Laser time transfer system and method based on high-speed pseudo code

Abstract

The invention discloses a laser time transfer system and method based on a high-speed pseudo code, and the system employs an optical comb to achieve the locking of a common narrow linewidth laser to an atomic clock reference frequency, and enables the optical carrier to be more stable and accurate. A laser carrier which is homologous with an atomic clock is adopted to carry a high-speed pseudo code to realize time transmission, and high-precision code correlation measurement is realized by combining two schemes of realizing chip-level coarse delay in an FPGA (Field Programmable Gate Array) and realizing fine delay superior to one chip by using a delay line. The transmitted high-speed pseudo code can realize time transmission and comparison, is an effective way for high-precision spatial atomic clock comparison, meets the time-frequency transmission comparison requirements of a novel atomic clock, and is suitable for industrial use and popularization.

Description

Technical Field

[0001] The invention belongs to the field of time frequency, and in particular relates to a laser time transfer system and method based on high-speed pseudo code. Background Art

[0002] In recent years, the frequency stability and uncertainty of new atomic clocks have been greatly improved, and the frequency stability of microwave atomic clocks has reached 10 -13 The daily frequency stability has reached 10 -16 It is of high order, and the integrating sphere atomic clock has been carried on the Chinese space station.

[0003] Optical atomic clock frequency stability reaches 10 in seconds -15 The frequency stability and uncertainty have reached 10 -18 The traditional space time-frequency transfer link is usually a microwave time-frequency transfer link and a time transfer link based on the laser pulse flight time measurement. The additional instability of the second-level time-frequency transfer is 10 -11 ~10 -12 Magnitude, additional instability of daily time-frequency transmission 10 -15 ~10 -16 The magnitude of this technology is insufficient to meet the needs of time and frequency transmission and comparison of new atomic clocks. Summary of the invention

[0004] The purpose of the present invention is to provide a laser time transfer system and method based on high-speed pseudocode to solve the problem that the short-term accuracy of time and frequency transfer of spatial time and frequency transfer links in the prior art is insufficient and cannot meet the time and frequency transfer comparison requirements of new atomic clocks.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0006] A laser time transfer system based on high-speed pseudo code includes a laser time-frequency transfer system, wherein the laser time-frequency transfer system includes an atomic clock, an optical comb frequency synthesis unit, two narrow linewidth lasers, two modulation modules, an amplifier, a digital signal processing unit, two optical phase-locked loops, an acousto-optic frequency shifter, two groups of delay lines, a coherent receiving module and a laser transceiver terminal;

[0007] The atomic clocks include various microwave atomic clocks and optical clocks;

[0008] The optical comb frequency synthesis unit comprises an optical comb, an optical comb locking unit and an optically generated microwave unit;

[0009] The optical comb locking unit comprises a photodetector, a mixer, a loop filter, a voltage-controlled crystal oscillator and an acousto-optic frequency shifter;

[0010] The digital signal processing unit includes an FPGA chip, a frequency synthesis circuit and an AD;

[0011] The coherent receiving module comprises a 90° optical mixer and two balanced detectors;

[0012] The laser time-frequency transfer system has two groups, namely a first laser time-frequency transfer system and a second laser time-frequency transfer system configured on different satellites; the first laser time-frequency transfer system and the second laser time-frequency transfer system have symmetrical structures and the same functions.

[0013] The present invention also has the following features:

[0014] Furthermore, the wavelength difference between the first laser time-frequency transfer system and the second laser time-frequency transfer system is ≥0.8 nm.

[0015] Furthermore, the sampling rate of the AD is ≥ twice the code rate;

[0016] The FPGA chip includes a high-speed data transmission interface.

[0017] A laser time transfer method based on high-speed pseudo-code, based on the above-mentioned laser time transfer system based on high-speed pseudo-code, comprises the following steps:

[0018] Step 1: for the first laser time-frequency transfer system, lock the optical comb of the optical comb frequency synthesis unit to the atomic clock;

[0019] Step 2: for the first laser time-frequency transfer system, lock the narrow linewidth laser to the optical comb of the optical comb frequency synthesis unit;

[0020] Step 3, the first laser time-frequency transmission system generates a clock for generating a pseudo code and a clock for AD sampling through an optical comb frequency synthesis unit, generates pseudo codes in parallel in multiple channels in the FPGA chip, modulates data on the pseudo codes, generates baseband signals, and outputs the multiple baseband signals to the modulation module after parallel-to-serial conversion. The modulation module modulates and amplifies the signals and sends them to the laser transceiver terminal;

