Microlens array, diffuser plate for projection device, and projection device

Abstract

To provide a microlens array which is excellent in cut-off characteristics and which suppresses the generation of diffraction luminescent spots.SOLUTION: A microlens array includes a base material transparent relative to a working wavelength and a plurality of aspherical lenses formed on a first surface of the base material. The centers of the aspherical lenses are at two or more different positions in a direction orthogonal to the first surface. A pitch variation relative to an average of all the pitches in a region excluding 25% of the aspherical lenses at both ends, which are arrayed in an arbitrary one-dimensional direction, is less than 7.5% in the first surface.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a microlens array and a projection device. [Background technology]

[0002] A technology is known in which multiple concave lenses are formed on the surface of a transparent substrate and light is diffused by utilizing the refraction phenomenon (see, for example, Patent Documents 1 and 2). FIG. 1 is a schematic diagram of a conventional lens array, with (A) being a top view and (B) being a vertical cross-sectional view. In a known diffuser having an array of concave lenses LNS, the depths of the concave lenses LNS vary as d1, d2, ..., and the center coordinate C of the concave lenses LNS varies in the in-plane direction. In (A) of FIG. 1, dotted circles indicate equally spaced positions in the XY plane as a reference. Compared to the equally spaced positions, the center coordinate C of the concave lenses LNS is shifted from the center of the equally spaced positions in both the X and Y directions, and the pitch varies as P1, P2, ..., in the XY plane. Varying the depth d and pitch P of the concave lenses LNS prevents diffracted light from being generated in only a specific direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6424418 [Patent Document 2] Patent No. 6680455 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors discovered that if the pitch of the lenses arranged in any one-dimensional direction in a microlens array varies, it becomes difficult to provide a good cutoff characteristic to the diffused light profile, and that depending on the degree of depth variation, diffracted bright spots may occur.

[0005] An object of the present invention is to provide a microlens array that has good cutoff characteristics and suppresses the occurrence of diffracted bright spots. [Means for solving the problem]

[0006] In one aspect of the present invention, the microlens array comprises: Transparent to the wavelength used Glass substrate and, The aforementioned Glass substrate a plurality of aspherical lenses formed on the first surface; and the center of the aspherical lens is at two or more different positions in a direction perpendicular to the first surface, a value σ / μ obtained by dividing 1σ by an average value μ when the center position of the aspherical lens in a direction orthogonal to the first surface follows a normal distribution is greater than 0.027 and less than 0.200, Both ends of the aspherical lens are arranged in an arbitrary one-dimensional direction within the plane of the first surface. In total, Average of all pitches in the area excluding 25% When is set to 1, the absolute value of the maximum possible difference in the relative pitch ratio σ p is 0.075 is less than. [Effects of the Invention]

