Diffractive optical element

Abstract

To provide a technique capable of reducing the influence of the variation in the thickness of a resin cured material layer having projecting parts for developing diffraction action on the light utilization efficiency of a diffraction optical element.SOLUTION: The diffractive optical element 10 is used for at least one of division and shaping of a laser beam having a wavelength in a near-infrared region, and includes a substrate 11 that transmits the laser beam, and a cured resin layer 12 that is provided on the substrate 11 and transmits the laser beam, the cured resin layer 12 having a refractive index of 1.6 or less at a wavelength of 9400 nm, and generating a plurality of convex portions 12P that exhibit a diffractive action on a surface of the diffractive optical element 10, each of the plurality of convex portions 12P having a height H in a range of 1.4 μm or more and 1.7 μm or less, the width W is in a range of 0.4 μm or more and 1.0 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, fingerprint and facial recognition technologies have been adopted for security measures on smartphones. Facial recognition technology can achieve a higher level of security than fingerprint recognition technology. Furthermore, facial recognition technology is a contactless personal authentication technology, which is more convenient and stress-free than fingerprint recognition technology.

[0003] However, face recognition technology has issues such as being unable to achieve high recognition accuracy in dark environments. For these reasons, infrared rays are sometimes used for face recognition technology.

[0004] Infrared facial recognition technology uses a projector that projects infrared rays onto the face and a light-receiving device that receives the infrared rays reflected by the face. For example, a projector that irradiates the face with multiple laser beams is used, and a ToF (Time of Flight) light-receiving device is used. In this case, not only can facial recognition be performed in dark environments, but three-dimensional facial information can also be obtained, increasing the security level in bright environments.

[0005] The above-mentioned projection device 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. If the beam splitter or beam shaper is configured with lenses and prisms, it is difficult to reduce the size of the projection device. Therefore, a diffractive optical element (DOE) is sometimes used as the beam splitter or beam shaper (see Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2019 / 240010 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a technique that can reduce the effect that variations in the thickness of a cured resin layer having convex portions that exhibit diffractive action have on the light utilization efficiency of a diffractive optical element. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a diffractive optical element used for at least one of splitting and shaping a laser beam having a wavelength in the near-infrared region, the diffractive optical element comprising: a substrate that transmits the laser beam; and a cured resin layer provided on the substrate that transmits the laser beam, wherein the cured resin layer has a refractive index of 1.6 or less at a wavelength of 940 nm; and a plurality of convex portions that exhibit a diffractive effect are formed on the surface of the diffractive optical element, each of the plurality of convex portions having a height within the range of 1.4 μm to 1.7 μm and a width within the range of 0.4 μm to 1.0 μm.

[0009] According to another aspect of the present invention, there is provided a diffractive optical element according to the above aspect, wherein the refractive index is 1.25 or more.

[0010] According to yet another aspect of the present invention, there is provided a diffractive optical element according to any one of the above aspects, wherein the refractive index is 1.45 or less.

[0011] According to yet another aspect of the present invention, there is provided a diffractive optical element according to any one of the above aspects, which functions as a beam splitter when the laser beam is incident thereon.

[0012] According to yet another aspect of the present invention, there is provided a diffractive optical element according to the above aspect, which splits the laser beam into three laser beams when the laser beam is incident thereon.

[0013] According to yet another aspect of the present invention, there is provided a diffractive optical element according to any one of the above aspects, wherein the plurality of convex portions form a striped pattern.

[0014] According to yet another aspect of the present invention, there is provided the diffractive optical element according to any one of the above aspects, wherein the cured resin layer contains a cured acrylic resin.

[0015] According to yet another aspect of the present invention, there is provided the diffractive optical element according to any one of the above aspects, wherein the cured resin layer further contains hollow particles.

[0016] According to yet another aspect of the present invention, there is provided an aggregate element including a plurality of element regions and being separated into a plurality of diffractive optical elements corresponding to the plurality of element regions, each of the plurality of diffractive optical elements being a diffractive optical element according to any of the above aspects.

[0017] According to yet another aspect of the present invention, there is provided an element assembly according to the above aspect, wherein one or more of the plurality of element regions has a different thickness of the cured resin layer from one or more of the plurality of element regions.

