JP5948949B2 - Diffractive optical element and measuring device - Google Patents

Description

  The present invention relates to a diffractive optical element and a measuring apparatus using the diffractive optical element.

  A diffractive optical element that diffracts at least part of incident light is used in various optical devices and optical devices. For example, an optical three-dimensional measurement apparatus irradiates a measurement object with a projection pattern of predetermined light, and acquires an image of the measurement object irradiated with the projection pattern of light. It is a device that performs. In such a three-dimensional measuring apparatus, the diffractive optical element is used for generating a predetermined light projection pattern.

  In a three-dimensional measuring apparatus, it is required to project light over a wide range. For this reason, the diffraction angle of the diffractive optical element is increased, and the amount of 0th-order diffracted light that is diffracted light that passes straight through the diffractive optical element is increased. It tends to be large. If the amount of such 0th-order diffracted light is higher than the amount of other diffracted light, the captured image of the three-dimensional measuring device may be blurred around the 0th-order diffracted light, leading to image degradation. Therefore, it is desirable that the amount of 0th-order diffracted light is low.

  Patent Document 1 discloses a method of irradiating a speckle pattern generated by a diffractive optical element as a projection pattern of light irradiated to a measurement object when performing three-dimensional measurement. Patent Document 2 discloses a method for reducing the amount of 0th-order diffracted light using two diffractive optical elements.

Special table 2009-530604 gazette Special table 2011-510344 gazette

  In the method disclosed in Patent Document 2, light is incident on the first diffractive optical element, and the light diffracted by the first diffractive optical element is incident on the second diffractive optical element to be diffracted. Thus, the rectangular diffracted light pattern can be distributed two-dimensionally.

  When the diffractive optical element is used for three-dimensional measurement or the like, as described above, the diffractive optical element is required to distribute the diffracted light over a wide range, but when two diffractive optical elements are used, the first sheet Since the sum of the diffraction angle of the diffractive optical element and the diffraction angle of the second diffractive optical element is the entire diffraction angle, the diffraction angle is widened and the diffracted light can be distributed over a wide range.

  By the way, when diffracted light is projected onto a plane using a diffractive optical element, when trying to distribute the diffracted light so that the projection area is substantially rectangular, the corner part of the projection area of the diffracted light is extended, A so-called pincushion type distortion occurs. In particular, when two diffractive optical elements are used, this tendency is significant because the diffraction angle can be widened. When such pincushion type distortion occurs, the density of the light spot of the diffracted light decreases from the vicinity of the center of the projection area of the diffracted light toward the vicinity of the four corners, that is, the center of the projection area of the diffracted light. The light spot of diffracted light generated in the vicinity of the four corners of the projection area of the diffracted light is lower than the density of the light spot of diffracted light generated in the vicinity. Therefore, when such a diffractive optical element that generates pincushion type distortion is used in a measuring apparatus or the like, the density of the light spot of the diffracted light in the vicinity of the periphery becomes low, and thus there is a problem that measurement sensitivity is lowered. ing.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a diffractive optical element having a plurality of diffractive surfaces, in which the density of light spots by diffracted light in the projection region can be made substantially uniform. Furthermore, it aims at providing the measuring device which can perform a precise measurement.

The present invention includes a first diffractive optical unit that generates two-dimensional diffracted light with respect to incident light, a second diffractive optical unit that generates two-dimensional diffracted light with respect to incident light, In either one or both of the first diffractive optical part and the second diffractive optical part, basic units are two-dimensionally and periodically arranged, and the first diffractive optical part When the diffracted light generated by making light incident on the diffractive optical part is incident on the second diffractive optical part and diffracted light is generated from the second diffractive optical part, the number of light spots is 100 or more. The diffraction angle in the first diffractive optical part is θ ₁ , the number of light spots of the generated diffracted light is k ₁ , and the diffraction angle in the second diffractive optical part is a theta _2, if the number of light spots of the diffracted light generated is k ₂ characterized in that it is a θ ₁ ≦ θ ₂ and _{k 1} ≦ _{k 2.}

In the present invention, the projection area of the light spot generated by the diffracted light generated by the first diffractive optical part is overlapped by the second diffractive optical part, thereby forming the projection area of the diffractive optical element. Or the projection region of the light spot generated by the diffracted light generated by the second diffractive optical unit is overlapped by the first diffractive optical unit to form the projection region of the diffractive optical element, It is characterized by.

  In addition, the present invention is characterized in that a plurality of basic units are two-dimensionally arranged in one or both of the first diffractive optical part and the second diffractive optical part.

Further, the present invention, the first diffractive optical portion is closed on one of the transparent substrate, the second diffractive optical unit is characterized in that it is closed on the other transparent substrate.

Further, the present invention is characterized in that it is one embodied in the the one transparent substrate and the other transparent substrate.

Further, the present invention, the first diffractive optical portion is closed on one surface of the transparent substrate, the second diffractive optical unit is characterized in that it is closed on the other surface of the transparent substrate. In the present invention, the diffracted light generated from the second diffractive optical unit when diffracted light generated by entering the light into the first diffractive optical unit is incident on the second diffractive optical unit. Is characterized by including a diffraction angle of 30 ° or more. In the present invention, the diffracted light generated from the second diffractive optical unit when diffracted light generated by entering the light into the first diffractive optical unit is incident on the second diffractive optical unit. The light spot is distributed more in the peripheral part than in the central part.

  Further, the present invention provides a light source that emits light, the diffractive optical element described above that emits diffracted light when the light is incident, an imaging unit that captures an image of a measurement object irradiated with the diffracted light, It is characterized by having.

  In the diffractive optical element according to the present invention, in the diffractive optical element having a plurality of diffractive surfaces, the density of the light spot by the diffracted light in the projection region can be made substantially uniform. In the measuring apparatus according to the present invention, precise and accurate measurement can be performed by using the diffractive optical element of the present invention.

Illustration of diffracted light by a conventional diffractive optical element Illustration of light spot distribution of conventional diffractive optical element Explanatory drawing of the diffracted light by the diffractive optical element in the first embodiment Explanatory drawing of the light spot distribution of the diffractive optical element in the first embodiment Structure diagram of the measuring device in the first embodiment Configuration diagram of diffractive optical element in first embodiment Explanatory drawing of light spot generated by diffractive optical element Explanatory drawing of the diffractive optical element in the first embodiment Structure diagram of first diffractive optical part and second diffractive optical part Structure of other first diffractive optical part and second diffractive optical part Configuration diagram of diffractive optical element in second embodiment Configuration of another diffractive optical element in the second embodiment (1) Configuration of another diffractive optical element in the second embodiment (2) Configuration diagram of another diffractive optical element according to the second embodiment (3) Configuration of another diffractive optical element in the second embodiment (4) Explanatory drawing of one diffractive optical part used for Examples 1 and 4 Explanatory drawing of the other diffractive optical part used for Examples 1 and 4 Light spots formed by the diffractive optical elements in Examples 1 and 4 Explanatory drawing of one diffractive optical part used for Example 2, 3 and 5 Explanatory drawing of the other diffractive optical part used for Example 2, 3 and 5 Light spots formed by the diffractive optical elements in Examples 2, 3 and 5 Explanatory drawing of one diffraction optical part used for Example 6 Explanatory drawing of the other diffractive optical part used for Example 6 Light spot formed by the diffractive optical element in Example 6 Explanatory drawing of one diffraction optical part used for Example 7 Explanatory drawing of the other diffractive optical part used for Example 7 Light spot formed by the diffractive optical element in Example 7 Explanatory drawing of one diffraction optical part used for Example 8 Explanatory drawing of the other diffractive optical part used for Example 8 Light spot formed by the diffractive optical element in Example 8

