Diffractive optical elements

Abstract

This technology provides a way to reduce the likelihood of changes in the performance of projection equipment caused by heat generated by the laser. [Solution] The diffractive optical element 10 is used for at least one of splitting and shaping a laser beam whose wavelength is in the near-infrared region, and comprises a substrate 11 that transmits the laser beam, and a resin cured layer 12 provided on the substrate 11 that transmits the laser beam, wherein the resin cured layer 12 has a plurality of first protrusions 12P1 that exhibit diffraction on the surface of the diffractive optical element 10, and the upper surface of the first protrusions 12P1 has an arithmetic mean height S a It is within the range of 40nm to 650nm, and kurtosis S ku The result is 3 or greater.

Description

[Technical Field]

[0001] This invention relates to a diffractive optical element. [Background technology]

[0002] In recent years, smartphones have been using fingerprint and facial recognition technologies as security measures. Facial recognition technology can achieve a higher level of security compared to fingerprint recognition technology. Furthermore, because facial recognition technology performs personal authentication without physical contact, it is more convenient and stress-free than fingerprint recognition technology.

[0003] However, facial recognition technology has challenges, such as its inability to achieve high recognition accuracy in dark environments. For this reason, infrared light is sometimes used in facial recognition technology.

[0004] In infrared-based facial recognition technology, a projection device that projects infrared light onto the face and a light-receiving device that receives the infrared light reflected by the face are used. For example, a projection device that irradiates the face with multiple laser beams is used, along with a Time of Flight (ToF) type light-receiving device. In this case, facial recognition becomes possible in dark environments, and three-dimensional facial information can be acquired, increasing the security level in bright environments as well.

[0005] The projection device described above includes, for example, an infrared laser, a collimator that collimates the laser beam emitted by the infrared laser, and a beam splitter or beam shaper that splits or shapes the collimated laser beam. When the beam splitter or beam shaper is composed of lenses and prisms, miniaturization of the projection device is difficult. Therefore, diffractive optical elements (DOEs) are sometimes used as beam splitters or beam shapers (see Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2019 / 240010 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a technology that reduces the likelihood of changes in the performance of a projection device caused by heat generation from a laser. [Means for solving the problem]

[0008] According to one aspect of the present invention, a diffractive optical element for use in at least one of splitting and shaping a laser beam whose wavelength is in the near-infrared region comprises a substrate that transmits the laser beam and a resin cured layer provided on the substrate that transmits the laser beam, wherein the resin cured layer has a plurality of first protrusions that exhibit diffraction on the surface of the diffractive optical element, and the upper surface of the first protrusions has an arithmetic mean height S a It is within the range of 40nm to 650nm, and kurtosis S ku A diffractive optical element is provided in which is 3 or greater.

[0009] Here, "arithmetic mean height S a " is a surface texture parameter defined in JIS B0681-2:2018. Also, "Curtosis S ku This is a surface texture parameter defined in JIS B0681-2:2018. Note that JIS B0681-2:2018 corresponds to ISO 25178-2.

[0010] According to another aspect of the present invention, a diffractive optical element is provided in which the resin cured layer contains an acrylic resin cured material.

[0011] According to yet another aspect of the present invention, a diffractive optical element according to any of the above aspects is provided, wherein the resin cured layer further contains hollow particles.

[0012] According to still another aspect of the present invention, there is provided a diffractive optical element according to any one of the above aspects, in which the plurality of first convex portions form a stripe pattern.

[0013] According to still another aspect of the present invention, there is provided a projection device including a diffractive optical element according to any one of the above aspects, and an infrared laser disposed so as to face the substrate with the cured resin layer interposed therebetween, and emitting laser light toward the diffractive optical element.

[0014] According to still another aspect of the present invention, there is provided a projection device according to any one of the above aspects, further including one or more lenses, wherein the cured resin layer is disposed so as to contact one of the one or more lenses between the diffractive optical element and the infrared laser, and further including a collimator that collimates the laser light emitted by the infrared laser and makes it incident on the diffractive optical element as the laser beam.

[0015] According to still another aspect of the present invention, there is provided a projection device according to any one of the above aspects, wherein the cured resin layer further forms a plurality of second convex portions that exhibit a collimating effect on the surface of the diffractive optical element.

