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 dividing light by developing a diffraction action on the branched light intensity ratio of a diffraction optical element.SOLUTION: The diffractive optical element 10 includes a substrate 11 that transmits a laser beam having a wavelength in a near-infrared region, and a cured resin layer 12 that is provided on the substrate 11 and transmits the laser beam, wherein the cured resin layer 12 has a refractive index of 1.5 or more and 1.6 or less at a wavelength of 9400 nm, and a plurality of convex portions 12P that generate a diffractive action are formed on a surface of the diffractive optical element 10, and each of the plurality of convex portions 12P has a height in a range of 0.5 μm or more and 1.5 μm or less. The width is in a range of 0.3 μm or more and 2.0 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 technology that can reduce the effect of variations in the thickness of a cured resin layer having convex portions that exhibit a diffractive effect and cause light division on the branched light intensity ratio 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 to split 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 at a wavelength of 940 nm that is in the range of 1.5 to 1.6, and wherein a plurality of convex portions that exhibit a diffractive effect are formed on the surface of the diffractive optical element, and each of the plurality of convex portions has a height that is in the range of 0.5 μm to 1.5 μm and a width that is in the range of 0.3 μm to 2.0 μm. According to another aspect of the present invention, there is provided a diffractive optical element relating to the above aspect, wherein each of the plurality of convex portions has a height in the range of 0.8 μm or more and 1.4 μm or less and a width in the range of 0.3 μm or more and 2.0 μm or less.

[0009] 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, when the laser beam is incident thereon, splits the laser beam into three laser beams.

[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 plurality of convex portions form a striped pattern.

[0011] 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.

[0012] 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.

[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 diffractive optical element is a transmissive diffractive optical element.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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]

[0021] The present invention provides a technology that can reduce the effect of variations in the thickness of a cured resin layer having convex portions that exhibit a diffractive effect and cause light division on the branched light intensity ratio of a diffractive optical element. [Brief explanation of the drawings]

[0022] [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 height of the convex portion and the branched light intensity ratio. [Figure 8] FIG. 8 is a graph showing the relationship between the height of the convex portion and the light utilization efficiency. [Figure 9] FIG. 9 is a graph showing the relationship between the height of the convex portion and the branched light intensity ratio. [Figure 10]FIG. 10 is a graph showing the relationship between the height of the convex portion and the light utilization efficiency. [Figure 11] FIG. 11 is a graph showing the relationship between the height of the convex portion and the branched light intensity ratio. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 FIG. 1 is a transmissive diffractive optical element used to split 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.

[0027] 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 5 mm.

[0028] The diffractive optical element 10 includes a substrate 11 and a cured resin layer 12 .

[0029] 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.

[0030] The substrate 11 is made of, for example, an inorganic material. In one example, the substrate 11 is a glass plate. In another example, the substrate 11 is made of quartz. Alternatively, the substrate 11 may be made of an organic material such as PET (polyethylene terephthalate), acrylic resin, or polycarbonate. Alternatively, the substrate 11 may be made of a compound semiconductor such as gallium oxide (Ga2O3), indium oxide (In2O3), or zinc oxide (ZnO). The substrate 11 may be made of a single material or multiple materials. For example, the substrate 11 may have a single-layer structure or a multi-layer structure.

[0031] The cured resin layer 12 is provided on the substrate 11, for example, on the first main surface. The cured resin layer 12 forms a plurality of convex portions 12P that exhibit diffractive properties on the surface of the diffractive optical element 10. The cured resin layer 12 transmits the laser beam.

[0032] The refractive index of the cured resin layer 12 at a wavelength of 940 nm is in the range of 1.5 to 1.6, preferably in the range of 1.55 to 1.6, more preferably 1.6.

[0033] When the refractive index of the cured resin layer 12 is set within the range of 1.5 to 1.6 and the convex portions 12P are formed so that their heights H and widths W fall within the ranges described below, the influence of variations in the thickness of the cured resin layer 12 that may occur during the manufacture of the diffractive optical element 10 on the branched light intensity ratio of the diffractive optical element can be reduced. Furthermore, when the refractive index of the cured resin layer 12 is set within the range of 1.5 to 1.6 and the convex portions 12P are formed so that their heights H and widths W fall within the ranges described below, it is possible to achieve a substantially equal branched light intensity ratio between the branched light beams. These effects can be further enhanced when the refractive index falls within the preferred ranges described above.

