JP2018013677A - Diffraction optical element and light irradiation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffraction optical element and a light irradiation device having high utilization efficiency of light, capable of obtain desired diffraction light stably with less influence on the diffraction light even if an incident angle of the light is deviated.SOLUTION: A diffraction optical element 10 is configured to shape light. The diffraction optical element includes a diffraction layer 15 including: a high refractive index part 11 with a plurality of projections 11a aligned with regard to a cross-sectional shape; and a low refractive index part 14 having a lower refractive index than the high refractive index part 11 and including a recess 12 formed at least between the projections 11a. A side shape of a projection 11a at least partially includes inclined parts (11b, 11c, 11d) inclined with regard to a plane P including the diffraction layer 15.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a diffractive optical element and a light irradiation apparatus.

  In recent years, the need for sensor systems has increased, such as the need for personal authentication to avoid security risks due to the spread of networks, the flow of automated driving of automobiles, or the spread of the so-called “Internet of Things”. Yes. There are various types of sensors and various types of information to be detected. One of them is to irradiate light from a light source to an object and obtain information from reflected light. . For example, pattern authentication sensors and infrared radars are examples.

  The light sources of these sensors are those having a wavelength distribution, brightness, and spread according to the application. Visible light to infrared light is often used as the wavelength of light. In particular, infrared light is not easily affected by external light, is invisible, and can be observed somewhat inside, so it is widely used. Yes. As the type of light source, an LED light source, a laser light source, or the like is often used. For example, a laser light source with a small light spread is preferably used for detecting a distant place, and an LED light source is suitably used for detecting a relatively close place or irradiating an area with a certain extent. It is done.

By the way, the size and shape of the target irradiation region do not necessarily match the spread (profile) of light from the light source. In that case, the light is shaped by a diffuser plate, a lens, a shielding plate, or the like. There is a need. Recently, a diffusion plate called Light Shaping Diffuser (LSD) that can shape the shape of light to some extent has been developed.
Another means for shaping the light is a diffractive optical element (DOE). This is an application of a diffraction phenomenon when light passes through a place where materials having different refractive indexes are arranged with periodicity. DOE is basically designed for light of a single wavelength, but theoretically, it is possible to shape light into almost any shape. In the above-described LSD, the light intensity in the irradiation region has a Gaussian distribution, whereas in the DOE, the uniformity of the light distribution in the irradiation region can be controlled. Such a characteristic of the DOE is advantageous in terms of high efficiency by suppressing irradiation to an unnecessary area, miniaturization of the apparatus by reducing the number of light sources, and the like (for example, see Patent Document 1).
The DOE can be applied to both a parallel light source such as a laser and a diffuse light source such as an LED, and is applicable to a wide range of wavelengths from ultraviolet light to visible light and infrared light. .

  DOE requires fine processing on the order of nm. In particular, in order to diffract long wavelength light, it is necessary to form a fine shape with a high aspect ratio. Therefore, conventionally, an electron beam lithography technique using an electron beam has been used for manufacturing the DOE. For example, after forming a hard mask or resist on a quartz plate that is transparent in the ultraviolet to near-infrared region, a predetermined shape is drawn on the resist using an electron beam, resist development, hard mask dry etching, and quartz drying. Etching is sequentially performed to form a pattern on the quartz plate surface, and then the hard mask is removed to obtain a desired DOE.

JP-A-2015-170320

DOE can shape light efficiently, but interface reflection occurs due to a sudden change in refractive index at the interface between DOE and air (or an interface between DOE and a material having a different refractive index). End up. This interface reflection reduces the light utilization efficiency.
In order to avoid the interface reflection, for example, a method of forming an antireflection film such as a dielectric multilayer film can be considered. However, in general, the cost is often increased. In addition, it is often difficult to form the antireflection film uniformly along the fine shape of the DOE.

Further, the DOE is generally designed so that desired shaping can be performed on light with respect to incident light from a certain fixed direction. In the case of using a laser light source, it is usually often incident perpendicularly to the DOE surface (the surface on which the DOE periodic structure exists or the back surface thereof). In addition, when a diffused light source such as an LED is used, the design considering that light enters obliquely with respect to the DOE plane (a surface including the periodic structure of the diffraction grating) based on the diffusion profile of the light source is Done.
However, when the DOE is actually used, light is not necessarily incident at an angle according to the diffusion profile used in the design, and the incident angle may change due to the effects of assembly accuracy of the apparatus and performance fluctuation of the light source. is there. In the conventional DOE, when the incident angle deviates from the design angle, the characteristics (for example, light distribution characteristics) of diffracted light (emitted light) tend to change greatly. For this reason, the design margin of the DOE and the light irradiation apparatus provided with the DOE tends to be narrowed, which makes it difficult to put it to practical use and raises concerns about the cost of the apparatus.

