Coherent detection laser radar system and multi-wavelength coherent ranging method

Abstract

The invention discloses a coherent detection laser radar system and a multi-wavelength coherent ranging method. The coherent detection laser radar system at least comprises at least two fiber lasers with different central wavelengths, a first DWDM, a pulse modulation unit, an optical power amplification unit, an optical lens, a second DWDM, at least two photoelectric detectors and an FPGA. According to the embodiment of the invention, the speckle effect is effectively suppressed through the multi-wavelength diversity design, and the speckle contrast is remarkably reduced through the incoherent superposition of a plurality of independent wavelengths; meanwhile, a wavelength division amplification scheme is adopted, and the overall SBS threshold value of the system is improved through a multi-wavelength spectrum broadening effect on the premise that the power of each channel is kept to be lower than the SBS threshold value, so that the unification of high-power output and high coherence is realized; in addition, the method has remarkable advantages in the aspects of environmental adaptability, system expansibility and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of detection, and particularly relates to a coherent detection laser radar system and a multi-wavelength coherent ranging method. BACKGROUND

[0002] Laser coherent ranging technology has important applications in industrial measurement, space exploration and other fields due to its high precision and high sensitivity. However, there are still some technical challenges in practical applications: first, the traditional single-wavelength coherent ranging system is prone to serious speckle noise when measuring rough surface targets, which significantly reduces the signal-to-noise ratio of the measurement signal. Although there are speckle suppression methods based on polarization diversity or spatial averaging, these schemes either have limited suppression effect or rely on complex mechanical structures, making it difficult to achieve a good balance between system performance and reliability; second, to improve the system output power, the stimulated Brillouin scattering (SBS) effect constitutes a major bottleneck. The traditional method of widening the laser linewidth to increase the SBS threshold will damage the coherence of the light source, which is in conflict with the coherence required for high-precision ranging; in addition, existing systems lack adaptability when dealing with dynamic targets or complex environmental conditions, and the measurement stability needs to be improved; at the same time, the existing technical solutions also have obvious limitations in system scalability and cost control, which is difficult to meet the growing demand for high-performance ranging applications. SUMMARY

[0003] Embodiments of the present application provide a coherent detection laser radar system and a multi-wavelength coherent ranging method to at least solve the problems of serious influence of speckle noise and SBS effect and poor adaptability to complex environments in related technologies.

[0004] In a first aspect, embodiments of the present application provide a coherent detection laser radar system, comprising: at least two fiber lasers with different center wavelengths, a first DWDM, a pulse modulation unit, an optical power amplification unit, an optical lens, a second DWDM, at least two photodetectors, and an FPGA;

[0005] The at least two fiber lasers are configured to output at least two seed lights, and each fiber laser corresponds to a wavelength of each seed light in a one-to-one manner.

[0006] The first DWDM is configured to combine the at least two seed lights into a composite spectral signal.

[0007] The pulse modulation unit is configured to modulate the composite spectral signal into a pulsed light signal with a preset pulse width and a preset repetition frequency, and to shift the modulated pulsed light signal in frequency spectrum by a preset frequency.

[0008] The optical power amplification unit is configured to amplify the frequency-shifted pulsed light signal to obtain a high-peak pulsed light signal.

[0009] the optical lens is configured to emit the high-peak pulse optical signal to a target to be measured and receive a return signal reflected by the target to be measured;

[0010] the second DWDM is configured to demultiplex the return signal into at least two optical signals of different wavelengths;

[0011] the at least two photodetectors are configured to perform coherent mixing of the at least two demultiplexed optical signals with local oscillator light of respective wavelengths corresponding to the at least two demultiplexed optical signals, and perform photoelectric conversion to obtain at least two electrical signals;

[0012] the FPGA is configured to perform fast Fourier transform on the at least two electrical signals to implement frequency spectrum analysis and obtain corresponding frequency spectrum information.

[0013] In a second aspect, an embodiment of the present application provides a multi-wavelength coherent ranging method, which is applied to the coherent detection laser radar system according to any one of the first aspect.

