Optoelectronic double down-conversion laser coherent detection method and system

Abstract

The application discloses a kind of photoelectric dual down-conversion laser coherent detection method and system, comprising: seed source output light is split according to preset proportion, and two phase quadrature local light signals are generated based on the light signal after splitting;Based on one of the light signal after splitting, as signal light, and the frequency of the signal light is modulated;With the generated phase quadrature local light signal, the received light signal based on the modulated signal light is quadrature down-converted to obtain intermediate frequency electrical signal;The intermediate frequency electrical signal is digitally down-converted to obtain target IQ signal;The target IQ signal is pulse compression processing to determine target distance information.The method of the application uses two quadrature signals as local light in the optical down-conversion stage, so that the signal-to-noise ratio of the detection system is further optimized, and the detection distance and accuracy are improved.

Description

Technical Field

[0001] This application relates to the field of laser ranging technology, and in particular to a photoelectric dual down-conversion laser coherent detection method and system. Background Technology

[0002] In known laser detection systems, intensity-based detection directly converts the laser signal into an electrical signal. The amplitude of the electrical signal output by the photodetector is proportional to the received optical power, and coherence is not required. Therefore, this detection method is also called incoherent detection, and it is widely used due to its simplicity, low cost, and good long-term stability. However, coherent detection has significant advantages in detection sensitivity and anti-interference performance.

[0003] In a coherent detection system, the lidar receiver needs to use coherent reception to demodulate the received signal. During coherent reception, a suitable local oscillator signal is typically selected based on the receiver's architecture. This local oscillator signal is then mixed with the received signal, and demodulated to obtain an intermediate frequency (IF) signal or a baseband signal. The demodulated signal is then further processed to obtain range information.

[0004] In coherent laser detection, since laser emission power cannot be increased indefinitely, improving the detection range and range resolution of lidar requires enhancing the signal-to-noise ratio (SNR) during demodulation. Currently, coherent laser radar receivers typically employ a double down-conversion process. The first down-conversion demodulates the lidar echo signal from an optical signal into an intermediate frequency (IF) electrical signal, and the second down-conversion demodulates the IF electrical signal back into a baseband signal for pulse compression and other signal processing. Similar to radio receivers, image frequency rejection capability significantly impacts the receiver's performance.

[0005] Mirror frequency refers to the frequency difference between the echo signal and the local oscillator signal during the down-conversion process of radar echo signals. The frequency component on the other side of the local oscillator frequency, which is one intermediate frequency, will be superimposed on the useful signal after frequency conversion during the mixing process, resulting in a decrease in the signal-to-noise ratio of the demodulated signal. Furthermore, since the useful signal in the original signal and the noise signal at the mirror frequency are both shifted to the intermediate frequency after mixing, it is impossible to separate the useful signal from the noise.

[0006] Image frequency interference also exists in coherent laser ranging radar. Currently, most coherent laser radar receivers use heterodyne down-conversion. In the first optical down-conversion stage, the local oscillator light and the signal light are usually directly mixed. Image frequency suppression is achieved through a pre-bandpass filter. However, due to the limitations of the filter's amplitude-frequency characteristics, the method of filtering the echo signal by image frequency before demodulation is not very effective. Image frequency interference is difficult to eliminate effectively, ultimately leading to a decrease in the signal-to-noise ratio of the demodulated signal and a reduction in the radar's effective range. Summary of the Invention

[0007] This application provides a laser coherent detection method and system with photoelectric dual downconversion, which proposes a novel photoelectric dual downconversion technology. In the photoelectric downconversion stage, two orthogonal signals are used as local oscillators, which further optimizes the signal-to-noise ratio of the detection system and improves the detection distance and accuracy.

[0008] This application provides a laser coherent detection method with photoelectric dual downconversion, comprising the following steps:

[0009] The output light from the seed source is split into beams according to a preset ratio, and two local oscillator light signals with orthogonal phases are generated based on the split light signals.

[0010] One of the split optical signals is used as the signal light, and the frequency of the signal light is modulated.