  An object of the present invention is to provide a diffractive optical element capable of obtaining desired diffracted light stably with little influence on diffracted light even when the light use efficiency is high and the incident angle of light is deviated. It is to provide a light irradiation device.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this.

  A first invention is a diffractive optical element that shapes light, and has a high refractive index portion (11, 21, 21) in which a plurality of convex portions (shapes of 11a, 21a, 31a, etc.) are arranged side by side in a cross-sectional shape. 31) and a refractive index lower than that of the high refractive index portion (11, 21, 31) and including a concave portion (12) formed at least between the convex portions (shapes of 11a, 21a, 31a, etc.). And a diffractive layer (15, 25, 35) having a low refractive index portion (14), and a side shape of the convex portion (11a, 21a, 31a) includes the diffractive layer (15, 25, 35). It is a diffractive optical element (10, 20, 30) provided with at least a part of inclined portions (11b, 11c, 11d, 21b, 21c, 21d, 31b) inclined with respect to a plane.

  According to a second aspect of the present invention, in the diffractive optical element (10, 20, 30) according to the first aspect of the present invention, the side surface shape of the convex portions (11a, 21a, 31a) is the convex portion (11a, 21a, 31a). First inclined portions (11b, 21b) inclined in a direction in which the width of the convex portions (11a, 21a, 31a) increases from the tip portions (11e, 21e, 31e) to the base portions (11f, 21f, 31f). , 31b). A diffractive optical element (10, 20, 30).

  According to a third invention, in the diffractive optical element (30) according to the second invention, the direction perpendicular to the diffraction layer (35) from the first inclined part (31b) toward the root part (31f) The diffractive optical element (30) is provided with a vertical portion (31h) extending in the direction.

  According to a fourth invention, in the diffractive optical element (10, 20) according to the second invention, the convex portion (11f, 21f) toward the root portion (11f, 21f) from the first inclined portion (11b, 21b). 11a, 21a) and a second inclined portion (11c, 21c) inclined in a direction in which the width thereof becomes narrower, and further toward the root portion (11f, 21f) from the second inclined portion (11c, 21c). A diffractive optical element (10, 20), comprising: a third inclined portion (11d, 21d) inclined in a direction in which the width of the convex portion (11a, 21a) increases.

  According to a fifth aspect of the present invention, in the diffractive optical element (10, 20) according to the fourth aspect, the second inclined portion (11c, 21c) and the third inclined portion (11d, 21d) are connected to each other. The diffractive optical element (10, 20) is characterized in that the width of the part is wider than the width of the tip (11e, 21e) of the convex part (11a, 21a).

  According to a sixth invention, in the diffractive optical element (20) according to any one of the first invention to the fifth invention, the tip (21e) of the convex portion (21a) has a plurality of vertices (21g). A diffractive optical element (20) characterized by comprising:

  According to a seventh invention, in the diffractive optical element (10) according to any one of the first to sixth inventions, the bottom portion (12a) of the concave portion (12) is formed by the convex portion (11a). The diffractive optical element (10) is characterized by projecting in a projecting direction.

  According to an eighth invention, in the diffractive optical element (10, 20, 30) according to any one of the first invention to the seventh invention, the high refractive index portion (11, 21, 31) is ionizing radiation. A diffractive optical element (10, 20, 30), which is obtained by curing a curable resin composition.

  According to a ninth invention, in the diffractive optical element (10, 20, 30) according to any one of the first invention to the eighth invention, the low refractive index portion (14) is air. The diffractive optical element (10, 20, 30) is characterized.

  A tenth invention is the diffractive optical element (10, 20, 30) according to any one of the first invention to the ninth invention, wherein the transparent substrate (41) and the diffractive layers (15, 25, 35) and covering layers (42, 43) covering the diffractive layers (15, 25, 35) are laminated in this order, (10, 20, 30) It is.

  An eleventh invention is the diffractive optical element (10, 20, 30) according to any one of the first to tenth inventions, wherein the diffraction layer (15, 25, 35) has a wavelength of 780 nm. A diffractive optical element (10, 20, 30) characterized by diffracting the above infrared rays.

