Diffraction optical device, projection device, and detection device

Abstract

To provide a diffraction optical device having a lens function and a branch function, in which diffraction efficiency is heightened, and yet the light passing through without being diffracted is reduced.SOLUTION: An diffraction optical device 30 converts the advance direction of incident light and causes the incident light to be branched in a plurality of directions. The diffraction optical device 30 includes a plurality of diffraction optical elements 35. A diffraction optical element 35 includes a connection surface 35b for connecting between a plurality of flat surfaces 35a and two flat surfaces 35a. The cubic volume of the diffraction optical element 35 divided by a product of the bottom area and the height of the diffraction optical element 35 is smaller than 0.5. The height of the diffraction optical element 35 is higher than a theoretical value of height for obtaining light of an inverse phase to light entering the diffraction optical device 30.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to a diffractive optical element, a projection device having the diffractive optical element, and a detection device having the projection device.

Background Art

[0002] A projection device that projects light of a predetermined pattern is known. The projection device is used, for example, in a detection device. The detection device projects light of a predetermined pattern from the projection device onto an object, and receives the light reflected by the object with a light receiving device, thereby detecting the shape of the object and the like. The projection device includes a plurality of light emitters, one or more lenses, and a diffractive optical element in order to project light of a predetermined pattern. The light emitter emits divergent light. The lens converts the traveling direction of the light from the light emitter. For example, one lens makes the light from the light emitter into parallel light, and another lens makes the parallel light into convergent light. The diffractive optical element diffracts light to branch the light in a plurality of directions.

[0003] Patent Document 1 describes a diffractive optical element having a lens function and a branching function. In a projection device having such a diffractive optical element, the lens can be omitted. The projection device can be miniaturized, and the cost of manufacturing the projection device can be reduced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] A diffractive optical element having a lens function and a branching function has a pitch of a pattern for diffracting light decreasing as it moves away from the center of the diffractive optical element. As a result, the diffraction efficiency of the diffractive optical element decreases. In order to increase the diffraction efficiency, it is conceivable to increase or extremely decrease the duty ratio of each diffractive optical element included in the diffractive optical element, or to decrease or extremely increase the height of each diffractive optical element below or above the theoretical value height for obtaining an opposite phase of the incident light. When each diffractive optical element is configured in this way, the amount of light transmitted without being diffracted by the diffractive optical element increases. The light transmitted without being diffracted deteriorates the visibility of the entire diffracted light. The present disclosure aims to reduce the light transmitted without being diffracted while increasing the diffraction efficiency in a diffractive optical element having a lens function and a branching function.

Means for Solving the Problem

[0007] The diffractive optical element of the present disclosure is a diffractive optical element that converts the traveling direction of incident light and branches the incident light in a plurality of directions, including a plurality of diffractive optical elements, the diffractive optical element includes a plurality of flat surfaces and a connection surface connecting between two of the flat surfaces, a value obtained by dividing the volume of the diffractive optical element by the product of the bottom area and the height of the diffractive optical element is less than 0.5, the height of the diffractive optical element is higher than the theoretical value height for obtaining light with an opposite phase of the light incident on the diffractive optical element.

Effects of the Invention

[0008] According to the present disclosure, in a diffractive optical element having a lens function and a branching function, it is possible to reduce the light transmitted without being diffracted while increasing the diffraction efficiency.

Brief Description of the Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] In the drawings attached to this specification, for the convenience of illustration and easy understanding, the scale, the aspect ratio of the vertical and horizontal dimensions, etc. are appropriately changed and exaggerated from those of the actual object. In some of the drawings, the configurations and the like shown may be omitted in other drawings.

[0011] To clarify the relationship of directions among the drawings, in some of the drawings, the X direction, Y direction, and Z direction are shown as common directions by arrows with common reference numerals. In the following examples, the X direction, Y direction, and Z direction are perpendicular to each other. An arrow pointing forward from the paper surface along the direction perpendicular to the paper surface of the drawing is shown by a symbol with a dot in a circle, as shown in FIG. 2 for example. An arrow pointing into the depth of the paper surface along the direction perpendicular to the paper surface of the drawing is shown by a symbol with an "x" in a circle, as shown in FIG. 3 for example.

[0012] In this specification, terms such as "parallel", "orthogonal", "identical", etc., which specify shapes, geometric conditions, and their degrees, as well as values such as lengths and angles, are not limited to strict meanings, but are interpreted to include ranges to the extent that similar functions can be expected.

[0013] In this specification, when a plurality of upper limit candidates and a plurality of lower limit candidates for a parameter are listed, the parameter may be a numerical range obtained by combining any one upper limit candidate and any one lower limit candidate.

