JP6946632B2 - Diffractive optical element, set member of diffractive optical element and holder, light irradiation device - Google Patents

Description

The present invention relates to a diffractive optical element, a holder, and a light irradiation device.

In recent years, there has been an increase in the need for sensor systems, such as the need for personal authentication to avoid security risks due to the spread of networks, the trend toward autonomous driving of automobiles, and the spread of the so-called "Internet of Things". There is. There are various types of sensors, and the information to be detected is also various. One of the means is to irradiate an object with light from a light source and obtain information from the reflected light. .. For example, a pattern authentication sensor, an infrared radar, and the like are examples.

As the light source of these sensors, one having a wavelength distribution, brightness, and spread according to the application is used. Visible light to infrared rays are often used as the wavelength of light, and infrared rays are widely used because they are not easily affected by external light, are invisible, and can observe the inside of an object. There is. Further, as a type of light source, an LED light source, a laser light source, or the like is often used. For example, a laser light source having a small spread of light is preferably used to detect a distant place, and an LED light source is preferably used to detect a relatively close place or to irradiate a region having a certain spread. Be done.

By the way, the size and shape of the target irradiation area do not always match the spread (profile) of the light from the light source, and 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 diffuser called Light Shipping Diffuser (LSD), which can shape the shape of light to some extent, has been developed.
Further, as another means for shaping light, a diffractive optical element (DOE) can be mentioned. This is an application of the diffraction phenomenon when light passes through a place where materials with different refractive indexes are arranged with periodicity. The DOE is basically designed for light of a single wavelength, but in theory, it is possible to shape the light into almost any shape. Further, in the above-mentioned LSD, the light intensity in the irradiation region has a Gaussian distribution, whereas in DOE, it is possible to control the uniformity of the light distribution in the irradiation region. Such characteristics of DOE are advantageous in terms of high efficiency by suppressing irradiation of unnecessary regions and miniaturization of the device by reducing the number of light sources (see, for example, Patent Document 1).
Further, DOE can be applied to both a parallel light source such as a laser and a diffused light source such as an LED, and can be applied to a wide range of wavelengths from ultraviolet light to visible light and infrared light. ..

DOE requires microfabrication on the order of nm, and particularly in order to diffract light having a long wavelength, it is necessary to form a fine shape having a high aspect ratio. Therefore, electron beam lithography technology using an electron beam has been conventionally used for manufacturing 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, and resist development, dry etching of the hard mask, and drying of quartz are performed. A desired DOE can be obtained by sequentially performing etching to form a pattern on the surface of the quartz plate and then removing the hard mask.

In DOE, the light emission efficiency is improved by a multi-step shape having a plurality of steps having different heights.
However, not only the improvement of the light emission efficiency by the improvement of the multi-step shape but also the further improvement of the efficiency is desired.

Japanese Unexamined Patent Publication No. 2015-170320

An object of the present invention is to provide a diffractive optical element, a holder, and a light irradiation device capable of further improving the efficiency of light utilization and suppressing unnecessary light emission.

The present invention solves the above problems by the following solutions. In addition, in order to facilitate understanding, the description will be given with reference numerals corresponding to the embodiments of the present invention, but the present invention is not limited thereto.

The first invention is a diffractive optical element (10) that shapes light, and at least in a state of use that shapes light, at least a part of the element surface forms an angle with respect to the element surface of another portion. A diffractive optical element (10) that is configured or has at least a part of the element surface held at an angle with respect to the element surface of another portion, and is the diffractive optical element (10). ) Is configured along a plane as a whole, and is configured at an angle with respect to the first region (10A) configured parallel to the plane and the first region (10A). A second region (10B) that is held or held at an angle to the first region (10A), and a normal in the first region (10A). The angle β formed by the first normal (N1) and the second normal (N2), which is the normal in the second region (10B), is 20 ° or more and 40 ° or less. It is a diffractive optical element (10) as a feature.

The second invention is the diffractive optical element (10) according to the first invention, wherein at least a part of the element surface is formed on a curved surface.

