Optical system and electromagnetic wave detection device

Abstract

An optical system and an electromagnetic wave detection device are provided that reduce noise caused by reflections from optical components. [Solution] The optical system (100) comprises an illumination unit (31), a separation unit (16) that propagates the illumination wave emitted from the illumination unit in a first direction and propagates the reflected wave, which is reflected by the illumination wave from the object, in a second direction opposite to the first direction, a scanning unit (50) that illuminates the object with the illumination wave that has propagated in the first direction while changing the direction of propagation, and propagates the reflected wave to the separation unit, and at least two scanning lenses (60) that propagate the illumination wave from the scanning unit into the space where the object exists so as to widen the field of view, and propagate the reflected wave to the scanning unit, wherein the first scanning lens is arranged so that its lens surface is tilted in a first direction with respect to the optical axes of the illumination wave and the reflected wave, and the second scanning lens is arranged so that its lens surface is tilted in a second direction with respect to the optical axes of the illumination wave and the reflected wave.

Description

[Technical Field]

[0001] The present disclosure relates to an optical system and an electromagnetic wave detection device. [Background Art]

[0002] In recent years, devices that acquire information related to surrounding objects and the like from results of detecting electromagnetic waves have been developed. In LiDAR (Light Detection and Ranging), which is an example of such devices, various optical components may be used to improve ranging accuracy. For example, Patent Document 1 discloses a LiDAR in which an optical component such as a lens is disposed on a path of an electromagnetic wave from a polarization beam splitter. [Prior Art Literature] [Patent Literature]

[0003] [Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2003-172612 [Summary of Invention] [Problem to be Solved by Invention]

[0004] Here, optical components are often disposed perpendicular to the optical axis. In the conventional LiDAR configuration in which optical components are disposed perpendicular to the optical axis, when electromagnetic waves emitted into space enter the optical component, a part of the electromagnetic waves is reflected and travels to a light receiving sensor (photodetection unit), causing noise, which may degrade performance.

[0005] In view of such circumstances, an object of the present disclosure is to provide an optical system and an electromagnetic wave detection device that reduce noise caused by reflection from optical components. [Means for Solving Problem]

[0006] (1) An optical system according to an embodiment of the present disclosure includes: an irradiation unit, and A separation unit that propagates the irradiation wave emitted from the irradiation unit in a first direction, and propagates the reflected wave, which is reflected by the object, in a second direction opposite to the first direction, A scanning unit that causes the irradiation wave propagating in the first direction to irradiate the target object while changing the direction of propagation, and propagates the reflected wave to the separation unit, The system comprises at least two scanning lenses that propagate the irradiation wave from the scanning unit into the space where the object exists in such a way that the field of view widens, and propagate the reflected wave to the scanning unit, The at least two scanning lenses include a first scanning lens and a second scanning lens, The first scanning lens is arranged such that its lens surface is inclined in a first direction with respect to the optical axes of the irradiated wave and the reflected wave. The second scanning lens is positioned such that its lens surface is inclined in the second direction with respect to the optical axes of the irradiated wave and the reflected wave.

[0007] (2) As one embodiment of the present disclosure, in (1), The first scanning lens and the second scanning lens are lenses of the same shape.

[0008] (3) As one embodiment of the present disclosure, in (1), The first scanning lens and the second scanning lens are lenses of different shapes.

[0009] (4) In one embodiment of the present disclosure, in any of (1) to (3), The total number of the at least two scanning lenses is even.