[0034] In this specification, the "branched light intensity ratio" is a value measured when a laser beam having a wavelength in the near-infrared region, for example, a laser beam having a wavelength of 940 nm, is incident on diffractive optical element 10 as a beam splitter and split into two or more laser beams (branched lights), and corresponds to the ratio E2 / E1 of the energy E2 of a specific branched light to the total energy E1 of all branched lights. Here, the measurement of light energy can be performed using, for example, a photodiode. For example, when a laser beam is incident on diffractive optical element 10 as a beam splitter and split into one laser beam as zeroth-order diffracted light and two laser beams as first-order diffracted lights, the branched light intensity ratio of each branched light is ideally approximately 33.3%.

[0035] Furthermore, when the refractive index of the cured resin layer 12 is set within the range of 1.5 to 1.6, and the convex portions 12P are formed so that their heights H and widths W fall within the ranges described below, the influence of variations in the thickness of the cured resin layer 12, which may occur during the production of the diffractive optical element 10, on the light utilization efficiency of the diffractive optical element 10 can be reduced, and a sufficiently high light utilization efficiency can be achieved.

[0036] 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 weakens Fresnel reflection at the interface between the cured resin layer 12 and the gas phase, tending to increase light utilization efficiency. Furthermore, at least a portion of the laser beam Fresnel-reflected at the interface becomes stray light, which can reduce the measurement accuracy of a measuring device, as described below.

[0037] In this specification, the "light utilization efficiency" is a value measured when a laser beam having a wavelength in the near-infrared region, for example, a laser beam having a wavelength of 940 nm, is incident on one principal 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 beams 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. Here, the light energy can be measured using, for example, a photodiode.

[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. This mixture may have a lower refractive index than the cured resin it contains. Hollow silica particles, for example, may be used as the hollow particles. The hollow particles may have a small particle size. 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] As described above, 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 portions of the diffractive optical element 10 corresponding to the convex portions 12P and a laser beam incident on portions of the diffractive optical element 10 corresponding to the concave portions, which are gaps between the convex portions 12P. The diffractive optical element 10 splits the laser beam by utilizing the interference caused by this. That is, the diffractive optical element 10 functions as a beam splitter when a laser beam is incident thereon. The diffractive optical element 10 may also function as a collimator when a laser beam is incident thereon.

[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 the first direction.

[0043] Each of the protrusions 12P has a rectangular cross section perpendicular to its length direction. This cross section may be forward tapered or reverse tapered, but is preferably rectangular. If the cross section of the protrusion 12P is not rectangular, the width W of the protrusion 12P varies in the height direction of the protrusion 12P. For example, if the cross section is forward tapered, the width W of the protrusion 12P decreases as the height of the protrusion 12P increases, while if the cross section is reverse tapered, the width W of the protrusion 12P increases as the height of the protrusion 12P increases. Therefore, if the cross section of the protrusion 12P is not rectangular, the width W of the protrusion 12P is defined as the width of the protrusion 12P at a height half the height of the protrusion 12P.

[0044] Each of the protrusions 12P has a height H in the range of 0.5 μm to 1.5 μm. If the height H is smaller than the lower limit of the range, the variation in the height H will have a greater effect on the branched light intensity ratio. Specifically, if the height H is smaller than the lower limit of the range, the branched light intensity ratio will vary greatly between the branched lights. If the height H is larger than the upper limit of the range, the variation in the height H will also have a greater effect on the branched light intensity ratio. Specifically, if the height H is larger than the upper limit of the range, the branched light intensity ratio will vary greatly between the branched lights.

[0045] The height H of the protrusions 12P is preferably in the range of 0.8 μm to 1.4 μm, and more preferably in the range of 0.9 μm to 1.3 μm.

[0046] When the refractive index of the cured resin layer 12 at a wavelength of 940 nm is within the range of 1.5 to 1.6 and the width W of the convex portions 12P is within the range described below, even if the height H varies within the range of 0.5 μm to 1.5 μm, the effect of this variation on the branched light intensity ratio is small. Furthermore, when the refractive index of the cured resin layer 12 at a wavelength of 940 nm is within the range of 1.5 to 1.6 and the width W of the convex portions 12P is within the range described below and the height H of the convex portions 12P is within the above range, a substantially equal branched light intensity ratio can be achieved between the branched lights.