[0014] at least two seed lights are output by at least two fiber lasers, and each of the fiber lasers corresponds to one of the seed lights in terms of wavelength;

[0015] the at least two seed lights are combined into a composite spectrum signal by a first DWDM;

[0016] the composite spectrum signal is modulated into a pulse optical signal with a preset pulse width and a preset repetition frequency by a pulse modulation unit, and the modulated pulse optical signal is moved by a preset frequency in the frequency spectrum;

[0017] the pulse optical signal after the frequency shift is amplified by an optical power amplification unit to obtain a high-peak pulse optical signal;

[0018] the high-peak pulse optical signal is emitted to a target to be measured by an optical lens, and a return signal reflected by the target to be measured is received;

[0019] the return signal is demultiplexed into at least two optical signals of different wavelengths by a second DWDM;

[0020] the at least two demultiplexed optical signals are respectively mixed with local oscillator light of respective wavelengths corresponding to the at least two demultiplexed optical signals by at least two photodetectors, and photoelectric conversion is performed to obtain at least two electrical signals;

[0021] fast Fourier transform is performed on the at least two electrical signals by a FPGA to implement frequency spectrum analysis and obtain corresponding frequency spectrum information;

[0022] a target distance from the laser radar system to the target to be measured is calculated according to the frequency spectrum information.

[0023] The coherent detection laser radar system and the multi-wavelength coherent ranging method provided by the embodiments of the present application can effectively suppress speckle effect through multi-wavelength diversity design, and the non-coherent superposition of multiple independent wavelengths can significantly reduce speckle contrast; meanwhile, the wavelength division amplification scheme is adopted to improve the overall SBS threshold of the system through multi-wavelength spectral broadening effect on the premise that the power of each channel is lower than the SBS threshold, thereby realizing the unification of high-power output and high coherence; secondly, the system exhibits excellent environmental adaptability, because different wavelengths have different water vapor absorption capacities, when a wavelength signal is attenuated due to atmospheric turbulence interference or water vapor absorption, other wavelengths can still maintain effective detection, ensuring the working reliability of the system in complex environments; in addition, the system has good scalability, the architecture design based on the standard DWDM allows flexible increase of the number of wavelengths, that is, the multi-wavelength configuration can be expanded, thereby further improving the system performance without changing the core architecture, providing convenience for future performance upgrade. Therefore, the embodiments of the present application exhibit significant advantages in speckle suppression, power improvement, environmental adaptability and system scalability. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced, and other drawings can be obtained by those skilled in the art without creative labor on the premise of not paying creative labor.

[0025] Figure 1 is a structural schematic diagram of a coherent detection laser radar system provided by the embodiments of the present application;

[0026] Figure 2 is a flow schematic diagram of a multi-wavelength coherent ranging method provided by the embodiments of the present application. DETAILED DESCRIPTION

[0027] The features and exemplary embodiments of various aspects of the present application will be described in detail below, in order to make the purposes, technical solutions and advantages of the present application more clear and apparent, the present application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, but not to limit the present application. The present application can be implemented without some of these specific details by those skilled in the art. The following description of the embodiments is only to provide a better understanding of the present application by showing examples of the present application.

[0028] It is to be noted that, in the present document, relational terms such as first and second, and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0029] Laser coherent ranging technology has important applications in industrial measurement, space exploration and other fields due to its high precision and high sensitivity. However, there are still some technical challenges in practical applications.

[0030] Firstly, when the coherent laser irradiates the rough target surface, serious speckle noise will be generated, resulting in the decrease of signal signal-to-noise ratio and the decrease of measurement accuracy. The traditional speckle suppression methods such as polarization diversity or spatial averaging have limited effect or require complex mechanical structure, which is difficult to balance system performance and reliability.

[0031] Secondly, in terms of improving system power, stimulated Brillouin scattering (SBS) effect becomes the main limiting factor. When the power of single-wavelength laser exceeds a certain threshold, SBS effect will cause serious signal degradation. Although the SBS threshold can be improved by broadening the linewidth, it will also reduce the coherence and ranging accuracy of the system, forming a difficult contradiction.