[0016] According to still another aspect of the present invention, there is provided a projection device according to any one of the above aspects, wherein the infrared laser includes a plurality of vertical cavity surface emitting lasers.

[0017] According to still another aspect of the present invention, there is provided a measuring device including a projection device according to any one of the above aspects, and a light receiving device that receives reflected light generated by reflecting the laser beam emitted by the projection device by an object.

Advantages of the Invention

[0018] According to the present invention, there is provided a technique for making it difficult to cause a change in the performance of a projection device due to heat generation of a laser.

Brief Description of the Drawings

[0019] [Figure 1]FIG. 1 is a schematic diagram showing a measuring device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a projection device included in the measuring device shown in FIG. 1. [Figure 3] FIG. 3 is a perspective view showing a part of the diffractive optical element of FIG. 1. [Figure 4] FIG. 4 is a cross-sectional view showing a first step in an example of a method for manufacturing the diffractive optical element shown in FIG. 3. [Figure 5] FIG. 5 is a cross-sectional view showing a second step in an example of a method for manufacturing the diffractive optical element shown in FIG. 3. [Figure 6] FIG. 6 is a cross-sectional view showing a third step in an example of a method for manufacturing the diffractive optical element shown in FIG. 3. [Figure 7] FIG. 7 is a perspective view showing a part of a diffractive optical element according to a modified example. [Figure 8] FIG. 8 is a cross-sectional view showing a cured resin layer included in a diffractive optical element according to another modified example.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are more specific examples of any of the above aspects. The matters described below can be incorporated into each of the above aspects alone or in combination.

[0021] In addition, the embodiments shown below are examples of configurations for embodying the technical idea of the present invention, and the technical idea of the present invention is not limited by the materials, shapes, structures, etc. of the following constituent members. Various changes can be made to the technical idea of the present invention within the technical scope defined by the claims described in the claims.

[0022] Elements with similar or identical functions are given the same reference numerals in the drawings referenced below, and redundant explanations are omitted. Furthermore, the drawings are schematic, and the relationships between dimensions in one direction and those in another, and the relationships between the dimensions of one component and those of other components, may differ from reality.

[0023] <Overall configuration of the measuring device> Figure 1 is a schematic diagram showing a measuring device according to an embodiment of the present invention.

[0024] The measuring device 500 shown in Figure 1 includes a projection device 100 and a light receiving device 200. The measuring device 500 emits a laser beam from the projection device 100 toward the object to be irradiated, and the light receiving device 200 receives the reflected light generated by the reflection from the object to be irradiated, thereby acquiring distance information.

[0025] The projection device 100 includes a diffractive optical element 10, an infrared laser 20, and a collimator 30.

[0026] The diffractive optical element 10 is used for at least one of splitting and shaping a laser beam whose wavelength is in the near-infrared region. Here, the "near-infrared region" is a wavelength range of 780 nm to 1200 nm. Preferably, the wavelength is within the range of 920 nm to 960 nm. For example, the wavelength is 940 nm. The diffractive optical element 10 comprises a substrate that transmits the laser beam and a resin cured layer provided on the substrate that also transmits the laser beam. The resin cured layer generates a plurality of first protrusions on the surface of the diffractive optical element 10 that exhibit diffraction. Details of the diffractive optical element 10 will be described later.

[0027] The infrared laser 20 is positioned facing the substrate with a resin curing layer in between, and emits laser light toward the diffractive optical element 10. The infrared laser 20 is a semiconductor laser, such as a vertical cavity surface-emitting laser (VCSEL). The infrared laser 20 outputs a laser beam having the above wavelength. The infrared laser 20 may include multiple vertical cavity surface-emitting lasers.

[0028] The laser beam output by the infrared laser 20 is normally diffuse light. The collimator 30 collimates the laser beam output by the infrared laser 20. Note that if the diffractive optical element 10 performs the role of a collimator, the collimator 30 can be omitted. This case will be discussed later.

[0029] The collimator 30 includes one or more lenses, and is positioned between the diffractive optical element 10 and the infrared laser 20 such that the resin curing layer is in contact with one of the one or more lenses. The collimator 30 collimates the laser light emitted by the infrared laser 20 and causes it to incident as a laser beam onto the main surface of the diffractive optical element on the resin curing layer side.