[0021] Step 4, using the two branch signals output by the coherent receiving module of the first laser time-frequency transfer system to obtain the error signal of the local laser and the receiving laser, inputting the error signal into two optical phase-locked loops, and realizing the optical carrier synchronization through the two-stage phase-locked loop;

[0022] Step 5, connecting the received optical signal output by the laser transceiver terminal of the first laser time-frequency transmission system and the local laser signal output by the modulation module and delayed by the delay line to the coherent receiving module to complete coherent reception and data demodulation;

[0023] Step 6, using the digital signal processing unit of the first laser time-frequency transfer system to perform chip-level multi-channel parallel code correlation processing, and delaying the pseudo code signal output by the digital signal processing unit through a delay line to achieve code synchronization;

[0024] Step 7, performing the same operations as those of the first laser time-frequency transfer system in steps 1-6 on the second laser time-frequency transfer system;

[0025] Step 8, collect the one-way delay measurement values ​​from the first laser time-frequency transfer system to the second laser time-frequency transfer system and the one-way delay measurement values ​​from the second laser time-frequency transfer system to the first laser time-frequency transfer system, calculate the clock difference between the two atomic clocks, and complete the comparison of the two atomic clocks.

[0026] Further, step 2 includes the following sub-steps:

[0027] Step 21, connecting the optical frequency comb signal inside the optical comb frequency synthesis unit of the first laser time-frequency transfer system and the optical frequency signal output by the narrow linewidth laser to a photodetector to obtain a radio frequency signal;

[0028] Step 22, dividing the RF signal and the output signal of the atomic clock and connecting them to a mixer, and connecting the mixed signal to a loop filter;

[0029] Step 23, connecting the signal output by the loop filter to a voltage-controlled crystal oscillator, and connecting the output signal of the voltage-controlled crystal oscillator to an acousto-optic frequency shifter;

[0030] Step 24, adjust the loop filter parameters, and after the loop is stable, lock the narrow linewidth laser of the first laser time-frequency transfer system onto the optical comb of the optical comb frequency synthesis unit.

[0031] Further, step 3 includes the following sub-steps:

[0032] Step 31, using the optical microwave module inside the optical comb frequency synthesis unit to generate a pseudo code clock and an AD sampling clock from the optical comb signal;

[0033] Step 32, the frequency synthesis circuit in the digital signal processing unit divides the clock for generating the pseudo code into a clock that can be used by the FPGA chip in the digital signal processing unit, and uses the clock as a reference to drive multiple channels to generate pseudo codes in parallel inside the FPGA chip, and modulates data on the pseudo codes to generate baseband signals;

[0034] Step 33, performing parallel-to-serial conversion on the generated multi-channel baseband signals in the FPGA chip, and outputting the baseband signals through the high-speed interface of the FPGA chip;

[0035] Step 34, the baseband signal is sent to the modulation module, and after being modulated and amplified by the modulation module, the baseband signal is modulated onto light, and the modulated signal is amplified and sent to the laser transceiver terminal.

[0036] Further, in step 4, the two branch signals of the coherent receiving module are respectively generated by two balanced detectors inside the coherent receiving module;

[0037] An optical phase-locked loop is used to adjust the piezoelectric ceramic port of the narrow-linewidth laser to achieve large-range slow tuning of the laser signal; at the same time, another optical phase-locked loop is used to adjust the acousto-optic frequency shifter to achieve small-range fast tuning of the laser signal, ultimately achieving optical carrier synchronization.

[0038] Furthermore, in step 5, the optical signal output by the laser transceiver terminal and the local laser signal output by the modulator after being delayed by a delay line are connected to a 90° optical mixer in the coherent receiving module;

[0039] The 90° optical mixer is configured to output four optical signals of 0°, 90°, 180° and 270°;

[0040] The optical signals at 0° and 180° are connected to a balanced detector, and the optical signals at 90° and 270° are connected to another balanced detector to achieve coherent reception and data demodulation.

