A laser time transfer system and method based on high-speed pseudocode

Abstract

This invention discloses a laser time transfer system and method based on high-speed pseudocode. It utilizes an optical comb to lock a conventional narrow-linewidth laser to the reference frequency of an atomic clock, making the optical carrier more stable and accurate. A high-speed pseudocode is carried on a laser carrier derived from the atomic clock to achieve time transfer. High-precision code correlation measurement is achieved by combining two schemes: implementing chip-level coarse delay within an FPGA and using delay lines to achieve a fine delay better than one chip. The transferred high-speed pseudocode enables time transfer and comparison, providing an effective method for high-precision spatial atomic clock comparison, meeting the time-frequency transfer and comparison requirements of new atomic clocks, and is suitable for industrial use and promotion.

Description

Technical Field

[0001] This invention belongs to the field of time and frequency, and specifically relates to a laser time transfer system and method based on high-speed pseudocode. Background Technology

[0002] In recent years, the frequency stability and uncertainty of new atomic clocks have been greatly improved, with microwave atomic clocks achieving second-level frequency stability of 10. -13 The magnitude and frequency stability have reached 10. -16 The magnitude is significant, and the integrating sphere atomic clock has already been carried onto the Chinese space station.

[0003] Optical atomic clocks achieve second-level frequency stability of 10 -15 The magnitude, frequency stability, and uncertainty have all reached 10. -18 Order of magnitude. Traditional space time-frequency transport links are typically microwave time-frequency transport links and time transport links based on laser pulse time-of-flight measurements. Second-level time-frequency transport incurs an additional instability of 10-1. -11 ~10 -12 The magnitude of the time-frequency transmission instability is 10. -15 ~10 -16 The scale is insufficient to meet the time-frequency transmission and comparison requirements of new atomic clocks. Summary of the Invention

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

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A laser time transfer system based on high-speed pseudocode 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 sets 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 includes an optical comb, an optical comb locking unit, and an optically generated microwave unit;

[0009] The optical comb locking unit includes 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 converter;

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

[0012] The laser time-frequency transmission system consists of two sets, namely a first laser time-frequency transmission system and a second laser time-frequency transmission system configured on different satellites; the first laser time-frequency transmission system and the second laser time-frequency transmission 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 transmission system and the second laser time-frequency transmission system is ≥0.8nm.

[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 pseudocode, which is based on the aforementioned laser time transfer system based on high-speed pseudocode, includes the following steps:

[0018] Step 1: For the first laser time-frequency transmission 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 transmission system, lock the narrow linewidth laser onto 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 pseudo-code and an AD sampling clock through the optical comb frequency synthesis unit. Pseudo-code is generated in parallel in multiple channels in the FPGA chip, and data is modulated on the pseudo-code to generate baseband signals. After parallel-to-serial conversion of multiple baseband signals, they are output to the modulation module. The modulation module modulates and amplifies the signals before sending them to the laser transceiver terminal.

[0021] Step 4: Use the two branch signals output by the coherent receiving module of the first laser time-frequency transmission system to obtain the error signals of the local laser and the received laser. Input the error signals into two optical phase-locked loops and realize optical carrier synchronization through two-stage phase-locked loops.

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

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

[0024] Step 7: Perform the same operations as steps 1-6 on the second laser time-frequency transfer system as on the first laser time-frequency transfer system;

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

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

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

[0028] Step 22: After the radio frequency signal is divided, it is connected to the mixer along with the output signal of the atomic clock, and the mixed signal is connected to the loop filter.

[0029] Step 23: Connect the signal output from the loop filter to the voltage-controlled crystal oscillator, and connect the output signal of the voltage-controlled crystal oscillator to the acousto-optic frequency shifter;

[0030] Step 24: Adjust the loop filter parameters. After the loop stabilizes, lock the narrow linewidth laser of the first laser time-frequency transmission system onto the optical comb of the optical comb frequency synthesis unit.