[0030] The diffractive optical element 10 performs at least one of splitting and shaping the laser beam. For example, when a laser beam is incident on the diffractive optical element 10, it splits the laser beam into three laser beams, specifically, one laser beam as zero-order diffracted light and two laser beams as first-order diffracted light. The projection device 100 projects these laser beams onto the object to be irradiated.

[0031] The light receiving device 200 includes an image sensor 40, a light collecting device 50, and a filter 60.

[0032] The focusing device 50 is positioned between the object to be illuminated and the image sensor 40. The focusing device 50 includes one or more lenses. The focusing device 50 focuses the reflected light generated by reflection from the object to be illuminated.

[0033] The filter 60 is installed between the focusing device 50 and the image sensor 40. The filter 60 exhibits high transmittance to light of the same wavelength as the laser beam and low transmittance to light of other wavelengths. The filter 60 transmits the reflected light focused by the focusing device 50 and blocks the ambient light that has passed through the focusing device 50.

[0034] The image sensor 40 includes a plurality of light-receiving elements, each containing a photoelectric conversion element. For example, each light-receiving element includes a plurality of pixels, each of which exhibits high sensitivity at the wavelength of the laser beam and low sensitivity at other wavelengths, such as the visible spectrum. The laser beam reflected from the object being irradiated reaches the image sensor 40 via the focusing device 50 and the filter 60.

[0035] For example, the measuring device 500 acquires information regarding the distance from the measuring device 500 to the beam spot on the object to be irradiated, for example, by the Time of Flight (ToF) method. Specifically, the measuring device 500 emits a laser beam in a pulsed manner from the projection device 100 toward the object to be irradiated, and the reflected light generated by reflection from the object to be irradiated is received by the light receiving device 200. The measuring device 500 calculates the distance from the measuring device 500 to the beam spot on the object to be irradiated from the delay time, which corresponds to the time from when the projection device 100 emits the laser beam until the light receiving device 200 receives the reflected light. The measuring device 500 may also acquire an infrared image having gradations corresponding to the distribution of the intensity of the reflected light.

[0036] <Example of a projection device> Figure 2 is a cross-sectional view showing an example of a projection device 100 included in the measuring device 500 shown in Figure 1. The projection device 100 shown in Figure 2 comprises a diffractive optical element 10, an infrared laser 20, a collimator 30, a first support 32, and a substrate 33.

[0037] The collimator 30 includes a second support 31 and one or more lenses. The second support 31 has a cylindrical shape. The second support 31 has a plurality of grooves on its inner surface that extend in the circumferential direction of the cylinder. The second support 31 is, for example, an assembly consisting of two parts. Each of the two parts has a shape obtained by dividing the second support 31 into two parts by a plane parallel to the height direction. The collimator 30 here includes one or more lenses: a first lens 30A, a second lens 30B, and a third lens 30C. As shown in Figure 2, these lenses are provided such that their thickness direction coincides with the height direction of the second support 31. The peripheral edges of each of the first lens 30A, the second lens 30B, and the third lens 30C are fitted into the grooves provided in the second support 31.

[0038] The first lens 30A faces the infrared laser 20 with an air gap in between. The third lens 30C is interposed between the first lens 30A and the diffractive optical element 10 and is in contact with the surface of the diffractive optical element 10 on the side of the resin cured layer 12. Specifically, the third lens 30C is in contact with the upper surface of the first convex portion 12P1 (see Figure 3) included in the resin cured layer 12. The second lens 30B is interposed between the first lens 30A and the third lens 30C.

[0039] The first support 32 has a bottomed cylindrical shape. An opening is provided at the bottom of the first support 32. The diffractive optical element 10 is installed inside the first support 32 such that its peripheral edge is in contact with the bottom of the first support 32 and its central portion is exposed at the location of the opening.

[0040] A collimator 30 is fitted into the first support 32. The diffractive optical element 10 is sandwiched between the first support 32 and the collimator 30 at its peripheral edge.

[0041] The substrate 33 is a wiring board on which the infrared laser 20 is mounted. The first support 32 is fixed to the substrate 33. The above describes an example of the projection device 100.