[0007] A microlens array having good cutoff characteristics and suppressing the occurrence of diffracted bright spots is realized. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a conventional lens array. [Figure 2] 1A and 1B are a cross-sectional schematic view and a top view image of a microlens array according to an embodiment. [Figure 3] 1 is a sample image of a microlens array according to an embodiment. [Figure 4] 4 is a cross-sectional view taken along the line XX' of FIG. [Figure 5] 4 is a diffusion profile of the microlens array of FIG. 3. [Figure 6] FIG. 10 is a diagram showing a simulation result of an aspherical lens array. [Figure 7]FIG. 10 is a simulation diagram of a diffusion profile when the depth variation of an aspherical lens is changed. [Figure 8] 10A and 10B are simulation diagrams of three-dimensional intensity distribution and two-dimensional intensity distribution when the depth variation of the aspherical lens is changed. [Figure 9A] This is a top view image of an actually fabricated sample. [Figure 9B] This is the actual measurement value of the lens depth at the line II' in FIG. 9A. [Figure 9C] This is the analysis result of the measured values ​​in FIG. 9B. [Figure 9D] FIG. 10 is a diagram showing the upper limit of the depth variation of an aspherical lens. [Figure 10] 9B is a diffusion profile in the Y direction of the sample of FIG. 9A. [Figure 11] FIG. 10 is a simulation diagram of a diffusion profile when the in-plane pitch variation of an aspherical lens is changed. [Figure 12] FIG. 10 illustrates the change in cutoff band as a function of pitch variation. [Figure 13] FIG. 10 is a diagram illustrating how to determine a cutoff band. [Figure 14] FIG. 10 is a simulation diagram of a two-dimensional intensity distribution when the pitch variation of an aspherical lens is changed only in the Y direction. [Figure 15] FIG. 10 is a diagram showing the change in the relative pitch ratio of samples produced by changing the maximum pitch variation in the Y direction. [Figure 16A] FIG. 10 is a diagram showing the results of measurements of diffusion characteristics when the maximum pitch variation in the Y direction is changed. [Figure 16B] FIG. 16B is a simulation diagram of the diffusion characteristics corresponding to FIG. 16A. [Figure 17] FIG. 16B is an enlarged view of a portion of FIG. 16A. [Figure 18] FIG. 10 is a diagram illustrating how to determine a slope as a cutoff characteristic. [Figure 19] FIG. 18 is a diagram showing the analysis results based on FIG. 17. [Figure 20] 1 is a schematic diagram of a projection device to which a microlens array according to an embodiment is applied. DETAILED DESCRIPTION OF THE INVENTION

[0009] In an embodiment, in a microlens array having a plurality of aspherical lenses formed on a first surface of a substrate transparent to the wavelength used, the center positions of the aspherical lenses are varied in a direction perpendicular to the first surface, thereby suppressing pitch variation of the aspherical lenses within the first surface. Specifically, as described below, pitch variation relative to the average of all pitches in a region excluding both ends of the aspherical lenses arranged in any one-dimensional direction within the first surface is suppressed to less than 7.5%, more preferably 5.0% or less. Suppressing pitch variation within the aspherical lenses improves the cutoff characteristics of the diffusion profile. Furthermore, by varying the center position of the aspherical lenses, i.e., lens depth variation, by a predetermined percentage or more relative to the average value, diffraction bright spots are suppressed.

[0010] 2 shows an example of a microlens array 10 according to an embodiment. In FIG. 2, (A) is a schematic cross-sectional view of the microlens array 10, and (B) is an image seen from above.

[0011] As shown in Figure 2(A), microlens array 10 has a plurality of aspherical lenses 13 formed on a first surface 101 of substrate 11 that is transparent to the wavelength used. In this example, aspherical lenses 13 are concave lenses with parabolic surfaces. Centers 14 of aspherical lenses 13 are located at two or more different positions in a direction perpendicular to first surface 101, which in this example is the depth direction of substrate 11. In other words, the depths d of aspherical lenses 13 vary.

[0012] On the other hand, the pitch P between the centers 14 of the aspherical lenses 13 is almost constant. "Almost constant" means that the pitch variation is suppressed to be smaller than a predetermined variation. In this specification, the pitch variation refers to the absolute value of the maximum possible difference in the randomly distributed relative pitch ratios in the entire pitch in the region of the lens in any one-dimensional direction, when the average pitch in the region excluding both ends is set to 1, and this is referred to as σ p In the microlens array 10, when the lens arrangement in any one-dimensional direction is taken into consideration, the pitch variation σ of the aspherical lenses 13 in the area excluding 25% at both ends is expressed as p is less than 0.075, that is, the variation from the average pitch is suppressed to less than 7.5%.

[0013] In Figure 2(B), the white dots in the center of each aspherical lens 13 indicate the lens center. The microlens array 10 includes a square lattice arrangement of aspherical lenses 13, with a nearly constant pitch in both the X direction (horizontal direction on the paper) and the Y direction (vertical direction on the paper). The absolute value of the pitch correlates with the diffusion angle in that direction. In the example of Figure 2(B), the aspect ratio of the pitch in the X and Y directions is set to be greater than 1. However, to form a square projected image, the pitch of the aspherical lenses 13 may be designed to be the same in both the X and Y directions. In either case, the pitch variation of the aspherical lenses 13 in one-dimensional directions, such as the X and Y directions, is kept to less than 7.5%, and more preferably to 5.0% or less, resulting in a nearly regular lens arrangement in the in-plane direction.

