cutoff performance.

[0006] Japanese Patent Laid-Open Publication No. 2017-26662 (Patent Document 1) describes that a desired top-hat distribution can be obtained by making the surface shape of a lens an aspherical shape with a negative Conic coefficient k. Figure 3 of Patent Document 1 illustrates the surface shape of a lens with a negative Conic coefficient k and the surface shape of a lens with a Conic coefficient k of zero.

[0007] As is clear from Figure 3 of Patent Document 1, the difference between the surface shape of a lens with a negative Conic coefficient k and the surface shape of a lens with a Conic coefficient k of zero is very small. Therefore, extremely high precision is required for lens processing. As a result, when a lens array is actually produced, there is a problem of variations in cutoff characteristics.

[0008] One aspect of the present disclosure provides a technology for obtaining a top-hat distribution with good uniformity and cutoff characteristics using a lens array with a simple structure.

[0009] A diffuser plate according to one aspect of the present disclosure includes a substrate having a first main surface and a second main surface facing opposite to the first main surface, and a lens array composed of a plurality of lenses formed on the first main surface of the substrate, where light rays are diffused and transmitted by the lens array. The plurality of lenses are arranged in a rectangular lattice pattern. The shape of the light rays at the first main surface of the substrate is circular or elliptical. A direction parallel to one side of the rectangle is defined as a first direction, and a direction perpendicular to the first direction is defined as a second direction. The average pitch of the lenses in the first direction is defined as Px, and the average pitch of the lenses in the second direction is defined as Py. The size of the light rays at the first main surface of the substrate is expressed by the length Φx of a first line segment that passes through the center of the light rays and is parallel to the first direction, and the length Φy of a second line segment that passes through the center of the light rays and is parallel to the second direction. The maximum wavelength of the light rays is defined as λ, and the units of Px, Py, Φx, Φy, and λ are consistent. The following formulas (1A), (1B), (2A) and (2B) hold: λ / Px<0.00380 (1A) λ / Py<0.00380 (1B) Φx / Px>7.0 (2A) Φy / Py>7.0 (2B).

[0010] A diffuser plate according to another aspect of the present disclosure includes a substrate having a first main surface and a second main surface facing opposite to the first main surface, and a lens array composed of a plurality of lenses formed on the first main surface of the substrate, and diffuses and transmits light rays through the lens array. The plurality of lenses are arranged in a lattice pattern of equilateral triangles. The shape of the light rays at the first main surface of the substrate is circular. A direction parallel to one side of the equilateral triangle is defined as a first direction, a direction parallel to another side of the equilateral triangle is defined as a second direction, and a direction parallel to the remaining side of the equilateral triangle is defined as a third direction. The average pitch of the lenses in the first direction, the second direction, and the third direction is defined as P. The size of the light rays at the first main surface of the substrate is defined as the length Φ of a first line segment that passes through the center of the light rays and is parallel to the first direction. θ１ and a length Φ of a second line segment that passes through the center of the light ray and is parallel to the second direction. θ２ and a length Φ of a third line segment that passes through the center of the light ray and is parallel to the third direction. θ３ It is expressed as Φ θ１ and Φ θ２ and Φ θ３ The minimum value of P is defined as Φmin, the maximum wavelength of the light is defined as λ, and the units of P, Φmin, and λ are the same. The following equations (1) and (2) hold: λ / P<0.00380 (1) Φmin / P>7.0 (2).

[0011] According to one aspect of the present disclosure, a top-hat distribution with good uniformity and cutoff characteristics can be obtained with a lens array having a simple structure.

