Phase modulation continuous wave distance measurement method and system

Abstract

The invention provides a phase modulation continuous wave distance measurement method and system, and is applied to the technical field of semiconductor photoelectric detection, and the method comprises the steps: carrying out the continuous wave phase modulation of initial dual-wavelength coherent light generated through a laser beam, determining modulated dual-wavelength coherent light, carrying out the beam splitting of the modulated dual-wavelength coherent light, and carrying out the continuous wave phase modulation. Dual-wavelength detection light and dual-wavelength local oscillation light are obtained; emitting the dual-wavelength detection light to a to-be-detected target, and receiving dual-wavelength reflected light; performing beat frequency processing on the dual-wavelength reflected light and the dual-wavelength local oscillation light to obtain an intermediate frequency signal, and performing filtering processing on the intermediate frequency signal to obtain a difference frequency signal; the square of the light intensity of the difference frequency signal is in direct proportion to the round-trip time of the dual-wavelength probe light; and determining the round-trip time according to the light intensity of the difference frequency signal and the phase difference and the frequency difference between the dual-wavelength probe light and the dual-wavelength local oscillator light, and determining the distance according to the round-trip time. According to the technical scheme, the ranging cost can be reduced, and long-distance measurement can be realized.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor photoelectric detection technology, and in particular to a phase-modulated continuous wave ranging method and system. Background Art

[0002] LiDAR (LiDAR) boasts high precision and high resolution and is widely used in various fields. Currently, methods such as Frequency Modulated Continuous Wave (FMCW) and Light Detection and Ranging (LiDAR) are mostly used for ranging. FMCW methods require lower power from the primary laser, are less susceptible to interference, and can simultaneously measure distance and velocity. However, they place strict requirements on the laser linewidth and frequency modulation linearity.

[0003] At present, in response to the strict requirements of the FMCW method on laser linewidth and frequency modulation linearity, some technologies use a single-wavelength phase-modulated continuous wave (PhMCW) method for ranging. This method achieves ranging by modulating the phase of the first laser rather than frequency or amplitude modulation to achieve high-precision ranging, thereby relaxing the requirements for the frequency modulation linearity of the laser system.

[0004] However, the maximum distance measured by the above technology is limited by the laser linewidth. Generally, a narrow linewidth laser with a smaller linewidth is required to maintain coherence for long-distance measurement, which results in higher ranging costs. Summary of the Invention

[0005] The present invention provides a phase-modulated continuous wave ranging method and system, which are used to overcome the defects in the prior art of using the FMCW method for ranging, such as the strict requirements on laser linewidth and frequency modulation linearity, which leads to increased costs, and the need to use a narrow-linewidth laser with a smaller linewidth to maintain coherence for long-distance measurement when using the PhMCW method for ranging, which leads to high costs and limited ranging distance. The method uses dual-wavelength coherent light combined with the phase-modulated continuous wave method for measurement, and can achieve high-precision long-distance ranging without using a narrow-linewidth laser, thereby reducing ranging costs.

[0006] The present invention provides a phase modulation continuous wave ranging method, which is applied to a phase modulation continuous wave ranging system, comprising: Acquire initial dual-wavelength coherent light generated by a dual-wavelength coherent light generating unit using a laser beam; the initial dual-wavelength coherent light includes two coherent beams of different wavelengths; performing continuous wave phase modulation on the initial dual-wavelength coherent light to determine modulated dual-wavelength coherent light, and splitting the modulated dual-wavelength coherent light to obtain dual-wavelength probe light and dual-wavelength local oscillator light; both the dual-wavelength probe light and the dual-wavelength local oscillator light are dual-wavelength coherent light; Transmitting dual-wavelength detection light to the target to be measured, and receiving dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured; the dual-wavelength reflected light is dual-wavelength coherent light; Performing beat frequency processing on the dual-wavelength reflected light and the dual-wavelength local oscillator light to obtain an intermediate frequency signal, and performing filtering processing on the intermediate frequency signal to obtain a difference frequency signal; wherein the phase difference and frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light in the difference frequency signal are fixed, and the square of the light intensity of the difference frequency signal is proportional to the round-trip time of the dual-wavelength detection light, where the round-trip time is the time it takes for the dual-wavelength detection light to travel back and forth between the target to be measured; The round-trip time is determined based on the light intensity of the difference frequency signal, the phase difference and frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light, and the distance between the phase-modulated continuous wave ranging system and the target to be measured is determined based on the round-trip time.

[0007] According to a phase-modulated continuous wave ranging method provided by the present invention, the dual-wavelength coherent light generating unit includes any one of the following devices: a first laser and a Mach-Zehnder modulator, two independent second lasers, a mode-locked laser, and an optical filter. The initial dual-wavelength coherent light generated by the dual-wavelength coherent light generating unit through the laser beam is obtained, including: Outputting a laser beam through a first laser and intensity-modulating the laser beam through a Mach-Zehnder modulator to generate carrier-suppressed sidebands, thereby obtaining initial dual-wavelength coherent light; Alternatively, two independent second lasers are used to generate respective laser beams, and the two laser beams are processed in a phase-locked manner to generate initial dual-wavelength coherent light; Alternatively, a broad spectrum pulse is generated by a mode-locked laser, and the broad spectrum pulse is filtered by an optical filter to generate initial dual-wavelength coherent light.

[0008] According to a phase-modulated continuous wave ranging method provided by the present invention, the above-mentioned continuous wave phase modulation of the initial dual-wavelength coherent light is performed to determine the modulated dual-wavelength coherent light, including: Acquire a continuous phase modulation signal generated by a function generator; the phase modulation signal is a periodic function, and the period of the phase modulation signal is greater than the phase difference between the dual-wavelength probe light and the dual-wavelength local oscillator light; The initial dual-wavelength coherent light is phase-modulated by a phase modulation signal to determine the modulated dual-wavelength coherent light.

[0009] According to a phase-modulated continuous wave ranging method provided by the present invention, the phase-modulated signal is a square wave signal.

[0010] The present invention also provides a phase-modulated continuous wave ranging system, comprising: a dual-wavelength coherent light generating unit, a phase modulation unit, a transmission and emission unit, and a detection and processing unit; The dual-wavelength coherent light generating unit is used to generate initial dual-wavelength coherent light by using a laser beam; the initial dual-wavelength coherent light includes two coherent beams of different wavelengths; The phase modulation unit is connected to the dual-wavelength coherent light generating unit and is used to perform continuous wave phase modulation on the initial dual-wavelength coherent light to determine the modulated dual-wavelength coherent light; and to split the modulated dual-wavelength coherent light to obtain dual-wavelength detection light and dual-wavelength local oscillator light; the dual-wavelength detection light and dual-wavelength local oscillator light are both dual-wavelength coherent light; The transmission unit is connected to the phase modulation unit and is used to transmit the dual-wavelength detection light to the target to be measured and receive the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured; the dual-wavelength reflected light is dual-wavelength coherent light; The detection and processing unit is connected to the phase modulation unit and the transmission and emission unit, and is configured to perform beat frequency processing on the dual-wavelength reflected light and the dual-wavelength local oscillator light to obtain an intermediate frequency signal, and to filter the intermediate frequency signal to obtain a difference frequency signal; the difference frequency signal has a fixed phase difference and a fixed frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light, and the square of the light intensity of the difference frequency signal is proportional to the round-trip time of the dual-wavelength detection light, where the round-trip time is the time it takes for the dual-wavelength detection light to travel back and forth between the targets to be detected; The detection processing unit is further configured to determine the round-trip time based on the light intensity of the difference frequency signal, the phase difference and the frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light, and to determine the distance between the phase-modulated continuous wave ranging system and the target to be measured based on the round-trip time.