[0014] By arranging the aspherical lenses 13 in a regular pattern in the XY plane, it is possible to improve the cutoff characteristics of the diffusion profile of the microlens array 10. In the direction perpendicular to the XY plane (i.e., the first surface 101), by varying the depth positions of the centers 14 of the aspherical lenses 13 of the microlens array 10 by a certain degree or more, it is possible to suppress the occurrence of diffraction bright spots. Below, (1) the variation in the direction perpendicular to the first surface 101 of the aspherical lenses 13, and (2) the regularity of the in-plane arrangement of the first surface 101 will be described in detail.

[0015] <Variation in the direction perpendicular to the first surface> Fig. 3 is a top view image of a sample of microlens array 10 according to an embodiment, and Fig. 4 is a schematic diagram of the X-X' cross section of Fig. 3. As shown in Fig. 3, a plurality of aspherical lenses 13 are regularly arranged in the XY plane. In the Z direction orthogonal to the XY plane, the centers 14 of the aspherical lenses 13 are located at two or more different positions, and therefore the conic coefficients, radii of curvature, etc. of the aspherical lenses 13 are different.

[0016] As shown in the cross-sectional profile of Figure 4, the pitch P between the centers 14 of the aspherical lenses 13 is almost constant, but the depth varies as d1, d2, d3, .... The difference Δd between the depths d1 and d2 is approximately 8 μm in the sample of Figure 3.

[0017] Aspherical lenses 13, which have a substantially uniform in-plane pitch on first surface 101 but which vary in depth or height in a direction perpendicular to first surface 101, are formed by wet etching a pre-treated glass substrate. The pre-treatment may involve irradiating a certain position on the glass substrate with pulsed laser light to modify a portion of the interior of the glass substrate, creating a density distribution in the thickness direction at least at the position irradiated with pulsed laser light, or by forming a predetermined wedge-shaped depression in the surface of the glass substrate using a chemical or physical technique (see, for example, WO 2019 / 189225). As shown in FIG. 4, wet etching is performed so that no flat surfaces remain between adjacent aspherical lenses 13. If flat surfaces remain, light will travel straight without being diffracted, generating zero-order light and resulting in bright spots.

[0018] When the aspherical lens 13 is a convex lens, a plurality of concave surfaces with a constant pitch and varying depths may be formed on a substrate using the method described above, and then a convex lens array may be formed using this substrate as a mold.

[0019] 3 has sufficient variation in the depth or height direction, but it is not clear how the degree of variation in the depth or height of the aspherical lenses 13 affects the diffraction bright spots. Therefore, we will consider how variation in the lens center position in the direction perpendicular to the first surface 101 affects the diffraction bright spots.

[0020] FIG. 5 shows the diffusion profile in the Y direction of the microlens array 10 in FIG. 3. The horizontal axis represents the diffusion angle (°), and the vertical axis represents the relative intensity. The diffusion profile of the microlens array 10 has a rectangular pulse shape. If typical frosted glass is used as a diffuser, the laser light will have a Gaussian diffusion profile in the far field. In contrast, the microlens array 10 in FIG. 3 is designed to diffuse light into a rectangular field of view. In this example, the field of view (FOV) in the Y direction is 45°.

[0021] In the embodiments, the "FOV" of the microlens array 10 refers to the angular range in which the relative intensity of the diffusion profile is 0.5 or greater. The relative intensity is the intensity obtained when the average intensity in the diffusion angle range of -10° to +10° is normalized to 1. The FOV of the diffusion profile of the microlens array 10 measured based on this definition is 60° in the X direction and 45° in the Y direction, as described above. The steepness of the rise of the diffusion profile indicates the cutoff characteristics, which will be discussed later. Here, we will discuss the suppression of diffracted bright spots.