  Modes for carrying out the invention will be described below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
(Pin cushion type distortion)
First, the cause of the pincushion type distortion will be described. As shown in FIG. 1, when light is diffracted by the two diffractive optical elements 410 and 420, the incident light 401 is incident on the first diffractive optical element 410 to generate diffracted light 402. The diffracted light 402 diffracted by the diffractive optical element 410 is diffracted at a diffraction angle θ _1A . FIG. 2A shows a light spot distribution by the diffracted light 402 generated by the diffractive optical element 410. Next, the diffracted light 403 is generated by causing the diffracted light 402 to enter the second diffractive optical element 420. The diffracted light 403 diffracted by the diffractive optical element 420 is diffracted at the diffraction angle θ _2A , and the distribution of the light spot by the diffracted light generated by the diffractive optical element 420 is shown in FIG. FIG. 2B shows a light spot distribution by the diffracted light when the incident light is perpendicularly incident on the diffractive optical element 420. When this diffracted light 403 is irradiated onto a flat projection surface 440, as shown in FIG. 2 (c), a shape in which four corners extend in the projection area 441 of the light spot by the diffracted light, that is, a so-called pincushion type distortion. Is projected in a state where

  By the way, in the cited document 2, the projection area 441 on the projection plane 440 is divided into a plurality of areas, and the areas corresponding to the light spot distribution shown in FIG. Specifically, the light spot 442 in the region indicated by a white circle in FIG. 2C is diffracted light by making the diffracted light 402 that becomes the light spot 411 indicated by a white circle in FIG. 403 is generated, and the light spot of the diffracted light 403 is projected onto the projection surface 440. Therefore, the four diffracted lights diffracted by the diffractive optical element 410 generate light spots corresponding to the light spot distributions of the diffracted lights shown in FIG. 2B, respectively, and these light spot distributions are joined together. Projection region 441 is formed.

  As described above, the diffracted light 402 incident on the diffractive optical element 420 is diffracted by the diffractive optical element 410. In order to widen the projection region 441, the diffraction angle of the diffracted light 402 generated by the diffractive optical element 410 is increased. Is wider.

  However, the cause of the pincushion type distortion is that the optical path between the diffracted light that is the central spot of the projection region 441 and the diffracted light that is the peripheral spot among the diffracted light generated by the diffractive optical element 420. This is because the length is different. Note that the distance w is the difference in optical path length between the diffracted light that becomes the light spot at the center of the projection region 441 and the diffracted light that becomes the light spot at the peripheral portion. That is, the diffracted light that becomes the light spot in the peripheral portion of the projection region 441 propagates by a distance w longer than the diffracted light that becomes the light spot in the central portion, and therefore, compared with the case where it is projected onto a spherical surface centered on the diffracted portion. Widened and projected. In particular, this tendency becomes remarkable at the four corners of the projection region 441 where the optical path is the longest, and a pincushion type distortion with the four corners extending occurs. Further, since the distance between the diffracted lights increases as the optical path of the diffracted light becomes longer, the distance between the light spots due to the diffracted light becomes wider especially at the four corners of the projection region 441 where the optical path becomes the longest. Becomes rough. The same applies to the case where the positions where the diffractive optical element 410 and the diffractive optical element 420 are installed are reversed.

Next, the diffractive optical element in the present embodiment will be described with reference to FIGS. The diffractive optical element 30 in the present embodiment has a first diffractive optical part 110 and a second diffractive optical part 120 corresponding to two diffractive optical elements as described later. In the diffractive optical element according to the present embodiment, the diffraction angle of the first diffractive optical unit 110 is θ ₁ , the number of light spots of the generated diffracted light is k ₁ , and the diffraction of the second diffractive optical unit 120 is performed. The angle is θ ₂ , and the number of light spots of the generated diffracted light is k ₂ . The incident light beam 11 is incident on the first diffractive optical unit 110 to generate the diffracted light group 111, and the diffracted light group 111 is incident on the second diffractive optical unit 120, thereby diffracted light group 121a, 121b, 121c,... Are generated, and a projection area 141 is formed on the projection surface 140 by a light spot by diffracted light.

The diffractive optical element in the present embodiment is configured so that the light spot of the diffracted light shown in FIG. 4A generated by the first diffractive optical unit 110 is set by satisfying θ ₁ ≧ θ ₂ and k ₁ ≧ k ₂ . By projecting the distribution (projection region) onto the projection surface 140 in a state where the positions of the light spot distributions are shifted by the second diffractive optical unit 120, the projection region 141 is formed. Thus, by superimposing the distribution of the light spots generated by the first diffractive optical unit 110 on the projection surface 140, the density of the light spots in the peripheral portions at the four corners of the projection region 141 is set to the central portion of the projection region 141. The light spots can be distributed substantially uniformly in the projection region 141. 4C shows the projection area 141 of the light spot projected on the projection surface 140, and FIG. 4B shows the incident light incident on the second diffractive optical unit 120 perpendicularly. The distribution of the light spot by the diffracted light in this case is shown. In the present embodiment, a region where a light spot generated by the first diffractive optical unit 110 is distributed is a projection region of the light spot generated by the first diffractive optical unit 110 and a light spot generated by the second diffractive optical unit 120. The distributed area is referred to as a projected area of the light spot generated by the second diffractive optical unit 120. Also, four light spots 142 indicated by white circles in FIG. 4C are diffracted by the second diffractive optical unit 120 and projected onto the projection surface 140 by the light spot 112 of diffracted light indicated by white circles in FIG. It has been done.

The above-mentioned contents are the same when θ ₁ ≦ θ ₂ and k ₁ ≦ k ₂ . Therefore, the same effect can be obtained if θ ₁ ≧ θ ₂ and k ₁ ≧ k ₂ , or θ ₁ ≦ θ ₂ and k ₁ ≦ k ₂ .

  In the present embodiment, as described above, pincushion-type distortion can be suppressed. However, when the diffractive optical element 30 is used for a measuring instrument or the like, the central portion of the projection region 141 and the peripheral portions of the four corners are more uniform. For example, the light spot distribution shown in FIG. 4A may be formed so that more light spots are generated in the peripheral part than in the central part.

  Hereinafter, this embodiment will be described in more detail.

(Measurement device)
A measuring apparatus according to the present embodiment will be described with reference to FIG. FIG. 5 shows an example of the configuration of the measuring apparatus according to the present embodiment. The measurement apparatus 10 in the present embodiment includes a light source 20, a diffractive optical element 30, and an image sensor 50. The diffractive optical element 30 is a diffractive optical element in the present embodiment, which will be described later, and generates diffracted light 12 by causing a light beam (incident light) 11 emitted from the light source 20 to enter. The imaging element 50 is for imaging the measurement objects 40 a and 40 b irradiated with the projection pattern of the light spot generated by the diffracted light 12.