[0047] Furthermore, when the refractive index of the cured resin layer 12 at a wavelength of 940 nm is within the range of 1.5 or more and 1.6 or less and the width W of the convex portion 12P is within the range described below, even if the height H varies within the range of 0.5 μm or more and 1.5 μm or less, the effect of this variation on the light utilization efficiency is small, and a sufficiently high light utilization efficiency can be achieved.

[0048] Each of the protrusions 12P has a width W in the range of 0.3 μm to 2.0 μm. Reducing the width W within this range tends to increase light utilization efficiency. The width W of the protrusions 12P is preferably in the range of 0.4 μm to 1.0 μm, and more preferably in the range of 0.4 μm to 0.6 μm.

[0049] 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.

[0050] Here, a transmissive diffractive optical element has been described as one embodiment of the diffractive optical element 10, but the diffractive optical element 10 may also be a reflective diffractive optical element.

[0051] The above-described diffractive optical element 10 can be manufactured, for example, by the following method.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] As described above, the height H of the convex portions 12P affects the branched light intensity ratio and the light utilization efficiency. However, as long as the variation in the height H of the convex portions 12P between the diffractive optical elements 10 is within the above-mentioned range, the effect of this variation on the branched light intensity ratio and the light utilization efficiency is small. Therefore, by setting the coating conditions of the photosensitive resin so that the variation in the height H of the convex portions 12P between the diffractive optical elements 10 is within the above-mentioned range, it is possible to achieve approximately the same branched light intensity ratio and approximately the same light utilization efficiency for all of the diffractive optical elements 10.

[0064] 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 a range of 1.5 to 1.6. Therefore, a light utilization efficiency of, for example, 70% or more, preferably 75% or more, can be achieved. The maximum light utilization efficiency is approximately 100%, and in one example, it is 95%, in another example, 90%, and in yet another example, it is 80%.

[0065] 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.

[0066] 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.

[0067] The above-described diffractive optical element 10 can be used in, for example, a projection device. Fig. 5 is a diagram schematically showing an example of a projection device including the diffractive optical element of Fig. 1.

[0068] The projection device 100 shown in FIG. 5 includes a diffractive optical element 10, an infrared laser 20, and a collimator 30.

[0069] The infrared laser 20 is, for example, a semiconductor laser, and outputs a laser beam having the wavelength described above.

[0070] 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.

[0071] 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.

[0072] The diffractive optical element 10 splits 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.

[0073] 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.

[0074] 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]

[0075] Tests and calculations performed in connection with the present invention are described below.

[0076] <1> When the refractive index of the cured resin layer is 1.6 (Production of Diffractive Optical Element According to Example 1) The diffractive optical element 10 shown in FIG. 1 was manufactured by the method described with reference to FIGS.

[0077] Here, the substrate 11 used was a glass wafer with a diameter of 300 mm and a thickness of 0.7 mm.

[0078] The cured resin layer 12 was formed using a negative photosensitive resin containing an acrylic resin. This negative photosensitive resin was prepared so that the refractive index of the cured resin layer 12 at a wavelength of 940 nm was 1.6. The cured resin layer 12 was formed so that the protrusions 12P had a rectangular cross section perpendicular to its length direction, a height H of 1.54 μm, a width W of 0.54 μm, and were arranged in the width direction at a pitch of 2.59 μm.

[0079] Specifically, the cured resin layer 12 was formed by the following method. First, a negative photosensitive resin was applied to one main surface of the substrate 11 by spin coating. The film thickness was controlled by the rotation speed. The resulting resin layer was heated at 70°C for 60 seconds. Thereafter, the resin layer was partially cured by irradiating it with ultraviolet light having a wavelength of 365 nm using an exposure machine and a photomask. Here, the exposure dose was 3000 J / m 2 The resin layer was then heated at 120°C for 1 minute and developed with a 2.38% aqueous solution of TMAH (tetramethylammonium hydroxide). Finally, the resin layer was heated at 100°C for 60 seconds to form a cured resin layer 12. In this way, the diffractive optical element 10 according to Example 1 was manufactured.