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

[0032] Step 31: Use the optically generated microwave module inside the optical comb frequency synthesis unit to generate the clock for pseudocode and the clock for AD sampling from the optical comb signal;

[0033] Step 32: The frequency synthesis circuit in the digital signal processing unit divides the clock that generates the pseudocode into a clock that the FPGA chip in the digital signal processing unit can use. Using this clock as a reference, the FPGA chip drives multiple parallel pseudocode generation and modulates data on the pseudocode to generate a baseband signal.

[0034] Step 33: The generated multi-channel baseband signals are converted from parallel to serial in the FPGA chip, and the baseband signals are output through the high-speed interface of the FPGA chip.

[0035] Step 34: The baseband signal is sent to the modulation module. After modulation and amplification by the modulation module, the baseband signal is modulated onto the light. The modulated signal is then amplified and sent to the laser transceiver terminal.

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

[0037] A single optical phase-locked loop is used to adjust the piezoelectric ceramic port of a narrow-linewidth laser to achieve slow tuning of the laser signal over a wide range; simultaneously, another optical phase-locked loop is used to tune an acousto-optic frequency shifter to achieve fast tuning of the laser signal over a small range, ultimately achieving optical carrier synchronization.

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

[0039] The 90° optical mixer outputs four optical signals: 0°, 90°, 180°, and 270°.

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

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

[0042] The two sets 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] Furthermore, in step 8, when the digital signal processing units of the first laser time-frequency transmission system and the second laser time-frequency transmission system find the maximum correlation peak, the corresponding chip-level delay adjustment and delay line adjustment of the FPGA chip are added together to obtain the one-way delay value from the first laser time-frequency transmission system to the second laser time-frequency transmission system and the one-way delay value from the second laser time-frequency transmission system to the first laser time-frequency transmission system.

[0044] Next, based on the measured one-way time delay ΔT from the first laser time-frequency transfer system to the second laser time-frequency transfer system... AB And the unidirectional time delay measurement value ΔT from the second laser time-frequency transmission system to the first laser time-frequency transmission system. BA The clock difference ΔT between two atomic clocks is calculated using the following formula:

[0045] ΔT=(ΔT BA -ΔT AB ) / 2-ΔT L

[0046] Where, ΔT L This represents the error value for link non-reciprocity error and device delay error.

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

[0048] This invention relates to a laser time transfer system and method based on high-speed pseudocode. It utilizes an optical comb to lock a conventional narrow-linewidth laser to the reference frequency of an atomic clock, resulting in a more stable and accurate optical carrier. A high-speed pseudocode (code rate ≥ 1 Gcps) is carried on a laser carrier derived from the atomic clock to achieve time transfer. High-precision code correlation measurements are achieved by combining two approaches: implementing chip-level coarse delay within an FPGA and using delay lines to achieve a fine delay better than one chip. The transferred high-speed pseudocode enables time transfer and comparison, providing an effective method for high-precision spatial atomic clock comparison. It meets the time-frequency transfer and comparison requirements of new atomic clocks and is suitable for industrial use and promotion. Attached Figure Description

[0049] Figure 1 This is a structural diagram of a laser time transfer system based on high-speed pseudocode in one embodiment of the present invention. Detailed Implementation

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

[0051] Unless otherwise specified, all operations in this invention employ methods known in the prior art. For example, in step 24, when adjusting the loop filter parameters, the adjustment method employs existing methods known in the prior art.

[0052] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0053] A laser time transfer system based on high-speed pseudocode 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 sets of delay lines, a coherent receiving module, and a laser transceiver terminal.

[0054] like Figure 1As shown, the first laser time and frequency transmission system includes an atomic clock 1, an optical comb frequency integration 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 and frequency transmission system includes an atomic clock 2, an optical comb frequency integration 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 transmission system and the connection methods between the components are all known existing contents in the prior art. Those skilled in the art know how the components are connected, and the connection relationship between the components is not the subject of this embodiment and will not be described in detail.

[0057] The laser time-frequency transmission 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 transmission system will be further explained below with reference to specific components.

[0058] Atomic clocks include various microwave atomic clocks and optical clocks, used to provide a frequency reference source for laser time and frequency transmission systems. Depending on the choice, 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 a frequency reference source for laser time and frequency transmission systems.