[0011] Using the generated phase-orthogonal local oscillator optical signal, the received optical signal based on the modulated signal light is orthogonally down-converted to obtain an intermediate frequency electrical signal;

[0012] The intermediate frequency electrical signal is digitally down-converted to obtain the target IQ signal;

[0013] The target IQ signal is subjected to pulse compression processing to determine the target distance information.

[0014] Optionally, the seed source output light is split into beams according to a preset ratio, and two orthogonal local oscillator light signals are generated based on the split light signals, including:

[0015] The output light from the seed source is split into beams according to a preset size ratio. The smaller beam is divided into the first beam and the second beam, and the larger beam is attenuated and modulated to generate the required frequency shift before being divided into the third beam and the fourth beam.

[0016] The first beam and the second beam are connected to two optical fibers of similar length, and then combined with the third beam and the fourth beam respectively based on the output ends of the two optical fibers.

[0017] The combined optical signals are then fed into photodetectors for mixing to obtain a mixed signal.

[0018] Optional, also includes:

[0019] One of the two optical paths connected to the first beam and the second beam is cut and then connected to the optical fiber fusion splicer.

[0020] Use an oscilloscope to observe the phase and amplitude of the mixed signal output by the photodetector;

[0021] If the phase and amplitude of the mixed signal output by the photodetector do not meet the orthogonality requirement, the displacement of the fiber end face is adjusted by the fiber fusion splicer until the orthogonality requirement is met, so as to obtain two local oscillator optical signals with orthogonal phases; and after the orthogonality requirement is met, the fiber fusion splicer is used to splice the fiber.

[0022] Optionally, taking one of the split optical signals as the signal light and modulating the frequency of the signal light includes:

[0023] The seed source output light is split into a large proportion according to a preset size ratio. The light is then chopped, modulated, and amplified to serve as signal light, and the frequency of the signal light is modulated.

[0024] Optionally, the received optical signal based on the modulated signal light is orthogonally down-converted using the generated phase-orthogonal local oscillator optical signal to obtain an intermediate frequency electrical signal, including:

[0025] The modulated signal light is emitted toward the target, and the emitted signal is divided into a first echo light signal and a second echo light signal after passing through the receiving lens.

[0026] The first echo optical signal and the second echo optical signal are orthogonally down-converted using the generated orthogonal local oscillator optical signals.

[0027] The optical signal after quadrature downconversion is detected by a photodetector, and the output of the photodetector is acquired to obtain the first IQ signal;

[0028] The first IQ signal is processed to obtain the intermediate frequency electrical signal.

[0029] Optionally, processing the first IQ signal to obtain the intermediate frequency electrical signal includes compensating for the amplitude and phase imbalance of the first IQ signal in the following manner:

[0030] For each s of the first IQ signal I (k) and s Q (k) is corrected using the following formula:

[0031]

[0032]

[0033] Among them, s I (k) and s Q (k) I / Q signal before correction, s I and s Q The vector form of the I / Q signal before correction, I out (k) and Q out(k) is the corrected IQ signal, E(s) Q E(s) represents the mathematical expectation of the Q-branch signal. I ) represents the mathematical expectation of the I branch signal. K takes values ​​from 1 to N, where N is the number of sampling points for the AD acquisition signal.

[0034] Optionally, processing the first IQ signal to obtain the intermediate frequency electrical signal further includes filtering and coupling the I / Q branches in the following manner:

[0035] Construct a digital Hilbert filter whose center frequency is the center frequency of the I / Q signal;

[0036] The I-branch signal is passed through the digital Hilbert filter, and the two branch signals are then added together to obtain the intermediate frequency electrical signal.

[0037] This application also proposes a photoelectric dual downconversion laser coherent detection system, including a processor and a memory. The memory stores a computer program, which, when executed by the processor, implements the steps of the aforementioned photoelectric dual downconversion laser coherent detection method.

[0038] This application also proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the aforementioned photoelectric dual downconversion laser coherent detection method.

[0039] This application proposes a novel photoelectric dual downconversion technology. In the optical downconversion stage, two orthogonal signals are used as local oscillators, which further optimizes the signal-to-noise ratio of the detection system and improves the detection distance and accuracy.

