CN113098623B - Optical fiber phase synchronization system based on optical active compensation - Google Patents
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- CN113098623B CN113098623B CN202110245163.6A CN202110245163A CN113098623B CN 113098623 B CN113098623 B CN 113098623B CN 202110245163 A CN202110245163 A CN 202110245163A CN 113098623 B CN113098623 B CN 113098623B
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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Abstract
The invention discloses an optical fiber phase synchronization system based on optical active compensation, which comprises: the device comprises a frequency reference, a phase-locked frequency multiplier, a pulse generator, a laser, a 1 multiplied by 2 optical coupler, a polarization scrambler, a circulator, an optical delay line, an optical fiber, a wavelength division demultiplexer, a photoelectric detector, a radio frequency amplifier, a pulse distribution amplifier, a radio frequency power divider, a phase discriminator, a time interval counter, a delay processing unit and a driving circuit. The invention can ensure that the phases of the frequency signals are consistent under the operations of closing and restarting or optical fiber routing change and the like, and realizes phase synchronization, thereby improving the time-frequency transmission coherence and meeting the requirements of coherent detection applications such as distributed radar arrays and the like.
Description
Technical Field
The invention relates to the field of optical fiber time-frequency transmission, in particular to an optical fiber phase synchronization system based on optical active compensation, which mainly aims to keep the phases of frequency signals consistent after being transmitted by optical fibers in different system states by utilizing an optical delay line active compensation mode, improve the coherence of time-frequency transmission and be applied to the fields of coherent array detection and the like.
Background
In recent years, with the rapid development of atomic frequency standards, time and frequency transmission technologies are also continuously perfected to meet the requirements of advanced basic research and important applications such as clock comparison, accurate time service, precise metering, navigation positioning, radar networking, deep space exploration and the like. Thanks to the advantages of low loss, anti-electromagnetic interference, high reliability and the like of the optical fiber link, the optical fiber time-frequency transmission technology is rapidly developed, the transmission precision of the optical fiber time-frequency transmission technology is far higher than that of the traditional satellite transmission method, and the optical fiber time-frequency transmission technology is actively applied to various fields.
However, for the current optical fiber frequency transmission method, the aim is to achieve frequency synchronization between stations, and since the frequency is the time differential of the phase, that is, the frequency difference is zero as long as the phase difference of the frequency signal is stable in each independent operation, that is, the frequency is synchronized. Then, when the system undergoes operations from shutdown to restart, etc., the phase difference constant after re-entering steady state may change, although the frequency remains synchronized. What is required in the field of coherent array detection is not only frequency synchronization, for example, multiple-input multiple-output radar requires that all transmitting and receiving sensors must have a common phase reference to achieve high target positioning accuracy through coherent processing. The phase synchronization problem needs to be taken into account. The optical fiber phase synchronization requires that the phases of frequency signals among different stations are consistent through optical fibers, so that the phase difference of the system when the system reaches a steady state after the system is switched on and off for many times is consistent.
In order to realize Optical Fiber Phase Synchronization, an Optical Fiber Phase Synchronization over Optical Fiber [ J ] Optics Express 2020,28(4):4603-4610 ] proposes an Optical Fiber Phase Synchronization method based on a Phase conjugation scheme. The essence of the scheme is a passive compensation method based on phase conjugation, frequency mixing operation is adopted between fundamental frequency and frequency multiplication signals, phase difference caused by a passive compensation optical fiber link can be repeated under the operations of closing, restarting, optical fiber path changing and the like, and the given experimental result shows that the consistency of the phase difference relative to the whole period is within 2 percent, which indicates that the optical fiber phase synchronization is feasible.
Because the technical scheme adopts a passive compensation mode, the phase synchronization can be realized only aiming at specific frequency signals, a plurality of frequency signals and time signals cannot be transmitted simultaneously, and the application range of the passive compensation mode is limited to a certain extent. The invention provides a feasible system scheme aiming at the problems, and realizes optical fiber phase synchronization based on optical active compensation.