[0012] FIG. 1 is a cross-sectional view showing an optical device according to an embodiment. FIG. 2 is a plan view showing an example of a rectangular lattice lens arrangement in which Px and Py are equal. FIG. 3 is a diagram showing an example of changes in the intensity distribution of an image formed on a screen when, for a diffuser having a FWHM (full width at half maximum) in the X-axis direction of 5.7°, λ is fixed at 450 nm, Φx and Φy are fixed at 3.0 mm, and Px and Py are changed from 60 μm to 200 μm in 20 μm increments. FIG. 4 is a supplementary diagram of FIG. 3. FIG. 5 is a graph of parts of FIGS. 3 and 4. FIG. 6 is a diagram showing an example of the relationship between (λ / Px) and Tθx. FIG. 7 is a diagram showing an example of diffracted light. FIG. 8 is a diagram showing an example of changes in the intensity distribution of an image formed on a screen when λ is fixed at 450 nm, Px and Py are fixed at 140 μm, and Φx and Φy are changed from 3.0 mm to 0.5 mm in 0.5 mm increments. FIG. 9 is a supplementary diagram of FIG. 8. FIG. 10 is a graph of a portion of FIGS. 8 and 9. FIG. 11 is a diagram showing an example of the relationship between (Φx / Px) and σ. FIG. 12 is a plan view showing an example of a rectangular lattice lens arrangement in which Px and Py are different. FIG. 13 is a plan view showing a modification of FIG. 12. FIG. 14 is a plan view showing an example of a regular triangular lattice lens arrangement. FIG. 15 is a diagram showing an example of the relationship between (λ / P) and cutoff characteristics. FIG. 16 is a supplementary diagram of FIG. 15. FIG. 17 is a flowchart showing a method for manufacturing a diffuser plate according to an embodiment. FIG. 18 is a cross-sectional view showing an example of S101 in FIG. 17. FIG. 19 is a cross-sectional view showing an example of S102 in FIG. 17.

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and their description may be omitted. In the specification, the symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0014] An optical device 1 according to one embodiment will be described with reference to Fig. 1 . The optical device 1 may be a projection device, a lighting device, a display device, or the like, and in this embodiment is a projection device. The projection device is not particularly limited, but examples thereof include a projector, a head-up display (HUD), and a head-mounted display (HMD). The projection device forms an image on a screen 5.

[0015] The optical device 1 includes, for example, a diffuser plate 2 and a light source 3. The diffuser plate 2 diffuses and transmits light beams LB emitted from the light source 3. The light beams LB are, for example, visible light. Although not limited to, the light beams LB are substantially parallel rays. The light source 3 irradiates the light beams LB onto the diffuser plate 2. The light beams LB are diffused and transmitted by the diffuser plate 2, forming an image on a screen 5. The diffuser plate 2 can make the brightness of the image uniform and also suppress glare (speckle).

[0016] The light source 3 includes, for example, a laser light source. While laser light sources have excellent brightness and color rendering properties, they also tend to accentuate glare. When the light source 3 includes a laser light source, the effect of suppressing glare with the diffuser 2 is significantly achieved. The light source 3 may include light sources of multiple colors, for example, a blue light source, a green light source, and a red light source.

[0017] 1 , a diffuser 2 according to one embodiment will be described. The diffuser 2 includes a substrate 10 and a lens array 20. The substrate 10 has a first major surface 11 and a second major surface 12 facing opposite to the first major surface 11. The lens array 20 is formed on the first major surface 11 of the substrate 10.

[0018] The lens array 20 is formed on the first main surface 11 of the substrate 10, but is not formed on the second main surface 12 of the substrate 10. The second main surface 12 of the substrate 10 is a flat surface in its entirety. However, the lens array 20 may be formed not only on the first main surface 11 of the substrate 10, but also on the second main surface 12 of the substrate 10.

[0019] In addition, when the entire second main surface 12 of the substrate 10 is flat, it is preferable that the first main surface 11 of the substrate 10 is disposed facing the light source 3. The unevenness of the lens array 20 can suppress perpendicular reflection of the light beam LB incident on the diffuser plate 2 from the light source 3. This reduces the intensity of the light beam LB returning to the laser light source, stabilizing the oscillation of the laser light source. In addition, multiple reflections of the light beam LB within the optical device 1 can be suppressed.

[0020] The substrate 10 is, but is not limited to, a glass substrate. The material of the glass substrate is, but is not limited to, aluminosilicate glass, borosilicate glass, or quartz glass. The thickness of the substrate 10 is preferably 0.2 mm to 2.0 mm, and more preferably 0.5 mm to 1.0 mm.

[0021] The lens array 20 is composed of a plurality of lenses 21 arranged regularly. In this embodiment, the plurality of lenses 21 have substantially the same shape and substantially the same dimensions. However, the shapes and dimensions of the lenses 21 may have some degree of variation. Here, the physical quantities that have variation include the XY coordinates of the bottom or apex of the lenses 21, the radius of curvature of the lenses 21, or the depth of the bottom or the height of the apex of the lenses 21. It is sufficient if a desired top-hat distribution, which will be described later, can be obtained.

