TW201839430A - Diffractive optical element - Google Patents

Abstract

Provided is a diffractive optical element capable of further reducing zero-order diffraction light. This diffractive optical element 10 comprises a diffraction layer 15 including: a high refractive index part 11 in which a plurality of projections 11a are arranged side by side in a cross-sectional shape; and a low refractive index part 14 that has a lower refractive index than the high refractive index part 11 and that includes a recess 12 formed at least between the projections 11a. The projections 11a have a sawtooth shape or a shape that imitates a sawtooth shape by a multi-stage outline shape. An inclined plane that is inclined with respect to a sheet surface of the diffractive optical element 10, which has a sawtooth shape or a sawtooth shape imitated by a multi-stage outline shape, has a concave curved plane that is concave toward the projections 11a.

Description

Diffractive optical element

This invention relates to a diffractive optical element.

In recent years, the demand for sensor systems for the need for personal authentication to avoid the security risks of network popularization, the autopilot process of automobiles, or the so-called "Internet of Things" has expanded. There are various types of sensors, and there are various kinds of information for detection. However, as one of the methods, there is a method in which light is irradiated from the light source and the light is self-reflected. For example, an example thereof is a pattern authentication sensor or an infrared radar. The light source of the sensors uses a wavelength distribution or a brightness and a breadth corresponding to the use. The wavelength of light is often used from visible light to infrared light. In particular, infrared light is widely used because it is not easily affected by external light and is invisible, and can also observe the slight internal characteristics of the object. Further, as a type of light source, an LED (Light Emitting Diode) light source or a laser light source or the like is often used. For example, when detecting a distant location, it is appropriate to use a laser light source with a small breadth of light, and use it when detecting relatively close places or when irradiating an area having a certain extent. LED light source. However, the size or shape of the irradiation region as the object is not necessarily limited to the extent (distribution) of the light from the light source. In this case, it is necessary to shape the light by a diffusion plate, a lens, a shielding plate, or the like. Recently, a diffusion plate called a Light Shaping Diffuser (LSD) that can shape the shape of light to some extent is being developed. Further, as another method of shaping light, a diffractive optical element (DOE) can be cited. It applies a diffraction phenomenon when light passes through a place where materials having different refractive indices are periodically arranged. The DOE system is basically designed for a single wavelength of light, but in theory it can be photoformed into almost any shape. Further, in the LSD, the light intensity in the irradiation region is Gaussian, and 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 that it is possible to reduce the size of the device due to the increase in efficiency of the irradiation of the unnecessary area or the reduction in the number of light sources (see, for example, Patent Document 1). Moreover, the DOE can be applied to any of a parallel light source such as a laser or 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. When the DOE is used to uniformly illuminate light to a specific region, there are cases where the diffracted light 0 is concentrated, for example, in the vicinity of the center of the irradiation region. This tendency is enhanced especially when the light source is a laser. Previously, if you want to reduce the diffracted light by 0 times, the required diffracted light will also be reduced. Therefore, it is required to reduce the amount of diffracted light required for one time while reducing the number of diffracted lights by 0 times. By blazing the lattice surface of the DOE, a specific wavelength can be efficiently and efficiently circulated with a certain number of times, and it has been previously constructed by mimicking the sawtooth shape by a stepped multi-order shape (for example, patent document) 1). However, if only the shape of a blaze is used, there are still many unnecessary diffracted lights, and it is expected that the diffracted light will be reduced by 0 times. [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Laid-Open No. 09-230121

[Problem to be Solved by the Invention] An object of the present invention is to provide a diffractive optical element which can further reduce 0-order diffracted light. [Technical means for solving the problem] The present invention solves the above problems by the following solution. In addition, for the sake of easy understanding, the symbols corresponding to the embodiments of the present invention are described, but the present invention is not limited thereto. The first invention is a diffractive optical element (10) which is shaped to light and has a diffraction layer (15) having a high refractive index portion (11) arranged side by side. a plurality of convex portions (11a); and a low refractive index portion (14) having a refractive index lower than the high refractive index portion (11) and including at least a concave portion formed between the convex portions (11a) (12) The convex portion (11a) has a multi-step shape formed by a plurality of steps different in height, and the high refractive index portion (11) has the largest area per unit area and the deepest surface, and the uppermost surface The area of the first order is the smallest. According to a second aspect of the invention, in the diffractive optical element (10) of the first aspect of the invention, the area of the uppermost surface of the high refractive index portion (11) is 0.6 to the area of the lowermost surface of the high refractive index portion. 0.9 times. According to a third aspect of the present invention, in the diffractive optical element (10) according to the first or second aspect of the present invention, the high refractive index portion (11) is one step from a deepest surface to a lowermost surface per unit area. On the other hand, the area of each step is gradually reduced. The fourth invention is a diffractive optical element (10) which is shaped to light and has a diffraction layer (15) having a high refractive index portion (11) in a cross section a plurality of convex portions (11a) are arranged side by side in the shape; and a low refractive index portion (14) having a refractive index lower than the high refractive index portion (11) and including at least between the convex portions (11a) a concave portion (12); the convex portion (11a) has a zigzag shape or a shape obtained by mimicking a zigzag shape by a multi-step contour shape, and the winding shape is imitated with respect to a sawtooth shape or a contour shape that is mimicked by a multi-step contour shape The inclined surface of the sheet surface of the incident optical element (10) has a concave curved surface that is recessed toward the convex portion (11a). According to a fifth aspect of the present invention, in the diffractive optical element (10), the convex portion (11a) has a plurality of steps different in height from at least one side of the side surface shape to mimic the sawtooth shape. The multi-step shape is formed, and the concave curved surface is simulated according to at least one of the height and the width of the step portion. According to a sixth aspect of the present invention, in the diffractive optical element according to the fourth or fifth aspect of the present invention, the convex portion has a plurality of steps different in height from at least one side of the side shape to imitate the zigzag shape. The shape of the step, and in the unit area, the area of the deepest surface is the largest, and the area of the first step below the uppermost surface is the smallest. According to a seventh aspect of the present invention, in the diffractive optical element (10) of the fifth aspect or the sixth aspect, the height of each step of the step portion is fixed, and the concave shape is mimicked according to a portion of the width of the step portion. Surface. According to a seventh aspect of the present invention, in the diffractive optical element (10), the x-axis is set such that the direction in which the convex portion (11a) is arranged in parallel, and the direction in which the inclined surface is raised is set to the positive x-axis. The direction is set to the y-axis orthogonal to the sheet surface of the diffractive optical element (10), and the direction in which the convex portion (11a) protrudes is set to the positive direction of the y-axis, and the front end of the convex portion (11a) is included The total order of the step obtained by the inner count is set to L, and the reduction rate of the width of each step is set to f, and the lowest position of the concave portion (12) is set as the order of the step of the object when the count is 0. For lv, the height of each step of the above step is set to a fixed value by h, and when the width ratio of the step 0 is set to C, the profile of the concave curved surface imitated by the multi-order shape becomes the order 0. The curve of the concave apex and the trajectory of each convex portion is set to S, and the ratio of the x coordinate to the pitch is set to S, and x'=0.5×f×lv ² +C×lv S=P/{tw+Σx'i} When Σ is set to i=0 to L-1, the top x and y coordinates of the step shape are represented by x=0.5×f×lv ² +C×lvy=lv×h. The diffractive optical element (10) according to any one of the first to eighth aspects of the present invention, characterized in that the high refractive index portion (11) forms a diffraction grating having a self-forming unevenness When viewed in the normal direction of the surface of the shape, the boundary between the convex portion (11a) and the concave portion (12) includes a pattern of at least one of a curved line and a polygonal line connecting a plurality of line segments. The diffractive optical element (10) according to any one of the first to eighth aspects of the present invention, characterized in that the high refractive index portion (11) forms a grating element array type (also referred to as "Grating Cell Arry type" Or a diffraction grating of the "GCA type", the diffraction grating pattern of the grating element array is formed by tiling a unit cell in which the same uneven shape is arranged side by side in the normal direction of the surface on which the uneven shape is formed. Made of a grid pattern. [Effects of the Invention] According to the present invention, it is possible to suppress a decrease in the diffraction efficiency of primary light and to reduce zero-order light.

