Laser ranging and time synchronization system with pseudo code modulation on sideband

Abstract

The invention discloses a laser ranging and time synchronization system with pseudo code modulation on a sideband. The system comprises a system A and a system B, the system A is arranged on a satellite A and comprises a first laser, a first clock, a first up-conversion unit, a first EOM, a first beam splitter, a first photoelectric detector, a first digital signal processing unit and a first laser transceiver module. The system B and the system A are basically the same in composition, and an optical phase-locked loop is additionally arranged. Pseudo codes and data are directly modulated on a sideband of dozens of MHz magnitude, and then a modulation signal is transmitted to an EOM after being up-converted to the GHz magnitude. Due to the fact that the pseudo code and the data are modulated on the clock sideband, the influence on a main carrier wave is smaller, in addition, due to the fact that the modulation degree of the pseudo code is low, the influence on the clock sideband is small, ranging and communication can be achieved, and laser interference measurement and clock sideband recovery are not affected.

Description

Technical Field

[0001] This invention relates to a laser ranging and time synchronization system with pseudocode modulation on the sideband, belonging to the field of time and frequency. Background Technology

[0002] In gravitational wave detection missions, high-precision laser ranging communication and sideband technology are crucial for achieving the detection target, directly determining the detection accuracy and success. Traditional space-based gravitational wave detection modulates a pseudocode signal onto the main carrier of laser interferometric displacement measurement (LIDM), with the modulated signal sharing the same spectrum and carrier with the LIDM signal. The pseudocode signal acts as noise relative to the LIDM signal, causing interference from the main lobe of the pseudocode signal, which limits the modulation depth and carrier-to-noise ratio of the pseudocode signal. To resolve the contradiction between ranging accuracy and LIDM measurement in space-based gravitational wave detection, it is urgent to research a pseudocode modulation method with low pseudocode equivalent noise at the main carrier. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a laser ranging and time synchronization system with pseudocode modulation on the sideband. The pseudocode is modulated on the sideband, and then the sideband signal with pseudocode is modulated onto the optical carrier to complete laser ranging and time synchronization. While realizing ranging and communication, it can reduce the impact of pseudocode equivalent noise on the main carrier. The technical solution of this invention is: A laser ranging and time synchronization system with pseudocode modulation on sidebands includes: system A and system B; system A is set on satellite A and includes a first laser, a first clock, a first up-conversion unit, a first EOM, a first beam splitter, a first photodetector, a first digital signal processing unit, and a first laser transceiver module; System B is installed on satellite B and includes a second laser, a second clock, an optical phase-locked loop, a second up-conversion unit, a second EOM, a second beam splitter, a second photodetector, a second digital signal processing unit, and a second laser transceiver module. The optical signal generated by the first laser of satellite A is sent to the first EOM; the first clock generates a clock reference signal and provides it to the first digital signal processing unit and the first up-conversion unit; The first upconversion unit generates a GHz-level modulation signal, i.e., a sideband modulation signal, based on the intermediate frequency signal output by the first digital signal processing unit and the clock reference signal. The signal is then sent to the first EOM to modulate the sideband modulation signal onto the optical signal and sent to the first beam splitter. The split optical signals are then sent to the first photodetector and the first laser transceiver module, respectively. The first laser transceiver module then sends the optical signal to the second laser transceiver module of satellite B. The second laser transceiver module coherently detects the received optical signal and the local oscillator optical signal from satellite B using a second photodetector. The coherent detection result is sent to an optical phase-locked loop to lock the output signal of the second laser onto the first laser. Simultaneously, the coherent detection result is also sent to a second digital signal processing unit for pseudocode ranging and data demodulation to obtain the one-way time delay measurement value ΔT from satellite A to satellite B. AB ; Similarly, the optical signal generated by the second laser of satellite B is modulated into an optical signal by the second clock, the second EOM, and the second up-conversion unit. This optical signal is then transmitted to the first laser transceiver module of satellite A via the second laser transceiver module. The first digital signal processing unit then measures the one-way time delay ΔT from satellite B to satellite A. BA ; Finally, the 1PPS clock difference ΔT of the first digital signal processing unit and the second digital signal processing unit, and the distance ΔL between satellite A and satellite B are obtained.

[0004] Furthermore, the laser generated by the first laser is an ultra-stable laser, serving as the master laser, while the second laser is a tunable narrow-linewidth laser, serving as the servo laser.