[0041] Furthermore, in step 6, the coherent receiving module output signal of the first laser time-frequency transfer system is used to enter the digital signal processing unit for chip-level multi-channel parallel code correlation processing, and then two groups of delay lines are used to delay the pseudo code signal output by the digital signal processing unit respectively to achieve code synchronization;

[0042] The two groups of delay lines are divided into optical delay lines and electrical delay lines. The optical delay lines delay the optical signal output by the modulation module, and the electrical delay lines delay the electrical signal output by the digital signal processing unit.

[0043] Further, in step 8, when the respective digital signal processing units of the first laser time-frequency transfer system and the second laser time-frequency transfer system find the maximum correlation peak, the corresponding FPGA chip internal chip-level delay adjustment amount and the delay line adjustment amount are added together to obtain the one-way delay value from the first laser time-frequency transfer system to the second laser time-frequency transfer system and the one-way delay value from the second laser time-frequency transfer system to the first laser time-frequency transfer system;

[0044] Next, according to the measured one-way delay value ΔT from the first laser time-frequency transfer system to the second laser time-frequency transfer system AB And the one-way delay measurement value ΔT from the second laser time-frequency transfer system to the first laser time-frequency transfer BA , use the following formula to calculate the clock difference ΔT between the two atomic clocks:

[0045] ΔT=(ΔT BA -ΔT AB ) / 2-ΔT L

[0046] Where, ΔT L Indicates the error value of link nonreciprocity error and device delay error.

[0047] Compared with the prior art, the present invention has the following technical effects:

[0048] The laser time transfer system and method based on high-speed pseudo-code of the present invention utilizes an optical comb to realize locking of a common narrow-linewidth laser to an atomic clock reference frequency, making the optical carrier more stable and accurate; a laser carrier homologous to the atomic clock is used to carry a high-speed pseudo-code (code rate ≥ 1Gcps) to realize time transfer, and high-precision code correlation measurement is realized by combining the two schemes of realizing coarse delay at the chip level in the FPGA and realizing fine delay better than 1 chip using a delay line. The transmitted high-speed pseudo-code can realize the transfer and comparison of time, which is an effective way to compare high-precision atomic clocks in space, meets the requirements of time-frequency transfer and comparison of new atomic clocks, and is suitable for industrial use and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a structural diagram of a laser time transfer system based on high-speed pseudo code in one embodiment of the present invention. DETAILED DESCRIPTION

[0050] It should be noted that, unless otherwise specified, all components in the present invention are components known in the prior art. For example, a 90° optical mixer is a known and commonly used 90° optical mixer.

[0051] All operations in the present invention, unless otherwise specified, all adopt methods known in the prior art. For example, in step 24, when adjusting the loop filter parameters, the adjustment method adopts the existing method known in the prior art.

[0052] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0053] A laser time transfer system based on high-speed pseudo code includes a laser time-frequency transfer system, which includes an atomic clock, an optical comb frequency synthesis unit, two narrow linewidth lasers, two modulation modules, an amplifier, a digital signal processing unit, two optical phase-locked loops, an acousto-optic frequency shifter, two groups of delay lines, a coherent receiving module, and a laser transceiver terminal;

[0054] like Figure 1As shown, the first laser time-frequency transfer system includes an atomic clock 1, an optical comb frequency synthesis unit 1, a narrow linewidth laser 1, a modulation module 1, an amplifier 1, a digital signal processing unit 1, an optical phase-locked loop 1, an optical phase-locked loop 2, a narrow linewidth laser 2, an acousto-optic frequency shifter 1, a modulation module 2, a delay line 1, a delay line 2, a coherent receiving module 1 and a laser transceiver terminal 1;

[0055] The second laser time-frequency transfer system includes an atomic clock 2, an optical comb frequency synthesis unit 2, a narrow linewidth laser 3, a modulation module 3, an amplifier 2, a digital signal processing unit 2, an optical phase-locked loop 3, an optical phase-locked loop 4, a narrow linewidth laser 4, an acousto-optic frequency shifter 2, a modulation module 4, a delay line 3, a delay line 4, a coherent receiving module 2 and a laser transceiver terminal 2.

[0056] It should be noted that the components in the laser time-frequency transfer system and the connection methods between the components are all known in the prior art. Those skilled in the art know how to connect the components, and the connection relationship between the components is not part of the content discussed in this embodiment and will not be elaborated on.

[0057] Among them, the laser time-frequency transfer system is mainly used to complete the functions of modulation and demodulation, transmission and reception, and signal processing. The working principle of the laser time-frequency transfer system is further explained below in combination with specific components.