The third invention is characterized in that, in the diffractive optical element (10) according to the first invention or the second invention, at least a part of the element surface is formed by combining a plurality of planes. This is a diffractive optical element (10).

The fourth invention is a holder for holding the diffractive optical element (10) according to any one of the first to third inventions, and is the surface of the element surface of the diffractive optical element (10). It is a holder that holds at least a part of the element surface at an angle with respect to the surface of the element at another part.

A fifth aspect of the present invention is a third aspect of the invention, wherein the light source unit (210) is arranged at a position where the light from the light source unit (210) is incident, and the light from the light source unit (210) is formed. A light irradiation device including the diffractive optical element (10) according to any one of the items up to the present invention.

A sixth aspect of the present invention is the light irradiation device according to the fifth aspect, wherein the light source unit (210) irradiates parallel light parallel to the first normal line (N1). It is a light irradiation device.

According to the present invention, it is possible to provide a diffractive optical element, a holder, and a light irradiation device capable of further improving the efficiency of light utilization and suppressing unnecessary light emission.

It is a top view which shows the embodiment of the diffraction optical element by this invention. It is a perspective view which shows an example of the partial periodic structure in the example of the diffraction optical element of FIG. It is sectional drawing which cut | cut the diffractive optical element at the position of the arrow GG'in FIG. It is a figure explaining the diffraction optical element. It is sectional drawing which shows typically the relationship between the diffraction optical element 10 and the light source 201 by this invention. It is a figure explaining the incident angle and the diffraction angle. It is the figure which summarized the result of the simulation analysis. It is the figure which summarized the simulation analysis result about Tin = 0 °. It is a figure explaining the relationship of the angle in the 1st region 10A and the 2nd region 10B.

Hereinafter, the best mode for carrying out the present invention will be described with reference to drawings and the like.

(Embodiment)
FIG. 1 is a plan view showing an 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 the position of the arrow GG'in FIG.
FIG. 4 is a diagram illustrating a diffractive optical element.
In addition, each figure shown below including FIG. 1 is a diagram schematically shown, and the size and shape of each part are exaggerated as appropriate for easy understanding.
Further, in the following description, specific numerical values, shapes, materials and the like will be described, but these can be changed as appropriate.

Note that the terms used in the present invention that specify the shape and geometric conditions and their degrees, such as terms such as "parallel", "orthogonal", and "same", and length and angle values, are used. Without being bound by the strict meaning, we will interpret it including the range where similar functions can be expected.

Further, in the present invention, "shaping the light" means that the shape of the light projected on the object or the target area (irradiation area) becomes an arbitrary shape by controlling the traveling direction of the light. To say. For example, as shown in the example of FIG. 4, a light source unit 210 that emits light 201 (FIG. 4B) whose irradiation region 202 becomes circular when directly projected onto a flat screen 200 is prepared. By transmitting the light 201 through the diffractive optical element 10 of the present invention, the irradiation region 204 can be made into a desired shape such as a square (FIG. 4 (a)), a rectangle, or a circle (not shown). It is called "shaping the light".
By combining the light source unit 210 and the diffractive optical element 10 of the present embodiment, which is arranged at least one at a position where the light emitted by the light source unit 210 passes, light that can be irradiated in a molded state. It can be an irradiation device.
Further, in the present invention, the term "transparent" means a substance that transmits light of at least the wavelength to be used. For example, even if it does not transmit visible light, if it transmits infrared rays, it shall be treated as transparent when used for infrared applications.

The diffractive optical element 10 of the present embodiment is a diffractive optical element (DOE) that shapes light. The diffractive optical element 10 has a cross-shaped shape with respect to light from a light source unit 210 that emits light having a wavelength of, for example, 500 nm, specifically, light that spreads at ± 50 degrees and a width of ± 3.3 degrees. It is designed to spread the light in the shape of two bands.
The diffractive optical element 10 of the present embodiment has a different depth at each position of A, B, C, and D shown in FIG. That is, the diffractive optical element 10 is configured by a multi-step shape having four steps of different heights. The diffractive optical element 10 usually has a plurality of regions having different periodic structures (partial periodic structure: for example, E and F regions in FIG. 1). 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 by, for example, _{processing the shape of quartz (SiO 2} , synthetic quartz) by etching. Further, the high-refractive index portion 11 may be formed by molding from a processed product of quartz to prepare a molding mold, and the ionizing radiation curable resin composition may be cured by using this molding mold. Various methods are known for producing a product having such a periodic structure using an ionizing radiation curable resin composition, and the high refractive index portion 11 of the diffractive optical element 10 utilizes these known methods. Can be appropriately produced.

