JP7238252B2 - 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, the need for sensor systems has increased, such as the need for personal authentication to avoid security risks due to the spread of networks, the trend toward automatic driving of automobiles, and the spread of the so-called "Internet of Things". there is There are various types of sensors, and the information they detect is also diverse. One of them is to irradiate the 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.

The light source of these sensors has a wavelength distribution, brightness, and spread according to the application. Visible light to infrared wavelengths are often used. In particular, infrared rays are not easily affected by external light, are invisible, and are widely used because they can be used to observe the inside of objects. there is As for the types of light sources, LED light sources, laser light sources, and the like are often used. For example, a laser light source with little 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 an area with a certain extent of spread. be done.

By the way, the size and shape of the target irradiation area does not necessarily match the spread (profile) of the light from the light source. There is a need. Recently, a diffusion plate called a Light Shaping Diffuser (LSD) has been developed that can shape the shape of light to some extent.
Another means for shaping light is a diffractive optical element (DOE). This applies the diffraction phenomenon when light passes through a place where materials with different refractive indices are arranged periodically. Although DOEs are designed primarily for light of a single wavelength, in theory they can be shaped into almost any shape. Further, in the above-described LSD, the light intensity in the irradiation area has a Gaussian distribution, whereas in the DOE, it is possible to control the uniformity of the light distribution in the irradiation area. Such characteristics of the DOE are advantageous in terms of high efficiency by suppressing irradiation to unnecessary areas and miniaturization of the apparatus by reducing the number of light sources (see, for example, Patent Document 1).
In addition, DOE can be used with both parallel light sources such as lasers and diffuse light sources such as LEDs, and can be applied to a wide range of wavelengths from ultraviolet light to visible light and infrared light. .

A DOE requires microfabrication on the order of nm, and in particular, in order to diffract long-wavelength light, it has been necessary to form a microscopic shape with a high aspect ratio. For this reason, electron beam lithography techniques using electron beams have been conventionally used for manufacturing DOEs. For example, after depositing a hard mask or resist on a quartz plate that is transparent in the ultraviolet to near-infrared region, electron beams are used to draw a predetermined shape on the resist, followed by resist development, dry etching of the hard mask, and drying of quartz. 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.

In the DOE, the light output efficiency is enhanced by a multi-stage shape having a plurality of steps with different heights.
Conventionally, when P is the number of steps in a multistep shape, λ is the wavelength of light, and n is the refractive index of the material of the DOE, the step L per step of the step satisfies the following equation. considered to be the most efficient.
L=λ/(P(n−1))

JP 2015-170320 A Japanese Patent Application Laid-Open No. 2000-199813

However, the step per step of the DOE stepped portion is not only determined uniquely by the above formula, but also by changing the dimension of the step, the efficiency can be further improved, and unnecessary light output (for example, zero-order It has been found that in some cases the light can be reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a diffractive optical element and a light irradiation device that can further increase the efficiency of light utilization and suppress unnecessary light output.

The present invention solves the above problems by means of the following solutions. In order to facilitate understanding, reference numerals corresponding to the embodiments of the present invention are used for explanation, but the present invention is not limited to these.

A first invention is a diffractive optical element (10) for shaping light, comprising a high refractive index portion (11) in which a plurality of convex portions (11a) are arranged side by side in a cross-sectional shape; A diffraction layer (15) having a low refractive index portion (14) having a lower refractive index than the portion (11) and including a recess (12) formed at least between the protrusions (11a); The convex portion (11a) has a multi-stage shape with a plurality of steps (11a-1, 11a-2, 11a-3, 11a-4) having different heights on at least one side of its side shape. P is the number of steps (11a-1, 11a-2, 11a-3, 11a-4) counted including the tip of the projection (11a), λ is the wavelength of light, and the high refractive index When n is the refractive index of the index portion (11) and F is the coefficient exceeding 1, the step difference L per step of the step portions (11a-1, 11a-2, 11a-3, 11a-4) is A diffractive optical element (10) configured to have a value that satisfies L=Fλ/(P(n−1)).