[0011] According to a phase-modulated continuous wave ranging system provided by the present invention, the dual-wavelength coherent light generating unit includes any one of the following devices: a first laser and a Mach-Zehnder modulator, two independent second lasers, a mode-locked laser and an optical filter; The first laser is used to output a laser beam, and the Mach-Zehnder modulator is used to modulate the intensity of the laser beam to generate carrier-suppressed sidebands to obtain initial dual-wavelength coherent light; The two independent second lasers are used to output two laser beams and process the two laser beams in a phase-locked manner to generate initial dual-wavelength coherent light; The mode-locked laser is used to generate broadband pulses, and the optical filter is used to filter the broadband pulses to generate initial dual-wavelength coherent light.

[0012] According to a phase-modulated continuous wave ranging system provided by the present invention, the phase-modulated continuous wave ranging system further comprises: a function generator; The function generator is connected to the phase modulation unit and is used to generate a continuous phase modulation signal and input the phase modulation signal to the phase modulation unit; the phase modulation signal is a periodic function, and the period of the phase modulation signal is greater than the phase difference between the dual-wavelength detection light and the dual-wavelength local oscillator light; The phase modulation unit is specifically configured to perform phase modulation on the initial dual-wavelength coherent light through a phase modulation signal to determine the modulated dual-wavelength coherent light.

[0013] According to a phase-modulated continuous wave ranging system provided by the present invention, the phase-modulated signal is a square wave signal.

[0014] According to a phase-modulated continuous wave ranging system provided by the present invention, the phase-modulated continuous wave ranging system further comprises: a polarization controller, wherein the input port of the polarization controller is connected to the phase modulation unit, and the output port of the polarization controller is connected to the detection processing unit; The polarization controller is used to modulate the polarization state of the dual-wavelength local oscillator light to be consistent with the polarization state of the dual-wavelength reflected light.

[0015] According to a phase modulated continuous wave ranging system provided by the present invention, the transmission and emission unit includes: a collimator connected to the phase modulation unit; The collimator is used to receive the dual-wavelength detection light transmitted by the phase modulation unit, collimate the dual-wavelength detection light and transmit it to the target to be measured, and receive the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured, and transmit the dual-wavelength reflected light to the detection processing unit.

[0016] The phase-modulated continuous wave ranging method and system provided by the present invention obtains the initial dual-wavelength coherent light generated by the dual-wavelength coherent light generating unit through the laser beam, performs continuous phase modulation processing on the initial dual-wavelength coherent light, determines the modulated dual-wavelength coherent light, and splits the modulated dual-wavelength coherent light to obtain dual-wavelength detection light and dual-wavelength local oscillation light, transmits the dual-wavelength detection light to the target to be measured, and receives the dual-wavelength reflected light after the dual-wavelength detection light is reflected on the target to be measured, performs beat frequency processing on the dual-wavelength reflected light and the dual-wavelength local oscillation light, obtains the intermediate frequency signal, and performs filtering processing on the intermediate frequency signal to obtain the difference signal. The invention provides a method for determining the round-trip time of the dual-wavelength probe light between the target to be measured and the distance between the system and the target to be measured based on the light intensity of the difference frequency signal, the phase difference and the frequency difference between the dual-wavelength probe light and the dual-wavelength local oscillator light. The method further provides a method for determining the distance between the system and the target to be measured based on the round-trip time. The method further provides a method for determining the distance between the system and the target to be measured based on the round-trip time. The method further provides a method for determining the distance between the system and the target to be measured based on the round-trip time. The method further provides a method for determining the distance between the system and the target to be measured based on the round-trip time. The method further provides a method for determining the distance between the system and the target to be measured based on the round-trip time. The method further provides a method for determining the distance between the system and the target to be measured based on the round-trip time. The method further provides a method for determining the distance between the system and the target to be measured based on the round-trip time. In this method, two beams of dual-wavelength coherent light can be obtained by phase modulating dual-wavelength coherent light, and after detecting a target, one beam of dual-wavelength coherent light is beat and filtered with the other beam of dual-wavelength coherent light to eliminate random terms in the difference frequency signal, thereby obtaining a proportional relationship between the square of the light intensity and the round-trip time and the frequency difference. Furthermore, the round-trip time and then the distance can be solved by using the light intensity and the frequency difference of the two beams of dual-wavelength coherent light. There is no need to limit the linewidth of a laser that generates the laser beam, and the round-trip time for solving the distance is only related to the light intensity and the frequency difference, and is not limited by the linewidth of the laser. Therefore, the ranging cost can be reduced and long-distance ranging can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a structural block diagram of the phase modulation continuous wave ranging system provided by the present invention.

[0019] Figure 2 This is a specific structural diagram of the phase modulation continuous wave ranging system provided by the present invention.

[0020] Figure 3 It is a flow chart of the phase modulation continuous wave ranging method provided by the present invention. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0022] Currently, when measuring distance using the FMCW method, the laser power requirement is relatively low (approximately 100 milliwatts, while time-of-flight lidar requires hundreds of watts), it is not easily susceptible to interference, and it can measure distance and speed simultaneously. However, the FMCW method has strict requirements on the laser linewidth and frequency modulation linearity. Therefore, the development of high-linearity narrow-linewidth lasers has become a more important research direction. Although there are various methods to obtain narrow-linewidth lasers, these methods often lead to more complex packaging and cost. On the other hand, the nonlinear frequency modulation characteristics of actual lasers will introduce spectral distortion. Therefore, the linearity source of the laser is a challenge faced by the laser in the FMCW solution, and complex linear correction methods are usually required, which will significantly increase the hardware cost and computational burden.

[0023] To address this issue, some technologies have proposed a single-wavelength phase-modulated continuous-wave (PhMCW) ranging method. This method achieves ranging by modulating the phase of the laser rather than frequency or amplitude modulation to achieve high-precision ranging, thereby relaxing the requirements for the frequency modulation linearity of the laser system. The PhMCW ranging scheme can achieve good ranging precision and accuracy. For example, the ranging error can be as low as 0.1 cm and the accuracy can reach 3.5 cm. However, these performance indicators are also closely related to the linewidth of the laser. The detection laser and the reference laser must maintain coherence to achieve an effective beat frequency between them. To achieve long-distance, high-precision detection, a laser with a narrower linewidth is required, which incurs higher light source costs. In other words, although the PhMCW ranging method circumvents the frequency modulation linearity problem, its maximum ranging distance is limited by the laser linewidth. A narrow linewidth laser with a linewidth of less than 100 kHz is required to maintain coherence for long-distance measurement, and the cost is still high. Therefore, it is necessary to simultaneously solve the problem of the frequency modulation linearity of the laser and the cost problem caused by the ranging distance being limited by the laser line width. Based on this, the embodiment of the present invention provides a phase-modulated continuous wave ranging method and system, which can solve the above technical problems.