[0032] In addition, the existing laser ranging system often lacks measurement stability and adaptability when facing complex environments or moving targets. Atmospheric turbulence, target motion and other factors will introduce additional noise and interference, affecting the reliability and repeatability of the system.

[0033] In addition, the existing technical solutions also have obvious limitations in system scalability and cost control, which are difficult to meet the growing demand for high-performance ranging applications.

[0034] In order to solve the problems of the related art, the embodiments of the present application provide a coherent detection laser radar system and a multi-wavelength coherent ranging method, which can realize the application of coherent detection laser radar in long-distance and high-precision ranging scenarios through multi-wavelength laser beam combination, pulse modulation and coherent detection.

[0035] The coherent detection laser radar system provided by the embodiments of the present application will be described in detail in combination with specific embodiments and application scenarios and the drawings.

[0036] Reference Figure 1 , a structure schematic diagram of a coherent detection laser radar system of an embodiment of the present application. As shown in Figure 1 , the coherent detection laser radar system comprises at least two optical fiber lasers with different center wavelengths, a first DWDM, a pulse modulation unit, an optical power amplification unit, an optical lens, a second DWDM, at least two photodetectors, and an FPGA.

[0037] Specifically, the at least two optical fiber lasers are configured to output at least two local oscillator lights; the first DWDM is configured to combine the at least two local oscillator lights into a composite spectral signal; the pulse modulation unit is configured to modulate the composite spectral signal into a pulsed light signal with a preset pulse width and a preset repetition frequency, and to move the modulated pulsed light signal by a preset frequency in the frequency spectrum; the optical power amplification unit is configured to amplify the frequency-shifted pulsed light signal to obtain a high-peak pulsed light signal; the optical lens is configured to emit the high-peak pulsed light signal to a target to be measured, and to receive a return signal reflected by the target to be measured; the second DWDM is configured to demultiplex the return signal into at least two light signals with different wavelengths; the at least two photodetectors are configured to coherently mix the at least two demultiplexed light signals with their respective corresponding local oscillator lights of the same wavelength, and to perform photoelectric conversion to obtain at least two electrical signals; and the FPGA is configured to perform fast Fourier transform on the at least two electrical signals to realize spectral analysis and obtain corresponding spectral information.

[0038] Optionally, the number of the at least two optical fiber lasers can be set according to application requirements, which is not specifically limited in the embodiment of the present application, for example but not limited to 4 (as shown in Figure 1 ), 8. That is, the architecture design of the embodiment of the present application allows flexible increase of the number of wavelengths, for example, to expand to an 8-wavelength configuration. Moreover, the coherent detection laser radar system of the embodiment of the present application has good scalability, and the architecture design based on the standard DWDM allows flexible increase of the number of wavelengths, and the system performance can be further improved by expanding to an 8-wavelength configuration, without changing the core architecture, which provides convenience for future performance upgrade.

[0039] Optionally, the center wavelengths corresponding to each optical fiber laser and the wavelength intervals therebetween can be set according to the first DWDM (Dense Wavelength Division Multiplexing) used for subsequent beam combination, that is, matched with the related parameters of the first DWDM. For example, the center wavelengths of the four optical fiber lasers can be set as 1550.92 nm, 1551.73 nm, 1552.54 nm and 1553.35 nm, and the wavelength intervals therebetween can be set as 80.81 nm, 82.63 nm, 84.45 nm and 86.27 nm. Figure 1The system in the embodiment includes four fiber lasers, and the corresponding wavelengths are, for example, but not limited to: the central wavelengths are 1549.32 nm, 1550.12 nm, 1550.92 nm and 1551.72 nm respectively, and the wavelength interval is 0.8 nm.

[0040] Optionally, the at least two fiber lasers are narrow-linewidth fiber lasers, and the linewidth of each laser is less than 100 Hz.

