JP2018072386A - Diffraction optical element, holding jig, and light irradiation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffraction optical element, a holding jig and a light irradiation device with which it is possible to further heighten the efficiency of light utilization and suppress unwanted light emission.SOLUTION: A diffraction light element 10 is constructed so that, in at least a state of use of shaping light, at least a portion of the element surface is formed at an angle to the element surface of an other region. The diffraction optical element 10 is constructed along a plane as a whole, and provided with a first area 10A constructed in parallel to this plane and a second area 10B constructed at an angle to the first area 10A, an angle β formed by a first normal N1 that is a normal in the first area 10A and a second normal N2 that is a normal in the second area 10B being 20° to 40° inclusive.SELECTED DRAWING: Figure 9

Description

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

  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, and 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 the 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 the 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 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 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.

In DOE, light output efficiency is increased by a multi-stage shape including a plurality of step portions having different heights.
However, not only the improvement of the light emission efficiency by improvement of a multistage shape but the further improvement in efficiency is desired.

JP-A-2015-170320

  An object of the present invention is to provide a diffractive optical element, a holder, and a light irradiation device that can further improve the light use efficiency or suppress unnecessary light emission.

  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 (10) for shaping light, wherein at least a part of the element surface forms an angle with respect to the element surface of another part at least in a use state for shaping light. A diffractive optical element (10) configured or held in a state where at least a part of the element surface is angled with respect to the element surface of another part, and the diffractive optical element (10 ) Is configured along a plane as a whole, and is formed at an angle with respect to the first region (10A) configured in parallel to the plane and the first region (10A). Or a second region (10B) held at an angle with respect to the first region (10A), and a normal line in the first region (10A) The first normal (N1) and the second region (10B) It is normal at the angle β between the second normal (N2), a diffractive optical element characterized, that at 20 ° to 40 ° (10).

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

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

  A fourth invention is a holder for holding the diffractive optical element (10) according to any one of the first to third inventions, wherein the diffractive optical element (10) has an element surface. It is a holder for holding at least a part so as to form an angle with respect to the element surface of another part.

  5th invention is arrange | positioned in the position into which the light from a light source part (210) and the said light source part (210) injects, The 1st invention to 3rd which shape | mold the light from the said light source part (210) It is a light irradiation apparatus provided with the diffractive optical element (10) of any one of the above to invention.

  6th invention is a light irradiation apparatus as described in 5th invention, Comprising: The said light source part (210) irradiates the parallel light parallel to the said 1st normal line (N1), It is characterized by the above-mentioned. This 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 that can further improve the light utilization efficiency or suppress unnecessary light emission.

It is a top view which shows embodiment of the diffractive optical element by this 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 G-G ′ in FIG. 2. It is a figure explaining a diffractive optical element. 2 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. FIG. It is a figure explaining an incident angle and a diffraction angle. It is the figure which put together the result of simulation analysis. It is the figure which put together the simulation analysis result about Tin = 0 degree. It is a figure explaining the relationship of the angle in 1st area | region 10A and 2nd area | region 10B.

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

(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 a position indicated by an arrow GG ′ in FIG.
FIG. 4 is a diagram illustrating a diffractive optical element.
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 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. 4, a light source unit 210 is prepared that emits light 201 (FIG. 4B) 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 is formed into a target shape such as a square (FIG. 4A), a rectangle, a circle (not shown), “Shaping light”.
The light that can be irradiated in a molded state by combining the light source unit 210 and the diffractive optical element 10 of the present embodiment, which is disposed at a position where at least one light emitted from the light source unit 210 passes. It can be set as an irradiation apparatus.
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 this embodiment is a diffractive optical element (DOE) that shapes light. The diffractive optical element 10 has, for example, a cross shape with respect to the light from the light source unit 210 that emits light having a wavelength of 500 nm, specifically, for example, light having a width of ± 50 degrees and a width of ± 3.3 degrees. The band is designed to spread the light into a shape with a tolerance of two.
The diffractive optical element 10 of the present embodiment has different depths at positions A, B, C, and D shown in FIG. That is, the diffractive optical element 10 has a multi-stage shape with four levels of height. The diffractive optical element 10 usually has a plurality of regions having different periodic structures (partial periodic structures: 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, for example, by processing the shape of quartz (SiO ₂ , synthetic quartz) by etching. Alternatively, the high refractive index portion 11 may be obtained by forming a mold from a quartz processed product and curing the ionizing radiation curable resin composition using the mold. Various methods for producing such a periodic structure using an ionizing radiation curable resin composition are known, and the high refractive index portion 11 of the diffractive optical element 10 uses these known methods. And can be appropriately manufactured.