Further, air is present in the upper portion of FIG. 3 including the concave portion 12 formed between the convex portions 11a and the space 13 near the top of the convex portion 11a, and the refractive index is higher than that of the high refractive index portion 11. Is a low refractive index portion 14. A diffraction layer 15 having an action of shaping light is formed by a periodic structure in which these high refractive index portions 11 and low refractive index portions 14 are arranged alternately.

The convex portion 11a has a multi-step shape having four stepped portions having different heights on one side (left side in FIG. 3) of the side surface shape. Specifically, the convex portion 11a is from the most protruding level 1 step portion 11a-1, the level 2 step portion 11a-2 which is one step lower than the level 1 step portion 11a-1, and the level 2 step portion 11a-2. Also has a level 3 step portion 11a-3 which is one step lower and a level 4 step portion 11a-4 which is one step lower than the level 3 step portion 11a-3 on one side surface side. Further, the other side (right side in FIG. 3) of the side surface shape of the convex portion 11a is a side wall portion 11b that connects the level 1 step portion 11a-1 to the level 4 step portion 11a-4 in a straight line.

FIG. 5 is a cross-sectional view schematically showing the relationship between the diffractive optical element 10 and the light source 201 according to the present invention.
The diffractive optical element 10 of the present embodiment can be expressed as a plane when viewed microscopically as shown in FIG. 2, but as a whole, a specific region is another region as shown in FIG. It is formed so as to be inclined with respect to. That is, the first region 10A formed on a plane parallel to the sheet surface of the diffractive optical element 10 as a whole and the second region 10A formed at an angle with respect to the first region 10A. It includes a region 10B.
In FIG. 5, the convex portion 11 is shown large in order to show the configuration in an easy-to-understand manner, but in reality, it does not look so large.
The diffractive optical element 10 of the present embodiment has a region inclined in the X direction in two orthogonal directions in the sheet surface, for example, the X direction and the Y direction in FIG. 2, but is along the Y direction. In terms of direction, it does not have a sloping area. That is, the diffractive optical element 10 includes a region inclined only in one direction.
Further, the light source unit 210 of the light irradiation device of the present embodiment is a line light source or a surface light source that irradiates parallel light parallel to the normal (first normal) in the first region 10A.

The diffractive optical element 10 of the present embodiment constitutes the above-mentioned inclined second region 10B in a free state in which no force is applied to the diffractive optical element 10. In order to manufacture the diffractive optical element 10 having such an inclined surface, for example, in the manufacturing process of the diffractive optical element 10, the diffractive optical element 10 is pressed against a mold in a heated state, and then cooled and then cooled in FIG. It is preferable to use a so-called hot press (also referred to as a hot press or a hot stamp) that enables the maintenance of such a shape.

Alternatively, a holder may be used to constrain the shape of the diffractive optical element 10 to form the second region 10B. When a holder is used, the diffractive optical element 10 may be formed in a flat sheet shape as a whole in a free state in which no force is applied.

Next, the reason why the second region 10B is provided in the diffractive optical element 10 and how much the second region 10B should be tilted will be described.
First, a simulation analysis was performed in order to clarify how the angle of incidence of the light incident on the diffraction optical element 10 affects the diffraction efficiency.