[0014] One embodiment of the present disclosure relates to the following [1] to [8]. [1] A diffractive optical element that converts the traveling direction of incident light and branches the incident light into a plurality of directions, including a plurality of diffractive optical elements, wherein the diffractive optical element includes a plurality of flat surfaces and connection surfaces connecting between two of the flat surfaces, a value obtained by dividing the volume of the diffractive optical element by the product of the bottom area and height of the diffractive optical element is less than 0.5, the height of the diffractive optical element is higher than the theoretical height for obtaining light of the opposite phase to the light incident on the diffractive optical element. [2] The refractive index of the diffractive optical element with respect to the wavelength of light incident on the diffractive optical element is 1.7 or more, the diffractive optical element according to [1]. [3] The value obtained by dividing the volume of the diffractive optical element by the product of the bottom area and the height of the diffractive optical element is 0.3 or more, and the diffractive optical element according to [1] or [2]. [4] The height of the diffractive optical element is 1.2 times or less the theoretical height for obtaining light of the opposite phase to the light incident on the diffractive optical element, and the diffractive optical element according to any one of [1] to [3]. [5] The diffractive optical element according to any one of [1] to [4], A plurality of light emitters for making light incident on the diffractive optical element, and a projection device comprising the same. [6] The plurality of light emitters are two-dimensionally arranged, and the projection device according to [5]. [7] The light emitted by the light emitter includes light having a wavelength of 940 nm, and the projection device according to [5] or [6]. [8] The projection device according to any one of [5] to [7], A light receiving device capable of detecting the light projected by the projection device, and a detection device comprising the same.

[0015] An embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 schematically shows a detection device 1 according to an embodiment. As shown in FIG. 1, the detection device 1 has a projection device 20 and a light receiving device 10. The projection device 20 projects light L12 onto the object 5. The light L12 projected by the projection device 20 may be visible light, infrared light, or radio waves. The light receiving device 10 can detect the light projected by the projection device 20. In the example shown in FIG. 1, the light receiving device 10 receives the light L13 that is projected by the projection device 20 and reflected by the object 5. By the light receiving device 10 receiving the light projected by the projection device 20, the detection device 1 can detect the object 5. The detection device 1 detects, for example, a three-dimensional shape. The detection device 1 functions as, for example, a face recognition device. In this case, the object 5 is a face. The detection device 1 may be incorporated into a portable terminal such as a smartphone.

[0016] As shown in FIG. 1, the projection device 20 includes a light source 25 and a diffractive optical element 30. The light L11 from the light source 25 is incident on the diffractive optical element 30. The light L11 from the light source 25 is diffracted by the diffractive optical element 30, and the projection device 20 projects the light L12. FIG. 2 shows the details of the projection device 20.

[0017] FIG. 2 is a front view of the light source 25. As shown in FIG. 2, the light source 25 includes a plurality of light emitters 25a. As shown in FIG. 2, in the light source 25, the plurality of light emitters 25a are two-dimensionally arranged in the X direction and the Y direction. The light source 25 may be a multi-emitter, for example, a vertical cavity surface emitting laser (VCSEL). In the example shown in FIG. 2, three light emitters 25a are arranged along the X direction and three light emitters 25a are arranged along the Y direction, respectively. Not limited to the illustrated example, the plurality of light emitters 25a may be arranged in any number in any direction. Each of the light emitters 25a emits divergent light. The light emitted by the light emitter 25a may be visible light, infrared light, or radio waves. The light emitted by the light emitter 25a may include light having a wavelength of 940 nm.

[0018] The diffractive optical element 30 diffracts the incident light to change the traveling direction of the incident light and branch the incident light into a plurality of directions. Changing the traveling direction of the incident light means making the incident light divergent, convergent, or parallel light. When the traveling direction of the incident light is changed, the divergence angle of the incident light is changed. FIG. 3 shows a state in which the projection device 20 projects light onto the object 5 in the XZ plane direction. FIG. 4 shows a state in which the projection device 20 projects light onto the object 5 in the YZ plane direction. As shown in FIGS. 3 and 4, the diffracted light L31 and L41 emitted from the light emitter 25a of the light source 25 are incident on the diffractive optical element 30. The diffractive optical element 30 has a lens function and a branching function. As a lens function, the diffractive optical element 30 diffracts, for example, the diffracted light emitted from the light emitter 25a so as to become parallel light. As a branching function, the diffractive optical element 30 diffracts, for example, the light emitted from each light emitter 25a so as to branch it into a plurality of directions. The diffractive optical element 30 branches the diffracted light emitted from the light emitter 25a into a plurality of parallel lights. In the example shown in FIG. 3, the diffractive optical element 30 branches the diffracted light L31 emitted from the light emitter 25a into three parallel lights L32 in the X direction. Not limited to the illustrated example, the diffractive optical element 30 may branch the light emitted from the light emitter 25a into three or more directions. In the example shown in FIG. 4, the light L42 diffracted by the diffractive optical element 30 is bent in the Y direction. As shown in FIG. 4, a part of the incident light on the diffractive optical element 30 becomes the light L43 that passes through the diffractive optical element 30 without being diffracted by the diffractive optical element 30.

[0019] FIG. 5 is a front view of the diffractive optical element 30 in the XY plane direction. The diffractive optical element 30 includes an uneven shape of a pattern as shown in FIG. 5 in an observation from the front so as to exhibit a lens function and a branching function. In FIG. 5, the darker the color, the closer it is to the base 33 described later. In other words, the light and dark in FIG. 5 represent the flat surface 35a of the diffractive optical element 35 described later, and the connection surface 35b of the diffractive optical element 35 described later is located at the boundary between the light and dark. In the example shown in FIG. 5, the uneven shape of the diffractive optical element 35 is formed by converting a phase distribution that exhibits both a lens function of converting the traveling direction of incident light and a branching function of branching the incident light in a plurality of directions into an uneven shape. Such a phase distribution is formed by, for example, a computer. In the conversion from the phase distribution to the uneven shape, the refractive index difference between the diffractive optical element 35 and the medium 3 that forms an interface with the diffractive optical element 35 is considered in determining the height of the uneven shape. The medium 3 may be air.