[0018] According to yet another aspect of the present invention, there is provided an element assembly according to the above aspect, wherein the difference between the maximum and minimum thicknesses of the cured resin layer is 0.01 μm or more.

[0019] According to yet another aspect of the present invention, there is provided a collecting element according to any of the above aspects, wherein the distribution of the thickness of the cured resin layer in the radial direction of the collecting element has a maximum value or a maximum value at or near the periphery of the collecting element, and a minimum value or a minimum value at a position closer to the center of the collecting element.

[0020] According to yet another aspect of the present invention, there is provided an element assembly including a plurality of diffractive optical elements, each of which is the diffractive optical element according to any one of the above aspects.

[0021] According to yet another aspect of the present invention, there is provided the element assembly according to the above aspect, wherein one or more of the plurality of diffractive optical elements and one or more of the other diffractive optical elements have a different thickness of the cured resin layer.

[0022] According to yet another aspect of the present invention, there is provided the element assembly according to the above aspect, wherein the difference between the maximum and minimum thicknesses of the cured resin layer is 0.01 μm or more. [Effects of the Invention]

[0023] The present invention provides a technique that can reduce the effect of variations in the thickness of a cured resin layer having convex portions that exhibit diffractive properties on the light utilization efficiency of a diffractive optical element. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a perspective view showing a part of a diffractive optical element according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a first step in an example of a method for manufacturing the diffractive optical element shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing a second step in the example of the method for manufacturing the diffractive optical element shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view showing a third step in the exemplary method for manufacturing the diffractive optical element shown in FIG. [Figure 5] FIG. 5 is a diagram schematically illustrating an example of a projection device including the diffractive optical element of FIG. [Figure 6] FIG. 6 is a graph showing the relationship between the height of the convex portion and the light utilization efficiency. [Figure 7] FIG. 7 is a graph showing the relationship between the width of the convex portion and the light utilization efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are more specific embodiments of any of the above aspects. The following items can be incorporated into each of the above aspects, either singly or in combination.

[0026] Furthermore, the embodiments shown below are merely 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 components described below. Various modifications can be made to the technical idea of ​​the present invention within the technical scope defined by the claims.

[0027] In the drawings, elements having the same or similar functions are denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, the drawings are schematic, and the relationship between dimensions in one direction and dimensions in another direction, and the relationship between the dimensions of one member and the dimensions of another member, etc. may differ from the actual relationship.

[0028] FIG. 1 is a perspective view showing a part of a diffractive optical element according to an embodiment of the present invention. The diffractive optical element 10 shown in Figure 1 is a transmissive diffractive optical element used to at least one of split and shape a laser beam having a wavelength in the near-infrared region. Here, the "near-infrared region" refers to a wavelength range of 780 nm to 1200 nm. The wavelength is preferably in the range of 920 nm to 960 nm. In one example, the wavelength is 940 nm.

[0029] The diffractive optical element 10 has a flat plate shape. According to one example, the maximum dimension of the diffractive optical element 10 in a direction perpendicular to its thickness direction is in the range of 1 mm to 50 mm.

[0030] The diffractive optical element 10 includes a substrate 11 and a cured resin layer 12 .

[0031] The substrate 11 has first and second principal 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 principal surfaces is an incident surface on which the laser beam is incident, and the other of the first and second principal surfaces is an exit surface from which the laser beam exits.

[0032] The substrate 11 is made of, for example, an inorganic material. In one 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 a plurality of materials. For example, the substrate 11 may have a single-layer structure or a multi-layer structure.

[0033] The cured resin layer 12 is provided on the substrate 11, for example, on the first main surface thereof. The cured resin layer transmits the laser beam.

[0034] The cured resin layer 12 has a refractive index of 1.6 or less at a wavelength of 940 nm. The refractive index of the cured resin layer 12 is preferably 1.5 or less, and more preferably 1.45 or less.

[0035] The diffractive optical element 10 is installed so that the surface of the cured resin 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 cured resin layer 12 and the gas phase. This reduces Fresnel reflection at the interface between the cured resin layer 12 and the gas phase, improving light utilization efficiency. Furthermore, at least a portion of the laser beam Fresnel-reflected at the interface becomes stray light, potentially reducing the measurement accuracy of a measuring device, as described below.

