Method for designing diffractive optical element, method for manufacturing diffractive optical element, and diffractive optical element

Abstract

This method for designing a diffractive optical element includes synthesizing first data indicating a first uneven structure exhibiting a first function with respect to incident light and second data indicating a second uneven structure exhibiting a second function with respect to the incident light, thereby generating third data indicating a third uneven structure exhibiting the first function and the second function with respect to the incident light.

Description

Method for designing a diffractive optical element, method for manufacturing a diffractive optical element, and diffractive optical element

[0001] The present invention relates to a method for designing a diffractive optical element, a method for manufacturing a diffractive optical element, and a diffractive optical element.

[0002] A diffractive optical element (hereinafter also referred to simply as a DOE) is used as a method for realizing a desired pattern. A common use of a DOE is to combine a Fourier-type DOE with an infinite focal length and a condenser lens with a predetermined focal length. Patent Document 1 describes a use of a Fourier-type DOE combined with a condenser lens.

[0003] Patent Application No. 2014-98526

[0004] Conventional diffractive optical elements have had problems such as zero-order light being easily noticeable in the central portion. One example of a problem that the present invention aims to solve is to provide a diffractive optical element that can prevent zero-order light from being noticeable in the central portion.

[0005] According to the present invention, there are provided the following design methods for diffractive optical elements, manufacturing methods for diffractive optical elements, and diffractive optical elements. [1] A design method for a diffractive optical element, comprising: generating third data representing a third concavo-convex structure that performs the first function and the second function for incident light by combining first data representing a first concavo-convex structure that performs a first function for incident light and second data representing a second concavo-convex structure that performs a second function for the incident light. [2] The design method for a diffractive optical element according to [1], comprising: acquiring at least one of unit data for generating the first data and unit data for generating the second data, wherein at least one of the first data and the second data represents a concavo-convex structure in which a plurality of unit structures represented by the unit data are arranged to have a predetermined size. [3] The design method for a diffractive optical element according to [1] or [2], wherein the first function includes a function of branching the incident light, and the second function includes a function of focusing the incident light. [4] The design method of a diffractive optical element according to [1] or [2], wherein the first function includes a function of branching the incident light in a first direction, and the second function includes a function of branching the incident light in a second direction. [5] A manufacturing method of a diffractive optical element, comprising: forming the third unevenness structure on one surface of an optical material having translucency or reflectivity, using the third data generated by the method of any of [1] to [4]. [6] A diffractive optical element having translucency or reflectivity, and having a third unevenness structure on one surface that combines a first unevenness structure that performs a first function for incident light and a second unevenness structure that performs a second function for the incident light.

[0006] According to the present invention, a diffractive optical element is provided that can prevent zero-order light from being noticeable in the central portion.

[0007] 11 is a diagram showing an example of a general diffractive optical element (DOE) and a diffractive optical device using the same. FIG. 12 is a diagram showing an example of a diffractive optical device and DOE according to the present embodiment. FIG. 13 is a diagram showing an example of a reflective diffractive optical device and DOE. FIG. 14 is a flowchart of a method for designing a DOE. FIG. 15 is a diagram showing an example of a two-dimensional phase distribution calculated from first data. FIG. 16 is a diagram showing an example of a two-dimensional phase distribution calculated from second data. FIG. 17 is a diagram showing an example of a two-dimensional phase distribution calculated from third data. FIG. 18 is a flowchart of a first step in a method for designing a diffractive optical element (DOE) according to the present embodiment. FIG. 19 is a diagram showing a two-dimensional phase distribution calculated from first data, in which the first data on which the two-dimensional phase distribution shown in FIG. 5 is based is created as unit data. FIG. 19 is a diagram showing a two-dimensional phase distribution calculated from second data corresponding to the first data. FIG. 20 is a diagram showing a two-dimensional phase distribution calculated from third data. FIG. 21 is a diagram showing a simulation result for the concave-convex structure shown in FIG. 7. FIG. 22 is a diagram showing a simulation result for the concave-convex structure shown in FIG. 11. FIG. 23 is a diagram showing a simulation result of a comparative example. FIG. 24 is a diagram showing a measurement result for the concave-convex structure shown in FIG. 11.

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, like components are designated by like reference numerals, and the description thereof will be omitted as appropriate.

[0009] [Reference Example] Fig. 1 is a diagram showing an example of a general diffractive optical element (DOE 11) and a diffractive optical device 110 using the same. The diffractive optical device 110 shown in Fig. 1 includes a Fourier-type diffractive optical element (DOE) 11 with an infinite focal length and a condenser lens 20 with a predetermined focal length. In the diffractive optical device 110, the DOE 11 splits incident light from a light source 30, and the condenser lens 20 further condenses the split incident light, thereby outputting a desired pattern on a screen 40.