The diffractive optical element 30 generates a plurality of diffracted lights 12, and a desired projection pattern is formed by a light spot generated by the diffracted lights 12. Therefore, information such as the three-dimensional shapes of the measurement objects 40a and 40b is obtained by irradiating the measurement objects 40a and 40b with the projection pattern and taking an image of the projection pattern irradiated with the imaging device 50. Is done. In order to perform three-dimensional measurement, the number of light spots is preferably 100 or more, and the diffractive optical element 30 has a maximum diffraction angle θ _xmin , θ _xmax of 30 ° or more. That is, it is preferably formed so that diffracted light having a diffraction angle of 30 ° or more can be generated.

(Diffraction optical element)
Next, the diffractive optical element 30 in the present embodiment will be described. As shown in FIG. 6, the diffractive optical element 30 in the present embodiment includes a first diffractive optical unit 110 and a second diffractive optical unit 120. The first diffractive optical unit 110 is a diffractive optical element that generates n ₁ diffracted light groups 111 of diffracted light 111a, 111b, 111c,. The second diffractive optical part 120 makes n ₂ diffracted light groups 121a, 121b, 121c,... Incident by causing n ₁ diffracted light groups 111 of diffracted light 111a, 111b, 111c,. Is a diffractive optical element that generates Thereby, the number of diffracted light can be increased and diffracted light with a large diffraction angle can be generated. Therefore, the light spot of the diffracted light can be distributed over a wide range of the projection surface 140. In the present embodiment, the direction of the optical axis 101 of the light beam 11 serving as incident light is the Z axis, and the direction perpendicular to the optical axis 101 of the light beam 11 is the X axis and the Y axis. Note that the X axis and the Y axis are orthogonal to each other.

  Both the first diffractive optical part 110 and the second diffractive optical part 120 forming the diffractive optical element in the present embodiment generate diffracted light, and are similar in this respect. Next, the diffractive optical element 230 serving as the first diffractive optical unit 110 and the second diffractive optical unit 120 will be described.

As shown in FIG. 7, a diffracted light group 211 is generated by causing a light beam 210 to be incident light to enter the diffractive optical element 230. Among diffracted beam group 211, the diffraction angle of the diffracted light 211a for the diffraction angle with respect to the optical axis 101 becomes maximum and theta _a, to do this the diffraction angle range theta _x. At this time, the angle (center angle) θ _{0 with} respect to the optical axis 101 at the center of the diffraction range is set to 0 °. In the case in the vicinity of a position opposite to the diffracted light 211a with respect to the optical axis 101, although the diffracted light 211b that diffraction angle becomes theta _b occurs, the difference between the theta _a and theta _b is large, for example, a theta _a When the difference from θ _b is 3 ° or more, the diffraction angle range θ _x = (θ _a + θ _b ) / 2 and the center angle θ ₀ = (θ _a −θ _b ) / 2 may be used.

Further, a case where diffracted light is not generated on the opposite side of the diffracted light 211a with respect to the optical axis 101, that is, a case where a diffracted light group is generated only on the side where the diffracted light 211a is generated with respect to the optical axis 101 is also conceivable. . In such a case, assuming that the diffraction angle of the diffracted light closest to the optical axis 101 is θ _c , the diffraction angle range θ _x = (θ _a −θ _c ) / 2 and the center angle θ ₀ = (θ _a + θ _c ) / 2.

In the present embodiment, as described above, the angle within the diffraction angle range θ _x is the diffraction angle, the diffraction angle in the first diffractive optical unit 110 is θ ₁ , and the diffraction angle in the second diffractive optical unit 120 is θ ₂ , and the diffraction angle in the diffractive optical element 30 in the present embodiment is denoted as θ.

Next, the diffractive optical element 230 will be described in more detail. The incident light beam 210 is incident on the diffractive optical element 230 to generate diffracted light 211. The diffracted light 211 is light diffracted to an angle θ _{x in} the X direction and an angle θ _y in the Y direction with reference to the Z-axis direction in the grating equation shown in Equation 1. In the formula shown in Formula 1, m _x is the diffraction order in the X direction, m _y is the diffraction order of the Y-direction, lambda is the wavelength of the light beam _210, P x, P _y is the diffractive optical element to be described later It is the pitch in the X-axis direction and Y-axis direction of the basic unit. By irradiating the diffracted light 12 onto a projection surface such as a screen or a measurement object, a plurality of light spots are generated in the irradiated region.

ここで、数１に示す式は、入射光が回折光学素子に対し垂直に入射する場合における式である。図１において、入射光１１が回折光学素子３０に対して垂直に入射している状態を示しているが、光源がレーザ光源等の場合には、回折光学素子３０からの反射光が戻り光となりレーザ光源等に入射することを防ぐため、回折光学素子３０に垂直な方向より傾けた方向より入射光１１を入射させてもよい。レーザ光源等に戻り光が入射すると干渉の影響によりレーザの発振が不安定となる場合があるからである。

Here, the equation shown in Equation 1 is an equation in the case where incident light is incident on the diffractive optical element perpendicularly. In FIG. 1, the incident light 11 is perpendicularly incident on the diffractive optical element 30, but when the light source is a laser light source or the like, the reflected light from the diffractive optical element 30 becomes return light. In order to prevent the light from entering a laser light source or the like, the incident light 11 may be incident from a direction inclined from the direction perpendicular to the diffractive optical element 30. This is because if the return light enters the laser light source or the like, the laser oscillation may become unstable due to the influence of interference.

As such a diffractive optical element 30, a diffractive optical element designed by an iterative Fourier transform method or the like can be used. Here, the diffractive optical element is an element in which basic units that generate a predetermined phase distribution are arranged periodically, for example, two-dimensionally. In such a diffractive optical element, the distribution of the diffraction orders of the diffracted light in the distance can be obtained by Fourier transform in the basic unit. This is explained by scalar diffraction theory. Although the electromagnetic field is a vector quantity, it can be represented by a scalar quantity in an isotropic medium, and the scalar function u (A, t _m ) at time t _m and point A is represented by the equation shown in Equation 2.

数２に示す式は、入射する光が単色光の場合を示しており、Ｕ（Ａ）は点Ａにおける複素振幅であり、ωは角周波数である。数２に示すスカラー関数は、全空間で数３に示す波動方程式を満たす。

The expression shown in Formula 2 shows a case where the incident light is monochromatic light, U (A) is a complex amplitude at point A, and ω is an angular frequency. The scalar function shown in Equation 2 satisfies the wave equation shown in Equation 3 in the entire space.

数２に示す式を数３に示す式に代入すると、数４に示すヘルムホルツ方程式を得ることができる。

By substituting the equation shown in Equation 2 into the equation shown in Equation 3, the Helmholtz equation shown in Equation 4 can be obtained.

