WO2022209789A1 - Optical beam generation device and optical detector - Google Patents

Abstract

Provided is an optical beam generation device comprising: a reference signal generator (110) that generates a reference signal, a pulse generator (110) that generates a pulse synchronized with the reference signal, a first optical beam generator that repeatedly generates, in synchronization with the reference signal, a first optical beam having a frequency which is continuously varied within a predetermined frequency range, and an optical amplifier (120) that generates a second optical beam by amplifying the first optical beam in synchronization with the pulse.

Description

Light beam generator and photodetector

The present disclosure relates to light beam generators and photodetectors.

With the progress of AD (Autonomous Driving) and ADAS (Advanced Driver Assistance System), a light beam is used as a sensor for grasping the surrounding environment and estimating self-location, etc. It is also called a light detector (LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging), an optical radar device, a light detection and ranging device, etc. that measures the distance to an object using the reflected light. ) have been drawing attention. Photodetectors have features that millimeter-wave radars do not have, such as high resolution and high-definition 3D mapping. As a sensor, research/development is actively progressing.

Non-Patent Document 1 describes a modulated continuous wave LiDAR. The LiDAR described in the same document is configured for the purpose of measuring the distance to an object and the relative velocity of the object with high resolution, and uses electro-optic modulation instead of an acousto-optic modulator (AOM). A laser beam with a wavelength of 1550 nm is modulated with a chirped pulse (sweep bandwidth 98 MHz, duration 10 μs, pulse repetition frequency 20 kHz).

The ranging principle used by photodetectors can be roughly divided into TOF (Time Of Flight) and modulated continuous wave methods. Of these, the TOF method irradiates time-divided pulsed light as irradiation light for irradiating an object. In addition, in the TOF method, in order to obtain the required FOV (Field Of View), a mechanical or optical scanning device (galvano scanner, MEMS mirror, etc.) is used to scan the irradiation light beam. done. On the other hand, in the modulated continuous wave method, in order to secure the FOV, the frequency-modulated irradiation light is passed through an optical element such as a prism, and is continuously deflected to irradiate the object. Based on an interference wave (beat wave) obtained by causing the reflected light from the object to interfere with the irradiation light, the distance to the object and the relative speed of the object are obtained.

By the way, from the viewpoint of ensuring measurement accuracy, it is preferable that the intensity of the irradiation light that the photodetector irradiates toward the object is as high as possible. Moreover, from the viewpoint of enabling stable measurement, it is preferable that the irradiation time is long. On the other hand, photodetectors generally use laser light with a wavelength in the absorption band of the retina of the human eye as irradiation light. It is preferable that the intensity is as low as possible and the irradiation time is as short as possible (for example, see the Japanese Industrial Standard "Safety Standards for Laser Products" (JIS C 6802)). Therefore, it is necessary to appropriately set the intensity and irradiation time of the irradiation light emitted from the photodetector by comprehensively considering the viewpoint of measurement accuracy and stability of measurement, and the viewpoint of safety for human eyes. be.

Here, in the TOF method, time-divided pulsed light is intermittently irradiated as irradiation light, and beam scanning of the irradiation light is also performed, so it can be said that the effect on the human eye is relatively small. Further, since the pulsed light is intermittently irradiated, the amount of energy that enters the human eye is limited even if beam scanning is stopped due to an abnormality in the control system, for example.

On the other hand, in the modulated continuous wave system, if the frequency of the irradiation light is fixed due to some abnormality, the irradiation range of the irradiation light will be fixed. Further, in the modulated continuous wave method, as in the TOF method, mechanical or optical beam scanning is performed as necessary. end up Therefore, in the modulated continuous wave system, it is necessary to take some measures to ensure safety even if the irradiation range of the irradiation light is fixed. As a measure for improving safety, for example, direct control of the laser light source, which is the source of the irradiation light, is conceivable so that the irradiation light is intermittently irradiated. In that case, the frequency stability of the irradiation light may be impaired.

Although Non-Patent Document 1 describes a modulated continuous wave LiDAR, it does not specifically describe how to ensure safety when the irradiation range of the irradiation light is fixed.　　　

