JP6958120B2 - Diffractive optical element, light irradiation device - Google Patents

Description

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

In recent years, there has been an increase in the need for sensor systems, such as the need for personal authentication to avoid security risks due to the spread of networks, the trend toward autonomous driving of automobiles, and the spread of the so-called "Internet of Things". There is. There are various types of sensors, and the information to be detected is also various. One of the means is to irradiate an object with light from a light source and obtain information from the reflected light. .. For example, a pattern authentication sensor, an infrared radar, and the like are examples.

As the light source of these sensors, one having a wavelength distribution, brightness, and spread according to the application is used. Visible light to infrared rays are often used as the wavelength of light, and infrared rays are widely used because they are not easily affected by external light, are invisible, and can observe the inside of an object. There is. Further, as a type of light source, an LED light source, a laser light source, or the like is often used. For example, a laser light source having a small spread of light is preferably used to detect a distant place, and an LED light source is preferably used to detect a relatively close place or to irradiate a region having a certain spread. Be done.

By the way, the size and shape of the target irradiation area do not always match the spread (profile) of the light from the light source, and in that case, the light is shaped by a diffuser plate, a lens, a shielding plate, or the like. There is a need. Recently, a diffuser called Light Shipping Diffuser (LSD), which can shape the shape of light to some extent, has been developed.
Further, as another means for shaping light, a diffractive optical element (DOE) can be mentioned. This is an application of the diffraction phenomenon when light passes through a place where materials with different refractive indexes are arranged with periodicity. The DOE is basically designed for light of a single wavelength, but in theory, it is possible to shape the light into almost any shape. Further, in the above-mentioned LSD, the light intensity in the irradiation region has a Gaussian distribution, whereas in DOE, it is possible to control the uniformity of the light distribution in the irradiation region. Such characteristics of DOE are advantageous in terms of high efficiency by suppressing irradiation of unnecessary regions and miniaturization of the device by reducing the number of light sources (see, for example, Patent Document 1).
In addition, DOE can be applied to both parallel light sources such as lasers and diffused light sources such as LEDs, and can be applied to a wide range of wavelengths from ultraviolet light to visible light and infrared light. ..

DOE requires microfabrication on the order of nm, and particularly in order to diffract light having a long wavelength, it is necessary to form a fine shape having a high aspect ratio. Therefore, electron beam lithography technology using an electron beam has been conventionally used for manufacturing DOE. For example, after forming a hard mask or resist on a quartz plate that is transparent in the ultraviolet to near-infrared region, a predetermined shape is drawn on the resist using an electron beam, and resist development, dry etching of the hard mask, and drying of quartz are performed. A desired DOE can be obtained by sequentially performing etching to form a pattern on the surface of the quartz plate and then removing the hard mask.

When the LED light source and the DOE are used in combination, the light having a certain spread reaches the DOE from the LED light source. Therefore, since the incident angle of the incident light incident on the DOE differs depending on the position on the DOE, the design of the diffraction grating is changed depending on the position on the DOE, that is, the incident angle. Since the diffraction angle of the DOE is determined by the wavelength of light and the pitch of the diffraction grating, the design is such that the pitch of the diffraction grating is changed according to the position on the DOE (depending on the incident angle). On the other hand, regarding the groove depth of the diffraction grating, in the case of two-level DOE, the following equation consisting of the wavelength λ of light and the refractive index n of the material constituting the diffraction grating is known.
Groove depth = λ / (2 (n-1))
In DOE, it is said that the light emission efficiency is the best when the groove depth obtained by the above formula is used, and conventionally, the design according to this formula has been performed.

Japanese Unexamined Patent Publication No. 2015-170320

However, the groove depth of DOE is not only uniquely determined by the above formula, but can be further improved in efficiency by changing the groove depth, or unnecessary light emission (for example, 0th order light) can be generated. I found that it could be reduced.

An object of the present invention is to provide a diffractive optical element and a light irradiation device capable of further improving the light utilization efficiency and suppressing unnecessary light emission.

The present invention solves the above problems by the following solutions. In addition, in order to facilitate understanding, the description will be given with reference numerals corresponding to the embodiments of the present invention, but the present invention is not limited thereto.

