WO2025220552A1 - Optical system device - Google Patents

Abstract

The purpose of the present invention is to provide: an optical system device that provides a high contrast for a dot pattern even when light sources are arranged in a hexagonal pattern and lenses are square or of a similar shape; and an optical system device capable of shortening the distance between a lens and a light source.　Provided is an optical system device comprising: an optical element in which lenses, through which light having a wavelength of λ is transmitted and which each have a width of P in the x direction passing through the center of the optical axis and a width of (√3)P/2 in the y direction, are arranged in a regular hexagonal pattern at a pitch of P in the x direction passing through the center of the optical axis; and an irradiation unit in which light sources for irradiating a plurality of the lenses with light having a wavelength of λ are arranged in a regular hexagonal pattern at a pitch of P in the x direction. When f represents the focal length of the lenses and n represents a natural number greater than or equal to 1, the distance L₁ between the irradiation unit and the focal position of the optical element satisfies formula 1.

Description

optical system equipment

The present invention relates to an optical system device.

Three-dimensional measurement sensors using the time-of-flight (TOF) method are being adopted in mobile devices, cars, robots, and more. This measures the distance to an object from the time it takes for light from a light source to be irradiated onto the object, reflected, and returned. If the light from the light source is irradiated evenly over a specified area of the object, the distance at each irradiated point can be measured, making it possible to detect the three-dimensional structure of the object.

The above sensor system consists of a transmitter (Tx module) that irradiates light onto the target, and a receiver (Rx module) that detects the light reflected from each point on the target. The transmitter is mainly composed of an irradiation unit that irradiates light and an optical element that controls and irradiates the light to a specified area. The receiver is mainly composed of a camera unit that receives light and a calculation unit that calculates the distance to the target from the signal received by the camera unit. Here, the receiver's camera unit and calculation unit can use existing CMOS imagers and CPUs, so the transmitter is the distinctive part of the above system.

The transmitter's optical elements include, for example, a diffusion filter that transmits light from the irradiating section, shaping the light and irradiating a target within a specified range with uniform light. Such a diffusion filter may be a microlens array with randomly arranged lenses.

On the other hand, TOF requires long-distance measurements, and the irradiated light must have sufficient light intensity and contrast to enable such measurements. However, because the irradiated light from a diffusion filter is highly uniform, the light intensity and contrast are low, making it unsuitable for long-distance measurements.

Therefore, as a transmitter that can save power and transmit a strong optical signal, an optical system device has been considered that uses an optical element to control the light of an irradiating unit to irradiate a dot pattern, which is a distribution of multiple dots of light. A dot pattern has lower resolution than a diffusion filter, but the light intensity and contrast of each dot are higher. One optical system device that irradiates a dot pattern includes an optical element with a regular arrangement of lenses at a predetermined pitch P and an irradiating unit disposed a predetermined distance from the optical element. Here, the optical element and the irradiating unit are arranged to satisfy the following formula A, where λ is the wavelength of the light from the light source, n is a natural number greater than or equal to 1, and _L0 is the distance between the optical element and the light source of the irradiating unit (see, for example, Patent Document 1):

WO 2021/229848

In recent years, there has been a demand for smaller and thinner optical devices. To achieve this, it is necessary to reduce the distance _L0 between the microlens and the light source. To reduce this distance _L0 , it is sufficient to reduce the lens pitch P of the optical element, based on Equation A.

On the other hand, the lens pitch P is restricted by the light source pitch, and so the lens pitch depends on the light source pitch and arrangement. Conventional light sources use VCSELs (Vertical Cavity Surface Emitting Lasers), which are expected to produce high output with little power. Most VCSELs are arranged in a hexagonal configuration, with quadrangular arrangements being costly. One option is to make the planar shape of the lens hexagonal, but with a hexagonal planar shape, it is difficult to design the irradiated dot pattern to be square. Therefore, it is preferable to use a lens with a square planar shape or a shape similar to this.

In a conventional case where the light source is a hexagonal array VCSEL and the planar shape of the lens is a square, the short side of the lens is designed to match the minimum pitch P of the light source and the long side is designed to match the second pitch (√3)P (see Figure 57 in Cited Document 1). However, in this case, in order for both the minimum pitch P and the second pitch (√3)P to satisfy Formula A, it is necessary to make n in Formula A a multiple of 3. This increases the distance _L0 , which hinders efforts to make the optical device smaller and thinner.

The present invention aims to provide an optical system device that has a hexagonal array of light sources, has a high contrast dot pattern even when the lens plane is rectangular or has a similar shape, and allows the distance between the lens and light source to be reduced.