FIG. 6 is a diagram illustrating an incident angle and a diffraction angle.
In the simulation analysis, conditions with different incident angles were set by arranging the diffractive optical elements 10 at an angle. When the angle of incidence Tin on the diffractive optical element 10 and the angle of exit Tout are set in the orientation shown in FIG. 9A, the diffractive angle Td at which the diffractive optical element 10 diffracts light is expressed as Td = Tin-Tout. Can be done. For example, FIGS. 6 (b) to 6 (d) show the cases where the diffraction angles Td = 10 °, but Tin = 0 °, 10 °, and 20 °, respectively. In FIGS. 6 (b), 6 (c), and 6 (d), the tilt angles of the diffractive optical element 10 are assumed to be 0 °, 10 °, and 20 ° with respect to the incident light, respectively. Can be done. Simulation analysis was performed using such a model.

As a variation parameter of the simulation analysis, Tin was changed from 0 ° to 60 ° in 10 ° increments. Further, the diffraction angle Td was changed from 5 ° to 60 ° in 5 ° increments. A simulation analysis was performed on the combination of these Tin and Td.
Diffraction efficiency analysis simulation used operations based on rigorous coupled-wave analysis (RCWA). RCWA is mathematically reduced to solving matrix eigenvalue problems and linear equations. Therefore, there is no difficulty in principle. Further, the simulation result of the electromagnetic field analysis based on this RCWA and the reality basically match except for the shape error in the actual product.

The simulation was performed under the following conditions.
Wavelength λ: 500 nm
Refractive index n: 1.5 in the high refractive index section
Refractive index of low refractive index part: 1.0
Multi-level number P: 4
Step per multi-step: 250 nm

The result of the simulation under the above conditions will be described.
FIG. 7 is a diagram summarizing the results of simulation analysis.
The simulated light emission value shown in FIG. 7 shows the light emission value in each direction when the input light is 1.
0th and 1st in FIG. 7 indicate 0th-order diffracted light and 1st-order diffracted light, respectively. In the usual usage, it is desirable that the first-order refracted light is large, and it is desirable that the zero-order diffracted light is small.

FIG. 8 is a diagram summarizing the simulation analysis results for Tin = 0 °.
Looking at FIGS. 7 and 8, when Tin = 0 °, the first-order refracted light (1th) is a very low value (0.319621) at Td = 35 °. Therefore, in a conventional flat diffractive optical element, when parallel light rays are incident on the diffractive optical element and emitted in various directions, the direction is approximately 35 ° with respect to the normal to the sheet surface of the diffractive optical element. The amount of light is extremely reduced only by the light emitted to.

Therefore, the diffractive optical element 10 of the present embodiment is provided with a second region 10B in addition to the first region 10A configured on the same plane as the conventional one. In the first region 10A, a concavo-convex shape having a different refraction angle other than Td = 35 °, which reduces the efficiency of the first refraction light (1th), is formed. The second region 10B is tilted with respect to the first region 10A so that Tin = 20 ° or more and Tin = 40 ° or less, which have relatively good diffraction efficiency, even when Td = 35 °. It is composed of.

FIG. 9 is a diagram illustrating the relationship between the angles in the first region 10A and the second region 10B.
In the diffractive optical element 10 of the present embodiment, the angle β formed by the first normal line N1 which is the normal line in the first region 10A and the second normal line N2 which is the normal line in the second region 10B is set. It is arranged so that it is 20 ° or more and 40 ° or less.
With such an arrangement, the light incident on the second region 10B from the light source unit 210 has Tin = 20 ° or more and Tin = 40 ° or less as described above. Therefore, even if the diffraction angle Td of the second region 10B is set to be around 35 °, the decrease in diffraction efficiency can be suppressed.

As described above, according to the present embodiment, the second region 10B is arranged at an angle with respect to the first region 10A. More specifically, the angle β formed by the first normal N1 which is the normal in the first region 10A and the second normal N2 which is the normal in the second region 10B is 20 ° or more and 40. It was set to ° or less. With such a configuration, the diffractive optical element 10 can be configured to avoid a configuration in which the incident angle is such that the diffraction efficiency is lowered, and the diffractive optical element 10 and the light irradiation device can be made more efficient. Can be done.