[0042] Although the collimator 30 described above includes three lenses, the number of lenses included in the collimator 30 may be two or less, or four or more. Also, the second support 31 and the lenses may be fixed to each other with adhesive. The diffractive optical element 10, the collimator 30 and the first support 32 may also be fixed to each other with adhesive.

[0043] <Details of diffractive optical elements> Figure 3 is a perspective view showing a part of the diffractive optical element 10. The diffractive optical element 10 shown in Figure 3 is a transmission-type diffractive optical element used for at least one of splitting and shaping a laser beam having the wavelength described above.

[0044] The diffractive optical element 10 has a flat plate shape. For example, the maximum dimension of the diffractive optical element 10 in the direction perpendicular to its thickness is within the range of 1 mm to 50 mm.

[0045] The diffractive optical element 10 includes a substrate 11 and a resin cured layer 12.

[0046] The substrate 11 has first and second main surfaces that are perpendicular to the thickness direction of the diffractive optical element 10 and parallel to each other. The substrate 11 transmits the laser beam. One of the first and second main surfaces is the incident surface to which the laser beam is incident, and the other of the first and second main surfaces is the exit surface from which the laser beam is emitted.

[0047] The substrate 11 is made of, for example, an inorganic material. For example, the substrate 11 is a glass plate. The substrate 11 may also be made of an organic material such as a cured acrylic resin. The substrate 11 may be made of a single material or of multiple materials. For example, the substrate 11 may have a single-layer structure or a multi-layer structure.

[0048] The resin cured layer 12 is provided on the substrate 11, for example, on the first main surface. The resin cured layer transmits the laser beam.

[0049] The resin curing layer 12 consists of a resin curing material such as an acrylic resin curing material. The resin curing layer 12 may further contain materials other than the resin curing material. For example, the resin curing layer 12 may be a mixture of the resin curing material and hollow particles having a small particle size. This mixture may have a smaller refractive index compared to the resin curing material it contains. As the hollow particles, for example, hollow silica particles can be used. The hollow particles preferably have an average particle size of several hundred nm as measured by the light scattering method. In one example, this average particle size is in the range of 100 nm to 1400 nm. The resin curing layer 12 has a refractive index at a wavelength of 940 nm, for example, in the range of 1.25 to 1.6.

[0050] The diffractive optical element 10 is positioned such that a portion of the surface of the resin cured layer 12 is in contact with a gas phase such as air. Reducing the refractive index reduces the difference between the refractive index of the resin cured layer 12 and the refractive index of the gas phase. Therefore, Fresnel reflection at the interface between the resin cured layer 12 and the gas phase is weakened, and the light utilization efficiency is increased. In addition, at least a portion of the laser beam reflected by Fresnel at the interface becomes stray light, which can reduce the measurement accuracy of the measuring device described above.

[0051] The "light utilization efficiency" is a value measured when a laser beam is incident on one main surface of the diffractive optical element 10, and is a value equivalent to the ratio E1 / E0 of the total energy E1 of the laser beam emitted from the other main surface of the diffractive optical element 10 to the energy E0 of the laser beam incident on the one main surface.

[0052] The resin curing layer 12 creates a plurality of first protrusions 12P1 on the surface of the diffractive optical element 10 that exhibit diffraction. Specifically, the first protrusions 12P1 create an optical path difference between the laser beam incident on the portion of the diffractive optical element 10 corresponding to the first protrusions 12P1 and the laser beam incident on the portion of the diffractive optical element 10 corresponding to the recess, which is the gap between the first protrusions 12P1. The diffractive optical element 10 utilizes the interference resulting from this to perform at least one of splitting and shaping the laser beam. That is, when a laser beam is incident on the diffractive optical element 10, it functions as at least one of a beam splitter and a beam shaper. The diffractive optical element 10 may also function as a collimator when a laser beam is incident on it. This will be described later.

[0053] When the diffractive optical element 10 functions as a beam splitter, there is no limit to the number of laser beams emitted by the diffractive optical element 10 when a laser beam is incident on it, that is, the maximum number of beam spots that these laser beams can form on the object being irradiated. For example, the number of laser beams produced by passing through the diffractive optical element 10 may be 3 or more, 9 or more, 100 or more, 1000 or more, or even 10000. Here, as an example, let's assume that the diffractive optical element 10 functions as a beam splitter that divides a laser beam into three laser beams when it is incident on it.