[0022] In a microlens array 10 that diffuses light into a rectangular field of view, it is desirable for the intensity distribution at the top of the diffusion profile to be flat. This is because if the intensity of the diffracted light is locally strong, diffracted bright spots will occur, causing uneven brightness in the projected image. There must be an appropriate range of depth variation where the top of the diffusion profile approaches flatness. Therefore, we conducted a simulation to investigate how the degree of depth variation of the aspherical lens 13 affects the diffracted bright spots.

[0023] Figure 6 shows the simulation results of an aspherical lens array. The substrate 11 is transparent to visible light and is made of "D263 T eco" glass (manufactured by SCHOTT) with a refractive index of 1.5230 for the D-line. The diffusion pattern obtained in the optical measurement is observed on a screen 103 mm away. The minimum measurement resolution is 0.5 μm, the wavelength of the measurement light is 940 nm, and the beam diameter is 3 mm. Next, multiple aspherical lenses 13 are placed on the substrate 11. The conic coefficient of the aspherical lenses 13 is set to -1, the pitch in the X direction is 100 μm, the pitch in the Y direction is 83 μm, and the pitch variation in the X and Y directions is 0. The depth variation of the aspherical lenses 13 is set to 2.00 μm. The depth variation is 1σ when the depth of the aspherical lenses 13 in the microlens array 10 follows a normal distribution, and is the variation (standard deviation) from the median or mean value.

[0024] The simulated FOV of the microlens array 10 in the X direction is 52.9°, and the FOV in the Y direction is 43.2°. When the depth variation of the aspherical lenses 13 is set to 2.0 μm, the relative intensity at both ends of the top of the diffusion profile in the X and Y directions is slightly higher, but there is no large ripple (fluctuation) between the peaks at both ends of the top, and it is almost flat. When we say that the top of the diffusion profile is "flat," we mean that diffraction bright spots are suppressed in the intensity distribution, or that almost the entire ripple at the top of the diffusion profile is within a relative intensity range of 0.8 to 1.2.

[0025] Next, under the above-mentioned conditions, a diffusion profile is obtained by changing only the depth variation of the aspherical lens 13. Figure 7 shows the simulation results when the depth variation (1σ) of the aspherical lens 13 is changed in seven ways: 0.00 μm, 0.40 μm, 0.80 μm, 1.20 μm, 1.60 μm, 2.00 μm, and 2.40 μm.

[0026] According to the simulation results shown in Figure 7, when the depth variation (1σ) is 0.00 μm, 0.40 μm, and 0.80 μm, the relative intensity fluctuates significantly at both ends of the top. However, when the depth variation is 1.20 μm or greater, the relative intensity remains between approximately 0.8 and 1.2. From this, it can be seen that the depth variation should be greater than 0.80 μm, preferably 1.20 μm or greater, more preferably 1.60 μm, even more preferably 2.00 μm or greater, and even more preferably 2.40 μm or greater. This suppresses the relative intensity within the FOV to 1.2 or less, making the intensity distribution closer to uniform.

[0027] Figure 8 shows the three-dimensional intensity distribution (top row) and the two-dimensional intensity distribution in the XY plane (bottom row) when the depth variation (1σ) of the aspherical lens 13 is 0.00 μm, 0.80 μm, 1.60 μm, and 2.40 μm. When the depth variation is 0.00 μm or 0.80 μm, many peaks appear along the edge of the diffusion region, and stripe-shaped intensity differences appear within the diffusion region. The peaks along the edge and the stripes within the diffusion region are due to the occurrence of diffraction bright spots. In contrast, when the depth variation is 1.60 μm, the intensity distribution within the diffusion region, especially in the center, becomes uniform. When the depth variation is 2.00 μm, the intensity distribution becomes uniform overall, including the edge region.