[0022] Although each of the lenses 21 is a concave lens in this embodiment, it may be a convex lens. Furthermore, although each of the lenses 21 is a spherical lens in this embodiment, it may be an aspherical lens. The lenses 21 are formed so that there is no flat surface between adjacent lenses 21, as shown in FIG. 1 .

[0023] As shown in FIG. 2, when the first main surface 11 of the substrate 10 (more specifically, the lens array 20) is viewed from the front, the multiple lenses 21 are arranged in a rectangular lattice pattern. The centers of the lenses 21 are located at the lattice points (vertices of the rectangle). The direction parallel to one side of the rectangle is the first direction (X-axis direction), and the direction perpendicular to the first direction is the second direction (Y-axis direction). In FIG. 2, the dashed line represents a straight line connecting two adjacent vertices of the rectangle. In FIGS. 2, 12, and 13, the grayscale represents the difference in elevation. The closer the color of the image is from white to black, the lower the elevation.

[0024] In Fig. 2, Px is the average pitch of the lenses 21 in the first direction. Also, in Fig. 2, Py is the average pitch of the lenses 21 in the second direction. The rectangular lattice is, for example, a square lattice. In this case, Px and Py are equal. Note that although the rectangle is a square in this embodiment, it may also be a rectangle in which the lengths of one pair of opposite sides are different from the lengths of the other pair of opposite sides, as shown in Figs. 12 and 13. In this case, Px and Py are different.

[0025] As shown in FIG. 2 , the size of the light ray LB on the first main surface 11 of the substrate 10 (more specifically, the lens array 20) is represented by the length Φx of a first line segment passing through the center of the light ray LB and parallel to the first direction, and the length Φy of a second line segment passing through the center of the light ray LB and parallel to the second direction. The shape of the light ray LB on the first main surface 11 of the substrate 10 is, for example, circular. In this case, Φx and Φy are equal. Note that although the shape of the light ray LB on the first main surface 11 of the substrate 10 is circular in this embodiment, it may also be elliptical, as shown in FIG. 12 . In this case, Φx and Φy are different. The ellipse shown in FIG. 12 has a minor axis parallel to the first direction and a major axis parallel to the second direction. However, as shown in FIG. 13 , the major and minor axes of the ellipse may be inclined with respect to the first and second directions.

[0026] Φ Ｘ and Φ Ｙ The ratio (Φ Ｘ / Φ Ｙ ) is P Ｘ and P Ｙ The ratio (P Ｘ / P Ｙ ) is preferably equal to

[0027] ΦＸ and Φ Ｙ represents the size of the outer edge of the light beam LB on the first main surface 11 of the substrate 10. The size is determined based on the intensity distribution of the light beam LB before passing through the lens array 20. The intensity distribution of the light beam LB before passing through the lens array 20 is, for example, a Gaussian distribution or a super-Gaussian distribution. ２ (approximately 13.5%) is defined as the outer edge of the light beam LB, where e is the natural logarithm.

[0028] As described above, the lens array 20 is a regular arrangement of a plurality of lenses 21. The lens array 20 can make the intensity distribution of the light beam LB after it has been diffused and transmitted through the diffuser plate 2 a top-hat distribution. A top-hat distribution is also called a flat-top distribution. The intensity distribution of the light beam LB before it has been diffused and transmitted through the diffuser plate 2 is, for example, a Gaussian distribution or a super-Gaussian distribution.

[0029] The characteristics of the top-hat distribution are evaluated in terms of uniformity and cutoff performance. The uniformity is evaluated, for example, by the variation in the intensity of the light beam LB when the diffusion angle of the light beam LB is within a predetermined range. The smaller the variation, the better the uniformity. The cutoff performance is evaluated, for example, by the gradient when the diffusion angle of the light beam LB exceeds the predetermined range and the intensity of the light beam LB decreases. The steeper the gradient, the better the cutoff performance.

[0030] The inventors of the present application focused on (λ / Px), (λ / Py), (Φx / Px), and (Φy / Py) in order to obtain a top-hat distribution with good uniformity and cutoff characteristics using a lens array 20 with a simple structure. Here, the units of Px, Py, Φx, Φy, and λ are all the same. λ is the maximum wavelength of the light beam LB. When the light beam LB is visible light, the wavelength range of visible light is, for example, 400 nm to 800 nm.