(Transformed form)
Not limited to the embodiments described above, various modifications and changes are possible, and these are also within the scope of the present invention.

(1) In the embodiment, the diffractive optical element has been described with reference to an example in which at least a part of the element surface is formed at an angle with respect to the element surface of another portion without using a holder. .. Not limited to this, for example, the diffractive optical element may be held so that at least a part of the element surface is held at an angle with respect to the element surface of another portion.

(2) In the embodiment, the diffractive optical element has been described with reference to an example in which a plurality of planes are combined. Not limited to this, for example, the diffractive optical element may be configured by combining a straight line and a curved line.

(3) In the embodiment, the diffractive optical element is shown as a simple form composed of only a high refractive index portion. Not limited to this, for example, a transparent base material for forming the high refractive index portion may be provided, the low refractive index portion 14 may be made of resin, or a coating layer for covering the diffraction layer may be provided. May be good.

(4) In the embodiment, the diffractive optical element has been described with reference to an example in which the diffractive optical element is designed to diffract light having a wavelength of 500 nm. Not limited to this, for example, the diffractive optical element may diffract infrared rays having a wavelength of 780 nm or more, and may diffract light of any wavelength such as visible light as well as infrared light. The present invention may be applied.

(5) In each embodiment, the light irradiation device has been described with reference to an example in which the light irradiation device is designed to diffract light having a wavelength of 500 nm. Not limited to this, for example, the light source unit may emit infrared light having a wavelength of 780 nm or more, and the light source unit that emits light of any wavelength, such as visible light, is not limited to infrared light. It may be applied to an irradiation device.

The embodiments and modifications can be used in combination as appropriate, but detailed description thereof will be omitted. Moreover, the present invention is not limited to each of the embodiments described above.

10 Diffractive optical element 10A 1st region 10B 2nd region 11 High refractive index portion 11a Convex portion 11a-1 Level 1 stage portion 11a-2 Level 2 stage portion 11a-3 Level 3 stage portion 11a-4 Level 4 stage portion 11b Side wall 12 Recess 13 Space 14 Low refractive index 15 Diffractive layer 100 Diffractive optical element 200 Screen 201 Light 202 Irradiation area 204 Irradiation area 210 Light source

Claims (6)

A diffractive optical element that shapes light
At least in the state of use that shapes the light
At least a part of the element surface is formed at an angle with respect to the element surface of another part.
Or
A diffractive optical element in which at least a part of the element surface is held at an angle with respect to the element surface of another part.
A first region having a periodic structure and being configured in a plane shape, and emitting light incident from the incident side as diffracted light from the emitting side on the opposite side, and
It has a periodic structure and is formed in a plane shape and is formed at an angle with respect to the first region, or has a periodic structure and is formed in a plane shape and is formed in a plane shape with respect to the first region. A second region that is held at an angle and emits light incident from the incident side as diffracted light from the opposite emitting side,
With
The diffractive optical element is formed in the form of a flat sheet as a whole in a free state in which no force is applied.
The second region is adjacent to the first region and is connected by a single member.
The angle β formed by the first normal, which is the normal in the first region, and the second normal, which is the normal in the second region, is 20 ° or more and 40 ° or less.
A diffractive optical element characterized by. In the diffractive optical element according to claim 1,
At least a part of the element surface is curved.
A diffractive optical element characterized by. In the diffractive optical element according to claim 1 or 2.
At least a part of the element surface shall be composed of a combination of multiple planes.
A diffractive optical element characterized by. The diffractive optical element according to any one of claims 1 to 3 ,
A holder for holding the diffractive optical element and
It is a set member of a diffractive optical element and a holder including the above.
The holder is a set member of the diffractive optical element and the holder that holds at least a part of the element surface of the diffractive optical element at an angle with respect to the element surface of another portion. Light source and
The diffractive optical element according to any one of claims 1 to 3, which is arranged at a position where the light from the light source unit is incident and forms the light from the light source unit.
A light irradiation device including. The light irradiation device according to claim 5.
The light source unit irradiates parallel light parallel to the first normal.
A light irradiation device characterized by.

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