The first invention is a diffractive optical element (10) that shapes light, and has a high refractive index portion (11) in which a plurality of convex portions (11a) are arranged side by side in a cross-sectional shape, and the high refractive index. A diffraction layer (15) having a low refractive index portion (14) having a refractive index lower than that of the portion (11) and including a concave portion (12) formed between at least the convex portions (11a) is provided. The width of the recess (12) differs depending on the position, and the wider the width of the recess (12), the deeper the depth of the recess (12) is configured in the diffractive optical element (10).

In the second invention, in the diffractive optical element (10) according to the first invention, the depth L of the recess (12) at the position where the width of the recess (12) is the narrowest is the wavelength of the light to be diffracted. Is λ, the refractive index of the high refractive index portion (11) is n, and when a coefficient of 0.8 or more and 1.2 or less is F, the depth is D = Fλ / (2 (n-1)). It is a diffractive optical element (10) characterized by being configured.

The third invention is the diffractive optical element (10) according to the second invention, wherein the coefficient F is 1 or more and 1.2 or less.

A fourth invention is a diffraction optical element (10) according to any one of the first to third inventions, wherein the wavelength λ of the light to be diffracted is 780 nm or more. The optical element (10).

The fifth invention is the diffractive optical element (10) according to any one of the first to fourth inventions, wherein the diffractive optical element (10) has an incident angle larger than 0 ° and 60 ° or less. The diffractive optical element (10) is characterized in that the light incident in the above is used as the light to be diffracted.

In the sixth invention, in the diffractive optical element (10) according to any one of the first to fifth inventions, the width of the recess (12) and the depth of the recess (12) are in a proportional relationship. The diffractive optical element (10) is characterized in that.

A seventh invention includes a light source unit (210), a diffractive optical element (10) that is arranged at a position where light from the light source unit (210) is incident and forms light from the light source unit (210). The diffractive optical element (10) has a high refraction rate portion (11) in which a plurality of convex portions (11a) are arranged side by side in a cross-sectional shape, and a refraction coefficient higher than that of the high refraction rate section (11). The diffraction layer (15) has a low refractive index portion (14) including a concave portion (12) formed between the convex portions (11a), and the width of the concave portion (12) is large. This is a light irradiation device in which the depth of the recess (12) is deeper as the width of the recess (12) becomes wider.

According to the eighth invention, in the light irradiation device according to the seventh invention, the light source unit (210) emits light at a depth L of the recess (12) at a position where the width of the recess (12) is the narrowest. When the wavelength of light is λ, the refractive index of the high refractive index portion (11) is n, and the coefficient of 0.8 or more and 1.2 or less is F, D = Fλ / (2 (n-1)). It is a light irradiation device characterized by being configured to a depth.

The ninth invention is the light irradiation device according to the eighth invention, wherein the coefficient F is 1 or more and 1.2 or less.

The tenth invention is the light irradiation device according to any one of the seventh to ninth inventions, wherein the wavelength λ of the light to be diffracted is 780 nm or more. be.

According to the eleventh invention, in the light irradiation device according to any one of the seventh to tenth inventions, the diffraction optical element (10) is diffracted at an incident angle larger than 0 ° and 60 ° or less. The light irradiation device is characterized in that the light source unit (210) and the diffractive optical element (10) are arranged so that the light of the above is incident.

According to the twelfth invention, in the light irradiation device according to any one of the seventh to eleventh inventions, the width of the recess (12) and the depth of the recess (12) have a proportional relationship. It is a light irradiation device characterized by being present.

According to the present invention, it is possible to provide a diffractive optical element and a light irradiation device capable of further improving the light utilization efficiency and suppressing unnecessary light emission.