In order to achieve the above object, the optical system device of the present invention includes an optical element in which lenses that transmit light of wavelength λ and have a width P in the x direction passing through the center of the optical axis and a width (√3)P/2 in the y direction are arranged in a regular hexagonal array with a pitch P in the x direction about the center of the optical axis, and an irradiation unit in which light sources that irradiate a plurality of the lenses with light of wavelength λ are arranged in a regular hexagonal array with a pitch P in the x direction, and wherein, when a focal length of the lens is f and n is a natural number of 1 or more, a distance _L1 between the irradiation unit and a focal position of the optical element is expressed by the following formula 1:
The present invention is characterized in that:

In this case, it is preferable that the optical element has a quadrangular lens shape in the xy plane, for example, a rectangular shape.

In addition, the distance _L1 is expressed by the following formula 2:
It is preferable to satisfy the following.

In addition, the distance _L1 is expressed by the following formula 3:
It is preferable to satisfy the following.

In addition, the distance L ₁ is expressed by the following formula 4:
It is preferable to satisfy the following.

The optical system device of the present invention can provide an optical system device that produces a high contrast dot pattern even when the light sources are arranged in a hexagonal array and the lenses are rectangular or similarly shaped. It can also provide an optical system device that allows the distance between the lens and the light source to be shortened.

1 is a schematic cross-sectional view showing an optical system device of the present invention. FIG. 1 is a plan view showing an optical system device of the present invention. FIG. 1 is a plan view showing an optical system device of the present invention. FIG. 1 is a plan view showing an optical system device of the present invention. FIG. 1 is a plan view showing an optical system device of the present invention. FIG. 10 is a diagram showing a light distribution in the far field of an irradiation unit used in a simulation. 1A is a schematic plan view of the optical system device of the present invention in Simulation 1, and FIG. 1B is a projection view thereof. 1A is a schematic plan view of a conventional optical system device in simulation 1, and FIG. 1B is a projection view thereof. 1A is a schematic plan view of the optical system device of the present invention in simulation 2, and FIG. 1B is a projection view thereof. 1A is a schematic plan view of a conventional optical system device in simulation 2, and FIG. 1B is a projection view thereof.

The optical system device of the present invention will be described below. As shown in Figure 1, the optical system device of the present invention is mainly composed of an optical element 1 having periodic lenses 11 and an irradiation unit 2 having a periodic light source that irradiates light of wavelength λ.

Optical element 1 transmits light of wavelength λ and is composed of lenses with a width P in the x direction passing through the optical axis center and a width (√3)P/2 in the y direction, arranged in a regular hexagonal array with a pitch P in the x direction about the optical axis center. A regular hexagonal array of lenses means, in other words, that the lenses are arranged periodically with a pitch P in the x direction and a pitch (√3)P/2 in the y direction perpendicular to the x direction, as shown in Figure 2, with adjacent rows in the x direction offset by P/2. For convenience, in this specification, the direction of the optical axis of optical element 1 is referred to as the z direction, and the x, y, and z directions are assumed to be perpendicular to one another. Furthermore, the optical axis center refers to the intersection of the xy plane and the optical axis.

Furthermore, lens 11 has a focal point at a position a predetermined distance f (f>0) away from lens 11. Note that in this specification, focal length means the distance between the focal point and the lens surface closest to the focal point, as shown in Figure 1. Furthermore, it is preferable that lens 11 have a focal point located on the irradiation side of lens 11.

The shape of lens 11 can be freely designed to match the dot pattern. For example, lens 11 can be a spherical lens or an aspherical lens. Lens 11 can also be a convex lens or a concave lens. Lens 11 can be any type that functions as a lens, and for example, a Fresnel lens, DOE lens, metalens, etc. can be used.

Furthermore, the shape of the xy plane of the lenses 11 (hereinafter referred to as the planar shape) may be any shape as long as the optical axis centers of the lenses 11 can be arranged in a regular hexagonal array at pitch P in the x direction. For example, as shown in Figure 2, the planar shape of the lenses 11 can be a square or a shape approximating this. Furthermore, if the planar shape of the lenses 11 is a square, a rectangle is preferable, but it can also be a parallelogram or a rhombus as shown in Figures 3 and 4. Furthermore, shapes approximating a square include those in which the sides of the square have a wave shape such as a sine wave, rectangular wave, triangular wave, or sawtooth wave, as shown in Figure 5.

Furthermore, the optical element 1 may be made of any material that can form a lens that transmits light of wavelength λ, and examples of such materials include resins such as polydimethylsiloxane (PDMS) and glass. Furthermore, the optical element 1 may be manufactured in any manner that can form the lens 11, and conventional methods such as imprinting and injection molding may be used.