[0040] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0041] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0042] Figure 1 This is a basic flowchart of the photoelectric dual downconversion laser coherent detection method according to an embodiment of this application;

[0043] Figure 2This is a schematic diagram of the optical path for generating a local oscillator light with a 90-degree phase difference, as described in an embodiment of this application.

[0044] Figure 3 This is a schematic diagram of the optical fiber connection for optical orthogonal downconversion according to an embodiment of this application. Detailed Implementation

[0045] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0046] This application proposes a novel photoelectric dual downconversion technology. In the photoelectric downconversion stage, two orthogonal signals are used as local oscillators. The signal light is split into two paths, and each local oscillator signal is mixed with one of the two signal lights. Compared to directly mixing a single local oscillator signal with the signal light, this effectively suppresses image frequencies. Then, the mixed signals are subjected to AD acquisition and compensation processing to eliminate the influence of inconsistent amplitudes and phase differences (not 90°) between the two orthogonal local oscillator signals on the orthogonal mixing. After compensation, coupling filtering is performed to obtain the electrical intermediate frequency (IF) signal. The IF signal is downconverted to obtain the baseband signal. The baseband signal is then processed, and the data processing method is related to the modulation method of the laser emission signal. If linear frequency modulation is used, pulse compression can be employed. Specifically, this application provides a photoelectric dual downconversion laser coherent detection method. First, a 90-degree phase difference is introduced into the local oscillator path. Then, the emitted signal is modulated. Next, the radar received optical signal is orthogonally downconverted, and finally, the IF electrical signal is downconverted.

[0047] like Figure 1 As shown, the method of this application includes the following steps:

[0048] In step S101, the output light from the seed source is split into beams according to a preset ratio, and two local oscillator light signals with orthogonal phases are generated based on the split light signals.

[0049] In some embodiments, splitting the seed source output light into beams according to a preset ratio and generating two orthogonal local oscillator light signals based on the split light signals includes:

[0050] The seed source output light is split into beams according to a preset ratio. A smaller beam is divided into a first beam and a second beam, while a larger beam, after attenuation and acousto-optic modulation to generate the required frequency shift, is divided into a third beam and a fourth beam. For example... Figure 2As shown, in some specific examples, the output light from the seed source can be split into two beams by a beam splitter (e.g., at a ratio of 2:8). 20% of this beam is then split into two beams (beam 1 (first beam) and beam 2 (second beam)). 80% of this beam is attenuated to 1 / 4 and then split into two beams (beam 3 (third beam) and beam 4 (fourth beam)) after being frequency-shifted by an acousto-optic modulator by 200MHz.

[0051] The first beam and the second beam are connected to two optical fibers of similar length, and then combined with the third beam and the fourth beam, respectively, based on the output ends of the two optical fibers. In some specific examples, beam 1 and beam 2 can be connected to two optical fibers of similar length, and the output ends of these two optical fibers can be combined with beam 3 and beam 4, respectively.

[0052] The combined optical signals are then fed into photodetectors for mixing, resulting in two mixed signals. In some specific examples, the combined beams are fed into photodetectors separately, and the two combined beams are mixed on the surface of the photodetectors. The resulting signal is a 200MHz electrical signal. The photodetectors are connected to an oscilloscope to observe the phase and amplitude of the two mixed signals. If the amplitudes of the two mixed signals are equal and their phases differ by 90°, then beam 1 and beam 2 are orthogonal local oscillators.

[0053] In step S102, one of the split optical signals is used as a signal light, and the frequency of the signal light is modulated. In some specific examples, using one of the split optical signals as a signal light and modulating the frequency of the signal light includes:

[0054] The seed source output light is split into a large proportion according to a preset size ratio. The light is then chopped, modulated, and amplified to serve as signal light, and the frequency of the signal light is modulated.

[0055] This application embodiment is further explained based on the aforementioned 2:8 beam splitting. In step S101, the subsequent attenuation, beam splitting, and other operations of generating 80% of this light path are used to assist in generating local oscillator light with a 90° phase difference. After generation, subsequent operations on this light path can be cut off.