It is a top view which shows the embodiment of the diffraction optical element by this invention. It is a perspective view which shows an example of the partial periodic structure in the example of the diffraction optical element of FIG. It is sectional drawing which cut | cut the diffractive optical element at the position of the arrow EE'in FIG. It is a figure explaining the diffraction optical element. It is a figure explaining the difference in the design of the diffraction grating due to the difference in the position on the diffraction optical element 10. It is a figure which shows side-by-side diffraction gratings with different diffraction angles. It is a figure which shows the cross-sectional shape of the diffraction grating of the diffraction optical element 10 of this embodiment at a different position. It is a figure which summarized the simulation result of the wavelength λ = 800 nm and the incident angle 15 degrees. It is a figure which summarized the simulation result of the wavelength λ = 800 nm and the incident angle 15 degrees. It is a figure which summarized the simulation result of the wavelength λ = 800 nm and the incident angle 30 degrees. It is a figure which summarized the simulation result of the wavelength λ = 800 nm and the incident angle 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 0.8λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 1λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 1.5λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 2λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 3λ, and the incident angle is 15 degrees. FIG. 17 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 800 nm, the pitch is 0.8 λ, and the incident angle is 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 1λ, and the incident angle is 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 1.5λ, and the incident angle is 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 2λ, and the incident angle is 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 800 nm, the pitch is 3λ, and the incident angle is 30 degrees. It is the figure which summarized the simulation result of the wavelength λ = 980 nm, the incident angle 15 degrees. It is the figure which summarized the simulation result of the wavelength λ = 980 nm, the incident angle 15 degrees. It is the figure which summarized the simulation result of the wavelength λ = 980 nm, the incident angle 30 degrees. It is the figure which summarized the simulation result of the wavelength λ = 980 nm, the incident angle 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 0.8λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 1λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 1.5λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 2λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 3λ, and the incident angle is 15 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 0.8λ, and the incident angle is 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 1λ, and the incident angle is 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 1.5λ, and the incident angle is 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 2λ, and the incident angle is 30 degrees. It is a graph which shows the influence of the depth on the light emission value when the wavelength λ = 980 nm, the pitch is 3λ, and the incident angle is 30 degrees. It is the figure which summarized the simulation result which changed the incident angle to 0 °, 15 °, 30 °, 60 ° for the wavelength λ = 800 nm and the pitch 0.8λ. It is the figure which summarized the simulation result which changed the incident angle to 0 °, 15 °, 30 °, 60 ° for the wavelength λ = 800 nm and the pitch 1λ. It is the figure which summarized the simulation result which changed the incident angle to 0 °, 15 °, 30 °, 60 ° for the wavelength λ = 800 nm and the pitch 1.5λ. It is the figure which showed the result of FIG. 36 in a graph and arranged side by side. It is the figure which showed the result of FIG. 37 in a graph and arranged side by side. It is the figure which showed the result of FIG. 38 in a graph and arranged side by side. It is the figure which summarized the simulation result which changed the incident angle to 0 °, 15 °, 30 °, 60 ° for the wavelength λ = 980 nm and the pitch 0.8λ. It is the figure which summarized the simulation result which changed the incident angle to 0 °, 15 °, 30 °, 60 ° for the wavelength λ = 980 nm and the pitch 1λ. It is the figure which summarized the simulation result which changed the incident angle to 0 °, 15 °, 30 °, 60 ° for the wavelength λ = 980 nm and the pitch 1.5λ. It is the figure which showed the result of FIG. 42 in a graph and arranged side by side. It is the figure which showed the result of FIG. 43 in a graph and arranged side by side. It is a figure which showed the result of FIG. 44 in a graph, side by side.

Hereinafter, the best mode for carrying out the present invention will be described with reference to drawings and the like.

(Embodiment)
FIG. 1 is a plan view showing an embodiment of a diffractive optical element according to the present invention.
FIG. 2 is a perspective view showing an example of a partial periodic structure in the example of the diffractive optical element of FIG.
FIG. 3 is a cross-sectional view of the diffractive optical element cut at the position of the arrow EE'in FIG.
FIG. 4 is a diagram illustrating a diffractive optical element.
It should be noted that each of the figures shown below, including FIG. 1, is a diagram schematically shown, and the size and shape of each part are exaggerated as appropriate for easy understanding.
Further, in the following description, specific numerical values, shapes, materials and the like will be described, but these can be changed as appropriate.