A second invention is the diffractive optical element (10) according to the first invention, characterized in that the coefficient F is a value of 1.2 or less.

A third aspect of the present invention is a light source section (210); a diffraction optical element (10) arranged at a position where light from the light source section (210) is incident and shaping the light from the light source section (210); The diffractive optical element (10) has a high refractive index portion (11) in which a plurality of convex portions (11a) are arranged in a row in a cross-sectional shape, and a refractive index higher than that of the high refractive index portion (11) and a low refractive index portion (14) including recesses (12) formed at least between the protrusions (11a), wherein the protrusions (11a) are At least one side of the side shape has a multi-stage shape having a plurality of steps (11a-1, 11a-2, 11a-3, 11a-4) with different heights, and the convex portion ( 11a) the number of steps (11a-1, 11a-2, 11a-3, 11a-4) counted including the tip, P is the wavelength of light, λ is the refractive index of the high refractive index portion (11) is n, and the coefficient exceeding 1 is F, the step difference L per step of the steps (11a-1, 11a-2, 11a-3, 11a-4) is L=Fλ/(P(n -1) It is a light irradiation device that is configured to have a value that satisfies.

A fourth invention is the light irradiation device according to the third invention, characterized in that the coefficient F is a value of 1.2 or less.

According to the present invention, it is possible to provide a diffractive optical element and a light irradiation device that can further increase the efficiency of light utilization and suppress unnecessary light output.

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. 1; FIG. FIG. 3 is a cross-sectional view of the diffractive optical element cut at the position of arrows G-G' in FIG. 2; It is a figure explaining a diffraction optical element. FIG. 10 is a diagram showing the difference in height between steps of the diffractive optical element 10 of the present embodiment and the conventional diffractive optical element 100 side by side. FIG. 6 is a diagram collectively showing the simulation results of the comparative example and the simulation results of the present embodiment at wavelength λ=500 nm. It is a graph showing a difference value when the count F=1.025 at a wavelength λ=500 nm. 10 is a graph showing difference values at a wavelength λ=500 nm and a count F=1.05. It is a graph showing a difference value when the count F=1.1 at the wavelength λ=500 nm. It is a graph showing a difference value when the count F=1.2 at the wavelength λ=500 nm. 10 is a graph showing difference values at a wavelength λ=500 nm and a count F=1.3. FIG. 6 is a diagram collectively showing the simulation results of the comparative example and the simulation results of the present embodiment at a wavelength λ=850 nm; For the wavelength λ=850 nm, the result of −1st order diffracted light is omitted. 10 is a graph showing difference values at a wavelength λ=850 nm and a count F=1.025; 10 is a graph showing difference values at a wavelength λ=850 nm and a count F=1.05; 10 is a graph showing difference values at a wavelength λ=850 nm and a count F=1.1. It is a graph showing a difference value when the count F=1.2 at the wavelength λ=850 nm. 10 is a graph showing difference values at a wavelength λ=850 nm and a count F=1.3.

BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below with reference to the drawings.

(embodiment)
FIG. 1 is a plan view showing an embodiment of a diffractive optical element according to the invention.
2 is a perspective view showing an example of a partial periodic structure in the example of the diffractive optical element of FIG. 1. FIG.
FIG. 3 is a cross-sectional view of the diffractive optical element taken along arrows GG' in FIG.
FIG. 4 is a diagram illustrating a diffractive optical element.
In addition, each figure shown below including FIG. 1 is a schematic diagram, and the size and shape of each part are shown exaggerated appropriately for easy understanding.
Also, in the following description, specific numerical values, shapes, materials, and the like are shown and described, but these can be changed as appropriate.

It should be noted that the terms used in the present invention to specify shapes and geometric conditions, and their degree, for example, terms such as "parallel", "perpendicular", "identical", length and angle values, etc. Without being bound by a strict meaning, it is interpreted to include the extent to which similar functions can be expected.