[0041] In this way, the coherent detection laser radar system in the embodiment adopts at least two narrow-linewidth fiber lasers as seed light sources, and has good wavelength stability and spectral controllability. Moreover, the Brillouin gain bandwidth of SBS is about 50 MHz, which is much smaller than the wavelength interval (0.8 nm corresponds to about 100 GHz in the 1550 nm band) set by the system. This means that, taking the system including four fiber lasers as an example, the acoustic wave grating formed by the wavelength λ1 does not match the "grid spacing" of the wavelengths λ2, λ3 and λ4. Therefore, λ2, λ3 and λ4 cannot be effectively scattered by the acoustic wave excited by λ1. As can be seen, the four wavelengths do not interfere with each other in the SBS effect, and can be regarded as completely independent channels.

[0042] It should be further noted that, for each fiber laser, two light paths are output: one is used as seed light for subsequent modulation; and the other is used as local light for subsequent coherent mixing.

[0043] Further, in some embodiments, the pulse modulation unit includes an acousto-optic modulator (AOM) and a signal source. Specifically, the signal source is configured to output a modulation signal to the acousto-optic modulator; and the acousto-optic modulator is configured to drive the modulation signal to modulate the composite spectrum signal into a pulsed light signal with a preset pulse width and a preset repetition frequency, and to move the modulated pulsed light signal in the frequency spectrum by a preset frequency (such as 200 MHz).

[0044] It should be noted that the preset pulse width and the preset repetition frequency are matched with the application requirements of the third amplifier used for subsequent third-stage amplification, for example, the pulse width can be set to 10 us, and the repetition frequency can be set to 1 kHz.

[0045] That is, the combined multi-wavelength continuous light is input to the AOM, which is driven by a high-frequency pulse modulation signal to modulate the multi-wavelength continuous light into a pulsed light signal with a set pulse width and a set repetition frequency, and to move the pulsed light signal in the frequency spectrum by a fixed frequency (such as 200 MHz). It should be understood that, if the frequency is not shifted, when the coherent detection is performed subsequently, the difference between the echo signal and the local light in the frequency spectrum is zero frequency, i.e., direct current, which is not easy to observe in the frequency spectrum. Therefore, by shifting the frequency, the signal can be more easily observed in the embodiment.

[0046] As an optional embodiment, the optical power amplification unit comprises a first amplifier, a second amplifier and a third amplifier connected in sequence, and the parameters of each of the amplifiers are different.

[0047] Specifically, the first amplifier, as a first-stage EDFA (pre-amplifier), is used to amplify the frequency-shifted pulse optical signal to improve its signal strength, reduce the subsequent gain noise effect, focus on low-noise performance, and minimize the deterioration of the signal signal-to-noise ratio, thereby providing a good noise figure for the entire amplification link. The second amplifier, as a second-stage EDFA (intermediate amplifier), is used to amplify the optical signal output by the first amplifier to provide the main gain and amplify the signal to a medium power. The third amplifier, as a third-stage EDFA (main power amplifier), is used to amplify the optical signal output by the second amplifier to obtain a high-peak pulse optical signal.

[0048] In this way, the modulated pulse light is sequentially amplified by the three-stage EDFA (Erbium-Doped Fiber Amplifier). Compared with directly amplifying the final signal using only one amplifier, the advantages are more significant: the pre-amplification stage can preferentially reduce noise and ensure signal-to-noise ratio, the intermediate amplification and main power amplification stages can segmentally control power to suppress nonlinear effects and improve output power, and more flexible gain adjustment can be achieved through independent parameter adjustment of each stage. At the same time, the dispersed amplification task reduces the single-stage pumping power, reduces the aging of the device due to overheating, improves the system stability, and is more suitable for scenarios such as optical fiber communication and laser ranging that require high signal quality and transmission distance.

[0049] In some optional embodiments, the laser radar system further comprises a fourth amplifier, which is used to amplify the echo signal output to the second

[0050] DWDM.