Disclosure of Invention
The invention provides an optical fiber phase synchronization system based on optical active compensation, which is based on a phase active compensation principle, combines the periodic resolution capability of pulse time interval measurement and the high-precision characteristic of frequency phase measurement, and realizes high-precision optical fiber phase synchronization by using an optical delay line active compensation mode.
The technical solution of the invention is as follows:
an optical fiber phase synchronization system based on optical active compensation is characterized by comprising a frequency reference, a phase-locked frequency multiplier, a pulse generator, a first laser, a second laser, a first 1 x 2 optical coupler, a first polarization scrambler, a first circulator, an optical delay line, an optical fiber, a second circulator, a first wavelength division demultiplexer, a first photoelectric detector, a second photoelectric detector, a first radio frequency amplifier, a first pulse distribution amplifier, a radio frequency power divider, a third laser, a fourth laser, a second 1 x 2 optical coupler, a second polarization scrambler, a second wavelength division demultiplexer, a third photoelectric detector, a fourth photoelectric detector, a second radio frequency amplifier, a second pulse distribution amplifier, a phase discriminator, a time interval counter, a delay processing unit and a driving circuit;
the frequency reference outputs two paths of frequency standard signals, the first path of frequency standard signal enters a base frequency input port of the phase-locked frequency multiplier, and the second path of frequency standard signal enters a time base input port of the pulse generator; the phase-locked frequency multiplier outputs two paths of frequency reference signals after frequency multiplication, the first path of frequency reference signal enters a signal modulation port of the first laser, the second path of frequency reference signal enters a reference signal input port of the phase discriminator, the pulse generator outputs two paths of time reference signals, the first path of time reference signal enters a signal modulation port of the second laser, and the second path of time reference signal enters a starting signal input port of the time interval counter;
the first laser and the second laser respectively modulate an input modulation signal to a laser amplitude and output a modulation optical signal, two paths of modulation optical signals respectively enter an input port of a first 1 x 2 optical coupler and output a synthesized optical signal from a single port, then the synthesized optical signal is input into the first polarization scrambler for polarization scrambling, then enters through a first port of the first circulator and is output from a second port, then enters from an optical first port of the optical delay line and is output from an optical second port, and finally the synthesized optical signal is sent to a far end through the first port of the optical fiber; the optical fiber transmits an optical signal from a local end to a remote end and outputs the optical signal from a second port, then the optical signal is input from a second port of the second circulator and output from a third port, the optical signal enters a common port of the first wavelength division multiplexer, the optical signal with the wavelength same as that of the first laser is output from a first output port after demultiplexing and input into a first photoelectric detector, the optical signal with the wavelength same as that of the second laser is output from a second output port and input into a second photoelectric detector, the first photoelectric detector demodulates a frequency signal and amplifies the frequency signal by a first radio frequency amplifier, the amplified frequency signal enters a radio frequency power divider for power distribution and then outputs two paths of frequency signals with equal power, wherein the first path of frequency signal is used as a frequency reference for a remote end user, and the second path of frequency signal is input into a third laser for laser modulation, the second photoelectric detector demodulates a time signal, inputs the time signal into the first pulse distribution amplifier for shaping and amplification, and then inputs the time signal into the fourth laser for laser modulation; the second 1 × 2 optical coupler also synthesizes two paths of modulated optical signals into one path, then the path of the modulated optical signals sequentially passes through a second polarization scrambler, a second circulator, an optical fiber and an optical delay line and then reaches a first circulator at a local end, the modulated optical signals enter from a second port of the first circulator and are output from a third port, the modulated optical signals pass through a second wavelength division multiplexer to be separated into two paths of optical signals, wherein the optical signals with the same wavelength as that of a third laser enter a third photoelectric detector to demodulate frequency signals, the frequency signals enter a to-be-detected signal input port of a phase discriminator after being amplified by a second radio frequency amplifier, the wavelength signals with the same wavelength as that of a fourth laser enter a fourth photoelectric detector to demodulate time signals, and the modulated optical signals enter a termination signal input port of a time interval counter after being shaped and amplified by a second pulse distribution amplifier;
the phase discriminator measures the phase difference of the frequency signal after round trip transmission relative to a reference frequency signal and outputs the round trip phase difference to a first data input port of the delay processing unit, meanwhile, the time interval counter measures the delay of the time signal after round trip transmission relative to the reference time signal and outputs the round trip delay to a second data input port of the delay processing unit, the delay processing unit obtains an error signal for guaranteeing one-way phase consistency of frequency through processing and calculation, the error signal is output to the driving circuit through an error output port and is converted into a control signal to be input to an electrical input port of the optical delay line, so that the transmission delay of the optical delay line is controlled and changed in real time, and the phase change of the frequency signal is compensated.