  A twelfth invention is a diffractive optical element (10, 20, 30) according to the eleventh invention, wherein the height of the convex portions (11a, 21a, 31a) is 650 nm or more. Optical elements (10, 20, 30).

  The thirteenth invention is the diffraction according to any one of claims 1 to 12, wherein at least one of the light source (L) and the light emitted from the light source (L) passes therethrough. An optical element (10, 20, 30).

  14th invention is the light irradiation apparatus as described in 13th invention, The said light source (L) can light-emit infrared rays with a wavelength of 780 nm or more.

  According to the present invention, a diffractive optical element that has high light utilization efficiency and can stably obtain desired diffracted light with little influence on diffracted light even when the incident angle of light is deviated. A light irradiation device can be provided.

1 is a plan view showing a first embodiment of a diffractive optical element according to the present invention. It is a perspective view which shows an example of the partial periodic structure in the example of the diffractive optical element of FIG. FIG. 3 is a cross-sectional view of the diffractive optical element cut at a position indicated by an arrow E-E ′ in FIG. 2. It is the figure which expanded and showed the convex part 11a. It is the figure which showed the diffraction optical element 20 of 2nd Embodiment in the cross section similar to FIG. It is the figure which expanded and showed the convex part 21a. It is the figure which showed the diffraction optical element 30 of 3rd Embodiment in the cross section similar to FIG. It is the figure which expanded and showed the convex part 31a. It is sectional drawing which showed the diffractive optical element of the comparative example similarly to FIG. It is a figure which shows the condition of evaluation. It is a figure explaining the reason that the diffractive optical element of this invention becomes less reflected light than the diffractive optical element of a comparative example. It is the figure which simplified and showed typically the relationship between the change of an incident angle, and diffracted light. It is a figure explaining a diffractive optical element. It is a figure which shows the example which has provided the transparent base material, and the example which has provided the coating layer as a deformation | transformation form of a diffractive optical element.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a plan view showing a first embodiment of a diffractive optical element according to the present invention.
FIG. 2 is a perspective view showing an example of a partial periodic structure in the example of the diffractive optical element of FIG.
FIG. 3 is a cross-sectional view of the diffractive optical element cut at a position indicated by an arrow EE ′ in FIG.
In addition, each figure shown below including FIG. 1 is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
In the following description, specific numerical values, shapes, materials, and the like are shown and described, but these can be changed as appropriate.

  As used in the present invention, the shape and geometric conditions, and terms specifying the degree thereof, for example, terms such as “parallel”, “orthogonal”, “same”, length and angle values, etc. Without being limited to a strict meaning, it should be interpreted to include a range where a similar function can be expected. In addition, the “plan view” in this specification means visual recognition from the side in which the fine shape is formed in the direction perpendicular to the plate surface of the diffractive optical element. That is, it corresponds to viewing from the direction perpendicular to the surface having the diffraction layer of the diffractive optical element (viewed from the positive side of the Z axis in FIG. Will be done).

In the present invention, “shaping the light” means controlling the light traveling direction so that the shape of the light projected on the target object or target region (irradiation region) becomes an arbitrary shape. Say. For example, as shown in the example of FIG. 13, light 201 (FIG. 13B) is prepared in which the irradiation region 202 becomes circular when directly projected onto a planar screen 200. By transmitting this light 201 through the diffractive optical element 10 of the present invention, the irradiation region 204 has a desired shape such as a square (FIG. 13A), a rectangle, or a circle (not shown). “Shaping light”.
In the present invention, the term “transparent” refers to a material that transmits at least light having a wavelength to be used. For example, even if it does not transmit visible light, as long as it transmits infrared light, it is handled as transparent when used for infrared applications.

The diffractive optical element 10 of the first embodiment is a diffractive optical element (DOE) that shapes light. The diffractive optical element 10 spreads light into a cross-shaped shape with respect to an infrared laser having a wavelength of 980 nm, specifically, ± 50 degrees and a width that is ± 3.3 degrees wide and has a tolerance of two bands of light. Designed to be The diffractive optical element 10 usually has a plurality of regions (partial periodic structures: for example, regions A to D in FIG. 1) having different periodic structures. In FIG. 2, an example of the partial periodic structure is extracted and shown.
As shown in FIG. 3, the diffractive optical element 10 includes a high refractive index portion 11 in which a plurality of convex portions 11a are arranged side by side in a cross-sectional shape. The high refractive index portion 11 extends in the depth direction of the cross section while maintaining the same cross sectional shape.