[0010] The inventors have found that the diffractive optical device 110 shown in FIG. 1 has the following problems. First, the diffractive optical device 110 shown in FIG. 1 requires the condenser lens 20, which increases the overall size of the diffractive optical device 110. Second, the diffractive optical device 110 shown in FIG. 1 is sensitive to deviations from the design value of the structural depth of the DOE 11, which tend to occur during fabrication of the DOE 11. This causes problems such as zero-order light being prominent in the central portion and significant variations in intensity at each branch point (these problems will be described in detail later). The diffractive optical device 100 and diffractive optical element 10 according to this embodiment, which will be described below, can solve the above problems.

[0011] First Embodiment FIG. 2 shows an example of a diffractive optical device 100 and a DOE 10 according to this embodiment. The diffractive optical element 100 according to this embodiment is used, for example, to display a logo using diffracted light, for spatial recognition by distance measurement, as a gesture sensor, and for laser processing using diffracted light. The diffractive optical device 100 shown in FIG. 2 includes a DOE 10. The diffractive optical device 100 outputs a desired pattern on a screen 40 by using the DOE 10 to split and focus incident light from a light source 30. In other words, the diffractive optical element 100 according to this embodiment has the diffractive optical element (DOE) 10 that has both splitting and focusing functions, and does not require a focusing lens 20. This solves the problems associated with the diffractive optical device 110 described above.

[0012] Although the DOE 10 in Fig. 2 is a transmissive type, it may be a reflective type as shown in Fig. 3. In this case, the pattern of the DOE 10 is formed on the surface of the DOE 10 facing the light source 30, as shown in Fig. 3. Furthermore, a transmissive DOE 10 is made of a material such as quartz, whereas a reflective DOE 10 is made of a metal material. Next, a method for designing the DOE 10 will be described.

[0013] 4 is a flowchart of a method for designing the DOE 10. The method for designing the DOE 10 includes a first step S10 of preparing first data representing a first concavo-convex structure that performs a first function for incident light and second data representing a second concavo-convex structure that performs a second function for incident light, and a second step S20 of combining the first data and the second data to generate third data representing a third concavo-convex structure that performs the first and second functions for incident light.

[0014] The first and second functions mentioned above include at least one of the following functions: a function of branching incident light in a predetermined direction or shape; a function of focusing incident light at a predetermined focal length; and a function of deforming incident light.

[0015] Furthermore, the first data and the second data can be expressed as, for example, complex functions of the coordinates (x, y) on one surface of the DOE. The first data and the second data can be expressed, for example, by the following formula, where f(x, y) and g(x, y) are predetermined functions of the coordinates (x, y): formula: f(x, y) + ig(x, y) Each step will be described in detail below.

[0016] <First Step> Fig. 5 shows an example of a two-dimensional phase distribution calculated from the first data. Fig. 5 shows the two-dimensional phase distribution in an area of ​​approximately 0.7 mm x 0.7 mm, and shows a concave-convex structure that performs a branching function as the first function. The concave-convex structure shown in the two-dimensional phase distribution shown in Fig. 5 performs the function of branching incident light into an "F" shape.

[0017] An example of a two-dimensional phase distribution calculated from the second data is shown in Fig. 6. Fig. 6 shows the two-dimensional phase distribution in an area of ​​approximately 0.7 mm x 0.7 mm, and shows a concave-convex structure that performs a focusing function as a second function, more specifically, the structure of an ideal focusing lens with a focal length of 200 mm.

[0018] The first data is calculated, for example, by an iterative Fourier transform algorithm (IFTA) based on the light intensity distribution to be output. However, the method for calculating the first data and the second data is not limited to the IFTA method. For example, the RCWA method or the FDTD method may also be used.

[0019] The second data is calculated by applying the phase of the lens that is uniquely determined from the focusing distance.

[0020] <Second Step> As described above, in the second step, the first data and the second data are combined to generate third data indicating a third concavo-convex structure that performs the first function and the second function. Note that combining the first data and the second data is, for example, calculating the third data by multiplying a complex function indicated by the first data by a complex function indicated by the second data. That is, an example of the third data is a complex function calculated by multiplying a complex function indicated by the first data by a complex function indicated by the second data.

[0021] Fig. 7 shows an example of a two-dimensional phase distribution calculated from the third data. The two-dimensional phase distribution shown in Fig. 7 is a two-dimensional phase distribution calculated from the third data generated by combining the first data on which the two-dimensional phase distribution shown in Fig. 5 was based and the second data on which the two-dimensional phase distribution shown in Fig. 6 was based. The uneven structure shown in the two-dimensional phase distribution shown in Fig. 7 functions to branch incident light into an "F" shape and to focus light like an ideal focusing lens with a focal length of 200 mm.