[0058] Atomic clocks include a variety of microwave atomic clocks and optical clocks, which are used to provide frequency reference sources for laser time and frequency transfer systems. According to conventional selection, atomic clocks include common microwave atomic clocks such as hydrogen clocks, cesium clocks, rubidium clocks, mercury ion clocks, and integrating sphere clocks. They can also include optical atomic clocks such as strontium atomic optical clocks, aluminum ion optical clocks, and calcium ion optical clocks to provide frequency reference sources for laser time and frequency transfer systems.

[0059] The optical comb frequency synthesis unit includes an optical comb, an optical comb locking unit and an optically generated microwave unit; the optical comb, the optical comb locking unit and the optically generated microwave unit are all known units in the prior art, and their connection relationship is well known in the prior art and will not be described in detail.

[0060] The optical comb locking unit includes a photodetector, a mixer, a loop filter, a voltage-controlled crystal oscillator and an acousto-optic frequency shifter.

[0061] The optical comb locking unit is used to lock the narrow line width laser to the optical comb, lock the optical comb of the optical comb frequency synthesis unit to the atomic clock, provide the required high frequency signal for the digital signal processing unit, generate the clock for pseudo code and the clock for AD sampling;

[0062] The digital signal processing unit includes FPGA chip, frequency synthesis circuit and AD;

[0063] The FPGA chip frequency synthesis circuit and AD are both known contents in the prior art, and the connection relationship between the FPGA chip and the frequency synthesis circuit and AD is also known contents in the prior art.

[0064] The following further describes the functions of the components in the digital signal processing unit in combination with specific components:

[0065] The FPGA chip can generate pseudo codes in parallel in multiple channels and modulate data on the pseudo codes, generate time reference signals, and convert multiple baseband signals into serial and parallel signals and output them to the modulation module;

[0066] The modulation module is used to modulate and amplify the received signal and then send it to the laser transceiver terminal;

[0067] The coherent receiving module contains a 90° optical mixer and two balanced detectors;

[0068] The coherent receiving module can output branch signals, and the error signals between the local laser and the receiving laser can be obtained according to the branch signals; the error signals are input into two optical phase-locked loops to realize optical carrier synchronization through two-stage optical phase-locked loops.

[0069] The coherent receiving module is also capable of coherent reception and separation of optical and electrical signals;

[0070] Furthermore, there are two groups of laser time-frequency transfer systems, namely a first laser time-frequency transfer system and a second laser time-frequency transfer system configured on different satellites; the first laser time-frequency transfer system and the second laser time-frequency transfer system are symmetrical in structure and have the same function.

[0071] Specifically, the wavelength difference between the first laser time-frequency transfer system and the second laser time-frequency transfer system is ≥ 0.8nm, and the AD sampling rate is ≥ twice the code rate; the FPGA chip includes a high-speed data transmission interface. The above settings are all preferred solutions based on actual use needs, which are beneficial to improving work efficiency in actual use.

[0072] A laser time transfer method based on high-speed pseudo-code, based on the above-mentioned laser time transfer system based on high-speed pseudo-code, comprises the following steps:

[0073] Step 1: for the first laser time-frequency transfer system, lock the optical comb of the optical comb frequency synthesis unit to the atomic clock;

[0074] Step 2: for the first laser time-frequency transfer system, lock the narrow linewidth laser to the optical comb of the optical comb frequency synthesis unit;

[0075] Step 3, the first laser time-frequency transmission system generates a clock for generating a pseudo code and a clock for AD sampling through an optical comb frequency synthesis unit, generates pseudo codes in parallel in multiple channels in the FPGA chip, modulates data on the pseudo codes, generates baseband signals, and outputs the multiple baseband signals to the modulation module after parallel-to-serial conversion. The modulation module modulates and amplifies the signals and sends them to the laser transceiver terminal;

[0076] Step 4, using the two branch signals output by the coherent receiving module of the first laser time-frequency transfer system to obtain the error signal of the local laser and the receiving laser, inputting the error signal into two optical phase-locked loops, and realizing the optical carrier synchronization through the two-stage phase-locked loop;

[0077] Step 5, connecting the received optical signal output by the laser transceiver terminal of the first laser time-frequency transmission system and the local laser signal output by the modulation module and delayed by the delay line to the coherent receiving module to complete coherent reception and data demodulation;