[0036] The "light utilization efficiency" is a value measured when a laser beam is incident on one of the principal surfaces of the diffractive optical element 10, and corresponds to the ratio E1 / E0 of the total energy E1 of the laser beam emitted from the other principal surface of the diffractive optical element 10 to the energy E0 of the laser beam incident on the one principal surface.

[0037] The cured resin layer 12 preferably has a refractive index of 1.25 or more at a wavelength of 940 nm. A smaller refractive index reduces the difference between this refractive index and the refractive index of the gas phase. A smaller refractive index difference increases the height H of the convex portions 12P required to achieve the desired optical effect.

[0038] The cured resin layer 12 is made of a cured resin such as a cured acrylic resin. The cured resin layer 12 may further contain materials other than the cured resin. For example, the cured resin layer 12 may be a mixture of a cured resin and hollow particles having a small particle size. This mixture may have a smaller refractive index than the cured resin it contains. Hollow silica particles, for example, may be used as the hollow particles. The hollow particles preferably have an average particle size of several hundred nanometers as measured by a light scattering method. According to one example, this average particle size is in the range of 100 nm to 1400 nm.

[0039] The cured resin layer 12 has a plurality of convex portions 12P on the surface of the diffractive optical element 10, which produce a diffractive effect. Specifically, the convex portions 12P create an optical path difference between a laser beam incident on a portion of the diffractive optical element 10 corresponding to the convex portions 12P and a laser beam incident on a portion of the diffractive optical element 10 corresponding to the concave portions, which are gaps between the convex portions 12P. The diffractive optical element 10 utilizes the interference caused by this to at least one of split and shape the laser beam. That is, when a laser beam is incident on the diffractive optical element 10, the diffractive optical element 10 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 the diffractive optical element 10.

[0040] 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 laser beams are incident on the diffractive optical element 10, i.e., the maximum number of beam spots that these laser beams can form on an object to be irradiated. For example, the number of laser beams generated by passing through the diffractive optical element 10 may be three or more, nine or more, 100 or more, 1,000 or more, or even 10,000. Here, as an example, it is assumed that the diffractive optical element 10 functions as a beam splitter that, when a laser beam is incident on the diffractive optical element 10, splits the laser beam into three laser beams.

[0041] The cured resin layer 12 includes a continuous film portion provided on the substrate 11 and a plurality of protrusions 12P provided thereon. The continuous film portion can be omitted.

[0042] The protrusions 12P here form a striped pattern, that is, the protrusions 12P each extend in a first direction and are arranged spaced apart from one another in a second direction that intersects with the first direction.

[0043] Each of the protrusions 12P has a rectangular cross section perpendicular to its longitudinal direction. This cross section may be tapered or inverted, but is preferably rectangular. If the protrusions 12P are not rectangular, the width W of the protrusions 12P is the width of the protrusions 12P at half the height of the protrusions 12P.

[0044] Each of the convex portions 12P has a height H in the range of 1.4 μm or more and 1.7 μm or less. If the height H is smaller than the lower limit of the above range, the light utilization efficiency decreases, and variations in the height H have a greater impact on the light utilization efficiency. If the height H is larger than the upper limit of the above range, the light utilization efficiency increases, but variations in the height H have a greater impact on the light utilization efficiency. When the width W of the convex portion 12P is within the range described below, even if the height H varies within the above range, the impact of this variation on the light utilization efficiency is small. Furthermore, when the width W of the convex portion 12P is within the range described below and the height H of the convex portion 12P is within the above range, a sufficiently high light utilization efficiency can be achieved.

[0045] Each of the convex portions 12P has a width W in the range of 0.4 μm or more and 1.0 μm or less. If the width W is smaller than the lower limit of the above range, the light utilization efficiency increases, but variations in the width W have a greater impact on the light utilization efficiency. If the width W is larger than the upper limit of the above range, the light utilization efficiency decreases, and variations in the width W have a greater impact on the light utilization efficiency. When the height H of the convex portion 12P is within the above range, even if the width W varies within the above range, the impact of this variation on the light utilization efficiency is small. Furthermore, when the height H of the convex portion is within the above range and the width W of the convex portion 12P is within the above range, a sufficiently high light utilization efficiency can be achieved.