[0054] The resin cured layer 12 includes a continuous film portion provided on the substrate 11 and a plurality of first protrusions 12P1 provided thereon. The continuous film portion can be omitted.

[0055] The first protrusions 12P1 here form a striped pattern. That is, each of the first protrusions 12P1 extends in a first direction and is arranged spaced apart from one another in a second direction that intersects with the first direction.

[0056] Each of the plurality of first convex portions 12P1 has a rectangular cross-section perpendicular to its length direction. This cross-section may be a forward taper shape or a reverse taper shape, but is preferably rectangular. When the first convex portion 12P1 is not rectangular, the width W of the first convex portion 12P1 is the width of the first convex portion 12P1 at a height of 1 / 2 of the height of the first convex portion 12P1.

[0057] Each of the first convex portions 12P1, for example, has a height H within a range of 0.5 μm or more and 1.7 μm or less, and a width W within a range of 0.3 μm or more and 2.0 μm or less. When the first convex portion 12P1 is not rectangular, the width W of the first convex portion 12P1 is the width of the first convex portion 12P1 at a height of 1 / 2 of the height of the first convex portion 12P1.

[0058] The period of the array of the first convex portions 12P1, that is, the pitch P, is preferably within a range of 2.4 μm or more and 2.7 μm or less, and more preferably within a range of 2.5 μm or more and 2.6 μm or less. When the pitch P is decreased, the maximum value of the emission angle of the laser beam emitted by the diffractive optical element 10 increases. That is, when the pitch P is decreased, the angular range of the laser beam emitted by the diffractive optical element 10 becomes wider. When the pitch P is increased, the maximum value of the emission angle of the laser beam emitted by the diffractive optical element 10 decreases. That is, when the pitch P is increased, the angular range of the laser beam emitted by the diffractive optical element 10 becomes narrower.

[0059] Among the diffractive optical element 10, the upper surface of the first convex portion 12P1 has an arithmetic mean height S a within a range of 40 nm or more and 650 nm or less, and a kurtosis S ku of 3 or more. Preferably, only on the upper surface of the first convex portion 12P1 among the surfaces of the first convex portion 12P1, the arithmetic mean height S a is within a range of 40 nm or more and 650 nm or less, and the kurtosis S ku is 3 or more. In this case, for example, the side surface of the first convex portion 12P1 among the surfaces of the first convex portion 12P1 is smooth. The arithmetic mean height S a is preferably within a range of 100 nm or more and 400 nm or less. Also, the kurtosis S kuFor example, it is 5 or less. Note that Kurtosis S ku This represents the sharpness of the height distribution.

[0060] Multiple protrusions P0 are provided on the upper surface of the first protrusion 12P1. Because multiple protrusions P0 are provided on the upper surface of the first protrusion 12P1, the upper surface of the first protrusion 12P1 has an arithmetic mean height S. a and Kurtsis S ku It falls within the range described above.

[0061] Multiple protrusions P0 are, for example, randomly arranged on the upper surface of the first protrusion 12P1. The load length ratio Rmr(10%) at the cutting level of 10% for the multiple protrusions P0 is preferably between 10 and 40. The load length ratio Rmr(10%) is the ratio of the load length of the roughness curve at the cutting level of 10% to the evaluation length. The cutting level of 10% is the level where the distance in the depth direction from the highest point of the roughness curve is 10% of the maximum cross-sectional height Rt. The load length ratio Rmr(10%) and the maximum cross-sectional height Rt are surface property parameters specified in JIS B0601:2013. If the load length ratio Rmr(10%) at the cutting level of 10% for the multiple protrusions P0 is within the above range, changes in the performance of the projection device 100, which will be described later, are particularly unlikely to occur.

[0062] <Method for manufacturing diffractive optical elements> The above-mentioned diffractive optical element 10 can be manufactured, for example, by the following method.

[0063] Figure 4 is a cross-sectional view showing the first step in an example of a method for manufacturing a diffractive optical element shown in Figure 3. Figure 5 is a cross-sectional view showing the second step in an example of a method for manufacturing a diffractive optical element shown in Figure 3. Figure 6 is a cross-sectional view showing the third step in an example of a method for manufacturing a diffractive optical element shown in Figure 3.

