Measuring device

Abstract

The light-receiving elements in measuring devices have relatively low detection sensitivity to long-wavelength light. [Solution] The measuring device comprises a light emitter that emits light, and a light receiver that receives the reflected light that returns when the light emitted by the light emitter is reflected off the object to be measured. The light receiver comprises an upconverter that converts the light emitted by the light emitter into converted light with a shorter wavelength than the light emitted by the light emitter, and a light receiving element that receives the converted light.

Description

Technical Field

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[0001] The technology disclosed in this specification relates to a measuring device.

Background Art

[0002] With the development of autonomous driving systems (AD) and advanced driver assistance systems (ADAS), research and development of LiDAR (light detection and ranging) has been underway as one of the measuring devices used for grasping the surrounding environment and estimating the self-position of a vehicle during driving. LiDAR includes a light projector that emits light and a light receiver that receives the reflected light that returns after the light emitted by the light projector is reflected by the measurement target. The light receiver includes a light receiving element (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The light receiving element in the above-described measuring device has low detection sensitivity to light of a relatively long wavelength.

[0005] This specification discloses a technology capable of solving the above-described problems.

Means for Solving the Problems

[0006] The technology disclosed in this specification can be realized, for example, in the following forms.

[0007] (1) The measuring device disclosed herein comprises a light emitter that emits light, and a light receiver that receives reflected light that returns when the light emitted by the light emitter is reflected off a target for measurement. The light receiver comprises an upconverter that converts the light emitted by the light emitter into converted light with a shorter wavelength than the light emitted by the light emitter, and a light receiving element that receives the converted light. With this measuring device, since the light emitted by the light emitter is converted into converted light with a shorter wavelength than the light emitted by the light emitter, the detection sensitivity of the light emitted by the light emitter by the light receiving element is improved.

[0008] (2) In the above measuring device, the photodetector may contain Si, the light emitted by the light emitter may have an energy less than the band gap of Si, and the converted light may have an energy greater than or equal to the band gap of Si. With this configuration, the upconverter can convert light having an energy less than the band gap of Si into light having an energy greater than or equal to the band gap of Si. Therefore, even if the energy of the light emitted by the light emitter is less than the band gap of Si, the photodetector can detect that the light emitted by the light emitter has entered the photodetector.

[0009] (3) In the above measuring device, the wavelength of the light emitted by the light emitter may be 1500 nm or more, and the wavelength of the converted light may be 800 nm or less. With this configuration, the upconverter can convert light having energy less than the band gap of Si into light having energy greater than or equal to the band gap of Si. Therefore, even if the energy of the light emitted by the light emitter is less than the band gap of Si, the light receiving element can detect that the light emitted by the light emitter has entered the light receiving element.

[0010] (4) The above measuring device may further include a microlens that focuses the light emitted by the light emitter, and the upconverter may be located between the microlens and the light receiving element. With this configuration, the light emitted by the light emitter is converted into converted light with a shorter wavelength than the light emitted by the light emitter, thereby improving the detection sensitivity of the light emitted by the light emitter by the light receiving element.

[0011] (5) In the above measuring device, the photodetector comprises a plurality of photodetectors adjacent to each other in the direction along the light-receiving surface, and the upconverter may be a thin film covering the plurality of photodetectors. With this configuration, for example, the arrangement of the upconverters becomes easier compared to a configuration comprising a plurality of upconverters covering each of the individual photodetectors.

[0012] (6) In the above measuring device, the upconverter may be a microlens that focuses the light emitted by the light emitter and converts the light emitted by the light emitter into the converted light. With this configuration, since a microlens is used as the upconverter, the arrangement of the upconverter becomes easier.