[0078] Step 6, using the digital signal processing unit of the first laser time-frequency transfer system to perform chip-level multi-channel parallel code correlation processing, and delaying the pseudo code signal output by the digital signal processing unit through a delay line to achieve code synchronization;

[0079] Step 7, performing the same operations as those of the first laser time-frequency transfer system in steps 1-6 on the second laser time-frequency transfer system;

[0080] Step 8, collect the one-way delay measurement values ​​from the first laser time-frequency transfer system to the second laser time-frequency transfer system and the one-way delay measurement values ​​from the second laser time-frequency transfer system to the first laser time-frequency transfer system, calculate the clock difference between the two atomic clocks, and complete the comparison of the two atomic clocks.

[0081] Further, step 2 includes the following sub-steps:

[0082] Step 21, connecting the optical frequency comb signal inside the optical comb frequency synthesis unit of the first laser time-frequency transfer system and the optical frequency signal output by the narrow linewidth laser to a photodetector to obtain a radio frequency signal;

[0083] Step 22, dividing the RF signal and the output signal of the atomic clock and connecting them to a mixer, and connecting the mixed signal to a loop filter;

[0084] Step 23, connecting the signal output by the loop filter to a voltage-controlled crystal oscillator, and connecting the output signal of the voltage-controlled crystal oscillator to an acousto-optic frequency shifter;

[0085] Step 24, adjust the loop filter parameters, and after the loop is stable, lock the narrow linewidth laser of the first laser time-frequency transfer system onto the optical comb of the optical comb frequency synthesis unit.

[0086] Further, step 3 includes the following sub-steps:

[0087] Step 31, using the optical microwave module inside the optical comb frequency synthesis unit to generate a pseudo code clock and an AD sampling clock from the optical comb signal;

[0088] Step 32, the frequency synthesis circuit in the digital signal processing unit divides the clock for generating the pseudo code into a clock that can be used by the FPGA chip in the digital signal processing unit, and uses the clock as a reference to drive multiple channels to generate pseudo codes in parallel inside the FPGA chip, and modulates data on the pseudo codes to generate baseband signals;

[0089] Step 33, performing parallel-to-serial conversion on the generated multi-channel baseband signals in the FPGA chip, and outputting the baseband signals through the high-speed interface of the FPGA chip;

[0090] Step 34, the baseband signal is sent to the modulation module, and after being modulated and amplified by the modulation module, the baseband signal is modulated onto light, and the modulated signal is amplified and sent to the laser transceiver terminal.

[0091] Furthermore, in step 4, two branch signals of the coherent receiving module are respectively generated by two balanced detectors inside the coherent receiving module; wherein the optical delay line output signal serves as the local laser of the coherent receiving module, and the laser transceiver terminal output signal serves as the receiving laser of the coherent receiving module.

[0092] An optical phase-locked loop is used to adjust the piezoelectric ceramic port of the narrow-linewidth laser to achieve large-range slow tuning of the laser signal; at the same time, another optical phase-locked loop is used to adjust the acousto-optic frequency shifter to achieve small-range fast tuning of the laser signal, so that the frequency and phase of the local laser signal are consistent with the received optical signal, realizing zero-difference reception.

[0093] Furthermore, in step 5, the optical signal output by the laser transceiver terminal and the local laser signal output by the modulator after being delayed by a delay line are connected to a 90° optical mixer in the coherent receiving module;

[0094] The 90° optical mixer is made to output four optical signals of 0°, 90°, 180° and 270°;

[0095] The optical signals at 0° and 180° are connected to a balanced detector, and the optical signals at 90° and 270° are connected to another balanced detector to achieve coherent reception and data demodulation.

[0096] Furthermore, in step 6, the delay lines are divided into two groups: optical delay lines and electrical delay lines. The optical delay lines delay the optical signals output by the modulation module, and the electrical delay lines delay the electrical signals output by the digital signal processing unit.