[0051] In some optional embodiments, the laser radar system further comprises a circulator connected with the third amplifier, the optical lens and the fourth amplifier, respectively. The circulator comprises a first port 1, a second port 2 and a third port 3. Specifically, the circulator is used to input the high-peak pulse optical signal output by the third amplifier from the first port 1 and output from the second port 2 to be emitted through the optical lens; and input the echo signal reflected by the target to be measured received by the optical lens from the second port 2 and output from the third port 3 to the fourth amplifier. In this way, the unidirectionality of signal transmission can be ensured.

[0052] In some optional embodiments, the laser radar system further comprises at least two analog-to-digital converters (ADCs). Specifically, one end of each of the at least two analog-to-digital converters is connected to a corresponding at least two photodetectors, and the other end of each of the at least two photodetectors is connected to the FPGA. The at least two analog-to-digital converters are configured to convert the signal type of the at least two electrical signals converted from light into a digital signal and output to the FPGA.

[0053] Thus, the coherent detection laser radar system of the embodiments of the present application adopts at least two narrow-linewidth fiber lasers as seed light sources; the continuous light signals output by the lasers are combined by the first DWDM to output a composite optical spectrum signal; the multi-wavelength continuous light after the combination is input to the acousto-optic modulator, which is driven by a high-frequency pulse modulation signal to be modulated into a pulsed light signal with a set pulse width and repetition frequency, and the light signal is moved by a fixed frequency in the spectrum; the modulated pulsed light is sequentially amplified by the three-stage EDFA; the multi-wavelength high-peak pulsed light beam output after the amplification by the three-stage EDFA is emitted to the target to be measured by the optical lens, the system adopts an integrated design architecture of transmission and reception, the echo signal reflected by the target is received by the same lens and coupled into the fourth EDFA for amplification processing; the amplified echo light signal is demultiplexed into multiple light signals of different wavelengths by the second DWDM, and is output to each channel respectively, and then each of the echo light signals and the local oscillator light of the corresponding wavelength are coherently mixed by the at least two photodetectors (PDs) respectively, and are converted into electrical signals, which are used for subsequent signal processing and analysis; the multi-channel electrical signals sampled and quantized by the high-speed ADC are sent to the FPGA parallel processing architecture for fast Fourier transform (FFT) to realize spectrum analysis.

[0054]

[0055] It should be understood that the multi-channel signals received by the FPGA are all from the same target and carry the same Doppler shift information, and thus the signals are highly correlated. The shot noise generated in each receiving channel is a completely independent random process, and thus the noises in the multi-channel signals are not correlated with each other.

[0056] ​In summary, the coherent detection laser radar system of the embodiments of the present application realizes effective suppression of speckle effect through multi-wavelength diversity design, and the non-coherent superposition of multiple independent wavelengths significantly reduces the speckle contrast. Meanwhile, the wavelength division amplification scheme is adopted to improve the overall SBS threshold of the system through the multi-wavelength spectral broadening effect while keeping the power of each channel below the SBS threshold, thereby realizing the unification of high-power output and high coherence. Secondly, the system exhibits excellent environmental adaptability. Since different wavelengths have different water vapor absorption capacities, when a certain wavelength signal is attenuated due to atmospheric turbulence interference or water vapor absorption, other wavelengths can still maintain effective detection, ensuring the working reliability of the system in complex environments. In addition, the system has good scalability. The architecture design based on the standard DWDM allows flexible addition of the number of wavelengths, that is, the multi-wavelength configuration can be expanded, thereby further improving the system performance without changing the core architecture, providing convenience for future performance upgrade. Thus, the embodiments of the present application exhibit significant advantages in speckle suppression, power improvement, environmental adaptability, and system scalability.

[0057] Further, the present application also provides a multi-wavelength coherent ranging method. It should be noted that the multi-wavelength coherent ranging method can be applied to the coherent detection laser radar system of any of the above embodiments.