The high refractive index portion 11 may be made, for example, by processing a shape of quartz (SiO ₂ , synthetic quartz) by dry etching, or by curing an ionizing radiation curable resin composition. There may be. Various methods are known for manufacturing such a periodic structure, and can be appropriately created by these known methods. The shape of the inclined portion and the like characteristic to the present application described below is realized mainly by adjusting various conditions of the dry etching process.

  In addition, air is present in the upper portion of FIG. 3 including the recess 12 formed between the protrusions 11 a and the space 13 near the top of the protrusion 11 a, and the refractive index is higher than that of the high refractive index portion 11. The low refractive index portion 14 is low. A diffraction layer 15 having a function of shaping light is constituted by a periodic structure in which the high refractive index portions 11 and the low refractive index portions 14 are alternately arranged.

FIG. 4 is an enlarged view of the convex portion 11a.
The side surface shape of the convex portion 11 a includes a plurality of inclined portions that are inclined with respect to the plane P including the diffraction layer 15. Specifically, the convex portion 11a is provided with a first inclined portion 11b, a second inclined portion 11c, and a third inclined portion 11d.

  The 1st inclination part 11b is the slope comprised by the curved surface inclined in the direction which the width of the convex part 11a spreads toward the root part 11f from the front-end | tip part 11e of the convex part 11a. The inclined surface including the inclined surface of the first inclined portion 11b mainly indicates a surface formed by a curved surface, and this will be described. However, these slopes may include a portion constituted by a plane.

  The 2nd inclination part 11c is the slope comprised by the curved surface inclined in the direction where the width | variety of the convex part 11a becomes narrow toward the base part 11f from the 1st inclination part 11b.

  The third inclined portion 11d is an inclined surface formed by a curved surface inclined in a direction in which the width of the convex portion 11a increases from the second inclined portion 11c toward the root portion 11f.

  The bottom portion 12a of the recess 12 is configured to protrude in the direction in which the protrusion 11a protrudes. Note that the root portion 11 f is formed in a curved surface and is connected to the bottom portion 12 a of the recess 12.

For example, when designing a rectangular diffusion shape having a long side of ± 50 ° × short side of ± 3.3 ° with 2-level for a 980 nm laser beam, the optimum depth of the diffraction grating Is 1087 nm, the finest pattern width is 250 nm, and the maximum aspect ratio exceeds 4.
These designs are performed using various simulation tools such as Grafting MOD (manufactured by Rsoft) using a rigorous coupled wave analysis (RCWA) algorithm and Virtuallab (manufactured by LightTrans) using an iterative Fourier transform algorithm (IFTA). be able to.
Further, the height of the convex portion 11a is desirably 650 nm or more. This is because the height of the convex portion 11a of 650 nm for 2-level, 975 nm for 4-level, and 1137 nm for 8-level is required when calculating with a wavelength of 780 nm and a refractive index of 1.6.

  As described above, since the first inclined portion 11b, the second inclined portion 11c, and the third inclined portion 11d are connected from the distal end portion 11e, the convex portion 11a has its width. However, it spreads from the tip part 11e toward the root part 11f and then narrows, and the width becomes the narrowest at the boundary part between the second inclined part 11c and the third inclined part 11d, and the constricted part is The third inclined portion 11d is widened and reaches the root portion 11f. Therefore, although the convex part 11a is a part which protruded in the substantially rectangular shape if it sees as a whole, when the cross-sectional shape is seen in detail, it is comprised combining the several slope from which direction differs.

  The operation and effect of the diffractive optical element 10 of the first embodiment will be described later with reference to evaluation results compared to other embodiments and comparative examples.

(Second Embodiment)
FIG. 5 is a view showing the diffractive optical element 20 of the second embodiment in the same cross section as FIG.
The diffractive optical element 20 of the second embodiment has the same form as that of the first embodiment, except that the shape of the convex portion 21a is different from that of the diffractive optical element 10 of the first embodiment. Therefore, the same reference numerals are given to the portions that perform the same functions as those in the first embodiment described above, and repeated descriptions are omitted as appropriate.
The diffractive optical element 20 includes a high refractive index portion 21 having a convex portion 21a and a low refractive index portion 14 including a concave portion 12 and a space 13, and the high refractive index portion 21 and the low refractive index portion 14 are alternately arranged. A diffractive layer 25 having an action of shaping light is configured by the arranged periodic structure.