[0020] FIG. 6 shows an example of a cross-sectional view of the diffractive optical element 30 in the YZ plane direction. As shown in FIG. 6, the diffractive optical element 30 includes a support 31, a base 33, a plurality of diffractive optical elements 35, a primer layer 37, and a low reflection layer 39.

[0021] The support 31 is a transparent plate-like member. The support 31 supports other members included in the diffractive optical element 30. The material of the support 31 may be glass, or may be a resin such as an acrylic resin or a polycarbonate. The thickness of the support 31 may be 0.2 mm or more and 1.0 mm or less.

[0022] The base 33 supports the diffractive optical element 35. The base 33 is formed of the same material as the diffractive optical element 35 in order to avoid forming an optical interface between the base 33 and the diffractive optical element 35. The base 33 is integrated with the diffractive optical element 35. The base 33 may be integrally molded with the diffractive optical element 35.

[0023] The diffractive optical element 35 diffracts incident light. In the present embodiment, the diffractive optical element 35 diffracts while transmitting the incident light. By diffracting light by a plurality of diffractive optical elements 35, the diffractive optical element 30 can change the traveling direction of the incident light and branch the incident light into a plurality of directions. The diffractive optical element 35 may be, for example, a hologram element. The diffractive optical element 35 may be a relief hologram. The diffractive optical element 35 may be fabricated as a computer-generated hologram (CGH). The computer-generated hologram is fabricated by calculating a structure having arbitrary diffraction characteristics on a computer. If it is a computer-generated hologram, it is possible to eliminate the need for generating object light and reference light using a light source and an optical system, and recording interference fringes on a hologram recording material by exposure. The projection device 20 is assumed to project light onto the object 5 with a predetermined contour shape, size, and orientation at a predetermined position with respect to the projection device 20. By inputting information about the object 5 as parameters into a computer, a structure having diffraction characteristics capable of projecting appropriate diffracted light onto the object 5, for example, an uneven shape, can be specified by calculation on the computer. By forming the specified structure, for example, by resin molding, the diffractive optical element 35 as a computer-generated hologram can be fabricated at low cost by a simple procedure.

[0024] As shown in FIG. 6, the diffractive optical element 35 forms an uneven shape. The diffractive optical element 35 includes a plurality of flat surfaces 35a, a plurality of connecting surfaces 35b, and an end surface 35c. In one diffractive optical element 35, the flat surfaces 35a and the connecting surfaces 35b are arranged alternately. The connecting surface 35b connects between two flat surfaces 35a. In the illustrated example, the flat surface 35a is parallel to the base 33. Not limited to the illustrated example, the flat surface 35a may be inclined with respect to the base 33. In this case, the diffractive optical element 35 has a so-called blazed shape. The end surface 35c is located between two diffractive optical elements 35. The end surface 35c is located at one end of one diffractive optical element 35. The uneven shape is formed by the flat surface 35a, the connecting surface 35b, and the end surface 35c.

[0025] The flat surface 35a and the connection surface 35b are gradually separated from the base 33. In the example shown in FIG. 5, the flat surface 35a and the connection surface 35b are perpendicular to each other. The number of flat surfaces 35a in the diffractive optical element 35 is the number of steps of the diffractive optical element 35. The number of steps of the diffractive optical element 35 may be 2 or more, or may be 32 or less. At each position of the diffractive optical element 30, the number of flat surfaces 35a and the number of connection surfaces 35b included in the diffractive optical element 35 may be different. At each position of the diffractive optical element 35, the number of steps of the diffractive optical element 35 may be different. The end surface 35c connects the flat surface 35a that is farthest from the base 33 among the flat surfaces 35a included in the diffractive optical element 35 and the flat surface 35a that is closest to the base 33 among the flat surfaces 35a included in the diffractive optical element 35 adjacent to the diffractive optical element 35 on the flat surface 35a. The end surface 35c is perpendicular to the flat surface 35a.

[0026] The refractive index of the diffractive optical element 35 may be 1.5 or more, or may be 1.6 or more, or may be 1.7 or more, or may be 1.8 or more, or may be 1.9 or more. The refractive index of the diffractive optical element 35 is the refractive index with respect to the wavelength of the light incident on the diffractive optical element 35. In the present embodiment, the refractive index of the diffractive optical element 35 is the refractive index with respect to the wavelength of the light emitted by the light emitter 25a included in the light source 25. When the light emitter 25a emits light having a wavelength of 940 nm, the refractive index of the diffractive optical element 35 with respect to the light having a wavelength of 940 nm may be 1.5 or more, or may be 1.6 or more, or may be 1.7 or more, or may be 1.8 or more, or may be 1.9 or more. The refractive index of the diffractive optical element 35 is a value measured by a spectroscopic ellipsometer (M-2000 manufactured by J. A. Woolam Japan Co., Ltd.).