[0024] The following first describes the phase-modulated continuous wave ranging system provided by an embodiment of the present invention.

[0025] Figure 1 This is a structural block diagram of the phase modulation continuous wave ranging system provided by the present invention, see Figure 1As shown, the phase-modulated continuous wave ranging system includes: a dual-wavelength coherent light generating unit, a phase modulation unit, a transmission and emission unit, and a detection and processing unit.

[0026] The dual-wavelength coherent light generating unit is configured to generate initial dual-wavelength coherent light by using a laser beam; the initial dual-wavelength coherent light comprises two coherent beams of different wavelengths; The phase modulation unit is connected to the dual-wavelength coherent light generating unit and is used to perform continuous wave phase modulation on the initial dual-wavelength coherent light to determine the modulated dual-wavelength coherent light; and to split the modulated dual-wavelength coherent light to obtain dual-wavelength detection light and dual-wavelength local oscillator light; the dual-wavelength detection light and dual-wavelength local oscillator light are both dual-wavelength coherent light; The transmission unit is connected to the phase modulation unit and is used to transmit the dual-wavelength detection light to the target to be measured and receive the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured; the dual-wavelength reflected light is dual-wavelength coherent light; The detection and processing unit is connected to the phase modulation unit and the transmission and emission unit, and is configured to perform beat frequency processing on the dual-wavelength reflected light and the dual-wavelength local oscillator light to obtain an intermediate frequency signal, and to filter the intermediate frequency signal to obtain a difference frequency signal; the difference frequency signal has a fixed phase difference and a fixed frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light, and the square of the light intensity of the difference frequency signal is proportional to the round-trip time of the dual-wavelength detection light, where the round-trip time is the time it takes for the dual-wavelength detection light to travel back and forth between the targets to be detected; The detection processing unit is also used to display the difference frequency signal and determine the round-trip time based on the light intensity of the difference frequency signal, the phase difference and frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light, and determine the distance between the phase-modulated continuous wave ranging system and the target to be measured based on the round-trip time.

[0027] The dual-wavelength coherent light generating unit primarily functions to generate two coherent light beams of different wavelengths using a laser beam for subsequent dual-wavelength coherent light phase-modulated continuous wave ranging. The dual-wavelength coherent light laser beam generated here can be generated by a laser. The dual-wavelength coherent light generating unit can be implemented using a combination of a laser and a Mach-Zehnder modulator, or multiple lasers, or a single laser using coherent wavelength modulation. In short, it can generate dual-wavelength coherent light. For the two different wavelengths of coherent light in the dual-wavelength coherent light, the two wavelengths can be determined based on the actual laser beam wavelength. It is understood that when generating dual-wavelength coherent light using a laser beam, there are no restrictions or requirements on parameters such as the laser linewidth of the laser generating the laser beam, thereby easing the selection of lasers and reducing laser costs. Furthermore, the dual-wavelength coherent light generating unit can further include a driving unit for driving the dual-wavelength coherent light generating unit to generate the laser beam and / or dual-wavelength coherent light.

[0028] After the dual-wavelength coherent light generation unit generates dual-wavelength coherent light, the dual-wavelength coherent light is unmodulated and can be referred to as initial dual-wavelength coherent light. This light is then transmitted directly or indirectly to a phase modulation unit for continuous wave phase modulation. The phase modulation unit's primary function is to modulate the phase of the initial dual-wavelength coherent light using a continuous wave, obtaining modulated coherent light, referred to as modulated dual-wavelength coherent light. Continuous wave phase modulation facilitates subsequent demodulation of the dual-wavelength coherent light of the probe light and the dual-wavelength coherent light of the local oscillator light, enabling rapid calculation of the round-trip time. The continuous wave can be a continuous optical signal, either periodic or non-periodic. Using continuous wave modulation facilitates demodulation of the round-trip time over a period of time. The phase modulation unit can be implemented solely by a phase modulator (PM) or by combining the PM with a function generator, with the function generator primarily providing an excitation signal or phase modulation signal to the phase modulator.

[0029] In addition, the phase modulation unit may include a beam splitter or coupler. After phase modulating the initial dual-wavelength coherent light, a modulated dual-wavelength coherent light beam can be obtained. That is, the modulated dual-wavelength coherent light beam is also dual-wavelength coherent light. The beam splitter or coupler can then be used to split the modulated dual-wavelength coherent light beam into a probe light beam and a local oscillator light beam. Both the probe light beam and the local oscillator light beam are dual-wavelength coherent light beams, i.e., coherent light beams comprising two different wavelengths, which can be referred to as dual-wavelength probe light and dual-wavelength local oscillator light beams. The dual-wavelength probe light beam is primarily used to detect the target to be measured, while the dual-wavelength local oscillator light beam serves as a reference signal for the dual-wavelength probe light beam to assist in the subsequent demodulation of the optical signal. When splitting the modulated dual-wavelength coherent light beam, taking the coupler as an example, the coupler may be an optical coupler (OC). Alternatively, the coupler may be a single-input, dual-output coupler, with the modulated dual-wavelength coherent light beam as its input and the dual-wavelength probe light and the dual-wavelength local oscillator light as its outputs. The coupling parameter of the coupler may be 50:50.

[0030] Optionally, the phase modulation unit may also include an amplifier. Before beam splitting the modulated dual-wavelength coherent light, the amplifier can amplify the optical signal's power. This is followed by beam splitting. This produces optimal dual-wavelength detection light and dual-wavelength local oscillator light, facilitating subsequent demodulation. The amplifier type can be selected based on practical needs, such as an erbium-doped fiber amplifier (EDFA).

[0031] After obtaining the dual-wavelength detection light and the dual-wavelength local oscillator light, the above-mentioned phase modulation unit can transmit the dual-wavelength detection light to the transmission and emission unit connected thereto. Signal detection can be performed between the transmission and emission unit and the target to be measured, that is, they are connected through a spatial optical path. The transmission and emission unit can emit the dual-wavelength detection light to the target to be measured. After the dual-wavelength detection light is reflected on the target to be measured, a reflection signal is generated. The reflection signal is also dual-wavelength coherent light, which can be recorded as dual-wavelength reflected light. The dual-wavelength reflected light will be transmitted to the transmission and emission unit along the above-mentioned spatial optical path, so that the transmission and emission unit can obtain the dual-wavelength reflected light. The target to be measured can be a stationary target or a moving target. The target to be measured can be an object to be measured, an animal or plant, a building, a human body, etc.

[0032] In addition, the transmission and emission unit can be connected to the detection and processing unit to transmit the dual-wavelength reflected light to the detection and processing unit. Optionally, the system can also include an optical circulator CIR, which is connected to the phase modulation unit and the transmission and emission unit respectively. The optical circulator has three ports, namely a first port, a second port, and a third port. The first port can receive the dual-wavelength detection light transmitted by the phase modulation unit and transmit the dual-wavelength detection light to the transmission and emission unit through the second port. The optical circulator can also transmit the dual-wavelength reflected light transmitted from the transmission and emission unit to the detection and processing unit through the third port.