[0028] The simulation results in Figures 7 and 8 show that the influence of diffraction spots can be suppressed by increasing the depth variation (1σ) of the aspherical lenses 13 to more than 0.80 μm. The depth variation of the aspherical lenses 13 is preferably 1.20 μm or more, more preferably 1.60 μm or more, even more preferably 2.00 μm or more, and even more preferably 2.40 μm or more. On the other hand, if the depth variation is too large, the diffusion profile will not be flat-topped but will be closer to a Gaussian distribution. When realizing a rectangular diffusion area using a microlens array 10 in which the aspherical lenses 13 are arranged in a square lattice, it is more desirable for the diffusion profile to be flat-topped rather than Gaussian. As will be described later with reference to Figure 9D, the depth variation (1σ) is preferably less than 6.00 μm, and more preferably 4.00 μm or less.

[0029] Fig. 9A is a top view image of an actually fabricated microlens array 10A, Fig. 9B is actual measurements of depth variation along line I-I' in Fig. 9A, and Fig. 9C is a histogram of the actual measurements of depth variation. As a result of measuring the depth of 63 aspherical lenses 13 along line I-I' in Fig. 9A, as shown in Fig. 9B, the in-plane pitch is almost constant, and only the depth of the aspherical lenses 13 varies.

[0030] The median depth of the aspherical lenses 13 in the microlens array 10A is 29.275 μm, the average is 29.486 μm, the maximum is 37.634 μm, the minimum is 25.139 μm, and the depth variation (standard deviation) is 2.643 μm. The depth variation that can suppress the effects of diffracted bright spots depends on the relative relationship to the average value, not the absolute value. Therefore, the average value is defined as μ, and the standard deviation σ divided by the average value (σ / μ) is introduced as a new index. The value of σ / μ for the above microlens array is 0.090 (2.643 / 29.486).

[0031] FIG. 9D is a diagram showing the upper limit of lens depth variation. When the depth variation is 6.00 μm or more, the flatness of the top of the diffusion profile becomes insufficient. The new index value in this case is 0.203. That is, as long as the new index value is less than 0.203, the flatness of the top of the diffusion profile is maintained. When the depth variation is 4.0 μm or less (the new index σ / μ value is 0.136 or less), the top of the diffusion profile becomes flatter.

[0032] Figure 10 shows the diffusion profile in the Y direction of the microlens array 10A in Figure 9A. When the value of the new index σ / μ is 0.090, the relative intensity of the top of the diffusion profile falls between 0.8 and 1.2, which has sufficient depth variation to suppress bright spots. This also applies when the microlens array 10A is a convex lens array; by providing appropriate height variation to the convex aspherical lenses, the variation in the relative intensity of the top of the diffusion profile can be kept between 0.8 and 1.2.

[0033] From the above considerations, diffraction bright spots can be suppressed by varying the center positions of aspherical lenses 13 to two or more different positions in a direction perpendicular to the surface on which aspherical lenses 13 of microlens array 10, 10A are formed. The top of the diffusion profile can be made flat by making the positional variation in the direction perpendicular to the lens formation surface, that is, the value (σ / μ) obtained by dividing the depth variation (1σ) by the average value (μ), greater than 0.027, preferably 0.041 or more, more preferably 0.054 or more, even more preferably 0.068 or more, and even more preferably 0.081 or more and less than 0.200.

[0034] <Regularity of in-plane arrangement of aspherical lenses> Next, we will consider the regularity of the lens arrangement on the first surface 101 of the substrate 11. As will be described later, regular arrangement of the aspherical lenses 13 within the two-dimensional plane is advantageous for cutoff characteristics. The cutoff characteristics of the microlens array 10 refer to the abruptness of change in whether light is diffused or blocked in a specified direction.

[0035] 11 is a simulation diagram of the diffusion profile when the pitch variation of the aspherical lens 13 is changed. As described above, when the average pitch in each of the X and Y directions is set to 1, the pitch variation indicates the absolute value of the maximum possible difference in the randomly distributed relative pitch ratio over the entire pitch in a predetermined area (area excluding 25% at both ends) of the first surface 101, and this is called σ P (See Figure 2.) In the simulation, the FOV in the Y direction is set to 45°, and the pitch variation in the Y direction is changed to 0.0%, 5.0%, 7.5%, 10.0%, 15.0%, 20.0%, and 25.0% to calculate the diffusion characteristics.