[0097] Further, in step 8, when the respective digital signal processing units of the first laser time-frequency transfer system and the second laser time-frequency transfer system find the maximum correlation peak, the corresponding FPGA chip internal chip-level delay adjustment amount and the delay line adjustment amount are added together to obtain the one-way delay value from the first laser time-frequency transfer system to the second laser time-frequency transfer system and the one-way delay value from the second laser time-frequency transfer system to the first laser time-frequency transfer system;

[0098] Next, according to the measured one-way delay value ΔT from the first laser time-frequency transfer system to the second laser time-frequency transfer system AB And the one-way delay measurement value ΔT from the second laser time-frequency transfer system to the first laser time-frequency transfer BA , use the following formula to calculate the clock difference ΔT between the two atomic clocks:

[0099] ΔT=(ΔT BA -ΔT AB ) / 2-ΔT L

[0100] Where, ΔT L Indicates the error value of the link non-reciprocity error and the device delay error. The error value of the link non-reciprocity error and the device delay error can be calculated and obtained by a conventional method in the art.

Claims

1. A laser time transfer system based on high-speed pseudo-code, characterized in that: It includes a laser time-frequency transmission system, which includes an atomic clock, an optical comb frequency synthesis unit, two narrow linewidth lasers, two modulation modules, an amplifier, a digital signal processing unit, two optical phase-locked loops, an acousto-optic frequency shifter, two groups of delay lines, a coherent receiving module and a laser transceiver terminal; The atomic clocks include various microwave atomic clocks and optical clocks; The optical comb frequency synthesis unit comprises an optical comb, an optical comb locking unit and an optically generated microwave unit; The optical comb locking unit comprises a photodetector, a mixer, a loop filter, a voltage-controlled crystal oscillator and an acousto-optic frequency shifter; The digital signal processing unit includes an FPGA chip, a frequency synthesis circuit and an AD; The coherent receiving module comprises a 90° optical mixer and two balanced detectors; The laser time-frequency transfer system has two groups, namely a first laser time-frequency transfer system and a second laser time-frequency transfer system configured on different satellites; the first laser time-frequency transfer system and the second laser time-frequency transfer system have symmetrical structures and the same functions.

2. The laser time transfer system based on high-speed pseudo-code as claimed in claim 1, characterized in that: The wavelength difference between the first laser time-frequency transfer system and the second laser time-frequency transfer system is ≥0.8nm.

3. The laser time transfer system based on high-speed pseudo-code as claimed in claim 1, characterized in that: The sampling rate of the AD is ≥ twice the code rate; The FPGA chip includes a high-speed data transmission interface.

4. A laser time transfer method based on high-speed pseudo-code, the method is based on the laser time transfer system based on high-speed pseudo-code according to claims 1-3, characterized in that: The following steps are involved: Step 1: for the first laser time-frequency transfer system, lock the optical comb of the optical comb frequency synthesis unit to the atomic clock; Step 2: for the first laser time-frequency transfer system, lock the narrow linewidth laser to the optical comb of the optical comb frequency synthesis unit; Step 3, the first laser time-frequency transmission system generates a clock for generating a pseudo code and a clock for AD sampling through an optical comb frequency synthesis unit, generates pseudo codes in parallel in multiple channels in the FPGA chip, modulates data on the pseudo codes, generates baseband signals, and outputs the multiple baseband signals to the modulation module after parallel-to-serial conversion. The modulation module modulates and amplifies the signals and sends them to the laser transceiver terminal; Step 4, using the two branch signals output by the coherent receiving module of the first laser time-frequency transfer system to obtain the error signal of the local laser and the receiving laser, inputting the error signal into two optical phase-locked loops, and realizing the optical carrier synchronization through the two-stage phase-locked loop; Step 5, connecting the received optical signal output by the laser transceiver terminal of the first laser time-frequency transmission system and the local laser signal output by the modulation module and delayed by the delay line to the coherent receiving module to complete coherent reception and data demodulation; Step 6, using the digital signal processing unit of the first laser time-frequency transfer system to perform chip-level multi-channel parallel code correlation processing, and delaying the pseudo code signal output by the digital signal processing unit through a delay line to achieve code synchronization; Step 7, performing the same operations as those of the first laser time-frequency transfer system in steps 1-6 on the second laser time-frequency transfer system; Step 8, collect the one-way delay measurement values ​​from the first laser time-frequency transfer system to the second laser time-frequency transfer system and the one-way delay measurement values ​​from the second laser time-frequency transfer system to the first laser time-frequency transfer system, calculate the clock difference between the two atomic clocks, and complete the comparison of the two atomic clocks.