ここで、ｋは波数であり、ｋ＝２π／λである。数３に示される式を解くことにより、空間におけるスカラー関数の分布が計算される。また、ある位相分布を与える十分に薄い平面スクリーンをΣで示し、Σ上における点をＡ_１とし、平面波がΣを透過した場合の点Ａ_０におけるスカラー関数をキルヒホッフの境界条件を用いて、数４に示す式から計算すると、ｒ_０１を点Ａ_０と点Ａ_１の距離とした場合、数５に示す式が得られる。

Here, k is the wave number, and k = 2π / λ. By solving the equation shown in Equation 3, the distribution of the scalar function in the space is calculated. Also, a sufficiently thin flat screen giving a certain phase distribution is denoted by Σ, a point on Σ is A _1, and a scalar function at a point A ₀ when a plane wave is transmitted through Σ is expressed by the Kirchhoff boundary condition as When calculated from the equation shown in FIG. 4, when r ₀₁ is the distance between the point A ₀ and the point A ₁ , the equation shown in Equation 5 is obtained.

更に、点Ａ_０における座標（ｘ_０、ｙ_０、０）、点Ａ_１における座標（ｘ_１、ｙ_１、ｚ）とし、ｚが｜ｘ_０−ｘ_１｜、｜ｙ_０−ｙ_１｜よりも十分大きな値であるものとすると、ｒ_０１を展開することにより、数６に示されるフラウンホーファー近似式を得ることができる。

Further, the coordinates at the point A ₀ (x ₀ , y ₀ , 0) and the coordinates at the point A ₁ (x ₁ , y ₁ , z) are set, and z is | x ₀ −x ₁ |, | y ₀ −y ₁ | Assuming that the value is sufficiently larger than the above, by expanding r ₀₁ , the Fraunhofer approximation expressed by Equation 6 can be obtained.

これは、スクリーンによって与えられる位相分布のフーリエ変換に相当する。特に、スクリーン後における位相分布ｕ（Ａ_１）がＸ軸方向にピッチＰ_ｘ、Ｙ軸方向にピッチＰ_ｙの周期性を有する場合、ｕ（Ａ_０）は、下記に示す数７に示す式のように、（ｍ、ｎ）次の回折光が発生する。

This corresponds to the Fourier transform of the phase distribution given by the screen. In particular, when the phase distribution u (A ₁ ) after the screen has a periodicity of a pitch P _{x in} the X-axis direction and a pitch P _{y in} the Y-axis direction, u (A ₀ ) is expressed by the following equation (7). As shown, (m, n) -order diffracted light is generated.

この際、（ｍ、ｎ）次の回折光の回折効率η_ｍｎは、周期性の基本ユニットが有する位相分布ｕ'（ｘ_１、ｙ_１）を用いて、下記数８に示す式で表わされる。尚、ｍ、ｎは整数、θｘ_ｉｎ及びθｙ_ｉｎは入射光におけるＸ方向及びＹ方向におけるＺ軸となす角度、θｘ_ｏｕｔ及びθｙ_ｏｕｔは出射光におけるＸ方向及びＹ方向におけるＺ軸となす角度である。

At this time, the diffraction efficiency η _mn of the (m, n) _-order diffracted light is expressed by the following formula 8 using the phase distribution u ′ (x ₁ , y ₁ ) of the periodic basic unit. . M and n are integers, θx _in and θy _in are angles formed with the Z axis in the X direction and the Y direction in the incident light, and θx _out and θy _out are angles formed with the Z axis in the X direction and the Y direction in the emitted light. is there.

従って、基本ユニットの位相分布が得られれば、そのフーリエ変換によって回折光における強度分布の計算ができるため、基本ユニットの位相分布を最適化することにより、所望の分布の回折光を発生させる回折光学素子が得られる。

Therefore, if the phase distribution of the basic unit is obtained, the intensity distribution in the diffracted light can be calculated by the Fourier transform. Therefore, by optimizing the phase distribution of the basic unit, diffractive optics that generates diffracted light with a desired distribution is obtained. An element is obtained.

Next, the structure of the diffractive optical element 230 will be described with reference to FIG. In the diffractive optical element 230, as shown in FIG. 8A, basic units 231 having a pitch P _{x in} the X-axis direction and a pitch P _{y in} the Y-axis direction are periodically arranged in a two-dimensional manner. Specifically, it has a phase distribution as shown in FIG. FIG. 8B shows the diffractive optical element 230 in which a concavo-convex pattern is formed so that a black-out region becomes a convex portion and a white region becomes a concave portion. The diffractive optical element 230 only needs to be able to generate a phase distribution. The diffractive optical element 230 has a structure in which a concavo-convex pattern is formed on the surface of a member that transmits light, such as glass or a resin material, or a transparent member in which a concavo-convex pattern is formed. On top of this, a member having a different refractive index from this member may be bonded to form a flat surface uneven pattern, or a transparent member may have a structure in which the refractive index is changed. . That is, here, the concave / convex pattern means not only the case where the surface shape is concave / convex, but also includes those having a structure capable of giving a phase difference to incident light. When the basic units 231 are two-dimensionally arranged on the diffractive optical element 230, the number of basic units does not have to be an integral number, and if one or more basic units are included in the uneven pattern, the uneven pattern and the uneven The boundary of the area having no pattern may not coincide with the boundary of the basic unit.

  FIG. 9 is a schematic cross-sectional view of a diffractive optical element 230 having a structure in which a concavo-convex pattern is formed by forming convex portions 233 on the surface of a transparent substrate 232 made of glass or the like as an example of the diffractive optical element 230. In the diffractive optical element 230, a region where the convex portion 233 is not formed becomes a concave portion 234 on the surface of the transparent substrate 232.

  The transparent substrate 232 only needs to be transparent to incident light, and various materials such as a resin substrate and a resin film can be used in addition to a glass substrate. However, optically isotropic materials such as glass and quartz can be used for transmitted light. It is preferable without affecting birefringence. In addition, the transparent substrate 232 can reduce light reflection due to Fresnel reflection, for example, by forming an antireflection film using a multilayer film at the interface with air.

  Moreover, as a material which forms the convex part 233, an organic material, an inorganic material, and an organic inorganic composite material can be used. As a method of forming the convex portion 233, that is, a method of forming a concave / convex pattern comprising the convex portion 233 and the concave portion 234, a method of forming by photolithography and etching, an injection molding or imprinting that transfers the concave / convex pattern by a mold, and the like. A method or the like can be used. Moreover, the convex part 233 does not need to be formed of a single material, and for example, the convex part 233 may be formed of a multilayer film made of an inorganic material. Furthermore, a structure provided with an antireflection film for reducing surface reflection or an antireflection structure may be formed on the surface of the convex portion 233.

  As shown in FIG. 10, the diffractive optical element 230 has a transparent substrate 235 provided on the side of the transparent substrate 232 on which the convex portions 233 are formed, on the side where the convex portions 233 are formed. The transparent resin 236 having a refractive index different from the refractive index of the material forming the convex portion 233 is embedded between the transparent substrate 235 and the transparent substrate 235. In addition, without providing the transparent substrate 235, the transparent resin 236 having a refractive index different from the refractive index of the material forming the convex portion 233 is formed on the side of the transparent substrate 232 where the convex portion 233 is formed, The surface of 236 may be flattened.

  Such a diffractive optical element 230 can be manufactured using a technique such as an iterative Fourier transform method. More specifically, since the phase distribution of the basic unit 231 in the diffractive optical element and the electric field distribution of the diffracted light are in a Fourier transform relationship, the phase distribution in the basic unit 231 is obtained by inverse Fourier transforming the electric field distribution of the diffracted light. Can be obtained.