Hereinafter, the best mode for carrying out the invention will be described with reference to the drawings and the like. (Embodiment) FIG. 1A is a plan view showing an example of a diffractive optical element in which a concave-convex shape of a diffraction grating obtained from a normal direction of a sheet surface is formed into a regular or irregular pattern including a curved line at a boundary between a convex portion and a concave portion. In the present embodiment, as an example, it can be applied to a diffractive optical element having a pattern of irregularities in an irregular shape as shown in Fig. 1A. In the following description, the diffractive optical element of the type shown in Fig. 1A is also referred to as an irregular type. However, there is also a case where the irregular pattern is a regular pattern by diffracting the target emission pattern of the optical element, and therefore the irregular type is referred to as a convenient name, and is not limited to the irregularity. Further, in FIG. 1A, the irregular pattern includes a curved line, but there is also a case where a pattern including a broken line which is formed by connecting a target emission pattern of the optical element to a straight line or connecting a line segment including a curved line is present. Therefore, the pattern of the irregular type diffraction grating is viewed from the normal direction of the surface on which the concave-convex shape of the high refractive index portion (described below) is formed, and the boundary between the convex portion and the concave portion includes a curve and connects a plurality of line segments. At least one of the broken lines. 1B is a view showing an example of a diffractive optical element in which a concave-convex shape of a diffraction grating obtained from a normal direction of a sheet surface is formed in a lattice pattern in which a plurality of unit cells of the same uneven shape are arranged side by side. Top view. In the present embodiment, as another example, it is applicable to a diffractive optical element in which a lattice pattern in which a plurality of unit cells having the same uneven shape are arranged side by side is formed as shown in FIG. 1B. In the following description, the diffractive optical element of the type shown in FIG. 1B is also referred to as a Grating Cell Array type or a GCA type. A grating element array type diffractive optical element is formed in each unit cell, and the direction and angle of the light diffracted by the diffraction grating are different, and the desired optical characteristics are obtained by tiling a large number of unit cells. Diffractive optical element. In the grating element array type diffractive optical element, the high refractive index portion is divided into a lattice shape as viewed from the normal direction of the surface on which the uneven shape is formed, and the same shape extending in a specific direction in the interval The convex portions are arranged side by side in a direction orthogonal to the specific extending direction, and the width and the extending direction of the convex portions are different in each of the sections. Fig. 2A is a perspective view showing an example of a partial periodic structure in an example of the irregular type diffractive optical element shown in Fig. 1A. Fig. 2B is a perspective view showing an example of a partial periodic structure in the example of the GCA type diffractive optical element shown in Fig. 1B. Figure 3 is a cross-sectional view showing the diffractive optical element cut off at the position of arrow G-G' in Figure 2A. In the following description, since it is necessary to explain the cross-sectional shape peculiar to the GCA type, the irregular type is mainly described as an example. However, the GCA type has the same cross-sectional shape as it is cut at the position of the arrow G-G' shown in Fig. 1A, and the present invention can be applied similarly as described above. Figure 4 is a diagram illustrating a diffractive optical element. In addition, each of the drawings shown below is schematically shown in FIG. 1, and the size and shape of each part are appropriately exaggerated for easy understanding. In the following description, specific numerical values, shapes, materials, and the like are described, but these may be appropriately changed. Furthermore, the shapes or geometric conditions used in the present invention, and the terms that specify such degrees, such as "parallel", "orthogonal", "identical", or the length or angle, are not limited. In the strict sense, the scope of the extent to which the same function can be expected is explained. Further, in the present invention, the term "shaping the light" means that the shape (irradiation region) of the light projected on the object or the target region has an arbitrary shape by controlling the traveling direction of the light. For example, as shown in the example of FIG. 4, the light source unit 210 is prepared, and the light source unit 210 is emitted as a circular light 201 when the light is projected onto the screen 200 of the planar shape (FIG. 4(b)). By passing the light 201 through the diffractive optical element 10 of the present invention, the target region of the irradiation region 204 such as a square (Fig. 4(a)) or a rectangle or a circle (not shown) is called "optical light". Perform plastic surgery." Further, by combining the light source unit 210 and the diffractive optical element 10 of the present embodiment in which at least one position of the light emitted from the light source unit 210 passes, it is possible to shape the light. A light irradiation device that is in a state of illumination. Further, in the present invention, the term "transparent" means that at least the light of the wavelength used is transmitted. For example, even if the visible light is not transmitted, if the infrared ray is transmitted, it is treated as transparent when it is used for infrared ray use. The diffractive optical element 10 of the present embodiment is a diffractive optical element (DOE) that shapes light. The diffractive optical element 10 is designed, for example, in such a manner that light is diffused into a cross shape for light from a light source unit 210 that emits light having a wavelength of 500 nm, specifically, for example, the light is diffused to within ±50 degrees. A shape in which two strips of light having a width of ±3.3 degrees are crossed. The diffractive optical element 10 of the present embodiment has different depths at positions A, B, C, and D shown in FIGS. 1A and 1B. That is, the diffractive optical element 10 is constituted by a multi-step shape having different heights of four stages. Further, the diffractive optical element 10 generally has a plurality of regions (partial periodic structures: for example, E and F regions in FIGS. 1A and 1B) having different periodic structures. In FIGS. 2A and 2B, an example of a partial cycle structure is extracted. As shown in FIG. 3, the diffractive optical element 10 is provided with a high refractive index portion 11 in which a plurality of convex portions 11a are arranged side by side in a cross-sectional shape. In the GCA type diffractive optical element, the high refractive index portion 11 maintains the same cross-sectional shape and extends directly in the depth direction of the cross section. On the other hand, in the irregular type of diffractive optical element, when the cross-sectional position is changed, the cross-sectional shape is changed, and the diffraction gratings having various cross-sectional shapes are arranged in a large number. Further, in the irregular type, a specific cross-sectional structure for performing a specific cross-section of the shape of the diffraction grating, that is, a diffraction grating for affecting the diffraction phenomenon of the diffracted light, must be set to The cross-sectional structure in the cross section cut in the direction orthogonal to the line (curve or line) drawn by the boundary between the convex portion and the concave portion when viewed from the normal direction of the sheet surface. The high refractive index portion 11 can also be treated by etching, for example, on quartz (SiO ₂ , synthetic quartz) is formed by processing. Further, the high refractive index portion 11 may be formed by collecting a shape of an object processed by quartz to form a molding die, and the free radiation curable resin composition may be cured by the molding die. There are various methods for producing an object of such a periodic structure using an free radiation curable resin composition, and the high refractive index portion 11 of the diffractive optical element 10 can be suitably produced by such known methods. Further, air is present in the upper portion of FIG. 3 including the space 13 formed near the top of the concave portion 12 and the convex portion 11a between the convex portions 11a, and the low refractive index portion 14 having a lower refractive index than the high refractive index portion 11 is formed. The diffraction layer 15 having a function of shaping light is configured by a periodic