[0033] The detection and processing unit, which can be a balanced photodetector (BPD) or other type of detector, is connected to the phase modulation unit and the transmission and emission unit to obtain dual-wavelength local oscillator light and dual-wavelength reflected light. Specifically, the detection and processing unit can be connected to an optical circulator to obtain dual-wavelength detection light, and to a coupler in the phase modulation unit to obtain dual-wavelength local oscillator light. After obtaining the dual-wavelength local oscillator light and dual-wavelength reflected light, the detection and processing unit can perform beat frequency processing on the two to obtain an intermediate frequency signal, and then filter the intermediate frequency signal to obtain a difference frequency signal. The round-trip time can then be determined based on the light intensity of the difference frequency signal and the phase and frequency differences between the dual-wavelength detection light and the dual-wavelength local oscillator light. The distance between the phase-modulated continuous wave ranging system and the target to be measured can then be determined based on the round-trip time.

[0034] The following describes the principle of performing beat frequency processing and filtering on the dual-wavelength local oscillator light and the dual-wavelength reflected light. For example, assuming that the dual-wavelength detection light / dual-wavelength local oscillator light can be expressed as: ; (1) in: and It is a dual-wavelength optical signal and The amplitude, is a phase modulated signal (including and ), t is the time.

[0035] Assuming that the dual-wavelength reflected light (i.e., the reflected dual-wavelength laser signal) returns to the transmission unit after a time delay τ, it can be expressed as: ; (2) Here, τ is the round-trip time of the dual-wavelength detection light between the transmission and transmission unit and the target to be measured. Assuming the speed of light is c, the distance between the transmission and transmission unit (or phase-modulated continuous wave ranging system) and the target to be measured can be expressed as: τ = 2d / c; where d is the distance between the transmission and transmission unit (or phase-modulated continuous wave ranging system) and the target to be measured.

[0036] The above-mentioned dual-wavelength local oscillator light and dual-wavelength reflected light are subjected to beat frequency processing (i.e. mixing processing) to generate an intermediate frequency signal I , which is expressed as follows: ; (3) Since the bandwidth of the photoelectric balance detector in the detection processing unit is limited and cannot respond, after substituting formulas (1) and (2) into (3) and expanding it using the Euler formula, eliminating the terms containing t and the constant term, the following formula can be obtained: ; (4) Then, by squaring both sides of the above formula (4), we can obtain the following formula: ; (5) in, 、 、 and It is a random phase, which will exceed the coherence distance when transmitted over long distances, making it impossible to measure. When measuring with dual wavelengths, it can be considered that the two beams and The phase difference is fixed ,Right now: Therefore, the above-mentioned squaring of the intermediate frequency signal can produce a difference frequency term that bypasses the coherence length / coherence distance limitation. , only the difference frequency term is retained after squaring, then the above formula (5) can be simplified to: ; (6) Where, I in formula (6) is the difference frequency signal after filtering the intermediate frequency signal, and the phase difference between the two wavelength optical signals is a constant value (or fixed value) , and the frequency difference between the two wavelengths of optical signals is also a constant value (or fixed value), then the phase difference of the two wavelengths of optical signals at two times in the above formula (6) can cancel each other out, and the remaining , meaning the square of the difference frequency signal is only related to the round-trip time / time of flight τ, and is independent of the laser linewidth. This means that the difference frequency signal can be used to obtain distance information to the measured object that is independent of linewidth. This allows distance measurement to be unrestricted by linewidth, enabling long-distance measurement and reducing ranging costs. This also eliminates the need to correct laser linearity, further reducing ranging costs.

[0037] Based on this, the mapping relationship between the square of the difference frequency signal and the round-trip time τ can be determined experimentally, for example: , where D and F are parameters in a mapping relationship determined experimentally based on the square of the difference frequency signal and the round-trip time of multiple known dual-wavelength coherent light signals. When determining the parameters based on multiple known dual-wavelength coherent light signals, the optical signals can be first converted into electrical signals by a detection processing unit and transmitted to a display device such as an oscilloscope for display. The parameters in the mapping relationship can then be determined based on parameters such as the intensity, frequency difference, and phase difference of the optical signals displayed on the oscilloscope, combined with the known round-trip time.

[0038] After determining the parameters in the above mapping relationship, after the detection and processing unit obtains the difference frequency signal, the difference frequency signal (which is an optical signal) can be converted into an electrical signal and transmitted to a display device such as an oscilloscope for display. The intensity of the displayed optical signal and the frequency difference of the dual-wavelength coherent light can then be read on the oscilloscope. The above mapping relationship is then solved to obtain the round-trip time τ. Taking the phase modulation signal in the phase modulation unit as a square wave as an example, the flight time τ can be finally calculated by examining the interference waveform of the two square wave signals. The distance d between the transmission and transmission unit (or phase modulation continuous wave ranging system) and the target to be measured can then be calculated according to the above formula τ=2d / c.

[0039] As can be seen from the above description, this embodiment replaces the traditional single-wavelength narrow-linewidth laser with a dual-wavelength coherent light source. Utilizing two coherent light beams of different wavelengths, their difference frequency signal contains phase information directly related to the target distance, enabling rapid distance calculation. Furthermore, this embodiment transforms the system's single-wavelength linewidth requirement into coherence between the dual light sources. The difference frequency mechanism eliminates the impact of phase noise on ranging, thereby relaxing the laser linewidth restriction and significantly reducing system cost. Furthermore, the dual-wavelength coherent light signal is phase-modulated using a continuous wave, splitting the modulated optical signal into two paths: probe light and local oscillator light. The probe light is converted into spatial light by a transmission and emission unit, irradiated onto the surface of the target, and then returned along the original path. The local oscillator light is mixed with the probe light to generate a difference frequency electrical signal. Because the dual-wavelength lasers have a fixed phase difference, detecting the difference frequency intermediate frequency signal can obtain stable phase information related to distance, enabling high-precision, interference-resistant ranging.

[0040] In this embodiment, the initial dual-wavelength coherent light generated by the dual-wavelength coherent light generating unit through the laser beam is obtained, the initial dual-wavelength coherent light is subjected to continuous phase modulation processing, the modulated dual-wavelength coherent light is determined, and the modulated dual-wavelength coherent light is split to obtain dual-wavelength detection light and dual-wavelength local oscillator light, the dual-wavelength detection light is emitted to the target to be measured, and the dual-wavelength reflected light after the dual-wavelength detection light is reflected on the target to be measured is received, the dual-wavelength reflected light and the dual-wavelength local oscillator light are subjected to beat frequency processing to obtain an intermediate frequency signal, which is filtered to obtain a difference frequency signal, and the difference frequency signal is obtained according to the difference frequency. The light intensity of the difference frequency signal, the phase difference and frequency difference between the dual-wavelength probe light and the dual-wavelength local oscillator light are used to determine the round-trip time of the dual-wavelength probe light between the target to be measured, and then the distance between the system and the target to be measured is determined based on the round-trip time. The initial dual-wavelength coherent light includes two coherent light beams of different wavelengths, the dual-wavelength probe light and the dual-wavelength local oscillator light are both dual-wavelength coherent light, the phase difference and frequency difference between the dual-wavelength probe light and the dual-wavelength local oscillator light in the difference frequency signal are fixed, and the square of the light intensity of the difference frequency signal is proportional to the round-trip time of the dual-wavelength probe light. In this method, two beams of dual-wavelength coherent light can be obtained by phase modulating dual-wavelength coherent light, and after detecting a target, one beam of dual-wavelength coherent light is beat and filtered with the other beam of dual-wavelength coherent light to eliminate random terms in the difference frequency signal, thereby obtaining a proportional relationship between the square of the light intensity and the round-trip time and the frequency difference. Furthermore, the round-trip time and then the distance can be solved by using the light intensity and the frequency difference of the two beams of dual-wavelength coherent light. There is no need to limit the linewidth of a laser that generates the laser beam, and the round-trip time for solving the distance is only related to the light intensity and the frequency difference, and is not limited by the linewidth of the laser. Therefore, the ranging cost can be reduced and long-distance ranging can be achieved.