  Further, when the diffractive optical element 230 is manufactured, only the intensity distribution of the diffracted light is a limiting condition, and the phase condition is not included. Therefore, the phase distribution of the basic unit 231 is arbitrary. In the iterative Fourier transform method, information on the phase distribution of the basic unit is extracted from the inverse Fourier transform of the light intensity distribution of the diffracted light, the obtained phase distribution is used as the phase distribution of the basic unit, and further Fourier transform is performed. As a result, the difference between the Fourier transform result and the light intensity distribution of the predetermined diffracted light becomes the evaluation value, and by repeating the above calculation, the phase distribution of the diffractive optical element that minimizes the evaluation value is optimized. Can be obtained as a design.

  In addition to the above, there are various design algorithms for diffractive optical elements as described in Bernard Kress, Patrick Meyrueis, “Digital Diffraction Optics” (Maruzen). As a Fourier transform method, a fast Fourier transform algorithm or the like can be used.

[Second Embodiment]
Next, a second embodiment will be described. The diffractive optical element in the present embodiment has a structure in which the first diffractive optical part and the second diffractive optical part are integrated, and the first diffractive optical part on one surface of one substrate And a convex portion that becomes the second diffractive optical portion is formed on the other surface. Thereby, alignment between the first diffractive optical part and the second diffractive optical part becomes unnecessary, and the diffractive optical element is miniaturized.

  In the diffractive optical element shown in FIG. 11, the convex portion 303 of the first diffractive optical portion is formed on one surface of the transparent substrate 302 so that the concave portion 304 and the convex portion of the region where the convex portion 303 is not formed are formed. The concave / convex pattern is formed by 303, and the convex portion 305 of the second diffractive optical part is formed on the other surface of the transparent substrate 302, whereby the concave portion 306 and the convex portion 305 in the region where the convex portion 305 is not formed. Thus, a concavo-convex pattern is formed.

  12 to 15 show a diffractive optical element having a structure in which a first diffractive optical part 310 and a second diffractive optical part 320 are bonded and bonded with an adhesive or the like. The first diffractive optical part 310 is formed by forming a convex part 313 on the surface of the transparent substrate 312 to form a concave / convex pattern by the concave part 314 and the convex part 313 in a region where the convex part 313 is not formed. In addition, the second diffractive optical unit 320 is formed by forming a convex portion 323 on the surface of the transparent substrate 322 to form a concave / convex pattern by the concave portion 324 and the convex portion 323 in the region where the convex portion 323 is not formed. is there. The first diffractive optical unit 310 and the like in the present embodiment correspond to the first diffractive optical unit 110 in the first embodiment, and the second diffractive optical unit 320 and the like correspond to those in the first embodiment. This corresponds to the second diffractive optical part 120 in the embodiment.

  The diffractive optical element shown in FIG. 12 opposes the surface where the convex portion 313 is not formed in the first diffractive optical portion 310 and the surface where the convex portion 323 is not formed in the second diffractive optical portion 320. The surfaces are joined together with an adhesive 340.

  In the diffractive optical element shown in FIG. 13, the surface on which the convex portion 313 is formed in the first diffractive optical portion 310 and the surface on which the convex portion 323 is formed in the second diffractive optical portion 320 face each other. The surfaces facing each other are joined by an adhesive 340.

  In the diffractive optical element shown in FIG. 14, the surface where the convex portion 313 is not formed in the first diffractive optical portion 310 and the surface where the convex portion 323 is formed in the second diffractive optical portion 320 are opposed to each other. The surfaces facing each other are joined by an adhesive 340.

  In the diffractive optical element shown in FIG. 15, the surface where the convex portion 313 is not formed in the first diffractive optical portion 310 and the surface where the convex portion 323 is formed in the second diffractive optical portion 320 are opposed to each other. The periphery of the opposing surfaces is joined by an adhesive 340.

Next, examples will be described. Tables 1 to 3 summarize the configurations of the diffractive optical elements shown in Examples 1 to 10. In the present application, Examples 1 to 8 are Examples 1 to 8, and Examples 9 and 10 are Comparative Examples 1 and 2. In Examples 1 to 10, quartz is used as the transparent substrate in the first diffractive optical part and the second diffractive optical part, and the wavelength λ of the incident light beam is 830 nm. In Table 1, the number of spots n ₁ generated by the first diffractive optical part, the maximum and minimum orders in the X direction among the generated orders, the maximum and minimum orders in the Y direction, the X direction and the Y direction in which the basic units are arranged. Pitches P _x and P _y , the number of steps of the diffraction section, and the height of each step. Further, the diffraction angle θ ₁ obtained in such a configuration is shown, and at the same time, the maximum possible value of the diffraction angle of the diffracted light on the X axis and the diffraction angle of the diffracted light on the Y axis is shown. .

表２には、第２の回折光学部によって発生するスポット数ｎ_２、発生させる次数のうちＸ方向で最大、最小の次数、Ｙ方向で最大、最小の次数、基本ユニットを配置させるＸ方向、Ｙ方向のピッチＰ_ｘ、Ｐ_ｙ、回折部の段数、各段の高さを示している。また、このような構成とした場合に得られる回折角度θ_２を示しており、同時にＸ軸上における回折光の回折角度、Ｙ軸上における回折光の回折角度の取りうる最大値を示している。第２の回折光学部では、所定の入射角で光束が入射した場合に発生する位相差を基準として設計されており、そのときの入射角を設計入射角φとして示している。設計入射角φから計算される１／ｃｏｓφ_ａｖｇおよびλｃｏｓφ_ａｖｇの値を同時に示しており、第２の回折光学部に光束を入射した場合に、分光測定をすると波長λｃｏｓφ_ａｖｇにおいて、波長λ、入射角φで入射場合と類似の特性を示す。尚、φ_ａｖｇは、第２の回折光学部に角度φ_０で光を入射させた場合に、第２の回折光学部において屈折する角度をφ_１とした場合、φ_ａｖｇ＝（φ_０＋φ_１）／２となる値である。ここで、第２の回折光学部の凹部として空気以外の媒質が用いられている場合には、凹部の媒質の屈折率からスネルの法則により計算される角度をφ_０の値として用いることができる。

Table 2 shows the number of spots n ₂ generated by the second diffractive optical unit, the maximum and minimum orders in the X direction among the generated orders, the maximum and minimum orders in the Y direction, and the X direction in which the basic units are arranged. Y-direction pitches P _x and P _y , the number of steps of the diffractive portion, and the height of each step are shown. Further, the diffraction angle θ ₂ obtained in such a configuration is shown, and at the same time, the maximum possible value of the diffraction angle of the diffracted light on the X axis and the diffraction angle of the diffracted light on the Y axis is shown. . The second diffractive optical unit is designed with reference to a phase difference generated when a light beam is incident at a predetermined incident angle, and the incident angle at that time is indicated as a designed incident angle φ. The values of 1 / cosφ _avg and λcosφ _avg calculated from the design incident angle φ are shown at the same time. When a light beam is incident on the second diffractive optical part, when the spectroscopic measurement is performed, at the wavelength λcosφ _avg , the wavelength λ is incident. The characteristic similar to the case of incidence is shown at an angle φ. Incidentally, phi _avg, when light was made to enter with an angle phi ₀ in the second diffractive optical part, when the angle of refraction at the second diffractive optical portion and _{φ 1, φ avg = (φ} 0 + φ 1 ) / 2. Here, when a medium other than air is used as the concave part of the second diffractive optical part, an angle calculated by Snell's law from the refractive index of the medium of the concave part can be used as the value of φ _0. .