The present disclosure has been made in view of this background, and a light beam generator and a photodetector that can ensure safety when irradiating an object with a light beam using a modulated continuous wave method intended to provide

One of the present disclosure for achieving the above object is a light beam generator, comprising: a reference signal generator for generating a reference signal; a pulse generator for generating a pulse synchronized with the reference signal; a first light beam generator for repeatedly generating a first light beam whose frequency is continuously varied within a range in synchronization with the reference signal; an optical amplifier for generating two light beams.

In addition, the problems disclosed by the present application and their solutions will be clarified in the section of the mode for carrying out the invention and the drawings.

According to the present disclosure, it is possible to ensure safety when irradiating an object with a light beam using a modulated continuous wave method.

It is a block diagram showing a schematic configuration of a photodetector. 4 is a timing chart for explaining the relationship between signals and light beams generated in each configuration of the photodetector; 4 is a timing chart for explaining how an arithmetic unit takes in beat waves in synchronization with pulses; 4 is a timing chart for explaining how an arithmetic unit takes in beat waves via an A/D converter; It is a figure explaining the principle which calculates|requires the distance to an object and the relative speed between objects by a photodetector.

Embodiments for carrying out the present disclosure will be described below with reference to the drawings. In the following description, the same or similar configurations may be denoted by common reference numerals and redundant description may be omitted.

FIG. 1 shows a photodetector 100 (LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) that employs a modulated continuous wave system, an optical radar device, a light detection ranging device, etc., which is shown as an embodiment of the present disclosure. ) is a block diagram showing a schematic configuration. The photodetector 100 irradiates a frequency-modulated light beam (for example, laser light in the near-infrared wavelength region (λ = 780 to 2500 nm), hereinafter referred to as “irradiation light”) toward the object 2, Based on an interference wave (hereinafter also referred to as a “beat wave”) obtained by causing the reflected light from the object 2 to interfere with the irradiation light (light beam), the distance to the object 2 and the distance to the object 2 are determined. Find the relative velocity of In the figure, thin arrows indicate the flow of electricity, and thick arrows indicate the flow of light.

As shown in the figure, the photodetector 100 includes an arbitrary waveform generator 101, a control power source 102, a laser light source 103, a temperature control device 104, a signal generator 110, an optical amplifier 120, an optical interferometer 130, and a photoelectric converter 140. , arithmetic unit 150 and beam scanning unit 160 .

Among them, the arbitrary waveform generator 101, the control power supply 102, the laser light source 103, the temperature control device 104, and the signal generator 110 generate laser light (hereinafter referred to as "first light beam") which is a source of irradiation light. ) to generate a first light beam generator. Further, the signal generator 110 and the optical amplifier 120 generate a light beam (hereinafter referred to as a "second light beam") as irradiation light based on the first light beam, which is a frequency-modulated light beam. Configure two light beam generators. Further, the optical interferometer 130 irradiates the object 2 with the irradiation light and receives the reflected light that is reflected from the object 2 and returns, and divides the reflected light and the irradiation light (part of the second light beam). An interferometer (beat wave generator) is configured to generate an interference wave (beat wave) by causing interference with the reference light obtained by the method. The photoelectric converter 140 also inputs a signal obtained by photoelectrically converting an interference wave (beat wave) (hereinafter referred to as an “interference signal”) to the arithmetic device 150 . The computing device 150 includes an A/D converter 151, and performs A/D conversion (analog/digital conversion) of the interference signal to analyze the distance to the object 2 and the relative speed between the objects 2. Ask. In the figure, transmission and reception of light beams between the components is performed using air as a medium or via optical fibers, for example. Each configuration will be described in detail below.

A signal generator 110 (reference signal generator, pulse generator) generates a clock signal (hereinafter referred to as a “reference signal”) that serves as a reference when the arbitrary waveform generator 101 generates a waveform, and generates an arbitrary waveform. Input to generator 101 . Also, the signal generator 110 generates a pulse synchronized with the reference signal and inputs it to the optical amplifier 120 and the arithmetic device 150 . In this embodiment, the reference signal is assumed to be a continuous rectangular wave (rectangular wave) along the time axis. Details of the pulse will be described later.

The arbitrary waveform generator 101 functions as a waveform generator (function generator) that generates signals of arbitrary waveforms (rectangular wave, triangular wave, sine wave, sawtooth wave, etc.). Arbitrary waveform generator 101 generates a waveform used to generate a current (hereinafter referred to as “control current”) for controlling the frequency of laser light generated by laser light source 103 . Arbitrary waveform generator 101 generates the above waveform in synchronization with the reference signal input from signal generator 110 . In this example, arbitrary waveform generator 101 generates a triangular wave and inputs it to control power supply 102 . The arbitrary waveform generator 101 may also have the function of the signal generator 110 .