[0058] Figure 2 The flowchart of the multi-wavelength coherent ranging method of the embodiments of the present application is shown. As shown in the figure, the multi-wavelength coherent ranging method can specifically include the following steps: Figure 2

[0059] S201, output at least two seed lights through at least two fiber lasers, each fiber laser corresponding to one wavelength of the seed light;

[0060] S202, combine the at least two seed lights into a composite spectral signal through a first DWDM;

[0061] S203, modulate the composite spectral signal into a pulse light signal with a preset pulse width and a preset repetition frequency through a pulse modulation unit, and move the modulated pulse light signal in the frequency spectrum by a preset frequency;

[0062] S204, amplify the frequency-shifted pulse light signal through an optical power amplification unit to obtain a high-peak pulse light signal;

[0063] S205, emit the high-peak pulse light signal to a target to be measured through an optical lens, and receive a return signal reflected by the target to be measured;

[0064] S206, demultiplex the return signal into at least two light signals with different wavelengths through a second DWDM; ​

[0065] S207, coherently mixing the at least two demultiplexed optical signals with local oscillator light of respective wavelengths by at least two photodetectors, and performing photoelectric conversion to obtain at least two electrical signals;

[0066] S208, performing fast Fourier transform on the at least two electrical signals by an FPGA to realize frequency spectrum analysis, and obtaining corresponding frequency spectrum information;

[0067] S209, calculating a target distance from the laser radar system to the target to be measured according to the frequency spectrum information.

[0068] The specific implementation modes of the above steps are described below.

[0069] In some embodiments, in S203, a signal source outputs a modulation signal to the acousto-optic modulator; the acousto-optic modulator drives based on the modulation signal, modulates the composite spectrum signal into a pulsed optical signal with a preset pulse width and a preset repetition frequency, and moves the modulated pulsed optical signal by a preset frequency in the frequency spectrum.

[0070] In some embodiments, in S204, a first amplifier amplifies the frequency-shifted pulsed optical signal to improve its signal strength; a second amplifier amplifies the optical signal output by the first amplifier to provide main gain; and a third amplifier amplifies the optical signal output by the second amplifier to obtain a high-peak pulsed optical signal.

[0071] In some embodiments, after S205 and before S206, that is, after receiving the echo signal reflected by the target to be measured by the optical lens, and before demultiplexing the echo signal into at least two optical signals with different wavelengths by the second DWDM, the method further comprises: amplifying the echo signal by a fourth amplifier and outputting it to the second DWDM.

[0072] In some embodiments, after S207 and before S208, that is, after coherently mixing the at least two demultiplexed optical signals with local oscillator light of respective wavelengths by at least two photodetectors and performing photoelectric conversion to obtain at least two electrical signals, and before performing fast Fourier transform on the at least two electrical signals by an FPGA to realize frequency spectrum analysis and obtain corresponding frequency spectrum information, the method further comprises: converting the signal type of the at least two photoelectrically converted electrical signals from an analog signal to a digital signal by at least two analog-to-digital converters, and outputting it to the FPGA.

[0073] Optionally, the frequency spectrum information at least includes an amplitude spectrum.

[0074] In some embodiments, in S209, according to the spectrum information, the target distance of the lidar system to the target to be measured is calculated in cooperation with the time domain synchronization information. Specifically, the amplitude spectrum of at least two signals is superimposed and averaged, and the peak value corresponding to the moving preset frequency is detected in the frequency domain to determine the target signal; according to the time delay between the target signal and the high-peak-value pulsed light signal, the TOF algorithm is used to calculate the target distance of the lidar system to the target to be measured.

[0075] In specific implementation, superimposing and averaging the amplitude spectrum of at least two signals is equivalent to averaging at least two independent measurement results, which can improve the signal-to-noise ratio by 2 times; then, the peak value is detected in the frequency domain for the characteristic frequency band introduced by AOM frequency shift; once the target signal is detected, the target distance of the lidar system to the target to be measured is accurately calculated by the TOF algorithm combined with the time delay between the target signal and the transmitted pulse (i.e., the high-peak-value pulsed light signal).

[0076] In specific implementation, the difference between the time at which the target signal is observed in the time domain and the time at which the high-peak-value pulsed light signal is observed, i.e., the difference between the transmission time and the echo reception time, is calculated, and the product of the difference and the velocity is taken as the target distance.