表３には、２つの回折部を透過した光束の回折角度θを示しており、同時にＸ軸上における回折光の回折角度、Ｙ軸上における回折光の回折角度の取りうる最大値を示している。

Table 3 shows the diffraction angle θ of the light beam that has passed through the two diffracting parts, and also shows the maximum value that can be taken by the diffraction angle of the diffracted light on the X axis and the diffraction angle of the diffracted light on the Y axis. Yes.

例１〜例１０に示される回折光学素子の特性値についてまとめたものを表４及び表５に示す。表４及び表５には第１の回折光学部に強度１の光束が入射する場合に得られる回折光の強度の平均値μ_１、標準偏差σ_１を計算によって求めたものを示す。計算では、回折部の界面によって発生する反射を考慮していない。また、平均値μ_１で除算した標準偏差σ_１の値をパーセントで表示しており、これを第１の回折光学部による光量ばらつきと呼ぶ。

Tables 4 and 5 summarize the characteristic values of the diffractive optical elements shown in Examples 1 to 10. Tables 4 and 5 show the values obtained by calculating the average value μ ₁ and standard deviation σ ₁ of the intensity of diffracted light obtained when a light beam with intensity 1 is incident on the first diffractive optical part. In the calculation, the reflection generated by the interface of the diffraction part is not taken into consideration. Further, the value of the standard deviation σ ₁ divided by the average value μ ₁ is displayed as a percentage, and this is referred to as a light amount variation due to the first diffractive optical unit.

In addition, an average value μ ₂ and standard deviation σ ₂ of the intensity of diffracted light obtained when a light beam having intensity 1 is incident on the second diffractive optical part at a predetermined incident angle are shown by calculation. In the calculation, the reflection generated by the interface of the diffraction part is not taken into consideration. Further, the value of the standard deviation σ ₂ divided by the average value μ ₂ is displayed as a percentage, and this is referred to as variation in the amount of light by the second diffractive optical unit 120. Furthermore, the light quantity variation of the diffractive optical element is obtained by σ = {(σ ₁ / μ ₁ ) ² + (σ ₂ / μ ₂ ) ² } ^0.5 . In addition, the light amount of the 0th-order diffracted light of the second diffractive optical unit 120 at each incident angle is shown.

  In addition, the calculation result when the spot of the diffracted light generated by design among the diffracted light generated by the diffractive optical element is measured on a screen at a predetermined position away from the diffractive optical element is shown. The position of the screen is shown as a measurement position, and a rectangular measurement range is shown using coordinates (X, Y) on the screen. Further, the angle in the diagonal direction of the measurement range measured from the position of the diffractive optical element is shown as the measurement range angle. At the time of spot measurement, the measurement range is divided into nine in the X direction, and the spot in the measurement region where the area divided into nine in the Y direction is uniform is measured. In Tables 4 and 5, when the measurement area where the X coordinate and Y coordinate are the smallest is R (1, 1), and the measurement area where the X coordinate and Y coordinate is the largest is R (9, 9), The average value of the number of spots in the region R (5, 5), the peripheral region R (1, 1), R (1, 9), R (9, 1), R (9, 9), the region R (1 1) to the maximum number and minimum value of the number of spots in R (9, 9).

Table 6 shows the second diffractive optics at each wavelength shown in Table 6 when the light is perpendicularly incident on the second diffractive optical element in the diffractive optical elements shown in Examples 3 to 5. The figure shows that the average value μ ₂ and standard deviation σ ₂ of the intensity of diffracted light obtained when a light beam with intensity 1 is incident on the part at a predetermined incident angle are calculated. In the calculation, the reflection generated by the interface of the diffraction part is not taken into consideration. In addition, the light amount of the 0th-order diffracted light of the second diffractive optical unit 120 at each wavelength is shown.

（実施例１）
実施例１は、表１〜４における例１に示す回折光学素子であり、第１の回折光学部１１０の回折角度θ_１と第２の回折光学部１２０の回折角度θ_２がθ_１≦θ_２を満たす場合の例を示す。第１の回折光学部１１０の基本ユニットを図１６（ａ）に示す。このような基本ユニットを表１に示すピッチＰ_ｘ、Ｐ_ｙ、回折部段数、１段高さとなるようにフォトリソグラフィ、エッチングによって加工する。このような回折部に光が垂直に入射した場合に、５５４．３ｍｍの位置にあるスクリーン上の設計によって発生させる回折光の光スポット分布を図１６（ｂ）に示す。

Example 1
Example 1 is a diffractive optical element shown in Example 1 in Tables 1-4, the diffraction angle theta ₂ of the diffraction angle theta ₁ and the second diffractive optical portion 120 of the first diffractive optical portion 110 is theta ₁ ≦ theta An example when ₂ is satisfied is shown. A basic unit of the first diffractive optical section 110 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 16B shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 17B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion. Diffracted light generated by the design on the screen at a position of 554.3 mm among the light transmitted through the first diffractive optical element 110 and the second diffractive optical part 120 of the first embodiment. The light spot distribution is shown in FIG.

  The first diffractive optical unit 110 emits a light beam in a diffraction angle range of 12.5 °, and as shown in Table 4, the second diffractive optical unit 120 3.9 with respect to a light beam with an incident angle of 12.5 °. % Of the light amount variation occurs, and together with the light amount variation of 5.2% by the first diffractive optical unit 110, the light amount variation of the maximum diffractive optical element is 6.5%. Further, the ratio of the number of spots in the peripheral area and the central area on the screen is 0.538.

(Example 2)
Example 2 is a diffractive optical element shown in Example 2 in Table 1 to 3 and 5, the diffraction angle theta ₂ of the diffraction angle theta ₁ and the second diffractive optical portion 120 of the first diffractive optical portion 110 is theta ₁ An example in which ≦ θ ₂ is satisfied is shown. A basic unit of the first diffractive optical section 110 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 19B shows the distribution of the light spot of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light is vertically incident on such a diffractive portion.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 20B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light enters the diffractive portion vertically. Of the light transmitted through the first diffractive optical element 110 and the second diffractive optical part 120, the diffracted light generated by the design on the screen at a position of 342.8 mm. The light spot distribution is shown in FIG.

  The first diffractive optical unit 110 emits a light beam in a diffraction angle range of 17.6 °. As shown in Table 5, the second diffractive optical unit 120 outputs 7.6 light with respect to a light beam having an incident angle of 17.6 °. % Of the light amount variation occurs, and together with the light amount variation of 5.2% by the first diffractive optical unit 110, the light amount variation of the entire diffractive optical element as a whole is 9.2%. Further, the ratio of the number of spots in the peripheral area and the central area on the screen is 0.215.