The control power supply 102 generates a control current based on the triangular wave input from the arbitrary waveform generator 101. In this embodiment, the control power supply 102 is assumed to generate a triangular wave control current.　　　

The laser light source 103 is a laser oscillation element (for example, a distributed feedback (DFB) laser element, a distributed reflection type ( (DBR: Distributed Bragg Reflector) laser element, MEMS-VCSEL wavelength sweep laser, etc.). In this embodiment, the laser light source 103 is configured using a distributed feedback (DFB) laser element. The laser light source 103 is a laser whose frequency is continuously changed within a predetermined frequency range (for example, the range of 193.4024 to 193.4266 [THz] (λ = 1549.903 to 1550.097 [nm])) by the control current input from the control power supply 102. Light (frequency-modulated light (chirped light), corresponding to the first light beam described above) is generated. A first light beam generated by the laser light source 103 is input to the optical amplifier 120 .

In this embodiment, the laser light source 103 is current controlled, but the laser light source 103 may be voltage controlled. conversion takes place. Further, in this embodiment, the laser light source 103 is an element whose oscillation frequency can be controlled from the outside. A modulated light may be generated.

The temperature control device 104 maintains the laser oscillation element forming the laser light source 103 at a predetermined temperature. The temperature control device 104 is configured using, for example, a temperature sensor or a thermoelectric cooling element (Peltier element). Maintain at temperature.

The optical amplifier 120 generates a light beam (second light beam) by amplifying the first light beam with a predetermined amplification factor during the time period when the pulse (pulse synchronized with the reference signal) is input from the signal generator 110. do. A second light beam generated by optical amplifier 120 is input to optical interferometer 130 . The optical amplifier 120 may be, for example, a semiconductor optical amplifier (SOA), a booster optical amplifier (BOA), a doped fiber amplifier (DFA), an erbium-doped fiber amplifier (EDFA). amplifier), etc. In this embodiment, the optical amplifier 120 is configured using a semiconductor optical amplifier (SOA). The optical amplifier 120 can also function as an optical switch by controlling the amplification factor. For example, when the gain is set to 0, the optical amplifier 120 stops generating the second light beam. Also, for example, when the amplification factor is 1, the optical amplifier 120 generates a second light beam having the same amplitude (energy) as that of the first light beam.

The optical interferometer 130 shown in FIG. 1 includes an optical splitter 131, a circulator 132, a collimator 133, an optical waveguide 134, and an optical coupler 135.

Of these, the optical splitter 131 is configured using, for example, an optical fiber coupler, a half mirror, and a beam splitter (half prism). The optical splitter 131 divides the second light beam incident from the optical amplifier 120 into a light beam (irradiation light) that irradiates the object 2 and a light (reflected light) that the irradiation light is reflected from the object 2 and returns. and a light beam for interfering with (hereinafter referred to as "reference light") at a predetermined intensity ratio (for example, irradiation light:reference light=9:1). The irradiation light split by the optical splitter 131 is input to the circulator 132 . On the other hand, the reference light is input to the optical coupler 135 via the optical waveguide 134 .

The circulator 132 guides the irradiation light input from the optical splitter 131 to the collimator 133 and guides the reflected light returning from the object 2 to the optical coupler 135 . The circulator 132 is configured using, for example, a Faraday rotator, a half-wave plate, a polarizing beam splitter, and a reflecting mirror (or prism).

The collimator 133 is configured using an optical component such as a collimating lens, and adjusts the spread of the irradiation light guided from the light splitter 131 (adjusts so that the illumination light becomes parallel (aberration correction)). Also, the collimator 133 collects reflected light returning from the object 2 .

The optical waveguide 134 adjusts the optical path length of the reference light from the optical splitter 131 to the optical coupler 135 via the optical waveguide 134 . The optical waveguide 134 is configured using, for example, an optical fiber.

The optical coupler 135 is configured using, for example, an optical fiber coupler, a half mirror, and a beam splitter (half prism), and functions as an interferometer that generates an interference wave (beat wave) by causing interference between the reflected light and the reference light. do. An interference wave generated in the optical coupler 135 is guided to the photoelectric converter 140 . When the opto-electric converter 140 in the latter stage is of a differential amplification type, the optical coupler 135 splits the light output from the opto-coupler 135 into two optical paths, which are sent to different ports of the opto-electric converter 140. input.