[0027] The duty ratio of the diffractive optical element 35 may be less than 0.5, may be 0.45 or less, may be 0.3 or more, or may be 0.35 or more. The duty ratio of the diffractive optical element 35 is a value obtained by dividing the volume of the diffractive optical element 35 by the sum of the volume of the flattened portion and the volume of the diffractive optical element 35 when the uneven shape formed by the diffractive optical element 35 is flattened along the flat surface 35a farthest from the base portion 33 of the diffractive optical element 35. In other words, the duty ratio of the diffractive optical element 35 means a value obtained by dividing the volume of the diffractive optical element 35 by the product of the bottom area S and the height H of the diffractive optical element 35. In the example shown in FIG. 6, the bottom area S is the sum of the areas of the flat surfaces 35a in the diffractive optical element 35 excluding the flat surface 35a closest to the base portion 33 of the diffractive optical element 35. The height H is the sum of the lengths of the connection surfaces 35b along the normal direction of the diffractive optical element 30, and is the length of the end surface 35c along the normal direction of the diffractive optical element 30. The normal direction of the diffractive optical element 30 refers to the normal direction to the sheet surface of the diffractive optical element 30. The sheet surface of the diffractive optical element 30 refers to the surface that coincides with the diffractive optical element 30 when the diffractive optical element 30 is viewed as a whole and globally.

[0028] The duty ratio of the diffractive optical element 35 is calculated from data measured using an atomic force microscope (AFM). For example, when measuring by scanning a range of 20 μm × 20 μm, the bottom area S is 400 μm 2 . When measuring under scanning conditions of, for example, 512 points × 64 lines, 32,768 points of data are plotted as a histogram. In the histogram, the flat surfaces 35a of the diffractive optical element 35 each form a peak. The height H of the diffractive optical element 35 is calculated from the difference between the peak formed by the flat surface 35a farthest from the base portion 33 and the peak formed by the flat surface 35a closest to the base portion 33. The average height of the diffractive optical element 35 is calculated by calculating and averaging the difference between the peak value formed by the closest flat surface 35a and all 32,768 points of data. The volume of the diffractive optical element 35 is calculated by the product of the bottom area S and the average height.

[0029] Data measured by AFM is generally greatly affected by the probe shape at the tip of the AFM needle. Therefore, it is preferable to perform correction processing to reduce the influence of the probe shape on the data measured by AFM. For example, by comparing the measurement data of a scanning electron microscope (SEM) or a transmission electron microscope (TEM) with the measurement data of AFM for a line-and-space pattern whose shape is easy to analyze, correction parameters for subtracting the probe shape are calculated.

[0030] When the number of steps of the diffractive optical element 35 is large, the flat surface 35a farthest from the base 33 or the flat surface 35a closest to the base 33 may not appear as the peak of the histogram of the data measured using AFM. In that case, it is preferable to perform shape observation using SEM or TEM to adjust the flat surface 35a farthest from the base 33 or the flat surface 35a closest to the base 33 to form a peak in the histogram of the data measured using AFM.

[0031] It is preferable to measure the duty ratio of the diffractive optical element 35 at three or more locations of the diffractive optical element 30 and use the average of the measured duty ratios as the duty ratio of the diffractive optical element 35 in the diffractive optical element 30. The three or more measurement locations for measuring the duty ratio of the diffractive optical element 35 are preferably included in the range where the divergent lights L31 and L41 emitted by the light emitter 25a of the light source 25 are incident.

[0032] The height H of the diffractive optical element 35 may be higher than the theoretical height for obtaining the inverse phase of the light incident on the diffractive optical element 30, may be 1.1 times or more of the height, may be 1.2 times or less of the height, or may be 1.1 times or less of the height. In the present embodiment, the theoretical height for obtaining the inverse phase of the light incident on the diffractive optical element 30 is expressed by the following formula (i).

Equation

[0033] The material of the base 33 and the diffractive optical element 35 may be a titania-containing acrylic resin (PixNIL ST1 manufactured by Pixelligent) or a zirconia-containing acrylic resin (PixNIL SZ1 manufactured by Pixelligent).

[0034] The primer layer 37 improves the adhesion between the support 31 and the base 33 and the diffractive optical element 35. The primer layer 37 is made of, for example, a silane coupling agent. The thickness of the primer layer 37 is, for example, 5 nm or more and 100 nm or less.

[0035] The antireflection layer 39 suppresses reflection on the surface of the diffractive optical element 30. The antireflection layer 39 is disposed so as to form one surface of the diffractive optical element 30. The antireflection layer 39 may be a single layer or may include a plurality of layers having different refractive indexes. When the antireflection layer 39 includes a plurality of layers having different refractive indexes, the light reflected at the interfaces between the layers having different refractive indexes interferes with each other so as to cancel each other out, thereby suppressing the observation of the light reflected on the surface of the diffractive optical element 30. The antireflection layer 39 is transparent. The thickness of the antireflection layer 39 may be 100 nm or more or may be 10 μm or less. The antireflection layer 39 is formed, for example, by sputtering or vapor-depositing titanium oxide or silicon dioxide on a base material such as glass, acrylic, or triacetyl cellulose, or by disposing an ultraviolet curable resin such as urethane acrylate, irradiating with ultraviolet rays to cure the resin, and then disposing an acrylic ultraviolet curable resin and irradiating with ultraviolet rays to cure the resin.