[0036] The positive side of the diffusion profile is shown enlarged. The larger the in-plane pitch variation, the more gradual the rise or fall of the diffusion profile becomes, and the worse the cutoff characteristics become. In particular, when the in-plane pitch variation exceeds 10.0%, the steepness of the base of the diffusion profile is lost.

[0037] Figure 12 is a plot of the cutoff band as a function of pitch variation from the simulation results of Figure 11. The cutoff band in this embodiment is the angular width required for the intensity of the diffusion profile to change to a predetermined level. A more precise definition of the cutoff band will be explained with reference to Figure 13.

[0038] FIG. 13 is a diagram illustrating how to determine the cutoff band. The "cutoff band" in this embodiment is the angular width required for the relative intensity to change between 0.2 and 0.8. The relative intensity of the diffusion profile is the intensity when the average intensity (light amount) in the diffusion angle range from -10° to +10° is normalized to 1, as defined in the study of depth variation of the aspherical lens 13. The angular widths at which the relative intensity changes from 0.2 to 0.8 or from 0.8 to 0.2 are determined on both the negative and positive sides of the diffusion profile, and the larger of the two angular widths is determined as the cutoff band.

[0039] The smaller the cutoff band, the steeper the rise and fall of the diffusion profile and the better the cutoff characteristics. The larger the cutoff band, the gentler the rise and fall of the diffusion profile and the worse the cutoff characteristics.

[0040] Returning to Figure 12, since the cutoff band (°) increases as the pitch variation of the aspherical lens increases, it is desirable to keep the cutoff band small by suppressing the pitch variation. In the simulation example of Figure 12, the pitch variation of the aspherical lens 13 is desirably less than 0.075 (or 7.5%), at which point the cutoff band begins to increase sharply, and more desirably 0.050 (or 5.0%) or less.

[0041] Figure 14 shows the results of a two-dimensional electromagnetic field simulation when the pitch variation of the aspherical lenses 13 of the microlens array 10 is changed only in the Y direction. When the pitch variation in the Y direction is 0.0% and 5.0%, there is little bleeding in the vertical direction of the paper, i.e., the Y direction. When the pitch variation in the Y direction is 10%, bleeding appears in the Y direction. The greater the pitch variation, the more pronounced the bleeding in the Y direction. Prominent bleeding means that the base of the diffusion profile is sagging. Because the axes in the X and Y directions can be defined arbitrarily, the same applies to pitch variation in the X direction.

[0042] Referring to the simulation results of FIGS. 12 and 14, it is clear that the in-plane pitch variation of the microlens array 10 is preferably less than 7.5%, and more preferably 5.0% or less.

[0043] Up to this point, we have examined the cutoff band as a cutoff characteristic based on simulations. Next, we will examine the cutoff characteristics based on actually fabricated samples.

[0044] Five types of samples were fabricated by setting the reference pitch in the Y direction to 84 μm and varying only the pitch variation. Sample a, with a pitch variation in the Y direction of 0.0%, was designed so that the centers of the aspherical lenses 13 were all equally spaced in the Y direction. Sample b, with a pitch variation in the Y direction of 5.0%, was designed so that the pitch was randomly distributed in the Y direction between a minimum pitch of 79.8 μm and a maximum pitch of 88.2 μm, so that the maximum variation in the Y direction was 0.05.

[0045] Similarly, sample c with a pitch variation in the Y direction of 7.5%, sample e with a pitch variation in the Y direction of 15.0%, and sample g with a pitch variation in the Y direction of 25.0% are fabricated. Samples a, b, c, e, and g correspond to the pitch variations a, b, c, e, and g in the simulation of FIG.

[0046] Figure 15 is a plot of the relative pitch ratios for approximately 40 rows (approximately 40 aspherical lenses lined up in the Y direction) of the five types of samples we fabricated. The intended pitch variation in the Y direction was achieved in all samples. The diffusion properties were measured using these samples.