Example 3
Example 3 is a diffractive optical element shown in Example 3 in Table 1～3,5,6, diffraction angle theta ₂ of the diffraction angle theta ₁ and the second diffractive optical portion 120 of the first diffractive optical portion 110 An example in which θ ₁ ≦ θ ₂ is satisfied and the design incident angle of the second diffractive optical unit 120 is 12.5 ° is shown. A basic unit of the first diffractive optical section 110 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 19B shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light is vertically incident on such a diffractive portion.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 20B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light enters the diffractive portion vertically. FIG. 21 shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm among the light beams transmitted through the two diffracting portions. Further, the second diffractive optical unit 120 is designed so that the light intensity varies at an incident angle of 12.5 ° and the 0th-order diffracted light is minimized, and when performing spectroscopy using a vertically incident light beam, the light intensity at a wavelength of 816 nm. Variation and zero-order diffracted light are minimized.

  The first diffractive optical unit 110 emits a light beam in a diffraction angle range of 17.6 °, and as shown in Table 5, the second diffractive optical unit 120 3.9 with respect to a light beam having an incident angle of 17.6 °. % Of the light amount variation occurs, and together with the light amount variation of 5.2% by the first diffractive optical unit 110, the light amount variation of the maximum diffractive optical element is 6.5%. Further, the ratio of the number of spots in the peripheral area and the central area on the screen is 0.215.

Example 4
Example 4 is a diffractive optical element shown in Example 4 in Table 1～4,6, diffraction angle theta ₂ of the diffraction angle theta ₁ and the second diffractive optical portion 120 of the first diffractive optical portion 110 is theta ₁ > a theta _2, showing an example of a case where the second diffractive optical portion 120 is designed at an incident angle of 18.5 °. A basic unit of the first diffractive optical section 110 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 17B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 16B shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion. FIG. 18 shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm among the light beams transmitted through the two diffractive portions. Further, the second diffractive optical unit 120 is designed so that the amount of light varies at an incident angle of 18.5 ° and the 0th-order diffracted light is minimized, and when performing spectroscopy using a vertically incident light beam, the amount of light is at a wavelength of 800 nm. Variation and zero-order diffracted light are minimized.

  The first diffractive optical unit 110 emits a light beam in a diffraction angle range of 25.9 °. As shown in Table 4, the second diffractive optical unit 120 is 6.1 for a light beam having an incident angle of 25.9 °. % Of light intensity variation occurs, and together with the light intensity variation of 0.4% by the first diffractive optical unit 110, the light intensity variation of the maximum diffractive optical element as a whole is 6.1%. Further, the ratio of the number of spots in the peripheral area and the central area on the screen is 0.538.

(Example 5)
Example 5 is a diffractive optical element shown in Example 5 in Table 1～3,5,6, diffraction angle theta ₂ of the diffraction angle theta ₁ and the second diffractive optical portion 120 of the first diffractive optical portion 110 An example is shown in which θ ₁ > θ ₂ and the second diffractive optical section 120 is designed with an incident angle of 27.2 °. A basic unit of the first diffractive optical section 110 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 20B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light enters the diffractive portion vertically.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 19B shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light is vertically incident on such a diffractive portion. FIG. 21 shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm among the light beams transmitted through the two diffracting portions. The second diffractive optical unit 120 is designed so that the amount of light varies at an incident angle of 27.2 ° and the 0th-order diffracted light is minimized. When performing spectroscopy using a vertically incident light beam, the amount of light at a wavelength of 765 nm is used. Variation and zero-order diffracted light are minimized.

  The first diffractive optical unit 110 emits a light beam in a diffraction angle range of 37.6 °, and as shown in Table 5, the second diffractive optical unit 120 uses 8.5 for a light beam with an incident angle of 37.6 °. % Of light intensity variation occurs, and together with the light intensity variation of 0.4% by the first diffractive optical unit 110, the light intensity variation of the entire diffractive optical element is 8.5% at maximum. Further, the ratio of the number of spots in the peripheral area and the central area on the screen is 0.215.

(Example 6)
Example 6 is a diffractive optical element shown in Example 6 in Tables 1-4, the diffraction angle theta ₂ of the diffraction angle theta ₁ and the second diffractive optical portion 120 of the first diffractive optical portion 110 is theta ₁ ≦ theta ₂ is satisfied, and the number n _{1 of} spots generated by the first diffractive optical unit 110 and the number of spots n ₂ generated by the second diffractive optical unit 120 satisfy n ₁ ≦ n ₂ . A basic unit of the first diffractive optical section 110 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 22B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 23B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion. Diffracted light generated by the design on the screen at a position of 554.3 mm among the light transmitted through the first diffractive optical element 110 and the second diffractive optical part 120 of the first embodiment. The light spot distribution is shown in FIG.

  The first diffractive optical unit 110 emits a light beam in a diffraction angle range of 2.6 °. As shown in Table 4, the second diffractive optical unit 120 generates 3.0 light beam with respect to an incident angle of 2.6 °. % Of light intensity variation occurs, and together with the light intensity variation of 0.5% by the first diffractive optical unit 110, the light intensity variation of the maximum diffractive optical element is 3.1%. The ratio of the number of spots in the peripheral area and the central area on the screen is 0.768.

(Example 7)
Example 7 is a diffractive optical element shown in Example 7 in Table 1-4, the diffraction angle theta ₂ of the diffraction angle theta ₁ and the second diffractive optical portion 120 of the first diffractive optical portion 110 is theta ₁ ≦ theta ₂ was filled, in the case where the number of spots _{n 2} generated by the spot number _{n 1} and a second diffractive optical portion 120 generated by the first diffractive optical portion 110 satisfies _{n 1} ≦ _{n 2,} the first diffractive optical portion An example is shown in which 110 and the second diffractive optical part 120 are each composed of two stages of diffractive parts. The projection patterns emitted from the first diffractive optical part 110 and the second diffractive optical part 120 are symmetrical with respect to the 0th-order diffracted light. A basic unit of the first diffractive optical section 110 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 25B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed on the back surface of the substrate on which the first diffractive optical part is formed by photolithography and etching so that the pitches P _x and P _y , the number of diffractive part stages, and the height of one stage shown in Table 2 are obtained. FIG. 26B shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion. Diffracted light generated by the design on the screen at a position of 554.3 mm among the light transmitted through the first diffractive optical element 110 and the second diffractive optical part 120 of the first embodiment. The light spot distribution is shown in FIG.

  The first diffractive optical unit 110 emits a light beam in a diffraction angle range of 2.6 °. As shown in Table 4, the second diffractive optical unit 120 performs 5.8 with respect to a light beam having an incident angle of 2.6 °. %, And a maximum of 5.8% of the light intensity variation of the entire diffractive optical element occurs together with the light quantity variation of 0.5% by the first diffractive optical unit 110. The ratio of the number of spots in the peripheral area and the central area on the screen is 0.768.