[0022] In the above example, the first function is a branching function and the second function is a focusing function, but the design method according to this embodiment is not limited to this. For example, both the first function and the second function may be branching functions, or the first function may be a branching function in a first direction and the second function may be a branching function in a second direction. For example, if the first function is a function of branching into three beams in the first direction and the second function is a function of branching into four beams in the second direction, and the first direction and the second direction are orthogonal to each other, the incident light will be branched into 3 x 4 points.

[0023] In the above example, the first data and the second data are combined, but the design method according to this embodiment is not limited to this. That is, three or more data representing the concave-convex structure may be prepared and combined to generate the third data.

[0024] <Method of manufacturing diffractive optical element 10> The diffractive optical element 10 according to this embodiment is obtained by forming a concave-convex structure on the surface of a material or by forming a refractive index distribution in the material, based on the third data obtained by the design method described above. When manufacturing a transmissive diffractive optical element 10, a transmissive material such as quartz is used as the material, and when manufacturing a reflective diffractive optical element 10, a reflective material such as metal is used as the material.

[0025] Furthermore, the DOE 10 according to this embodiment has a feature that the complex function of the first data can be obtained by dividing the complex function representing the concave-convex structure of the DOE 10 by the complex function of the second data.

[0026] As described above, the design method for a diffractive optical element (DOE) according to this embodiment makes it possible to design a DOE that performs the first and second functions. Furthermore, by using the branching function of a conventional DOE as the first function and the focusing function of a focusing lens as the second function, it is possible to realize a diffractive optical device 100 that does not require the focusing lens 20, and to solve the problems of the conventional diffractive optical device 110, such as the zero-order light being prominent in the central portion and the significant variation in intensity at each branch point.

[0027] Second Embodiment The design method of a diffractive optical element (DOE) according to this embodiment is the same as that of the first embodiment, except for the following points.

[0028] 8 is a flowchart showing the first step in the design method for a diffractive optical element (DOE) according to this embodiment. The design method according to this embodiment uses unit data in the first step.

[0029] In this embodiment, the first step involves acquiring at least one of unit data for generating first data and unit data for generating second data (S11). The unit data is data representing unit structures of the concave-convex structure, and is, for example, a complex function similar to the first data and the second data. In this embodiment, at least one of the first data and the second data represents a concave-convex structure in which a plurality of unit structures represented by the unit data are arranged to form a predetermined size (S12).

[0030] The unit structure has the same function as the uneven structure obtained by arranging a plurality of the unit structures. In other words, the function does not change basically even if a plurality of unit structures are arranged. However, the uneven structure obtained by arranging the unit structures has a large light receiving area, and therefore the diameter of the light incident from the light source 30 can be increased. The diameter of the light is measured from the distribution curve of the light intensity, and when the intensity at the center of the light is 1, the diameter of the light from the center of the light is 1 / e ２ is twice the distance to the point where

[0031] The unit structure is designed according to a desired function. For example, the structure shown in the two-dimensional phase distribution in Fig. 5 may be used as the unit structure. In other words, the first data on which the two-dimensional phase distribution in Fig. 5 is based may be used as the unit data.

[0032] Fig. 9 shows a two-dimensional phase distribution calculated from the first data, which is created using the first data on which the two-dimensional phase distribution shown in Fig. 5 is based as unit data. The two-dimensional phase distribution shown in Fig. 9 shows a concavo-convex structure in which the concavo-convex structures shown in the two-dimensional phase distribution shown in Fig. 5 are arranged. The dashed line portion S1 in Fig. 9 is the two-dimensional phase distribution shown in Fig. 5.

[0033] Fig. 10 shows a two-dimensional phase distribution calculated from the second data corresponding to the first data. The concave-convex structure shown in Fig. 10 also functions as a condenser lens with a focal length of 200 mm, similar to the concave-convex structure shown in Fig. 6. However, the concave-convex structure shown in the second data in Fig. 10 is adjusted to the size (approximately 3.5 mm x 3.5 mm) of the concave-convex structure shown in the first data in Fig. 9.

[0034] Fig. 11 shows a two-dimensional phase distribution calculated from third data generated by combining the first data on which the two-dimensional phase distribution shown in Fig. 9 was based and the second data on which the two-dimensional phase distribution shown in Fig. 10 was based. The concavo-convex structure shown in the third data in Fig. 11 has the function of branching incident light into an "F" shape and the function of focusing light of an ideal focusing lens with a focal length of 200 mm, similar to the concavo-convex structure shown in the third data in Fig. 7. Furthermore, the concavo-convex structure shown in the third data in Fig. 11 can be used for incident light with a larger diameter than the concavo-convex structure shown in the third data in Fig. 7.