[0005] Furthermore, the system composition and operation mode of System A and System B are basically the same. By setting up an additional optical phase-locked loop in System B to receive the output signal of the second photodetector, performing frequency mixing and low-pass filtering to extract the phase error signal, and then controlling the second laser, so that the output signal of the second laser is locked on the received signal light, and then locked on the first laser.

[0006] Furthermore, the first digital signal processing unit uses the clock reference signal generated by the first clock as a reference to generate a 70MHz±20MHz signal, a pseudo code, and a data signal, and modulates the pseudo code and data signal onto the 70MHz±20MHz signal to generate an intermediate frequency signal, with a pseudo code modulation degree ≤2%; the modulated intermediate frequency signal is sent to the first up-conversion unit. The second digital signal processing unit uses the clock reference signal generated by the second clock as a reference to generate a 70MHz±20MHz signal, a pseudo code, and a data signal. It then modulates the pseudo code and data signal onto the 70MHz±20MHz signal to generate an intermediate frequency signal. The pseudo code modulation degree is ≤2%. The modulated intermediate frequency signal is then sent to the second up-conversion unit.

[0007] The first digital signal processing unit demodulates the signal output by the first photodetector using a clock reference signal generated by the first clock, and measures the one-way time delay ΔT from satellite B to satellite A. BAThe second digital signal processing unit demodulates the signal output by the second photodetector using a clock reference signal generated by the second clock, and measures the one-way time delay ΔT from satellite A to satellite B. AB .

[0008] Furthermore, the first clock generates two clock reference signals, which are sent to the first digital signal processing unit and the first up-conversion unit as clock references, respectively; the second clock generates three clock reference signals, which are sent to the optical phase-locked loop, the second digital signal processing unit, and the second up-conversion unit as clock references, respectively.

[0009] Furthermore, the first up-conversion unit generates a GHz-level modulation signal, i.e., a sideband modulation signal, based on the intermediate frequency signal output by the first digital signal processing unit and the clock reference signal, specifically: 1) Using the first clock output signal as a reference, generate a microwave signal in the GHz range; 2) The intermediate frequency signal output by the first digital signal processing unit is mixed and filtered with a microwave signal in the GHz range to obtain a modulation signal in the GHz range, namely the sideband modulation signal, wherein the sideband modulation degree is ≤20% and the ratio to the pseudocode modulation degree is ≥10. The second upconversion unit generates GHz-level modulation signals based on the clock reference signal in the same way as the first upconversion unit.

[0010] Furthermore, the 1PPS clock difference ΔT between the first digital signal processing unit and the second digital signal processing unit is ΔT = (ΔT AB -ΔT BA ) / 2-ΔT L1 ;ΔT L1 The sum of link non-reciprocity and device delay error; the distance between satellite A and satellite B, ΔL = (ΔT) AB +ΔT BA ) / 2-ΔT L2 ΔT L2 This refers to equipment delay error.

[0011] Secondly, the present invention also proposes a method for laser ranging and time synchronization with pseudocode modulation on sidebands, comprising: (1) Set up a first laser, a first clock, a first up-conversion unit, a first EOM, a first beam splitter, a first photodetector, a first digital signal processing unit, and a first laser transceiver module on satellite A; A second laser, a second clock, an optical phase-locked loop, a second up-conversion unit, a second EOM, a second beam splitter, a second photodetector, a second digital signal processing unit, and a second laser transceiver module are installed on satellite B. (2) An optical signal is generated by the first laser, and the optical signal generated by the first laser is sent to the first EOM; (3) The first clock generates two clock reference signals, which are sent to the first digital signal processing unit and the first up-conversion unit respectively as clock references; (4) Use the first up-conversion unit to generate a sideband modulation signal; (5) Modulate the sideband modulation signal of satellite A onto the optical signal and transmit it; send the sideband modulation signal of satellite A into the first EOM, the first EOM modulates the sideband modulation signal onto the optical signal, one beam is sent into the first photodetector; the other beam is sent into the first laser transceiver module; the first laser transceiver module sends the signal of satellite A to the second laser transceiver module of satellite B; (6) Satellite B processes the received signal; after receiving the signal, the second laser transceiver module of Satellite B sends the signal and the local oscillator light of Satellite B to the second photodetector for coherent detection; the beat frequency signal output by the second photodetector is split into two paths, one path is sent to the optical phase-locked loop, and the other path is sent to the second digital signal processing unit for pseudocode ranging and data demodulation to obtain the time delay value ΔT from Satellite A to Satellite B. AB ;ΔT AB Includes clock difference, equipment delay, and path delay information for both satellites, ΔT AB As data modulation on pseudocode; (7) The second laser of satellite B is locked to the first laser through an optical phase-locked loop. After receiving the output signal of the second photodetector, the optical phase-locked loop first mixes and filters it with the reference signal provided by the second clock to obtain a phase error signal. The phase error signal drives the second laser to adjust its frequency and phase. After the phase-locked loop completes the locking, the output signal of the second laser is locked to the first laser. (8) Use the second up-conversion unit to generate a modulation signal; (9) The sideband modulation signal of satellite B is modulated onto the optical signal and transmitted. The second EOM modulates the sideband modulation signal output by the second upconversion unit onto the optical carrier signal output by the second laser. The laser modulation signal output by the second EOM is transmitted to the first laser transceiver module of satellite A through the second beam splitter and the second laser transceiver module. (10) Satellite A processes the received signal; after receiving the signal, the first laser transceiver module of Satellite A sends the signal and the local oscillator light of Satellite A to the first photodetector for coherent detection; the beat frequency signal output by the first photodetector is sent to the first digital signal processing unit for pseudocode ranging and data demodulation to obtain the time delay value ΔT from Satellite B to Satellite A. BA ;ΔT BA Includes clock difference, equipment delay, and path delay information for both satellites; ΔT BA As data modulation on pseudocode; (11) By measuring ΔT AB ΔT BAThe time delay information is used to calculate the clock difference and distance information between satellite A and satellite B; based on the measured one-way time delay ΔT from satellite A to satellite B... AB And the one-way time delay measurement ΔT from satellite B to satellite A. BA After deducting link non-reciprocity and device delay errors, denoted here as ΔT L1 Finally, the 1PPS clock difference ΔT between the first digital signal processing unit and the second digital signal processing unit is obtained as follows: ΔT AB -ΔT BA ) / 2-ΔT L1 The distance ΔL between satellite A and satellite B is obtained as ΔT = (ΔT / ΔL) AB +ΔT BA ) / 2-ΔT L2 ΔT L2 This refers to equipment delay error.

[0012] Furthermore, the specific steps for generating the sideband modulation signal using the first up-conversion unit are as follows: (4.1) Using the first clock output signal as a reference, generate a microwave signal in the GHz range; (4.2) The intermediate frequency signal output by the first digital signal processing unit is mixed and filtered with a microwave signal in the GHz range to obtain a modulation signal in the GHz range, namely the sideband modulation signal; wherein the sideband modulation degree is ≤20% and the ratio to the pseudocode modulation degree is ≥10.

[0013] Furthermore, the specific steps for generating the sideband modulation signal using the second up-conversion unit are as follows: (8.1) Using the second clock output signal as a reference, generate a microwave signal in the GHz range; (8.2) The intermediate frequency signal output by the second digital signal processing unit is mixed and filtered with the microwave signal in the GHz range to obtain the modulation signal in the GHz range, namely the sideband modulation signal of satellite B; wherein the sideband modulation degree is ≤20% and the ratio to the pseudocode modulation degree is ≥10.

[0014] The beneficial effects of this invention compared to the prior art are: This invention proposes a laser ranging and time synchronization system and method with pseudocode modulation on the sideband. The pseudocode and data are directly phase-modulated on a sideband in the tens of MHz range, and then the modulated signal is up-converted to the GHz range before being sent to the EOM (External Optical Array). Because the pseudocode and data are modulated on the clock sideband, and through reasonable selection of the pseudocode bandwidth, the transmitted optical carrier is only affected by aliasing interference from the pseudocode sidelobes during interferometric measurement. Sidelobe suppression techniques can further reduce the impact of the pseudocode on the main carrier. Furthermore, due to the low modulation depth of the pseudocode, its impact on the clock sideband is minimal. This invention achieves both ranging and communication without affecting laser interferometry and clock sideband recovery. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a laser ranging and time synchronization system with pseudocode modulation on the sideband. Detailed Implementation

[0016] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0017] The pseudocode modulation laser ranging and time synchronization system disclosed in this invention is as follows: Figure 1 As shown, it includes System A and System B. System A is installed on satellite A and includes laser 1, clock 1, upconversion unit 1, EOM 1, beam splitter 1, photodetector 1, digital signal processing unit 1, and laser transceiver module 1. It mainly performs signal modulation and demodulation, transmission and reception, and signal processing functions for satellite A.

[0018] System B is located on satellite B and includes laser 2, clock 2, optical phase-locked loop, up-conversion unit 2, EOM 2, beam splitter 2, photodetector 2, digital signal processing unit 2, and laser transceiver module 2. Its main functions include signal modulation / demodulation, transmission / reception, and signal processing on satellite B.

[0019] Systems A and B have the same composition and working principle. System B is additionally equipped with an optical phase-locked loop, which is used to lock laser 2 onto laser 1.

[0020] Laser 1 is an ultra-stable laser, responsible for providing the carrier frequency for EOM1 of satellite 1, serving as the main laser. Laser 2 is a tunable narrow-linewidth laser, responsible for providing the carrier frequency for EOM2 of satellite 2, serving as the servo laser.

[0021] Clocks 1 and 2 have the same function, mainly providing frequency signals (clock reference signals) for the digital signal processing unit, up-conversion unit, and optical phase-locked loop.

[0022] Upconversion units 1 and 2 have the same function. The upconversion unit generates a microwave signal in the GHz range based on the clock reference signal, and upconverts the modulated intermediate frequency signal generated by the digital signal processing unit to a GHz-level modulated signal, i.e., a sideband modulated signal.

[0023] EOM1 and EOM2 have the same function. Their main function is to modulate sideband modulation signals onto light. Beam splitter 1 and beam splitter 2 have the same function. Their main function is to split a beam of light into two beams. Photodetector 1 and photodetector 2 have the same function. Their main function is to detect ranging communication signals. Laser transceiver module 1 and laser transceiver module 2 are used for transmitting and receiving optical signals.

[0024] Digital signal processing unit 1 and digital signal processing unit 2 have the same function. Using the clock output signal as a reference, they generate an intermediate frequency signal modulated with pseudo-code and data, and demodulate the signal output by the photodetector to calculate the distance and clock difference.

[0025] The optical phase-locked loop receives the output signal from the photodetector 2 module, performs frequency mixing (the reference signal is provided by clock 2), low-pass filtering, and then extracts the phase error signal. This signal is then used to control the laser 2, so that the output signal of the laser 2 is locked onto the received signal light, that is, indirectly locked onto the laser 1.

[0026] The work process is as follows: The optical signal generated by laser 1 of satellite A is sent to EOM1; clock 1 generates a clock reference signal and provides it to digital signal processing unit 1 and up-conversion unit 1; Digital signal processing unit 1 uses the clock signal 1 as a reference to generate a 70MHz±20MHz signal, a pseudo-code, and a data signal. It then modulates the pseudo-code and data signals onto the 70MHz±20MHz signal, with a pseudo-code modulation depth ≤2%, to form an intermediate frequency (IF) signal. The modulated IF signal is then sent to up-conversion unit 1. Digital signal processing unit 2 uses the clock signal 2 as a reference to generate a 70MHz±20MHz signal. It also generates a pseudo-code and data signal, and modulates them onto the 70MHz±20MHz signal, with a pseudo-code modulation depth ≤2%. The modulated IF signal is then sent to up-conversion unit 2. The upconversion unit 1 generates a GHz-level modulation signal, i.e., a sideband modulation signal, based on the intermediate frequency signal output by the digital signal processing unit 1 and the clock reference signal. The signal is then sent to the EOM1 to modulate the sideband modulation signal onto the optical signal and sent to the beam splitter 1. The split optical signals are then sent to the photodetector 1 and the laser transceiver module 1, respectively. The laser transceiver module 1 sends the optical signal to the laser transceiver module 2 of satellite B. Laser transceiver module 2 coherently detects the received optical signal and the local oscillator optical signal from satellite B using photodetector 2. The coherent detection result is sent to an optical phase-locked loop to lock the output signal of laser 2 onto laser 1. Simultaneously, the coherent detection result is also sent to digital signal processing unit 2 for pseudocode ranging and data demodulation to obtain the one-way time delay measurement value ΔT from satellite A to satellite B. AB ; Similarly, the optical signal generated by the laser of satellite B is modulated into an optical signal by the sideband modulation signal through clock 2, EOM2, and up-conversion unit 2. The optical signal is then transmitted to the laser transceiver module 1 of satellite A through laser transceiver module 2. The digital signal processing unit 1 then measures the one-way time delay ΔT from satellite B to satellite A. BA ; Finally, the 1PPS clock difference ΔT of digital signal processing unit 1 and digital signal processing unit 2 and the distance ΔL between satellite A and satellite B are obtained.

[0027] ΔT = (ΔT) AB -ΔT BA ) / 2-ΔT L1 ;ΔT L1 This is the sum of errors such as link non-reciprocity and device delay. ΔL=(ΔT AB +ΔT BA ) / 2-ΔT L2 ΔT L2 This refers to equipment delay error.

[0028] In this invention, the digital signal processing unit 1 demodulates the signal output by the photodetector 1 using the clock reference signal generated by the clock 1, and measures the one-way time delay ΔT from satellite B to satellite A. BA The digital signal processing unit 2 demodulates the signal output by the photodetector 2 using the clock reference signal generated by clock 2, and measures the one-way time delay ΔT from satellite A to satellite B. AB Clock 1 generates two clock reference signals, which are sent to digital signal processing unit 1 and up-conversion unit 1 respectively as clock references; Clock 2 generates three clock reference signals, which are sent to optical phase-locked loop, digital signal processing unit 2 and up-conversion unit 2 respectively as clock references.

[0029] Up-conversion unit 1 generates a GHz-level modulation signal, i.e., a sideband modulation signal, based on the intermediate frequency signal output by digital signal processing unit 1 and the clock reference signal, specifically: 1) Using the clock 1 output signal as a reference, generate a microwave signal in the GHz range; 2) The intermediate frequency signal output by the digital signal processing unit 1 is mixed and filtered with a microwave signal in the GHz range to obtain a modulation signal in the GHz range, namely the sideband modulation signal, wherein the sideband modulation degree is ≤20% and the ratio to the pseudocode modulation degree is ≥10. The upconversion unit 2 generates a GHz-level modulation signal based on the clock reference signal in the same way as the upconversion unit 1.

[0030] This invention also proposes a method for laser ranging and time synchronization with pseudocode modulation on sidebands, comprising the following steps: (1) The optical signal is generated by laser 1. The optical signal generated by laser 1 is sent to EOM1 (electro-optic modulator 1) as an optical carrier to modulate the signal generated by the upconversion unit.

[0031] (2) Clock 1 generates two clock reference signals. One signal is sent to digital signal processing unit 1 as the clock reference of digital signal processing unit 1. The other signal is sent to up-conversion unit 1 as the clock reference.

[0032] (3) Use upconversion unit 1 to generate a modulation signal (combined with the output of digital signal processing unit 1). The specific steps are as follows: 3.1) The digital signal processing unit 1 uses the clock reference signal generated by the clock 1 as a reference (e.g., 10MHz) to generate a 70MHz±20MHz (e.g., 80MHz) signal; 3.2) Digital signal processing unit 1 generates pseudo-code and data signals. The pseudo-code and data signals are modulated onto a 70MHz±20MHz signal to generate an intermediate frequency signal, with the pseudo-code modulation degree ≤2% (e.g., 1.2%).

[0033] 3.3) Up-conversion unit 1 uses the first clock output signal as a reference (e.g., 10MHz) to generate a GHz-level microwave signal (e.g., 2.32GHz); the modulated intermediate frequency signal is mixed and filtered with the GHz-level microwave signal to obtain a GHz-level modulated signal (e.g., a 2.4GHz sideband modulated signal), i.e., a sideband modulated signal. The modulation degree of the GHz-level sideband signal is ≤20% (e.g., 12%), and the ratio of the modulation degree to the pseudocode is ≥10.

[0034] (4) Modulate the sideband modulation signal of satellite A onto the optical signal and transmit it. The sideband modulation signal generated by satellite A is sent to EOM1. The output optical signal of EOM1 is sent to photodetector 1 through beam splitter 1. The other beam is sent to laser transceiver module 1. Laser transceiver module 1 sends the signal of satellite A to laser transceiver module 2 of satellite B.

[0035] (5) Satellite B processes the received signal. After receiving the signal sent by the laser transceiver module of Satellite A, the laser transceiver module 2 of Satellite B sends the signal and a local oscillator light signal split from the beam splitter 2 of Satellite B to the photodetector 2 for coherent detection. The beat frequency signal output by the photodetector 2 is split into two paths: one path is sent to the optical phase-locked loop; the other path is sent to the digital signal processing unit 2 for pseudocode ranging and data demodulation to obtain the one-way time delay measurement value ΔT from Satellite A to Satellite B. AB ΔT AB It includes information such as the clock difference between the two satellites, equipment delay, and path delay. Digital signal processing unit 2 will process ΔT... AB As data modulation on pseudocode.

[0036] (6) Satellite B laser is locked to laser 1 via an optical phase-locked loop (PLL). After receiving the output signal from the photodetector, the PLL first mixes and filters it with a reference signal (e.g., 10MHz) provided by clock 2 to obtain a phase error signal. The error signal drives laser 2 to adjust its frequency and phase. After the PLL completes locking, the output signal of laser 2 is locked to laser 1.

[0037] (7) Use digital signal processing unit 2 and up-conversion unit 2 to generate a modulation signal. The specific steps are as follows: 7.1) The digital signal processing unit 2 generates a 70MHz±20MHz signal (e.g., 80MHz) with reference to the signal generated by the clock 2 (e.g., 10MHz). 7.2) Digital signal processing unit 2 generates pseudo-code and data signals. The pseudo-code (e.g., code rate of 0.5 Mcps) and data signals are modulated onto a signal of 70MHz ± 20MHz (e.g., 80MHz) to generate an intermediate frequency signal, with the pseudo-code modulation degree ≤ 2% (e.g., 1.2%). 7.3) Up-conversion unit 2 uses the second clock output signal as a reference (e.g., 10MHz) to generate a GHz-level microwave signal (e.g., 2.321GHz); the modulated intermediate frequency signal is mixed and filtered with the GHz-level microwave signal to obtain a GHz-level modulated signal (e.g., a 2.401GHz sideband modulated signal), i.e., a sideband modulated signal. The modulation degree of the GHz sideband signal is ≤20% (e.g., 12%), and the ratio of the modulation degree to the pseudocode is ≥10.

[0038] (8) The sideband modulation signal of satellite B is modulated onto the optical signal and transmitted. EOM2 modulates the sideband modulation signal output by upconversion unit 2 onto the optical carrier output by laser 2. The laser modulation signal output by EOM2 is transmitted to laser transceiver module 1 of satellite A via beam splitter 2 and laser transceiver module 2.

[0039] (9) Satellite A processes the received signal. After receiving the signal from the laser transceiver module 2 of satellite B, the laser transceiver module 1 of satellite A sends the signal to the photodetector 1, where it is coherently detected with one local oscillator signal from the beam splitter 1 of satellite A. The beat frequency signal output by the photodetector 1 is sent to the digital signal processing unit 1 for pseudocode ranging and data demodulation to obtain the time delay value ΔT from satellite B to satellite A. BA ΔT BA It includes information such as the clock difference between the two satellites, equipment delay, and path delay. Digital signal processing unit 1 will process ΔT... BA As data modulation on pseudocode.

[0040] (10) By measuring ΔT AB ΔT BAThe time delay information is used to calculate the clock difference and distance between satellite A and satellite B. This is based on the measured one-way time delay ΔT from satellite A to satellite B. AB And the one-way time delay measurement ΔT from satellite B to satellite A. BA After deducting errors such as link non-reciprocity error and device delay error, denoted here as ΔT L1 Finally, the 1PPS clock difference ΔT between digital signal processing unit 1 and digital signal processing unit 2 is obtained as follows: ΔT = (ΔT AB -ΔT BA ) / 2-ΔT L1 The distance ΔL between satellite A and satellite B is obtained as ΔT = (ΔT / ΔL) / ΔL. AB +ΔT BA ) / 2-ΔT L2 ΔT L2 This includes error terms such as equipment delay error.

[0041] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A laser ranging and time synchronization system with pseudocode modulation on sidebands, characterized in that, include: System A and System B; System A is installed on satellite A and includes a first laser, a first clock, a first up-conversion unit, a first EOM, a first beam splitter, a first photodetector, a first digital signal processing unit, and a first laser transceiver module; System B is installed on satellite B and includes a second laser, a second clock, an optical phase-locked loop, a second up-conversion unit, a second EOM, a second beam splitter, a second photodetector, a second digital signal processing unit, and a second laser transceiver module. The optical signal generated by the first laser of satellite A is sent to the first EOM; the first clock generates a clock reference signal and provides it to the first digital signal processing unit and the first up-conversion unit; The first upconversion unit generates a GHz-level modulation signal, i.e., a sideband modulation signal, based on the intermediate frequency signal output by the first digital signal processing unit and the clock reference signal. The signal is then sent to the first EOM to modulate the sideband modulation signal onto the optical signal and sent to the first beam splitter. The split optical signals are then sent to the first photodetector and the first laser transceiver module, respectively. The first laser transceiver module then sends the optical signal to the second laser transceiver module of satellite B. The second laser transceiver module coherently detects the received optical signal and the local oscillator optical signal from satellite B using a second photodetector. The coherent detection result is sent to an optical phase-locked loop to lock the output signal of the second laser onto the first laser. Simultaneously, the coherent detection result is also sent to a second digital signal processing unit for pseudocode ranging and data demodulation to obtain the one-way time delay measurement value ΔT from satellite A to satellite B. AB ; Similarly, the optical signal generated by the second laser of satellite B is modulated into an optical signal by the second clock, the second EOM, and the second up-conversion unit. This optical signal is then transmitted to the first laser transceiver module of satellite A via the second laser transceiver module. The first digital signal processing unit then measures the one-way time delay ΔT from satellite B to satellite A. BA ; Finally, the 1PPS clock difference ΔT of the first digital signal processing unit and the second digital signal processing unit, and the distance ΔL between satellite A and satellite B are obtained.

2. The laser ranging and time synchronization system with pseudocode modulation on sidebands according to claim 1, characterized in that: The laser generated by the first laser is an ultra-stable laser and serves as the master laser, while the second laser is a tunable narrow-linewidth laser and serves as the servo laser.

3. The laser ranging and time synchronization system with pseudocode modulation on sidebands according to claim 2, characterized in that: Except for the optical phase-locked loop, System B has the same system composition and operation mode as System A. By additionally setting the optical phase-locked loop in System B to receive the output signal of the second photodetector, performing frequency mixing and low-pass filtering to extract the phase error signal, and then controlling the second laser, so that the output signal of the second laser is locked on the received signal light, and then locked on the first laser.

4. The laser ranging and time synchronization system with pseudocode modulation on sidebands according to claim 1, characterized in that: The first digital signal processing unit uses the clock reference signal generated by the first clock as a reference to generate a 70MHz±20MHz signal, a pseudo code, and a data signal, and modulates the pseudo code and data signal onto the 70MHz±20MHz signal to generate an intermediate frequency signal, with a pseudo code modulation degree ≤2%; the modulated intermediate frequency signal is sent to the first up-conversion unit. The second digital signal processing unit uses the clock reference signal generated by the second clock as a reference to generate a 70MHz±20MHz signal, a pseudo code, and a data signal. It then modulates the pseudo code and data signal onto the 70MHz±20MHz signal to generate an intermediate frequency signal. The pseudo code modulation degree is ≤2%. The modulated intermediate frequency signal is then sent to the second up-conversion unit. The first digital signal processing unit demodulates the signal output by the first photodetector using a clock reference signal generated by the first clock, and measures the one-way time delay ΔT from satellite B to satellite A. BA ; The second digital signal processing unit demodulates the signal output by the second photodetector using a clock reference signal generated by the second clock, and measures the one-way time delay ΔT from satellite A to satellite B. AB .

5. A laser ranging and time synchronization system with pseudocode modulation on sidebands according to claim 1, characterized in that: The first clock generates two clock reference signals, which are sent to the first digital signal processing unit and the first up-conversion unit respectively as clock references; The second clock generates three clock reference signals, which are sent to the optical phase-locked loop, the second digital signal processing unit, and the second up-conversion unit as clock references, respectively.

6. A laser ranging and time synchronization system with pseudocode modulation on sidebands according to claim 5, characterized in that: The first up-conversion unit generates a GHz-level modulation signal, i.e., a sideband modulation signal, based on the intermediate frequency signal output by the first digital signal processing unit and the clock reference signal, specifically: 1) Using the first clock output clock reference signal as a reference, generate a microwave signal in the GHz range; 2) The intermediate frequency signal output by the first digital signal processing unit is mixed and filtered with a microwave signal in the GHz range to obtain a modulation signal in the GHz range, namely a sideband modulation signal, wherein the sideband modulation degree is ≤20% and the ratio to the pseudocode modulation degree is ≥10. The second upconversion unit generates GHz-level sideband modulation signals based on the clock reference signal in the same way as the first upconversion unit.

7. The laser ranging and time synchronization system with pseudocode modulation on sidebands according to claim 1, characterized in that: The 1PPS clock difference ΔT between the first digital signal processing unit and the second digital signal processing unit is (ΔT) AB -ΔT BA ) / 2-ΔT L1 ;ΔT L1 The sum of link non-reciprocity and device delay error; the distance between satellite A and satellite B, ΔL = (ΔT) AB +ΔT BA ) / 2-ΔT L2 ΔT L2 This refers to equipment delay error.

8. A method for laser ranging and time synchronization with pseudocode modulation on sidebands, characterized in that, include: (1) Set up a first laser, a first clock, a first up-conversion unit, a first EOM, a first beam splitter, a first photodetector, a first digital signal processing unit, and a first laser transceiver module on satellite A; A second laser, a second clock, an optical phase-locked loop, a second up-conversion unit, a second EOM, a second beam splitter, a second photodetector, a second digital signal processing unit, and a second laser transceiver module are installed on satellite B. (2) An optical signal is generated by the first laser, and the optical signal generated by the first laser is sent to the first EOM; (3) The first clock generates two clock reference signals, which are sent to the first digital signal processing unit and the first up-conversion unit respectively as clock references; (4) Use the first up-conversion unit to generate a sideband modulation signal; (5) Modulate the sideband modulation signal of satellite A onto the optical signal and transmit it; send the sideband modulation signal of satellite A into the first EOM, the first EOM modulates the sideband modulation signal onto the optical signal, one beam is sent into the first photodetector; the other beam is sent into the first laser transceiver module; the first laser transceiver module sends the signal of satellite A to the second laser transceiver module of satellite B; (6) Satellite B processes the received signal; after receiving the signal, the second laser transceiver module of Satellite B sends the signal and the local oscillator light of Satellite B to the second photodetector for coherent detection; the beat frequency signal output by the second photodetector is split into two paths, one path is sent to the optical phase-locked loop, and the other path is sent to the second digital signal processing unit for pseudocode ranging and data demodulation to obtain the time delay value ΔT from Satellite A to Satellite B. AB ;ΔT AB Includes clock difference, equipment delay, and path delay information for both satellites, ΔT AB As data modulation on pseudocode; (7) The second laser of satellite B is locked to the first laser through an optical phase-locked loop. After receiving the output signal of the second photodetector, the optical phase-locked loop first mixes and filters it with the reference signal provided by the second clock to obtain a phase error signal. The phase error signal drives the second laser to adjust its frequency and phase. After the phase-locked loop completes the locking, the output signal of the second laser is locked to the first laser. (8) Use the second up-conversion unit to generate a modulation signal; (9) The sideband modulation signal of satellite B is modulated onto the optical signal and transmitted. The second EOM modulates the sideband modulation signal output by the second upconversion unit onto the optical carrier signal output by the second laser. The laser modulation signal output by the second EOM is transmitted to the first laser transceiver module of satellite A through the second beam splitter and the second laser transceiver module. (10) Satellite A processes the received signal; after receiving the signal, the first laser transceiver module of Satellite A sends the signal and the local oscillator light of Satellite A to the first photodetector for coherent detection; The beat frequency signal output by the first photodetector is sent to the first digital signal processing unit for pseudocode ranging and data demodulation to obtain the time delay value ΔT from satellite B to satellite A. BA ;ΔT BA Includes clock difference, equipment delay, and path delay information for both satellites; ΔT BA As data modulation on pseudocode; (11) By measuring ΔT AB ΔT BA The time delay information is used to calculate the clock difference and distance information between satellite A and satellite B; based on the measured one-way time delay ΔT from satellite A to satellite B... AB And the one-way time delay measurement ΔT from satellite B to satellite A. BA After deducting link non-reciprocity and device delay errors, denoted here as ΔT L1 Finally, the 1PPS clock difference ΔT between the first digital signal processing unit and the second digital signal processing unit is obtained as follows: ΔT AB -ΔT BA ) / 2-ΔT L1 The distance ΔL between satellite A and satellite B is obtained as ΔT = (ΔT / ΔL) AB +ΔT BA ) / 2-ΔT L2 ΔT L2 This refers to equipment delay error.

9. The method for laser ranging and time synchronization with pseudocode modulation on sidebands according to claim 8, characterized in that: The specific steps for generating the sideband modulation signal using the first up-conversion unit are as follows: (4.1) Using the clock reference signal output by the first clock as a reference, generate a microwave signal in the GHz range; (4.2) The intermediate frequency signal output by the first digital signal processing unit is mixed and filtered with a microwave signal in the GHz range to obtain a modulation signal in the GHz range, i.e., a sideband modulation signal. Among them, the sideband modulation degree is ≤20%, and the ratio of it to the pseudocode modulation degree is ≥10.

10. A method for laser ranging and time synchronization with pseudocode modulation on sidebands according to claim 8, characterized in that: The specific steps for generating the sideband modulation signal using the second up-conversion unit are as follows: (8.1) Using the clock reference signal output by the second clock as a reference, generate a microwave signal in the GHz range; (8.2) The intermediate frequency signal output by the second digital signal processing unit is mixed and filtered with the microwave signal in the GHz range to obtain the modulation signal in the GHz range, namely the sideband modulation signal of satellite B; wherein the sideband modulation degree is ≤20% and the ratio to the pseudocode modulation degree is ≥10.

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