[0041] The following embodiments illustrate specific forms of the dual-wavelength coherent light generating unit.

[0042] In one embodiment, the dual-wavelength coherent light generating unit comprises any one of the following devices: a first laser and a Mach-Zehnder modulator, two independent second lasers, a mode-locked laser, and an optical filter; The first laser is used to output a laser beam, and the Mach-Zehnder modulator is used to modulate the intensity of the laser beam to generate carrier-suppressed sidebands to obtain initial dual-wavelength coherent light; The two independent second lasers are used to output two laser beams and process the two laser beams in a phase-locked manner to generate initial dual-wavelength coherent light; The mode-locked laser is used to generate broadband pulses, and the optical filter is used to filter the broadband pulses to generate initial dual-wavelength coherent light.

[0043] When the dual-wavelength coherent light generating unit includes a first laser and a Mach-Zehnder modulator, the first laser can output a laser beam, which can then be intensity-modulated by the Mach-Zehnder modulator to generate carrier-suppressed sidebands, thereby generating initial dual-wavelength coherent light. When the dual-wavelength coherent light generating unit includes two independent second lasers, the two second lasers can each generate a laser beam, and the phases of the two laser beams can be processed using a phase-locking method to maintain a constant phase difference between the two laser beams, thereby generating initial dual-wavelength coherent light.

[0044] When the dual-wavelength coherent light generating unit includes a mode-locked laser and an optical filter, a broad spectrum pulse can be generated by the mode-locked laser and filtered by the optical filter to generate initial dual-wavelength coherent light.

[0045] It should be noted that the above does not impose any specific restrictions on the types of the first laser, the second laser, and the mode-locked laser, that is, there is no restriction on their bandwidth, thereby broadening the selection of lasers and reducing the laser cost during ranging.

[0046] In this embodiment, the dual-wavelength coherent light generating unit generates dual-wavelength coherent light using laser beams in a variety of ways, which can increase the flexibility of dual-wavelength coherent light generation.

[0047] The following embodiments illustrate the specific phase modulation process of the phase modulation unit.

[0048] In one embodiment, the phase-modulated continuous wave ranging system further comprises: a function generator; the function generator is connected to the phase modulation unit and is configured to generate a continuous phase modulation signal and input the phase modulation signal into the phase modulation unit; the phase modulation signal is a periodic function, and the period of the phase modulation signal is greater than the phase difference between the dual-wavelength detection light and the dual-wavelength local oscillator light; The phase modulation unit is specifically configured to perform phase modulation on the initial dual-wavelength coherent light through a phase modulation signal to determine the modulated dual-wavelength coherent light.

[0049] The function generator is primarily used to generate a continuous phase modulation signal, which can be an arbitrary function generator. The phase modulation signal is a periodic function, such as a sine wave, sawtooth wave, square wave, rectangular wave, etc. The function generator can input the generated phase modulation signal into the phase modulation unit to drive the phase modulation unit to perform phase modulation. In this way, the phase modulation unit can phase modulate the initial dual-wavelength coherent light based on the phase modulation signal, for example, superimposing the phase modulation signal on the initial dual-wavelength coherent light to obtain modulated dual-wavelength coherent light.

[0050] In addition, the period of the above-mentioned phase modulation signal is greater than the phase difference between the dual-wavelength detection light and the dual-wavelength local oscillator light. In this way, the phase difference between the dual-wavelength detection light and the dual-wavelength local oscillator light will be distributed within the period of one phase modulation signal, thereby achieving the correspondence between the phase difference and the phase in the phase modulation signal, making it easier for the subsequent detection processing unit to demodulate the optical signals of the two wavelength coherent lights and their frequency difference, phase difference and other information from the processed difference frequency signal.

[0051] Furthermore, as an option, the above-mentioned phase modulation signal is a square wave signal. Since the square wave signal consists of only two signals, high and low levels, the square wave signal is used here as the phase modulation signal, so that the subsequent detection and processing unit can demodulate the optical signals of the two wavelengths of coherent light and their frequency difference, phase difference and other information from the processed difference frequency signal more simply and quickly.

[0052] For example, an arbitrary function generator generates a square wave signal, and the phase modulation unit performs phase modulation on the initial dual-wavelength coherent light. The modulated dual-wavelength coherent light loaded with the square wave signal is connected to a 1×2 optical coupler and divided into a detection light and a local oscillator light. The excitation phase of the phase modulation signal is Modulated by a rectangular wave / square wave, it can be expressed as follows: ; (7) in, is the initial optical phase; is the modulation depth; is an integer; is the phase modulation period, that is, the period of the phase modulation signal.

[0053] Specifically, the arbitrary function generator generates a square wave signal to drive the phase modulator, performing periodic phase modulation on the dual-wavelength optical signal. The modulated optical signal is divided into two paths, detection light and local oscillator light, by an optical coupler. The detection light is converted into spatial light (including collimation by an optical circulator and a collimator) by a transmission and emission unit, irradiated onto the surface of the target object, and then returned along the original path. The local oscillator light is mixed with the detection light to generate a difference frequency electrical signal. Since the dual-wavelength laser has a fixed phase difference, stable phase information related to distance can be obtained by detecting the intermediate frequency signal of the difference frequency, thereby achieving high-precision, interference-resistant ranging.

[0054] In this embodiment, a phase modulation signal is generated by a function generator and input into the phase modulation unit to modulate the initial dual-wavelength coherent light. The phase modulation signal is a periodic function with a period greater than the phase difference between the dual-wavelength probe light and the dual-wavelength local oscillator light. This facilitates subsequent demodulation of the desired information by modulating the dual-wavelength coherent light. Furthermore, the phase modulation signal is a square wave signal, allowing the subsequent detection and processing unit to quickly and easily demodulate the optical signals of the two coherent wavelengths, along with information such as the frequency difference and phase difference, from the processed difference frequency signal.

[0055] The following embodiments illustrate the modulation process of the polarization state of dual-wavelength local oscillation light.

[0056] In one embodiment, the phase-modulated continuous wave ranging system further includes: a polarization controller, wherein the input port of the polarization controller is connected to the phase modulation unit, and the output port of the polarization controller is connected to the detection processing unit; the polarization controller is used to modulate the polarization state of the dual-wavelength local oscillator light to be consistent with the polarization state of the dual-wavelength reflected light.