[0010] (5) An electromagnetic wave detection device according to one embodiment of the present disclosure, Irradiation area and, A separation unit that propagates the irradiation wave emitted from the irradiation unit in a first direction, and propagates the reflected wave, which is reflected by the object, in a second direction opposite to the first direction, A scanning unit that causes the irradiation wave propagating in the first direction to irradiate the target object while changing the direction of propagation, and propagates the reflected wave to the separation unit, The system comprises at least two scanning lenses that propagate the irradiation wave from the scanning unit into the space where the object exists in such a way that the field of view widens, and propagate the reflected wave to the scanning unit, The at least two scanning lenses include a first scanning lens and a second scanning lens, The first scanning lens is arranged such that its lens surface is inclined in a first direction with respect to the optical axes of the irradiated wave and the reflected wave. The second scanning lens is positioned such that its lens surface is inclined in the second direction with respect to the optical axes of the irradiated wave and the reflected wave. [Effects of the Invention]

[0011] According to this disclosure, it is possible to provide an optical system and an electromagnetic wave detection device that reduce noise generated by reflections from optical components. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a diagram showing a schematic configuration of an electromagnetic wave detection device including an optical system according to one embodiment of the present disclosure. [Figure 2] Figure 2 shows a schematic configuration of at least two scanning lenses included in an optical system according to one embodiment of the present disclosure. [Figure 3] Figure 3 shows the difference in light-gathering performance due to the tilt of the scanning lens, as determined by simulation. [Figure 4] Figure 4 shows an optical system with only one scanning lens. [Figure 5] Figure 5 shows another optical system that has only one scanning lens. [Modes for carrying out the invention]

[0013] Hereinafter, an optical system 100 (see FIG. 1) and an electromagnetic wave detection device according to an embodiment of the present disclosure will be described with reference to the drawings. In each of the drawings, the same or corresponding parts are denoted by the same reference numerals. In the description of the present embodiment, descriptions of the same or corresponding parts will be omitted or simplified as appropriate.

[0014] FIG. 1 is a diagram showing a schematic configuration of an electromagnetic wave detection device including the optical system 100 according to the present embodiment. In this embodiment, the electromagnetic wave detection device constitutes a part of LiDAR that irradiates an electromagnetic wave that is laser light and measures the distance to an object ob, the shape of the object ob, and the like based on reflected waves. LiDAR may measure the distance to the object ob by a Time-of-Flight (ToF) method.

[0015] The electromagnetic wave detection device is configured to include the optical system 100. As shown in FIG. 1, the optical system 100 includes an irradiation unit 31, a separation unit 16 (optical separator), a scanning unit 50, and at least two scanning lenses 60. As shown in FIG. 1, the optical system 100 may further include a condenser lens 19, a photodetection unit 20, and a lens 41. Here, the optical system 100 is not limited to the configuration shown in FIG. 1, and may be configured to further include an optical member such as a reflecting mirror, for example.

[0016] The irradiation unit 31 irradiates electromagnetic waves. In this embodiment, the irradiation unit 31 irradiates infrared rays (infrared light) as electromagnetic waves. However, the electromagnetic wave irradiated by the irradiation unit 31 is not limited to infrared rays, and may be other types of light or the like. The irradiation unit 31 may include, as a light source, a semiconductor laser (laser diode) that functions as a laser using recombination light emission of semiconductors. In addition, the irradiation unit 31 may be configured to include a laser light source different from a semiconductor laser, such as a fiber laser.

[0017] The lens 41 propagates the electromagnetic wave irradiated from the irradiation unit 31 to the separation unit 16. For example, the lens 41 focuses the electromagnetic wave irradiated from the irradiation unit 31. A known lens may be used as the lens 41.

[0018] The separation unit 16 propagates the irradiation wave emitted from the irradiation unit 31 in a first direction and propagates the reflected wave, which is reflected by the object ob, in a second direction. Here, the first direction is, for example, the direction from the separation unit 16 toward the scanning unit 50 and corresponds to the negative z-axis direction of the three-dimensional coordinate system shown in Figure 1. The second direction is, for example, the direction from the separation unit 16 toward the photodetection unit 20 and corresponds to the positive z-axis direction of the three-dimensional coordinate system shown in Figure 1. The second direction is also the opposite direction to the first direction. Here, the three-dimensional coordinate system shown in Figure 1 is also used in common in Figures 2 to 5.