[0031] When Px and Py are equal as shown in Figure 2, the image formed by light beam LB on screen 5 is square as shown in Figures 3 and 4. When Px and Py are different as shown in Figures 12 and 13, the image formed by light beam LB on screen 5 is rectangular, having long and short sides (not shown). The shape of the image formed by light beam LB on screen 5 is determined primarily by the shape of the grating. Figures 3 and 4 show the change in the intensity distribution of the image when λ is fixed at 450 nm, Φx and Φy are fixed at 3.0 mm, and Px and Py are changed from 60 μm to 200 μm in 20 μm increments as shown in Table 1.

[0032]

[0033] In Figures 3 and 4, θx represents the diffusion angle in the first direction, θy represents the diffusion angle in the second direction, and RI represents the relative intensity. RI is normalized based on the intensity when θx is 0° and θy is 0°. RI was calculated by simulation using Fresnel diffraction theory. The step size of θx and θy was 0.1°. In Figures 3 and 4, the RI increases as the image color approaches white from black. Figure 5 shows a graph of parts of Figures 3 and 4. It can be seen from Figures 3, 4, and 5 that the smaller (λ / Px) and (λ / Py), the better the cutoff performance.

[0034] The smaller (λ / Px), the better the cutoff performance. This is thought to be due to the smaller θxm, which will be described later. θxm is the diffusion angle of the m-th order diffracted light in the first direction (see FIG. 7). It is known that θxm is proportional to sin(λ / Px). Therefore, the smaller (λ / Px), the smaller θxm.

[0035] Furthermore, the smaller (λ / Py), the better the cutoff performance. This is thought to be due to the smaller θym, which will be described later. θym is the diffusion angle of the m-th order diffracted light in the second direction. θym is known to be proportional to sin(λ / Py). Therefore, the smaller (λ / Py), the smaller θym.

[0036] The smaller (λ / Px) and (λ / Py) are, the more orders of diffracted light fall within a predetermined diffusion angle range. It is believed that the cutoff performance improves when high-order diffracted light falls within a predetermined diffusion angle range. From the viewpoint of cutoff performance, it is preferable that the following formulas (1A) and (1B) be satisfied: λ / Px<0.00380 (1A) λ / Py<0.00380 (1B).

[0037] The cutoff characteristic is evaluated by, for example, Tθx and Tθy. Tθx and Tθy are the ranges of change in θx and θy when RI changes from 0.8 to 0.2. An example of the relationship between (λ / Px) and Tθx is shown in FIG. 6. Ｙ The relationship between (λ / Px) and Tθy is the same as the relationship between (λ / Px) and Tθx, and is therefore not shown in the figures. It can also be seen from Figure 6 that if the above formulas (1A) and (1B) are established, the cutoff characteristics are good.

[0038] When Px and Py are equal as shown in Fig. 2, the image formed by the light beam LB on the screen 5 is a square as shown in Fig. 8 and Fig. 9. Fig. 8 and Fig. 9 show an example of the change in the intensity distribution of the image when λ is fixed at 450 nm, Px and Py are fixed at 140 μm, and Φx and Φy are changed from 3.0 mm to 0.5 mm in 0.5 mm increments.

[0039] In Figures 8 and 9, θx indicates the diffusion angle in the first direction, θy indicates the diffusion angle in the second direction, and RI indicates relative intensity. RI is normalized based on the intensity when θx is 0° and θy is 0°. RI was calculated by simulation using Fresnel diffraction theory. The step size of θx and θy was 0.1°. In Figures 8 and 9, the RI increases as the image color approaches white from black. Figure 10 shows graphs of parts of Figures 8 and 9.

[0040] 8, 9, and 10, it can be seen that the larger (Φx / Px) and (Φy / Py) are, the better the uniformity is. It is thought that the larger (Φx / Px) and (Φy / Py) are, the more lenses 21 that contribute to image formation, and therefore the better the uniformity is. From the viewpoint of uniformity, it is preferable that the following formulas (2A) and (2B) are satisfied: Φx / Px>7.0 (2A) Φy / Py>7.0 (2B).