[0057] Among them, the phase modulation unit may include a first coupler, which is used to split the modulated dual-wavelength coherent light into dual-wavelength detection light and dual-wavelength local oscillator light. The above-mentioned polarization controller is specifically connected to the port of the first coupler that outputs the dual-wavelength local oscillator light, and is used to receive the dual-wavelength local oscillator light and modulate its polarization state to be consistent with the polarization state of the dual-wavelength reflected light / dual-wavelength detection light, and then transmit the modulated dual-wavelength local oscillator light to the detection processing unit.

[0058] Optionally, the above-mentioned phase-modulated continuous wave ranging system also includes: a second coupler, an optical circulator, the optical circulator having three ports, namely a first port, a second port and a third port, the first port being connected to the port of the first coupler outputting the dual-wavelength detection light, for receiving the dual-wavelength detection light and transmitting it to the second port, the second port being connected to the transmission and emission unit, for receiving the dual-wavelength reflected light transmitted by the transmission and emission unit, and transmitting it to the third port, the third port being connected to the second coupler, for inputting the dual-wavelength reflected light to the second coupler.

[0059] The second coupler includes two input ports and two output ports. The two input ports are respectively connected to the above-mentioned polarization controller and the optical circulator, and are used to input dual-wavelength local oscillator light and dual-wavelength reflected light, and modulate the power of the two dual-wavelength optical signals to be consistent, and then output the power-modulated dual-wavelength local oscillator light and the power-modulated dual-wavelength reflected light to the detection processing unit.

[0060] Optionally, the phase-modulated continuous wave ranging system further includes an oscilloscope, which can display the optical signal of the dual-wavelength coherent light demodulated by the detection processing unit and obtain information such as light intensity, phase difference, and frequency difference therefrom.

[0061] In this embodiment, the polarization state of the dual-wavelength local oscillator light is modulated to be consistent with the polarization state of the dual-wavelength reflected light by the polarization controller, which can facilitate the subsequent detection and processing unit to demodulate the dual-wavelength local oscillator light and the dual-wavelength reflected light accurately. The following embodiments illustrate the specific structure of the transmission and emission unit.

[0062] In one embodiment, the transmission and emission unit includes: a collimator, which is connected to the phase modulation unit; the collimator is used to receive the dual-wavelength detection light transmitted by the phase modulation unit, collimate the dual-wavelength detection light and then transmit it to the target to be measured, as well as receive the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured, and transmit the dual-wavelength reflected light to the detection processing unit.

[0063] Among them, the collimator is specifically connected to the second port of the optical circulator, and is used to receive the dual-wavelength detection light transmitted from the first port, and collimate the dual-wavelength detection light and then transmit it to the target to be measured, and then receive the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured through the second port, and transmit the dual-wavelength reflected light to the third port, and then transmit it from the third port to the second coupler, and then transmit it to the detection processing unit through the second coupler for demodulation processing.

[0064] In this embodiment, the transmission and emission unit includes a collimator, which can collimate the dual-wavelength detection light and then transmit it to the target to be measured, and receive the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured and transmit it to the detection processing unit. The collimation process can improve the parallelism of the emitted dual-wavelength detection light and reduce the divergence of the light beam, thereby improving the transmission efficiency and focusing ability of the dual-wavelength detection light, which is helpful for the subsequent demodulation processing of the dual-wavelength reflected light.

[0065] The following takes a scenario where a dual-wavelength coherent light generating unit includes a laser and a Mach-Zehnder modulator as an example to provide a complete embodiment to illustrate the ranging process of the phase-modulated continuous wave ranging system according to an embodiment of the present invention.

[0066] Figure 2 A specific structural diagram of the phase modulation continuous wave ranging system provided by the present invention is shown in FIG. Figure 2As shown, the system may include a radio frequency (RF) signal source, a laser (LASER), a voltage source (VS), a first polarization controller (PC1), a Mach-Zehnder modulator (MZM), an arbitrary function generator (AFG), a phase modulator (PM), an erbium-doped fiber amplifier (EDFA), a first optical coupler (OC), a second polarization controller (PC2), an optical circulator (CIR), a collimator (Collimator), a target to be measured (Target), a second coupler (Coupler), a photoelectric balanced detector (BPD), and an oscilloscope (OSC). The system involves an electrical path, an optical path in fiber, and an optical path in space. The system structure and construction process of the phase-modulated continuous wave ranging system in this embodiment are as follows: 1. Load the laser with appropriate current and connect the output light to the first polarization controller.

[0067] 2. Connect an optical power meter after the Mach-Zehnder modulator and adjust the first polarization controller so that the polarization state of the laser incident on the Mach-Zehnder modulator matches that of the Mach-Zehnder modulator.

[0068] 3. Disconnect the Mach-Zehnder modulator output from the optical power meter and connect it to the spectrometer to observe the subsequent modulated optical signal.

[0069] 4. The Mach-Zehnder modulator splits the input optical signal into two paths, passing through two interferometer arms respectively, and then recombines them at the output. A microwave cable connects the RF signal source to the Mach-Zehnder modulator. The RF signal source and current source are configured to generate a high-frequency electrical signal to drive the Mach-Zehnder modulator. By applying this electrical signal, the phase difference between the two light paths is changed, thereby modulating the output optical signal to generate multiple sidebands.

[0070] 5. The operating point of the Mach-Zehnder modulator can be adjusted by bias voltage. A cable connects the voltage source to the Mach-Zehnder modulator. By selecting a suitable bias voltage, the intensity of the main peak is minimized while the intensity of the sideband is enhanced to achieve main peak compression.

[0071] 6. Disconnect the Mach-Zehnder modulator from the spectrometer and connect the output signal light to the optical input port of the phase modulator. Connect the arbitrary function generator to the modulation port of the phase modulator via a microwave cable. The square wave signal generated by the arbitrary function generator can be used to drive the phase modulator, thereby adding square wave phase variation to the signal light.

[0072] 7. Connect to the erbium-doped fiber amplifier to amplify the optical signal.

[0073] 8. Connect the first optical coupler (i.e., 1×2 optical coupler) to realize the beam splitting of the dual-wavelength local oscillator light and the dual-wavelength detection light.

[0074] 9. The dual-wavelength detection light is connected to the circulator port 1, the circulator port 2 is connected to the collimator, and the circulator port 3 is connected to the port 1 of the second optical coupler (i.e., 2×2 optical coupler) to realize the connection of the detection light path.

[0075] 10. Place the target to be measured so that the light can be reflected back to the collimator along the original path after measuring the surface of the target.

[0076] 11. The dual-wavelength local oscillator light is connected to the second polarization controller for polarization control of the dual-wavelength local oscillator light and the dual-wavelength detection light / dual-wavelength reflected light, and then connected to port 2 of the second optical coupler to realize the connection of the local oscillator light path.

[0077] 12. The optical output ports 3 and 4 of the second optical coupler are connected to a photoelectric balanced detector to detect the difference between the two optical signals and convert the optical signals into electrical signals.

[0078] 13. Connect the microwave cable to the oscilloscope and adjust the second polarization controller to obtain a better output waveform in the oscilloscope.