[0019] The separation unit 16 is composed of a light-reflecting section that reflects light and a light-transmitting section that transmits light. The separation unit 16 is arranged so that the irradiation wave emitted from the irradiation unit 31 is reflected by the light-reflecting section and propagated in a first direction, and the reflected wave that has been reflected by the object ob is passed through the light-transmitting section and propagated in a second direction. Here, the positional relationship, shape, and area ratio of the light-reflecting section and the light-transmitting section are not limited. Furthermore, the light-reflecting section is not limited to a specific material as long as it reflects light. Similarly, the light-transmitting section is not limited to a specific material as long as it transmits light. Note that the separation unit 16 may be composed of a half mirror or a polarizing beam splitter.

[0020] The scanning unit 50 irradiates the object ob with the irradiation wave propagating in the first direction, changing its direction of propagation, and propagates the reflected wave to the separation unit 16. The scanning unit 50 may be configured to include, for example, a reflective mirror that changes the irradiation direction of the incident irradiation wave. The reflective mirror of the scanning unit 50 may be, for example, a MEMS (Micro Electro Mechanical Systems) mirror, a polygon mirror, or a galvanometer mirror.

[0021] The scanning lens 60 propagates the illumination wave from the scanning unit 50 into the space where the object ob exists, widening the field of view, and propagates the reflected wave, which is reflected by the object ob, back to the scanning unit 50. As described above, in this embodiment, the scanning lens 60 consists of at least two lenses, including a first scanning lens 60A and a second scanning lens 60B. Each of the at least two scanning lenses 60 may be a known lens and is not limited to a particular type or shape of lens.

[0022] Figure 2 shows a schematic configuration of at least two scanning lenses 60 provided in the optical system 100 according to this embodiment. The first scanning lens 60A is positioned so that its lens surface is inclined in a first direction with respect to the optical axes of the irradiated and reflected waves. The second scanning lens 60B is positioned so that its lens surface is inclined in a second direction with respect to the optical axes of the irradiated and reflected waves. The lens surface is the surface of the lens into which the irradiated or reflected wave is incident. In a cross-sectional view as shown in Figure 2, the first scanning lens 60A has an angle (α) greater than 0 with respect to the optical axes of the irradiated and reflected waves in the first direction at the intersection of the optical axes of the irradiated and reflected waves and the lens surface. In a cross-sectional view as shown in Figure 2, the second scanning lens 60B has an angle (α) greater than 0 with respect to the optical axes of the irradiated and reflected waves in the second direction at the intersection of the optical axes of the irradiated and reflected waves and the lens surface. Here, if the normal to the lens surface has an angle greater than 0 in the first direction with respect to the optical axes of the irradiated and reflected waves, that angle is indicated with a positive sign, and if it has an angle greater than 0 in the second direction, that angle is indicated with a negative sign. The first scanning lens 60A has a lens surface that is tilted in the first direction with respect to the optical axes of the irradiated and reflected waves, and below, the tilt state of the first scanning lens 60A shown in Figure 2 will be expressed as a tilt of +α. The second scanning lens 60B has a lens surface that is tilted in the second direction with respect to the optical axes of the irradiated and reflected waves, and below, the tilt state of the second scanning lens 60B shown in Figure 2 will be expressed as a tilt of -α. For example, the tilt of a scanning lens 60 that is arranged perpendicular to the optical axes of the irradiated and reflected waves is 0. The tilt settings of the at least two scanning lenses 60 provided in the optical system 100 will be described later.

[0023] The focusing lens 19 concentrates the reflected waves propagated in the second direction by the separation unit 16 onto the light-receiving surface of the light detection unit 20. Any known lens may be used as the focusing lens 19.

[0024] The light detection unit 20 detects reflected waves. The light detection unit 20 may include elements such as an APD (Avalanche PhotoDiode), a PD (PhotoDiode), or a distance measuring image sensor. The light detection unit 20 may also include an array of elements such as an APD array, a PD array, or a distance measuring imaging array.