structure in which the high refractive index portions 11 and the low refractive index portions 14 are alternately arranged in parallel. The convex portion 11a has a multi-step shape of four step portions having different heights on one side of the side surface shape (the left side in FIG. 3). Specifically, the convex portion 11a has the most prominent step 3 step portion 11a-3 on one side surface side, the lower order third step portion 11a-3, the lower order second order portion 11a-2, and the more order second step portion 11a- 2, further, the first-order portion 11a-1 of the first-order lower order and the first-order portion 11a-1 of the first-order portion, and the lower-order first-order portion 11a-0. Further, the other side (the right side in FIG. 3) of the side surface shape of the convex portion 11a is a side wall portion 11b which is connected in a straight line from the step 3 step portion 11a-3 to the step 0 step portion 11a-0. Here, the convex portion 11a of the present embodiment is shaped by imitating a zigzag shape by a multi-step contour shape, and is inclined with respect to a sheet surface of the diffractive optical element 10 which is imitated by a multi-step contour shape. The slope has a concave curved surface that is recessed toward the convex portion 11a. Here, the "simulation of the contour shape by a plurality of steps" means that the concave curved surface is pseudo-constructed by the line connecting the corner portions of the respective step portions. However, the present invention is not limited to the corner portion, and may be a connection step. The line between the center of the part can also be the line connecting the side parts. Further, the statement of "imitation" means that the concave curved surface is pseudoscopically formed. In the present embodiment, the macroscopic view shows a concave curved surface, and the microscopic view shows a stepped shape. Another expression can also be "approximate". In the example described so far, the fourth-order form has been described. Therefore, it is a form that is relatively roughly imitated, and if it is set to the following order of 16 or more, it can be more accurately imitated. The shape. Fig. 5 is a view for explaining a concave curved surface of the convex portion 11a in the diffractive optical element 10. Fig. 6A is a view showing the diffraction optical element 10 of the present embodiment in comparison with the prior art. Fig. 6A(a) shows a cross section obtained by cutting the previous diffractive optical element at the position of the arrow HH in Fig. 6A(b). Fig. 6A(b) is a plan view of the prior diffractive optical element viewed from the normal direction of the sheet surface. Fig. 6A(c) is a plan view of the diffractive optical element 10 of the present embodiment as seen from the normal direction of the sheet surface. Fig. 6A(d) is a view in which Fig. 6A(b) and Fig. 6A(c) are superimposed. In the prior diffractive optical element, as shown by the two-dot chain line in Fig. 5, the depth (height) of each step of each step is fixed, and the width is also fixed. Therefore, in the cross section shown in FIG. 5, the slope L0 in which the corner portions of the respective step portions of the previous diffractive optical element are connected is a plane (a straight line in the cross section). On the other hand, in the diffractive optical element 10 of the present embodiment, the inclined surface L in which the corner portions of the respective step portions are connected is a concave curved surface that is recessed toward the convex portion 11a (a concave curved line in the cross section). In order to simulate the concave curved surface, the depth (height) of each step portion may be changed, the width of each step portion may be changed, or the two may be combined. However, in consideration of a manufacturing method of manufacturing a step by etching, the method of manufacturing the most simple is a method of changing the width of each step. Therefore, in order to simulate the concave curved surface, the diffractive optical element 10 of the present embodiment gradually narrows the width of each step portion as the depth of the concave portion becomes shallower. Therefore, as shown in FIGS. 5 and 6, the width of the convex portion 11a is narrowed as a whole. In the irregular type of diffractive optical element 10, as shown in FIG. 1A, the line drawn by the boundary between the convex portion and the concave portion is designed to have a large portion of the curve. Further, as described above, the cross-sectional structure that affects the optical characteristics of the diffractive optical element is a cross-sectional structure in a cross section in a direction orthogonal to the curve (normal direction). However, in the actual diffractive optical element 10, a polygonal line shape in which a straight line shape is formed, in particular, a straight line in two directions orthogonal to each other as shown in FIG. 6A is formed, so that the boundary between the convex portion and the concave portion is made. The shape of the line drawn is similar to the shape of the curve. It depends mainly on the manufacturing situation. In this case, if the cross-sectional structure shown in FIG. 5 is studied in a cross section cut as shown, for example, in FIG. 6A(a), the width of each step is affected by the cutting position and is assumed to be a cross section as compared with the original one. The width of the study was widened or narrowed so that the correct study could not be performed. Fig. 6B is a view in which the curve of the original design pattern is superimposed on the graph of Fig. 6A. 6B(b) is a diagram in which the curve of the ideal design pattern is superimposed on FIG. 6A(b), and FIG. 6B(c) is a diagram in which the curve of the ideal design pattern and the curve of the design pattern of the embodiment are overlapped with FIG. 6A (c). ) on the map. Further, in Fig. 6B(c), the solid line is a curve of an ideal design pattern, and the broken line is a curve of the design pattern of the embodiment. The case where the width of each step portion is gradually narrowed as the depth of the concave portion becomes shallow is clearly shown in FIG. 6B. In this way, when the width of each step portion is studied in the actually fabricated diffractive optical element, as shown in FIG. 6B, the curve of the design is obtained by connecting the curve of the vertex, and the cross section in the direction orthogonal to the curve is obtained. It is important to study the shape or width dimension. In the description so far, an example of a multi-order shape of the fourth order is shown, but the order may be more. Fig. 7 is a view showing a diffractive optical element 10 having a multi-order shape of 8th order. If the order is increased as described above, the accuracy of imitating the concave curved surface becomes high. Here, the slope of the sawtooth shape is a shape in which a concave curved surface is formed, and the shape of the curved surface is described. Fig. 8 is a view showing a curve and a multi-order shape in a cross section of a concave curved surface. Set the xy orthogonal coordinates as shown in Figure 8. In other words, the x-axis is set to the direction in which the convex portions 11a are arranged side by side, the direction in which the inclined surface is raised is set to the positive direction of the x-axis, and the y-axis orthogonal to the sheet surface of the diffractive optical element 10 is set, and the convex portion 11a is protruded. The direction is set to the positive direction of the y-axis. The total order of the steps obtained by counting the front end including the convex portion 11a is set to L. Further, the reduction rate of the width of each step is set to f. Further, the order of the step portion of the object when the lowest position of the concave portion is 0 is lv, and the height of each step of each step is set to h and is set to a fixed value, and the width ratio of the step 0 is defined as C. Thus, the curve in the cross section of the concave curved surface imitated by the multi-order shape (the curve which becomes the trajectory of the concave apex of the step 0 and the apex of each convex portion) is represented by the following equation. Set the ratio of the x coordinate to the spacing to S, x'=0.5×f×lv ² +C×lv S=P/{tw+Σx'i} When =0 is set to i=0 to L-1, the top x and y coordinates of the step shape are expressed as follows. x=S×(0.5×f×lv ² +C×lv) y=lv×h Furthermore, when the order of the multi-order shape is set to n and the width of the uppermost step is set to tw, the pitch is 0.5×f×(n-1)2+C×( N-1)+tw is standardized. Further, the width ratio C of the step 0 indicates the ratio of the width of the step 0 which is the lowest position of the concave portion to the width of each step when the width of each of the previous step portions is fixed. Here, regarding the height of each step of each step is h, a good result can be obtained by setting h=ht×1.05 to h=ht×1.15 with respect to the theoretical value ht. Furthermore, the theoretical value ht = wavelength / {level number (refractive index - 1)}. Further, the