The method for performing the phase active compensation of the optical fiber phase synchronization system based on the optical active compensation is characterized by comprising the following steps of:
1) the delay processing unit first sets a round trip phase reference value
2) Delay processing unit real-time calculating round-trip phase difference
Relative to a predetermined round trip phase reference
Produces an error signal:
and the delay variation of the optical delay line is controlled accordingly to keep the error value as 0, at this time, the system enters a closed loop state, and the phase difference of the frequency signal output by the far-end radio frequency power divider relative to the frequency signal output by the local-end phase-locked frequency multiplier is as follows:
wherein
The extra phase difference introduced for system asymmetry effects, etc.;
3) in the above closed loop state, the delay processing unit continuously measures a set of round trip delays Δ t of the time interval counter for a long time r As the round trip delay reference value Δ t 0 ；
4) When the system is subjected to a restart operation or a change of the optical fiber link, the delay processing unit and the optical delay line first perform delay compensation according to step 2), and after the system enters a closed loop state, the delay processing unit performs delay compensation according to the round trip delay deltat measured at that time r And a round trip delay reference value Δ t 0 Calculating the round trip delay relative period change coefficient:
n＝[(Δt r -Δt 0 )/T]，
wherein T is the period of the frequency signal, "[ ]" means rounding operation;
5) when n is odd number, the delay processing unit controls the optical delay line to have more delay or less delay T/2 in the current state, when n is even number, the current state is maintained, and after re-entering the closed loop, the following steps are provided:
thereby realizing one-way phase difference constancy.
The optical fiber phase synchronization system based on optical active compensation is characterized in that the optical delay line is formed by connecting a fast-changing optical fiber delay line based on a PZT (piezoelectric transducer) stretching principle and a slow-changing optical fiber delay line based on a temperature change principle in series so as to adapt to the requirements of fast, accurate and large-range delay compensation.
The invention has the characteristics and advantages that:
1) the optical fiber phase synchronization system based on optical active compensation provides a feasible scheme for an optical fiber phase synchronization technology, pulse measurement is added to identify the periodic variation of frequency phases on the basis of the original bidirectional return noise compensation, the phase of frequency signals in different states of the system is kept consistent in an optical delay line active compensation mode, the time-frequency transmission coherence is improved, and more application requirements are met.
2) Compared with the prior art, the invention utilizes the active compensation mode of the optical delay line, not only can realize the phase synchronization of the frequency signals, but also allows the transmission of time signals or frequency signals of other frequency points, and can simultaneously provide frequency reference, phase reference and time reference for a plurality of remote sites.
Drawings
FIG. 1 is a block diagram of an optical fiber phase synchronization system based on optical active compensation according to the present invention.
Detailed Description
The present invention will be further described with reference to the following examples and drawings, but the scope of the present invention should not be limited thereto.