[0077] Therefore, the multi-wavelength coherent ranging method of the embodiments of the present application effectively suppresses speckle noise and SBS effect while maintaining high coherence, enhances the adaptability of the system to complex environments, and can provide a more superior solution for high-precision ranging applications.

[0078] It should be noted that the above describes some embodiments of the present application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in an order different than that described in the above embodiments and still achieve the desired result. In addition, the processes depicted in the figures do not necessarily require the particular order shown or sequential order to achieve the desired results. In certain implementations, multitasking and parallel processing can be advantageous or possible.

[0079] In the present application, the phrase "embodiment" means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it independent or alternative to other embodiments.

[0080] In the description of the application, it should be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "attachment" should be understood broadly, for example, can be fixedly connected, can be detachably connected, or integrally connected; can be directly connected, or indirectly connected through an intermediate medium; can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0081] In the embodiments of the application, the same reference signs represent the same components, and for the sake of brevity, the detailed description of the same components is omitted in different embodiments. It should be understood that the thickness, length, width and other dimensions of various components in the embodiments of the application shown in the drawings, and the overall thickness, length, width and other dimensions of the integrated device are only exemplary and should not constitute any limitation on the application.

[0082] "Multiple" appearing in the application refers to more than two (including two).

[0083] Although the application has been described with reference to the preferred embodiments, various modifications can be made to it without departing from the scope of the application, and equivalent components can be substituted therefor, especially, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0084] It should also be noted that the exemplary embodiments mentioned in the application describe some methods or systems based on a series of steps or devices. However, the application is not limited to the order of the above steps, that is, the steps can be performed in the order mentioned in the embodiments, or in an order different from that in the embodiments, or several steps can be performed simultaneously.

[0085] The above is only a specific implementation of the application, and those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the above-described system, module and unit can refer to the corresponding process in the foregoing method embodiments, which will not be described here. It should be understood that the protection scope of the application is not limited thereto, and any skilled person in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in the application, and these modifications or replacements should be covered within the protection scope of the application.

Claims

1. A coherent detection lidar system, characterized by, The laser radar system comprises at least two fiber lasers, a first DWDM, a pulse modulation unit, an optical power amplification unit, an optical lens, a second DWDM, at least two photodetectors, and an FPGA. The at least two fiber lasers are configured to output at least two seed lights, and each of the fiber lasers corresponds to a wavelength of each of the seed lights. The first DWDM is configured to combine the at least two seed lights into a composite optical signal. The pulse modulation unit is configured to modulate the composite optical signal into a pulsed optical signal with a preset pulse width and a preset repetition frequency, and to shift the modulated pulsed optical signal in the frequency spectrum by a preset frequency. The optical power amplification unit is configured to amplify the frequency-shifted pulsed optical signal to obtain a high-peak pulsed optical signal. The optical lens is configured to emit the high-peak pulsed optical signal to a target to be detected, and to receive a return signal reflected by the target to be detected. The second DWDM is configured to demultiplex the return signal into at least two optical signals with different wavelengths. The at least two photodetectors are configured to coherently mix the at least two demultiplexed optical signals with local oscillator lights of the corresponding wavelengths, respectively, and to perform photoelectric conversion to obtain at least two electrical signals. The FPGA is configured to perform fast Fourier transform on the at least two electrical signals to realize frequency spectrum analysis and obtain corresponding frequency spectrum information. The pulse modulation unit comprises an acousto-optic modulator and a signal source.

2. The lidar system of claim 1, wherein, The signal source is configured to output a modulation signal to the acousto-optic modulator. The acousto-optic modulator is configured to drive the composite optical signal to be modulated into a pulsed optical signal with a preset pulse width and a preset repetition frequency by the modulation signal, and to shift the modulated pulsed optical signal in the frequency spectrum by a preset frequency. The optical power amplification unit comprises a first amplifier, a second amplifier, and a third amplifier connected in sequence, and the parameters of each amplifier are different.