The photoelectric converter 140 photoelectrically converts the light input from the optical coupler 135 and generates a current signal (interference signal) according to the intensity of the input light. The interference signal generated by photoelectric converter 140 is input to arithmetic unit 150 . The photoelectric converter 140 is configured using, for example, a photodetector (balanced (differential amplification) photodetector, photodiode, etc.). 　　　

The arithmetic unit 150 includes, for example, a processor (CPU (Central Processing Unit), MPU (Micro Processing Unit), etc.), a storage device (main storage device, auxiliary storage device), an A/D converter 151 (A/D (analog/ (digital) conversion board, etc.), a communication device (network card, etc.), and an information processing device (computer). The arithmetic device 150 captures the voltage signal input from the amplifier 117 as a digital signal by the A/D converter 151, performs signal analysis processing such as Fourier transform (FFT) and peak search in the frequency domain on the captured digital signal, Based on the analysis results, the distance to the object 2 and the relative speed with respect to the object 2 are obtained. A specific method of calculating the distance to the object 2 and the relative speed with respect to the object 2 will be described later.

The beam scanning device 160 is a mechanical or optical device for enlarging the scanning range (FOV) of irradiation light, such as a galvano scanner, MEMS mirror, or the like. Note that the photodetector 100 does not necessarily have to include the beam scanning device 160 .

FIG. 2 is a timing chart explaining the relationship between signals and light beams generated by each component of the photodetector 100. FIG. Hereinafter, description will be made with reference to the same figure.

As shown in the figure, the arbitrary waveform generator 101 generates a triangular wave 22 in synchronization with a rectangular wave reference signal 21 input from the signal generator 110 . In this example, the arbitrary waveform generator 101 generates the triangular wave 22 so that the period from rising to falling of the triangular wave 22 matches one period of the reference signal 21 .

The control power supply 102 generates a control current based on the triangular wave 22 and inputs the generated control current to the laser light source 103 . The laser light source 103 generates the first light beam 23 frequency-modulated with the period of the reference signal 21 based on the control current.

The signal generator 110 generates a pulse 24 (rectangular wave in this example) at timing synchronized with the reference signal 21 and inputs the generated pulse 24 to the optical amplifier 120 and the arithmetic device 150 . In this example, the signal generator 110 generates the pulse 24 such that the period from the rise to the fall of the pulse 24 corresponds to one period of the reference signal 21 .

Incidentally, in this example, the rising timing of the pulse 24 is slightly delayed from the rising of the reference signal 21 . This takes into consideration the time required for the optical amplifier 120 to start up (the time required for the optical amplifier 120 to operate stably). As this delay time, for example, a value measured in a laboratory system is set. As will be described later, the amplification factor of optical amplifier 120 is controlled according to the amplitude of pulse 24 . The amplitude of the pulse 24 and the time interval (duty ratio) of the pulse 24 are set in comprehensive consideration of the viewpoints of measurement accuracy and stability and safety.

The optical amplifier 120 amplifies the first light beam 23 guided from the optical amplifier 120 with a predetermined amplification factor during the time period when the pulse 24 input from the signal generator 110 exists, and the second light beam 25 (irradiated light beam 25) is amplified. light). In this example, the optical amplifier 120 amplifies the first light beam 23 with an amplification factor corresponding to the amplitude of the pulse 24 to generate the second light beam 25 . The second light beam 25 is applied to the object 2 by the optical interferometer 130 .

In this way, the optical amplifier 120 intermittently generates the second light beam 25 only in the time interval where the pulse 24 exists, so the illumination light based on the second light beam 25 is intermittently emitted from the optical interferometer 130. will be output. Therefore, for example, even if the irradiation range of the irradiation light is fixed due to an abnormality in the control system or the like, the influence on human eyes can be suppressed, and safety can be ensured. In addition, by appropriately setting the amplitude of the pulse 24 and the time interval (duty ratio) of the pulse 24, the energy amount of the irradiation light per unit time (the integrated value of the energy of the irradiation light irradiated in the unit time) is limited. This can also ensure safety.