Referring to fig. 1, fig. 1 is a block diagram of an optical fiber phase synchronization system based on optical active compensation according to the present invention, and it can be seen from the figure that the optical fiber phase synchronization system based on optical active compensation according to the present invention includes a frequency reference 10, a phase-locked frequency multiplier 11, a pulse generator 12, a first laser 13, a second laser 14, a first 1 × 2 optical coupler 15, a first polarization scrambler 16, a first circulator 17, an optical delay line 18, an optical fiber 19, a second circulator 20, a first demultiplexer 21, a first photodetector 22, a second photodetector 23, a first rf amplifier 24, a first pulse distribution amplifier 25, a rf power splitter 26, a third laser 27, a fourth laser 28, a second 1 × 2 optical coupler 29, a second polarization scrambler 30, a second demultiplexer 31, a third photodetector 32, a fourth photodetector 33, a second rf amplifier 34, a second demultiplexer 29, a third photodetector 32, a second optical coupler, a second, A second pulse distribution amplifier 35, a phase detector 36, a time interval counter 37, a delay processing unit 38, and a driving circuit 39.
In fig. 1, a frequency reference 10 outputs two paths of standard frequency signals, a first path of frequency standard signal 101 enters a fundamental frequency input port 111 of a phase-locked frequency multiplier 11, and a second path of frequency standard signal 102 enters a time-based input port 121 of a pulse generator 12; in fig. 1, the phase-locked frequency multiplier 11 outputs two frequency-multiplied frequency reference signals, a first frequency reference signal 112 enters a signal modulation port of the first laser 13, and a second frequency reference signal 113 enters a reference signal input port 361 of the phase detector 36; in fig. 1, the pulse generator 12 outputs two paths of time reference signals, the first path of time reference signal 122 enters the signal modulation port of the second laser 14, and the second path of time reference signal 123 enters the start signal input port 371 of the time interval counter 37.
The above-mentioned phase-locked frequency multiplier 11 and the pulse generator 12 generate a frequency reference signal and a time reference signal according to the standard frequency signal output by the frequency reference 10. In an embodiment of the present invention, the frequency reference 10 is a desktop rubidium clock and is capable of outputting multiple 10MHz standard signals, the phase-locked frequency multiplier 11 phase-locks the internal crystal oscillator to 10MHz output by the rubidium clock, and outputs at least two 1GHz frequency reference signals through a frequency multiplication operation (the frequency signals after frequency multiplication are transmitted because the transmission performance of high frequency signals is better), and the pulse generator outputs at least two 1PPS (pulse per second) time reference signals with a pulse width of 10us by using the rubidium clock 10MHz as a reference time base.
In fig. 1, the first laser 13 and the second laser 14 respectively modulate an input modulation signal to a laser amplitude and output a modulated optical signal, the two modulated optical signals respectively enter the input port of the first 1 × 2 optical coupler 15 and output a combined optical signal from a single port, then the combined optical signal enters the first polarization scrambler 16 for polarization scrambling, then enters the first port 171 of the first circulator 17 and is output from the second port 172, and then enters the first optical port 181 of the optical delay line 18, is output from the second optical port 182, and is transmitted to a remote end through the first port 191 of the optical fiber 19; at the far end, the optical signal is input from the second port 192 of the optical fiber 19 to the second port 202 of the second circulator and output from the third port 203, and then enters the common port 211 of the first demultiplexer 21, after demultiplexing, the optical signal with the same wavelength as the first laser 13 is output from the first output port 212 and input to the first photodetector 22, the optical signal with the same wavelength as the second laser 14 is output from the second output port 213 and input to the second photodetector 23, the first photodetector 22 in fig. 1 demodulates the frequency signal and amplifies by the first radio frequency amplifier 24, the amplified frequency signal enters the radio frequency power divider 26 for power distribution, and then outputs two paths of frequency signals with equal power, wherein the first path of frequency signal 262 is used as a frequency reference for a far end user, and the second path of frequency signal 263 is input to the third laser 27 for laser modulation, the second photodetector 23 in fig. 1 demodulates the time signal and inputs the demodulated time signal to the first pulse distribution amplifier 25 for shaping and amplifying, and then inputs the demodulated time signal to the fourth laser 28 for laser modulation; in fig. 1, the second 1 × 2 optical coupler 29 also combines two modulated optical signals into one path, and then sequentially passes through the second polarization scrambler 30, the second circulator 20, the optical fiber 19, and the optical delay line 18 to reach the first circulator 17 at the local end, enters from the second port 172 of the first circulator 17 to be output from the third port 173, and then passes through the second demultiplexer 31 to separate two optical signals, wherein the optical signals with the same wavelength as the third laser 27 enter the third photodetector 32 to be demodulated into frequency signals, and enter the to-be-measured signal input port 362 of the phase discriminator 36 after being amplified by the second radio frequency amplifier 34, and the optical signals with the same wavelength as the fourth laser 28 enter the fourth photodetector 33 to be demodulated into time signals, and enter the termination signal input port 372 of the time interval counter 37 after being shaped and amplified by the second pulse distribution amplifier 35.
The above process realizes the round trip transmission of the time-frequency signal from the local end to the remote end and back to the local end, the first output 262 of the rf power divider 26 is the frequency reference recovered at the remote end, and a time reference can be obtained from other ports of the first pulse distribution amplifier 25, which is not shown temporarily in fig. 1. In an embodiment of the present invention, the output light wavelength of the first laser 13 is 1548.51nm, the output light wavelength of the second laser 14 is 1550.12nm, the output light wavelength of the third laser 27 is 1547.72nm, the output light wavelength of the fourth laser 28 is 1549.32nm, the bandwidths of the first photodetector 22 and the third photodetector 32 are 1GHz for detecting 1GHz frequency signals, the bandwidths of the second photodetector 23 and the fourth photodetector 33 are 100MHz for detecting 1PPS time signals, and the polarization-disturbing rate of the first polarization-scrambler 16 and the second polarization-scrambler 30 is 700kHz for suppressing the influence of polarization mode dispersion on transmission delay in optical fiber transmission.
The phase detector 36 in fig. 1 measures the phase difference of the frequency signal after round trip transmission relative to the reference frequency signal and outputs the round trip phase difference to the first data input port 381 of the delay processing unit 38, while the time interval counter 37 measures the delay of the time signal after round trip transmission relative to the reference time signal and outputs the round trip delay to the second data input port 382 of the delay processing unit 38, the delay processing unit 38 obtains an error signal ensuring one-way phase consistency of the frequency through processing calculation, and outputs the error signal to the driving circuit 39 through the error output port 383 and converts the error signal into a control signal to be input to the electrical input port 183 of the optical delay line 18, so as to control and change the transmission delay of the optical delay line 18 in real time and compensate the phase change of the frequency signal.
The active phase compensation from the delay processing unit 38 to the optical delay line 18 specifically includes:
the delay processing unit 38 first sets a round trip phase reference value
The delay processing unit 38 calculates the round-trip phase difference in real time when the system is in operation
Relative to a predetermined round trip phase reference
Produces an error signal:
and accordingly, the delay variation of the optical delay line 18 is controlled to keep the error value at 0, at this time, the system enters a closed loop state, and the phase difference between the frequency signal output by the far-end rf power divider 26 and the frequency signal output by the local phase-locked frequency multiplier 11 is:
wherein
The extra phase difference introduced for system asymmetry effects, etc.; in the closed loop state, the delay processing unit 38 continuously measures a set of round trip delays Δ t of the time interval counter 37 for a long time r As the round trip delay reference value Δ t 0 ；
When the system is operated again after being restarted or the optical fiber link is changed, the delay processing unit 38 and the optical delay line 18 first perform the delay compensation according to the above steps, and after the system enters the closed loop state, the delay processing unit 38 performs the delay compensation according to the round trip delay Δ t measured at this time r And a round trip delay reference value Δ t 0 Calculating the round trip delay relative period change coefficient:
n＝[(Δt r -Δt 0 )/T]，
wherein T is the period of the frequency signal, "[ ]" means rounding operation; when n is an odd number, the one-way phase difference is
Therefore, the delay processing unit 38 controls the optical delay line 18 to have more or less delay T/2 (eliminating the extra pi phase change) in the current state, and when n is even, the current state is maintained, and after re-entering the closed loop, there will be:
this achieves one-way phase difference constancy.