[0059] The optical comb frequency synthesis unit includes an optical comb, an optical comb locking unit, and an optical microwave generation unit; the optical comb, optical comb locking unit, and optical microwave generation unit are all known units in the prior art, and their connection relationships are common knowledge in the prior art, so they will not be described in detail here.

[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 linewidth laser onto the optical comb, the optical comb frequency synthesis unit locks the optical comb onto the atomic clock, provides the required high-frequency signal to the digital signal processing unit, generates the clock for pseudocode, and provides the clock for AD sampling.

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

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

[0064] The following section further explains the role of specific components within the digital signal processing unit:

[0065] FPGA chips can generate pseudocode in multiple parallel channels and modulate data on the pseudocode to generate time base signals. They can also convert multiple baseband signals from serial to parallel and output them to the modulation module.

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

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

[0068] The coherent receiving module can output tributary signals, and the error signals of the local laser and the received laser can be obtained from the tributary signals. By inputting the error signals into two optical phase-locked loops, optical carrier synchronization can be achieved through two-stage optical phase-locked loops.

[0069] The coherent receiver module can also coherently receive and separate optical and electrical signals;

[0070] Furthermore, there are two sets of laser time and frequency transmission systems, namely the first laser time and frequency transmission system and the second laser time and frequency transmission system, which are configured on different satellites; the first laser time and frequency transmission system and the second laser time and frequency transmission system have symmetrical structures and the same functions.

[0071] Specifically, the wavelength difference between the first laser time-frequency transmission system and the second laser time-frequency transmission 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 usage needs, which are conducive to improving work efficiency in actual use.

[0072] A laser time transfer method based on high-speed pseudocode, which is based on the aforementioned laser time transfer system based on high-speed pseudocode, includes the following steps:

[0073] Step 1: For the first laser time-frequency transmission 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 transmission system, lock the narrow linewidth laser onto 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 pseudo-code and an AD sampling clock through the optical comb frequency synthesis unit. Pseudo-code is generated in parallel in multiple channels in the FPGA chip, and data is modulated on the pseudo-code to generate baseband signals. After parallel-to-serial conversion of multiple baseband signals, they are output to the modulation module. The modulation module modulates and amplifies the signals before sending them to the laser transceiver terminal.

[0076] Step 4: Use the two branch signals output by the coherent receiving module of the first laser time-frequency transmission system to obtain the error signals of the local laser and the received laser. Input the error signals into two optical phase-locked loops and realize optical carrier synchronization through two-stage phase-locked loops.

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

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

[0079] Step 7: Perform the same operations as steps 1-6 on the second laser time-frequency transfer system as on the first laser time-frequency transfer system;

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

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

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

[0083] Step 22: After the radio frequency signal is divided, it is connected to the mixer along with the output signal of the atomic clock, and the mixed signal is connected to the loop filter.

[0084] Step 23: Connect the signal output from the loop filter to the voltage-controlled crystal oscillator, and connect the output signal of the voltage-controlled crystal oscillator to the acousto-optic frequency shifter;

[0085] Step 24: Adjust the loop filter parameters. After the loop stabilizes, lock the narrow linewidth laser of the first laser time-frequency transmission system onto the optical comb of the optical comb frequency synthesis unit.

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

[0087] Step 31: Use the optically generated microwave module inside the optical comb frequency synthesis unit to generate the clock for pseudocode and the clock for AD sampling from the optical comb signal;

[0088] Step 32: The frequency synthesis circuit in the digital signal processing unit divides the clock that generates the pseudocode into a clock that the FPGA chip in the digital signal processing unit can use. Using this clock as a reference, the FPGA chip drives multiple parallel pseudocode generation and modulates data on the pseudocode to generate a baseband signal.

[0089] Step 33: The generated multi-channel baseband signals are converted from parallel to serial in the FPGA chip, and the baseband signals are output through the high-speed interface of the FPGA chip.

[0090] Step 34: The baseband signal is sent to the modulation module. After modulation and amplification by the modulation module, the baseband signal is modulated onto the light. The modulated signal is then amplified and sent to the laser transceiver terminal.