[0013] Furthermore, the technologies disclosed herein can be implemented in various forms, for example, in the form of a measuring device, a method for manufacturing a measuring device, or a method for measuring using a measuring device. [Brief explanation of the drawing]

[0014] [Figure 1] Block diagram showing the configuration of the measuring device [Figure 2] Diagram illustrating the detailed configuration of the light receiving device of the first embodiment. [Figure 3] Diagram illustrating the detailed configuration of the light receiving device of the second embodiment. [Figure 4] Diagram illustrating the detailed configuration of the light receiving device of the third embodiment. [Modes for carrying out the invention]

[0015] (First Embodiment) Figure 1 is a block diagram showing the configuration of the measuring device 1. In this embodiment, the measuring device 1 is a LiDAR. The measuring device 1 is installed, for example, in a vehicle equipped with an autonomous driving system or an advanced driver assistance system. The measuring device 1 assists the driver in recognizing people, other vehicles, and other objects while the vehicle is in motion. The measuring device 1 also provides various types of information to other devices and users that are useful in ensuring the safety of the driver and those around the vehicle, and in reducing damage to objects in the surrounding area while the vehicle is in motion.

[0016] The measuring device 1 comprises a light emitter 100, a light receiver 400, an information processing device 500, and a communication interface 600.

[0017] Measurement by the measuring device 1 is performed by receiving light from the light emitter 100 after it has been reflected by the object to be measured W. In each figure, of the light emitted by the light emitter 100, the light emitted by the light emitter 100 that is directed toward the object to be measured W is shown as emitted light Lout, and of the light emitted by the light emitter 100 that is reflected by the object to be measured W and incident on the light receiver 400 is shown as reflected light Lre.

[0018] The floodlight 100 emits light. The floodlight 100 comprises a light projection optical system 110, a light source unit 120, a current source 130, and a control circuit board 210.

[0019] The light source unit 120 has, for example, a plurality of light-emitting elements (not shown) or a plurality of light-emitting element arrays. A light-emitting element array is a configuration in which light-emitting elements are arranged linearly (one-dimensionally) or planarly (two-dimensionally). Each light-emitting element is, for example, a laser diode, a surface-emitting type laser light-emitting element (hereinafter referred to as "surface-emitting element"), a surface-emitting element array, etc. A surface-emitting element is, for example, a VCSEL (Vertical Cavity Surface Emitting Laser). A surface-emitting element array is a configuration in which a plurality of surface-emitting elements are arranged one-dimensionally or two-dimensionally on a substrate (semiconductor substrate, ceramic substrate, etc.) (for example, a VCSEL array).

[0020] The light emitted by the projector 100 using the light source unit 120 as a light source is, for example, an optical beam (laser light). The light emitted by the projector 100 may be, for example, short-wave infrared light, near-infrared light, visible light, or ultraviolet light. In this specification, short-wave infrared light means light with a wavelength of about 1000 nm or more and less than 2500 nm, near-infrared light means light with a wavelength of about 780 nm or more and less than 1000 nm, visible light means light with a wavelength of about 380 nm or more and less than 780 nm, and ultraviolet light means light with a wavelength of about 10 nm or more and less than 380 nm. In this embodiment, the light emitted by the projector 100 is short-wave infrared light. More specifically, the wavelength of the light emitted by the projector 100 of this embodiment is 1500 nm or more.

[0021] The projection optical system 110 adjusts the light distribution of the emitted light Lout by, for example, applying an optical action (refraction, scattering, diffraction, etc.) to the emitted light Lout emitted from the light source unit 120. The projection optical system 110 includes, for example, various lenses such as a collimating lens and optical components such as a reflector (mirror). The projection optical system 110 is disposed on the optical path of the emitted light Lout output from each light-emitting element of the light source unit 120. In other words, the projection optical system 110 is disposed so as to face each light-emitting element in the optical axis direction of each light-emitting element. The projection optical system 110 is disposed away from each light-emitting element in the optical axis direction.

[0022] The current source 130 supplies current to the light-emitting elements included in the light source unit 120. The current source 130 supplies, for example, a periodic pulse-wave current for turning on and off the current flowing through each light-emitting element to each light-emitting element.

[0023] The control circuit board 210 is a circuit board on which electronic components and the like for controlling the light emission of each light-emitting element of the light source unit 120 are mounted. The control circuit board 210 is communicably connected to each of the current source 130, the TOF measurement device 440 described later in the light receiver 400, and the information processing device 500.