[0080] (Calculation of light utilization efficiency) The light utilization efficiency of the diffractive optical element 10 according to Example 1 and a similar diffractive optical element 10 except for varying the height H of the convex portions 12P was calculated by RCWA (Rigorous Coupled-Wave Analysis). The wavelength used was 940 nm. The height H of the convex portions 12P was varied within a range of 0.6 to 1.5 μm. The results are shown in FIG. 6.

[0081] (Calculation of branched light intensity ratio) The branched light intensity ratios of the diffractive optical element 10 according to Example 1 and a similar diffractive optical element 10 except for varying the height H of the convex portions 12P were calculated using the RCWA method. The wavelength used here was 940 nm. The incident laser beam was split into three laser beams, specifically, one laser beam as a zero-order beam and two laser beams as first-order beams. The height H of the convex portions 12P was varied within a range of 0.6 to 1.5 μm. The results are shown in FIG. 7. In FIG. 7, the dashed line indicates the "target value + 15% of the target value" (i.e., "approximately 33% + 5%), and the dash-dot line indicates the range up to the "target value - 15% of the target value" (i.e., "approximately 33% - 5%).

[0082] (result) FIG. 6 shows the relationship between the height of the convex portions and the light utilization efficiency. FIG. 7 shows the relationship between the height of the convex portions and the branched light intensity ratio. As shown in FIG. 6, when the refractive index of the cured resin layer is 1.6, even when the height H of the convex portions 12P is varied within a range of 0.6 μm to 1.5 μm, the light utilization efficiency is within a range of 74% to 78%. This indicates that a sufficiently high light utilization efficiency can be achieved, and the influence of the variation in height H on the light utilization efficiency is small. Furthermore, as shown in FIG. 7, when the refractive index of the cured resin layer is 1.6 and the height H of the convex portions 12P is within a range of 0.7 μm to 1.4 μm, the branched light intensity ratio of the zeroth-order light and the branched light intensity ratio of the first-order light are within a range of "target value + 15% of the target value" to "target value - 15% of the target value." This indicates that a substantially equal branched light intensity ratio can be achieved, and the influence of the variation in height H on the branched light intensity ratio is small.

[0083] <2> When the refractive index of the cured resin layer is 1.7 (method) The diffractive optical element 10 of Example 2 was manufactured according to the same procedure as in the manufacture of the diffractive optical element 10 of Example 1, except that the cured resin layer 12 was formed so that the refractive index at a wavelength of 940 nm was 1.7.

[0084] The light utilization efficiency of the diffractive optical element 10 according to Example 2 and a similar diffractive optical element 10 except for varying the height H of the convex portions 12P was calculated by the RCWA method. The wavelength used here was 940 nm. The height H of the convex portions 12P was varied within the range of 0.6 to 1.5 μm. The results are shown in FIG. 8.

[0085] The RCWA method was used to calculate the split light intensity ratios of the diffractive optical element 10 according to Example 2 and a similar diffractive optical element 10 except for varying the height H of the convex portions 12P. The wavelength used here was 940 nm. The incident laser beam was split into three laser beams, specifically, one laser beam as a zero-order beam and two laser beams as first-order beams. The height H of the convex portions 12P was varied within a range of 0.6 to 1.5 μm. The results are shown in FIG. 9. In FIG. 9, the dashed line indicates the "target value + 15% of the target value" (i.e., "approximately 33% + 5%), and the dashed-dotted line indicates the range up to the "target value - 15% of the target value" (i.e., "approximately 33% - 5%).

[0086] (result) FIG. 8 shows the relationship between the height of the convex portions and the light utilization efficiency. FIG. 9 shows the relationship between the height of the convex portions and the branched light intensity ratio. As shown in FIG. 8, when the refractive index of the cured resin layer is 1.7, even when the height H of the convex portions 12P is varied within a range of 0.6 μm or more and 1.5 μm or less, the light utilization efficiency falls within a range of 69% or more and 76% or less. This means that a sufficiently high light utilization efficiency can be achieved, and the effect of variations in the height H on the light utilization efficiency is small. On the other hand, as shown in FIG. 9, when the refractive index of the cured resin layer is 1.7, when the height H of the convex portions 12P is varied within the above range, the branched light intensity ratio of the zeroth-order light and the branched light intensity ratio of the first-order light do not fall within the range from "target value + 15% of the target value" to "target value - 15% of the target value," and it is not possible to achieve approximately equal branched light intensity ratios between the branched lights.