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

[0092] A piezoelectric ceramic port of a narrow-linewidth laser is adjusted using an optical phase-locked loop to achieve slow tuning of the laser signal over a wide range; at the same time, another optical frequency shifter is used to tune the laser signal over a small range to achieve fast tuning, so that the frequency and phase of the local laser signal are consistent with the received optical signal, thus achieving zero-difference reception.

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

[0094] The 90° optical mixer outputs four optical signals: 0°, 90°, 180°, and 270°.

[0095] The optical signals at 0° and 180° are connected to one balanced detector, while the optical signals at 90° and 270° are connected to another balanced detector, enabling 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 signal output by the modulation module, and the electrical delay lines delay the electrical signal output by the digital signal processing unit.

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

[0098] Next, based on the measured one-way time delay ΔT from the first laser time-frequency transfer system to the second laser time-frequency transfer system... AB And the unidirectional time delay measurement value ΔT from the second laser time-frequency transmission system to the first laser time-frequency transmission system. BA The clock difference ΔT between two atomic clocks is calculated using the following formula:

[0099] ΔT=(ΔT BA -ΔT AB ) / 2-ΔT L

[0100] Where, ΔT L This represents the error values ​​of link non-reciprocity error and device delay error. The error values ​​of link non-reciprocity error and device delay error can be calculated using conventional methods in this field.

Claims

1. A laser time transfer system based on high-speed pseudocode, characterized in that, The system includes a laser time and frequency transmission system, which comprises an atomic clock, an optical comb frequency integration 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 sets 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 includes an optical comb, an optical comb locking unit, and an optically generated microwave unit; The optical comb locking unit includes 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 converter; The coherent receiving module includes a 90° optical mixer and two balanced detectors; The laser time-frequency transmission system consists of two sets, namely a first laser time-frequency transmission system and a second laser time-frequency transmission system configured on different satellites; the first laser time-frequency transmission system and the second laser time-frequency transmission system have symmetrical structures and the same functions; The laser time transfer system based on high-speed pseudocode includes the following steps: Step 1: For the first laser time-frequency transmission system, lock the optical comb of the optical comb frequency synthesis unit to the atomic clock; Step 2: For the first laser time-frequency transmission system, lock the narrow linewidth laser onto the optical comb of the optical comb frequency synthesis unit; Step 3: The first laser time-frequency transmission system generates a clock for generating pseudo-code and an AD sampling clock through the optical comb frequency synthesis unit. Pseudo-code is generated in parallel in multiple channels in the FPGA chip, and data is modulated on the pseudo-code to generate baseband signals. After parallel-to-serial conversion of multiple baseband signals, they are output to the modulation module. The modulation module modulates and amplifies the signals before sending them to the laser transceiver terminal. Step 4: Use the two branch signals output by the coherent receiving module of the first laser time-frequency transmission system to obtain the error signals of the local laser and the received laser. Input the error signals into two optical phase-locked loops and realize optical carrier synchronization through two-stage phase-locked loops. Step 5: Connect the received optical signal output from the laser transceiver terminal of the first laser time-frequency transmission system and the local laser signal output from the modulation module and delayed by the delay line to the coherent receiving module to complete coherent reception and data demodulation. Step 6: Use the digital signal processing unit of the first laser time-frequency transmission system to perform chip-level multi-channel parallel code correlation processing, and delay the pseudo-code signal output by the digital signal processing unit through a delay line to achieve code synchronization; Step 7: Perform the same operations as steps 1-6 on the second laser time-frequency transfer system as on the first laser time-frequency transfer system; Step 8: Collect the one-way time delay measurement values ​​from the first laser time-frequency transmission system to the second laser time-frequency transmission system and the one-way time delay measurement values ​​from the second laser time-frequency transmission system to the first laser time-frequency transmission system, calculate the clock difference between the two atomic clocks, and complete the comparison of the two atomic clocks.