[0046] The period of the arrangement of the convex portions 12P, i.e., the pitch P, is preferably in the range of 2.4 μm to 2.7 μm, and more preferably in the range of 2.5 μm to 2.6 μm. Reducing the pitch P increases the maximum value of the exit angle of the laser beam emitted from the diffractive optical element 10. In other words, reducing the pitch P widens the angular range of the laser beam emitted from the diffractive optical element 10. Increasing the pitch P decreases the maximum value of the exit angle of the laser beam emitted from the diffractive optical element 10. In other words, increasing the pitch P narrows the angular range of the laser beam emitted from the diffractive optical element 10.

[0047] The above-described diffractive optical element 10 can be manufactured, for example, by the following method.

[0048] Fig. 2 is a cross-sectional view showing a first step in an example of a method for manufacturing the diffractive optical element shown in Fig. 1. Fig. 3 is a cross-sectional view showing a second step in an example of a method for manufacturing the diffractive optical element shown in Fig. 1. Fig. 4 is a cross-sectional view showing a third step in an example of a method for manufacturing the diffractive optical element shown in Fig. 1.

[0049] 2 to 4, first, the substrate 11C shown in Fig. 2 is prepared. Substrate 11C is similar to the above-described substrate 11 except that the dimension in the direction perpendicular to the thickness direction is larger. According to one example, the maximum dimension of substrate 11C in the direction perpendicular to the thickness direction is in the range of 100 mm to 300 mm.

[0050] Next, a negative photosensitive resin is applied to one main surface of the substrate 11C to obtain a resin layer 12R. This photosensitive resin is the raw material of the cured resin layer 12. For example, spin coating, roll coating, or slot coating can be used to apply the photosensitive resin. When using spin coating, the thickness of the resin layer 12R can be controlled by the rotation speed.

[0051] Next, the resin layer 12R is subjected to pattern exposure. For example, as shown in Fig. 3, the resin layer 12R is irradiated with ultraviolet light 16 through a photomask 15. This causes a crosslinking reaction to occur in the exposed portions 12E of the resin layer 12R without causing a crosslinking reaction in the unexposed portions 12N of the resin layer 12R.

[0052] Resin layer 12R is then subjected to a development process. In this development process, for example, an alkaline aqueous solution is used as the developer. In this manner, assembly element 10C shown in FIG. 4 is obtained.

[0053] The assembly element 10C includes a substrate 11C and a cured resin layer 12C provided on one of its main surfaces. The assembly element 10C also includes a plurality of element regions each corresponding to a diffractive optical element 10. The portions of the cured resin layer 12C corresponding to these element regions each correspond to the cured resin layer 12 of the diffractive optical element 10. In the assembly element 10C shown in FIG. 4, the cured resin layer 12C is composed only of a plurality of convex portions 12P, but the cured resin layer 12C may further include a continuous film portion interposed between these convex portions 12P and the substrate 11C.

[0054] Thereafter, aggregate element 10C is subjected to a singulation process such as dicing, thereby obtaining a plurality of diffractive optical elements 10 corresponding to the plurality of element regions, respectively.

[0055] 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 having openings at positions corresponding to the gaps between the convex portions 12P is formed on the resulting cured resin layer. Next, the exposed portions of the cured resin layer are removed by dry etching to obtain the cured resin layer 12C. Thereafter, the mask layer is removed from the cured resin layer 12C to obtain the collective element 10C. The collective element 10C is then subjected to a singulation process to obtain a plurality of diffractive optical elements 10.

[0056] As described above, the resin layer 12R is formed by coating a resin. The resin layer 12R formed by coating has a substantially uniform thickness in each of the portions corresponding to the element regions, but the thickness varies when viewed as a whole. For example, the resin layer 12R formed by spin coating has a thickness distribution in the radial direction of the substrate 11C that has a maximum value at or near the periphery of the substrate 11C and a minimum value closer to the center of the substrate 11C.