The irradiation unit 2 has light sources 20 that irradiate multiple lenses 11 with light of wavelength λ, arranged in a regular hexagonal array at a pitch P in the x direction. Furthermore, the irradiation unit 2 and optical element 1 are preferably arranged so that the optical axis direction of the light sources 20 of the irradiation unit 2 coincides with the optical axis direction of the lenses 11 of the optical element 1. Any light source 20 can be used as long as it can irradiate multiple lenses 11 with light of wavelength λ. A specific example of the irradiation unit 2 is a VCSEL (Vertical Cavity Surface Emitting Laser), which is expected to produce high output with little power. A VCSEL has multiple light sources 20 that can irradiate light in a direction perpendicular to the light-emitting surface.

[Positional relationship between the irradiation unit and the optical element]
As shown in Figure 1, the distance _L1 between the irradiation unit 2 and the focal plane of the optical element 1 can convert incident light into a dot pattern with high contrast when it satisfies the following formula α: where n is a natural number greater than or equal to 1, P is the pitch of the lens in the x direction, λ is the wavelength of light incident from the irradiation unit 2, f is the focal length of the lens 11, and a and b are coefficients indicating the allowable error. Note that the focal plane refers to a plane that is perpendicular to the optical axis (z direction) of the lens 11 and is located at the focal position of the lens 11. Furthermore, the distance _L1 refers to the distance (optical path length) that light travels in a vacuum in the same time as it travels through a medium, and is expressed as the product NL, where N is the refractive index of the medium and L is the actual distance.

Here, the smaller the values of the coefficients a and b in formula α are, the more preferable they are, i.e., 1, 0.5, 0.3, and 0.1. When the coefficients of formula α are a=b=1, formula α becomes formula 1 below.

Furthermore, the distance _L1 can most effectively strengthen the light when it satisfies the following formula 2 where a=b=0.

Furthermore, in formula α, the smaller the value of n, the smaller the distance _L1 between the irradiation unit 2 and the focal plane of the optical element 1 becomes, and when n=1, the following formula β is obtained.

Here, the smaller the values of the coefficients a and b in formula β are, the more preferable they are, i.e., 1, 0.5, 0.3, and 0.1. When the coefficients of formula β are a=b=1, formula β becomes formula 3 below.

Furthermore, the distance _L1 is the shortest distance between the irradiation unit 2 and the focal plane of the optical element 1 when the light can be most reinforced when the following formula 4 is satisfied, where a=b=0.

Note that if the pitch P is too small compared to the wavelength λ of the light from the light source 20, diffraction will be difficult to achieve. Therefore, as long as there are enough lenses 11 within the light distribution angle of the light source 20 to produce diffraction, the pitch P should be sufficiently larger than the wavelength λ of the light from the light source 20; for example, 5 times or more, and preferably 10 times or more.

[Simulation 1]
Simulations were performed for the optical system device of the present invention and a conventional optical system device as a comparative example. In these simulations, the same irradiation unit was used for both optical system devices. As shown in FIGS. 7(a) and 8(a), the irradiation unit had a plurality of light sources 20A arranged in a regular hexagonal array at a pitch P in the x direction. Furthermore, the light sources 20A of the irradiation unit emitted light with a pitch P of 20 μm (P=20), a wavelength of 940 nm (λ=0.94), and a batwing light distribution as shown in FIG. 6. The distance _L1 between the irradiation unit and the focal position of the optical element was calculated using the following equation 2:
The simulation was performed using optical simulation software BeamPROP (manufactured by Synopsys).

As shown in Figure 7(a), the optical element 1A used in the optical system device of the present invention is a lens 11A arranged in a regular hexagonal array with a pitch P in the x direction around the optical axis center. Lens 11A of this optical element 1A transmits light of wavelength λ (λ = 0.94), and has a width of 20 μm in the x direction passing through the optical axis center and a width of 10√3 μm in the y direction. Lens 11A also has a refractive index of 1.5 and a focal length f of 10 μm.

The distance L ₁ between the irradiation part and the focal position 9 of the optical element 1A was set to 426 μm [L ₁ =2×20 ² /(2×0.94)=426], which is the distance when n=2 in the above formula 2.

Figure 7(b) shows the image projected 1 m from optical element 1A. The average contrast of each dot in this case was 14.40.

As shown in Figure 8(a), the optical element 1B used in the conventional optical system device was a square array of lenses 11B arranged around the optical axis center at a pitch P in the x direction and √3P in the y direction. Lenses 11B of this optical element 1B transmit light of wavelength λ (λ = 0.94), and have a width of 20 μm in the x direction passing through the optical axis center and a width of 20√3 μm in the y direction. Lenses 11B also have a refractive index of 1.5 and a focal length f of 12 μm.