[0087] <3> When the refractive index of the cured resin layer is 1.5 (method) The diffractive optical element 10 of Example 3 was manufactured according to the same procedure as in the manufacture of the diffractive optical element 10 of Example 1, except that the cured resin layer 12 was formed so that the refractive index at a wavelength of 940 nm was 1.5.

[0088] The light utilization efficiency of the diffractive optical element 10 according to Example 3 and a similar diffractive optical element 10 except for varying the height H of the convex portions 12P was calculated by the RCWA method. The wavelength used here was 940 nm. The height H of the convex portions 12P was varied within the range of 0.6 to 1.5 μm. The results are shown in FIG. 10.

[0089] The branched light intensity ratios of the diffractive optical element 10 according to Example 3 and a similar diffractive optical element 10 except for varying the height H of the convex portions 12P were calculated using the RCWA method. The wavelength used here was 940 nm. The incident laser beam was split into three laser beams, specifically, one laser beam as a zero-order beam and two laser beams as first-order beams. The height H of the convex portions 12P was varied within a range of 0.6 to 1.5 μm. The results are shown in FIG. 11. In FIG. 11, the dashed line indicates the "target value + 15% of the target value" (i.e., "approximately 33% + 5%), and the dashed-dotted line indicates the range up to the "target value - 15% of the target value" (i.e., "approximately 33% - 5%).

[0090] (result) FIG. 10 shows the relationship between the height of the convex portions and the light utilization efficiency. FIG. 11 shows the relationship between the height of the convex portions and the branched light intensity ratio. As shown in FIG. 10, when the refractive index of the cured resin layer is 1.5, even when the height H of the convex portions 12P is varied within a range of 0.6 μm to 1.5 μm, the light utilization efficiency is within a range of 75% to 79%. This indicates that a sufficiently high light utilization efficiency can be achieved, and the influence of the variation in height H on the light utilization efficiency is small. Furthermore, as shown in FIG. 11, when the refractive index of the cured resin layer is 1.5 and the height H of the convex portions 12P is within a range of 0.8 μm to 1.5 μm, the branched light intensity ratio of the zeroth-order light and the branched light intensity ratio of the first-order light are within a range of "target value + 15% of the target value" to "target value - 15% of the target value." This indicates that a substantially equal branched light intensity ratio can be achieved, and the influence of the variation in height H on the branched light intensity ratio is small. [Explanation of symbols]

[0091] 10...diffractive optical element, 10C...collective element, 11...substrate, 11C...substrate, 12...cured resin layer, 12C...cured resin layer, 12E...exposed portion, 12N...unexposed portion, 12P...convex portion, 12R...resin layer, 15...photomask, 16...ultraviolet light, 20...infrared laser, 30...collimator, 100...projection device

Claims

1. A diffractive optical element used to split 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 in the range of 1.5 to 1.6 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 0.5 μm to 1.5 μm and a width in the range of 0.3 μm to 2.0 μm.

2. 2. The diffractive optical element according to claim 1, wherein when the laser beam is incident on the element, the element splits the laser beam into three laser beams.

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

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

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

6. The diffractive optical element according to claim 1 , wherein the diffractive optical element is a transmissive diffractive optical element.

7. A collective element including a plurality of element regions and separated into a plurality of diffractive optical elements each corresponding to the plurality of element regions, wherein each of the plurality of diffractive optical elements is a diffractive optical element according to any one of claims 1 to 6.

8. The element assembly according to claim 7 , wherein one or more of the plurality of element regions has a different thickness from one or more of the other element regions.

9. The element assembly according to claim 8, wherein the difference between the maximum and minimum thicknesses of the cured resin layer is 0.01 μm or more.

10. The assembly element according to claim 8, wherein the distribution of the thickness of the cured resin layer in the radial direction of the assembly element has a maximum value or a maximum value at or near the periphery of the assembly element, and a minimum value or a minimum value at a position closer to the center of the assembly element.

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

12. The element assembly according to claim 11 , wherein one or more of the plurality of diffractive optical elements have a different thickness of the cured resin layer from the other one or more of the plurality of diffractive optical elements.

13. 13. The element assembly according to claim 12, wherein the difference between the maximum and minimum thicknesses of the cured resin layer is 0.01 μm or more.

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