[0064] In the method shown in Figures 4 to 6, first, the substrate 11C shown in Figure 4 is prepared. Substrate 11C is the same as substrate 11 described above, except that its dimensions in the direction perpendicular to the thickness direction are larger. For example, the maximum value of the dimension perpendicular to the thickness direction of substrate 11C is within the range of 100 mm to 300 mm.

[0065] Next, a negative-type photosensitive resin is coated onto one main surface of the substrate 11C to obtain a resin layer 12R. This photosensitive resin is the raw material for the cured resin layer 12. For coating the photosensitive resin, for example, a spin coating method, a roll coating method, or a slot coating method can be used. With the spin coating method, the thickness of the resin layer 12R can be controlled by the rotation speed.

[0066] Next, the resin layer 12R is pattern-exposed. For example, as shown in Figure 5, ultraviolet light 16 is irradiated onto the resin layer 12R via a photomask 15. This causes a crosslinking reaction to occur in the exposed portion 12E of the resin layer 12R without causing a crosslinking reaction in the unexposed portion 12N of the resin layer 12R.

[0067] Next, the resin layer 12R is subjected to a developing process. In this developing process, for example, an alkaline aqueous solution is used as the developer.

[0068] Next, only the upper surface of the first protrusion 12P1 on the surface of the resin layer 12R is subjected to a surface roughening treatment. Examples of surface roughening treatments include oxygen plasma treatment. This treatment results in the arithmetic mean height S of the upper surface. a and Kurtsis S ku It is possible to increase the arithmetic mean height S. a When a surface with a thickness of 30 nm is subjected to the above treatment, its arithmetic mean height S a It is possible to make it 40nm or larger. In this way, the aggregate element 10C shown in Figure 6 is obtained.

[0069] The aggregate element 10C includes a substrate 11C and a resin cured layer 12C provided on one of its main surfaces. Furthermore, each aggregate element 10C contains multiple element regions corresponding to the diffractive optical elements 10. Each portion of the resin cured layer 12C corresponding to these element regions corresponds to the resin cured layer 12 of the diffractive optical elements 10. Note that in the aggregate element 10C shown in Figure 6, the resin cured layer 12C consists only of multiple first protrusions 12P1, but the resin cured layer 12C may further include a continuous film portion interposed between these first protrusions 12P1 and the substrate 11C.

[0070] Subsequently, the aggregate element 10C is subjected to a fragmentation process such as dicing. This yields multiple diffractive optical elements 10, each corresponding to a different element region.

[0071] The diffractive optical element 10 can also be manufactured by other methods. For example, first, a resin layer 12R is formed on a substrate 11C. The material of the resin layer 12R may be a photosensitive resin or a non-photosensitive resin. Next, the resin layer 12R is cured, and a mask layer is formed on the resulting cured resin layer, with openings corresponding to the gaps between the first protrusions 12P1. Subsequently, the exposed parts of the cured resin layer are removed by dry etching to obtain a cured resin layer 12C. After that, the mask layer is removed from the cured resin layer 12C to obtain an aggregate element 10C. Furthermore, by subjecting the aggregate element 10C to a fragmentation process, multiple diffractive optical elements 10 can be obtained.

[0072] The diffractive optical element 10 can be distributed individually. That is, multiple diffractive optical elements 10 can be distributed individually rather than as a set. However, it is common practice to distribute an assembly of multiple diffractive optical elements 10.

[0073] Instead of distributing the diffractive optical element 10 or element assembly as a finished product, an intermediate product, the element assembly 10C, may be distributed. That is, the element assembly 10C may be distributed first, and then the individual diffractive optical elements 10 may be separated from it.

[0074] <Effects> In the projection device 100 described above, the infrared laser 20 generates heat as the laser beam output increases. This heat is transferred to the diffractive optical element 10 via the collimator 30. When the temperature of the diffractive optical element 10 rises, its optical properties change. In this case, changes in the performance of the projection device 100 occur, such as the laser beam not splitting or shaping as designed.