[0079] 14. Read the phase difference in the oscilloscope to obtain the measured distance information, that is, the distance between the system and the target to be measured.

[0080] As can be seen from the above description, the embodiments of the present invention utilize dual-wavelength coherent light in combination with a phase-modulated continuous wave method for measurement, converting the system's limitation on single-wavelength linewidth into a coherence requirement for the dual light source. Specifically, dual-wavelength coherent light with a constant phase difference is phase-modulated for distance measurement. During coherent detection, target distance phase information is obtained by detecting the difference frequency term of the two beams of light. The measurement result is independent of the single-wavelength linewidth, thus breaking through the limitation of linewidth on measurement distance in principle. In this way, high-precision long-distance ranging can be achieved without using a narrow-linewidth laser. Therefore, the ranging solution of this embodiment does not require a high-linearity light source, which can solve the difficulty of requiring a high-linearity light source in the traditional FMCW solution. At the same time, it can significantly reduce the cost of the traditional single-wavelength ranging solution that relies on a narrow-linewidth laser.

[0081] Based on the above-mentioned phase-modulation continuous wave ranging system, a phase-modulation continuous wave ranging method based on the phase-modulation continuous wave ranging system is described below.

[0082] Figure 3 FIG. 1 is a flow chart of the phase modulation continuous wave ranging method provided by the present invention, as shown in FIG. Figure 3As shown, the method includes the following: Step 302 : obtaining initial dual-wavelength coherent light generated by a dual-wavelength coherent light generating unit through a laser beam; the initial dual-wavelength coherent light includes two coherent light beams of different wavelengths.

[0083] In step 304 , continuous wave phase modulation is performed on the initial dual-wavelength coherent light to determine modulated dual-wavelength coherent light, and the modulated dual-wavelength coherent light is split to obtain dual-wavelength detection light and dual-wavelength local oscillator light; both the dual-wavelength detection light and the dual-wavelength local oscillator light are dual-wavelength coherent light.

[0084] Step 306 , transmitting the dual-wavelength detection light to the target to be measured, and receiving the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured; the dual-wavelength reflected light is dual-wavelength coherent light.

[0085] In step 308, beat frequency processing is performed on the dual-wavelength reflected light and the dual-wavelength local oscillator light to obtain an intermediate frequency signal, and the intermediate frequency signal is filtered to obtain a difference frequency signal. In the difference frequency signal, the phase difference and frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light are fixed, and the square of the light intensity of the difference frequency signal is proportional to the round-trip time of the dual-wavelength detection light, where the round-trip time is the time it takes for the dual-wavelength detection light to travel back and forth between the targets to be measured.

[0086] Step 310 , determining the round trip time based on the light intensity of the difference frequency signal, the phase difference and the frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light, and determining the distance between the phase modulated continuous wave ranging system and the target to be measured based on the round trip time.

[0087] For the explanation of this embodiment, please refer to the explanation of the phase modulation continuous wave ranging system mentioned above, which will not be repeated here.

[0088] In this embodiment, the initial dual-wavelength coherent light generated by the dual-wavelength coherent light generating unit through the laser beam is obtained, the initial dual-wavelength coherent light is subjected to continuous phase modulation processing, the modulated dual-wavelength coherent light is determined, and the modulated dual-wavelength coherent light is split to obtain dual-wavelength detection light and dual-wavelength local oscillator light, the dual-wavelength detection light is emitted to the target to be measured, and the dual-wavelength reflected light after the dual-wavelength detection light is reflected on the target to be measured is received, the dual-wavelength reflected light and the dual-wavelength local oscillator light are subjected to beat frequency processing to obtain an intermediate frequency signal, which is filtered to obtain a difference frequency signal, and the difference frequency signal is obtained according to the difference frequency. The light intensity of the difference frequency signal, the phase difference and frequency difference between the dual-wavelength probe light and the dual-wavelength local oscillator light are used to determine the round-trip time of the dual-wavelength probe light between the target to be measured, and then the distance between the system and the target to be measured is determined based on the round-trip time. The initial dual-wavelength coherent light includes two coherent light beams of different wavelengths, the dual-wavelength probe light and the dual-wavelength local oscillator light are both dual-wavelength coherent light, the phase difference and frequency difference between the dual-wavelength probe light and the dual-wavelength local oscillator light in the difference frequency signal are fixed, and the square of the light intensity of the difference frequency signal is proportional to the round-trip time of the dual-wavelength probe light. In this method, two beams of dual-wavelength coherent light can be obtained by phase modulating dual-wavelength coherent light, and after detecting a target, one beam of dual-wavelength coherent light is beat and filtered with the other beam of dual-wavelength coherent light to eliminate random terms in the difference frequency signal, thereby obtaining a proportional relationship between the square of the light intensity and the round-trip time and the frequency difference. Furthermore, the round-trip time and then the distance can be solved by using the light intensity and the frequency difference of the two beams of dual-wavelength coherent light. There is no need to limit the linewidth of a laser that generates the laser beam, and the round-trip time for solving the distance is only related to the light intensity and the frequency difference, and is not limited by the linewidth of the laser. Therefore, the ranging cost can be reduced and long-distance ranging can be achieved.

[0089] In one embodiment, the dual-wavelength coherent light generating unit includes any one of the following devices: a first laser and a Mach-Zehnder modulator, two independent second lasers, a mode-locked laser, and an optical filter. The process of obtaining the initial dual-wavelength coherent light generated by the dual-wavelength coherent light generating unit through the laser beam includes: Outputting a laser beam through a first laser and intensity-modulating the laser beam through a Mach-Zehnder modulator to generate carrier-suppressed sidebands, thereby obtaining initial dual-wavelength coherent light; Alternatively, two independent second lasers are used to generate respective laser beams, and the two laser beams are processed in a phase-locked manner to generate initial dual-wavelength coherent light; Alternatively, a broad spectrum pulse is generated by a mode-locked laser, and the broad spectrum pulse is filtered by an optical filter to generate initial dual-wavelength coherent light.

[0090] For the explanation of this embodiment, please refer to the explanation of the phase modulation continuous wave ranging system mentioned above, which will not be repeated here.

[0091] In one embodiment, performing continuous wave phase modulation on the initial dual-wavelength coherent light to determine the modulated dual-wavelength coherent light includes: Acquire a continuous phase modulation signal generated by a function generator; the phase modulation signal is a periodic function, and the period of the phase modulation signal is greater than the phase difference between the dual-wavelength probe light and the dual-wavelength local oscillator light; The initial dual-wavelength coherent light is phase-modulated by a phase modulation signal to determine the modulated dual-wavelength coherent light.

[0092] Optionally, the phase modulation signal is a square wave signal.

[0093] For the explanation of this embodiment, please refer to the explanation of the phase modulation continuous wave ranging system mentioned above, which will not be repeated here.