  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.

  The convex portion 11a has a multi-stage shape including four step portions having different heights on one side (left side in FIG. 3) of the side surface shape. Specifically, the convex portion 11a includes the most protruding level 1 step portion 11a-1, the level 2 step portion 11a-2 that is one step lower than the level 1 step portion 11a-1, and the level 2 step portion 11a-2. Furthermore, it has a level 3 step portion 11a-3 that is one step lower and a level 4 step portion 11a-4 that is one step lower than the level 3 step portion 11a-3 on one side surface side. Moreover, 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 is connected in a straight line from the level 1 step portion 11a-1 to the level 4 step portion 11a-4.

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 in a planar shape when viewed microscopically as shown in FIG. 2 above, but when viewed as a whole, a specific region is another region as shown in FIG. It is formed to be inclined with respect to. That is, the first region 10A configured in a plane parallel to the sheet surface as a whole of the diffractive optical element 10 and the second region configured to form an angle with respect to the first region 10A. And a region 10B.
In FIG. 5, the convex portion 11 is shown large for easy understanding of the configuration, but actually, it does not look so large.
The diffractive optical element 10 of the present embodiment includes a region that is inclined with respect to the X direction in two orthogonal directions within the sheet surface, for example, the X direction and the Y direction in FIG. The direction is not provided with an inclined area. That is, the diffractive optical element 10 has a region that is inclined only in one direction.
In addition, the light source unit 210 of the light irradiation apparatus according to the present embodiment is a line light source or a surface light source that irradiates parallel light parallel to a normal line (first normal line) in the first region 10A.

  The diffractive optical element 10 of the present embodiment constitutes the above-described inclined second region 10B in a free state where 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. It is preferable to use a so-called hot press (also referred to as hot press or hot stamp) that can maintain the shape as described above.

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

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

FIG. 6 is a diagram for explaining the incident angle and the diffraction angle.
In the simulation analysis, conditions with different incident angles were set by arranging the diffractive optical element 10 at an angle. When the incident angle Tin to the diffractive optical element 10 and the outgoing angle Tout are set in the direction of FIG. 9A, the diffraction angle Td at which the diffractive optical element 10 diffracts light is expressed as Td = Tin−Tout. Can do. For example, FIGS. 6 (b) to 6 (d) show the cases where the diffraction angle Td = 10 °, but Tin = 0 °, 10 °, and 20 °, respectively. 6 (b), 6 (c), and 6 (d) grasp that the tilt angles of the diffractive optical element 10 are 0 °, 10 °, and 20 °, respectively, with respect to the incident light. Can do. Simulation analysis was performed using such a model.

As a variable parameter for simulation analysis, Tin was changed from 0 ° to 60 ° in increments of 10 °. Further, the diffraction angle Td was changed from 5 ° to 60 ° in steps of 5 °. A simulation analysis was performed on the combination of these Tin and Td.
The analysis based on the rigorous coupled wave theory (RCWA) was used for the simulation of the diffraction efficiency. Mathematically, the RCWA is reduced to solving the matrix eigenvalue problem and the linear equation. Therefore, there is no fundamental difficulty, and the simulation result of the electromagnetic field analysis based on the RCWA and the reality are basically matched except for the shape error in the actual product.

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

The result of the simulation performed under the above conditions will be described.
FIG. 7 summarizes the results of the simulation analysis.
The simulated light output value shown in FIG. 7 indicates the light output value in each direction when the input light is 1.
In FIG. 7, 0th and 1st indicate 0th-order diffracted light and 1st-order diffracted light, respectively. In a normal usage method, it is desirable that the first-order diffracted light is large, and it is desirable that the zero-order diffracted light is small.