[0075] In a projection device similar to the projection device 100 described above, except that the upper surface of the first protrusion 12P1 is smooth, the contact area between the diffractive optical element 10 and the collimator 30, specifically the contact area between the diffractive optical element 10 and the third lens 30C, is relatively large. In such a projection device, heat conduction from the collimator 30 to the diffractive optical element 10 is likely to occur. Therefore, in this projection device, changes in the performance of the projection device 100 due to the heat generated by the laser described above are likely to occur.

[0076] On the other hand, in the projection device 100 described above, the upper surface of the first protrusion 12P1 has the surface properties described above. That is, in the projection device 100, the upper surface of the first protrusion 12P1 has the above-described multiple protrusions P0. Since the protrusions P0 are sharp and have an appropriate height, the contact area between the diffractive optical element 10 and the collimator 30 is smaller than the contact area in the projection device in which the upper surface of the first protrusion 12P1 is smooth. In addition, the heat transferred to the diffractive optical element 10 can be dissipated into the air layer from between two adjacent protrusions P0. For this reason, the temperature rise of the diffractive optical element 10 is less likely to occur in the projection device 100 described above. Consequently, the performance of the projection device 100 caused by the heat generated by the laser is less likely to occur in the projection device 100 described above.

[0077] <Variation> The following describes some modified versions of the diffractive optical element 10 described above. Figure 7 is a perspective view showing a part of a modified diffractive optical element. The diffractive optical element 10 shown in Figure 7 is the same as the diffractive optical element 10 shown in Figure 3, except that it has a resin cured layer consisting of a first layer and a second layer, which will be described below, instead of the resin cured layer 12 shown in Figure 3.

[0078] The resin cured layer 12 shown in Figure 7 consists of a first layer 120 and a second layer 121. The first layer 120 is interposed between the second layer 121 and the substrate 11. In the resin cured layer 12 shown in Figure 7, a portion of the first layer 120 and the second layer 121 form the aforementioned multiple first protrusions 12P1. As the material for the first layer, for example, a material that can achieve high durability such as epoxy resin, silicone resin, or acrylic resin can be used.

[0079] The second layer 121 includes the upper surface of the first protrusion 12P1. The second layer 121 has the above-mentioned plurality of protrusions P0 on its upper surface. Examples of materials for the second layer include so-called sacrificial film materials, and it is preferable to use materials that can achieve high pattern accuracy, such as polymer-based materials, silicon oxides, and silicon nitrides.

[0080] The following describes an example of a manufacturing method for the diffractive optical element 10 shown in Figure 7. First, the substrate 11C is prepared. Next, the material for the first layer 120 is coated onto one main surface of the substrate 11C to obtain the first resin layer.

[0081] Next, a negative-type photosensitive resin is coated onto the first resin layer as the material for the second layer 121 to obtain the second resin layer. For coating the first and second resin layers, the above-described methods, such as the spin coating method, can be used.

[0082] Next, the second resin layer is pattern-exposed using the same method as the pattern exposure method for the resin layer 12R described above. Subsequently, the second resin layer is subjected to a development process using the same method as the development process for the resin layer 12R described above. In this way, the second resin layer is patterned.

[0083] Next, the first resin layer is etched using the patterned second resin layer as a mask. In this way, the first layer 120 is obtained.

[0084] Next, the upper surface of the first protrusion 12P1 on the surface of the second resin layer is subjected to the surface roughening treatment described above. In this way, the second layer 121 is obtained.

[0085] The above describes an example of a method for manufacturing a diffractive optical element having a resin cured layer with a first layer 120 and a second layer 121. By this method, a first protrusion 12P1 with high pattern accuracy and excellent durability can be obtained.

[0086] Figure 8 is a cross-sectional view showing the resin curing layer included in another modified diffractive optical element. This modified diffractive optical element is the same as the diffractive optical element 10 shown in Figure 3, except that it has the resin curing layer shown in Figure 8 instead of the resin curing layer 12 shown in Figure 3.

[0087] The resin cured layer 12 shown in Figure 8 has multiple second protrusions 12P2 on its surface, which exhibit a collimating effect, along with the multiple first protrusions 12P1 described above. Here, as an example, the multiple second protrusions 12P2 have a structure similar to that of a Fresnel lens. Multiple first protrusions 12P1 are provided on the inclined surface of the second protrusions 12P2. Note that the first protrusions 12P1 are not shown in Figure 8.