In the present invention, "to shape light" means to control the traveling direction of the light so that the shape of the light projected onto the target object or target region (irradiation region) has an arbitrary shape. Say. For example, as shown in the example of FIG. 4, a light source unit 210 is prepared that emits light 201 (FIG. 4B) that forms a circular irradiation area 202 when directly projected onto a planar screen 200 . By transmitting this light 201 through the diffractive optical element 10 of the present invention, the irradiation area 204 can be made into a desired shape such as a square (FIG. 4A), a rectangle, a circle (not shown), or the like. It is said to "shape light".
In addition, by combining the light source unit 210 and at least one diffractive optical element 10 of the present embodiment, which is arranged at a position through which the light emitted by the light source unit 210 passes, light can be irradiated in a shaped state. It can be an irradiation device.
In the present invention, the term "transparent" refers to a material that transmits at least the light of the wavelength used. For example, even if a material does not transmit visible light, if it transmits infrared light, it is treated as transparent when used for infrared applications.

The diffractive optical element 10 of the first embodiment is a diffractive optical element (DOE) that shapes light. For example, the diffractive optical element 10 has a cross shape with respect to the light from the light source unit 210 that emits light with a wavelength of 500 nm. It is designed to spread the light in two intersecting bands.
The diffractive optical element 10 of the first embodiment has different depths at positions A, B, C, and D shown in FIG. That is, the diffractive optical element 10 has a multi-stage shape with four different heights. The diffractive optical element 10 usually has a plurality of regions having different periodic structures (partial periodic structures: regions E and F in FIG. 1, for example). FIG. 2 extracts and shows an example of the partial periodic structure.
As shown in FIG. 3, the diffractive optical element 10 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. 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 made by etching quartz (SiO ₂ , synthetic quartz) into a shape, for example. Alternatively, the high refractive index portion 11 may be obtained by forming a mold from a processed quartz material and curing the ionizing radiation-curable resin composition using the mold. Various techniques are known for producing an object having such a periodic structure using an ionizing radiation-curable resin composition, and the high refractive index portion 11 of the diffractive optical element 10 is produced using these known techniques. can be produced as appropriate.

3, including the recesses 12 formed between the protrusions 11a and the spaces 13 near the tops of the protrusions 11a, air exists and has a higher refractive index than the high refractive index portion 11. is low refractive index portion 14. The periodic structure in which the high refractive index portions 11 and the low refractive index portions 14 are alternately arranged constitutes the diffraction layer 15 having the function of shaping light.

The convex portion 11a has a multi-stage shape with four steps having different heights on one side (the left side in FIG. 3) of the side shape. Specifically, the convex portion 11a has a level 1 stepped portion 11a-1 that protrudes most, a level 2 stepped portion 11a-2 that is one step lower than the level 1 stepped portion 11a-1, and a level 2 stepped portion 11a-2. It has a level 3 stepped portion 11a-3 which is one step lower than the level 3 stepped portion 11a-3 and a level 4 stepped portion 11a-4 which is one step lower than the level 3 stepped portion 11a-3. The other side (the right side in FIG. 3) of the side surface shape of the convex portion 11a is a side wall portion 11b that linearly connects from the level 1 stepped portion 11a-1 to the level 4 stepped portion 11a-4.

Here, the level difference between the level 1 step portion 11a-1 and the level 2 step portion 11a-2, the step difference between the level 2 step portion 11a-2 and the level 3 step portion 11a-3, the level 3 step portion 11a-3 and the level The three stepped portions L (see FIG. 5) of the stepped portion 11a-4 are values obtained by the following equations.
L=Fλ/(P(n−1))
In the above formula, P is the number of steps counted including the tip of the convex portion 11a, λ is the wavelength of light, n is the refractive index of the high refractive index portion 11, and F is the coefficient exceeding 1.
Note that the count F must be a value exceeding 1, but is preferably 1.2 or less. This is because when F exceeds 1.2, the light output of the 1st-order diffracted light decreases, and the light utilization efficiency decreases.
In this embodiment, P=4, λ=500 nm, n=1.5, F=1.025, and L= 256.25 nm as one step.