(Example 8)
Example 8 is a diffractive optical element shown in Example 8 in Table 1 to 3 and 5, the diffraction angle theta ₂ of the diffraction angle theta ₁ and the second diffractive optical portion 120 of the first diffractive optical portion 110 is theta ₁ An example is shown in which ≦ θ ₂ is satisfied, and the number of spots n ₁ generated by the first diffractive optical unit 110 and the number of spots n ₂ generated by the second diffractive optical unit 120 satisfy n ₁ ≦ n ₂ . A basic unit of the first diffractive optical section 110 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 28B shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light is vertically incident on such a diffractive portion.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 29B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion. Of the light transmitted through the first diffractive optical element 110 and the second diffractive optical part 120, the diffracted light generated by the design on the screen at a position of 342.8 mm. The light spot distribution is shown in FIG.

  The first diffractive optical unit 110 emits a light beam in a diffraction angle range of 3.5 °. As shown in Table 5, the second diffractive optical unit 120 has a light beam of 2.5 ° with respect to an incident angle of 3.5 °. % Of the light amount variation occurs, and together with the light amount variation of 0.5% by the first diffractive optical unit 110, the light amount variation of the maximum diffractive optical element is 2.5%. Further, the ratio of the number of spots in the peripheral area and the central area on the screen is 0.581.

(Comparative Example 1)
Comparative Example 1 is the diffractive optical element shown in Example 9 in Tables 1 to 4, where the diffraction angle θ ₁ of the first diffractive optical part and the diffraction angle θ _{2 of} the second diffractive optical part satisfy θ ₁ > θ ₂ . An example of the case when it satisfies is shown. FIG. 17A shows the basic unit of the first diffractive optical part. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 17B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion.

A basic unit of the second diffractive optical section 120 is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 16B shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 554.3 mm when the light is vertically incident on such a diffractive portion. FIG. 18 shows a light spot distribution of diffracted light generated by the design on the screen at a position of 554.3 mm among the light transmitted through the diffractive optical element of this comparative example.

  The first diffractive optical unit emits a light beam in a diffraction angle range of 25.9 °. As shown in Table 4, the second diffractive optical unit 120 is 8.3% with respect to the light beam having an incident angle of 25.9 °. In other words, the maximum diffractive optical element has a light amount variation of 8.3% in combination with the light amount variation of 0.4% by the first diffractive optical unit. Further, the ratio of the number of spots in the peripheral area and the central area on the screen is 0.538.

(Comparative Example 2)
Comparative Example 2 is the diffractive optical element shown in Example 10 in Tables _{1 to 3,} and the diffraction angle θ ₁ of the first diffractive optical part and the diffraction angle θ _{2 of} the second diffractive optical part are θ ₁ > θ. An example when ₂ is satisfied is shown. The basic unit of the first diffractive optical part is shown in FIG. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 1 are obtained. FIG. 20B shows the light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light enters the diffractive portion vertically.

FIG. 19A shows the basic unit of the second diffractive optical part. Such a basic unit is processed by photolithography and etching so that the pitches P _x , P _y , the number of diffractive part steps, and the height of one step shown in Table 2 are obtained. FIG. 19B shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm when the light is vertically incident on such a diffractive portion. FIG. 21 shows a light spot distribution of the diffracted light generated by the design on the screen at a position of 342.8 mm among the light transmitted through the diffractive optical element of this comparative example.

  The first diffractive optical unit emits a light beam in a diffraction angle range of 37.6 °, and as shown in Table 5, the second diffractive optical unit 120 has 14.9% of the light beam with an incident angle of 37.6 °. The light intensity variation of 14.9% at the maximum occurs in the entire diffractive optical element, together with the light intensity variation of 0.4% by the first diffractive optical unit. Further, the ratio of the number of spots in the peripheral area and the central area on the screen is 0.215.

Example 9
The diffractive optical elements of Examples 1 to 8 are used for the measuring device. By doing so, the variation in the amount of light can be reduced, and measurement can be performed with high accuracy. In addition, the amount of zero-order diffracted light generated by the second diffractive optical unit 120 can be suppressed, and image degradation due to strong diffracted light can be suppressed.

  From the above, the peripheral average / center and maximum / minimum values of the number of spots of the diffractive optical element in Examples 6 to 8 are the peripheral average / center and maximum / minimum of the number of spots of the diffractive optical element in Comparative Examples 1 and 2. The light spot distribution can be more uniformly distributed over the entire projection area. Further, compared to the diffractive optical elements in Comparative Examples 1 and 2, the diffractive optical elements in Examples 6 to 8 can suppress the occurrence of pincushion-type distortion.

  In addition, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention.

10 Measuring device 11 Luminous flux (incident light)
12 Diffracted light (emitted light)
20 Light source 30 Diffractive optical element 40a Measurement object 40b Measurement object 50 Imaging element 101 Optical axis 110 First diffractive optical part 111 Diffracted light group (by first diffractive optical part)
120 Second diffractive optical part 121a, 121b, 121c Diffracted light group (by first diffractive optical part and second diffractive optical part)
230 Diffractive optical element (becomes first diffractive optical part and second diffractive optical part)
231 Basic unit 232 Transparent substrate 233 Convex part

Claims (8)

A first diffractive optical unit that generates two-dimensional diffracted light with respect to incident light;
A second diffractive optical unit that generates two-dimensional diffracted light with respect to incident light;
Have
In either one or both of the first diffractive optical part and the second diffractive optical part, basic units are two-dimensionally and periodically arranged,
When diffracted light generated by entering light into the first diffractive optical part is incident on the second diffractive optical part and diffracted light is generated from the second diffractive optical part, 100 or more lights The number of spots can be obtained,
Wherein a _first diffraction angle theta in the first diffractive optical portion, the number of light spots of the diffracted light generated is a k _1, the diffraction angle in the second diffractive optical part is theta _2, generated If the number of light spots of the diffracted light is k _2,
θ ₁ ≦ θ ₂ and k ₁ ≦ k ₂
A diffractive optical element characterized by the above. A projection region of the light spot generated by the diffracted light generated by the first diffractive optical unit is overlapped by the second diffractive optical unit to form a projection region of the diffractive optical element;
Alternatively, the projection area of the diffractive optical element is formed by overlapping the projection area of the light spot by the diffracted light generated by the second diffractive optical section with the first diffractive optical section. The diffractive optical element described. The first diffractive optical portion is closed on one of the transparent substrate, the second diffractive optical portion diffractive optical element according to claim 1 or 2 which is closed on the other transparent substrate. The diffractive optical element according to claim 3 , wherein the one transparent substrate and the other transparent substrate are integrated. The first diffractive optical portion is closed on one surface of the transparent substrate, the diffraction of the second diffractive optical part according to any one of the four claims 1, which is closed on the other surface of the transparent substrate Optical element. When diffracted light generated by entering light into the first diffractive optical part is incident on the second diffractive optical part, the diffracted light generated from the second diffractive optical part has a diffraction angle of 30. The diffractive optical element according to any one of claims 1 to 5 , which includes at least °. When the diffracted light generated by entering light into the first diffractive optical part is incident on the second diffractive optical part, the light spot of the diffracted light generated from the second diffractive optical part is the center the diffractive optical element according to any one of claims 1 to 6, which distributed more in the peripheral portion than the portion. A light source that emits light;
A diffractive optical element according to any one of claims 1 to 7 in which diffracted light is incident the light is emitted,
An imaging unit that captures an image of the measurement object irradiated with the diffracted light;
A measuring apparatus comprising:

Images