5. The laser time transfer method based on high-speed pseudo code as claimed in claim 4, characterized in that: Step 2 includes the following sub-steps: Step 21, connecting the optical frequency comb signal inside the optical comb frequency synthesis unit of the first laser time-frequency transfer system and the optical frequency signal output by the narrow linewidth laser to a photodetector to obtain a radio frequency signal; Step 22, dividing the RF signal and the output signal of the atomic clock and connecting them to a mixer, and connecting the mixed signal to a loop filter; Step 23, connecting the signal output by the loop filter to a voltage-controlled crystal oscillator, and connecting the output signal of the voltage-controlled crystal oscillator to an acousto-optic frequency shifter; Step 24, adjust the loop filter parameters, and after the loop is stable, lock the narrow linewidth laser of the first laser time-frequency transfer system onto the optical comb of the optical comb frequency synthesis unit.

6. The laser time transfer method based on high-speed pseudo code as claimed in claim 5, characterized in that: Step 3 includes the following sub-steps: Step 31, using the optical microwave module inside the optical comb frequency synthesis unit to generate a pseudo code clock and an AD sampling clock from the optical comb signal; Step 32, the frequency synthesis circuit in the digital signal processing unit divides the clock for generating the pseudo code into a clock that can be used by the FPGA chip in the digital signal processing unit, and uses the clock as a reference to drive multiple channels to generate pseudo codes in parallel inside the FPGA chip, and modulates data on the pseudo codes to generate baseband signals; Step 33, performing parallel-to-serial conversion on the generated multi-channel baseband signals in the FPGA chip, and outputting the baseband signals through the high-speed interface of the FPGA chip; Step 34, the baseband signal is sent to the modulation module, and after being modulated and amplified by the modulation module, the baseband signal is modulated onto light, and the modulated signal is amplified and sent to the laser transceiver terminal.

7. The laser time transfer method based on high-speed pseudo code as claimed in claim 5, characterized in that: In step 4, two branch signals of the coherent receiving module are respectively generated by two balanced detectors inside the coherent receiving module; An optical phase-locked loop is used to adjust the piezoelectric ceramic port of the narrow-linewidth laser to achieve large-range slow tuning of the laser signal; at the same time, another optical phase-locked loop is used to adjust the acousto-optic frequency shifter to achieve small-range fast tuning of the laser signal, ultimately achieving optical carrier synchronization.

8. The laser time transfer method based on high-speed pseudo code as claimed in claim 5, characterized in that: In step 5, the optical signal output by the laser transceiver terminal and the local laser signal output by the modulator after being delayed by a delay line are connected to the 90° optical mixer in the coherent receiving module; The 90° optical mixer is configured to output four optical signals of 0°, 90°, 180° and 270°; The optical signals at 0° and 180° are connected to a balanced detector, and the optical signals at 90° and 270° are connected to another balanced detector to achieve coherent reception and data demodulation.

9. The laser time transfer method based on high-speed pseudo code as claimed in claim 5, characterized in that: In step 6, the coherent receiving module output signal of the first laser time-frequency transfer system is used to enter the digital signal processing unit for chip-level multi-channel parallel code correlation processing, and then two groups of delay lines are used to delay the pseudo code signal output by the digital signal processing unit to achieve code synchronization; The two groups of delay lines are divided into optical delay lines and electrical delay lines. The optical delay lines delay the optical signal output by the modulation module, and the electrical delay lines delay the electrical signal output by the digital signal processing unit.

10. The laser time transfer method based on high-speed pseudo code as claimed in claim 5, characterized in that: In step 8, when the respective digital signal processing units of the first laser time-frequency transfer system and the second laser time-frequency transfer system find the maximum correlation peak, the corresponding FPGA chip internal chip-level delay adjustment amount and the delay line adjustment amount are added together to obtain the one-way delay value from the first laser time-frequency transfer system to the second laser time-frequency transfer system and the one-way delay value from the second laser time-frequency transfer system to the first laser time-frequency transfer system; Next, according to the measured one-way delay value ΔT from the first laser time-frequency transfer system to the second laser time-frequency transfer system AB And the one-way delay measurement value ΔT from the second laser time-frequency transfer system to the first laser time-frequency transfer BA , use the following formula to calculate the clock difference ΔT between the two atomic clocks: ΔT=(ΔT BA -ΔT AB ) / 2-ΔT L Where, ΔT L Indicates the error value of link nonreciprocity error and device delay error.

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