3. The lidar system of claim 1, wherein, The first amplifier is configured to amplify the frequency-shifted pulsed optical signal to increase the signal strength thereof. The second amplifier is configured to amplify the optical signal output by the first amplifier to provide a main gain. The third amplifier is configured to amplify the optical signal output by the second amplifier to obtain a high-peak pulsed optical signal. The laser radar system further comprises a fourth amplifier configured to amplify the return signal and output the amplified return signal to the second DWDM.

4. The lidar system of claim 3, wherein, The laser radar system further comprises a circulator connected to the third amplifier, the optical lens, and the fourth amplifier, respectively.

5. The lidar system of claim 4, wherein, The circulator is configured to input the high-peak pulsed optical signal output by the third amplifier from the first port, and output the high-peak pulsed optical signal from the second port to be emitted by the optical lens. The circulator is further configured to input the return signal reflected by the target to be detected received by the optical lens from the second port, and output the return signal from the third port to the fourth amplifier. The laser radar system further comprises at least two analog-to-digital converters.

6. The lidar system of claim 1, wherein, ​ One end of the at least two analog-to-digital converters is connected with the corresponding at least two photodetectors, and the other end of the at least two photodetectors is connected with the FPGA; The at least two analog-to-digital converters are used to convert the signal type of the at least two electrical signals converted by photoelectricity from an analog signal to a digital signal and output to the FPGA.

7. A multi-wavelength coherent ranging method, characterized by, The method is applied to the coherent detection laser radar system according to any one of claims 1-6, and the method comprises: At least two seed lights are output through at least two fiber lasers, and each of the fiber lasers corresponds to the wavelength of each of the seed lights; The at least two seed lights are combined into a composite spectrum signal through a first DWDM; The composite spectrum signal is modulated into a pulsed light signal with a preset pulse width and a preset repetition frequency through a pulse modulation unit, and the modulated pulsed light signal is moved by a preset frequency in the frequency spectrum; The pulsed light signal after the frequency shift is amplified through an optical power amplification unit to obtain a high-peak pulsed light signal; The high-peak pulsed light signal is transmitted to a target to be measured through an optical lens, and a return signal reflected by the target to be measured is received; The return signal is demultiplexed into at least two optical signals with different wavelengths through a second DWDM; The at least two optical signals after the demultiplexing are respectively mixed with local oscillator lights with corresponding wavelengths through at least two photodetectors, and photoelectric conversion is performed to obtain at least two electrical signals; Fast Fourier transform is performed on the at least two electrical signals through an FPGA to realize frequency spectrum analysis and obtain corresponding frequency spectrum information; According to the frequency spectrum information, the target distance from the laser radar system to the target to be measured is calculated.

8. The method of claim 7, wherein, The frequency spectrum information comprises an amplitude spectrum; According to the frequency spectrum information, the target distance from the laser radar system to the target to be measured is calculated, which comprises: The amplitude spectra of the at least two signals are superimposed and averaged, and a peak corresponding to the preset frequency is detected in the frequency domain to determine a target signal; According to the time delay between the target signal and the high-peak pulsed light signal, the TOF algorithm is used to calculate the target distance from the laser radar system to the target to be measured.

9. The method of claim 7, wherein, After receiving the return signal reflected by the target to be measured through the optical lens, before demultiplexing the return signal into at least two optical signals with different wavelengths through the second DWDM, the method further comprises: The return signal is amplified through a fourth amplifier and then output to the second DWDM.

10. The method of claim 7, wherein, After the at least two optical signals after the demultiplexing are respectively mixed with local oscillator lights with corresponding wavelengths through the at least two photodetectors and photoelectric conversion is performed to obtain at least two electrical signals, before fast Fourier transform is performed on the at least two electrical signals through the FPGA to realize frequency spectrum analysis and obtain corresponding frequency spectrum information, the method further comprises: The at least two analog-to-digital converters are used to convert the signal type of the at least two electrical signals converted by photoelectricity from an analog signal to a digital signal and output to the FPGA.

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