[0047] Figure 16A shows the measured diffusion characteristics of five samples. Figure 16B shows the pitch variations a, b, c, e, and g corresponding to Figure 16A extracted from the simulation results of Figure 11. Comparing the measured results of Figure 16A with the simulation results of Figure 16B, the overall diffusion profile trends are the same. Because Figure 16A does not allow for accurate calculation of the cutoff band compared to Figure 16B due to measurement resolution, there is a concern that significant differences in cutoff characteristics due to pitch variations may be hidden by the above-mentioned uncertainty. Therefore, we introduce a new index of cutoff characteristics: a slope [deg / au] that allows for fair comparisons using the closest approximation of a given relative intensity and diffusion angle.

[0048] Fig. 17 is an enlarged view of the region from -28° to -17° of the diffusion angle of the diffusion characteristics of Fig. 16A. The slope is determined for each of the measurement results of the five samples.

[0049] Figure 18 is a diagram explaining how to determine the slope. The average intensity (light amount) within the diffusion angle range of -10° to +10° is normalized to 1. On the negative and positive sides of the diffusion profile, the points with the closest relative intensity values ​​of 0.2 and 0.8 are connected, and the slope of the line is found. The smaller of the absolute values ​​of the two found slopes is taken as the slope.

[0050] Figure 19 shows the analysis results of the diffusion characteristics of samples a, b, c, e, and g in Figure 17. From the measured values ​​of the diffusion characteristics of each sample, The closest relative intensity of 0.2 (1) The diffusion angle at the closest value (1), The closest relative intensity of 0.8 (2) The diffusion angle at the closest value (2), The slope is the difference between the closest relative intensities of 0.2 and 0.8 divided by the difference in the diffusion angle at each closest value.

[0051] There is no significant difference between when the in-plane pitch variation is 0.0% and when it is 5.0%. When the pitch variation exceeds 7.5%, the cutoff band increases, the slope decreases, and the cutoff characteristics clearly deteriorate. Therefore, in order to make the slope of the diffusion profile greater than 0.139 (for example, 0.14 or greater), it is desirable to keep the in-plane pitch variation below 7.5%.

[0052] Thus, based on the actual measurement data, it is confirmed that the in-plane pitch variation is preferably less than 7.5%, and more preferably 5.0% or less. This result is consistent with the simulation result in FIG.

[0053] 11 to 19, the microlens array 10 has been examined in the Y direction, but the same results are obtained in the X direction, and cutoff characteristics similar to those in the Y direction are obtained. In the microlens array 10, the pitch variation (σ P ) to be less than 7.5%, an appropriate cutoff characteristic can be obtained. When light is diffused over a rectangular area, a projected image with little blur can be obtained.

[0054] As mentioned above, the microlens array 10 has sufficient variation in the depth or height of the aspherical lenses 13. In addition to the variation in the depth or height direction, the pitch variation relative to the average of all pitches in a predetermined region of the aspherical lenses 13 within the plane (region excluding 25% at both ends) is kept to less than 7.5%, thereby realizing a microlens array 10 that suppresses diffraction bright spots and has good cutoff characteristics.

[0055] <Application examples of microlens arrays> FIG. 20 is a schematic diagram of a projection device 20 to which the microlens array 10 of the embodiment is applied. The projection device 20 includes a light source 21, a lens 22, and a microlens array 10. The light source 21 is, for example, a light-emitting diode (LED). Light emitted from the light source 21 is collimated by the lens 22 to parallel light and enters the microlens array 10. The microlens array 10 is arranged so that a first surface 101 on which an array of concave aspherical lenses 13 is formed faces the light incident side. In this example, the microlens array 10 is used as a diffuser.

[0056] The microlens array 10 diffuses the incident parallel light in the X and Y directions over a predetermined FOV and projects it onto the screen 25. If a laser light source is used instead of an LED as the light source, the collimating lens 22 may be omitted. To obtain a color projection image, a microlens array 10 may be arranged for each of a red light source, a green light source, and a blue light source, and the light emitted from each microlens array 10 may be combined using a prism or the like and projected onto the screen 25.