widths d0 to d7 of the respective levels are defined in the ratio of the pitch as follows. Di=C+i×f where i is an integer from 0 to 6. Here, f<0. Further, in the diffractive optical element having a maximum diffraction angle of 10 or more, -20 ≤ C / f ≤ -6, preferably -16 ≤ C / f ≤ -10.5 - 0.0275 ≤ f ≤ -0.0125 When 0.13 ≤ C ≤ 0.4, when C is in this range, it is more preferably -0.0225 ≤ f ≤ -0.0125. When the ratio of the width of the uppermost position to the width of the 0 level which is the deepest surface is t, it is preferable that 0.5 ≤ t ≤ 0.9 and 0.6 ≤ t ≤ 0.8. Hereinafter, a specific example will be exemplified. Fig. 9 is a view showing a specific example of the cross-sectional shape of the eighth step. The values of x' and y are collectively shown in the table below in FIG. The x' indicates the lateral position of the top portion when the cross section of the step structure is observed, and y indicates the longitudinal position, which is the coordinate data (vertex coordinates) of the cross-sectional shape (step structure) shown as a graph in FIG. Furthermore, in the following figures, the values in the tables together with the graphs represent the coordinate data in the graph. In the example of Fig. 9, the wavelength is 850 nm, the pitch is 3284 nm (the diffraction angle is 15°), 8 level, f=-0.02, C=0.25, t=0.8, h=850/8*1.1*(n). -1), n = 1.5. In this case, it becomes C/f = -12.5. According to x'=0.5×f×lv ² +C × lv, the width from 0 level to the highest level becomes 1.4542, and the width of each level becomes the width derived from the value of x × 3284 / 1.4542. At this time, the zero-order light intensity is sufficiently small to 0.15776%. Fig. 10 is a view showing a specific example of the cross-sectional shape of the fourth order. The values of x and y are collectively shown in FIG. In the example of Fig. 10, the wavelength is 850 nm, the pitch is 3284 nm (the diffraction angle is 15°), 4 level, f=-0.02, C=0.2, t=0.8, h=850/4*1.1 (n- 1.0), n=1.5. In this case, it becomes C/f=-10. According to x'=0.5×f×lv ² In the formula of +C × lv, the width from 0 level to the highest level becomes 0.662, and the width of each level becomes the width × 3284/0.662 derived from the value of x. The zero-order light at this time is sufficiently small as 0.2803%. Then, the above-described embodiments and comparative examples were actually produced, and the results obtained by actually measuring the intensity of the 0-time diffracted light were shown. Fig. 11 is a view showing a method of measuring the intensity of 0-time diffracted light. When measuring the intensity of the 0-order diffracted light, first, as shown in FIG. 11(a), after the light of a specific wavelength emitted from the light source LS is passed through the diffractive optical element 10, only the 0-throwing light is made by the aperture AP. The light passing through the specific range reaches the sensor S, and the strength when the diffractive optical element 10 is present is measured by the power meter M. Then, as shown in Fig. 11 (b), only the diffractive optical element 10 is removed from the state of Fig. 11 (a), and the intensity at the time of the absence of the diffractive optical element 10 is measured. The intensity of the 0-time diffracted light can be obtained by (the intensity in the case where the optical element 10 is diffracted) / (the intensity in the case where the optical element 10 is not diffracted). Further, the light source LS used for the measurement is set to two types of a laser light source and a halogen light source, and the wavelength is set to 850 nm. The intensity of the 0-time diffracted light was measured for the diffractive optical element 10 of the present invention by the above method. Further, as the diffractive optical element 10 of the present invention, the four levels shown in Figs. 3 and 5 and the eight levels shown in Figs. The height of each of the four levels of the diffractive optical element 10 of the present invention is h = 470 nm. This value is equivalent to h = ht x 1.106. Further, it is assumed that C = 0.1825 and f = -0.02. Further, since the pitch is various as shown in FIG. 1 and FIG. 6, it is difficult to specify. Further, in the diffractive optical element 10 of the present invention, the line connecting the respective step portions has a concave curve in the cross section. Further, in order to compare with the diffractive optical element 10 of the present invention, the comparative example also prepares a 4-level product and an 8-level product. Fig. 12 is a view showing a diffraction optical element of a comparative example. As a comparative example, as shown in FIG. 12, the line connecting the respective step portions is a straight line in the cross section. Further, regarding the comparative example, two types of 4 levels and 8 levels are also prepared. The height h of each step is set to be the same as that of the present invention. Fig. 13 is a graph showing the results of measuring the intensity of 0-time diffracted light for the diffractive optical element 10 of the present invention and a comparative example. In Fig. 13, the data indicated by the circular mark and the square mark indicates the data of the laser light source, and the data indicated by the curve indicates the data of the halogen light source. As shown in Fig. 13, whether it is a laser light source or a halogen light source, the intensity of the 0-time diffracted light of the present invention is greatly reduced as compared with the comparative example. Therefore, it has been confirmed in the actual product that if the portion corresponding to the inclined surface of the sawtooth shape is formed as a concave curved surface, the intensity of the diffracted light of 0 times can be reduced. Then, a simulation was performed in order to study the effects of the present invention in more detail. The analytical simulation of diffraction efficiency uses rigorous coupled-wave analysis (RCWA). RCWA is mathematically attributed to solving the eigenvalue problem of the matrix and the first-order equation, so there is no principle difficulty. In the simulation results and actual reality based on the electromagnetic field analysis of the RCWA, if the shape errors or the like in the present object are excluded, they are basically identical. Furthermore, the simulation does not take into consideration the three-dimensional shape as shown in FIG. 2A. The calculation is performed by setting one dimension as shown in Fig. 2B to the infinite length. The simulation is performed under the following conditions: Wavelength: 850 nm Refractive index of the high refractive index portion n: 1.5 Low refractive index portion Refractive index: 1.0 Pitch: 2 μm, 2 μm of two orders: 8 level As a comparative example, first, the height ht=212.5 nm whose height is the theoretical value of each step is set as Comparative Example 1. The height h = ht × 1.106 = 235 nm of each step is set as Comparative Example 2. The height h = ht × 1.106 = 235 nm is the same as that used previously for the measurement. Also, the equivalent of the bevel of the present invention Part of the concave surface For example, two types of preparations are prepared. First, the width of the deeper portion is formed in the same manner as the previous actual measurement, and the width is set to be the same as in the first embodiment. Further, the width is not changed and the height of the deep portion is adjusted. The form in which the portion corresponding to the inclined surface is a concave curved surface is reduced to the second embodiment. Fig. 14 is a view showing the shape of the second embodiment in which the height of each step is changed. 14 The height of each step is changed, and the concave surface can also be simulated. Figure 15 is a summary of the results of the simulation. In the simulation, the reference value is also obtained for the first diffracted light. As a result, as long as the portion corresponding to the slope becomes a concave curved surface, the diffracted light can be greatly reduced by 0. Further, the order (level number) when the sawtooth shape is pseudo-reproduced by the multi-order shape is not limited to Fig. 16 is a diagram showing an example of simulating a sawtooth shape in a 16th order. Further, if the order is increased, a smoother slope can be obtained, and the degree can be regarded as substantially no step. Person, that is, essentially regarded as a curved surface. According to the above As a result of measurement and simulation, it can be said that even in the case of a smooth slope, if the slope is a concave curved surface, the intensity of the diffracted light of 0 times can be reduced. Then, the width change rate C for the order 0 is expressed. The simulation results are explained by the influence of the ratio of the decrease rate f of the width of each step and the width of the uppermost layer. (8-level) The wavelength is set to 850 nm, and the refractive index of the diffractive optical element is set to 1.5. The results of the simulation of the 8-level structure represented by the equation are shown in Fig. 17 to Fig. 19. The theoretical value of the height