The convex portion 21a is the same as the convex portion 11a of the first embodiment except that the shape is different. Hereinafter, the shape of the convex portion 21a will be described.
FIG. 6 is an enlarged view of the convex portion 21a.
The side surface shape of the convex portion 21 a includes a plurality of inclined portions inclined with respect to the plane P including the diffraction layer 25. Specifically, the convex portion 21a is provided with a first inclined portion 21b, a second inclined portion 21c, and a third inclined portion 21d.

  The 1st inclination part 21b is the slope comprised by the curved surface inclined in the direction which the width | variety of the convex part 21a spreads toward the root part 21f from the front-end | tip part 21e of the convex part 21a. However, the first inclined portion 21b of the second embodiment has a larger curvature than the first inclined portion 11b of the first embodiment.

  The 2nd inclination part 21c is the slope comprised by the curved surface inclined in the direction in which the width | variety of the convex part 21a becomes narrow toward the root part 21f from the 1st inclination part 21b.

  The third inclined portion 21d is a slope formed by a curved surface that is inclined in a direction in which the width of the convex portion 21a is further expanded from the second inclined portion 21c toward the root portion 21f. The root portion 21f is formed in a curved surface and is connected to the bottom portion 12a of the recess 12.

  The tip portion 21e of the convex portion 21a of the second embodiment has two vertices 21g. Therefore, the center part of the front-end | tip part 21e becomes a shape which became depressed between the two vertexes 21g.

As described above, since the first inclined portion 21b, the second inclined portion 21c, and the third inclined portion 21d are connected from the distal end portion 21e, the convex portion 21a has a width thereof. However, it spreads from the tip 21e toward the root 21f, then narrows, the width becomes the narrowest at the boundary between the second inclined part 21c and the third inclined part 21d, and the constricted part becomes It is formed, the width is widened by the third inclined portion 21d, and reaches the root portion 21f. Therefore, the convex portion 21a is a portion protruding into a substantially rectangular shape as a whole, but when the cross-sectional shape thereof is viewed in detail, it is configured by combining a plurality of inclined surfaces having different directions.
Furthermore, the tip portion 21e of the convex portion 21a of the second embodiment has two apexes 21g, and the center portion of the tip portion 21e has a recessed shape.

  Note that the shape of the diffractive optical element 20 of the second embodiment is a reverse plate shape of the diffractive optical element 10 of the first embodiment. Therefore, the diffractive optical element 20 according to the second embodiment is manufactured by manufacturing the diffractive optical element 10 according to the first embodiment, and then performing mold making from the diffractive optical element 10 to manufacture the reverse plate 1. Then, the reverse plate 1 is further molded to produce a reverse plate 2, and the reverse plate 2 is used for shaping with an ionizing radiation curable resin, whereby the diffractive optical element 20 is obtained.

  The operation and effect of the diffractive optical element 20 of the second embodiment will also be described later with reference to evaluation results compared to other embodiments and comparative examples.

(Third embodiment)
FIG. 7 is a view showing the diffractive optical element 30 of the third embodiment in the same cross section as FIG.
The diffractive optical element 30 of the third embodiment has the same form as that of the first embodiment, except that the shape of the convex portion 31a is different from that of the diffractive optical element 10 of the first embodiment. Therefore, the same reference numerals are given to the portions that perform the same functions as those in the first embodiment described above, and repeated descriptions are omitted as appropriate.
The diffractive optical element 30 includes a high refractive index portion 31 having a convex portion 31a and a low refractive index portion 14 including the concave portion 12 and the space 13, and the high refractive index portion 31 and the low refractive index portion 14 are alternately arranged. A diffractive layer 35 having an action of shaping light is constituted by the arranged periodic structure.

The convex portion 31a is the same as the convex portion 11a of the first embodiment except that the shape is different. Hereinafter, the shape of the convex portion 31a will be described.
FIG. 8 is an enlarged view of the convex portion 31a.
The side surface shape of the convex portion 21a includes a first inclined portion 31b and a vertical portion 31h.

  The 1st inclination part 31b is the slope comprised by the curved surface inclined in the direction which the width | variety of the convex part 31a spreads toward the root part 31f from the front-end | tip part 31e of the convex part 31a.