The reflected light 26 enters the collimator 133 of the optical interferometer 130 after being delayed by the time required for the light to make a round trip to the object 2 . The time interval of reflected light 26 matches the time interval between consecutive pulses 24 . The amplitude of the reflected light 26 is attenuated more than that of the irradiated light due to the influence of scattering and the like.

The reflected light 26 interferes with the irradiation light (second light beam 25) (reference light) in the optical interferometer 130, thereby generating a beat wave 27 (interference wave). The time interval between successive beat waves 27 matches the time interval between successive pulses 24 .

<Capturing beat waves>
FIG. 3 is a timing chart for explaining the relationship between the pulse 24 and the beat wave 27 when the computing device 150 captures the beat wave 27 in synchronization with the pulse 24 input from the signal generator 110 .

The arithmetic unit 150 monitors in real time the amplitude of the pulse 24 (for example, the voltage of the pulse input terminal) input to the input terminal of the pulse 24 (hereinafter referred to as the “pulse input terminal”). When the absolute value of the amplitude exceeds a preset threshold value, the capture of the beat wave 27 is started. Also, when the absolute value of the amplitude of the pulse 24 becomes equal to or less than the threshold value after the start of capturing, the capturing of the beat wave 27 is stopped.

In this way, the arithmetic unit 150 receives the beat wave 27 in synchronization with the pulse 24 at the pulse input terminal, that is, in the time interval in which the beat wave 27 exists. , the beat wave 27 can be reliably captured. In the example shown in the figure, the trailing portion of the beat wave 27 is not captured, but this portion has a high noise content rate, and even if it is not captured, there is little effect on accuracy.

FIG. 4 is a timing chart for explaining the relationship between the pulse 24 and the beat wave 27 when the computing device 150 captures the beat wave 27 in synchronization with the pulse 24 input from the signal generator 110 .

In the example of FIG. 3, the absolute value of the amplitude of the pulse 24 input to the pulse input terminal is compared with a threshold value to control the start/end of capture of the beat wave 27. In this example, the arithmetic unit 150 At the timing when the input of the pulse 24 to the pulse input terminal is started (at the timing when the rise of the pulse 24 is detected), the A/D conversion of the beat wave 27 by the A/D converter 151 is started, and The above A/D conversion is stopped at the timing when the input of the pulse 24 ends (at the timing when the fall of the pulse 24 is detected).

By controlling the start/stop of the A/D conversion by the A/D converter 151 in synchronization with the pulse 24 in this way, the A/D converter 151 is not caused to function unnecessarily, and the beat can be efficiently and reliably performed. A wave 27 can be captured.

<Calculation of distance and relative speed>
FIG. 5 is a diagram for explaining the principle of calculating the distance to the object 2 and the relative velocity between the object 2 and the arithmetic unit 150. The time t and the angular velocity ω of the frequency modulated wave (triangular modulated wave) are shown in FIG. , and the relationship between time t and frequency f.

Assuming that the distance to the object 2 is R and the speed of light is c, there is the following relationship between the distance R and the time delay τ.

As described above, ατ is observed as the angular velocity (frequency), so if there is no relative velocity between the object 2 and the object 2, the two frequencies obtained by the signal analysis processing of the optical beat signal are , f ₁ and f ₂ , the frequency f _R corresponding to the distance can be obtained from the following equation.

There is the following relationship between the rate of change α of modulation with respect to the modulation period _Tm and Δf.

On the other hand, the frequency _fD corresponding to the relative velocity can be expressed by the following equation based on the Doppler effect theory.

Here, ν is the relative velocity with respect to the object 2, and _λ0 is the center wavelength of the frequency-modulated light (reciprocal of the center frequency _f0 ).

<Summary>
As described above in detail, according to the photodetector 100 of the present embodiment, it is possible to realize a mechanism for intermittently irradiating a light beam in a modulated continuous wave system. In addition, the photodetector 100 does not directly control the laser light source 103 that generates the first light beam from which the second light beam (irradiation light) is generated (the second light beam (irradiation light) is generated by the optical amplifier 120). is controlled.) Therefore, the second light beam can be stably generated.

The optical amplifier 120 amplifies the first light beam with an amplification factor corresponding to the amplitude of the pulse 24 to generate the second light beam. can be efficiently controlled by the same pulse 24, and the optical amplifier 120 having a simple configuration can be realized.

In addition, by appropriately setting the duty ratio of the pulse 24 and the amplification factor of the optical amplifier 120, the energy per unit time of the second light beam is set to a predetermined upper limit value (statutory upper limit value, etc.) or less. be able to.