[0094] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0095] Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented using software plus a necessary general-purpose hardware platform, or of course, hardware. Based on this understanding, the essence of the above technical solution, or the portion that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, or an optical disk, and includes a number of instructions for causing a computer device (such as a personal computer, server, or network device) to execute the methods described in each embodiment or certain portions of the embodiments.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A phase modulated continuous wave ranging method, characterized in that: Applied to a phase-modulated continuous wave ranging system, the method includes: Acquire initial dual-wavelength coherent light generated by a dual-wavelength coherent light generating unit using a laser beam; the initial dual-wavelength coherent light includes two coherent beams of different wavelengths; performing continuous wave phase modulation on the initial dual-wavelength coherent light to determine modulated dual-wavelength coherent light, and splitting the modulated dual-wavelength coherent light to obtain dual-wavelength probe light and dual-wavelength local oscillator light; both the dual-wavelength probe light and the dual-wavelength local oscillator light are dual-wavelength coherent light; The dual-wavelength detection light is emitted to the target to be measured, and the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured is received; the dual-wavelength reflected light is dual-wavelength coherent light; Performing beat frequency processing on the dual-wavelength reflected light and the dual-wavelength local oscillator light to obtain an intermediate frequency signal, and performing filtering processing on the intermediate frequency signal to obtain a difference frequency signal; wherein the phase difference and frequency difference between the dual-wavelength probe light and the dual-wavelength local oscillator light in the difference frequency signal are fixed, and the square of the light intensity of the difference frequency signal is proportional to the round-trip time of the dual-wavelength probe light, where the round-trip time is the time it takes for the dual-wavelength probe light to travel back and forth between the target to be measured; The round-trip time is determined according to the light intensity of the difference frequency signal, the phase difference and the frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light, and the distance between the phase-modulated continuous wave ranging system and the target to be measured is determined according to the round-trip time.

2. The phase modulated continuous wave ranging method according to claim 1, characterized in that: The dual-wavelength coherent light generating unit includes any one of the following devices: a first laser and a Mach-Zehnder modulator, two independent second lasers, a mode-locked laser, and an optical filter. The initial dual-wavelength coherent light generated by the dual-wavelength coherent light generating unit through the laser beam is obtained, including: Outputting a laser beam through a first laser, and intensity-modulating the laser beam through a Mach-Zehnder modulator to generate carrier-suppressed sidebands, thereby obtaining the initial dual-wavelength coherent light; Alternatively, two independent second lasers are used to generate laser beams respectively, and the two laser beams are processed in a phase-locked manner to generate the initial dual-wavelength coherent light; Alternatively, a broad spectrum pulse is generated by a mode-locked laser, and the broad spectrum pulse is filtered by an optical filter to generate the initial dual-wavelength coherent light.

3. The phase modulated continuous wave ranging method according to claim 1, characterized in that: The performing continuous wave phase modulation on the initial dual-wavelength coherent light to determine the modulated dual-wavelength coherent light includes: Acquire a continuous phase modulation signal generated by a function generator; the phase modulation signal is a periodic function, and the period of the phase modulation signal is greater than the phase difference between the dual-wavelength detection light and the dual-wavelength local oscillator light; The initial dual-wavelength coherent light is phase-modulated by the phase modulation signal to determine the modulated dual-wavelength coherent light.

4. The phase-modulated continuous wave ranging method according to claim 3, characterized in that: The phase modulation signal is a square wave signal.

5. A phase modulated continuous wave ranging system, characterized in that: The phase-modulated continuous wave ranging system includes: a dual-wavelength coherent light generating unit, a phase modulation unit, a transmission and emission unit, and a detection and processing unit; The dual-wavelength coherent light generating unit is configured to generate initial dual-wavelength coherent light by using a laser beam; the initial dual-wavelength coherent light comprises two coherent light beams of different wavelengths; The phase modulation unit is connected to the dual-wavelength coherent light generating unit and is used to perform continuous wave phase modulation on the initial dual-wavelength coherent light to determine the modulated dual-wavelength coherent light; and to split the modulated dual-wavelength coherent light to obtain dual-wavelength detection light and dual-wavelength local oscillator light; the dual-wavelength detection light and the dual-wavelength local oscillator light are both dual-wavelength coherent light; The transmission unit is connected to the phase modulation unit and is used to transmit the dual-wavelength detection light to the target to be measured and receive the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured; the dual-wavelength reflected light is dual-wavelength coherent light; The detection processing unit is connected to the phase modulation unit and the transmission and emission unit, and is used to perform beat frequency processing on the dual-wavelength reflected light and the dual-wavelength local oscillation light to obtain an intermediate frequency signal, and to perform filtering processing on the intermediate frequency signal to obtain a difference frequency signal; the phase difference and frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillation light in the difference frequency signal are fixed, and the square of the light intensity of the difference frequency signal is proportional to the round-trip time of the dual-wavelength detection light, where the round-trip time is the time it takes for the dual-wavelength detection light to travel back and forth between the target to be detected; The detection processing unit is further used to determine the round-trip time based on the light intensity of the difference frequency signal, the phase difference and frequency difference between the dual-wavelength detection light and the dual-wavelength local oscillator light, and determine the distance between the phase-modulated continuous wave ranging system and the target to be measured based on the round-trip time.

6. The phase-modulated continuous wave ranging system according to claim 5, characterized in that: The dual-wavelength coherent light generating unit includes any one of the following devices: a first laser and a Mach-Zehnder modulator, two independent second lasers, a mode-locked laser and an optical filter; The first laser is used to output a laser beam, and the Mach-Zehnder modulator is used to perform intensity modulation on the laser beam to generate carrier-suppressed sidebands to obtain the initial dual-wavelength coherent light; The two independent second lasers are used to output two laser beams and process the two laser beams in a phase-locked manner to generate the initial dual-wavelength coherent light; The mode-locked laser is used to generate broadband pulses, and the optical filter is used to filter the broadband pulses to generate the initial dual-wavelength coherent light.

7. The phase-modulated continuous wave ranging system according to claim 5, characterized in that: The phase modulation continuous wave ranging system further includes: a function generator; The function generator is connected to the phase modulation unit and is used to generate a continuous phase modulation signal and input the phase modulation signal to the phase modulation unit; the phase modulation signal is a periodic function, and the period of the phase modulation signal is greater than the phase difference between the dual-wavelength detection light and the dual-wavelength local oscillator light; The phase modulation unit is specifically configured to perform phase modulation on the initial dual-wavelength coherent light by using the phase modulation signal to determine the modulated dual-wavelength coherent light.

8. The phase-modulated continuous wave ranging system according to claim 7, characterized in that: The phase modulation signal is a square wave signal.

9. The phase-modulated continuous wave ranging system according to claim 5, characterized in that: The phase-modulated continuous wave ranging system further includes: a polarization controller, wherein an input port of the polarization controller is connected to the phase modulation unit, and an output port of the polarization controller is connected to the detection processing unit; The polarization controller is used to modulate the polarization state of the dual-wavelength local oscillation light to be consistent with the polarization state of the dual-wavelength reflected light.

10. The phase modulated continuous wave ranging system according to claim 5, characterized in that: The transmission and emission unit includes: a collimator, which is connected to the phase modulation unit; The collimator is used to receive the dual-wavelength detection light transmitted by the phase modulation unit, collimate the dual-wavelength detection light and then transmit it to the target to be measured, and receive the dual-wavelength reflected light returned after the dual-wavelength detection light is reflected on the target to be measured, and transmit the dual-wavelength reflected light to the detection processing unit.

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