[0088] When a diffractive optical element equipped with the resin curing layer 12 shown in Figure 8 is used in the projection device 100, the collimator 30 can be omitted. Even in this case, heat conduction from the infrared laser 20 to the diffractive optical element 10 is unlikely to occur, and therefore the changes in the performance of the projection device 100 caused by the heat generated by the laser, as described above, are unlikely to occur.

[0089] Furthermore, as the diffractive optical element 10, instead of the resin cured layer 12 shown in Figure 3, a similar diffractive optical element 10 to the one shown in Figure 3 may be used, except that it comprises the first layer 120 and the second layer 121 described above, and has a resin cured layer having the plurality of second protrusions 12P2 described above on the surface of the second layer 121.

[0090] As another variation, the projection device 100 described above may further include a heat sink and a heat transfer element. For example, the projection device 100 includes a heat transfer element provided inside the first support 32 and a heat sink that is in contact with the heat transfer element and provided outside the first support 32.

[0091] Each of the heat transfer element and heat sink is made of, for example, a highly thermally conductive material. Highly thermally conductive materials include, for example, metals such as copper, aluminum, iron, silver, titanium, molybdenum, tantalum, tungsten, and niobium; alloys containing one or more of these metals; carbides such as tungsten carbide; carbon materials such as graphite, graphene, carbon nanotubes, and diamond; other insulating ceramics; or composite materials containing one or more of these. Each of the heat transfer element and heat sink may have a single-layer structure or a multi-layer structure.

[0092] When the projection device 100 includes a heat sink and a heat transfer element, the heat generated from the infrared laser 20 is dissipated from the diffractive optical element 10 to the outside air via the heat sink and heat transfer element. Therefore, in the above case, changes in the performance of the projection device 100 caused by the heat generated by the laser are particularly unlikely to occur. [Explanation of Symbols]

[0093] 10...Diffractive optical element, 10C...Assembly element, 11...Substrate, 11C...Substrate, 12...Resin cured layer, 12E...Exposed area, 12N...Unexposed area, 12R...Resin layer, 15...Photomask, 16...Ultraviolet light, 20...Infrared laser, 30...Collimator, 30A...First lens, 30B...Second lens, 30C...Third lens, 31...Second support, 32...First support, 33...Substrate, 40...Image sensor, 50...Collecting device, 60...Filter, 100...Projection device, 120...First layer, 121...Second layer, 200...Light receiving device, 500...Measurement device.

Claims

1. A diffractive optical element used for at least one of splitting and shaping a laser beam whose wavelength is in the near-infrared region, The system comprises a substrate that transmits the laser beam, and a resin cured layer provided on the substrate that transmits the laser beam. The resin cured layer has a plurality of first protrusions that exhibit diffraction properties on the surface of the diffractive optical element. The upper surface of the first protrusion has an arithmetic mean height S ａ It is within the range of 40 nm to 650 nm, and kurtosis S ｋｕ A diffractive optical element in which the ratio is 3 or greater.

2. The diffractive optical element according to claim 1, wherein the resin cured layer comprises an acrylic resin cured material.

3. The diffractive optical element according to claim 1, wherein the resin cured layer further contains hollow particles.

4. The diffractive optical element according to claim 1, wherein the plurality of first protrusions form a stripe-like pattern.

5. A diffractive optical element according to any one of claims 1 to 4, An infrared laser is positioned facing the substrate with the resin cured layer in between, and emits laser light toward the diffractive optical element. A projection device equipped with a projection system.

6. The projection device according to claim 5, further comprising one or more lenses, wherein the resin cured layer is positioned between the diffractive optical element and the infrared laser so as to be in contact with one of the one or more lenses, and a collimator is provided to collimate the laser light emitted by the infrared laser and cause it to be incident on the diffractive optical element as a laser beam.

7. The projection apparatus according to claim 5, wherein the resin cured layer further generates a plurality of second protrusions that exhibit a collimating effect on the surface of the diffractive optical element.

8. The projection apparatus according to claim 5, wherein the infrared laser includes a plurality of vertical cavity type surface-emitting lasers.

9. The projection device according to claim 5, A light receiving device that receives reflected light generated when the laser beam emitted by the projection device is reflected by an object, and A measuring device equipped with the following features.

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