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

  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 in the same plane as the conventional one. In the first region 10A, a concavo-convex shape is formed so as to have other diffraction angles except for Td = 35 ° at which the efficiency of the first-order diffracted light (1th) decreases. And even if Td = 35 °, the second region 10B is inclined with respect to the first region 10A so that the diffraction efficiency is relatively good Tin = 20 ° or more and Tin = 40 ° or less. Is configured.

FIG. 9 is a diagram for explaining the angle relationship between 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 that is the normal line in the first region 10A and the second normal line N2 that is the normal line in the second region 10B is It arrange | positions so that it may become 20 degrees or more and 40 degrees or less.
With such an arrangement, the light incident on the second region 10B from the light source unit 210 is Tin = 20 ° or more and Tin = 40 ° or less. Therefore, even if the diffraction angle Td of the second region 10B is set to be around 35 °, it is possible to suppress a decrease in diffraction efficiency.

  As described above, according to the present embodiment, the second region 10B is disposed to be inclined with respect to the first region 10A. More specifically, the angle β formed by the first normal line N1 that is the normal line in the first region 10A and the second normal line N2 that is the normal line in the second region 10B is set to 20 ° or more and 40 °. ° or less. By adopting such a configuration, the diffractive optical element 10 can be configured so as to avoid a configuration with an incident angle at which the diffraction efficiency is reduced, and the diffractive optical element 10 and the light irradiation device are more efficient. Can do.

(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 embodiment, the diffractive optical element has been described by giving 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 part without using a holder. . For example, the diffractive optical element may be held in a state in which at least a part of the element surface forms an angle with respect to the element surface of another part.

(2) In the embodiment, the diffractive optical element has been described with an example in which a plurality of planes are combined. 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 the high refractive index portion. 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 that covers the diffraction layer is provided. Also good.

(4) In the embodiment, the diffractive optical element has been described with an example designed to diffract light having a wavelength of 500 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.

(5) In each embodiment, the light irradiation device has been described with an example designed to diffract light having a wavelength of 500 nm. For example, the light source unit may emit infrared light having a wavelength of 780 nm or more. The light source unit emits light of any wavelength such as visible light as well as infrared light. You may apply to an irradiation apparatus.

  In addition, although embodiment and a deformation | transformation form can also be used in combination as appropriate, detailed description is abbreviate | omitted. Further, the present invention is not limited by the embodiments described above.

DESCRIPTION OF SYMBOLS 10 Diffractive optical element 10A 1st area | region 10B 2nd area | region 11 High refractive index part 11a Convex part 11a-1 Level 1 step part 11a-2 Level 2 step part 11a-3 Level 3 step part 11a-4 Level 4 step part 11b Side wall part 12 Concave part 13 Space 14 Low refractive index part 15 Diffraction layer 100 Diffraction optical element 200 Screen 201 Light 202 Irradiation area 204 Irradiation area 210 Light source part

Claims (6)

A diffractive optical element for shaping light,
At least in use condition to shape 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,
The diffractive optical element is configured along a plane as a whole, and a first region configured parallel to the plane;
A second region configured at an angle with respect to the first region or held at an angle with respect to the first region;
With
An angle β formed by a first normal line that is a normal line in the first region and a second normal line that is a normal line in the second region is 20 ° or more and 40 ° or less,
A diffractive optical element characterized by the above. The diffractive optical element according to claim 1,
That at least a part of the element surface is curved,
A diffractive optical element characterized by the above. The diffractive optical element according to claim 1 or 2,
At least a part of the element surface is configured by combining a plurality of planes;
A diffractive optical element characterized by the above. A holder for holding the diffractive optical element according to any one of claims 1 to 3,
A holder for holding the diffractive optical element so that at least a part of the element surface is at an angle with respect to the element surface of another part. A light source unit;
The diffractive optical element according to any one of claims 1 to 3, wherein the diffractive optical element is disposed at a position where light from the light source unit is incident, and shapes light from the light source unit.
A light irradiation apparatus comprising: It is a light irradiation apparatus of Claim 5, Comprising:
The light source unit emits parallel light parallel to the first normal line;
The light irradiation apparatus characterized by this.

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