[0057] Cured resin layer 12C obtained from resin layer 12R having such thickness variations will have thickness variations similar to those of resin layer 12R. For example, cured resin layer 12C obtained when resin layer 12R is formed by spin coating will have a thickness distribution in the radial direction of collective element 10C that has a maximum value or maximum value at or near the periphery of collective element 10C and a minimum value or minimum value at a position closer to the center of collective element 10C. As a result, while height H of convex portions 12P is approximately uniform in each diffractive optical element 10, height H of convex portions 12P will vary between diffractive optical elements 10.

[0058] The difference between the maximum and minimum thicknesses of the cured resin layer 12C formed on a single substrate 11C is, for example, 0.01 μm or more. This difference depends on the resin coating conditions, but is, for example, 0.06 μm or less. The height H of the protrusions 12P may vary within this range.

[0059] Furthermore, the width W of the convex portion 12P may also vary depending on the thickness of the resin layer 12R. Therefore, while the width W of the convex portion 12P is approximately uniform in each diffractive optical element 10, the width W of the convex portion 12P may vary between diffractive optical elements 10.

[0060] As described above, the height H and width W of the convex portions 12P affect the light utilization efficiency. However, as long as the variations in the height H and width W of the convex portions 12P between the diffractive optical elements 10 are within the above-mentioned ranges, the effect of these variations on the light utilization efficiency is small. Therefore, by setting the coating conditions of the photosensitive resin so that the variations in the height H and width W of the convex portions 12P between the diffractive optical elements 10 are within the above-mentioned ranges, it is possible to achieve approximately the same light utilization efficiency for all of the diffractive optical elements 10.

[0061] Furthermore, in the above-described diffractive optical element 10, the refractive index of the cured resin layer 12 at a wavelength of 940 nm is set to 1.6 or less. Therefore, a light utilization efficiency of 70% or more, preferably 75% or more, more preferably 80% or more, even more preferably 85% or more, and most preferably 90% or more can be achieved. The maximum light utilization efficiency is approximately 100%, and in one example, it is 99%, and in another example, it is 95%.

[0062] The diffractive optical element 10 can be distributed singly. That is, a plurality of diffractive optical elements 10 can be distributed individually, rather than collectively. However, it is common to distribute an element assembly including a plurality of diffractive optical elements 10. The diffractive optical elements 10 included in the element assembly have the same variations as described above in the thickness of the cured resin layer 12, etc.

[0063] Instead of distributing the diffractive optical element 10 or element assembly as a finished product, the assembly of elements 10C may be distributed as an intermediate product. That is, the assembly of elements 10C may be distributed, and then singulated into the diffractive optical elements 10.

[0064] The above-described diffractive optical element 10 can be used, for example, in a projection device. FIG. 5 is a diagram schematically illustrating an example of a projection device including the diffractive optical element of FIG.

[0065] The projection device 100 shown in FIG. 5 includes a diffractive optical element 10, an infrared laser 20, and a collimator 30.

[0066] The infrared laser 20 is, for example, a semiconductor laser, and outputs a laser beam having the wavelength described above.

[0067] The laser beam output by the infrared laser 20 is usually divergent light. The collimator 30 collimates the laser beam output by the infrared laser 20. Note that if the diffractive optical element 10 serves as the collimator, the collimator 30 can be omitted.

[0068] A collimated laser beam is incident on the diffractive optical element 10. This laser beam may be incident on either main surface of the diffractive optical element 10. According to one example, the laser beam is incident on the main surface of the diffractive optical element 10 that faces the cured resin layer 12.

[0069] The diffractive optical element 10 performs at least one of splitting and shaping of this laser beam. As described above, when a laser beam is incident on the diffractive optical element 10, the diffractive optical element 10 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 an irradiation target.

[0070] The projection device 100 can be used, for example, in a measurement device. The measurement device includes the projection device 100 and a light receiving device. The light receiving device includes a plurality of light receiving elements, each including a photoelectric conversion element. According to one example, the light receiving device includes a plurality of pixels, each of which has an image sensor including a light receiving element that exhibits high sensitivity at the wavelength of the laser beam and low sensitivity in other wavelength ranges, such as the visible range.