[0024] The light receiver 400 receives the reflected light Lre that returns after the light emitted by the light emitter 100 is reflected off the object to be measured W. The light receiver 400 comprises a light receiving device 40 and a TOF measuring device 440.

[0025] The light receiving device 40 is a device that receives light incident on the light receiver 400. The detailed configuration of the light receiving device 40 will be described later.

[0026] The TOF measuring device 440 has, for example, a time measurement IC (integrated circuit) equipped with a TDC (time-to-digital converter) circuit. The TOF measuring device 440 is communicatively connected to the control circuit board 210, the light receiving device 40, and the information processing device 500. The TOF measuring device 440 receives a timing signal indicating the light emission timing output from the control circuit board 210 and a light receiving signal output from the light receiving device 40. Based on these, the TOF measuring device 440 determines the difference between the timing at which the emitted light Lout was emitted and the timing at which the reflected light Lre was received. In other words, the TOF measuring device 440 determines the time of flight (TOF) of the laser light. The TOF measuring device 440 outputs a signal corresponding to the determined TOF and the light receiving signal received from the light receiving device 40.

[0027] The information processing device 500 has a processor. The processor may be, for example, a CPU (central processing unit), an MPU (microprocessing unit), an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), or a DSP (digital signal processor). The information processing device 500 is communicatively connected to the control circuit board 210, the TOF measuring device 440, and the communication interface 600. The information processing device 500 receives the signal corresponding to the TOF output and the received signal from the TOF measuring device 440. Based on these, the information processing device 500 generates various information such as the distance to the measurement target W. This information includes, for example, a histogram used in time-correlated single photon counting, the distance to each point of the measurement target W, and point cloud information.

[0028] The communication interface 600 is connected to the information processing device 500 and the external device 700, which will be described later, in a manner that allows communication between them. The communication interface 600 transmits the information processed by the information processing device 500 to the external device 700.

[0029] The external device 700 may be, for example, a device that creates an environmental map using a point cloud, or a device that performs self-localization estimation (SLAM: Simultaneous Localization and Mapping) using scan matching algorithms such as NDT (Normal Distributions Transform) or ICP (Iterative Closest Point).

[0030] Figure 2 is an explanatory diagram showing the detailed configuration of the light receiving device 40 of the first embodiment. The light receiving device 40 comprises a light receiving optical system 410, an upconverter 420, and a light receiving unit 430.

[0031] The light-receiving optical system 410 is an optical system for receiving light incident on the light receiver 400 in the light-receiving unit 430. The light-receiving optical system 410 may be various lenses such as focusing lenses, various filters such as wavelength filters, or reflective mirrors. The light-receiving optical system 410 is arranged on the optical path of the incident light incident on each of the light-receiving elements 432 in the light-receiving unit 430, which will be described later. In this embodiment, the light-receiving optical system 410 includes microlenses 412. The microlenses 412 focus the light (reflected light Lre) emitted from the light emitter 100. In this embodiment, the light-receiving optical system 410 comprises a plurality of microlenses 412 that are adjacent to each other in a direction along the light-receiving surface 430S of the light-receiving unit 430.

[0032] The light-receiving unit 430 generates a photodetector signal with a current level or voltage level corresponding to the intensity of the light incident on the photodetector 400 by photoelectric conversion of the light incident on the photodetector 400. The light-receiving unit 430 in this embodiment is a complementary metal-oxide-semiconductor (CMOS). The light-receiving unit 430 includes a plurality of photodetectors 432 and a substrate 434.

[0033] The light-receiving element 432 is, for example, a photodiode, an avalanche photodiode, or a single-photon-avalanche diode (SPAD). The material of the light-receiving element 432 may be, for example, Si (silicon), Ge (germanium), InGaAs (indium gallium arsenide), etc. The light-receiving element 432 in this embodiment contains Si. The light-receiving element 432 in this embodiment contains Si as its main component. Multiple light-receiving elements 432 are adjacent to each other in a direction along the light-receiving surface 430S. The substrate portion 434 is the part in the light-receiving section 430 where photoelectric conversion does not occur. The substrate portion 434 is located between adjacent light-receiving elements 432. The substrate portion 434 in this embodiment contains Si as its main component.