[0057] In the microlens array 10, the center positions of the multiple aspherical lenses 13 (see FIG. 2) formed on the first surface 101 vary in the direction perpendicular to the first surface 101 (Z direction), but are arranged in a generally regular pattern within the plane of the first surface 101 (XY plane). In the area excluding both end 25% of the aspherical lenses 13 within the first surface 101, the pitch variation is suppressed to less than 7.5%, more preferably 5.0% or less, resulting in a projected image with a steep diffusion profile and minimal blurring. Furthermore, the variation in the Z direction of the aspherical lenses 13 suppresses diffracted bright spots, resulting in a uniform intensity distribution.

[0058] While the present invention has been described above based on specific configuration examples, the present invention is not limited to the above configuration examples. Each aspherical lens 13 of the microlens array 10 may be formed as a convex lens having a parabolic surface. In this case, the apex positions of the convex lenses are varied to suppress in-plane pitch variation to less than 7.5%. A microlens array including an arrangement of convex aspherical lenses 13 may be fabricated from resin or the like using the microlens array 10 fabricated in the embodiment as a mold.

[0059] The microlens array 10 of the embodiment can be applied not only to projection devices, but also to lighting devices, imaging systems, etc. Wavelength selectivity can be achieved by tuning the pitch itself while suppressing in-plane pitch variation of the aspherical lenses. In this case, light of a specific wavelength can be diffused, making it suitable for application to color projection devices. [Explanation of symbols]

[0060] 10, 10A Microlens Array 11 Base material 13 Aspheric lenses 14 center 20 Projection device 21 Light source 22 Lens 25 screens 101 First Side

Claims

1. A glass substrate that is transparent to the wavelength used, a microlens array having a plurality of aspherical lenses formed on the first surface of the glass substrate, the center of the aspherical lens is at two or more different positions in a direction perpendicular to the first surface, the plurality of aspherical lenses include a plurality of aspherical lenses having different conic coefficients and / or different radii of curvature; a value σ / μ obtained by dividing the value of the depth variation σ by an average value μ when the center positions of the aspherical lens in a direction orthogonal to the first surface follow a normal distribution is 0.068 or more and less than 0.200, when the average of all pitches of a region excluding a total of 25% from both ends of the aspherical lenses arranged in an arbitrary one-dimensional direction within the first surface is set to 1, an absolute value σp of the maximum possible difference of the relative pitch ratio is less than 0.075, The diffusion pattern obtained in the optical measurement is observed on a screen 103 mm away, the minimum measurement resolution is 0.5 μm, the measurement light is parallel light with a wavelength of 940 nm, and the beam diameter is 3 mm. When the average light amount in the diffusion angle range of −10 degrees to +10 degrees of the diffused light of the microlens array is normalized to 1 and the relative intensity is plotted as a function of the diffusion angle, the maximum relative intensity in the angle range where the value of the relative intensity is 0.5 or more is 1.0 or more and 1.2 or less. Microlens array.

2. the aspherical lenses are arranged in a square lattice; the absolute value σp is less than 0.075 in each of a first direction and a second direction that are orthogonal to each other within the plane of the first surface; The microlens array of claim 1 .

3. The absolute value σp is 0.05 or less. The microlens array according to claim 1 or 2.

4. The depth variation σ is 2.40 μm or more and less than 6.00 μm. The microlens array according to claim 1 .

5. the slope between the relative intensity values ​​of 0.2 and 0.8 is 0.14 or greater; The microlens array according to claim 1 .

6. the aspherical lenses provided on the first surface are continuous with each other without any flat surface between adjacent aspherical lenses; The microlens array according to claim 1 .

7. A diffuser for a projection device, comprising a microlens array described in any one of claims 1 to 6.

8. A light source and the microlens array according to claim 1 provided on the output side of the light source; The microlens array is a projection device that diffuses and projects the light emitted from the light source.

9. The aspherical lens is a concave lens, and the microlens array is disposed with the first surface facing the light source.

9. The projection device according to claim 8.

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