[0036] FIG. 7 is a schematic perspective view showing a state in which light is projected from the projection device 20 onto the object 5. The light-emitting bodies 25a included in the light source 25 each emit divergent light. The emitted divergent light L71 is incident on the diffractive optical element 30. The diffractive optical element 30 converts the traveling direction of the incident light so as to make the divergent light into parallel light. The diffractive optical element 30 branches the incident light in a plurality of directions. In the example shown in FIG. 7, the light L72 diffracted by the diffractive optical element 30 branches in three directions in the X direction. Since the light-emitting bodies 25a are arranged in groups of three along the X direction and in groups of three along the Y direction, three dot-like images are arranged in the Y direction and nine dot-like images are arranged in the X direction on the object 5. Not limited to the illustrated example, the light diffracted by the diffractive optical element 30 may also branch in the Y direction. The light branched in three directions is the 0th-order diffracted light and the ±1st-order diffracted light diffracted by the diffractive optical element 35 of the diffractive optical element 30. The diffractive optical element 35 is designed so that diffracted light of ±2nd order or higher is sufficiently weaker than the 0th-order diffracted light and the ±1st-order diffracted light and is not observed. The light diffracted by the diffractive optical element 30 may branch in five or more directions. In this case, the diffractive optical element 35 is designed so that diffracted light of ±2nd order or higher is also observed. By the diffractive optical element 30 branching the incident light in a plurality of directions, the number of images irradiated on the object 5 can be increased without increasing the number of light-emitting bodies 25a of the light source 25.

[0037] A diffractive optical element having a conventional lens function and a branching function has a significantly lower diffraction efficiency as it moves away from the center of the diffractive optical element compared to a diffractive optical element having only a branching function. The center of the diffractive optical element means the center of a concentric pattern for exerting the lens function, and means a position where the traveling direction of the incident light is not converted and the light is branched in a plurality of directions. In this case, as approaching the outer periphery of the object, the diffraction efficiency decreases and the image becomes thinner. When there is a thin image, for example, when a projection device having a diffractive optical element is used as part of a detection device, the detection accuracy varies depending on the position. As a result, appropriate detection cannot be performed.

[0038] By increasing the duty ratio of the diffractive optical element, the diffraction efficiency of the diffractive optical element can be increased. When the duty ratio of the diffractive optical element is increased, the light that passes through the diffractive optical element without being diffracted increases. The light that passes through the diffractive optical element without being diffracted becomes noise and deteriorates the visibility of the entire diffracted light. It is difficult to reduce the light that passes through without being diffracted while increasing the diffraction efficiency only by adjusting the duty ratio.

[0039] In the diffractive optical element 30 of the present embodiment, the duty ratio of the diffractive optical element 35, in other words, the value obtained by dividing the volume of the diffractive optical element 35 by the product of the bottom area S and the height H of the diffractive optical element 35 is less than 0.5, and the height H of the diffractive optical element 35 is higher than the theoretical value height for obtaining light of the opposite phase of the light incident on the diffractive optical element 30. Since the duty ratio of the diffractive optical element 35 is not too high, the light that passes through the diffractive optical element 30 without being diffracted by the diffractive optical element 35 can be reduced. Since the height H of the diffractive optical element 35 is sufficiently high, the diffraction efficiency of the diffractive optical element 30 is increased. In the diffractive optical element 30 having a lens function and a branching function, the light that passes through without being diffracted can be reduced while increasing the diffraction efficiency.

[0040] The refractive index of the diffractive optical element 35 with respect to the wavelength of the light incident on the diffractive optical element 35 may be 1.7 or more. When the refractive index of the diffractive optical element 35 increases, the theoretical value height for obtaining the opposite phase of the light incident on the diffractive optical element 30 can be lowered, so the height of the diffractive optical element 35 can be lowered. When the height of the diffractive optical element 35 is lowered, the three-dimensional effect is reduced, so that a decrease in diffraction efficiency can be suppressed even at a position away from the center of the diffractive optical element 30.

[0041] The refractive index of the diffractive optical element 35 with respect to the wavelength of the light incident on the diffractive optical element 30 may be 1.8 or less. Since the refractive index of the diffractive optical element 35 is not too high, the diffractive optical element 30 can be easily manufactured by molding.

[0042] The value obtained by dividing the volume of the diffractive optical element 35 by the product of the bottom area S and the height H of the diffractive optical element 35 may be 0.3 or more. Since the duty ratio of the diffractive optical element 35 is not too low, the diffraction efficiency of the diffractive optical element 30 does not become too low.

[0043] The height H of the diffractive optical element 35 may be 1.2 times or less the theoretical height for obtaining light of the opposite phase to the light incident on the diffractive optical element 30. Since the height of the diffractive optical element 35 is not too high, light of the opposite phase to the light incident on the diffractive optical element 30 can be obtained by the diffractive optical element 35. The diffractive optical element 30 can diffract light appropriately, and the diffraction efficiency is improved.

[0044] The diffractive optical element 30 of the present embodiment converts the traveling direction of incident light and branches the incident light in a plurality of directions. The diffractive optical element 30 includes a plurality of diffractive optical elements 35. The diffractive optical element 35 includes a plurality of flat surfaces 35a and a connection surface 35b connecting between the two flat surfaces 35a. The value obtained by dividing the volume of the diffractive optical element 35 by the product of the bottom area and the height of the diffractive optical element 35 is less than 0.5. The height of the diffractive optical element 35 is higher than the theoretical height for obtaining light of the opposite phase to the light incident on the diffractive optical element 30. According to the diffractive optical element 30 of the present embodiment, in a diffractive optical element having a lens function and a branching function, light that is transmitted without being diffracted can be reduced while increasing the diffraction efficiency.