[0034] The upconverter 420 converts the light incident on it into light with a shorter wavelength than the wavelength of the light incident on it. In other words, the upconverter 420 converts the light incident on it into light with a higher energy than the energy of the light incident on it. That is, photon upconversion (UC) occurs in the upconverter 420. As shown in Figure 2, the upconverter 420 of this embodiment converts the light emitted by the light emitter 100 (reflected light Lre) into converted light Lco, which has a shorter wavelength than the light emitted by the light emitter 100 (reflected light Lre). The light receiving element 432 receives the converted light Lco.

[0035] The wavelength of the light after the wavelength conversion by the upconverter 420 only needs to be shorter than the wavelength of the light before the wavelength conversion by the upconverter 420. That is, the upconverter 420 may, for example, convert short-wave infrared light to near-infrared light, visible light, or ultraviolet light, or convert near-infrared light to visible light or ultraviolet light, or convert visible light to ultraviolet light. The upconverter 420 may, for example, convert light with a wavelength of 1500 nm or more to light with a wavelength of 800 nm or less, or convert light with a wavelength of 1100 nm to 1200 nm to light with a wavelength of 800 nm to 900 nm. In this embodiment, the upconverter 420 converts light with a wavelength of 1500 nm or more to light with a wavelength of 800 nm or less. As described above, the wavelength of the light emitted by the light emitter 100 is 1500 nm or more, so the wavelength of the converted light Lco is 800 nm or less. In other words, the light emitted by the light emitter 100 has an energy less than the band gap of Si (approximately 1.12 eV), while the converted light Lco has an energy greater than or equal to the band gap of Si. To put it another way, the upconverter 420 converts light with an energy less than the band gap of Si into light with an energy greater than or equal to the band gap of Si.

[0036] In this embodiment, the upconverter 420 is located between the microlens 412 and the photodetector 432. In other words, the upconverter 420 is positioned further from the light source 120 than the photodetector optical system 410 on the optical path of the incident light incident on the photodetector 432. In this embodiment, the upconverter 420 is a thin film covering multiple photodetectors 432. The thickness of the upconverter 420 is, for example, about 10 μm.

[0037] The upconverter 420 may undergo UC based on sum-frequency generation (SFG). If the upconverter 420 undergoes UC based on sum-frequency generation, it may contain, for example, LiNbO3 (lithium niobate). The upconverter 420 may undergo UC based on triplet-triplet annihilation (TTA). If the upconverter 420 undergoes UC based on triplet-triplet annihilation, it may contain, for example, diphenylanthracene as an acceptor and platinum-porphyrin as a donor. The upconverter 420 may undergo UC based on heavy rare-earth UC emission. If the upconverter 420 undergoes UC based on heavy rare-earth UC emission, it may contain, for example, Yb (ytterbium) as a sensitizer and Er (erbium), Tm (thulium), or Ho (holmium) as emission centers. The upconverter 420 may undergo unintended harmonic emission (UC) based on second-harmonic generation (SHG). If the upconverter 420 undergoes UC based on second-harmonic generation, it may include, for example, a silica-based optical fiber. The sum-frequency generation, triplet-triplet annihilation, heavy rare-earth UC emission, and second-harmonic generation described above are merely examples of processes by which UC occurs, and the process by which UC occurs in the upconverter 420 is not particularly limited.