[0041] The uniformity is evaluated, for example, by σ, which is the standard deviation of the relative intensity RI in a predetermined range Δθx, Δθy. Δθx and Δθy are half of the range Ax, Ay in which RI is 0.5 or more. RI is measured by changing θx in Δθx in increments of 0.1°. RI is also measured by changing θy in Δθy in increments of 0.1°. An example of the relationship between (Φx / Px) and σ is shown in FIG. 11. Note that the relationship between (Φy / Py) and σ is the same as the relationship between (Φx / Px) and σ, and is therefore not shown.

[0042] It can also be seen from FIG. 11 that if the above formulas (2A) and (2B) are established, the uniformity is good.

[0043] It should be noted that multiple light sources 3 may separately irradiate light rays LB onto the same or different regions of one diffuser plate 2. The wavelengths of the multiple light sources 3 may be the same or different. The light rays LB of different light sources 3 do not interfere with each other. Therefore, in this case, it is sufficient that the above formulas (2A) and (2B) are satisfied for each light ray LB.

[0044] As shown in FIG. 14 , when the first major surface 11 of the substrate 10 (more specifically, the lens array 20) is viewed from the front, the multiple lenses 21 may be arranged in a lattice pattern of equilateral triangles. The centers of the lenses 21 are located at the lattice points (vertices of the equilateral triangle). The direction parallel to one side of the equilateral triangle is the first direction (θ1 direction), the direction parallel to another side of the equilateral triangle is the second direction (θ2 direction), and the direction parallel to the remaining side of the equilateral triangle is the third direction (θ3 direction). In FIG. 14 , the dashed lines represent the lines connecting two adjacent vertices of the equilateral triangle. Note that a regular triangular lattice is also called a regular hexagonal lattice.

[0045] 14, P is the average pitch of the lenses 21 in the first, second, and third directions. As shown in FIG. 14, the size of the light ray LB on the first main surface 11 of the substrate 10 is the length Φ of a first line segment that passes through the center of the light ray LB and is parallel to the first direction. θ１ and the length Φ of a second line segment that passes through the center of the light ray LB and is parallel to the second direction. θ２ and the length Φ of the third line segment that passes through the center of the ray LB and is parallel to the third direction. θ３ The shape of the light ray LB on the first main surface 11 of the substrate 10 is circular or elliptical. In Fig. 14, the outer edge of the light ray LB on the first main surface 11 of the substrate 10 is defined based on the intensity distribution of the light ray LB before passing through the lens array 20, similar to Fig. 2.

[0046] The inventors of the present application focused on (λ / P) and (Φmin / P) in order to obtain a top hat distribution with good uniformity and cutoff characteristics using a lens array 20 with a simple structure. Here, the units of P, Φmin, and λ are the same. λ is the maximum wavelength of the light beam LB. When the light beam LB is visible light, the wavelength range of visible light is, for example, 400 nm to 800 nm. Φmin is calculated by multiplying Φ θ１ and Φ θ２ and Φ θ３ is the minimum value of

[0047] When a plurality of lenses 21 are arranged in a regular triangular lattice as shown in Fig. 14, the image formed by the light beam LB on the screen 5 is circular (more specifically, a regular hexagon with rounded corners) as shown in Fig. 15 and Fig. 16. Figs. 15 and 16 show the case where λ is fixed at 450 nm and Φ θ１ and Φ θ２ and Φ θ３ 1 shows the change in the intensity distribution of the image when Φmin and Φmin are fixed at 3.0 mm and P is changed from 60 μm to 200 μm in 20 μm increments.

[0048] In Figures 15 and 16, θx indicates the diffusion angle in the first direction (θ1 direction), θy indicates the diffusion angle in the direction perpendicular to the first direction, and RI indicates the relative intensity. RI is normalized based on the intensity when θx is 0° and θy is 0°. RI was calculated by simulation using Fresnel diffraction theory. In Figures 15 and 16, the RI increases as the image color approaches white from black.

[0049] 15 and 16, it can be seen that the smaller (λ / P), the better the cutoff performance. From the viewpoint of cutoff performance, it is preferable that the following formula (1) λ / P<0.00380 (1) is satisfied.

[0050] From the viewpoint of uniformity, it is preferable that the following formula (2) be satisfied: Φmin / P>7.0 (2).