[0045] Aspects of the present disclosure are not limited to the above-described embodiments, but also include various modifications that can be conceived by those skilled in the art, and the effects of the present disclosure are not limited to the content related to the above-described embodiments and their modifications. Various additions, changes, and partial deletions are possible without departing from the conceptual ideas and spirit derived from the content defined in the claims and their equivalents.

Example

[0046] The present disclosure will be described in more detail with reference to examples. The present disclosure is not limited to the following examples.

[0047] As examples and comparative examples, diffraction efficiency and the ratio of light that is transmitted without being diffracted by the diffractive optical element were simulated for different diffractive optical elements. The wavelength of the light incident on each diffractive optical element was 940 nm. In each diffractive optical element, the number of stages of the diffractive optical element was 8. Each diffractive optical element converts the traveling direction of the incident light and branches the incident light into a plurality of directions. The lens function of each diffractive optical element is the function of a collimating lens with an effective focal length of 2 mm. The branching function of each diffractive optical element is a function of branching light into three directions with respect to the X direction. The diffractive optical elements are arranged with a pitch of 2.68 μm in the X direction and are arranged with a pitch that appropriately exhibits the lens function in the Y direction. The incident light on the diffractive optical element is diffracted so that the first-order diffracted light spreads 20.53° in the X direction.

[0048] In each diffractive optical element, the refractive index, duty ratio, and height of the diffractive optical element are different. Specifically, in each diffractive optical element, the refractive index of the diffractive optical element is 1.5, 1.6, 1.7, 1.8, or 1.9. In each diffractive optical element, the duty ratio of the diffractive optical element is 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, or 0.6. In each diffractive optical element, the height of the diffractive optical element is 1.0 times, 1.1 times, 1.2 times, or 1.3 times the theoretical value height for obtaining light of the opposite phase of light with a wavelength of 940 nm. Each diffractive optical element was assumed to be in air, and the refractive index n0 of the medium was set to 1.

[0049] The radiation intensity of the diffracted light in each diffractive optical element was calculated by the RCWA method, and the integrated value of the diffraction efficiency of the 0th-order diffracted light and the ±1st-order diffracted light with respect to the length in the Y direction from the center of the diffractive optical element with respect to the incident light, and the ratio of the light that was transmitted without being diffracted by the diffractive optical element with respect to the incident light were calculated. The ratio of the integrated value of the diffraction efficiency of the 0th-order diffracted light and the ±1st-order diffracted light to the ratio of the light that was transmitted without being diffracted by the diffractive optical element at the same length in the Y direction from the center of the diffractive optical element with respect to the incident light was calculated.

[0050] For each diffractive optical element, the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the distance in the Y direction from the center of the diffractive optical element, the result of calculating the ratio of the light transmitted without being diffracted by the diffractive optical element, and the result of calculating the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light are shown in separate graphs. The horizontal axis of the graph represents the length [μm] in the Y direction from the center of the diffractive optical element. The vertical axis of the graph represents the integrated value [%] of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light, the ratio [%] of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light, or the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light. The ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light is represented by a semi-logarithmic graph. The numerical values from 1.5 to 1.9 representing each line of the graph represent the refractive index of the diffractive optical element. The relationship between the length in the Y direction from the center of the diffractive optical element, which is the horizontal axis of the graph, and the pitch in the X direction and the pitch in the Y direction of the diffractive optical element is as shown in Table 1 below.

[0051]

Table 1

[0052] Figure 8 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights at each refractive index of the diffractive optical element of a diffractive optical element having a duty ratio of 0.3 and a height that is 1.0 times the height for obtaining light of the opposite phase to light with a wavelength of 940 nm. Figure 9 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in Figure 8. Figure 10 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in Figures 8 and 9.

[0053] FIG. 11 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.3 and the height of the diffractive optical element is 1.1 times the height for obtaining light with an inverse phase of light having a wavelength of 940 nm. FIG. 12 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 11. FIG. 13 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 11 and 12.

[0054] FIG. 14 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.3 and the height of the diffractive optical element is 1.2 times the height for obtaining light with an inverse phase of light having a wavelength of 940 nm. FIG. 15 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 14. FIG. 16 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 14 and 15.

[0055] FIG. 17 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.3 and the height of the diffractive optical element is 1.3 times the height for obtaining light with an opposite phase to the light of a wavelength of 940 nm. FIG. 18 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 17. FIG. 19 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 17 and 18.

[0056] FIG. 20 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.35 and the height of the diffractive optical element is 1.0 times the height for obtaining light with an opposite phase to the light of a wavelength of 940 nm. FIG. 21 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 20. FIG. 22 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 20 and 21.

[0057] FIG. 23 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.35 and the height of the diffractive optical element is 1.1 times the height for obtaining light with an opposite phase to the light of a wavelength of 940 nm. FIG. 24 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 23. FIG. 25 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 23 and 24.