[0056] In step S101, 80% of the light generated is chopped, modulated, and amplified before being emitted as signal light. The laser emission signal frequency can be modulated using a linear frequency modulated signal (such as a 300MHz-700MHz linear frequency modulated (Chirp) signal) or a single frequency modulated signal (such as a 500MHz signal).

[0057] In step S103, the generated phase-orthogonal local oscillator optical signal is used to perform orthogonal down-conversion on the received optical signal based on the modulated signal light to obtain an intermediate frequency electrical signal.

[0058] In some specific examples, the received optical signal based on the modulated signal light is orthogonally down-converted using the generated phase-orthogonal local oscillator optical signal to obtain an intermediate frequency electrical signal, including:

[0059] The modulated signal light is emitted toward the target, and the emitted signal is divided into a first echo light signal and a second echo light signal after passing through the receiving lens.

[0060] The first echo optical signal and the second echo optical signal are orthogonally down-converted using the generated local oscillator optical signals with orthogonal phases.

[0061] The optical signal after quadrature downconversion is detected by a photodetector, and the output of the photodetector is acquired to obtain the first IQ signal.

[0062] Optical orthogonal downconversion fiber connection relationship as follows Figure 3 As shown, the laser emission signal is split into two equal echo beams after passing through the receiving lens. The two orthogonal local oscillator signals (beam 1 and beam 2) generated above are used to perform orthogonal down-conversion with the two echo beams. A photodetector detects the orthogonally down-converted optical signal, and the outputs of the two photodetectors are connected to an AD conversion module to acquire the mixed electrical signal. The IQ signal is obtained, and s is obtained respectively. I (k), s Q (k). The value of k ranges from 1 to N, where N is the number of sampling points for the AD acquisition signal. The first IQ signal is then processed to obtain the intermediate frequency electrical signal.

[0063] In step S104, the intermediate frequency electrical signal is digitally down-converted to obtain the target IQ signal.

[0064] In step S105, the target IQ signal is subjected to pulse compression processing to determine the target distance information.

[0065] This application proposes a novel photoelectric dual downconversion technology. In the optical downconversion stage, two orthogonal signals are used as local oscillators, which further optimizes the signal-to-noise ratio of the detection system and improves the detection distance and accuracy.

[0066] In some embodiments, the process of obtaining two local oscillator optical signals with orthogonal phases further includes: cutting the optical fiber and connecting it to an optical fiber fusion splicer in one of the two optical signals connected to the first beam and the second beam;

[0067] Use an oscilloscope to observe the phase and amplitude of the mixed signal output by the photodetector;

[0068] If the phase and amplitude of the mixed signal output by the photodetector do not meet the orthogonality requirement, the displacement of the fiber end face is adjusted by the fiber fusion splicer until the orthogonality requirement is met, so as to obtain two local oscillator optical signals with orthogonal phases; and after the orthogonality requirement is met, the fiber fusion splicer is used to splice the fiber.

[0069] Specifically, in this embodiment of the application, to control the phase of the local oscillator light, one of the optical fibers transmitting the local oscillator light signal is cut and connected to a high-precision fiber optic fusion splicer. The displacement of the fiber end face in the fusion splicer is precisely controlled, and the relative changes in the phase and amplitude of the two signals are observed on an oscilloscope. After the two signals produce a stable 90-degree phase difference and equal amplitude, fusion splicing is performed. The fiber connection is as follows: Figure 2 As shown.

[0070] I / Q demodulation requires a strict 90-degree phase difference between the local oscillator signal and equal amplitudes in the I / Q branches to achieve complete image frequency suppression. Imbalance in amplitude and phase will reduce image frequency suppression and introduce additional noise, resulting in a lower signal-to-noise ratio. In actual I / Q modulation and demodulation, non-ideal devices, differences in circuit design, and errors in fiber length can all lead to amplitude and phase imbalance. Furthermore, the influence of the DC component must be considered. Therefore, compensation of the demodulated signal is necessary to reduce the impact of I / Q branch imbalance.