The terms used in the present invention that specify the shape and geometric conditions and their degrees, such as terms such as "parallel", "orthogonal", and "same", and length and angle values, are strictly defined. Without being bound by meaning, we will interpret it including the range in which similar functions can be expected.

Further, in the present invention, "shaping the light" means that the shape of the light projected on the object or the target area (irradiation area) becomes an arbitrary shape by controlling the traveling direction of the light. To say. For example, as shown in the example of FIG. 4, a light source unit 210 that emits light 201 (FIG. 4B) whose irradiation region 202 becomes circular when directly projected onto a flat screen 200 is prepared. By transmitting the light 201 through the diffractive optical element 10 of the present invention, the irradiation region 204 can be made into a desired shape such as a square (FIG. 4 (a)), a rectangle, or a circle (not shown). It is called "shaping the light".
By combining the light source unit 210 and the diffractive optical element 10 of the present embodiment, which is arranged at least one at a position where the light emitted by the light source unit 210 passes, light that can be irradiated in a molded state. It can be an irradiation device.
Further, in the present invention, the term "transparent" means a substance that transmits light of at least the wavelength to be used. For example, even if it does not transmit visible light, if it transmits infrared rays, it shall be treated as transparent when used for infrared applications.

The diffractive optical element 10 of the present embodiment is a diffractive optical element (DOE) that shapes light. The diffractive optical element 10 has a cross-shaped shape with respect to an infrared laser having a wavelength of 980 nm, specifically, two bands of light having a width of ± 3.3 degrees at ± 50 degrees. Designed to spread light in shape. The diffractive optical element 10 usually has a plurality of regions having different periodic structures (partial periodic structure: for example, regions A to D in FIG. 1). In FIG. 2, an example of the partial periodic structure is extracted and shown.

As shown in FIG. 3, the diffractive optical element 10 includes a high refractive index portion 11 in which a plurality of convex portions 11a are arranged side by side in a cross-sectional shape. The high refractive index portion 11 extends in the depth direction of the cross section while maintaining the same cross-sectional shape.

The high-refractive index portion 11 may _{be formed by processing the shape of quartz (SiO 2} , synthetic quartz) by dry etching, or may be obtained by curing an ionizing radiation-curable resin composition. There may be. Various methods are known for manufacturing such a periodic structure, and the methods can be appropriately produced by these known methods.

Further, air is present in the upper portion of FIG. 3 including the concave portion 12 formed between the convex portions 11a and the space 13 near the top of the convex portion 11a, and the refractive index is higher than that of the high refractive index portion 11. Is a low refractive index portion 14. A diffraction layer 15 having an action of shaping light is formed by a periodic structure in which these high refractive index portions 11 and low refractive index portions 14 are arranged alternately.

FIG. 5 is a diagram illustrating a difference in the design of the diffraction grating due to the difference in the position on the diffraction optical element 10.
For example, as shown in FIG. 5A, the incident angle of the light incident on the position F is smaller than the incident angle of the light incident on the position G even if the light is emitted from the same light source unit 210. By designing the diffraction angle of the diffraction grating to an optimum value at the position F and the position G according to the difference in the incident angle, light can be emitted in the same direction at either position.

FIG. 5B shows a case where light is vertically incident on the diffractive optical element 10.
In this case, the diffraction angle θ of the diffraction optical element 10 is determined by the following equation, where λ is the wavelength of light and P is the pitch of the diffraction grating.
sin (θ) = mλ / P
θ = asin (mλ / P)
However, m is 0, ± 1, ± 2, ....
Further, FIG. 5C shows a case where light is incident on the diffractive optical element 10 at an incident angle θi.
In this case, the diffraction angle θ of the diffraction optical element 10 is determined by the following equation.
sin (θ) -sin (θi) = mλ / P
θ = asin (mλ / P + sin (θi))
However, m is 0, ± 1, ± 2, ....
Therefore, since the wavelength of light is determined by the light source unit 210, the pitch P of the diffraction grating may be changed according to the above equation in order to obtain a desired diffraction angle. A diffraction grating with a large diffraction angle has a narrow pitch, and a diffraction grating with a small diffraction angle has a wide pitch.

FIG. 6 is a diagram showing side-by-side diffraction gratings having different diffraction angles.
The diffraction grating of FIG. 6A has a larger diffraction angle than the diffraction grating of FIG. 6B, that is, the pitch is narrower.
Here, when the refractive index of the material constituting the diffraction grating (refractive index of the high refractive index portion 11) is n, the following equation is known for the groove depth (depth of the recess) D.
D = λ / (2 (n-1))
As described above, conventionally, in a diffractive optical element, it is considered that the light emission efficiency is the best when the groove depth obtained by the above formula is used, and conventionally, the design is performed according to this formula. Was there.
Therefore, in the conventional diffraction optical element, as shown in FIG. 6, the groove depth is constant even if the diffraction angle is different, that is, the pitch of the diffraction grating is different.

However, the groove depth of DOE is not only uniquely determined by the above formula, but can be further improved by changing the groove depth, or unnecessary light emission (for example, 0th-order light) can be generated. The applicant of the present application has found that it may be reduced. Hereinafter, the groove depth in the diffractive optical element 10 of the present embodiment will be described.

FIG. 7 is a diagram showing a cross-sectional shape of a diffraction grating at different positions of the diffraction optical element 10 of the present embodiment.
The diffractive optical element 10 of the present embodiment is designed so that the pitch of the diffraction grating differs depending on the position in response to the different incident angles of light from the light source unit 210 depending on the position. Then, this change in pitch brings about a change in the groove width (width of the recess). That is, since the ratio of the width of the convex portion 11a to the width of the concave portion 12 (groove width) is determined in advance, for example, 1: 1, the pitch and the width of the concave portion 12 (groove width). ), And as the pitch increases, so does the groove width.
In the example shown in FIG. 7, the pitch P2 is wider than the pitch P1 and the pitch P3 is wider than the pitch P2. Correspondingly, the groove width W2 is wider than the groove width W1 and the groove width is further widened. The groove width W3 is wider than W2. Here, the diffraction grating having a pitch P1 is the diffraction grating having the narrowest pitch in the diffraction optical element 10, and is arranged at a position farthest from the light source unit 210. This pitch P1 is set to a pitch determined by the equation of diffraction angle = asin (λ / P) shown above, and the groove depth D1 is determined by D1 = λ / (2 (n-1)). It is set to depth.

Here, as described above, the groove depth D1 is set to D1 = λ / (2 (n-1)), which means that the groove depth exactly matches the value obtained by this mathematical formula. It's not something to do. That is, in the production of the diffractive optical element, dimensional variation always occurs, and the numerical width of such variation is also included. Specifically, even if it is carefully manufactured using high processing technology, an error of about ± 10% will occur, and if a processing technology that emphasizes productivity is used, an error of about ± 15% will occur. May occur. Therefore, the numerical value obtained by the above formula should be regarded as including the range of ± 15%.
This is not limited to this embodiment, and also includes an error range of ± 15% in the claims.

Further, at the position of the pitch P2, the groove depth D2 is set deeper than the groove depth D1 in response to the groove width W2 being wider than the groove width W1.
Similarly, at the position of the pitch P3, the groove depth D3 is set deeper than the groove depth D2 in response to the groove width W3 being wider than the groove width W2.
Further, the relationship between the groove width and the groove depth is proportional.

Next, the change in the light emission value when the groove depth is changed from the design value based on the above-mentioned conventional mathematical formula has four types of pitches of 0.8λ, 1λ, 1.5λ, 2λ, and 3λ, and the incident angle. The results of simulations for two types, 15 degrees and an incident angle of 30 degrees, are shown. The simulation was performed for two types, a wavelength λ = 800 nm and a wavelength λ = 980 nm.
8 and 9 are diagrams summarizing the simulation results at a wavelength of λ = 800 nm and an incident angle of 15 degrees.
10 and 11 are diagrams summarizing the simulation results at a wavelength of λ = 800 nm and an incident angle of 30 degrees.
The simulations of FIGS. 8 to 11 were performed with the wavelength of light λ = 800 nm and the refractive index n = 1.5 of the material constituting the diffraction grating. Therefore, the groove depth D = λ / (2 (n-1)) = 800 nm is the design value that is the conventional standard. This value is referred to as a design value in the present specification, and the ratio of the depth to the design value is shown together with the depth in FIGS. 8 to 11. Therefore, when the design value ratio is larger than 1.0, it means that the groove depth is deeper than the design value. The numerical values in these and the table of the simulation results described later indicate the light output value when the amount of incident light is 1.