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

3. The laser time transfer system based on high-speed pseudocode as described 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. The laser time transfer system based on high-speed pseudocode as described in any one of claims 1-3, characterized in that, Step 2 includes the following sub-steps: Step 21: Connect the optical frequency comb signal inside the optical comb frequency synthesis unit of the first laser time-frequency transmission system and the optical frequency signal output by the narrow linewidth laser to the photodetector to obtain the radio frequency signal; Step 22: After the radio frequency signal is divided, it is connected to the mixer along with the output signal of the atomic clock, and the mixed signal is connected to the loop filter. Step 23: Connect the signal output from the loop filter to the voltage-controlled crystal oscillator, and connect the output signal of the voltage-controlled crystal oscillator to the acousto-optic frequency shifter; Step 24: Adjust the loop filter parameters. After the loop stabilizes, lock the narrow linewidth laser of the first laser time-frequency transmission system onto the optical comb of the optical comb frequency synthesis unit.

5. The laser time transfer system based on high-speed pseudocode as described in claim 4, characterized in that, Step 3 includes the following sub-steps: Step 31: Use the optically generated microwave module inside the optical comb frequency synthesis unit to generate the clock for pseudocode and the clock for AD sampling from the optical comb signal; Step 32: The frequency synthesis circuit in the digital signal processing unit divides the clock that generates the pseudocode into a clock that the FPGA chip in the digital signal processing unit can use. Using this clock as a reference, the FPGA chip drives multiple parallel pseudocode generation and modulates data on the pseudocode to generate a baseband signal. Step 33: The generated multi-channel baseband signals are converted from parallel to serial in the FPGA chip, and the baseband signals are output through the high-speed interface of the FPGA chip. Step 34: The baseband signal is sent to the modulation module. After modulation and amplification by the modulation module, the baseband signal is modulated onto the light. The modulated signal is then amplified and sent to the laser transceiver terminal.

6. The laser time transfer system based on high-speed pseudocode as described in claim 5, characterized in that, In step 4, the two branch signals of the coherent receiving module are generated by two balanced detectors inside the coherent receiving module, respectively; A single optical phase-locked loop is used to adjust the piezoelectric ceramic port of a narrow-linewidth laser to achieve slow tuning of the laser signal over a wide range; simultaneously, another optical phase-locked loop is used to tune an acousto-optic frequency shifter to achieve fast tuning of the laser signal over a small range, ultimately achieving optical carrier synchronization.

7. The laser time transfer system based on high-speed pseudocode as described in claim 6, characterized in that, In step 5, the optical signal output from the laser transceiver terminal and the local laser signal output from the modulator and delayed by the delay line are connected to the 90° optical mixer in the coherent receiving module. The 90° optical mixer outputs four optical signals: 0°, 90°, 180°, and 270°. The optical signals at 0° and 180° are connected to one balanced detector, while the optical signals at 90° and 270° are connected to another balanced detector, enabling coherent reception and data demodulation.

8. The laser time transfer system based on high-speed pseudocode as described in claim 7, characterized in that, In step 6, the output signal of the coherent receiving module of the first laser time-frequency transmission system is used to enter the digital signal processing unit for chip-level multi-channel parallel code correlation processing. Then, two sets of delay lines are used to delay the pseudo-code signal output by the digital signal processing unit to achieve code synchronization. The two sets 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.

9. The laser time transfer system based on high-speed pseudocode as described in claim 8, characterized in that, In step 8, when the digital signal processing units of the first laser time-frequency transmission system and the second laser time-frequency transmission system find the maximum correlation peak, the corresponding chip-level delay adjustment and delay line adjustment of the FPGA chip are added together to obtain the one-way delay value from the first laser time-frequency transmission system to the second laser time-frequency transmission system and the one-way delay value from the second laser time-frequency transmission system to the first laser time-frequency transmission system. Next, based on the measured one-way time delay value from the first laser time-frequency transfer system to the second laser time-frequency transfer system... ΔT AB And the unidirectional time delay measurement value from the second laser time-frequency transmission system to the first laser time-frequency transmission system. ΔT BA The clock difference between two atomic clocks can be calculated using the following formula. ΔT : ΔT= （ ΔT BA -ΔT AB ） / 2-ΔT L in, ΔT L This represents the error value for link non-reciprocity error and device delay error.

Images