[0071] To improve real-time signal processing efficiency and eliminate the influence of the DC component of the signal, embodiments of this application use an improved GSOP algorithm to correct the I / Q branch imbalance. In some specific examples, processing the first IQ signal to obtain the intermediate frequency electrical signal includes compensating for the amplitude and phase imbalance of the first IQ signal in the following manner:

[0072] For each s of the first IQ signal I (k) and s Q (k) is corrected using the following formula:

[0073]

[0074]

[0075] Among them, s I (k) and s Q (k) I / Q signal before correction, s I and s Q The vector form of the I / Q signal before correction, I out (k) and Q out (k) is the corrected IQ signal, E(s) Q E(s) represents the mathematical expectation of the Q-branch signal. I) represents the mathematical expectation of the I branch signal. K takes values ​​from 1 to N, where N is the number of sampling points for the AD acquisition signal.

[0076] Filtering and coupling the I / Q branches, in some specific examples, processing the first IQ signal to obtain the intermediate frequency electrical signal further includes filtering and coupling the I / Q branches in the following manner:

[0077] Construct a digital Hilbert filter whose center frequency is the center frequency of the I / Q signal.

[0078] If the phase difference between the Q branch signal and the I branch signal in the aforementioned local oscillator signal is +90 degrees, then the I branch signal is passed through the digital Hilbert filter, and the two branch signals are added together to obtain the intermediate frequency electrical signal.

[0079] When using a 300MHz-700MHz chirp signal as the modulating signal, the Hilbert filter is of FIR type, with a center frequency of 500MHz, a passband of 500MHz, and an order of 60. When using a 500MHz single-frequency signal as the modulating signal, the Hilbert filter is of FIR type, with a center frequency of 500MHz, a passband of 100MHz, and an order of 60.

[0080] Using the above method to downconvert the radar echo signal, the signal-to-noise ratio of the resulting intermediate frequency demodulated signal is improved by about 3dB compared to direct mixing.

[0081] In some specific examples, step S104, which digitally down-converts the intermediate frequency (IF) signal to obtain the target IQ signal, includes: digitally down-converting the aforementioned IF signal. If the IF signal is a 300MHz to 700MHz linear frequency modulated (Chirp) signal, then after digital down-conversion, the signal becomes a -200MHz to 200MHz IQ signal (different from the aforementioned IQ signal; this application uses photoelectric dual down-conversion, and this step is the second down-conversion of the IQ signal). This photoelectric dual down-conversion method proposed in this application effectively eliminates image frequency interference in the first optical down-conversion stage, improves the signal-to-noise ratio of the demodulated signal, and increases the radar's effective range. In the second electrical down-conversion stage, it improves system computational efficiency and, combined with subsequent pulse compression processing, enhances the system's ranging accuracy.

[0082] The target distance information can then be obtained by further pulse compression processing of the I and Q signals.

[0083] This application proposes a novel photoelectric dual down-conversion technology. In the optical down-conversion stage, two orthogonal signals are used as local oscillators, splitting the signal light into two paths. Each local oscillator signal is then mixed with one of the two signal lights. Compared to directly mixing a single local oscillator signal with the signal light, this effectively suppresses image frequencies. The mixed signals are then subjected to AD acquisition and compensation processing to eliminate the effects of inconsistent amplitudes and phase differences (not 90°) between the two orthogonal local oscillators on the orthogonal mixing. After compensation, coupling filtering is performed to obtain the electrical intermediate frequency (IF) signal. The IF signal is then down-converted to obtain the baseband signal. The baseband signal is then processed, and the data processing method is related to the modulation method of the laser emission signal. If linear frequency modulation is used, pulse compression can be employed. In laser coherent detection, optimizing the receiver down-conversion structure using the method described in this application can further optimize the signal-to-noise ratio of the detection system, improving detection distance and accuracy.

[0084] This application also proposes a photoelectric dual downconversion laser coherent detection system, including a processor and a memory. The memory stores a computer program, which, when executed by the processor, implements the steps of the aforementioned photoelectric dual downconversion laser coherent detection method.

[0085] This application also proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the aforementioned photoelectric dual downconversion laser coherent detection method.

[0086] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0087] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0088] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of this application.