[0038] As described above, the measuring device 1 of this embodiment includes a light emitter 100 that emits light, and a light receiver 400 that receives reflected light Lre that is reflected back from the measurement target W after the light emitted by the light emitter 100 has reflected off it. The light receiver 400 includes an upconverter 420 that converts the light emitted by the light emitter 100 into converted light Lco, which has a shorter wavelength than the light emitted by the light emitter 100, and a light receiving element 432 that receives the converted light Lco. According to the measuring device 1 of this embodiment, since the light emitted by the light emitter 100 is converted into converted light Lco, which has a shorter wavelength than the light emitted by the light emitter 100, the detection sensitivity of the light emitted by the light emitter 100 by the light receiving element 432 is improved.

[0039] In the measuring device 1 of this embodiment, the light-receiving element 432 contains Si, the light emitted by the light emitter 100 has energy less than the band gap of Si, and the converted light Lco has energy greater than or equal to the band gap of Si. According to the measuring device 1 of this embodiment, the upconverter 420 can convert light having energy less than the band gap of Si into light having energy greater than or equal to the band gap of Si. Therefore, even if the energy of the light emitted by the light emitter 100 is less than the band gap of Si, the light-receiving element 432 can detect that the light emitted by the light emitter 100 has entered the light-receiving element 400. Furthermore, according to the measuring device 1 of this embodiment, relatively inexpensive Si can be used as the material for the light-receiving element 432, thus reducing the cost of measurement by the measuring device 1.

[0040] In the measuring device 1 of this embodiment, the wavelength of the light emitted by the light emitter 100 is 1500 nm or more, and the wavelength of the converted light Lco is 800 nm or less. According to the measuring device 1 of this embodiment, the upconverter 420 can convert light having energy less than the band gap of Si into light having energy greater than or equal to the band gap of Si. Therefore, even if the energy of the light emitted by the light emitter 100 is less than the band gap of Si, the light receiving element 432 can detect that the light emitted by the light emitter 100 has entered the light receiving element 400. Furthermore, according to the measuring device 1 of this embodiment, relatively inexpensive Si can be used as the material for the light receiving element 432, thus reducing the cost of measurement by the measuring device 1.

[0041] In the measuring device 1 of this embodiment, a microlens 412 is further provided to focus the light emitted by the light emitter 100, and the upconverter 420 is located between the microlens 412 and the light receiving element 432. According to the measuring device 1 of this embodiment, the light emitted by the light emitter 100 is converted into converted light Lco, which has a shorter wavelength than the light emitted by the light emitter 100, so the detection sensitivity of the light emitted by the light emitter 100 by the light receiving element 432 is improved.

[0042] In the measuring device 1 of this embodiment, the photodetector 400 comprises a plurality of photodetectors 432 adjacent to each other in the direction along the photodetector surface 430S, and the upconverter 420 is a thin film covering the plurality of photodetectors 432. According to the measuring device 1 of this embodiment, the arrangement of the upconverter 420 becomes easier compared to a configuration in which, for example, a plurality of upconverters covering each of the individual photodetectors are provided.

[0043] (Second Embodiment) Figure 3 is an explanatory diagram showing the detailed configuration of the light receiving device 40a of the second embodiment. In the following, for components of the light receiving device 40a of the second embodiment that are the same as those of the light receiving device 40 of the first embodiment, the same reference numerals are used, and their explanations will be omitted as appropriate.

[0044] The measuring device 1a of this embodiment includes a light receiving device 40a. The light receiving device 40a includes an upconverter 420a and a light receiving unit 430. The upconverter 420a focuses the light (reflected light Lre) emitted by the light emitter 100 and converts the light (reflected light Lre) emitted by the light emitter 100 into converted light Lco. In other words, the upconverter 420a of this embodiment is a lens. More specifically, the upconverter 420a of this embodiment is a microlens. The upconverter 420a of this embodiment not only functions as a field where UC occurs, but also functions as a light receiving optical system. Such an upconverter 420a can be manufactured, for example, by mixing a material involved in UC together with a known microlens material in a known microlens manufacturing method.

[0045] As described above, in the measuring device 1a of this embodiment, the upconverter 420a is a microlens that focuses the light emitted by the light emitter 100 and converts the light emitted by the light emitter 100 into converted light Lco. According to the measuring device 1a of this embodiment, since a microlens is used as the upconverter 420a, the arrangement of the upconverter 420a becomes easier.