of each step becomes ht = 212.5 nm, and is set to 223.125 nm of h = ht × 1.1. The ratio of the uppermost level (level-7) to the width of the lowest level (level-0). The formula is the same as the above formula, and the following formula is used. Set the ratio of the x coordinate to the spacing to S, x'=0.5×f×lv ² +C×lv S=P/{tw+Σx'i} When =0 is set to i=0 to L-1, the top x and y coordinates of the step shape are expressed as follows. x=S×(0.5×f×lv ² +C×lv) y=lv×h Fig. 17 is set to f=-0.02, t=0.8, and is set to zero-order light when C is changed when the diffraction angle of the diffraction grating becomes 15° at 3284 nm. A graph of the intensity. It is found that in the case of 0.21 ≤ C ≤ 0.40, the zero-order light is low and becomes 0.5% or less. Fig. 18 is a graph showing the zero-order light intensity when f is changed when the diffraction angle of the diffraction grating is 15° at a distance of 3284 nm. It is found that when -0.0225 ≤ f ≤ -0.0125, the zero-order light is low and becomes 0.5% or less. Fig. 19 is a graph showing the zero-order light intensity when t is changed when the diffraction angle of the diffraction grating becomes a 3284 nm pitch at a diffraction angle of 15°. It is found that when t is from 0.5 to 0.9, the zero-order light is small and becomes 0.5% or less. Based on these results, an appropriate range of C/f in the 8-level can be obtained. Here, the range in which the zero-order light intensity is 1% or less is set to an appropriate range of C/f. From the result of Fig. 17, it is found that in the case of 0.18 < C, the zero-order light becomes 1% or less. In the example of Fig. 17, f = -0.02, so it is preferable to set C/f &lt; -9. Further, as is clear from the results of Fig. 18, in the case of -0.0275 < f < - 0.005, the zero-order light becomes 1% or less. In the example of Fig. 18, C = 0.25, so it is preferable to set -50 < C / f < -9. As a range shared by the two ranges, an appropriate range of C/f in 8-level is -50 < C/f < -9. (4-level) The results obtained by simulating the structure of the 4-level represented by the following equation when the wavelength is 850 nm and the refractive index of the diffractive optical element is 1.5 are shown in Figs. 20 to 22 . The theoretical value of the height of each step becomes ht = 425 nm and is set to 467.5 nm of h = ht x 1.1. t is the ratio of the width of the uppermost level (level-3) to the lowest level (level-0). The formula is the same as the above formula, and the following formula is used. Set the ratio of the x coordinate to the spacing to S, x'=0.5×f×lv ² +C×lv S=P/{tw+Σx'i} When =0 is set to i=0 to L-1, the top x and y coordinates of the step shape are expressed as follows. x=S×(0.5×f×lv ² +C × lv) y = lv × h Fig. 20 is a f--0.02, t = 0.8, and is set to the zero-order light intensity when C is changed when the diffraction angle of the diffraction grating becomes 15° at a distance of 3284 nm. The graph. It is found that in the case of 0.13 ≤ C ≤ 0.33, the zero-order light is low and becomes 0.5% or less. Fig. 21 is a graph showing the zero-order light intensity when f is changed when C = 0.18 and t = 0.8 are set and the diffraction angle of the diffraction grating is 15° at a distance of 3284 nm. It is found that when -0.0275 ≤ f ≤ -0.0125, the zero-order light is low and becomes 0.5% or less. Fig. 22 is a graph showing the zero-order light intensity when t is changed when the diffraction angle of the diffraction grating is 15° at a distance of 3284 nm, which is set to f = -0.02 and C = 0.18. It is found that when t is 0.3 to 0.9, the zero-order light is small and becomes 0.5% or less. Based on these results, an appropriate range of C/f in 4-level can be obtained. Here, the range in which the zero-order light intensity is 1% or less is set to an appropriate range of C/f. As is clear from the results of FIG. 20, in the case of 0.1 < C, the zero-order light becomes 1% or less. In the example of Fig. 20, f = -0.02, so it is preferable to set it to -5 < C/f. Moreover, as is clear from the result of FIG. 21, when f<0, the zero-order light becomes 1% or less. In the example of Fig. 21, C = 0.18, and therefore the range of C/f cannot be obtained based on the condition of f < 0, and any value can be obtained under the condition. As a range shared by the two ranges, an appropriate range of C/f in 4-level is -5 < C/f. As described above, the appropriate range of C/f in 8-level is -50 < C/f < -9, and the appropriate range of C/f in 4-level is -5 < C/f. Therefore, as a range shared by the above, -5 < C/f < -9 can be set to an appropriate range of C/f. Here, if attention is paid to the reduction rate f, the reduction rate f has an inverse proportional relationship of C/f. Therefore, if the above range is rewritten so that the reduction rate f becomes a molecule, it is preferably in the range of -0.2 < f / C < -0.1. The reduction rate f is the reduction rate of the width of each step, and is a value without dimension. Further, it is considered that if C is fixed, the rate of change of the area is preferably within the above range. Therefore, the reduction rate of the area reduction of each step portion is preferably in the range of -5% or more and -20% or less. Further, it is considered that, in the 8-level, it is preferable that t is 0.5 to 0.9 in the 8-level, and it is considered that t is preferably 0.3 to 0.9 in the 4-level according to Fig. 22 . t is the ratio of the width of the uppermost level (level-3) to the lowest level (level-0). Therefore, it can be said that the area of the uppermost surface of the high refractive index portion is preferably 0.5 to 0.9 times the area of the lowermost surface of the high refractive index portion. Next, a diffractive optical element having a configuration in which a trajectory connecting the apex of the present invention is a concave curved surface, a diffractive optical element having a configuration in which a apex of a theoretical structure is linearly arranged, and a connection opposite to the present invention The results of the simulation of the comparison of the diffractive optical elements in which the trajectory of the apex is a convex curved surface are shown in Figs. 23 to 25 . In the simulations of FIGS. 23 to 25, it is assumed that f=-0.02, C=0.18, t=0.8, and 3248 nm pitch (diffraction angle of 15°). Fig. 23 is a view showing a cross-sectional shape and a simulation result of a diffractive optical element having a configuration in which a trajectory connecting the apex of the present invention is a concave curved surface. In addition, in FIGS. 23 to 25, in order to easily understand the difference in the cross-sectional shape, a straight line is collectively described by a single chain line. As shown in Fig. 23, in the configuration of the present invention, the zero-order light becomes 0.26%. Fig. 24 is a view showing a cross-sectional shape and a simulation result of a diffractive optical element having a configuration in which the apexes of the theoretical structure are linearly arranged side by side. As shown in Fig. 24, when all the steps of the theoretical structure are the same, the zero-order light becomes 0.88%. Fig. 25 is a view showing a cross-sectional shape and a simulation result of a diffractive optical element having a configuration in which a trajectory connecting vertices opposite to the present invention has a convex curved surface. As shown in Fig. 25, in the configuration in which the blade-shaped inclined surface of the saw is convex in the opposite direction to the present invention, the zero-order light becomes 2.90%. From the results of Figs. 23 to 25, it was confirmed that in the diffractive optical element having the configuration in which the trajectory connecting the vertices is a concave curved surface as in the present invention, the zero-order light can be reduced. Next, a method of comparing the structure of the present invention which is easier to understand with the previous structure will be described instead of the method of confirming the concave curved surface by the above equation. In the configuration of the present invention, since the trajectory connecting the vertices is a concave curved surface, the area of the upper surface of each step differs depending on the step. The following is an explanation of this aspect. Figure 26 is a plan view showing a parallel arrangement of a diffractive optical element of the prior art and a diffractive optical element of the present invention. Fig. 26(a) shows the four-level faces of the diffractive optical element designed by a method known as the ideal design, and shows one side to four sides. Fig. 26(b) is a view showing the structure of Fig. 26(a) based on the structure of the present invention. In each of the faces, the lowermost surface (the order 0 step portion 11a-0: see FIG. 3) is referred to as the zero plane, and the uppermost plane (the third step portion 11a-3) is shown as the three faces in the drawing. Figure 27A is a graph showing the ratio of the faces of Figure 26 to the area of the 4-level diffractive optical element based on the previously ideal design of Figure 26(a). Figure 27B is a graph showing the ratio of the faces to the area of the 8-level diffractive optical element based on the previous ideal design. Figure 28A is a graph showing the ratio of the faces of Figure 26 to the area of the 4-level diffractive optical element of the present invention of Figure 26(b). Figure 28B is a graph showing the ratio of the faces of the faces to the area of the 8-level diffractive optical element of the present invention. 