A time and frequency double-compensated optical fiber time transfer system and method

Abstract

The application provides a time and frequency double-compensation optical fiber time transfer system and method, and belongs to the optical fiber communication field.The system comprises an optical fiber frequency transfer part, an oscillator phase is controlled according to an error signal, so that the optical fiber frequency transfer compensation is realized; the optical fiber time transfer part calculates the time delay needing compensation through the round-trip link time difference value and compensates, so that the link delay compensation of the optical fiber time transfer is realized; the real-time link time delay change compensation of the optical fiber time transfer is realized through the optical fiber frequency compensation, so that the optical fiber time transfer compensation is realized; the output time signal, the frequency signal and the round-trip link time difference value are output to the user after adjustment; the time and frequency signal only needs to occupy one wavelength channel, so that the optical fiber resources are saved; the time signal and the frequency signal are phase-related; and the transmission stability of the time signal is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical fiber communication, and relates to optical fiber time transfer, in particular to an optical fiber time transfer system and method with time and frequency double compensation. BACKGROUND

[0002] In the fields of aerospace, radar synchronization, control of cutting-edge weapons, high-speed communication, deep space exploration, etc., very high requirements are put forward for time signal synchronization and frequency signal phase synchronization. The current long-wave time service can only achieve microsecond synchronization accuracy, satellite common view can only achieve nanosecond synchronization accuracy, and even the satellite two-way comparison method which is expensive can only achieve hundred picosecond synchronization accuracy. The optical fiber time and frequency transfer method can achieve hundred picosecond time synchronization accuracy, e-19 / day frequency synchronization stability, and the equipment price is much lower than that of the satellite two-way comparison method, so the optical fiber time and frequency transfer method has broad application prospects.

[0003] The existing technology is often realized by two independent devices for optical fiber time transfer and optical fiber frequency transfer, which is high in cost and needs more optical fiber resources. Even if the optical fiber time and frequency transfer can be realized in one wavelength channel, the frequency signal to be transferred is often used as a carrier for round trip transmission and compensation. This method has low frequency transfer index and cannot eliminate the noise fluctuation caused by lasers, beam splitters, circulators and other out-of-loop devices. The time and frequency signals obtained by the above method are not phase-related, while in actual applications, the phase correlation of time and frequency signals is often required, such as time and frequency synchronization between radar fixed stations and time and frequency synchronization between VLBI observation stations.

[0004] Patent document (CN106788840B) proposes a high-precision optical fiber time synchronization method based on optical fiber frequency transfer. The main technical scheme uses optical fiber frequency transfer to realize the phase stability of the frequency signals of the transmitting end and the receiving end, uses the frequency signal to generate the time signal, and uses the optical fiber time synchronization to calibrate the time signal. The two systems used by the method separately transfer the time signal and the frequency signal, and need to occupy two wavelength channels. The receiving end uses the received time signal and frequency signal and a programmable delay to enhance the precision of the time signal transmission by using the frequency signal. Since the time transfer and the frequency transfer are in two systems, the noises of the two systems at the receiving end will be superimposed, which affects the output index and cannot achieve the complete synchronization of the phase of the output time signal and the frequency signal.

[0005] The patent document (CN106712886A) adopts a time division multiplexing mode to realize the simultaneous transmission of time signals and frequency signals, and the main technical solution is to realize the time frequency and time code service of a transmitter of a transmitting center to multiple users in different places in the form of a bus, which is convenient for networking. The method adopts a time division multiplexing mode to realize the simultaneous transmission of time signals and frequency signals; the frequency transmission performed by the method has a low frequency transmission index because the 10MHz frequency signal is used in the transmission system, and the noise fluctuation caused by the out-of-loop devices such as lasers, beam splitters and circulators cannot be eliminated.

[0006] The patent document (CN113708878A) adopts a wavelength division multiplexing mode to realize the transmission of optical fiber microwave signals; the free optical fiber link noise is obtained by comparing the phase of the compensated frequency signal and the reference frequency signal; and the transmission noise of the time signal is pre-compensated by using the free optical fiber link noise to realize the optical fiber time transmission. The method adopts a wavelength division multiplexing mode, which needs to occupy two wavelength channels; and the optical fiber time transmission is realized by pre-compensating the transmission noise of the time signal by using the free optical fiber link noise, which can only compensate the noise within one period of the corresponding frequency signal and cannot accurately compensate the delay of the real optical fiber link. SUMMARY

[0007] To solve the above technical problems, the application provides a time frequency double-compensated optical fiber time transmission system, a frequency reference signal and a time reference signal are generated by a time frequency source, the frequency reference signal is input into a first frequency doubling module and a second frequency doubling module, and the time reference signal is input into a time difference measurement module and an encoding and modulation module;

[0008] A first mixing module mixes the frequency signal from the first frequency doubling module and the frequency signal from the first demodulation and decoding module, and then inputs the mixed signal into a second mixing module;

[0009] A third mixing module mixes the frequency signal from the second frequency doubling module and the frequency signal from the second demodulation and decoding module, and then inputs the mixed signal into the second mixing module;

[0010] The second mixing module mixes the frequency signal from the first mixing module and the frequency signal from the third mixing module, and then inputs the error signal obtained by the mixing into a phase-locked loop;

[0011] The phase-locked loop controls the phase of an oscillator according to the error signal input by the second mixing module, to realize the optical fiber frequency transmission;

[0012] The time difference measurement module measures the difference between the time reference signal from the time frequency source and the time signal from the second demodulation and decoding module, and then inputs the difference into the encoding and modulation module;

[0013] The encoding modulation module encodes and modulates the time reference signal from the time frequency source, the difference of the time signals from the time difference measurement module and the frequency signal from the oscillator, and sends the signals into the laser;

[0014] The laser modulates the laser signal with the signals from the encoding modulation module, and sends the modulated optical signal into the first beam splitter;

[0015] The first beam splitter sends part of the optical signal into the first photodetector, and sends another part of the optical signal into the first optical circulator;

[0016] The first optical circulator sends the signal from the first beam splitter into the fiber link, and sends the signal from the fiber link into the second photodetector;

[0017] The fiber link sends the signal from the first optical circulator into the second optical circulator, and sends the signal from the second optical circulator into the first optical circulator;

[0018] The second beam splitter sends part of the optical signal into the third photodetector, and sends another part of the optical signal into the second optical circulator;

[0019] The second optical circulator sends the signal from the second beam splitter into the fiber link, and sends the signal from the fiber link into the optical amplification module; the optical amplification module amplifies the received signal from the second optical circulator and sends the amplified signal into the second beam splitter;

[0020] The third demodulation and decoding module demodulates the time signal, the frequency signal and the round-trip link time difference value, and outputs the signals to the time signal generation module and the frequency divider;

[0021] The time signal generation module calculates the time compensation amount according to the round-trip link time difference value, compensates the time signal, and outputs the compensated time signal to the user;

[0022] The frequency divider divides the frequency signal and outputs the divided frequency signal to the user.

[0023] Further, the first photodetector is used to convert the optical signal into an electrical signal, and sends the electrical signal into the first demodulation and decoding module; the first demodulation and decoding module demodulates and decodes the signal from the first photodetector into a frequency signal, and sends the frequency signal into the first mixing module;

[0024] The second photodetector is used to convert the optical signal into an electrical signal, and sends the electrical signal into the second demodulation and decoding module; the second demodulation and decoding module demodulates and decodes the signal from the second photodetector into a frequency signal, and sends the frequency signal into the third mixing module;

[0025] The third photoelectric detector is used for converting the optical signal into an electric signal and sending the electric signal into a third demodulation and decoding module.

[0026] Further, the round-trip link time difference is T d , and the time compensation amount required by the time signal generation module is T d / 2, the time signal is compensated, and output to the user, wherein the change of the optical fiber link delay is corrected by real-time optical fiber frequency transmission frequency phase compensation.

[0027] Further, the first frequency multiplication module is an M frequency multiplier, and the second frequency multiplication module is an N frequency multiplier.

[0028] Further, the reference clock of the encoding and modulation of the time signal comes from an oscillator, realizing the compensation of the link delay change of the optical fiber time transmission.

[0029] The application further provides an optical fiber time transmission method with time and frequency double compensation, which is realized by an optical fiber time transmission system.

[0030] The frequency signal generated by the first frequency multiplication module is V1=cos(w1t+Φ1), and the frequency signal generated by the second frequency multiplication module is V2=cos(w2t+Φ2).

[0031] The first photoelectric detector detects V'0=cos(w0t+Φ'0), and the third photoelectric detector detects V3=cos(w0t+Φ'0+Φ p );

[0032] After the returned signal is passed through the second photoelectric detector at the transmitting end, a frequency signal V4=cos(w0t+Φ'0+2Φ p ) containing twice the optical fiber link phase noise is obtained.

[0033] The signal V1 and V'0 are mixed, and low-pass filtering is performed to obtain:

[0034] V e1 =cos[(w0-w1)t+(Φ'0-Φ1)];

[0035] The signal V2 and V4 are mixed, and low-pass filtering is performed to obtain:

[0036] V e2 =cos[(w2-w0)t+(Φ2-Φ'0-2Φ p)]

[0037] V e1 and V e2 mixing, low-pass filtering, we get:

[0038] V e = cos[(2w0-w2-w1)t+2Φ′0+2Φ p -Φ1-Φ2];

[0039] = cos[2(w0-w r )t+2(Φ′0+Φ p -Φ r -ε)];

[0040] V e is the error signal fed back to the oscillator, through V e feedback control the frequency and phase of the oscillator, so that it satisfies:

[0041] w0= w r ;

[0042] Φ′0+Φ p = Φ r ;

[0043] The signal V3 received by the receiving end is expressed as:

[0044] V3= cos(w0t+Φ′0+Φ p ) = cos(w r t+Φ r );

[0045] The signal V3 is phase-locked to the frequency signal V r transmitted by the transmitting end at the receiving end.

[0046] Further, the frequency signal transmitted by the oscillator outwardly is: V r = cos(w r t+Φ r ).

[0047] Further, w1+w2=2w0; Φ1+Φ2=2(Φ r +ε);

[0048] wherein ε is a fixed phase difference.

[0049] Compared with the prior art, the present application has the following beneficial technical effects:

[0050] The transmission of the time and frequency signals only occupies one wavelength channel, saving optical fiber resources; the phase of the time signal is related to the frequency signal; and the transmission stability of the time signal is improved. BRIEF DESCRIPTION OF DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings described below are only some of the embodiments of the present application, and all other drawings obtained by those of ordinary skill in the art without creative labor based on these drawings are within the protection scope of the present application.

[0052] Figure 1 is a schematic diagram of a time and frequency double-compensated optical fiber time transfer system of the present application. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the following will clearly and completely describe the technical solutions in the embodiments of the present application in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the protection scope of the present application.

[0054] In the specific embodiment drawings of the present application, in order to better and more clearly describe the working principles of the elements in the system and show the connection relationship of the parts in the device, only the relative position relationship between the elements is distinguished, and it cannot be regarded as the limitation of the signal transmission direction, connection order and the size, dimension and shape of the parts in the element or structure.

[0055] As Figure 1 The schematic diagram of a time and frequency double-compensated optical fiber time transfer system of the present application is shown. The present application provides a time and frequency double-compensated optical fiber time transfer system 100, which comprises a time and frequency source 10, a first frequency doubling module 20, a second frequency doubling module 21, a first mixing module 30, a second mixing module 31, a third mixing module 32, a first demodulation and decoding module 40, a second demodulation and decoding module 41, a third demodulation and decoding module 42, a time signal generation module 43, a frequency divider 44, a phase-locked loop 50, an oscillator 51, an encoding and modulation module 52, a time difference measurement module 60, a first photoelectric detector 70, a second photoelectric detector 71, a third photoelectric detector 72, a first beam splitter 73, a laser 74, a second beam splitter 75, an optical amplification module 76, a first optical circulator 80, a second optical circulator 81 and an optical fiber link 90.

[0056] The time and frequency source 10 generates a frequency reference signal f refThe frequency reference signal is input into the first frequency multiplication module 20 and the second frequency multiplication module 21, and the time reference signal is input into the time difference measurement module 60 and the encoding modulation module 52. In this embodiment, the frequency reference signal is 10MHz, and the time reference signal is 1PPS signal.

[0057] The first frequency multiplication module 20 is M frequency multiplier, which multiplies the input 10MHz frequency signal to 380MHz frequency signal and inputs into the first mixing module 30. In this embodiment, the value of M is 38.

[0058] The second frequency multiplication module 21 is N frequency multiplier, which multiplies the input 10MHz frequency signal to 400MHz frequency signal and inputs into the third mixing module 32. In this embodiment, the value of N is 40.

[0059] The first mixing module 30 mixes the 380MHz frequency signal from the first frequency multiplication module 20 and the frequency signal from the first demodulation and decoding module 40, and then inputs into the second mixing module 31.

[0060] The third mixing module 32 mixes the 400MHz frequency signal from the second frequency multiplication module 21 and the frequency signal from the second demodulation and decoding module 41, and then inputs into the second mixing module 31.

[0061] The second mixing module 31 mixes the frequency signal from the first mixing module 30 and the frequency signal from the third mixing module 32, and then inputs into the phase-locked loop 50.

[0062] The first demodulation and decoding module 40 demodulates and decodes the signal from the first photoelectric detector 70 to frequency signal and inputs into the first mixing module 30.

[0063] The second demodulation and decoding module 41 demodulates and decodes the signal from the second photoelectric detector 71 to frequency signal and inputs into the first mixing module 30.

[0064] The third demodulation and decoding module 42 demodulates and decodes the signal from the third photoelectric detector 72 to time signal, frequency signal and round-trip link time difference value, and inputs into the time signal generation module 43; wherein the frequency signal is input into the frequency divider 44.

[0065] The time signal generation module 43 is used to generate time signal and output to user; wherein the time signal generation module 43 calculates the time compensation amount T d / 2 which the time signal generation module 43 needs to perform according to the demodulated round-trip link time difference value T d , compensates the time signal and outputs to user; wherein the change of the fiber link time delay is corrected by the real-time frequency phase compensation of the fiber frequency transmission.

[0066] The frequency divider 44 divides the frequency signal according to the user's frequency requirement and outputs it for the user to use. For example, the frequency signal of the atomic clock in the example is 10 MHz, and the oscillator is 390 MHz. If the user requires a frequency signal with the same frequency as the atomic clock, the frequency divider can be set to 39.

[0067] The phase-locked loop 50 controls the phase of the oscillator 51 according to the error signal input by the second mixing module, thereby realizing fiber frequency transfer. Since the reference clock for the encoding and modulation of the time signal by the encoding and modulation module 52 comes from the oscillator, the link delay variation of the fiber time transfer is compensated.

[0068] The oscillator 51 outputs a 390 MHz frequency signal, which is sent to the encoding and modulation module 52.

[0069] The encoding and modulation module 52 encodes and modulates the time reference signal from the time frequency source 10, the round-trip link time difference value from the time difference measurement module 60, and the frequency signal from the oscillator 51, and sends them to the laser 74.

[0070] The time difference measurement module 60 measures the difference between the time reference signal from the time frequency source 10 and the time signal from the second demodulation and decoding module 41, and sends the round-trip link time difference value to the encoding and modulation module 52 for encoding and modulation.

[0071] The first photodetector 70 is used to convert the optical signal into an electrical signal and send it to the first demodulation and decoding module 40.

[0072] The second photodetector 71 is used to convert the optical signal into an electrical signal and send it to the second demodulation and decoding module 41.

[0073] The third photodetector 72 is used to convert the optical signal into an electrical signal and send it to the third demodulation and decoding module 42.

[0074] The first beam splitter 73 has a splitting ratio of 1:99. The optical signal output from the port with a ratio of 1 is sent to the first photodetector 70, and the optical signal output from the port with a ratio of 99 is sent to the first optical circulator 80. The splitting ratio of the first beam splitter 73 is not limited to 1:99 and can be adjusted according to the actual link.

[0075] The laser 74 modulates the signal from the encoding and modulation module 52 on the optical signal and sends it to the first beam splitter 73.

[0076] The second beam splitter 75 has a splitting ratio of 1:99, the light signal output from the port with a ratio of 1 is sent to the third photodetector 72, and the light signal output from the port with a ratio of 99 is sent to the second optical circulator 81. The splitting ratio of the second beam splitter 75 is not limited to 1:99, and can be adjusted according to the actual link.

[0077] The optical amplification module 76 amplifies the received signal of the second optical circulator 81 and sends it to the second beam splitter 75.

[0078] The first optical circulator 80 sends the signal from the first beam splitter 73 to the fiber link 90, and sends the signal from the fiber link 90 to the second photodetector 71.

[0079] The second optical circulator 81 sends the signal from the second beam splitter 75 to the fiber link 90, and sends the signal from the fiber link 90 to the optical amplification module 76.

[0080] The fiber link 90 can be an on-site fiber or a disk fiber with a length of less than 100 km, which sends the signal from the first optical circulator 80 to the second optical circulator 81, and sends the signal from the second optical circulator 81 to the first optical circulator 80.

[0081] The time frequency source 10, the first frequency doubling module 20, the second frequency doubling module 21, the first mixing module 30, the second mixing module 31, the third mixing module 32, the first demodulation and decoding module 40, the second demodulation and decoding module 41, the third demodulation and decoding module 42, the frequency divider 44, the phase-locked loop 50, the oscillator 51, the encoding and modulation module 52, the first photodetector 70, the second photodetector 71, the third photodetector 72, the first beam splitter 73, the laser 74, the second beam splitter 75, the optical amplification module 76, the first optical circulator 80, the second optical circulator 81, and the fiber link 90 form a fiber frequency transfer part, and the phase-locked loop 50 controls the phase of the oscillator 51 according to the error signal input by the second mixing module, thereby realizing fiber frequency transfer compensation.

[0082] The time frequency source 10, the second demodulation and decoding module 41, the third demodulation and decoding module 42, the time signal generation module 43, the encoding and modulation module 52, the second photodetector 71, the third photodetector 72,

[0083] The first beam splitter 73, the laser 74, the second beam splitter 75, the optical amplification module 76, the first optical circulator 80, the second optical circulator 81, and the fiber link 90 form a fiber time transfer part.

[0084] The time delay to be compensated is calculated and compensated by the time signal generating module 43 through the round-trip link time difference value of the time difference measuring module 60, realizing the compensation of the link delay of the fiber time transfer; since the frequency signal of the encoding and modulating module 52 is the same as the signal transmitted in the fiber frequency transfer, the compensation of the real-time link delay variation of the fiber time transfer is realized through the fiber frequency compensation, thereby realizing the compensation of the fiber time transfer.

[0085] The phase noise introduced by the fiber transmission is proactively detected and pre-compensated at the transmitting end, so that the frequency signal phase-locked to the atomic clock at the transmitting end is obtained at the receiving end. The phase noise of the transmission link is compensated by feedback controlling the phase of an oscillator 51, and the frequency signal generated by the oscillator 51 is denoted as V0 = cos(w0t + Φ0), wherein w0 and Φ0 are the initial frequency and phase of the frequency signal generated by the oscillator, respectively. The initial frequency used in the embodiment is 390 MHz. The output optical signal of the laser 74 is amplitude-modulated by using the frequency signal V0. The frequency signal generated by the first frequency doubling module 20 in the system is locked to the atomic clock and denoted as V1 = cos(w1t + Φ1), and the frequency signal generated by the second frequency doubling module 21 is locked to the atomic clock and denoted as V2 = cos(w2t + Φ2), wherein w1 and Φ1 are the frequency and phase of the frequency signal generated by the first frequency doubling module, and w2 and Φ2 are the frequency and phase of the frequency signal generated by the second frequency doubling module.

[0086] The frequency signal V r that the oscillator 51 intends to emit outward is cos(w r t + Φ r ), and satisfies:

[0087] w1 + w2 = 2w0;

[0088] Φ1 + Φ2 = 2(Φ r + ε);

[0089] wherein ε is a fixed phase difference, w r and Φ r are the frequency and phase of the frequency signal that the oscillator 51 intends to emit outward, and the frequency used in the embodiment is 390 MHz.

[0090] V1, V2 are two phase-locked frequency signals of an atomic clock, in this embodiment, the frequency signals V1, V2 have frequencies of 380 MHz and 400 MHz respectively, which are used to generate auxiliary frequency signals of the error signal for feedback control of the frequency signal V0 generated by the oscillator. The laser modulated by V0 passes through the first beam splitter 73, the first optical circulator 80 and enters the fiber link 90. In order to further compensate for the phase noise introduced by the out-of-loop device in the transmission system, such as the single transmission path between the laser and the first beam splitter, the first beam splitter 73 transmits part of the laser to the first photodetector 70, and the detection obtains the frequency signal V'0 = cos(w0t + Φ'0), that is, the phase information Φ'0 of the transmission signal at the first photodetector 70 contains the frequency signal V0 of the oscillator and the phase noise of the out-of-loop device.

[0091] The optical signal received by the third photodetector 72 is demodulated to obtain the frequency signal V3 = cos(w0t + Φ'0 + Φ p ) after demodulation. In order to compensate for the phase noise Φ p introduced by the fiber link in the transmission process, the returned signal is returned through the second optical amplifier module 76 after optical amplification at the receiving end, and the returned signal is obtained through the second photodetector 71 at the transmitting end, which contains the frequency signal V4 = cos(w0t + Φ'0 + 2Φ p ).

[0092] In order to obtain the error signal for feedback control of the frequency signal V0 of the oscillator 51, the following operations are performed:

[0093] Mixing the frequency signals V1 and V'0, low-pass filtering to obtain the mixing signal V e1 :

[0094] V e1 = cos[(w0-w1)t+(Φ'0-Φ1)];

[0095] Mixing the frequency signals V2 and V4, low-pass filtering to obtain the mixing signal V e2 :

[0096] V e2 = cos[(w2-w0)t+(Φ2-Φ'0-2Φ p )];

[0097] Mixing the two mixing signals V e1 and V e2 , low-pass filtering to obtain the error signal V e fed back to the oscillator 51:

[0098] V e = cos[(2w0-w2-w1)t+2Φ'0+2Φp -Φ1-Φ2];

[0099] = cos [2 (w0- w r )t + 2 (Φ'0+ Φ p -Φ r -ε)] ;

[0100] where ε is a fixed phase difference, which has no effect on the stability of frequency and can be ignored. The error signal V e feedback controls the frequency and phase of the oscillator 51 to satisfy:

[0101] w0= w r ;

[0102] Φ'0+ Φ p = Φ r ;

[0103] where w r , Φ r are the frequency and phase of the frequency signal which the oscillator 51 intends to transmit outward.

[0104] Thus, the frequency signal V3 received at the receiving end by the third photodetector 72 can be expressed as:

[0105] V3= cos (w0t+ Φ'0+ Φ p ) = cos (w r t+ Φ r ) ;

[0106] The frequency signal V3 at the receiving end is reproduced in phase locking to the frequency signal V r at the transmitting end, i.e. the high-stability transmission and synchronization of frequency are realized.

[0107] As the laser and other devices increase with running time, they produce phase which is not a fixed value and changes with power fluctuation, temperature change, wavelength drift of the laser, etc. This method can also eliminate such phase changes.

[0108] The present application combines time and frequency transmission in one system, which simultaneously carries out time compensation and frequency compensation, only occupies one wavelength channel, and saves optical fiber resources.

[0109] The transmission frequency value is improved by combining frequency multiplier and oscillator, the error signal is obtained by double mixing to realize fiber frequency transmission, and the noise fluctuation caused by lasers, beam splitters, circulators and other out-of-loop devices is eliminated, and the stability of fiber frequency transmission is improved.

[0110] The time delay to be compensated is calculated and compensated by the time signal generation module 43 through the round-trip link time difference value of the time difference measurement module 60, realizing the compensation of the link delay of the optical fiber time transfer; since the frequency signal of the encoding modulation module 52 is the same as the signal transmitted in the optical fiber frequency transfer, the time signal and the frequency signal sent to the user are phase-related; the requirements of the time and frequency synchronization between radar fixed stations, the time and frequency synchronization between VLBI observation stations and the like can be met.

[0111] According to the scheme, the optical fiber frequency transfer stability can reach the e-14 order of magnitude, and the optical fiber time signal transmission stability relies on the frequency transfer stability, thereby improving the optical fiber time transfer stability.

[0112] In the above embodiments, all or part of the embodiments can be realized by software, hardware, firmware or any combination thereof. When realized by software, all or part of the embodiments can be realized in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted by the computer-readable storage medium. The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server, data center and the like including one or more available media sets. The available medium can be a magnetic medium (for example, a floppy disk, a hard disk, a magnetic tape), an optical medium (for example, a DVD), or a semiconductor medium (for example, a solid state disk (SSD)) and the like.

[0113] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art can easily think of various equivalent modifications or replacements within the technical range disclosed in the present application, and these modifications or replacements should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A fiber optic time transfer system with dual time and frequency compensation, characterized in that, The time frequency source generates a frequency reference signal and a time reference signal. The frequency reference signal is sent to the first frequency multiplication module and the second frequency multiplication module, and the time reference signal is sent to the time difference measurement module and the coding modulation module. The first mixing module mixes the frequency signal from the first frequency multiplier module and the frequency signal from the first demodulation and decoding module, and then sends the mixture to the second mixing module. The third mixing module mixes the frequency signal from the second frequency multiplier module and the frequency signal from the second demodulation and decoding module, and then sends the mixture to the second mixing module. The second mixing module mixes the frequency signals from the first mixing module and the frequency signals from the third mixing module, and the resulting error signal is sent to the phase-locked loop. The phase-locked loop controls the phase of the oscillator based on the error signal input from the second mixer module, thereby enabling fiber frequency transmission. The time difference measurement module measures the difference between the time reference signal from the time frequency source and the time signal from the second demodulation and decoding module, and sends it to the encoding and modulation module; The encoding and modulation module encodes and modulates the difference between the time reference signal from the time frequency source and the time signal from the time difference measurement module, as well as the frequency signal from the oscillator, and sends them to the laser. The laser uses a signal from the encoding modulation module to perform amplitude modulation on the laser signal, and the modulated optical signal is sent into the first beam splitter. The first beam splitter sends part of the optical signal to the first photodetector and the other part of the optical signal to the first optical circulator; The first optical circulator sends the signal from the first beam splitter into the optical fiber link, and sends the signal from the optical fiber link into the second photodetector; The fiber optic link sends the signal from the first optical circulator to the second optical circulator, and sends the signal from the second optical circulator to the first optical circulator. The second beam splitter sends part of the optical signal to the third photodetector, and the other part of the optical signal to the second optical circulator. The second optical circulator sends the signal from the second beam splitter into the optical fiber link, and sends the signal from the optical fiber link into the optical amplification module; The optical amplification module amplifies the received signal from the second optical circulator and sends it to the second beam splitter. The third demodulation and decoding module demodulates the time signal, frequency signal, and round-trip link time difference, and outputs them to the time signal generation module and the frequency divider. The time signal generation module calculates the time compensation amount based on the round-trip link time difference value, compensates the time signal, and outputs it to the user; The frequency divider divides the frequency signal and outputs it to the user.

2. The fiber optic time transfer system according to claim 1, characterized in that, The first photodetector is used to convert optical signals into electrical signals and send them to the first demodulation and decoding module. The first demodulation and decoding module demodulates and decodes the signals from the first photodetector to obtain frequency signals and sends them to the first mixing module. The second photodetector is used to convert optical signals into electrical signals and send them to the second demodulation and decoding module. The second demodulation and decoding module demodulates and decodes the signals from the second photodetector to produce frequency signals, which are then sent to the third mixing module. The third photodetector is used to convert optical signals into electrical signals, which are then sent to the third demodulation and decoding module. The third demodulation and decoding module demodulates and decodes the signals from the third photodetector to obtain time signals, frequency signals, and round-trip time difference values, which are then sent to the time signal generation module.

3. The fiber optic time transfer system according to claim 1, characterized in that, The round-trip link time difference is T d The time compensation amount required by the time signal generation module is calculated to be T. d / 2, compensates for the time signal and outputs it to the user, where changes in fiber optic link delay are corrected by frequency phase compensation transmitted in real time via fiber optic frequency.

4. The fiber optic time transfer system according to claim 1, characterized in that, The first frequency multiplier module is an M-multiplier, and the second frequency multiplier module is an N-multiplier.

5. The fiber optic time transfer system according to claim 1, characterized in that, The encoding and modulation module uses an oscillator as the reference clock for encoding and modulating the time signal, thus compensating for the link delay variations in fiber optic time transmission.

6. A time-frequency dual-compensation optical fiber time transfer method, implemented using the optical fiber time transfer system according to any one of claims 1-5, characterized in that, The frequency signal generated by the oscillator is denoted as V0 = cos(w0t + Φ0). Where w0 and Φ0 are the initial frequency and phase of the frequency signal generated by the oscillator, respectively, and the output optical signal of the laser is amplitude modulated using this frequency signal V0; The frequency signal generated by the first frequency multiplier module is denoted as V1 = cos(w1t + Φ1), and the frequency signal generated by the second frequency multiplier module is denoted as V2 = cos(w2t + Φ2), where w1 and Φ1 are the frequency and phase of the frequency signal generated by the first frequency multiplier module, respectively, and w2 and Φ2 are the frequency and phase of the frequency signal generated by the second frequency multiplier module, respectively. The first photodetector detects the frequency signal V′0 = cos(w0t + Φ′0), where Φ′0 is the phase information of the transmitted signal at the first photodetector. The third photodetector detects the frequency signal V3 = cos(w0t + Φ′0 + Φ). p ), Φ p Phase noise introduced by the fiber optic link during transmission; After the returned signal is passed through the second photodetector at the transmitting end, a frequency signal V4 = cos(w0t + Φ′0 + 2Φ) containing twice the phase noise of the fiber optic link is obtained. p ); The two mixing signals V1 and V′0 are mixed and then low-pass filtered to obtain the mixed signal V. e1 : V e1 =cos[(w0-w1)t+(Φ′0-Φ1)]; The two mixing signals V2 and V4 are mixed and then low-pass filtered to obtain the mixed signal V. e2 : V e2 =cos[(w2-w0)t+(Φ2-Φ′0-2Φ p )]; Then mix the two frequency signals V e1 and V e2 The mixing and low-pass filtering processes yield the error signal V fed back to the oscillator. e : V e =cos[(2w0-w2-w1)t+2Φ′0+2Φ p -Φ1-Φ2]; =cos[2(w0-w r )t+2(Φ′0+Φ p -F r -e)]; Where ε is a fixed phase difference; Through V e The frequency and phase of the feedback-controlled oscillator are adjusted to satisfy the following: w0=w r ; Φ′0+Φ p =Φ r ; Among them, w r Φ r These are the frequency and phase of the frequency signal that the oscillator intends to emit. The signal V3 received by the third photodetector at the receiving end is represented as: V3=cos(w0t+Φ′0+Φ p )=cos(w r t+Φ r ); The receiver reproduces the phase-locked frequency signal V from the transmitter. r The frequency signal V3.

7. The optical fiber time transfer method according to claim 6, characterized in that, The frequency signal emitted by the oscillator is: V r =cos(w r t+Φ r ).

8. The optical fiber time transfer method according to claim 6, characterized in that, w1+w2=2w0;Φ1+Φ2=2(Φ r +e).

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