[0071] This measurement device emits a laser beam from the projection device 100 toward an object to be irradiated and receives the reflected light generated by reflection from the object to be irradiated, thereby acquiring information regarding distance. For example, the measurement device may acquire information regarding the distance from the measurement device to a beam spot on the object to be irradiated, for example, by a ToF method. Specifically, the measurement device emits a pulsed laser beam from the projection device 100 toward the object to be irradiated, and receives the reflected light generated by reflection from the object to be irradiated with a light receiving device. The measurement device calculates the distance from the measurement device to the beam spot on the object to be irradiated from the delay time corresponding to the time from when the projection device 100 emits the laser beam to when the light receiving device receives the reflected light. Note that the measurement device may also acquire an infrared image having a gradation corresponding to the distribution of the intensity of the reflected light. [Example]

[0072] Tests and calculations performed in connection with the present invention are described below.

[0073] <1> Effect of refractive index of cured resin layer on light utilization efficiency (Example 1) The diffractive optical element 10 shown in FIG. 1 was manufactured by the method described with reference to FIGS. 2 to 4. Here, a glass plate was used as the substrate 11. The cured resin layer 12 was formed using a negative photosensitive resin containing an acrylic resin. This photosensitive resin was prepared so that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was 1.25. The cured resin layer 12 was formed so that the convex portions 12P had a rectangular cross section perpendicular to its length direction, a height H of 1.51 μm, a width W of 0.58 μm, and were arranged in the width direction at a pitch of 2.58 μm.

[0074] (Example 2) The diffractive optical element 10 shown in FIG. 1 was manufactured by the method described with reference to FIGS. 2 to 4. Here, a glass plate was used as the substrate 11. The cured resin layer 12 was formed using a negative photosensitive resin containing an acrylic resin. This photosensitive resin was prepared so that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was 1.34. The cured resin layer 12 was formed so that the convex portions 12P had a rectangular cross section perpendicular to its length direction, a height H of 1.54 μm, a width W of 0.59 μm, and were arranged in the width direction at a pitch of 2.56 μm.

[0075] (Example 3) The diffractive optical element 10 shown in FIG. 1 was manufactured by the method described with reference to FIGS. 2 to 4. Here, a glass plate was used as the substrate 11. The cured resin layer 12 was formed using a negative photosensitive resin containing an acrylic resin. This photosensitive resin was prepared so that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was 1.41. The cured resin layer 12 was formed so that the convex portions 12P had a rectangular cross section perpendicular to its length direction, a height H of 1.52 μm, a width W of 0.57 μm, and were arranged in the width direction at a pitch of 2.58 μm.

[0076] (Comparative Example) The diffractive optical element 10 shown in FIG. 1 was manufactured by the method described with reference to FIGS. 2 to 4. Here, a glass plate was used as the substrate 11. The cured resin layer 12 was formed using a negative photosensitive resin containing an acrylic resin. This photosensitive resin was prepared so that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was 1.65. The cured resin layer 12 was formed so that the convex portions 12P had a rectangular cross section perpendicular to its length direction, a height H of 1.51 μm, a width W of 0.58 μm, and were arranged in the width direction at a pitch of 2.57 μm.

[0077] (Calculation of light utilization efficiency) The light utilization efficiency of the diffractive optical elements 10 according to Examples 1 to 3 and the comparative example was calculated by the Rigorous Coupled-Wave Analysis (RCWA) method. The results are shown in Table 1 below.

[0078] [Table 1]

[0079] As shown in Table 1, by reducing the refractive index of the cured resin layer 12, it was possible to increase the light utilization efficiency.

[0080] <2> Effect of convex height on light utilization efficiency The light use efficiency was calculated by the RCWA method for the diffractive optical element 10 according to Example 1 and a similar diffractive optical element 10 except that the height H of the convex portions 12P was changed. The results are shown in FIG.

[0081] Fig. 6 is a graph showing the relationship between the height of the convex portion and the light utilization efficiency. As shown in Fig. 6, when the height H of the convex portion 12P is in the range of 1.4 μm or more and 1.7 μm or less, the effect of the height H on the light utilization efficiency is extremely small.