The distance L ₁ between the irradiation part and the focal position 9 of the optical element 1B was set to 426 μm [L ₁ =2×20 ² /(2×0.94)=426], which is the distance when n=2 in the above formula 2.

Figure 8(b) shows the image projected 1 m away from optical element 1B. The average contrast of each dot in this case was 6.62.

Comparing the optical system of the present invention with the conventional optical system, it can be seen that although _L1 is the same at 426 μm, the optical system of the present invention has a higher average contrast than the conventional optical system, and the dots in the projected image are clearer.

[Simulation 2]
Next, a simulation was performed for the optical system device of the present invention and a conventional optical system device as a comparative example. In the simulation, the distance between the irradiation unit and the focal position of the optical element was the same in both optical system devices. Furthermore, the distance _L1 between the irradiation unit and the focal position of the optical element was calculated using the following formula 2.
The simulation was performed using optical simulation software BeamPROP (manufactured by Synopsys).

As shown in Figure 9(a), the irradiation section of the optical system device of the present invention uses multiple light sources 20B arranged in a regular hexagonal array at a pitch P in the x direction. The light sources 20B of the irradiation section have a pitch P of 20√3 μm (P = 20√3), a wavelength of 940 nm (λ = 0.94), and emit light with a batwing light distribution as shown in Figure 6.

The optical element 1C of the optical system device of the present invention uses lenses 11C arranged in a regular hexagonal array with a pitch P around the optical axis center in the x direction, as shown in Figure 9(a). Lenses 11C of this optical element 1C transmit light of wavelength λ (λ = 0.94), and have a width of 20√3 μm in the x direction passing through the optical axis center and a width of 30 μm in the y direction. Lenses 11C also have a refractive index of 1.5 and a focal length f of 10 μm.

The distance L ₁ between the irradiation part and the focal position 9 of the optical element 1C was set to 1277 μm [L ₁ =2×(20√3) ² /(2×0.94)=1277], which is the distance when n=2 in the above formula 2.

Figure 9(b) shows the image projected 1 m away from optical element 1C. The average contrast of each dot in this case was 41.96.

The illumination section of the conventional optical system device used multiple light sources 20A arranged in a regular hexagonal array at a pitch P in the x direction, as shown in Figure 10(a). The light sources 20A in the illumination section had a pitch P of 20 μm (P = 20), a wavelength of 940 nm (λ = 0.94), and emitted light with a batwing light distribution as shown in Figure 6.

Furthermore, as shown in Figure 10(a), the optical element 1B of the conventional optical system device was configured with lenses 11B arranged in a square array with a pitch P in the x direction and √3P in the y direction around the optical axis center. Lenses 11B of this optical element 1B transmit light of wavelength λ (λ = 0.94), and have a width of 20 μm in the x direction passing through the optical axis center and a width of 20√3 μm in the y direction. Lenses 11B also had a refractive index of 1.5 and a focal length f of 12 μm.

The distance L ₁ between the irradiation unit 2 and the focal position 9 of the optical element 1B was set to 1277 μm [L ₁ =6×20 ² /(2×0.94)=1277], which is the distance when n=6 in the above formula 2.

Figure 10(b) shows the projected image 1 m away from optical element 1B. The average contrast of each dot in this case was 28.61.

When comparing the optical system of the present invention with the conventional optical system, it can be seen that although _L1 is the same at 1277 μm, the optical system of the present invention has a higher average contrast than the conventional optical system, and the dots in the projected image are clearer.

1, 1A, 1B, 1C Optical element 2 Irradiation unit 9 Focal position 10 Substrate 11 Lens 20 Light source 51 Mold

Claims (6)

an optical element in which lenses that transmit light of wavelength λ and have a width P in the x direction passing through the optical axis center and a width (√3)P/2 in the y direction are arranged in a regular hexagonal array with a pitch P in the x direction about the optical axis center;
an illumination unit in which light sources that illuminate a plurality of lenses with light of wavelength λ are arranged in a regular hexagonal array at a pitch P in the x direction;
When the focal length of the lens is f and n is a natural number of 1 or more, the distance _L1 between the irradiation unit and the focal position of the optical element is expressed by the following formula 1:
An optical system device characterized by satisfying the above. The optical system device according to claim 1, characterized in that the optical element has a lens whose xy plane shape is rectangular. The optical system device of claim 1, characterized in that the optical element has a lens with a rectangular shape in the xy plane. The distance _L1 is expressed by the following formula 2:
4. The optical system according to claim 1, wherein the following is satisfied: The distance _L1 is expressed by the following formula 3:
4. The optical system according to claim 1, wherein the following is satisfied: The distance _L1 is expressed by the following formula 4:
4. The optical system according to claim 1, wherein the following is satisfied: