Bidirectional optical time frequency comparison system and comparison method based on virtual synthetic wavelength

Abstract

A bidirectional optical time-frequency comparison system and method based on virtual synthesized wavelength is disclosed. The master and slave ends synthesize multiple wavelength signals to form a virtual synthesized wavelength, expanding the time difference measurement range of the optical carrier. The master and slave ends respectively send the virtual synthesized wavelength to the slave and master ends. The master and slave ends respectively measure the time difference between their local virtual synthesized wavelength and the virtual synthesized wavelength received by the slave end. The slave end, combining coarse time difference measurement with the bidirectional comparison principle, obtains the clock difference between the master and slave ends, completing the bidirectional time-frequency comparison. Simultaneously, the slave end adjusts the optical carrier frequency and phase to achieve time-frequency synchronization between the master and slave ends. This invention overcomes the problems of small time difference measurement range in existing optical carrier time-frequency comparison methods and insufficient accuracy of electro-optic modulation-based time-frequency comparison methods. The system has the advantages of low noise floor, simple structure, and high reliability.

Description

Technical Field

[0001] This invention relates to the field of optical time-frequency transmission, and in particular to bidirectional time-frequency comparison and transmission for free-space link transmission. Background Technology

[0002] Time-frequency comparison and transmission enables frequency standard comparison between master and slave locations (or multiple locations) and remote frequency standard calibration, allowing users in different geographical locations to share a unified time-frequency reference source. To ensure performance, the accuracy of the time-frequency comparison must be at least an order of magnitude higher than the time-frequency signal being compared. Currently, the mainstream comparison methods are based on space microwave and fiber optic links. In recent years, based on the superior characteristics of fiber optic transmission, significant progress has been made in large-scale, long-distance fiber optic time-frequency comparison and synchronization technology. However, fiber optic links have limitations in coverage, especially when involving mobile platforms (such as vehicle-to-ground, satellite-to-ground, inter-satellite, and sea-to-land connections), making it impossible to provide full-coverage, high-precision time-frequency comparison across "air-space-land-sea." Satellite-based space-based microwave time-frequency comparison systems offer advantages such as flexibility and lack of geographical limitations, but their accuracy is limited.

[0003] Although bidirectional time-frequency comparison can effectively suppress the coherence time degradation between the two reference optical carriers caused by atmospheric turbulence, space links, especially near-ground links, are susceptible to random signal fading or even loss due to weather and atmospheric turbulence. In other words, free-space optical links are actually intermittent (hereinafter referred to as intermittent free-space links), and their duration and intervals are random. When the link interruption time exceeds the coherence time between the two reference optical carriers, it causes periodic ambiguity (cycle slip) in phase measurements, leading to deviations in phase and time measurements. Currently, the commonly used two-way time-frequency comparison (FC-OTWTFT) based on linear optical sampling using fiber optic frequency combs (hereinafter referred to as optical combs) has the capability of measuring time difference over a large range and with high accuracy, and can even measure clock differences between two locations after an interruption [FRGiorgetta, et al., Optical two-way time and frequency transfer over free space. Nature Photonics, vol.7, no.6, pp.434-438, 2013. EDCaldwell, et al., Quantum-limited optical time transfer for future geosynchronous links. arXiv:2212.12541, 2022]. However, the size and complexity of currently used fiber optic combs limit the application scope of the system, especially for satellites and mobile platforms. In contrast, time-frequency comparison technology based on optical carrier phase only requires relatively simple optical and detection hardware at remote sites. Therefore, it has advantages in terms of size, weight, and stability, making it suitable for mobile platforms such as satellites. More importantly, time difference measurement technology based on optical carrier phase can achieve higher measurement accuracy. For example, it can achieve attosecond-level time difference measurement accuracy for a relative phase measurement accuracy of 1 / 1000. However, the aperiodic ambiguity range of time difference measurement based on optical carrier phase is only on the femtosecond level. For non-discontinuous links, algorithms such as Kalman filtering can be used to extend the aperiodic ambiguity range. However, for discontinuous free-space optical links with frequent on / off cycles, integer period information may be lost after the interruption is recovered, leading to a decrease in time-frequency comparison performance. This is the main obstacle limiting its system performance and application. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a bidirectional optical time-frequency comparison system and method based on virtual synthetic wavelength. This system can achieve time-frequency comparison and synchronization based on optical carrier phase. By adopting this structure, high-precision time difference measurement of optical carrier phase can be achieved while significantly improving the time difference measurement range. This overcomes the problems of insufficient time measurement range based on optical carrier phase and insufficient accuracy based on spread spectrum code modulation and demodulation, thus meeting the requirements for high-precision time-frequency comparison and transmission of intermittent free space links.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] On one hand, the present invention provides a bidirectional optical time-frequency comparison method based on virtual synthesized wavelength, including a master end and a slave end, and a free-space link connecting the master end and the slave end, characterized by comprising the following steps:

[0007] The master end synthesizes multiple wavelength signals to form a virtual synthesized wavelength and sends it to the slave end. At the same time, the slave end synthesizes multiple wavelength signals to form a virtual synthesized wavelength and sends it to the master end.

[0008] The time difference T between the local optical virtual synthesis wavelength measured at the master end and the virtual synthesis wavelength received from the slave end. BA The signal is sent to the slave end, and simultaneously, the slave end measures the time difference T between the local optical virtual synthesis wavelength and the virtual synthesis wavelength received from the master end. AB ;

[0009] The slave end calculates the clock difference ΔT between the master and slave ends based on the bidirectional comparison principle, ΔT = (T AB -T BA ) / 2, and adjust the optical carrier frequency and phase of the slave end to make ΔT→0, thereby synchronizing the time and frequency of the master and slave ends.

[0010] Furthermore, the time difference T between the locally synthesized virtual wavelength measured by the master end and the virtual synthesized wavelength received by the slave end is... BA Specifically:

[0011] The main multi-channel frequency and phase discrimination module measures the phase difference between the wavelength of the output light from each main laser and the wavelength received from the corresponding slave lasers at the slave end, and demodulates the main end precise time difference T measured by virtual synthesized wavelength based on the phase information between the multiple wavelengths. f，BA Measurement range T f Simultaneously, the main multi-channel frequency and phase discrimination module measures the main coarse time difference T between the local spreading code of the main signal processing module and the spreading code received from the slave end. c，BA Measurement range T c And based on the master-slave precision time difference T f，BA Coarse time difference T between the master and the masterc，BA Demodulate the time difference T measured at the master end BA .

[0012] Furthermore, the time difference T between the locally measured virtual synthesized wavelength from the slave end and the virtual synthesized wavelength received from the master end... AB Specifically:

[0013] The multi-channel frequency and phase discrimination module measures the phase difference between the wavelength of the output light from each slave laser and the wavelength of the corresponding master laser received from the master end, and demodulates the slave-end precise time difference T measured by virtual synthesized wavelength based on the phase information between the multiple wavelengths. f，AB Measurement range T f Simultaneously, the multi-channel frequency and phase discrimination module measures the coarse time difference T between the local spreading code of the master signal processing module and the spreading code received from the master. c，AB Measurement range T c And based on the time difference T from the end f，AB and the coarse time difference T from the end c，AB Demodulate the time difference T measured at the master end AB .

[0014] On the other hand, the present invention also provides a bidirectional optical time-frequency comparison system based on virtual synthesized wavelength, including a master end and a slave end, and a free-space link connecting the master end and the slave end. The master end is characterized in that it includes N master virtual synthesized wavelength modules, a first master multiplexer / demultiplexer, a master optical frequency comb module, a master Faraday rotator, an N+1th master coupler, a second master multiplexer / demultiplexer, a master optical telescope, an N+1th master laser, a master signal processing module, a master multi-channel frequency and phase discrimination module, an N+1th master photodetector, and a master circulator.

[0015] The first main virtual synthesized wavelength module includes a first main laser, a first main coupler, a first main photodetector, a first main bandpass filter, and a first main servo controller. The laser output port of the first main laser is connected to the first port of the first main coupler, the electrical control port of the first main laser is connected to the output port of the first main servo controller, the second port of the first main coupler is connected to the optical input port of the first main photodetector, the electrical output port of the first main photodetector is connected to the input port of the first main bandpass filter, the first output port of the first main bandpass filter is connected to the input port of the first main servo controller, the second output port of the first main bandpass filter is connected to the first input port of the main multi-channel frequency and phase discrimination module, and the third port of the first main coupler is connected to the first port of the first main multiplexer / demultiplexer.

[0016] Similarly, the Nth main virtual synthesized wavelength module includes an Nth main laser, an Nth main coupler, an Nth main photodetector, an Nth main bandpass filter, and an Nth main servo controller. The laser output port of the Nth main laser is connected to the first port of the Nth main coupler, the electrical control port of the Nth main laser is connected to the output port of the Nth main servo controller, the second port of the Nth main coupler is connected to the optical input port of the Nth main photodetector, the electrical output port of the Nth main photodetector is connected to the input port of the Nth main bandpass filter, the first output port of the Nth main bandpass filter is connected to the input port of the Nth main servo controller, the second output port of the Nth main bandpass filter is connected to the Nth input port of the main multi-channel frequency and phase discrimination module, and the third port of the Nth main coupler is connected to the Nth port of the first main multiplexer / demultiplexer.

[0017] The N+1 port of the first main multiplexer / demultiplexer is connected to the 1 port of the main Faraday rotator. The 2 port of the main Faraday rotator is connected to the 1 port of the N+1 main coupler. The 2nd and 3rd ports of the N+1 main coupler are respectively connected to the 1st port of the second main multiplexer / demultiplexer and the output terminal of the main optical frequency comb module. The 2nd and 3rd ports of the second main multiplexer / demultiplexer are respectively connected to the 3rd port of the main circulator and the input port of the main optical telescope. The 1st and 2nd ports of the main circulator are respectively connected to the output port of the N+1 main laser and the input port of the N+1 main photodetector. The 1st, 2nd, and 3rd ports of the main signal processing module are respectively connected to the output port of the main multi-channel frequency and phase discrimination module, the output port of the N+1 main photodetector, and the electrical modulation and control port of the N+1 main laser.

[0018] The slave end includes an N-channel virtual synthesized wavelength module, a first slave multiplexer / demultiplexer, a slave optical frequency comb module, a slave Faraday rotator, an N+1 slave coupler, a second slave multiplexer / demultiplexer, a slave optical telescope, an N+1 slave laser, a slave signal processing module, a slave multi-channel frequency and phase detector module, an N+1 slave photodetector, a slave circulator, and an N+1 slave servo controller;

[0019] The first slave virtual synthesized wavelength module includes a first slave laser, a first slave coupler, a first slave photodetector, a first slave bandpass filter, and a first slave servo controller. The laser output port of the first slave laser is connected to the first port of the first slave coupler, the electrical control port of the first slave laser is connected to the output port of the first slave servo controller, the second port of the first slave coupler is connected to the optical input port of the first slave photodetector, the electrical output port of the first slave photodetector is connected to the input port of the first slave bandpass filter, the first output port of the first slave bandpass filter is connected to the input port of the first slave servo controller, the second output port of the first slave bandpass filter is connected to the first input port of the slave multi-channel frequency and phase discrimination module, and the third port of the first slave coupler is connected to the first port of the first slave multiplexer / demultiplexer.

[0020] Similarly, the Nth virtual synthesized wavelength module includes an Nth laser, an Nth coupler, an Nth photodetector, an Nth bandpass filter, and an Nth servo controller. The laser output port of the Nth laser is connected to the first port of the Nth coupler, the electrical control port of the Nth laser is connected to the output port of the Nth servo controller, the second port of the Nth coupler is connected to the optical input port of the Nth photodetector, the electrical output port of the Nth photodetector is connected to the input port of the Nth bandpass filter, the first output port of the Nth bandpass filter is connected to the input port of the Nth servo controller, the second output port of the Nth bandpass filter is connected to the Nth input port of the multi-channel frequency and phase discrimination module, and the third port of the Nth coupler is connected to the Nth port of the first multiplexer / demultiplexer.

[0021] The first slave multiplexer's N+1 port is connected to the first port of the slave Faraday rotator. The second port of the slave Faraday rotator is connected to the first port of the N+1 slave coupler. The second and third ports of the N+1 slave coupler are respectively connected to the first port of the second multiplexer and the output terminal of the slave optical frequency comb module. The second and third ports of the second multiplexer are respectively connected to the third port of the slave circulator and the input port of the slave optical telescope. The first and second ports of the slave circulator are respectively connected to the output port of the N+1 slave laser and the input port of the N+1 slave photodetector. The first, second, third, and fourth ports of the signal processing module are respectively connected to the output port of the multi-channel frequency and phase discrimination module, the output port of the N+1 slave photodetector, the electrical modulation and control port of the N+1 slave laser, and the input port of the N+1 slave servo controller. The output port of the N+1 slave servo controller is connected to the repetition rate and time delay control port of the slave optical frequency comb module.

[0022] The N optical waves output from the N-channel main virtual synthesized wavelength module at the main end are combined by the first main multiplexer and demultiplexer, and then incident on the main Faraday rotator, where they are split into two parts:

[0023] A portion of the signal returns along the original path along with the main optical frequency comb signal output by the main optical frequency comb module. After being split by the first main multiplexer and splitter, the signals are respectively sent to each main photodetector via their respective main couplers. The beat frequency signal output by each main photodetector is fed back to control the output frequency of each main laser through each main servo controller, thereby realizing a virtual composite wavelength with N wavelengths coherently combined.

[0024] Another part of the signal enters the second main multiplexer and demultiplexer together with the time difference information and spreading code signal output by the main signal processing module and modulated by the N+1 main laser. After being combined by the second main multiplexer and demultiplexer, it is sent to the slave end through the main optical telescope.

[0025] Similarly, the N optical waves output from the virtual synthesized wavelength module at the slave end are combined by the first slave multiplexer and then incident on the slave Faraday rotator, where they are split into two parts:

[0026] A portion of the signal, along with the optical frequency comb signal output from the optical frequency comb module, returns along the original path. After being split by the first multiplexer, the signals are respectively sent to each photodetector via their respective photocouplers. The beat frequency signal output by each photodetector is fed back to control the output frequency of each laser through each servo controller, thereby realizing a virtual composite wavelength with N wavelengths coherently combined.

[0027] Another part of the signal enters the second slave multiplexer and demultiplexer together with the time difference information and spreading code signal output by the slave signal processing module and modulated by the N+1 slave laser through the N+1 slave coupler. After being multiplexed by the second slave multiplexer and demultiplexer, it is sent to the master end through the slave optical telescope.

[0028] The master end: The master multi-channel frequency and phase discrimination module measures the phase difference between the wavelength of the output light from each master laser and the wavelength of the corresponding slave laser received from the slave end, and demodulates the master end precise time difference T measured by virtual synthesized wavelength based on the phase information between multiple wavelengths. f，BA Measurement range T f Simultaneously, the main multi-channel frequency and phase discrimination module measures the main coarse time difference T between the local spreading code of the main signal processing module and the spreading code received from the slave end. c，BA Measurement range T c The main multi-channel frequency and phase detection module uses the master-end precise time difference T. f，BA Coarse time difference T between the master and the master c，BA Demodulate the time difference T measured at the master end BA ;

[0029] The slave end: The multi-channel frequency and phase discrimination module measures the phase difference between the wavelength of the output light from each slave laser and the wavelength of the corresponding output light from each master laser received from the master end, and demodulates the slave-end precise time difference T measured by virtual synthesized wavelength based on the phase information between multiple wavelengths. f，AB Measurement range T f Simultaneously, the multi-channel frequency and phase discrimination module measures the coarse time difference T between the local spreading code of the slave signal processing module and the spreading code received from the master. c，AB Measurement range T c The multi-channel frequency and phase detection module uses the slave end's precise time difference T... f，AB and the coarse time difference T from the end c，AB Demodulate the time difference T measured from the slave end AB ;

[0030] The master end will measure the time difference T. BA The data is sent to the slave end, which then transmits the data based on the time difference T measured by the master end. BA The time difference T between the measured ends AB The clock difference ΔT at both ends is calculated, i.e., ΔT = (T AB -T BA The output frequency and delay of the slave reference optical carrier are adjusted according to the clock difference ΔT at both ends, so that ΔT→0, thereby achieving time and frequency synchronization between the master and slave ends.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] This invention expands the time difference measurement range of optical carrier phase by using a virtual synthetic wavelength formed by multiple phase-locked wavelengths. This invention overcomes the shortcomings of the insufficient time difference measurement range of existing optical carrier time-frequency comparison methods, and effectively improves the accuracy of traditional time-frequency comparison methods based on optical carrier modulation. The system has the advantages of low noise, simple structure and high reliability. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of an embodiment of the bidirectional optical time-frequency comparison system based on virtual synthetic wavelength of the present invention.

[0034] Figure 2 This is a schematic diagram of an embodiment of the bidirectional optical time-frequency comparison system based on three-wavelength synthesis of virtual synthesized wavelength according to the present invention.

[0035] Figure 3 This is a schematic diagram of the virtual synthesized wavelength based on three-wavelength synthesis according to the present invention. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments and accompanying drawings. The embodiments are implemented based on the technical solutions of the present invention, and detailed implementation methods and specific workflows are given. However, the scope of protection of the present invention is not limited to the following embodiments.

[0037] Please see Figure 1 , Figure 1 The figure shows a schematic diagram of an embodiment of the bidirectional optical time-frequency comparison system based on virtual synthetic wavelength of the present invention.

[0038] A bidirectional optical time-frequency comparison system based on virtual synthesized wavelength is characterized in that the master terminal 1 includes a first master laser 101, a second master laser 106, an Nth master laser 111, an N+1th master laser 122, a first master servo controller 105, a second master servo controller 110, an Nth master servo controller 115, a first master photodetector 103, a second master photodetector 108, an Nth master photodetector 113, an N+1th master photodetector 125, a first master coupler 102, a second master coupler 107, and an Nth master coupler. 112, N+1th main coupler; 119, first main photodetector; 103, second main photodetector; 108, Nth main photodetector; 113, N+1th main photodetector; 125, first main bandpass filter; 104, second main bandpass filter; 109, Nth main bandpass filter; 114, first main multiplexer / demultiplexer; 116, second main multiplexer / demultiplexer; 120, main Faraday rotator; 118, main signal processing module; 123, main multi-channel frequency and phase detector module; 124, main optical frequency comb module; 117, main circulator; 126, main optical telescope; 121.

[0039] The laser output ports of the first master laser 101, the second master laser 106, and the Nth master laser 111 are respectively connected to the first port of the first master coupler 102, the second master coupler 107, and the Nth master coupler 112. The electrical control ports of the first master laser 101, the second slave laser 106, and the Nth master laser 111 are respectively connected to the output ports of the first master servo controller 105, the second master servo controller 110, and the Nth master servo controller 115. The first master coupler 102, the second master coupler 107, and the Nth master coupler 112 are respectively connected to the first port of the first master servo controller 105, the second master servo controller 110, and the Nth master servo controller 115. The second port of 12 is connected to the optical input ports of the first main photodetector 103, the second main photodetector 108, and the Nth main photodetector 113, respectively. The electrical output ports of the first main photodetector 103, the second main photodetector 108, and the Nth main photodetector 113 are connected to the input ports of the first main bandpass filter 104, the second main bandpass filter 109, and the Nth main bandpass filter 114, respectively. The first output ports of the first main bandpass filter 104, the second main bandpass filter 109, and the Nth main bandpass filter 114 are connected to the first main servo... The input ports of controller 105, the second main servo controller 110, and the Nth main servo controller 115 are connected. The second output ports of the first main bandpass filter 104, the second main bandpass filter 109, and the Nth main bandpass filter 114 are respectively connected to the first, second, and Nth input ports of the main multi-channel frequency and phase discrimination module 124. The third ports of the first main coupler 102, the second main coupler 107, and the Nth main coupler 112 are respectively connected to the first, second, and Nth ports of the first main multiplexer / demultiplexer 116. The N+1th port of the first main multiplexer / demultiplexer 116 is connected to the main Faraday rotator 1. The first port of the main Faraday rotator 118 is connected to the first port of the (N+1)th main coupler. The first and second ports of the (N+1)th coupler are respectively connected to the first port of the second main multiplexer / demultiplexer 120 and the output terminal of the main optical frequency comb module 117. The second and third ports of the second main multiplexer / demultiplexer 120 are respectively connected to the third port of the main circulator 126 and the input port of the main optical telescope 121. The first and second ports of the main circulator 126 are respectively connected to the output port of the (N+1)th main laser 122 and the input port of the (N+1)th main photodetector 225.The first, second, and third ports of the main signal processing module 123 are respectively connected to the output port of the main multi-channel frequency and phase discrimination module 124, the output port of the (N+1)th main photodetector 225, and the electrical modulation and control port of the (N+1)th main laser 122.

[0040] This invention provides a bidirectional optical time-frequency comparison system based on virtual synthesized wavelength, characterized in that the slave end 2 includes a first slave laser 201, a second slave laser 206, an Nth master laser 211, an N+1th slave laser 222, a first slave servo controller 205, a second slave servo controller 210, an Nth slave servo controller 215, an N+1th slave servo controller 227, a first slave photodetector 203, a second slave photodetector 208, an Nth slave photodetector 213, an N+1th slave photodetector 225, a first slave coupler 202, and a second slave coupler. 207, Nth slave coupler 212, N+1th slave coupler 219, first slave photodetector 203, second slave photodetector 208, Nth slave photodetector 213, N+1th slave photodetector 225, first slave bandpass filter 204, second slave bandpass filter 209, Nth slave bandpass filter 214, first slave multiplexer / demultiplexer 216, second slave multiplexer / demultiplexer 220, slave Faraday rotator 218, slave signal processing module 223, slave multichannel frequency and phase discrimination module 224, slave optical frequency comb module 217, slave circulator 226, slave optical telescope 221.

[0041] The laser output ports of the first slave laser 201, the second slave laser 206, and the Nth slave laser 211 are respectively connected to the first port of the first slave coupler 202, the second slave coupler 207, and the Nth slave coupler 212. The electrical control ports of the first slave laser 201, the second slave laser 206, and the Nth slave laser 211 are respectively connected to the output ports of the first slave servo controller 205, the second slave servo controller 210, and the Nth slave servo controller 215. The first slave coupler 202, the second slave coupler 207, and the Nth slave coupler 212... The second port of 212 is connected to the optical input ports of the first slave photodetector 203, the second slave photodetector 208, and the Nth slave photodetector 213, respectively. The electrical output ports of the first slave photodetector 203, the second slave photodetector 208, and the Nth slave photodetector 213 are connected to the input ports of the first slave bandpass filter 204, the second slave bandpass filter 209, and the Nth slave bandpass filter 214, respectively. The first output ports of the first slave bandpass filter 204, the second slave bandpass filter 209, and the Nth slave bandpass filter 214 are connected to the first slave photodetector 213. The input ports of the slave controller 205, the second slave controller 210, and the Nth slave controller 215 are connected. The second output ports of the first slave bandpass filter 204, the second slave bandpass filter 209, and the Nth slave bandpass filter 214 are respectively connected to the first, second, and Nth input ports of the slave multi-channel frequency and phase discrimination module 224. The third port of the first slave coupler 202, the second slave coupler 207, and the Nth slave coupler 212 are respectively connected to the first, second, and Nth ports of the first slave multiplexer / demultiplexer 216. The N+1th port of the first slave multiplexer / demultiplexer 216 is connected to the slave Faraday rotator 2. The first port of Faraday rotator 218 is connected to the first port of the (N+1)th slave coupler. The first and second ports of the (N+1)th slave coupler are respectively connected to the first port of the second slave multiplexer / demultiplexer 220 and the output terminal of the optical frequency comb module 217. The second and third ports of the second slave multiplexer / demultiplexer 220 are respectively connected to the third port of the circulator 226 and the input port of the optical telescope 221. The first and second ports of the circulator 226 are respectively connected to the output port of the (N+1)th slave laser 222 and the input port of the (N+1)th slave photodetector 225.The first, second, third, and fourth ports of the signal processing module 223 are respectively connected to the output port of the multi-channel frequency and phase discrimination module 224, the output port of the (N+1)th slave photodetector 225, the electrical modulation and control port of the (N+1)th slave laser 222, and the input port of the (N+1)th slave servo controller 227. The output port of the (N+1)th slave servo controller 227 is connected to the repetition rate and time delay control port of the optical frequency comb module 217.

[0042] On the other hand, the present invention also provides a two-way optical time-frequency comparison method based on virtual synthetic wavelength, characterized in that the method includes the following steps:

[0043] The N wavelengths of the main laser array module at the main end 1 are combined by the main coupler module and the first main multiplexer / demultiplexer 116. The main Faraday rotator 118 then splits the signal into two parts. One part of the signal, along with the input signal from the main optical frequency comb module 117, passes through the first main multiplexer / demultiplexer 116 and the main coupler module to reach the main photodetector array module. The beat frequency signal output by the main photodetector array module is fed back to control the output frequency of the laser through the main servo controller array module to achieve a virtual composite wavelength with N wavelengths coherently. The selection of the laser wavelength in the virtual composite wavelength of this invention needs to consider the phase measurement accuracy of the main multi-channel phase meter 124 and the optical comb spectral width of the main optical frequency comb 117, and needs to create sufficient wavelength spacing conditions for the first main multiplexer / demultiplexer 116 in the virtual composite wavelength. The other part of the signal after passing through the main Faraday rotator 118, along with the optical signal modulated by the spread spectrum code carrying time difference information, is combined by the second main multiplexer / demultiplexer 120 and then sent to the slave end 2 through the main optical telescope 121.

[0044] Similarly, the N wavelengths from the laser array module at the slave end 2 are combined by the coupler module and the first multiplexer / demultiplexer 216, and then the signal is split into two parts by the Faraday rotator 218. One part of the signal, along with the input signal from the optical frequency comb module 217, passes through the first multiplexer / demultiplexer 216 and the coupler module to reach the photodetector array module. The beat frequency signal output from the photodetector array module is fed back to control the output frequency of the laser through the servo controller array module to achieve a virtual composite wavelength with N wavelengths coherently. The selection of the laser wavelength in the virtual composite wavelength of this invention needs to consider the phase measurement accuracy of the multi-channel phase meter 224 and the optical comb spectral width of the optical frequency comb 217, and needs to create sufficient wavelength spacing conditions for the first multiplexer / demultiplexer 216 in the virtual composite wavelength. The other part of the signal after passing through the Faraday rotator 218, along with the spread spectrum code modulated optical signal, is combined by the second multiplexer / demultiplexer 220 and then sent to the master end 1 through the optical telescope 221.

[0045] The master terminal 1 measures the phase difference between each wavelength of the master laser array module and each wavelength of the slave laser array module received from the slave terminal 2 through the master multi-channel frequency and phase discrimination module 124. The local terminal demodulates the "precise time difference" T measured by the virtual synthesized wavelength based on the phase information between the multiple wavelengths. f，BA (Measurement range T) f Simultaneously, the "coarse time difference" T between the local spreading code and the spreading code received from the slave end 2 is measured. c，BA (Measurement range T) c The main terminal 1 is based on T. f，BA and T c，BA Demodulate the time difference T measured at the master end BA .

[0046] The slave end 2 measures the phase difference between each wavelength of the slave laser array module and the wavelength received from the master end 1 through the multi-channel frequency and phase discrimination module 224. The local end demodulates the "precise time difference" T measured by the virtual synthesized wavelength based on the phase information between the multiple wavelengths. f，AB (Measurement range T) f Simultaneously, the "coarse time difference" T between the local spreading code and the spreading code received from the master terminal 1 is measured. c，AB (Measurement range T) c The slave end 2 is based on T f，AB and T c，AB Demodulate the time difference T measured at the master end AB .

[0047] The master end will measure the time difference data T BAThe data is sent to the slave end. Based on the principle of bidirectional time-frequency comparison, the slave end obtains the clock difference between the two ends as follows:

[0048] ΔT=(T AB -T BA ) / twenty one)

[0049] As can be seen, the above process achieves bidirectional time-frequency comparison. Simultaneously, the slave end can adjust the output frequency and delay of the slave-end reference optical carrier based on the obtained clock difference between the two ends, making ΔT→0, thus completing time-frequency synchronization between the master and slave ends.

[0050] Figure 2 This is a schematic diagram of an embodiment of the bidirectional optical time-frequency comparison system based on three-wavelength virtual synthesized wavelengths of the present invention. As shown in the figure, it includes a master end 1 and a slave end 2, as well as a free-space link 3 connecting the master end 1 and the slave end 2. The master end 1 includes a three-way master virtual synthesized wavelength module, a first master multiplexer / demultiplexer 116, a master optical frequency comb module 117, a master Faraday rotator 118, a fourth master coupler 119, a second master multiplexer / demultiplexer 120, a master optical telescope 121, an Nth master laser 122, a master signal processing module 123, a master multi-channel frequency and phase discrimination module 124, a fourth master photodetector 125, and a master circulator 126.

[0051] The first main virtual synthesized wavelength module includes a first main laser 101, a first main coupler 102, a first main photodetector 103, a first main bandpass filter 104, and a first main servo controller 105. The laser output port of the first main laser 101 is connected to the first port of the first main coupler 102. The electrical control port of the first main laser 101 is connected to the output port of the first main servo controller 105. The second port of the first main coupler 102 is connected to the optical input port of the first main photodetector 103. The electrical output port of the first main photodetector 103 is connected to the input port of the first main bandpass filter 104. The first output port of the first main bandpass filter 104 is connected to the input port of the first main servo controller 105. The second output port of the first main bandpass filter 104 is connected to the first input port of the main multi-channel frequency and phase discrimination module 124. The third port of the first main coupler 102 is connected to the first port of the first main multiplexer / demultiplexer 116.

[0052] The second main virtual synthesized wavelength module includes a second main laser 106, a second main coupler 107, a second main photodetector 108, a second main bandpass filter 109, and a second main servo controller 110. The laser output port of the second main laser 106 is connected to the first port of the second main coupler 107, the electrical control port of the second main laser 106 is connected to the output port of the second main servo controller 110, the second port of the second main coupler 107 is connected to the optical input port of the second main photodetector 108, the electrical output port of the second main photodetector 108 is connected to the input port of the second main bandpass filter 109, the first output port of the second main bandpass filter 109 is connected to the input port of the second main servo controller 110, the second output port of the second main bandpass filter 109 is connected to the second input port of the main multi-channel frequency and phase discrimination module 124, and the third port of the second main coupler 107 is connected to the second port of the first main multiplexer / demultiplexer 116.

[0053] The third main virtual synthesized wavelength module includes a third main laser, a third main coupler, a third main photodetector, a third main bandpass filter, and a third main servo controller. The laser output port of the third main laser is connected to the first port of the third main coupler, the electrical control port of the third main laser is connected to the output port of the third main servo controller, the second port of the third main coupler is connected to the optical input port of the third main photodetector, the electrical output port of the third main photodetector is connected to the input port of the third main bandpass filter, the first output port of the third main bandpass filter is connected to the input port of the third main servo controller, the second output port of the third main bandpass filter is connected to the third input port of the main multi-channel frequency and phase discrimination module 124, and the third port of the third main coupler is connected to the third port of the first main multiplexer / demultiplexer 116.

[0054] The fourth port of the first main multiplexer / demultiplexer 116 is connected to the first port of the main Faraday rotator 118. The second port of the main Faraday rotator 118 is connected to the first port of the fourth main coupler 119. The second and third ports of the fourth main coupler are respectively connected to the first port of the second main multiplexer / demultiplexer 120 and the output terminal of the main optical frequency comb module 117. The second and third ports of the second main multiplexer / demultiplexer 120 are respectively connected to the third port of the main circulator 126 and the input port of the main optical telescope 121. The first and second ports of the main circulator 126 are respectively connected to the output port of the fourth main laser and the input port of the fourth main photodetector. The first, second, and third ports of the main signal processing module 123 are respectively connected to the output port of the main multi-channel frequency and phase discrimination module 124, the output port of the fourth main photodetector, and the electrical modulation and control port of the fourth main laser 122.

[0055] The slave end 2 includes a three-way virtual synthesized wavelength module, a first slave multiplexer / demultiplexer 216, a slave optical frequency comb module 217, a slave Faraday rotator 218, a fourth slave coupler 2, a second slave multiplexer / demultiplexer 220, a slave optical telescope 221, a fourth slave laser 222, a slave signal processing module 223, a slave multi-channel frequency and phase detector module 224, a fourth slave photodetector 225, a slave circulator 226, and a fourth slave servo controller 227;

[0056] The first slave virtual synthesized wavelength module includes a first slave laser 201, a first slave coupler 202, a first slave photodetector 203, a first slave bandpass filter 204, and a first slave servo controller 205. The laser output port of the first slave laser 201 is connected to the first port of the first slave coupler 202, the electrical control port of the first slave laser 201 is connected to the output port of the first slave servo controller 205, the second port of the first slave coupler 202 is connected to the optical input port of the first slave photodetector 203, the electrical output port of the first slave photodetector 203 is connected to the input port of the first slave bandpass filter 204, the first output port of the first slave bandpass filter 204 is connected to the input port of the first slave servo controller 205, the second output port of the first slave bandpass filter 204 is connected to the first input port of the slave multi-channel frequency and phase discrimination module 224, and the third port of the first slave coupler 202 is connected to the first port of the first slave multiplexer / demultiplexer 216.

[0057] The second slave virtual synthesized wavelength module includes a second slave laser 206, a second slave coupler 207, a second slave photodetector 208, a second slave bandpass filter 209, and a second slave servo controller 210. The laser output port of the second slave laser 206 is connected to the first port of the second slave coupler 207, the electrical control port of the second slave laser 206 is connected to the output port of the second slave servo controller 210, the second port of the second slave coupler 207 is connected to the optical input port of the second slave photodetector 208, the electrical output port of the second slave photodetector 208 is connected to the input port of the second slave bandpass filter 209, the first output port of the second slave bandpass filter 209 is connected to the input port of the second slave servo controller 210, the second output port of the second slave bandpass filter 209 is connected to the second input port of the slave multi-channel frequency and phase discrimination module 224, and the third port of the second slave coupler 207 is connected to the second port of the first slave multiplexer / demultiplexer 216.

[0058] The third slave virtual synthesized wavelength module includes a third slave laser, a third slave coupler, a third slave photodetector, a third slave bandpass filter, and a third slave servo controller. The laser output port of the third slave laser is connected to the first port of the third slave coupler, the electrical control port of the third slave laser is connected to the output port of the third slave servo controller, the second port of the third slave coupler is connected to the optical input port of the third slave photodetector, the electrical output port of the third slave photodetector is connected to the input port of the third slave bandpass filter, the first output port of the third slave bandpass filter is connected to the input port of the third slave servo controller, the second output port of the third slave bandpass filter is connected to the third input port of the slave multi-channel frequency and phase discrimination module 224, and the third port of the third slave coupler is connected to the third port of the first slave multiplexer / demultiplexer 216.

[0059] The fourth port of the first slave multiplexer / demultiplexer 216 is connected to the first port of the slave Faraday rotator 218. The second port of the slave Faraday rotator 218 is connected to the first port of the fourth slave coupler 219. The second and third ports of the fourth slave coupler 219 are respectively connected to the first port of the second slave multiplexer / demultiplexer 220 and the output terminal of the slave optical frequency comb module 217. The second and third ports of the second slave multiplexer / demultiplexer 220 are respectively connected to the third port of the slave circulator and the input port of the slave optical telescope 221. The first and third ports of the slave circulator are connected to the first port of the second multiplexer / demultiplexer 220 and the input port of the slave optical telescope 221. Port 2 is connected to the output port of the fourth slave laser 222 and the input port of the fourth slave photodetector 225, respectively. Ports 1, 2, 3, and 4 of the slave signal processing module 223 are connected to the output port of the slave multi-channel frequency and phase discrimination module 224, the output port of the N+1 slave photodetector 225, the electrical modulation and control port of the fourth slave laser 222, and the input port of the fourth slave servo controller 225, respectively. The output port of the fourth slave servo controller 225 is connected to the repetition rate and time delay control port of the slave optical frequency comb module 217.

[0060] The three optical waves output from the three main virtual synthesized wavelength modules of the main terminal 1 are combined by the first main combiner / demultiplexer 116 and then incident on the main Faraday rotator 118, where they are split into two parts:

[0061] A portion of the signal, along with the main optical frequency comb signal output by the main optical frequency comb module 117, returns along the original path. After being split by the first main multiplexer / demultiplexer 116, the signals are respectively delivered to each main photodetector via their respective main couplers. The beat frequency signals output by each main photodetector are fed back to control the output frequency of each main laser through each main servo controller, thereby achieving a virtual composite wavelength with three coherent wavelengths.

[0062] Another part of the signal enters the second main multiplexer / demultiplexer 120 together with the time difference information and spreading code signal output by the main signal processing module 123 and modulated by the fourth main laser 122 through the fourth main coupler 119. After being combined by the second main multiplexer / demultiplexer 120, it is sent to the slave end 2 through the main optical telescope 121.

[0063] Similarly, the three optical waves output from the virtual synthesized wavelength module at the slave end 2 are combined by the first slave multiplexer / demultiplexer 216 and then incident on the slave Faraday rotator 218, where they are split into two parts:

[0064] A portion of the signal, along with the optical frequency comb signal output from the optical frequency comb module 217, returns along the original path. After being split by the first multiplexer / demultiplexer 216, the signals are respectively sent to each photodetector via their respective photocouplers. The beat frequency signal output by each photodetector is fed back to control the output frequency of each laser through each servo controller, thereby achieving a virtual composite wavelength with three coherent wavelengths.

[0065] Another part of the signal enters the second slave multiplexer / demultiplexer 220 together with the time difference information and spreading code signal output by the slave signal processing module 223, which is modulated by the fourth slave laser 222, through the fourth slave coupler 219. After being multiplexed by the second slave multiplexer / demultiplexer 220, it is sent to the master terminal 1 through the slave optical telescope 221.

[0066] The main terminal 1: The main multi-channel frequency and phase discrimination module 124 measures the phase difference between the wavelengths of the output light from the three main lasers and the wavelengths received from the corresponding three slave lasers from the slave terminal 2. Based on the phase information between the multiple wavelengths, the main terminal demodulates the "precise time difference" T measured by the virtual synthesized wavelength. f，BA (Measurement range T) f Simultaneously, the main multi-channel frequency and phase discrimination module 124 measures the "coarse time difference" T between the local spreading code of the main signal processing module 123 and the spreading code received from the slave end 2. c，BA (Measurement range T) c The main multi-channel frequency and phase discrimination module 124, according to T f，BA and T c，BA Demodulate the time difference T measured at the master end BA ;

[0067] Slave terminal 2: The multi-channel frequency and phase discrimination module 224 measures the phase difference between the wavelengths of the output light from the three slave lasers and the wavelengths of the corresponding output light from the master lasers received from the master terminal 1. Based on the phase information between the multiple wavelengths, the slave terminal demodulates the "precise time difference" T measured by the virtual synthesized wavelength. f，AB (Measurement range T) f Simultaneously, the multi-channel frequency and phase discrimination module 224 measures the "coarse time difference" T between the local spreading code of the signal processing module 223 and the spreading code received from the master terminal 1. c，AB (Measurement range T) c The multi-channel frequency and phase discrimination module 224, based on T... f，AB and T c，AB Demodulate the time difference T measured from the slave end AB ;

[0068] The master end will measure the time difference T. BAThe data is sent to the slave end, which then transmits the data based on the time difference T measured by the master end. BA The time difference T between the measured ends AB The clock difference ΔT at both ends is calculated, i.e., ΔT = (T AB -T BA The output frequency and delay of the slave reference optical carrier are adjusted according to the clock difference ΔT at both ends, so that ΔT→0, thereby achieving time and frequency synchronization between the master and slave ends.

[0069] like Figure 3 As shown, the measurement range of time difference (phase difference) can be effectively extended by employing multiple wavelengths. The first-stage virtual synthesized wavelength chain, based on the wavelength λ0 (period τ0) of the first master laser 101 and the first slave laser 201, selects the wavelength λ1 of the second master laser 106 and the second slave laser 206, extending the time difference measurement range to the picosecond level. The second-stage virtual synthesized wavelength chain, based on the existing wavelengths λ0 and λ1, determines the wavelength λ2 of the third master laser 111 and the third slave laser 211, extending the time difference measurement range to the hundreds of picoseconds. The selection of wavelengths in the virtual synthesized wavelengths of this invention needs to consider the phase measurement accuracy of the master multi-channel frequency and phase discrimination module 124 and the slave multi-channel frequency and phase discrimination module 224, the optical comb spectral width of the master optical frequency comb module 117 and the slave optical frequency comb module 217, and needs to create sufficient wavelength spacing conditions for multi-wavelength demodulation in the virtual synthesized wavelengths.

[0070] For the virtual synthesis wavelength, the first-order synthesis wavelength is selected as: λ 01 =λ0λ1 / |λ0-λ1|=β1λ0, then the expansion factor is: β1=λ1 / |λ0-λ1|. Considering that the phase measurement accuracies of the two wavelengths are independent of each other and have a confidence interval of ±3σ (σ is the standard deviation of the phase measurement), the combined uncertainty of the phase measurement u 01 It can be represented as:

[0071]

[0072] In the formula, δ p Phase measurement accuracy for each wavelength. The project team has previously achieved a phase measurement accuracy better than 10 ps with a 10 MHz phase meter, δ p The relative measurement accuracy of the phase is 1 / 10000. At this point, the spread factor β1 cannot exceed 589, corresponding to a minimum interval of approximately 2.63 nm between the two wavelengths. To ensure measurement reliability, and considering that the on-chip electro-optic modulation optical comb to be implemented in this project has a spectral width of approximately 10-15 nm, a wavelength interval of Δλ = 5 nm is selected. Figure 2As shown. For a light wavelength λ0≈1550nm, λ1=1545nm can be selected, with a corresponding scaling factor β1≈309. Its equivalent virtual composite wavelength is approximately 463.5μm, the non-periodic ambiguity range is 231μm, and the corresponding time difference measurement range is 0.77ps.

[0073] The second-level virtual synthesis wavelength consists of two first-level synthesis wavelengths λ. 01 and λ 02 Re-synthesis is achieved by selecting λ2. The fractional part of the virtual synthesized wavelength phase measurement can then be expressed as Δe. sw =e1-2e0+e2,u 012 The phase uncertainty compared to u 01 If the expansion factor is increased by a factor of 2, then the expansion factor must also be reduced to satisfy the inter-level fusion condition. Taking β²≈154, then 193λ 01 =194λ 02 Or 194λ 01 =193λ 02 At this point, λ2 has two possible values: λ2 < λ0 or λ2 > λ0. For ease of multi-wavelength demodulation, we choose λ2 > λ0, resulting in λ2 around 1555 nm. The second-order equivalent composite wavelength is approximately 71 mm, and the aperiodic ambiguity range is 35.5 mm. A time difference measurement range of 118 ps can be achieved using the second-order composite wavelength.

[0074] The main terminal 1: The main multi-channel frequency and phase discrimination module 124 measures the phase difference between the wavelengths of the output light from the first main laser 101, the second main laser 106, and the third main laser 111 and the wavelengths received from the corresponding slave lasers from the slave terminal 2. The main terminal demodulates the "precise time difference" T measured by virtual synthesized wavelength based on the phase information between the three wavelengths. f，BA (Measurement range T) f Simultaneously, the main multi-channel frequency and phase discrimination module 124 measures the "coarse time difference" T between the local spreading code of the main signal processing module 123 and the spreading code received from the slave end 2. c，BA (Measurement range T) c The main multi-channel frequency and phase discrimination module 124, according to T f，BA and T c，BA Demodulate the time difference T measured at the master end BA ;

[0075] Slave terminal 2: The multi-channel frequency and phase discrimination module 224 measures the phase difference between the wavelengths of the output light from the three slave lasers (first master laser 101, second master laser 106, and third master laser 111) and the wavelengths of the corresponding output light from each master laser received from the master terminal 1. Based on the phase information between the multiple wavelengths, the slave terminal demodulates the "precise time difference" T measured by virtual synthesized wavelength. f，AB (Measurement range T) f Simultaneously, the multi-channel frequency and phase discrimination module 224 measures the "coarse time difference" T between the local spreading code of the signal processing module 223 and the spreading code received from the master terminal 1. c，AB (Measurement range T) c The multi-channel frequency and phase discrimination module 224, based on T... f，AB and T c，AB Demodulate the time difference T measured from the slave end AB ;

[0076] The master end will measure the time difference T. BA The data is sent to the slave end, which then transmits the data based on the time difference T measured by the master end. BA The time difference T between the measured ends AB The clock difference ΔT at both ends is calculated, i.e., ΔT = (T AB -T BA ) / 2, to complete the bidirectional time comparison. At the same time, the slave end can adjust the output frequency and delay of the slave end reference optical carrier according to the clock difference ΔT between the two ends, so that ΔT→0, thereby realizing the time and frequency synchronization between the master and slave ends.

Claims

1. A bidirectional optical time-frequency comparison method based on virtual synthesized wavelength, comprising a master end (1) and a slave end (2), and a free-space link (3) connecting the master end (1) and the slave end (2), characterized in that, The steps include the following: The master end synthesizes multiple wavelength signals to form a virtual synthesized wavelength and sends it to the slave end. At the same time, the slave end synthesizes multiple wavelength signals to form a virtual synthesized wavelength and sends it to the master end. The time difference between the local optical virtual synthesis wavelength measured at the master end and the virtual synthesis wavelength received at the slave end. The signal is sent to the slave end, and simultaneously, the slave end measures the time difference between the local optical virtual synthesis wavelength and the virtual synthesis wavelength received from the master end. ; The slave end calculates the clock difference between the master and slave ends based on the two-way comparison principle. , And adjust the optical carrier frequency and phase at the slave end, so that Thus, the time and frequency of the master and slave ends are synchronized.

2. The bidirectional optical time-frequency comparison method based on virtual synthesized wavelength according to claim 1, characterized in that, The time difference between the locally virtual synthesized wavelength measured by the master end and the virtual synthesized wavelength received from the slave end is... Specifically: The main multi-channel frequency and phase discrimination module (124) measures the phase difference between the wavelength of the output light of each main laser and the wavelength of the corresponding slave laser received from the slave end (2), and demodulates the main end precise time difference measured by virtual synthesized wavelength based on the phase information between the multiple wavelengths. Measurement range Meanwhile, the main multi-channel frequency and phase discrimination module (124) measures the coarse time difference between the local spreading code of the main signal processing module (123) and the spreading code received from the slave end (2). Measurement range And based on the master-slave precision time difference Coarse time difference with master end Demodulate the time difference measured at the master end .

3. The bidirectional optical time-frequency comparison method based on virtual synthesized wavelength according to claim 1, characterized in that, The time difference between the locally virtual synthesized wavelength measured by the slave end and the virtual synthesized wavelength received by the master end Specifically: The phase difference between the wavelength of the output light from each slave laser and the wavelength of the corresponding master laser received from the master end (1) is measured by the multi-channel frequency and phase discrimination module (224), and the slave end precise time difference measured by virtual synthesized wavelength is demodulated based on the phase information between the multiple wavelengths. Measurement range Meanwhile, the multi-channel frequency and phase discrimination module (224) measures the coarse time difference between the local spreading code from the main signal processing module (223) and the spreading code received from the main terminal (1). Measurement range And based on the time difference from the end and coarse time difference from end Demodulate the time difference measured at the master end .