[0058] FIG. 26 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.35 and the height of the diffractive optical element is 1.2 times the height for obtaining light with an opposite phase to the light of a wavelength of 940 nm. FIG. 27 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 26. FIG. 28 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 26 and 27.

[0059] FIG. 29 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.35 and the height of the diffractive optical element is 1.3 times the height for obtaining light of opposite phase to the light with a wavelength of 940 nm. FIG. 30 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 29. FIG. 31 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 29 and 30.

[0060] FIG. 32 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.4 and the height of the diffractive optical element is 1.0 times the height for obtaining light of opposite phase to the light with a wavelength of 940 nm. FIG. 33 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 32. FIG. 34 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 32 and 33.

[0061] FIG. 35 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.4 and the height of the diffractive optical element is 1.1 times the height for obtaining light of opposite phase to the light with a wavelength of 940 nm. FIG. 36 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 35. FIG. 37 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 35 and 236.

[0062] FIG. 38 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.4 and the height of the diffractive optical element is 1.2 times the height for obtaining light of opposite phase to the light with a wavelength of 940 nm. FIG. 39 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 38. FIG. 40 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 38 and 39.

[0063] FIG. 41 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.4 and the height of the diffractive optical element is 1.3 times the height for obtaining light with an inverse phase of light having a wavelength of 940 nm. FIG. 42 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 41. FIG. 43 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 41 and 42.

[0064] FIG. 44 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.45 and the height of the diffractive optical element is 1.0 times the height for obtaining light with an inverse phase of light having a wavelength of 940 nm. FIG. 45 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 44. FIG. 46 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 44 and 45.

[0065] FIG. 47 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.45 and the height of the diffractive optical element is 1.1 times the height for obtaining light with an opposite phase to the light of wavelength 940 nm. FIG. 48 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 47. FIG. 49 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 47 and 48.

[0066] FIG. 50 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.45 and the height of the diffractive optical element is 1.2 times the height for obtaining light with an opposite phase to the light of wavelength 940 nm. FIG. 51 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 50. FIG. 52 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 50 and 51.

[0067] FIG. 53 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.45 and the height of the diffractive optical element is 1.3 times the height for obtaining light with an opposite phase to the light of a wavelength of 940 nm. FIG. 54 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 53. FIG. 55 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 53 and 54.

[0068] FIG. 56 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.5 and the height of the diffractive optical element is 1.0 times the height for obtaining light with an opposite phase to the light of a wavelength of 940 nm. FIG. 57 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 56. FIG. 58 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 56 and 57.

[0069] FIG. 59 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.5 and the height of the diffractive optical element is 1.1 times the height for obtaining light of the opposite phase to the light with a wavelength of 940 nm. FIG. 60 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 59. FIG. 61 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 59 and 60.

[0070] FIG. 62 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.5 and the height of the diffractive optical element is 1.2 times the height for obtaining light of the opposite phase to the light with a wavelength of 940 nm. FIG. 63 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 62. FIG. 64 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 62 and 63.

[0071] FIG. 65 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.5 and the height of the diffractive optical element is 1.3 times the height for obtaining light of opposite phase to the light with a wavelength of 940 nm. FIG. 66 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 65. FIG. 67 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 65 and 66.

[0072] FIG. 68 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.55 and the height of the diffractive optical element is 1.0 times the height for obtaining light of opposite phase to the light with a wavelength of 940 nm. FIG. 69 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 68. FIG. 70 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 68 and 69.

[0073] FIG. 71 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.55 and the height of the diffractive optical element is 1.1 times the height for obtaining light with a phase opposite to that of light with a wavelength of 940 nm. FIG. 72 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 71. FIG. 73 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 71 and 72.

[0074] FIG. 74 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.55 and the height of the diffractive optical element is 1.2 times the height for obtaining light with a phase opposite to that of light with a wavelength of 940 nm. FIG. 75 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 74. FIG. 76 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 74 and 75.

[0075] FIG. 77 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.55 and the height of the diffractive optical element is 1.3 times the height for obtaining light of the opposite phase to the light with a wavelength of 940 nm. FIG. 78 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 77. FIG. 79 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 77 and 78.

[0076] FIG. 80 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.6 and the height of the diffractive optical element is 1.0 times the height for obtaining light of the opposite phase to the light with a wavelength of 940 nm. FIG. 81 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 80. FIG. 82 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 80 and 81.

[0077] FIG. 83 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.6 and the height of the diffractive optical element is 1.1 times the height for obtaining light with a phase opposite to that of light with a wavelength of 940 nm. FIG. 84 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 83. FIG. 85 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 83 and 84.

[0078] FIG. 86 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element at each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights, where the duty ratio of the diffractive optical element is 0.6 and the height of the diffractive optical element is 1.2 times the height for obtaining light with a phase opposite to that of light with a wavelength of 940 nm. FIG. 87 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 86. FIG. 88 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted lights with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 86 and 87.

[0079] FIG. 89 is a graph showing the relationship between the length in the Y direction from the center of a diffractive optical element to each refractive index of the diffractive optical element and the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted light of the diffractive optical element, where the duty ratio of the diffractive optical element is 0.6 and the height of the diffractive optical element is 1.3 times the height for obtaining light of opposite phase to light with a wavelength of 940 nm. FIG. 90 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the light transmitted without being diffracted by the diffractive optical element for the same diffractive optical element as in FIG. 89. FIG. 91 is a graph showing the relationship between the length in the Y direction from the center of the diffractive optical element and the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted light with respect to the incident light to the ratio of the light transmitted without being diffracted by the diffractive optical element with respect to the incident light for the same diffractive optical element as in FIGS. 89 and 90.