[0046] (Third embodiment) Figure 4 is an explanatory diagram showing the detailed configuration of the light receiving device 40b of the third embodiment. In the following, for the components of the light receiving device 40b of the third embodiment that are the same as those of the light receiving device 40 of the first embodiment, the same reference numerals are used, and their explanations will be omitted as appropriate.

[0047] The measuring device 1b of this embodiment includes a light receiving device 40b. The light receiving device 40b includes a light receiving optical system 410b, an upconverter 420, and a light receiving unit 430. The light receiving optical system 410b includes a microlens 412 and a bandpass filter 414. The bandpass filter 414 is a filter that removes noise such as sunlight. The bandpass filter 414 transmits light with wavelengths included in a specific wavelength band and blocks light with wavelengths not included in that specific wavelength band. For example, the bandpass filter 414 transmits light emitted by the light emitter 100 and light with wavelengths similar to those emitted by the light emitter 100. As in the third embodiment, the light receiving optical system may include a bandpass filter.

[0048] (modified version) The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from their essence, for example, the following modifications are possible.

[0049] In the above embodiment, the light-receiving element 432 contains Si, but the light-receiving element does not necessarily have to contain Si.

[0050] In the above embodiment, the upconverter 420 converts light having energy less than the band gap of Si into light having energy greater than or equal to the band gap of Si. However, the upconverter may also convert light having energy greater than or equal to the band gap of Si into light with even higher energy.

[0051] In the first and third embodiments, the upconverter 420 is positioned further from the light source 120 than the light-receiving optical system 410 in the optical path of the incident light incident on the light-receiving element 432. However, the upconverter may be positioned closer to the light source than the light-receiving optical system in the optical path of the incident light incident on the light-receiving element.

[0052] In the first and third embodiments, the upconverter 420 is a thin film covering a plurality of photodetectors 432, but the upconverter may be an assembly of a plurality of thin films covering each of the individual photodetectors. [Explanation of Symbols]

[0053] 1,1a,1b: Measuring device 40,40a,40b: Light receiving device 100: Light emitter 110: Light emission optics 120: Light source unit 130: Current source 210: Control circuit board 400: Light receiver 410,410b: Light receiving optics 412: Microlens 414: Bandpass filter 420,420a: Upconverter 430: Light receiving unit 430S: Light receiving surface 432: Light receiving element 434: Substrate unit 440: TOF measuring device 500: Information processing device 600: Communication interface 700: External device Lout: Emitted light Lre: Reflected light Lco: Converted light W: Measurement target

Claims

1. A measuring device, A floodlight that emits light, A light receiver that receives the reflected light that returns after the light emitted by the aforementioned light emitter is reflected off the object to be measured, Equipped with, The aforementioned light receiver is, An upconverter that converts the light emitted by the light emitter into converted light with a shorter wavelength than the light emitted by the light emitter, A measuring device comprising a light-receiving element that receives the converted light.

2. A measuring device according to claim 1, The aforementioned light-receiving element includes Si, The light emitted by the aforementioned light source has an energy less than the band gap of Si, The aforementioned conversion light has an energy greater than the band gap of Si, and is used as a measuring device.

3. A measuring device according to claim 2, The wavelength of the light emitted by the aforementioned light source is 1500 nm or greater. The wavelength of the converted light is 800 nm or less, according to the measuring device.

4. A measuring device according to any one of claims 1 to 3, further, The aforementioned light emitter is equipped with a microlens that focuses the light it emits. The upconverter is a measuring device located between the microlens and the photodetector.

5. A measuring device according to claim 4, The light receiver comprises a plurality of light-receiving elements adjacent to each other in the direction along the light-receiving surface, The measurement device wherein the upconverter is a thin film covering the plurality of light-receiving elements.

6. A measuring device according to any one of claims 1 to 3, The upconverter is a microlens that focuses the light emitted by the light emitter and converts the light emitted by the light emitter into the converted light, in a measuring device.

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