[0025] Here, Figure 4 is a diagram illustrating unwanted light 102 in an optical system 200 (first comparative example) equipped with only one scanning lens 60. Unwanted light 102 is light reflected from the lens surface of the scanning lens 60 when the tilt is 0 (i.e., positioned perpendicular to the optical axis). When the irradiation wave is incident on the scanning lens 60, a portion is reflected and becomes unwanted light 102, which propagates to the photodetector 20 and generates noise, thus degrading the performance of the electromagnetic wave detection device, such as the signal-to-noise ratio.

[0026] Figure 5 is a diagram illustrating unwanted light 102 in an optical system 200 (second comparative example) equipped with only one scanning lens 60. Unwanted light 102 is light reflected from the lens surface of the scanning lens 60, which has a non-zero tilt (i.e., is positioned at an inclination with respect to the optical axis). When the illumination wave is incident on the scanning lens 60, a portion is reflected and becomes unwanted light 102, but since it does not propagate to the photodetector 20, noise reduction is possible. However, the presence of a non-zero tilt in the scanning lens 60 complicates the optical design, and optical performance such as the light-gathering performance of the photodetector 20 deteriorates, for example, because the light spot is asymmetrical. As a result, the performance of the electromagnetic wave detection device, such as the signal-to-noise ratio, may deteriorate.

[0027] In the optical system 100 or electromagnetic wave detection device according to this embodiment, at least two scanning lenses 60 include a first scanning lens 60A and a second scanning lens 60B. The first scanning lens 60A is positioned so that its lens surface is tilted in a first direction with respect to the optical axes of the irradiated and reflected waves, and the second scanning lens 60B is positioned so that its lens surface is tilted in a second direction with respect to the optical axes of the irradiated and reflected waves. By tilting the first scanning lens 60A and the second scanning lens 60B in symmetrical directions (opposite directions), unwanted light 102 is prevented from reaching the photodetector 20, and the optical performance is not reduced. Here, as shown in the example in Figure 2, by positioning the first scanning lens 60A and the second scanning lens 60B so that the sum of their tilts is 0 (i.e., the overall tilt of the scanning lenses 60 is 0), the light-gathering performance of the photodetector 20 is not reduced. For example, if the tilt of the first scanning lens 60A is +α, the tilt of the second scanning lens 60B should be -α. α is 8° as an example, but is not particularly limited. According to several simulations, α is preferably in the range of 5° to 20°. Furthermore, the first scanning lens 60A may be tilted in the second direction, and the second scanning lens 60B may be tilted in the first direction. For example, if the tilt of the first scanning lens 60A is -α, the tilt of the second scanning lens 60B should be +α. Here, the tilt of the scanning lenses 60 may be determined by simulations of the irradiated and reflected waves. That is, simulations can be performed by treating the irradiated and reflected waves as a collection of many light rays while changing the tilt of the scanning lens 60, and a tilt can be selected where not all light rays are incident perpendicularly on the lens surface. Also, since it is sufficient to arrange at least two scanning lenses 60 so that the sum of their tilts is 0, the optical design will not become complicated. Furthermore, the first scanning lens 60A and the second scanning lens 60B may be lenses of the same shape or lenses of different shapes.

[0028] Here, the optical system 100 may include three or more scanning lenses 60 tilted so that the sum of their tilts is 0. Also, to facilitate optical design, the total number of at least two scanning lenses 60 may be even. In this case, the optical system 100 may include scanning lenses 60 composed of multiple pairs of lens groups (pairs) whose sum of tilts is 0, such as the first scanning lens 60A and the second scanning lens 60B in Figure 2. However, it is sufficient that the sum of the tilts of all scanning lenses 60 is 0, so the sum of the tilts of one pair of lens groups (pairs) does not need to be 0. For example, if the optical system 100 includes four scanning lenses 60, the sum of the tilts of one pair of lens groups may be +β, and the sum of the tilts of another pair of lens groups may be -β.