This value is obtained by multiplying the following formula, which is conventionally known, by a factor F.
L0=λ/(P(n−1))
Substituting P=4, λ=500 nm, and n=1.5 into these conventional values yields L0= 250 nm, which is smaller than in the case of the diffractive optical element 10 of this embodiment. In a conventional diffractive optical element, this value of L0 is used as a step per step.

FIG. 5 is a diagram showing the height difference between the stepped portions of the diffractive optical element 10 of this embodiment and the conventional diffractive optical element 100 side by side.
As shown in FIG. 5, in the diffractive optical element 10 of this embodiment, the steps per step of each step are uniformly longer by the factor F compared to the conventional diffractive optical element 100 .

Next, the results of simulations performed on the diffractive optical element 10 of this embodiment and the conventional diffractive optical element 100 will be shown, and light output efficiency and unnecessary light will be described.
The analysis simulation of the diffraction efficiency used calculations based on rigorous coupled-wave analysis (RCWA).RCWA is mathematically reduced to solving a matrix eigenvalue problem and a linear equation. Moreover, the simulation result of the electromagnetic field analysis based on this RCWA basically agrees with the reality, except for the shape error in the actual product.

The simulation was performed under the following conditions.
Wavelength λ: 500 nm and 850 nm
Refractive index n of high refractive index portion: 1.5
Refractive index of low refractive index part: 1.0
Pitch: 6 types of 2λ, 3λ, 4λ, 6λ, 8λ, 10λ Number of multi-stage levels P: 4

The step per step of each step portion is provided by a coefficient F to differentiate between the diffractive optical element 10 of this embodiment and the conventional diffractive optical element 100 as follows.
This embodiment: L = Fλ / (P (n-1))
Conventional: L0=λ/(P(n-1))
Also, in this embodiment, the coefficient F is set to three types of 1.025, 1.05, and 1.1.

The results of the simulation performed under the above conditions will be described.
FIG. 6 is a diagram collectively showing the simulation results of the comparative example and the simulation results of the present embodiment at wavelength λ=500 nm.
The simulated light output value in FIG. 6 indicates the light output value in each direction when the input light is set to 1. In FIG.
0th, 1st, and -1st in FIG. 6 indicate 0th-order diffracted light, 1st-order diffracted light, and -1st-order diffracted light, respectively. In normal usage, it is desirable that the 1st-order diffracted light is large, and that the 0th-order diffracted light and the −1st-order diffracted light are small.
Further, in FIG. 6, difference values between the comparative example and the present embodiment are shown so as to clarify the difference between them. The difference value indicates a value obtained by subtracting the numerical value of the comparative example from the numerical value of the present embodiment. Therefore, when looking at the first-order diffracted light, the larger the numerical value, the better the result. In terms of diffracted light, the smaller the numerical value, the better the result.

In order to make the difference values easier to understand, graphs are shown in FIGS. 7 to 9. FIG.
FIG. 7 is a graph showing difference values for a wavelength λ=500 nm and a count F=1.025.
FIG. 8 is a graph showing difference values at a wavelength λ=500 nm and a count F=1.05.
FIG. 9 is a graph showing difference values when the count F=1.1 at the wavelength λ=500 nm.
FIG. 10 is a graph showing difference values when the count F=1.2 at the wavelength λ=500 nm.
FIG. 11 is a graph showing difference values at a wavelength λ=500 nm and a count F=1.3.

FIG. 12 is a diagram collectively showing the simulation results of the comparative example and the simulation results of the present embodiment at wavelength λ=850 nm. For the wavelength λ=850 nm, the result of −1st order diffracted light is omitted.
FIG. 13 is a graph showing difference values for a wavelength λ=850 nm and a count F=1.025.
FIG. 14 is a graph showing difference values for a wavelength λ=850 nm and a count F=1.05.
FIG. 15 is a graph showing difference values when the count F=1.1 at the wavelength λ=850 nm.
FIG. 16 is a graph showing difference values when the count F=1.2 at the wavelength λ=850 nm.
FIG. 17 is a graph showing difference values when the count F=1.3 at the wavelength λ=850 nm.

Looking at FIGS. 7 to 11, the first-order diffracted light is mostly not improved in this embodiment, but in the range where the pitch exceeds 7λ when the coefficient F=1.025, the first-order diffracted light is It increases (the difference value is positive), and by using it within this range, it is possible to improve the efficiency of the first-order diffracted light.
In addition, for the 0th-order diffracted light and the -1st-order diffracted light, the light output value is smaller than the conventional value (the difference value is negative) for all the coefficients F in the range of the pitch of 3λ or more. It is found to be effective for
Furthermore, it can be seen that when the coefficient F exceeds 1.2, the light output value of the first-order diffracted light is greatly reduced. Therefore, from the viewpoint of maintaining the light output efficiency of the first-order diffracted light, it is desirable that the coefficient F is 1.2 or less.

Also, at the wavelength λ=850 nm, if the coefficient F exceeds 1.2, the 0th-order diffracted light increases (the difference value is positive), which is undesirable. Therefore, it is desirable that the coefficient F is 1.2 or less even at the wavelength λ=850 nm.

As described above, according to the present embodiment, the step is set to be larger than the conventionally known step per step. As a result, under specific conditions, it is possible to further increase the light utilization efficiency and suppress unnecessary light emission. This is something that can never be obtained with conventionally known design theories.

(deformed form)
Various modifications and changes are possible without being limited to the embodiments described above, and they are also within the scope of the present invention.

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

(2) In the embodiments, an example was given in which the diffractive optical element was designed to diffract light with a wavelength of 500 nm. Not limited to this, for example, the diffractive optical element may be one that diffracts infrared light with a wavelength of 780 nm or more, and is not limited to infrared light, and may be one that diffracts light of any wavelength, such as visible light. The present invention may be applied.

(3) In each embodiment, the light irradiation device has been described with an example designed to diffract light with a wavelength of 500 nm. For example, the light source unit may emit infrared light having a wavelength of 780 nm or more. You may apply to an irradiation apparatus.

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

10 Diffractive optical element 11 High refractive index portion 11a Convex portion 11a-1 Level 1 step portion 11a-2 Level 2 step portion 11a-3 Level 3 step portion 11a-4 Level 4 step portion 11b Side wall portion 12 Concave portion 13 Space 14 Low refraction Index section 15 Diffractive layer 100 Diffractive optical element 200 Screen 201 Light 202 Irradiation area 204 Irradiation area 210 Light source section

Claims (2)

A diffractive optical element that shapes light,
a high refractive index portion in which a plurality of protrusions are arranged side by side in a cross-sectional shape;
a low refractive index portion having a refractive index lower than that of the high refractive index portion and having a refractive index of 1 including at least concave portions formed between the convex portions;
a diffractive layer having
The convex portion has a multi-stage shape having a plurality of step portions with different heights on at least one side of the side surface shape and arranged at a pitch of 4000 nm or more,
P is the number of steps counted including the tip of the convex portion, λ=500 nm is the wavelength of light, n is the refractive index of the high refractive index portion, and F is the coefficient of 1.025 or more and 1.03 or less. Sometimes, the step L per step of the stepped portion is
L=Fλ/(P(n−1))
A diffractive optical element configured to a value that satisfies a light source;
a diffractive optical element arranged at a position where the light from the light source unit is incident and shaping the light from the light source unit;
with
The diffractive optical element is
a high refractive index portion in which a plurality of protrusions are arranged side by side in a cross-sectional shape;
a low refractive index portion having a refractive index lower than that of the high refractive index portion and having a refractive index of 1 including at least concave portions formed between the convex portions;
a diffractive layer having
The convex portion has a multi-stage shape having a plurality of step portions with different heights on at least one side of the side surface shape and arranged at a pitch of 4000 nm or more,
P is the number of steps counted including the tip of the convex portion, λ=500 nm is the wavelength of light, n is the refractive index of the high refractive index portion, and F is the coefficient of 1.025 or more and 1.03 or less. Sometimes, the step L per step of the stepped portion is
L=Fλ/(P(n−1))
A light irradiation device that is configured to a value that satisfies

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