In one embodiment of the present invention, T is 1ns, and n is an even number calculated after a certain closed loop, and then T is directly followed by n 4
And r-3 calculated after the optical delay line is restarted and closed again is an odd number, the optical delay line is controlled to have multiple delays of 500ps at the moment, and the optical delay line has the same delay value after being closed again
The above process achieves phase synchronization with delay control accuracy determined by the phase detector 36, the time interval counter 37 and the optical delay line 18. In one embodiment of the invention, the measurement resolution of the phase detector is 6.5 x 10 -5 rad, corresponding to a retardation resolution of 3.3X 10 -5 2 pi multiplied by 1ns is 10fs, which has extremely high measurement precision and is used for real-time compensation, the measurement resolution of a time interval counter is 25ps and is only used for distinguishing phase period change, an optical delay line is formed by connecting a quick-change optical fiber delay line based on a PZT stretching principle and a slow-change optical fiber delay line based on a temperature change principle in series, wherein the response speed of the quick-change optical fiber delay line is more than 1kHz, the delay range is 80ps, the delay precision is 20fs, the effect speed of the slow-change optical fiber delay line is less than 1Hz, the delay range is 20ns, and the delay precision is 4ps, so that the quick-change optical fiber delay line can adapt to the delay compensation requirement of the quick precision and the large range after the series connection, the delay control precision of a system can reach 20fs, and the phase synchronization under the long-distance optical fiber transmission can be accurately realized.
Claims (3)
1. An optical fiber phase synchronization system based on optical active compensation is characterized by comprising a frequency reference (10), a phase-locked frequency multiplier (11), a pulse generator (12), a first laser (13), a second laser (14), a first 1 x 2 optical coupler (15), a first polarization scrambler (16), a first circulator (17), an optical delay line (18), an optical fiber (19), a second circulator (20), a first wavelength division multiplexer (21), a first photoelectric detector (22), a second photoelectric detector (23), a first radio frequency amplifier (24), a first pulse distribution amplifier (25), a radio frequency power divider (26), a third laser (27), a fourth laser (28), a second 1 x 2 optical coupler (29), a second polarization scrambler (30), a second wavelength division multiplexer (31), a third photoelectric detector (32), The device comprises a fourth photoelectric detector (33), a second radio frequency amplifier (34), a second pulse distribution amplifier (35), a phase discriminator (36), a time interval counter (37), a delay processing unit (38) and a driving circuit (39);
the frequency reference (10) outputs two paths of frequency standard signals, the first path of frequency standard signal (101) enters a fundamental frequency input port (111) of the phase-locked frequency multiplier (11), and the second path of frequency standard signal (102) enters a time base input port (121) of the pulse generator (12);
the phase-locked frequency multiplier (11) outputs two paths of frequency reference signals after frequency multiplication, a first path of frequency reference signal (112) enters a signal modulation port of a first laser (13), a second path of frequency reference signal (113) enters a reference signal input port (361) of a phase detector (36), the pulse generator (12) outputs two paths of time reference signals, a first path of time reference signal (122) enters a signal modulation port of a second laser (14), and a second path of time reference signal (123) enters a starting signal input port (371) of a time interval counter (37);
the first laser (13) and the second laser (14) respectively modulate an input modulation signal to a laser amplitude and output a modulation optical signal, the two paths of modulation optical signals respectively enter an input port of a first 1 × 2 optical coupler (15) and output a synthesized optical signal from a single port, then the synthesized optical signal is input into the first polarizer (16) for polarization scrambling, then enters through a first port (171) of the first circulator (17), is output from a second port (172), then enters from an optical first port (181) of the optical delay line (18), is output from an optical second port (182), and finally is sent to a remote end through a first port (191) of the optical fiber (19);