In addition, since the photodetector 100 acquires an interference signal based on the interference wave (beat wave 27) between the irradiation light and the reflected light from the object in synchronization with the pulse, it does not take in unnecessary signals. Moreover, an interference signal can be reliably acquired.

In addition, since the photodetector 100 uses the same pulse 24 for multiple purposes to generate the first light beam, to generate the second light beam, and to capture the interference signal to the arithmetic unit 150, the light detector 100 has a simple configuration. Locator 100 can be implemented.

In addition, since the photodetector 100, for example, causes the A/D converter 151 to function in synchronization with the input of the pulse, the A/D converter 151 can be efficiently operated, and the interference signal can be reliably detected. can be obtained.

In addition, since the photodetector 100 generates the pulse 24 at a timing that takes into consideration the time required for the optical amplifier 120 to start up, unnecessary information (information (signal )) can be prevented from being acquired.

Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments, and includes various modifications. In addition, the above-described embodiment describes the configuration in detail in order to explain the present disclosure in an easy-to-understand manner, and is not necessarily limited to those having all the described configurations. Moreover, it is possible to add, delete, or replace a part of the configuration of the above embodiment with another configuration.

This application is based on a Japanese patent application (Japanese Patent Application No. 2021-054764) filed on March 29, 2021, the contents of which are incorporated herein by reference.

According to the present disclosure, it is possible to provide a light beam generator and a photodetector that can ensure safety when irradiating an object with a light beam using a modulated continuous wave method.

2 Object 100 Photodetector 101 Arbitrary waveform generator 102 Control power supply 103 Laser light source 104 Temperature control device 110 Signal generator 120 Optical amplifier 130 Optical interferometer 131 Optical splitter 132 Circulator 133 Collimator 134 Optical waveguide 135 Optical coupler 140 Photoelectric conversion Unit 150 Arithmetic device 151 A/D converter 160 Beam scanning device

Claims (8)

1. a reference signal generator for generating a reference signal;
   a pulse generator that generates pulses synchronized with the reference signal;
   a first light beam generator for repeatedly generating a first light beam whose frequency is continuously changed within a predetermined frequency range in synchronization with the reference signal;
   an optical amplifier that generates a second light beam by amplifying the first light beam in synchronization with the pulse;
   A light beam generator, comprising:
2. The optical amplifier amplifies the first light beam with an amplification factor corresponding to the amplitude of the pulse to generate the second light beam.
   2. A light beam generating device according to claim 1.
3. The pulse duty ratio and the amplification factor are set so that the energy per unit time of the second light beam is equal to or less than a predetermined upper limit.
   3. A light beam generator according to claim 2.
4. a reference signal generator for generating a reference signal;
   a pulse generator that generates pulses synchronized with the reference signal;
   a first light beam generator for repeatedly generating a first light beam whose frequency is continuously changed within a predetermined frequency range in synchronization with the reference signal;
   an optical amplifier for generating a second light beam by amplifying the first light beam in synchronization with the pulse;
   an optical interferometer that irradiates an object with the second light beam as irradiation light, receives reflected light from the object, and generates an interference wave obtained by causing the irradiation light and the reflected light to interfere with each other; ,
   a photoelectric converter that generates an interference signal that is a signal obtained by photoelectrically converting the interference wave;
   a computing device that acquires the interference signal in synchronization with the pulse and analyzes the acquired interference signal;
   A light detector.
5. The computing device acquires the interference signal during a period in which the absolute value of the amplitude of the pulse exceeds a preset threshold.
   5. A photodetector according to claim 4.
6. The computing device comprises an A/D converter that A/D converts the interference signal,
   The A/D converter starts A/D conversion of the interference signal at the timing when the input of the pulse is started, and stops A/D conversion of the interference signal at the timing when the input of the pulse is finished. ,
   The computing device analyzes the interference signal converted into a digital signal by the A/D converter.
   5. A photodetector according to claim 4.
7. The pulse generator generates the pulse at a timing that takes into consideration the time required for the optical amplifier to rise.
   7. A photodetector according to any one of claims 4-6.
8. The computing device obtains the distance to the object or the relative velocity of the object based on the frequency of the interference wave obtained by analyzing the interference signal.
   8. A photodetector according to any one of claims 4-7.
   

Images