FIG. 12 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 800 nm, the pitch is 0.8 λ, and the incident angle is 15 degrees.
FIG. 13 is a graph showing the effect of depth on the light emission value when the wavelength λ = 800 nm, the pitch is 1λ, and the incident angle is 15 degrees.
FIG. 14 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 800 nm, the pitch is 1.5 λ, and the incident angle is 15 degrees.
FIG. 15 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 800 nm, the pitch is 2λ, and the incident angle is 15 degrees.
FIG. 16 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 800 nm, the pitch is 3λ, and the incident angle is 15 degrees.
In the case of an incident angle of 15 degrees, if the pitch is 2λ and 3λ and the groove depth is set to a depth of 1.1, the emission value can be reduced, but the 0th-order light can be reduced. As a result, when the 0th-order light becomes stray light or the like and has an adverse effect, it can be said that it is effective to make the groove depth deeper than the design value at a position having a wide pitch (wide groove width).

FIG. 17 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 800 nm, the pitch is 0.8 λ, and the incident angle is 30 degrees.
FIG. 18 is a graph showing the effect of depth on the light emission value when the wavelength λ = 800 nm, the pitch is 1λ, and the incident angle is 30 degrees.
FIG. 19 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 800 nm, the pitch is 1.5 λ, and the incident angle is 30 degrees.
FIG. 20 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 800 nm, the pitch is 2λ, and the incident angle is 30 degrees.
FIG. 21 is a graph showing the effect of depth on the light emission value when the wavelength λ = 800 nm, the pitch is 3λ, and the incident angle is 30 degrees.
When the incident angle is 30 degrees, there is a range in which the light emission value increases and the 0th-order light decreases by making the groove depth deeper than the design value at a position with a wide pitch (wide groove width). doing. In particular, at a pitch of 1.5λ, this tendency is remarkable.

22 and 23 are diagrams summarizing the simulation results at a wavelength of λ = 980 nm and an incident angle of 15 degrees.
24 and 25 are diagrams summarizing the simulation results at a wavelength of λ = 980 nm and an incident angle of 30 degrees.
The simulations of FIGS. 22 to 25 were performed with the wavelength of light λ = 980 nm and the refractive index n = 1.5 of the material constituting the diffraction grating. Therefore, the groove depth D = λ / (2 (n-1)) = 980 nm is the design value that is the conventional standard. This value is referred to as a design value in the present specification, and in FIGS. 22 to 25, the ratio of the design value of the depth to the design value is shown together with the depth. Therefore, when the design value ratio is larger than 1.0, it means that the groove depth is deeper than the design value.

FIG. 26 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 980 nm, the pitch is 0.8 λ, and the incident angle is 15 degrees.
FIG. 27 is a graph showing the effect of depth on the light emission value when the wavelength λ = 980 nm, the pitch is 1λ, and the incident angle is 15 degrees.
FIG. 28 is a graph showing the effect of depth on the light emission value when the wavelength λ = 980 nm, the pitch is 1.5 λ, and the incident angle is 15 degrees.
FIG. 29 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 980 nm, the pitch is 2λ, and the incident angle is 15 degrees.
FIG. 30 is a graph showing the effect of depth on the light emission value when the wavelength λ = 980 nm, the pitch is 3λ, and the incident angle is 15 degrees.
In the case of an incident angle of 15 degrees, as in the case of λ = 800 nm, when the pitch is 2λ and 3λ and the groove depth is set to a depth of 1.1 compared to the design value, the emission value decreases, but the 0th order light Can be reduced. As a result, when the 0th-order light becomes stray light or the like and has an adverse effect, it can be said that it is effective to make the groove depth deeper than the design value at a position having a wide pitch (wide groove width).