4. A bidirectional optical time-frequency comparison system based on virtual synthesized wavelength, comprising a master end (1) and a slave end (2), and a free-space link (3) connecting the master end (1) and the slave end (2), characterized in that, The main terminal (1) includes The main virtual synthesized wavelength module, the first main multiplexer / demultiplexer (116), the main optical frequency comb module (117), the main Faraday rotator (118), and the first... Main coupler (119), second main multiplexer / demultiplexer (120), main optical telescope (121), and the first... Main laser (122), main signal processing module (123), main multi-channel frequency and phase discrimination module (124), and the first The main photodetector (125) and the main circulator (126); The first main virtual synthesized wavelength module includes a first main laser (101), a first main coupler (102), a first main photodetector (103), a first main bandpass filter (104), and a first main servo controller (105). The laser output port of the first main laser (101) is connected to the first port of the first main coupler (102), the electrical control port of the first main laser (101) is connected to the output port of the first main servo controller (105), and the second port of the first main coupler (102) is connected to the first main photodetector. The optical input port of the detector (103) is connected, the electrical output port of the first main photodetector (103) is connected to the input port of the first main bandpass filter (104), the first output port of the first main bandpass filter (104) is connected to the input port of the first main servo controller (105), the second output port of the first main bandpass filter (104) is connected to the first input port of the main multi-channel frequency and phase discrimination module (124), and the third port of the first main coupler (102) is connected to the first port of the first main multiplexer (116). And so on, the Nth main virtual synthesis wavelength module, including the Nth... Main laser, the first Main coupler, Main photodetector, the first The main bandpass filter and the first The main servo controller, the first The laser output port of the main laser and the first The first port of the main coupler is connected, and the second... The electrical control port of the main laser and the first The output port of the main servo controller is connected, the first The second port of the main coupler and the first The optical input port of the main photodetector is connected, and this... The electrical output port of the main photodetector is connected to the first The input port of the main bandpass filter is connected, and this... The first output port of the main bandpass filter and the... The input port of the main servo controller is connected, and this... The second output port of the main bandpass filter is connected to the main multi-channel frequency and phase discrimination module (124). The input port is connected, the first The third port of the main coupler is connected to the first main multiplexer / demultiplexer (116) at its third port. The ports are connected; The first main multiplexer (116) The port is connected to the first port of the main Faraday rotator (118), and the second port of the main Faraday rotator (118) is connected to the first port of the main Faraday rotator (118). The first port of the main coupler (119) is connected, and the second... The second and third ports of the main coupler are respectively connected to the first port of the second main multiplexer / demultiplexer (120) and the output terminal of the main optical frequency comb module (117). The second and third ports of the second main multiplexer / demultiplexer (120) are respectively connected to the third port of the main circulator (126) and the input port of the main optical telescope (121). The first and second ports of the main circulator (126) are respectively connected to the first port of the main optical circulator (126) and the input port of the main optical telescope (121). The output port of the main laser (122), the first The input port of the main photodetector (225) is connected to the main signal processing module (123). The first, second, and third ports of the main signal processing module (123) are respectively connected to the output port of the main multi-channel frequency and phase discrimination module (124) and the input port of the main multi-channel frequency and phase discrimination module (125). The output port of the main photodetector (225), the aforementioned... The main laser (122) is electrically modulated and connected to the control port; The slave end (2) includes N slave virtual synthesized wavelength modules, a first slave multiplexer / demultiplexer (216), a slave optical frequency comb module (217), a slave Faraday rotator (218), and a second slave... From coupler (219), second from multiplexer / demultiplexer (220), from optical telescope (221), the first From the laser (222), from the signal processing module (223), from the multi-channel frequency and phase discrimination module (224), the first From the photodetector (225), from the circulator (226) and the first From the servo controller (227); The first slave virtual synthesis wavelength module includes a first slave laser (201), a first slave coupler (202), a first slave photodetector (203), a first slave bandpass filter (204), and a first slave servo controller (205). The laser output port of the first slave laser (201) is connected to the first port of the first slave coupler (202), the electrical control port of the first slave laser (201) is connected to the output port of the first slave servo controller (205), and the second port of the first slave coupler (202) is connected to the first slave photodetector. The first slave photodetector (203) is connected to the optical input port of the first slave photodetector (203), the first slave bandpass filter (204) is connected to the input port of the first slave bandpass filter (204), the first slave bandpass filter (204) is connected to the input port of the first slave servo controller (205), the second slave bandpass filter (204) is connected to the first input port of the slave multi-channel frequency and phase discrimination module (224), and the third slave coupler (202) is connected to the first slave multiplexer (216). And so on, the Nth path from the virtual synthesized wavelength module, including the Nth... From lasers, the first From the coupler, the From photodetectors, the first From bandpass filter and the From the servo controller, the first From the laser output port of the laser and the first Connected from the first port of the coupler, the first... From the electrical control port of the laser and the first Connected to the output port of the servo controller, the first From the second port of the coupler and the first Connected to the optical input port of the photodetector, this... From the electrical output port of the photodetector and the first Connected from the input port of the bandpass filter, this first... From the first output port of the bandpass filter and the... Connected to the input port of the servo controller, this first The second output port of the bandpass filter is connected to the multi-channel frequency and phase discrimination module (224). The input port is connected, the first From the third port of the coupler and the first from the multiplexer (216) The ports are connected; The first from the multiplexer (216) The port is connected to the first port of the Faraday rotator (218), and the second port of the Faraday rotator (218) is connected to the first port of the Faraday rotator (218). Connected from the first port of the coupler (219), the first... The second and third ports of the coupler (219) are respectively connected to the first port of the second multiplexer / demultiplexer (220) and the output of the optical frequency comb module (217). The second and third ports of the second multiplexer / demultiplexer (220) are respectively connected to the third port of the circulator and the input port of the optical telescope (221). The first and second ports of the circulator are respectively connected to the first... From the output port of the laser (222), the first The input port of the photodetector (225) is connected to the input port of the photodetector (225), and the first, second, third, and fourth ports of the signal processing module (223) are respectively connected to the output port of the multi-channel frequency and phase discrimination module (224), the second, and the third ports of the signal processing module (223). From the output port of the photodetector (225), the first From the electrical modulation and control port of the laser (222), the first Connected to the input port of the servo controller (225), this... The output port of the servo controller (225) is connected to the repetition rate and delay control port of the optical frequency comb module (217); The main end (1) The output of the main virtual synthesized wavelength module After being combined by the first main multiplexer (116), the light wave is incident on the main Faraday rotator (118), where it is split into two parts: A portion of the signal, along with the main optical frequency comb signal output from the main optical frequency comb module (117), returns along the original path. After being split by the first main multiplexer (116), the signals are respectively delivered to the main photodetectors via their respective main couplers. The beat frequency signals output by each main photodetector are fed back to control the output frequency of each main laser through each main servo controller, thereby achieving... Virtual composite wavelengths coherent with each wavelength; Another part of the signal passes through the first The main coupler (119) and the first The signal carrying time difference information and spreading code signal, modulated by the main laser (122) and output by the main signal processing module (123), enters the second main multiplexer (120). After being combined by the second main multiplexer (120), it is sent to the slave end (2) through the main optical telescope (121). Similarly, the N channels output from the virtual synthesized wavelength module at the slave end (2) After being combined by the first combiner / demultiplexer (216), the light wave is incident on the Faraday rotator (218), where it is split into two parts: A portion of the signal, along with the optical frequency comb signal output from the optical frequency comb module (217), returns along the original path. After being split by the first multiplexer / demultiplexer (216), the signals are respectively delivered to the respective photodetectors via their respective couplers. The beat frequency signals output by each photodetector are fed back to control the output frequency of each laser through the respective servo controllers, thereby achieving... Virtual composite wavelengths coherent with each wavelength; Another part of the signal passes through the first From the coupler (219) and via the first The time difference information and spreading code signal modulated by the laser (222) and output by the signal processing module (223) enter the second slave multiplexer (220). After being multiplexed by the second slave multiplexer (220), the signal is sent to the main end (1) through the slave optical telescope (221). The main end (1): The main multi-channel frequency and phase discrimination module (124) measures the phase difference between the wavelength of the output light of each main laser and the wavelength of the corresponding slave laser received from the slave end (2), and demodulates the main end precise time difference measured by virtual synthesized wavelength based on the phase information between the multiple wavelengths. Measurement range Meanwhile, the main multi-channel frequency and phase discrimination module (124) measures the main coarse time difference between the local spreading code of the main signal processing module (123) and the spreading code received from the slave end (2). Measurement range The main multi-channel frequency and phase discrimination module (124) is based on the main end precise time difference. Coarse time difference with master end Demodulate the time difference measured at the master end ; The slave end (2): The multi-channel frequency and phase discrimination module (224) measures the phase difference between the wavelength of the output light of each slave laser and the wavelength of the output light of the corresponding master laser received from the master end (1), and demodulates the slave end precise time difference measured by virtual synthesized wavelength based on the phase information between the multiple wavelengths. Measurement range Meanwhile, the multi-channel frequency and phase discrimination module (224) measures the coarse time difference between the local spreading code of the signal processing module (223) and the spreading code received from the master terminal (1). Measurement range The multi-channel frequency and phase discrimination module (224) uses the slave end's precise time difference... and coarse time difference from end Demodulate the time difference measured from the slave end ; The master end will measure the time difference. The data is sent to the slave end, which then uses the time difference measured by the master end. Time difference measured from the end The clock difference at both ends was calculated. ,Right now And based on the clock difference at both ends Adjust the output frequency and delay of the slave-end reference optical carrier so that This enables time and frequency synchronization between the master and slave ends.

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