27A and 27B and Figs. 28A and 28B determine the area ratio for a square region of 10 μm, 50 μm, and 100 μm on one side of the diffractive optical element (DOE). The larger the size of the square region, the more the surface becomes the sample, and therefore tends to converge to a fixed value. 27A and 27B, the ratio of each face in the previous ideal design is approximately 25% for each of the 4-level faces, and 11 to 14% for the 8-level faces, which are approximately equal ratios. On the other hand, as shown in Figs. 28A and 28B, in the structure of the present invention, the area of level-0 which is the lowermost plane is the largest, and the area of the first level (level-2, level-6) below the uppermost plane. The smallest. Fig. 29 is a result of actual measurement of the diffractive optical element and measurement of zero-order light based on the data of Figs. 26(a) and (b). Further, the measured values of 4-level and 8-level are collectively shown in FIG. Looking at Fig. 29, it is found that 4-level and 8-level are reduced in the zero-order light compared with the previous form in the configuration of the present invention. In the example of the above-described FIG. 28A, if the size is arranged from large to small, the order is level-0, level-1, level-3, and level-2 (hereinafter referred to as type1). In the following, an example in which the size of the area is in the order of level-0, level-3, level-1, and level-2 (hereinafter referred to as type2) is described, and the basic conditions are the same under the same conditions. The form of the design is compared. Further, in this comparison, the difference between the heights of level-0 to level-3, that is, the depth of the unevenness (hereinafter, also referred to as DOE height) was changed and the influence on the DOE height was also examined. Furthermore, the DOE height typically depends on the wavelength of the light that is being diffracted. Figure 30 is a graph showing the area ratio of three types of diffractive optical elements. Figure 31 is a view showing a diffractive optical element of an ideal design viewed from the normal direction of the sheet surface. Fig. 32 is a view showing the diffractive optical element of type 1 as seen from the normal direction of the sheet surface. Fig. 33 is a view showing the diffractive optical element of type 2 as seen from the normal direction of the sheet surface. Figure 34 is a graph showing numerical simulation results of three types of diffractive optical elements. Fig. 35 is a graph showing the simulation results of three kinds of diffractive optical elements in a graph. Further, the simulations of Figs. 34 and 35 were carried out at a wavelength of 850 nm using rigorous coupled-wave analysis (RCWA). 34 and 35, even if the DOE height is changed, the zero-order light intensity of the type 1 of the present invention is smaller than the zero-order light intensity of the ideal design. Also, type 2 has a portion where the DOE height is small and the zero-order light intensity is smaller than the ideal design. In the above description, the simulation results are mainly described. However, in the case of actually fabricating a diffractive optical element, it is necessary to determine the area ratio of each step based on the complex uneven shape of the object. In order to obtain the area ratio, the area of each step is required. However, the produced diffractive optical element has many small and complicated irregularities, and it is not easy to obtain an area. Therefore, an example of a method of relatively easily obtaining an area ratio is exemplified below. Further, the method of determining the area ratio may be a method other than the method shown below. Here, a method of measuring the area of each step of the DOE using a laser microscope (VK-X250, manufactured by Keyence Corporation) will be described. The laser microscope has high measurement accuracy and repeatability of 3σ=12 nm, but it is sufficient as long as it is tens of nm. Fig. 36 is a view showing an example of a black-and-white (grayscale) image obtained from a laser microscope. The image obtained from the laser microscope obtained a black and white image as shown in FIG. Further, an image (not shown) obtained by coloring the heights of the respective steps in different colors in the black and white image is also obtained. As long as the area of each of the colored colors is obtained, generally, even if the heights of the respective steps are the same, the height is measured subtly differently, so that color unevenness (chromaticity change) is present, and it is not suitable for direct seeking. Area ratio. Therefore, first, image processing for making the image of Fig. 36 black and white (Fig. 37) is performed. For the binarization, for example, a commercially available image processing software can be used as appropriate, and the threshold value can be set so that the value that best expresses the characteristics of the microscope image can be selected while observing the processing result. Fig. 37 is a view showing the result of binarizing a black-and-white image obtained from a laser microscope. Then, using the binarized image, referring to the separately obtained image obtained by coloring the heights of the respective steps in different colors, the white area is coated in each step with, for example, a halftone color (gray). color. For the coloring process, for example, a commercially available image processing software can be used as appropriate. Fig. 38 is a view showing an example of coloring level-3. Fig. 39 is a view showing an example of coloring level-2. Fig. 40 is a view showing an example of coloring level-1. Fig. 41 is a view showing an example of coloring level-0. The pixels of the respective painted grays are counted using images for each coloring. Regarding the process of counting the number of pixels of each color, for example, a commercially available image processing software can be suitably used. Further, in the above example, the color is composed of three kinds of white, black, and gray, so the number of pixels of gray is counted. For example, in the illustrated example, the level-3 count value is 15167, the level-2 count value is 24859, the level-1 count value is 27541, and the level-0 count value is 29391. This number corresponds to the area, so the area ratio can be obtained. In the image output from the microscope, there is a portion where the boundaries of the respective stages become thick, and it is presumed that the thicker portion becomes a slope. In the above-described area measurement method using image processing, by performing binarization of the image output from the microscope, the slope is black and is not included in the calculation of the area ratio. Therefore, the slope can be excluded and the area calculation can be simplified. This point is the advantage of this assay. As described above, according to the present embodiment, the diffractive optical element 10 has a chamfered shape as a concave curved surface or a multi-step shape that mimics a concave curved surface, so that the intensity of the zero-order diffracted light can be greatly reduced. Further, it is also possible to suppress a decrease in the diffraction efficiency of the primary light. (Modifications) The present invention is not limited to the embodiments described above, and various changes and modifications may be made without departing from the scope of the invention. (1) An example in which only one of the width or the height of the multi-order shape is changed by emulating a concave curved surface by a multi-step shape has been described. The present invention is not limited thereto, and for example, the two may be slowly changed. (2) In the embodiment, the diffractive optical element is represented by a simple form composed only of the high refractive index portion. The present invention is not limited thereto. For example, a transparent substrate for forming a high refractive index portion may be provided, and the low refractive index portion 14 may be formed of a resin, or a coating layer covering the diffraction layer may be provided. (3) In the embodiment, the diffractive optical element having a multi-order shape is mainly described. However, the present invention is not limited thereto. For example, the multi-step shape may be formed finely until the limit is reached, and the optical element may not be recognized. A diffractive optical element formed by a multi-step shape or a continuous bevel (curved surface) shape. Further, the embodiment and the modifications may be combined as appropriate, and detailed descriptions thereof will be omitted. Further, the present invention is not limited to the embodiments described above.