[0051] It should be noted that multiple light sources 3 may separately irradiate light rays LB onto the same or different regions of one diffuser plate 2. The wavelengths of the multiple light sources 3 may be the same or different. The light rays LB of different light sources 3 do not interfere with each other. Therefore, in this case, it is sufficient that the above formula (2) is satisfied for each light ray LB.

[0052] 17 to 19, a method for manufacturing the diffuser plate 2 according to one embodiment will be described. The method for manufacturing the diffuser plate 2 includes, for example, steps S101 to S102, as shown in FIG. 17. The method for manufacturing the diffuser plate 2 may include steps other than steps S101 to S102. For example, after step S101 and before step S102, a step of heating the entire substrate 10 may be performed to reduce residual stress in the substrate 10.

[0053] 18 , step S101 includes irradiating the first main surface 11 of the substrate 10 with a laser beam LB2 at positions where the lenses 21 are to be formed, thereby forming recesses 22. The recesses 22 are formed at the positions irradiated with the laser beam LB2. Step S101 forms a plurality of recesses 22 by changing the irradiation position of the laser beam LB2 on the first main surface 11 of the substrate 10. In this embodiment, the irradiation position of the laser beam LB2 is changed by moving the substrate 10, but may also be changed by moving an optical element (e.g., a mirror) that constitutes the optical system 52.

[0054] The laser beam LB2 forms the recesses 22 by sublimating or evaporating the glass. The shape and dimensions of the recesses 22 are controlled by the focusing position, focusing angle, focusing diameter, and irradiation time of the laser beam LB2. Compared to blasting, laser processing can suppress damage to the substrate 10 (e.g., the occurrence of latent scratches) and improve the strength of the diffusion plate 2. Furthermore, laser processing makes it easier to control the position where the recesses 22 are formed and the shape and dimensions of the recesses 22 than blasting.

[0055] As described above, the laser beam LB2 forms the recesses 22 by sublimating or evaporating the glass. Therefore, the wavelength of the laser beam LB2 is not particularly limited, but is preferably 9.2 μm to 10.8 μm from the viewpoint of the absorption rate by glass. The light source 51 of the laser beam LB2 is preferably, for example, a CO ２ The light source 51 is, for example, a continuous wave laser.

[0056] Another example of the light source 51 is a pulsed laser. The pulse width is not particularly limited, but examples include 1 ps to 10 μs. The wavelength of the laser beam LB2 is not particularly limited, but examples include 1064 nm or 355 nm.

[0057] Immediately after being emitted from the light source 51, the polarization of the laser beam LB2 is linearly polarized, and the intensity distribution of the cross section of the laser beam LB2 is a Gaussian distribution or a super-Gaussian distribution. An optical system 52 is provided between the light source 51 and the substrate 10. The optical system 52 irradiates the substrate 10 with the laser beam LB2 emitted from the light source 51. The laser beam LB2 is incident perpendicularly on the first main surface 11 of the substrate 10. The optical system 52 includes, for example, a wave plate 53, a condenser lens 54, etc.

[0058] The wave plate 53 converts the polarization of the laser beam LB2 from linearly polarized light to circularly polarized light. The wave plate 53 is configured, for example, with a quarter-wave plate. The wave plate 53 is disposed, for example, between the light source 51 and the condenser lens 54. The wave plate 53 may be omitted, and the optical system 52 may irradiate the substrate 10 with the linearly polarized laser beam LB2.

[0059] The condenser lens 54 condenses and irradiates the laser beam LB2 onto the substrate 10. The condensing position of the laser beam LB2 is, for example, on the first main surface 11 of the substrate 10 or in the vicinity thereof. The substrate 10 is locally heated, the heated portion is removed, and the recess 22 is formed. The condenser lens 54 is disposed, for example, between the wave plate 53 and the substrate 10.

[0060] The optical system 52 may include a homogenizer. The homogenizer converts the cross-sectional intensity distribution of the laser beam LB2 from a Gaussian or super-Gaussian distribution to a top-hat distribution. The homogenizer is disposed, for example, between the wave plate 53 and the condenser lens 54.