  The vertical portion 31h is a plane extending in a direction perpendicular to the plane P including the diffraction layer 35 from the first inclined portion 31b toward the root portion 31f. The vertical part 31h extends to the root part 31f as it is. Note that the root portion 31 f is formed in a curved surface and is connected to the bottom portion 12 a of the recess 12.

  The operation and effect of the diffractive optical element 30 of the third embodiment will also be described later with reference to evaluation results compared to other embodiments and comparative examples.

(Operation and effect of each embodiment)
Next, the operation and effect of each of the above embodiments will be described in comparison with a comparative example.
In order to confirm the action and curing of the diffractive optical element of each embodiment, a comparative example to which the configuration of the present invention was not applied was prepared.
FIG. 9 is a cross-sectional view showing the diffractive optical element of the comparative example as in FIG.
The diffractive optical element 50 of the comparative example does not include the inclined portion included in the diffractive optical element of each embodiment, and is configured as a substantially complete rectangular shape. Note that the diffractive optical element 50 of the comparative example, like the diffractive optical element of each embodiment, is a light that specifically spreads to ± 50 degrees and a width of ± 3.3 degrees with respect to an infrared laser having a wavelength of 980 nm. It is designed to spread light in a cross shape with two tolerance bands.

FIG. 10 is a diagram showing the status of evaluation.
Diffraction optical elements 10 of the first embodiment to diffractive optical element 30 of the third embodiment and the diffractive optical element 50 of the comparative example are diffracted in a situation as shown in FIG. The shape of the light and the reflected light were confirmed.
As the screen S, commercially available copy paper was used.
Infrared cameras CAM1 and CAM2 used Radiant Zemax's Prometric capable of detecting a wavelength of 980 nm. Infrared cameras CAM1 and CAM2 were measured with a visible light cut filter attached to prevent noise.
The light source L was set so as to irradiate an infrared laser having a wavelength of 980 nm to the DOE (diffractive optical element 10 to the diffractive optical element 30 of the third embodiment and the diffractive optical element 50 of the comparative example) with an inclination of 1 degree. In addition, the light irradiation apparatus is comprised by arrange | positioning any one of the said diffractive optical elements 10-30 in the position through which the light emitted from the light source L and the light source L passes.
Under these conditions, the light reflected on the surface of the diffractive optical element (DOE) and the light projected on the screen S were observed with the infrared cameras CAM1 and CAM2, respectively, and compared.
Further, the variation of the screen projection shape when the incident angle of the infrared laser was varied by 1 ± 1 degree was also confirmed. The results are shown in Table 1.

Looking at the results in Table 1, it can be seen that the projection shape by one-time incidence has the same result as that of the comparative example even if the inclined portion is provided as in the first to third embodiments. Recognize.
Next, regarding the weakness of the DOE reflected light due to the one-time incidence shown in Table 1, the first to third embodiments are better than the comparative example, that is, the reflected light is weak. It has been. This result will be described.
FIG. 11 is a diagram for explaining the reason why the diffractive optical element of the present invention has less reflected light than the diffractive optical element of the comparative example.
In FIG. 11, the change in the apparent refractive index is also shown as a graph in accordance with the position of the cross-sectional shape. FIG. 11A shows the case of the diffractive optical element 50 of the comparative example, and FIG. 11B shows the case of the diffractive optical element 10 of the first embodiment.

  In the diffractive optical element 50 of the comparative example, since the change in shape becomes abrupt, the apparent refractive index also changes abruptly, whereas in the diffractive optical element 10 of the first embodiment, an inclined portion is provided. Therefore, the change in shape is not abrupt, and the change in the apparent refractive index is also a gradual change. Since reflection occurs at the interface where the refractive index is changed, in the diffractive optical element 10 of the first embodiment, the change in the apparent refractive index is moderate, so that reflection at the interface is suppressed. It is. This phenomenon is the same in the diffractive optical element 20 of the second embodiment and the diffractive optical element 30 of the third embodiment. However, as can be seen from the results in Table 1, the diffractive optical element 10 of the first embodiment has the highest suppression effect of reflected light. This is because the diffractive optical element 10 of the first embodiment has more inclined portions than the diffractive optical element 30 of the third embodiment. Further, in the diffractive optical element 20 of the second embodiment and the diffractive optical element 10 of the first embodiment, both are in a reverse plate shape relationship (inverted symmetrical shape), and therefore the number of inclined portions is the same. However, in the diffractive optical element 10 of the first embodiment, the bottom portion 12a of the concave portion 12 protrudes in the direction in which the convex portion 11a protrudes. This is because it is advantageous to obtain the bottom portion 12a.