FIG. 31 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 980 nm, the pitch is 0.8 λ, and the incident angle is 30 degrees.
FIG. 32 is a graph showing the effect of depth on the light emission value when the wavelength λ = 980 nm, the pitch is 1λ, and the incident angle is 30 degrees.
FIG. 33 is a graph showing the effect of depth on the light emission value when the wavelength λ = 980 nm, the pitch is 1.5 λ, and the incident angle is 30 degrees.
FIG. 34 is a graph showing the effect of depth on the light emission value when the wavelength is λ = 980 nm, the pitch is 2λ, and the incident angle is 30 degrees.
FIG. 35 is a graph showing the effect of depth on the light emission value when the wavelength λ = 980 nm, the pitch is 3λ, and the incident angle is 30 degrees.
When the incident angle is 30 degrees, the light emission value is increased and the light emission value is increased by making the groove depth deeper than the design value at a position where the pitch is wide (the groove width is wide), as in the case of λ = 800 nm. There is a range in which the 0th order light is reduced. In particular, at a pitch of 1.5λ, this tendency is remarkable.

Further, in order to investigate the influence of the incident angle, the simulation was performed by changing the incident angle to 0 °, 15 °, 30 °, and 60 °. In this simulation, the incident angle is changed in the above range for three types of pitches of 0.8λ, 1λ, and 1.5λ. The depth was changed in the range of 0.7 to 1.3 in terms of the design value ratio. The simulation was performed for two types, a wavelength λ = 800 nm and a wavelength λ = 980 nm.
FIG. 36 is a diagram summarizing the simulation results in which the incident angles were changed to 0 °, 15 °, 30 °, and 60 ° for the wavelength λ = 800 nm and the pitch 0.8λ.
FIG. 37 is a diagram summarizing the simulation results in which the incident angles are changed to 0 °, 15 °, 30 °, and 60 ° for the wavelength λ = 800 nm and the pitch 1λ.
FIG. 38 is a diagram summarizing the simulation results in which the incident angles were changed to 0 °, 15 °, 30 °, and 60 ° for the wavelength λ = 800 nm and the pitch 1.5λ.
FIG. 39 is a graph showing the results of FIG. 36 side by side.
FIG. 40 is a graph showing the results of FIG. 37 side by side.
FIG. 41 is a graph showing the results of FIG. 38 side by side.

FIG. 42 is a diagram summarizing the simulation results in which the incident angles were changed to 0 °, 15 °, 30 °, and 60 ° for the wavelength λ = 980 nm and the pitch 0.8λ.
FIG. 43 is a diagram summarizing the simulation results in which the incident angles were changed to 0 °, 15 °, 30 °, and 60 ° for the wavelength λ = 980 nm and the pitch 1λ.
FIG. 44 is a diagram summarizing the simulation results in which the incident angles were changed to 0 °, 15 °, 30 °, and 60 ° for the wavelength λ = 980 nm and the pitch 1.5λ.
FIG. 45 is a graph showing the results of FIG. 42 side by side.
FIG. 46 is a graph showing the results of FIG. 43 side by side.
FIG. 47 is a graph showing the results of FIG. 44 side by side.

As shown in FIGS. 36 to 47, the larger the incident angle, the deeper the groove depth, and the higher the effect of suppressing the 0th-order light. Therefore, from these results, when light is incident at an angle rather than vertically incident, the light utilization efficiency obtained by making the groove depth deeper than the design value at a position where the groove width is wide is improved. It can be seen that the effect is high and the effect of suppressing unnecessary 0th-order light is high. Specifically, it can be said that the light incident on the diffractive optical element 10 should be incident at an incident angle larger than 0 ° and 60 ° or less.

As described above, according to the present embodiment, since the groove depth is made deeper than the design value at the position where the groove width is wide, it is possible to further improve the light utilization efficiency and suppress unnecessary light emission. can.

(Transformed form)
Not limited to the embodiments described above, various modifications and changes are possible, and these are also within the scope of the present invention.