[0080] A method for measuring the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted light will be described. A diffractive optical element is disposed movably on a stage. The diffractive optical element is irradiated with divergent light from a light source. The light source consists of a single emitter such as LP940 SF30 manufactured by THORLABS, for example. By moving the diffractive optical element, while diffracting the divergent light from the light source by the diffractive optical element, the position for measuring the diffraction efficiency in the diffractive optical element is accurately specified. The diffraction efficiency is measured by making the light diffracted by the diffractive optical element incident on a power sensor. The power sensor is an integrating sphere power sensor such as S142C manufactured by THORLABS, for example. The distance between the diffractive optical element and the integrating sphere power sensor is adjusted so that the light diffracted by the diffractive optical element is directly incident on the integrating sphere power sensor. The distance between the diffractive optical element and the integrating sphere power sensor is adjusted to be 100 mm or more and 1000 mm or less.

[0081] A method for measuring light that passes through a diffractive optical element without being diffracted will be described. The diffractive optical element is placed movably on a stage. The diffractive optical element is irradiated with collimated light from a light source. As the light source, for example, a system in which LP940 SF30 manufactured by THORLABS is used as a light emitter and PAF-X-5-B manufactured by THORLABS is connected as a FiberPort Collimator lens is applied. By moving the diffractive optical element, the light that has passed through the diffractive optical element without being diffracted is appropriately separated from the light diffracted by the diffractive optical element. The light that has passed through the diffractive optical element without being diffracted is measured by making it incident on a power sensor. The power meter is an integrating sphere power sensor such as S142C manufactured by THORLABS, for example. The distance between the diffractive optical element and the integrating sphere power sensor is adjusted so that the light that has passed through the diffractive optical element without being diffracted is directly incident on the integrating sphere power sensor. The distance between the diffractive optical element and the integrating sphere power sensor is adjusted to be 100 mm or more and 1000 mm or less.

[0082] From FIGS. 8 to 91, the following can be understood. By making the duty ratio of the diffractive optical element smaller than 0.5, the light passing through the diffractive optical element without being diffracted by the diffractive optical element can be reduced. By making the height of the diffractive optical element higher than the height for obtaining light of the opposite phase to the light incident on the diffractive optical element, the diffraction efficiency of the diffractive optical element is increased. When these conditions are satisfied, regardless of the value of the length in the Y direction from the center of the diffractive optical element, the ratio of the integrated value of the diffraction efficiencies of the 0th-order diffracted light and the ±1st-order diffracted light with respect to the incident light to the ratio of the light passing through the diffractive optical element without being diffracted with respect to the incident light is sufficiently large. The diffraction efficiency of the diffractive optical element is high, and the light passing through the diffractive optical element without being diffracted is reduced. By making the refractive index of the diffractive optical element 1.7 or more, a decrease in the diffraction efficiency can be suppressed even at a position away from the center of the diffractive optical element. By making the duty ratio of the diffractive optical element 0.3 or more, the diffraction efficiency of the diffractive optical element does not become too low. By making the height of the diffractive optical element 1.2 times or less the height for obtaining light of the opposite phase to the light incident on the diffractive optical element, the diffraction efficiency of the diffractive optical element is improved.

Explanation of Reference Numerals

[0083] 1 Detection device 3 Medium 5 Object 10 Light receiving device 20 Projection device 25 Light source 25a Light emitter 30 Diffractive optical element 31 Support 33 Base 35 Diffractive optical element 35a Flat surface 35b Connection surface 35c End face 37 Primer layer 39 Low reflection layer

Claims

1. A diffractive optical element that converts the traveling direction of incident light and branches the incident light into a plurality of directions, comprising a plurality of diffractive optical elements, wherein the diffractive optical element includes a plurality of flat surfaces and a connecting surface connecting between two of the flat surfaces, a value obtained by dividing the volume of the diffractive optical element by the product of the bottom area and the height of the diffractive optical element is less than 0.5, and the height of the diffractive optical element is higher than a theoretical value height for obtaining light of an opposite phase to the light incident on the diffractive optical element.

2. The diffractive optical element according to claim 1, wherein a refractive index of the diffractive optical element with respect to a wavelength of light incident on the diffractive optical element is 1.7 or more.

3. The diffractive optical element according to claim 1, wherein a value obtained by dividing the volume of the diffractive optical element by the product of the bottom area and the height of the diffractive optical element is 0.3 or more.

4. The diffractive optical element according to claim 1, wherein the height of the diffractive optical element is 1.2 times or less of a theoretical value height for obtaining light of an opposite phase to the light incident on the diffractive optical element.

5. A projection device comprising the diffractive optical element according to claim 1 and a plurality of light emitters that emit light onto the diffractive optical element.

6. The projection device according to claim 5, wherein the plurality of light emitters are two-dimensionally arranged.

7. The projection device according to claim 5, wherein the light emitted by the light emitter includes light having a wavelength of 940 nm.

8. A detection device comprising the projection device according to claim 5 and a light receiving device capable of detecting light projected by the projection device.

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