Next, regarding the small change in the projection shape due to the incident angle fluctuation in Table 1, the results of the first to third embodiments are better than the comparative example, that is, the reflected light is weak. Has been obtained. This result will be described.
FIG. 12 is a diagram schematically showing a relationship between a change in incident angle and diffracted light.
FIG. 12A shows a diffraction state of light when light from the vertical direction as the design position is incident on the diffractive optical element 50 of the comparative example. Light incident perpendicularly to the diffractive optical element 50 is diffracted equally to the left and right as primary light.
FIG. 12B shows a light diffraction state when light enters the diffractive optical element 50 of the comparative example from a position shifted from the design position. When light is incident on the diffractive optical element 50 from an oblique direction, the uniformity of the light is lost as shown in FIG. Since the optical design of the diffractive optical element is usually based on a simple shape as shown in FIG. 12A, if the incident state of light changes, the diffractive state of the light as a whole of the diffractive optical element. Will change.
FIG. 12C shows a light diffraction state when light from the vertical direction as the design position is incident on the diffractive optical element 10 of the first embodiment. Even in the diffractive optical element 10 in which the inclined portion is provided in a part of the cross-sectional shape, the vertically incident light is diffracted equally to the left and right as primary light.
FIG. 12D shows a light diffraction state when light is incident on the diffractive optical element 10 of the first embodiment from a position shifted from the design position. In the diffractive optical element 10 in which the inclined part is provided in a part of the cross-sectional shape, even if the incident direction of the light slightly varies, a part of the surface perpendicular to the light always exists, and the distribution of the diffracted light Hard to influence. Therefore, as shown in Table 1, the result that the change in the projected shape is small is obtained.
Note that the diffractive optical element 30 of the third embodiment has obtained better results than the diffractive optical element 50 of the comparative example with respect to the small change in the projection shape due to the incident angle variation, but from the other embodiments. Even bad results have been obtained. This is because the diffractive optical element 30 of the third embodiment includes the vertical portion 31h, and thus there are many parts that are affected by the incident angle.

As described above, according to the diffractive optical elements 10, 20, and 30 of the first to third embodiments, since the convex portion is provided with the inclined portion, the light reflected at the interface can be reduced. It is possible to increase the light use efficiency.
Further, according to the diffractive optical elements 10, 20, and 30 of the first to third embodiments, since the convex portion is provided with the inclined portion, the incident angle is affected by the assembly accuracy of the apparatus and the performance fluctuation of the light source. Even if it changes, it is difficult to be affected, and the desired diffracted light can be stably obtained with little influence on the diffracted light.

(Deformation)
The present invention is not limited to the embodiment described above, and various modifications and changes are possible, and these are also within the scope of the present invention.

(1) In the first embodiment and the second embodiment, the width of the constricted portion in the portion where the second inclined portion and the third inclined portion are connected is substantially the same as or slightly narrower than the tip portion. did. For example, the width of the constricted portion in the portion where the second inclined portion and the third inclined portion are connected may be wider than the width of the tip portion of the convex portion.

(2) In each embodiment, the diffractive optical element is shown as a simple form composed of only a high refractive index portion. For example, a transparent substrate for forming the high refractive index portion may be provided, or a coating layer for covering the diffraction layer may be provided.
FIG. 14 is a diagram showing an example in which a transparent substrate is provided and an example in which a coating layer is provided as a modification of the diffractive optical element.
In FIG. 14A, the diffractive optical element 10 shown in the first embodiment is formed on a transparent substrate 41, and this whole is configured as a diffractive optical element. Thus, by providing the transparent base material 41, the manufacturing method using resin molding can be used, and manufacture can be performed easily.
In FIG. 14B, in addition to the configuration of FIG. 14A, the coating layer 42 is laminated as it is, and the whole is configured as a diffractive optical element. By adopting such a form, the convex shape can be protected by providing the covering layer 42.
In FIG. 14C, in addition to the form of FIG. 14A, the covering layer 43 is formed of a transparent resin that penetrates into the recesses, and the whole is configured as a diffractive optical element. In this case, the transparent resin forming the covering layer 43 is a resin having a lower refractive index than that of the high refractive index portion in order to obtain a low refractive index portion. By setting it as such a form, a convex shape can be protected more effectively.