(1) In the embodiment, the diffractive optical element is shown as a simple form composed of only a high refractive index portion. Not limited to this, for example, a transparent base material for forming a high refractive index portion may be provided, the low refractive index portion 14 may be made of resin, or a coating layer for covering the diffraction layer may be provided. May be good.

(2) In the embodiment, the diffractive optical element has been described with reference to an example designed to diffract an infrared laser having a wavelength of 980 nm. Not limited to this, for example, the diffractive optical element may diffract infrared rays having a wavelength of 780 nm or more, and may diffract light of any wavelength such as visible light as well as infrared light. The present invention may be applied.

(3) In each embodiment, the light irradiation device has been described with reference to an example in which the light source emits an infrared laser having a wavelength of 980 nm. Not limited to this, for example, the light source may emit infrared light having a wavelength of 780 nm or more, and the light source is not limited to infrared light but emits light of any wavelength such as visible light. May be applied to.

The embodiments and modifications can be used in combination as appropriate, but detailed description thereof will be omitted. Moreover, the present invention is not limited to each of the embodiments described above.

10 Diffractive optical element 11 High refractive index part 11a Convex part 12 Concave part 13 Space 14 Low refractive index part 15 Diffractive layer 200 Screen 201 Light 202 Irradiation area 204 Irradiation area 210 Light source part

Claims (10)

A diffractive optical element that shapes light
A high-refractive index portion in which a plurality of rectangular convex portions are arranged side by side in a cross-sectional shape,
A low refractive index portion having a lower refractive index than the high refractive index portion and including at least a rectangular concave portion formed between the convex portions.
With a diffractive layer having
The width of the recess varies depending on the position.
The depth D of the recess at the position where the width of the recess is the narrowest is λ for the wavelength of the light to be diffracted, n for the refractive index of the high refractive index portion, and F for a coefficient of 0.8 or more and 1.2 or less. When you do
D = Fλ / (2 (n-1))
It is composed of the depth of
A diffractive optical element in which the depth of the recess is deeper as the width of the recess is wider. In the diffractive optical element according to claim 1,
The coefficient F is 1 or more and 1.2 or less.
A diffractive optical element characterized by. In the diffractive optical element according to claim 1 or 2.
The wavelength λ of the light to be diffracted shall be 780 nm or more.
A diffractive optical element characterized by. In the diffractive optical element according to any one of claims 1 to 3.
The diffractive optical element uses light that is incident at an incident angle of 60 ° or less, which is larger than 0 °, as the light to be diffracted.
A diffractive optical element characterized by. In the diffractive optical element according to any one of claims 1 to 4.
The width of the recess and the depth of the recess are in a proportional relationship.
A diffractive optical element characterized by. Light source and
A diffractive optical element that is arranged at a position where the light from the light source unit is incident and shapes the light from the light source unit.
With
The diffractive optical element is
A high-refractive index portion in which a plurality of rectangular convex portions are arranged side by side in a cross-sectional shape,
A low refractive index portion having a lower refractive index than the high refractive index portion and including at least a rectangular concave portion formed between the convex portions.
With a diffractive layer having
The width of the recess varies depending on the position.
The depth D of the recess at the position where the width of the recess is the narrowest is λ for the wavelength of light emitted by the light source unit, n for the refractive index of the high refractive index unit, and a coefficient of 0.8 or more and 1.2 or less. When is set to F
D = Fλ / (2 (n-1))
It is composed of the depth of
A light irradiation device in which the depth of the recess is deeper as the width of the recess is wider. In the light irradiation device according to claim 6,
The coefficient F is 1 or more and 1.2 or less.
A light irradiation device characterized by. In the light irradiation device according to claim 6 or 7.
The wavelength λ of the light to be diffracted shall be 780 nm or more.
A light irradiation device characterized by. In the light irradiation device according to any one of claims 6 to 8.
The light source unit and the diffractive optical element are arranged so that the light to be diffracted is incident on the diffractive optical element at an incident angle larger than 0 ° and 60 ° or less.
A light irradiation device characterized by. In the light irradiation device according to any one of claims 6 to 9.
The width of the recess and the depth of the recess are in a proportional relationship.
A light irradiation device characterized by.

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