[0035] As described above, the design method for a diffractive optical element (DOE) according to this embodiment also makes it possible to realize a diffractive optical device 100 that does not require the condenser lens 20. Furthermore, the design method for a DOE according to this embodiment makes it possible to easily design DOEs that correspond to various diameters of incident light by using unit data.

[0036] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various other configurations can also be adopted.

[0037] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions of these examples.

[0038] Light was irradiated from a light source onto the uneven structure shown in the two-dimensional phase distribution of Fig. 7 and the uneven structure shown in the two-dimensional phase distribution of Fig. 11, and a simulation was performed of the diffracted light obtained 200 mm ahead. Fig. 12 shows the simulation results for the uneven structure shown in the two-dimensional phase distribution of Fig. 7, and Fig. 13 shows the simulation results for the uneven structure shown in the two-dimensional phase distribution of Fig. 11. Note that the diameter of the light incident on the uneven structure shown in the two-dimensional phase distribution of Fig. 7 was 0.25 mm, while the diameter of the light incident on the uneven structure shown in the two-dimensional phase distribution of Fig. 11 was 1.00 mm.

[0039] 12 and 13, it was confirmed that all of the concave-convex structures output the shape of "F." In other words, it was confirmed that a concave-convex structure obtained by arranging unit structures exhibits the same function as the unit structures, and that by arranging unit structures to design a concave-convex structure, it is possible to design a concave-convex structure that corresponds to the diameter of incident light while maintaining the function of the unit structures.

[0040] The reason why the simulation results shown in FIG. 13 are more condensed than the simulation results shown in FIG. 12 is presumably because the diameter of the incident light is larger, resulting in more condensation of the incident light.

[0041] Next, for comparison, data on the uneven structure shown in the two-dimensional phase distribution in Fig. 9 and the uneven structure (condenser lens) shown in the two-dimensional phase distribution in Fig. 10 were prepared, and these were arranged as shown in Fig. 1, and a simulation was performed on the diffracted light obtained 200 mm ahead. The simulation results are shown in Fig. 14.

[0042] Comparing the simulation results shown in FIG. 13 with those shown in FIG. 14, it can be seen that the zero-order light D1 is less noticeable in the simulation results shown in FIG.

[0043] Next, the uneven structure shown in the two-dimensional phase distribution in FIG. 11 was fabricated, and light with a diameter of 1.00 mm was irradiated. A beam profiler was placed 200 mm ahead of the structure, and the measurement results of the diffracted light obtained are shown in FIG. 15. Note that D2 and D3 are graphs showing "light intensity at each point on a line parallel to the vertical axis passing through the zeroth-order light" and "light intensity at each point on a line parallel to the horizontal axis passing through the zeroth-order light," respectively. As shown by the simulation results in FIG. 13, the measurement results of D1, D2, and D3 also confirmed that the zeroth-order light D1 was not very noticeable. From the above, it was confirmed that the diffractive optical element 10 according to this embodiment can solve the problem of the conventional diffractive optical element 11 in that the zeroth-order light is noticeable in the central portion.

[0044] This application claims priority based on Japanese Patent Application No. 2024-061571, filed April 5, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0045] 10 Diffractive optical element (DOE) 20 Condenser lens 30 Light source 40 Screen 100 Diffractive optical device

Claims

1. A method for designing a diffractive optical element, comprising: generating third data representing a third concavo-convex structure that performs the first function and the second function for incident light by combining first data representing a first concavo-convex structure that performs a first function for incident light and second data representing a second concavo-convex structure that performs a second function for the incident light.

2. A method for designing a diffractive optical element according to claim 1, wherein at least one of unit data for generating the first data and unit data for generating the second data is acquired, and at least one of the first data and the second data indicates a concave-convex structure in which a plurality of unit structures indicated by the unit data are arranged to have a predetermined size.

3. The method for designing a diffractive optical element according to claim 1 or 2, wherein the first function includes a function of branching the incident light, and the second function includes a function of converging the incident light.

4. A method for designing a diffractive optical element according to claim 1 or 2, wherein the first function includes a function of splitting the incident light in a first direction, and the second function includes a function of splitting the incident light in a second direction.

5. A method for manufacturing a diffractive optical element, comprising forming the third uneven structure on one surface of an optical material having translucency or reflectivity using the third data generated by the method described in claim 1 or 2.

6. A diffractive optical element having translucency or reflectivity and having on one surface a third concave-convex structure that combines a first concave-convex structure that performs a first function for incident light and a second concave-convex structure that performs a second function for the incident light.

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