(3) In each embodiment, the diffractive optical element has been described with an example designed to diffract an infrared laser having a wavelength of 980 nm. For example, the diffractive optical element may be one that diffracts infrared light having a wavelength of 780 nm or more, or is not limited to infrared light, but may diffract light having any wavelength such as visible light. The present invention may be applied.

(4) In each embodiment, the light irradiation device has been described with an example in which the light source emits an infrared laser having a wavelength of 980 nm. For example, the light source may emit infrared light having a wavelength of 780 nm or more, and the light irradiation device may be a light source that emits light of any wavelength such as visible light as well as infrared light. You may apply to.

  In addition, although 1st Embodiment-3rd Embodiment and modification can also be used in combination suitably, detailed description is abbreviate | omitted. Further, the present invention is not limited by the embodiments described above.

DESCRIPTION OF SYMBOLS 10 Diffractive optical element 11 High refractive index part 11a Convex part 11b 1st inclination part 11c 2nd inclination part 11d 3rd inclination part 11e Tip part 11f Root part 12 Recess 12a Bottom part 13 Space 14 Low refractive index part 15 Diffraction Layer 20 Diffractive optical element 21 High refractive index portion 21a Convex portion 21b First inclined portion 21c Second inclined portion 21d Third inclined portion 21e Tip portion 21f Root portion 21g Vertex 25 Diffraction layer 30 Diffractive optical element 31 High refractive index Part 31a convex part 31b first inclined part 31e tip part 31f root part 31h vertical part 35 diffraction layer 41 transparent substrate 42 covering layer 43 covering layer 50 diffractive optical element 200 screen 201 light 202 irradiation area 204 irradiation area CAM1 infrared camera CAM2 Infrared camera L Light source P Plane S Screen

Claims (14)

A diffractive optical element for shaping light,
A high refractive index portion in which a plurality of convex portions are arranged side by side in a cross-sectional shape;
A refractive index lower than that of the high refractive index portion, and including a concave portion formed at least between the convex portions; and
Comprising a diffractive layer having
A side surface shape of the convex part is a diffractive optical element provided with at least a part of an inclined part inclined with respect to a plane including the diffraction layer. The diffractive optical element according to claim 1,
The side surface shape of the convex portion includes a first inclined portion that is inclined in a direction in which the width of the convex portion widens from the tip end portion to the root portion of the convex portion,
A diffractive optical element characterized by the above. The diffractive optical element according to claim 2,
A vertical portion extending from the first inclined portion toward the root portion in a direction perpendicular to the diffraction layer;
A diffractive optical element characterized by the above. The diffractive optical element according to claim 2,
A second inclined portion inclined in a direction in which the width of the convex portion becomes narrower from the first inclined portion toward the root portion;
A third inclined portion inclined in a direction in which the width of the convex portion is further expanded from the second inclined portion toward the root portion;
Providing
A diffractive optical element characterized by the above. The diffractive optical element according to claim 4,
The width of the constricted portion where the second inclined portion and the third inclined portion are connected is wider than the width of the tip portion of the convex portion;
A diffractive optical element characterized by the above. The diffractive optical element according to any one of claims 1 to 5,
The tip of the convex part has a plurality of vertices;
A diffractive optical element characterized by the above. In the diffractive optical element according to any one of claims 1 to 6,
The bottom portion of the recess protrudes in the direction in which the protrusion protrudes;
A diffractive optical element characterized by the above. The diffractive optical element according to any one of claims 1 to 7,
The high refractive index part is obtained by curing an ionizing radiation curable resin composition;
A diffractive optical element characterized by the above. The diffractive optical element according to any one of claims 1 to 8,
The low refractive index portion is air;
A diffractive optical element characterized by the above. The diffractive optical element according to any one of claims 1 to 9,
A transparent base material, the diffraction layer, and a coating layer covering the diffraction layer are laminated in this order;
A diffractive optical element characterized by the above. The diffractive optical element according to any one of claims 1 to 10,
The diffraction layer diffracts infrared rays having a wavelength of 780 nm or more;
A diffractive optical element characterized by the above. The diffractive optical element according to claim 11,
The height of the convex portion is 650 nm or more;
A diffractive optical element characterized by the above. A light source;
The diffractive optical element according to any one of claims 1 to 12, wherein at least one of the diffractive optical elements is disposed at a position through which light emitted from the light source passes.
A light irradiation apparatus comprising: In the light irradiation apparatus of Claim 13,
The light source can emit infrared light having a wavelength of 780 nm or more;
The light irradiation apparatus characterized by this.

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