10‧‧‧Diffractive optical components

11‧‧‧High refractive index

11a‧‧‧ convex

11a-0‧‧‧level 0

11a-1‧‧‧level 1st order

11a-2‧‧‧level 2nd order

11a-3‧‧‧level 3

11b‧‧‧ Sidewall

12‧‧‧ recess

13‧‧‧ Space

14‧‧‧ Low refractive index

15‧‧‧Diffraction layer

200‧‧‧ screen

201‧‧‧Light

202‧‧‧ illuminated area

204‧‧‧ illuminated area

210‧‧‧Light source department

A‧‧‧ position

AP‧‧‧ aperture

B‧‧‧ position

C‧‧‧ position

D‧‧‧ position

Width of d0‧‧‧

Width of d1‧‧‧

D2‧‧‧Width

D3‧‧‧Width

D4‧‧‧Width

D5‧‧‧Width

D6‧‧‧Width

D7‧‧‧Width

E‧‧‧ area

F‧‧‧Area

H‧‧‧ Height of each step

L‧‧‧ total order

L0‧‧‧ Bevel

Level-0‧‧‧step-0

Level-1‧‧‧step-1

Level-2‧‧‧step-2

Level-3‧‧‧3

Level-4‧‧‧step-4

Level-5‧‧‧step-5

Level-6‧‧‧step-6

Level-7‧‧‧step-7

LS‧‧‧ light source

M‧‧‧Power Meter

S‧‧‧ sensor

1A is a plan view showing an example of a diffractive optical element in which a concave-convex shape of a diffraction grating obtained from a normal direction of a sheet surface is formed into a regular or irregular pattern in which a boundary between a convex portion and a concave portion includes a curved line. 1B is a view showing an example of a diffractive optical element in which a concave-convex shape of a diffraction grating obtained from a normal direction of a sheet surface is formed in a lattice pattern in which a plurality of unit cells of the same uneven shape are arranged side by side. Top view. Fig. 2A is a perspective view showing an example of a partial periodic structure in an example of the irregular type diffractive optical element shown in Fig. 1A. Fig. 2B is a perspective view showing an example of a partial periodic structure in the example of the GCA type diffractive optical element shown in Fig. 1B. Figure 3 is a cross-sectional view showing the diffractive optical element cut off at the position of arrow G-G' in Figure 2A. 4(a) and 4(b) are views for explaining a diffractive optical element. Fig. 5 is a view for explaining a concave curved surface of the convex portion 11a in the diffractive optical element 10. Fig. 6A(a)-(d) are views showing the diffractive optical element 10 of the present embodiment in comparison with the prior art. 6B(b) and (c) are diagrams in which the curve of the original design pattern is superimposed on the graph of FIG. 6A. Fig. 7 is a view showing a diffractive optical element 10 having a multi-order shape of 8th order. Fig. 8 is a view showing a curve and a multi-order shape in a cross section of a concave curved surface. Fig. 9 is a view showing a specific example of the cross-sectional shape of the eighth step. The values of x and y are collectively shown in FIG. Fig. 10 is a view showing a specific example of the cross-sectional shape of the fourth order. The values of x and y are collectively shown in FIG. Fig. 11 (a) and (b) are views showing a method of measuring the intensity of zero-order diffracted light. Fig. 12 is a view showing a diffraction optical element of a comparative example. Fig. 13 is a graph showing the results of measuring the intensity of 0-time diffracted light for the diffractive optical element 10 of the present invention and a comparative example. Fig. 14 is a view showing the shape of the embodiment 2 in which the height of each step is changed. Figure 15 is a summary of the results of the simulation. Fig. 16 is a view showing an example of simulating a sawtooth shape in a 16th order. Fig. 17 is a graph showing the zero-order light intensity when C is changed when the diffraction angle of the diffraction grating is 15° at a distance of 3284 nm. Fig. 18 is a graph showing the zero-order light intensity when f is changed when the diffraction angle of the diffraction grating is 15° and the diffraction angle of the diffraction grating is 15°. Fig. 19 is a graph showing the zero-order light intensity when t is changed when the diffraction angle of the diffraction grating is 15° and the diffraction angle of the diffraction grating is 15°. Fig. 20 is a graph showing the zero-order light intensity when C is changed when the diffraction angle of the diffraction grating is 15° and the diffraction angle of the diffraction grating is 15°. Fig. 21 is a graph showing the zero-order light intensity when f is changed when the diffraction angle of the diffraction grating is 15° and the diffraction angle of the diffraction grating is 15°. Fig. 22 is a graph showing the zero-order light intensity when t is changed when the diffraction angle of the diffraction grating is 15° and the diffraction angle of the diffraction grating is 15°. Fig. 23 is a view showing a cross-sectional shape and a simulation result of a diffractive optical element having a configuration in which a trajectory connecting the apex of the present invention is a concave curved surface. Fig. 24 is a view showing a cross-sectional shape and a simulation result of a diffractive optical element having a configuration in which the apexes of the theoretical structure are linearly arranged side by side. Fig. 25 is a view showing a cross-sectional shape and a simulation result of a diffractive optical element having a configuration in which a trajectory connecting the vertices opposite to the present invention is a convex curved surface. 