[0061] The optical system 52 may also have an aperture. The aperture has a circular opening smaller than the cross section of the laser beam LB2 and shields the peripheral portion of the cross section of the laser beam LB2, thereby increasing the circularity of the cross section of the laser beam LB2. The aperture is disposed, for example, between the wave plate 53 and the condenser lens 54. The aperture is also disposed, for example, between the homogenizer and the condenser lens 54.

[0062] Before step S101, various functional films may be formed on the substrate 10. For example, a protective film may be formed on at least one of the first main surface 11 and the second main surface 12 of the substrate 10. The protective film prevents adhesion of processing debris that scatters from the first main surface 11 due to irradiation with the laser beam LB2. The protective film is preferably a removable film, for example, a water-soluble film.

[0063] Step S102 includes wet-etching the substrate 10 with the recesses 22 formed therein to form the lens array 20 as shown in Fig. 19. The etching solution is selected depending on the material of the substrate 10, and is, for example, a mixed acid of hydrofluoric acid (HF) and hydrochloric acid (HCl). Step S102 includes, for example, immersing the substrate 10 in the etching solution.

[0064] The recesses 22 are etched to form the lenses 21. In this case, concave lenses are formed as the lenses 21. Compared to cutting, wet etching can suppress damage to the substrate 10 (for example, the occurrence of latent scratches) and can improve the strength of the diffusion plate 2.

[0065] The diffuser plate and optical device according to the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure.

[0066] The disclosure of Japanese Patent Application No. 2024-100750 is incorporated herein by reference in its entirety.

[0067] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A diffusion plate comprising: a substrate having a first main surface and a second main surface facing opposite to the first main surface; and a lens array consisting of a plurality of lenses formed on the first main surface of the substrate, wherein light rays are diffused and transmitted by the lens array, wherein the plurality of lenses are arranged in a rectangular lattice pattern, and the shape of the light rays on the first main surface of the substrate is circular or elliptical, a direction parallel to one side of the rectangle is defined as a first direction, and a direction perpendicular to the first direction is defined as a second direction, wherein Px is the average pitch of the lenses in the first direction, and Py is the average pitch of the lenses in the second direction, and the size of the light rays on the first main surface of the substrate is expressed by Φx, the length of a first line segment that passes through the center of the light rays and is parallel to the first direction, and Φy, the length of a second line segment that passes through the center of the light rays and is parallel to the second direction, and wherein λ is the maximum wavelength of the light rays, and when Px, Py, Φx, Φy and λ are all in the same unit, A diffusion plate in which the following formulas (1A), (1B), (2A) and (2B) are satisfied: λ / Px<0.00380 (1A) λ / Py<0.00380 (1B) Φx / Px>7.0 (2A) Φy / Py>7.0 (2B).

2. A diffusion plate comprising a substrate having a first main surface and a second main surface facing opposite to the first main surface, and a lens array consisting of a plurality of lenses formed on the first main surface of the substrate, wherein light rays are diffused and transmitted by the lens array, wherein the plurality of lenses are arranged in a lattice pattern of equilateral triangles, the shape of the light rays on the first main surface of the substrate is circular or elliptical, a direction parallel to one side of the equilateral triangle is defined as a first direction, a direction parallel to another side of the equilateral triangle is defined as a second direction, and a direction parallel to the remaining side of the equilateral triangle is defined as a third direction, the average pitch of the lenses in the first direction, the second direction, and the third direction is defined as P, and the size of the light rays on the first main surface of the substrate is defined as the length Φ of a first line segment that passes through the center of the light rays and is parallel to the first direction. θ１ and a length Φ of a second line segment that passes through the center of the light ray and is parallel to the second direction. θ２ and a length Φ of a third line segment that passes through the center of the light ray and is parallel to the third direction. θ３ and Φ θ１ and Φ θ２ and Φ θ３ The diffusion plate has the following formulas (1) and (2): λ / P<0.00380 (1) Φmin / P>7.0 (2) where Φmin is the minimum value of the above and λ is the maximum wavelength of the light beam, and the units of P, Φmin, and λ are the same.

3. The diffuser plate according to claim 1 or 2, wherein each of the plurality of lenses is a spherical lens.

4. An optical device comprising: the diffuser plate according to claim 1 or 2; and a light source that irradiates the diffuser plate with the light beam.

5. An optical device comprising: the diffuser plate according to claim 3; and a light source that irradiates the diffuser plate with the light beam.

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