[0082] Next, the effect of the height H of the convex portions 12P on light use efficiency was investigated using the same method as above, except that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was set to 1.34. The effect of the height H of the convex portions 12P on light use efficiency was also investigated using the same method as above, except that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was set to 1.41. The effect of the height H of the convex portions 12P on light use efficiency was also investigated using the same method as above, except that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was set to 1.56. As a result, regardless of the magnitude of the refractive index, when the height H of the convex portions 12P was within the above range, the effect of the height H on light use efficiency was extremely small.

[0083] <3> Effect of convex width on light utilization efficiency The light use efficiency was calculated by the RCWA method for the diffractive optical element 10 according to Example 1 and a similar diffractive optical element 10 except that the width W of the convex portions 12P was changed. The results are shown in FIG.

[0084] Fig. 7 is a graph showing the relationship between the width of the convex portion and the light utilization efficiency. As shown in Fig. 7, when the width W of the convex portion 12P is in the range of 0.4 μm or more and 1.0 μm or less, the effect of the width W on the light utilization efficiency is extremely small.

[0085] Next, the effect of the width W of the convex portions 12P on light use efficiency was investigated using the same method as above, except that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was set to 1.34. The effect of the width W of the convex portions 12P on light use efficiency was also investigated using the same method as above, except that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was set to 1.41. The effect of the width W of the convex portions 12P on light use efficiency was also investigated using the same method as above, except that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was set to 1.56. As a result, regardless of the magnitude of the refractive index, when the width W of the convex portions 12P was within the above range, the effect of the width W on light use efficiency was extremely small. [Explanation of symbols]

[0086] 10...diffractive optical element, 10C...collective element, 11...substrate, 11C...substrate, 12...resin cured layer, 12E...exposed portion, 12N...unexposed portion, 12R...resin layer, 15...photomask, 16...ultraviolet light, 20...infrared laser, 30...collimator, 100...projection device

Claims

1. A diffractive optical element used for at least one of splitting and shaping a laser beam having a wavelength in the near-infrared region, a substrate that transmits the laser beam; and a cured resin layer that is provided on the substrate and transmits the laser beam, the cured resin layer has a refractive index of 1.6 or less at a wavelength of 940 nm, and a plurality of convex portions that exhibit diffractive properties are formed on a surface of the diffractive optical element; A diffractive optical element in which each of the plurality of convex portions has a height in the range of 1.4 μm to 1.7 μm and a width in the range of 0.4 μm to 1.0 μm.

2. 2. The diffractive optical element according to claim 1, wherein the refractive index is 1.25 or more.

3. 2. The diffractive optical element according to claim 1, wherein the refractive index is 1.45 or less.

4. 2. The diffractive optical element according to claim 1, which functions as a beam splitter when the laser beam is incident thereon.

5. 5. The diffractive optical element according to claim 4, wherein when the laser beam is incident on the element, the element splits the laser beam into three laser beams.

6. The diffractive optical element according to claim 1 , wherein the plurality of convex portions form a striped pattern.

7. The diffractive optical element according to claim 1 , wherein the cured resin layer contains a cured acrylic resin.

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

9. A collective element including a plurality of element regions and separated into a plurality of diffractive optical elements corresponding to the plurality of element regions, each of the plurality of diffractive optical elements being a diffractive optical element according to any one of claims 1 to 8.

10. The element assembly according to claim 9 , wherein one or more of the plurality of element regions has a different thickness from one or more of the other element regions.

11. The element assembly according to claim 10 , wherein the difference between the maximum and minimum thicknesses of the cured resin layer is 0.01 μm or more.

12. The collective element according to claim 10, wherein the distribution of the thickness of the cured resin layer in the radial direction of the collective element has a maximum value or a maximum value at or near the periphery of the collective element, and a minimum value or a minimum value at a position closer to the center of the collective element.

13. An element assembly comprising a plurality of diffractive optical elements, each of which is the diffractive optical element according to claim 1 .

14. The element assembly according to claim 13 , wherein one or more of the plurality of diffractive optical elements have a different thickness of the cured resin layer from one or more of the remaining diffractive optical elements.

15. 15. The element assembly according to claim 14, wherein the difference between the maximum and minimum thicknesses of the cured resin layer is 0.01 μm or more.

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