[0029] Figure 3 shows the difference in light-gathering performance due to the tilt of the scanning lens 60, as determined by simulation. The conditions (tilt state) are indicated in parentheses. Simulations were performed for the cases where the two scanning lenses 60 are "perpendicular to the optical axis," "both tilted in the same direction" (both tilted to +α), and "tilted in opposite directions" (tilted to -α and +α). The simulation results for each condition are shown in a diagram illustrating the outline of the light ray path and a diagram showing the light ray gathering performance at the light-receiving surface of the photodetector 20. In the case where the lenses are "perpendicular to the optical axis," there is no degradation in light-gathering performance, but the signal-to-noise ratio (SNR) is degraded because unwanted light 102 is also received by the photodetector 20. In the case where the lenses are "two tilts," the spot spreads out in an irregular shape, and the light-gathering performance decreases. In contrast, in the case where the lenses are "two tilts," there is no degradation in light-gathering performance, and the SNR is not degraded because unwanted light 102 does not reach the photodetector 20.

[0030] As described above, the optical system 100 and electromagnetic wave detection device according to this embodiment can reduce noise caused by reflections from optical components by appropriately tilting and arranging the scanning lens 60.

[0031] While embodiments of this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art will find it easy to make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are within the scope of this disclosure. For example, each component can be rearranged in a logically consistent manner, and multiple components can be combined into one or separated. [Explanation of Symbols]

[0032] 16 Separation part 19. Focusing lens 20 Light detection unit 31 Irradiation area 41 lenses 50 Scanning Unit 60 scanning lenses 60A First scanning lens 60B Second scanning lens 100 Optical system 102 Unnecessary light 200 Optical system

Claims

1. Irradiation area and, A separation unit that propagates the irradiation wave irradiated from the irradiation unit in a first direction, and propagates the reflected wave, which is reflected by the object, in a second direction opposite to the first direction, A scanning unit that causes the irradiation wave propagating in the first direction to irradiate the target object while changing the direction of propagation, and propagates the reflected wave to the separation unit, The system comprises at least two scanning lenses that propagate the irradiation wave from the scanning unit into the space where the object exists in such a way that the field of view widens, and propagate the reflected wave to the scanning unit, The at least two scanning lenses include a first scanning lens and a second scanning lens. The first scanning lens is arranged such that its lens surface is inclined in a first direction with respect to the optical axes of the irradiated wave and the reflected wave. The optical system is configured such that the second scanning lens has a lens surface that is inclined in the second direction with respect to the optical axes of the irradiated wave and the reflected wave.

2. The optical system according to claim 1, wherein the first scanning lens and the second scanning lens are lenses of the same shape.

3. The optical system according to claim 1, wherein the first scanning lens and the second scanning lens are lenses of different shapes.

4. The optical system according to any one of claims 1 to 3, wherein the total number of the at least two scanning lenses is even.

5. Irradiation area and, A separation unit that propagates the irradiation wave irradiated from the irradiation unit in a first direction, and propagates the reflected wave, which is reflected by the object, in a second direction opposite to the first direction, A scanning unit that causes the irradiation wave propagating in the first direction to irradiate the target object while changing the direction of propagation, and propagates the reflected wave to the separation unit, The system comprises at least two scanning lenses that propagate the irradiation wave from the scanning unit into the space where the object exists in such a way that the field of view widens, and propagate the reflected wave to the scanning unit, The at least two scanning lenses include a first scanning lens and a second scanning lens. The first scanning lens is arranged such that its lens surface is inclined in a first direction with respect to the optical axes of the irradiated wave and the reflected wave. The electromagnetic wave detection device is configured such that the second scanning lens is positioned such that its lens surface is inclined in the second direction with respect to the optical axes of the irradiated wave and the reflected wave.

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