[0089] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

Claims

1. A photoelectric dual down-conversion laser coherent detection method, characterized in that, Includes the following steps: The output light from the seed source is split into beams according to a preset ratio, and two local oscillator light signals with orthogonal phases are generated based on the split light signals. One of the split optical signals is used as the signal light, and the frequency of the signal light is modulated. Using the generated phase-orthogonal local oscillator optical signal, the received optical signal based on the modulated signal light is orthogonally down-converted to obtain an intermediate frequency electrical signal; The intermediate frequency electrical signal is digitally down-converted to obtain the target IQ signal; The target IQ signal is subjected to pulse compression processing to determine the target distance information; The seed source output light is split into beams according to a preset ratio, and two orthogonal local oscillator light signals are generated based on the split light signals, including: The output light from the seed source is split into beams according to a preset size ratio. The smaller beam is divided into the first beam and the second beam, and the larger beam is attenuated and modulated to generate the required frequency shift before being divided into the third beam and the fourth beam. The first beam and the second beam are connected to two optical fibers of similar length, and then combined with the third beam and the fourth beam respectively based on the output ends of the two optical fibers. The combined optical signals are then fed into photodetectors for mixing to obtain mixed signals. Using the generated phase-orthogonal local oscillator optical signal, the received optical signal based on the modulated signal light is orthogonally down-converted to obtain an intermediate frequency electrical signal, including: The modulated signal light is emitted toward the target, and the emitted signal is divided into a first echo light signal and a second echo light signal after passing through the receiving lens. The first echo optical signal and the second echo optical signal are orthogonally down-converted using the generated orthogonal local oscillator optical signals. The optical signal after quadrature downconversion is detected by a photodetector, and the output of the photodetector is acquired to obtain the first IQ signal; The first IQ signal is processed to obtain the intermediate frequency electrical signal; Processing the first IQ signal to obtain the intermediate frequency electrical signal includes compensating for the amplitude and phase imbalance of the first IQ signal in the following manner: For each of the first IQ signals and The following formula is used for correction: in, and These are the I and Q signals before correction, respectively. and These are the vector forms of the I and Q signals before correction, respectively. and These are the corrected I and Q signals, respectively. This represents the mathematical expectation of the Q-branch signal. This represents the mathematical expectation of the I-branch signal, where k ranges from 1 to N, and N is the number of sampling points for the AD acquisition signal.

2. The photoelectric dual down-conversion laser coherent detection method as described in claim 1, characterized in that, Also includes: One of the two optical paths connected to the first beam and the second beam is cut and then connected to the optical fiber fusion splicer. Use an oscilloscope to observe the phase and amplitude of the mixed signal output by the photodetector; If the phase and amplitude of the mixing signal output by the photodetector do not meet the orthogonality requirement, the displacement of the fiber end face is adjusted by the fiber fusion splicer until the orthogonality requirement is met, thereby obtaining two local oscillator optical signals with orthogonal phases; and, After meeting the orthogonality requirements, the optical fibers are spliced ​​using the optical fiber fusion splicer.

3. The photoelectric dual down-conversion laser coherent detection method as described in claim 2, characterized in that, Using one of the split optical signals as the signal light, and modulating the frequency of the signal light, includes: The seed source output light is split into a large proportion according to a preset size ratio. The light is then chopped, modulated, and amplified to serve as signal light, and the frequency of the signal light is modulated.

4. The photoelectric dual down-conversion laser coherent detection method as described in claim 1, characterized in that, Processing the first IQ signal to obtain the intermediate frequency electrical signal further includes filtering and coupling the I / Q branches in the following manner: Construct a digital Hilbert filter whose center frequency is the center frequency of the I / Q signal; The I-branch signal is passed through the digital Hilbert filter, and the two branch signals are then added together to obtain the intermediate frequency electrical signal.

5. A photoelectric dual down-conversion laser coherent detection system, characterized in that, It includes a processor and a memory, wherein the memory stores a computer program, which, when executed by the processor, implements the steps of the photoelectric dual downconversion laser coherent detection method as described in any one of claims 1 to 4.

6. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the photoelectric dual downconversion laser coherent detection method as described in any one of claims 1 to 4.

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