26(a) and 26(b) are plan views showing the diffractive optical element of the prior art and the diffractive optical element of the present invention in parallel for comparison. Figure 27A is a graph showing the ratio of the faces of Figure 26 to the area of the 4-level (4-step) diffractive optical element based on the prior art design of Figure 26(a). Figure 27B is a graph showing the ratio of the faces to the area of an 8-level (8-order) diffractive optical element based on the previous ideal design. Figure 28A is a graph showing the ratio of the faces of Figure 26 to the area of the 4-level diffractive optical element of the present invention of Figure 26(b). Figure 28B is a graph showing the ratio of the faces to the area of the 8-level diffractive optical element of the present invention. Fig. 29 shows the results of actually measuring the diffractive optical element and measuring the zero-order light based on the data of Figs. 26(a) and (b). Figure 30 is a graph showing the area ratio of three types of diffractive optical elements. Figure 31 is a view showing a diffractive optical element of an ideal design viewed from the normal direction of the sheet surface. Fig. 32 is a view showing a diffractive optical element of type 1 viewed from the normal direction of the sheet surface. Fig. 33 is a view showing the diffractive optical element of type 2 as seen from the normal direction of the sheet surface. Figure 34 is a graph showing numerical simulation results of three types of diffractive optical elements. Fig. 35 is a graph showing the simulation results of three kinds of diffractive optical elements in a graph. Fig. 36 is a view showing an example of a black-and-white (grayscale) image obtained from a laser microscope. Fig. 37 is a view showing the result of binarizing a black-and-white image obtained from a laser microscope. Fig. 38 is a view showing an example of coloring level-3. Fig. 39 is a view showing an example of coloring level-2. Fig. 40 is a view showing an example of coloring level-1. Fig. 41 is a view showing an example of coloring level-0.

Claims (10)

A diffractive optical element that is shaped to light and has a diffraction layer having: a high refractive index portion in which a plurality of convex portions are arranged side by side; and a low refractive index portion having a refractive index a portion lower than the high refractive index portion and including at least a concave portion formed between the convex portions; the convex portion having a multi-step shape formed by a plurality of step portions having different heights, wherein the high refractive index portion is per unit area The area of the deepest surface is the largest, and the area of the first step below the uppermost plane is the smallest. The diffractive optical element according to claim 1, wherein an area of the uppermost surface of the high refractive index portion is 0.6 to 0.9 times an area of a lowermost surface of the high refractive index portion. The diffractive optical element according to claim 1 or 2, wherein the high refractive index portion is successively reduced from the deepest surface to the lowermost surface of the uppermost plane per unit area, and the area of each step portion is successively decreased. A diffractive optical element which is shaped to light and has a diffraction layer, the diffraction layer comprising: a high refractive index portion in which a plurality of convex portions are arranged side by side in a cross-sectional shape; and a low refractive index portion The refractive index is lower than the high refractive index portion, and includes at least a concave portion formed between the convex portions; the convex portion has a zigzag shape or a shape obtained by mimicking a zigzag shape by a multi-step contour shape, relative to the sawtooth The inclined surface of the sheet surface of the diffractive optical element having a shape or a zigzag shape mimicked by a multi-step contour shape has a concave curved surface that is recessed toward the convex portion. The diffractive optical element of claim 4, wherein the convex portion has a multi-step shape formed by mimicking the zigzag shape by a plurality of steps different in height from at least one side of the side shape thereof, by the height of the step portion At least one of the widths and the width mimics the concave curved surface depending on the location. The diffractive optical element of claim 4 or 5, wherein the convex portion has a multi-step shape formed by mimicking the zigzag shape by a plurality of steps different in height from at least one side of the side shape, in each unit area The area of the deepest surface is the largest, and the area of the first step below the uppermost plane is the smallest. The diffractive optical element of claim 5 or 6, wherein the height of each of the steps is fixed, and the concave curved surface is mimicked according to the width of the step. The diffractive optical element according to claim 7, wherein the x-axis is set to a direction in which the convex portions are arranged side by side, and a direction in which the inclined surface is raised is set to a positive direction of the x-axis, and a sheet surface of the diffractive optical element is set. In the y-axis, the direction in which the convex portion protrudes is the positive direction of the y-axis, and the total order of the step portion including the front end of the convex portion is set to L, and the width of each step is reduced. The rate is set to f, and the order of the step of the object when the lowest position of the concave portion is 0 is set to lv, and the height of each step of the step is set to a fixed value by h, and the order is 0. When the width ratio is set to C, the curve of the vertices of the concave vertices of the order 0 and the vertices of the convex portions in the cross section of the concave curved surface imitated by the multi-order shape is set to set the ratio of the x coordinate to the pitch S, and x'=0.5×f×lv ² +C×lv S=P/{tw+Σx'i} When =0 is set to i=0～L-1, the top of the step shape x, the y coordinate is x=0.5×f ×lv ² +C×lvy=lv×h. The diffractive optical element according to any one of claims 1 to 8, wherein the high refractive index portion forms a diffraction grating having a normal direction from a surface on which the uneven shape is formed, the convex portion and the above The intersection of the recesses includes a pattern of at least one of a curve and a fold line connecting a plurality of line segments. The diffractive optical element according to any one of claims 1 to 8, wherein the high refractive index portion forms a diffraction grating pattern of a grating element array type, and the diffraction grating pattern of the grating unit array type is formed from a surface having a concave-convex shape When viewed in the normal direction, it is formed into a lattice pattern in which a plurality of unit cells in which the same uneven shape is arranged side by side is laid.