the optical fiber (19) transmits an optical signal from a local end to a remote end and outputs the optical signal from a second port (192), then the optical signal is input from a second port (202) of the second circulator (20), output from a third port (203) and enter a common port (211) of the first wavelength division multiplexer (21), after demultiplexing, an optical signal with the same wavelength as that of the first laser (13) is output from a first output port (212) and input into a first photoelectric detector (22), an optical signal with the same wavelength as that of the second laser (14) is output from a second output port (213) and input into a second photoelectric detector (23), the first photoelectric detector (22) demodulates a frequency signal and amplifies the frequency signal through a first radio-frequency amplifier (24), and the amplified frequency signal enters a radio-frequency power divider (26) to be power-distributed so as to output two paths of frequency signals with equal power, the first path of frequency signal (262) is used as a frequency reference for a remote end user, the second path of frequency signal (263) is input into a third laser (27) for laser modulation, the second photoelectric detector (23) demodulates a time signal and inputs the time signal into a first pulse distribution amplifier (25) for shaping and amplification, and then the time signal is input into a fourth laser (28) for laser modulation;
the second 1 x 2 optical coupler (29) also combines two paths of modulated optical signals into one path, the optical signal sequentially passes through a second polarization scrambler (30), a second circulator (20), an optical fiber (19) and an optical delay line (18) and then reaches a first circulator (17) at the local end, enters from a second port (172) of the first circulator (17) and is output from a third port (173), and then passes through a second wavelength division multiplexer (31) to divide two optical signals, optical signals with the same wavelength as the third laser (27) enter a third photoelectric detector (32) to demodulate frequency signals, the optical signals are amplified by a second radio frequency amplifier (34) and then enter a signal input port (362) to be detected of a phase discriminator (36), optical signals with the same wavelength as the fourth laser (28) enter a fourth photoelectric detector (33) to demodulate time signals, and the optical signals are shaped and amplified by a second pulse distribution amplifier (35) and then enter a termination signal input port (372) of a time interval counter (37);
the phase detector (36) measures the phase difference of the frequency signal after the round trip transmission relative to the reference frequency signal, and outputs the round trip phase difference to a first data input port (381) of a delay processing unit (38), at the same time, the time interval counter (37) measures the delay of the time signal after the round trip transmission relative to the reference time signal, and outputs the round trip delay to a second data input port (382) of the delay processing unit (38), the delay processing unit (38) obtains an error signal which guarantees one-way phase consistency of frequency through processing calculation, and is output to a driving circuit (39) by an error output port (383) and converted into a control signal to be input to an electrical input port (183) of the optical delay line (18), thereby controlling and changing the transmission delay of the optical delay line (18) in real time and compensating the phase change of the frequency signal.
2. A method for performing active phase compensation using the optical fiber phase synchronization system based on active optical compensation of claim 1, comprising the steps of:
1) the delay processing unit (38) first sets a round trip phase reference value
2) The delay processing unit (38) calculates the round-trip phase difference in real time
Relative to a predetermined round trip phase reference
Produces an error signal:
and control the delay variation of the optical delay line (18) accordingly to make the error value keep 0, at this moment the system enters the closed loop state, the phase difference of the frequency signal outputted by the far-end radio frequency power divider (26) relative to the frequency signal outputted by the local-end phase-locked frequency multiplier (11) is:
wherein
The extra phase difference introduced for the system asymmetry effect;
3) in the closed loop state, the delay processing unit (38) continuously measures a set of round trip delays Δ t of the time interval counter (37) for a long time r As the round trip delay reference value Δ t 0 ；
4) When the system is subjected to a restart operation or a change in the optical fiber link, the delay processing unit (38) and the optical delay line (18) first perform delay compensation in accordance with step 2), and after the system enters the closed loop state, the delay processing unit (38) performs delay compensation based on the round trip delay Δ t measured at that time r And a round trip delay reference value Δ t 0 Calculating the round trip delay relative period change coefficient:
n＝[(Δt r -Δt 0 )/T]，
wherein T is the period of the frequency signal, "[ ]" means rounding operation;
5) when n is odd, the delay processing unit (38) controls the optical delay line (18) to have more delay or less delay T/2 in the current state, when n is even, the current state is maintained, and after re-entering the closed loop, the following steps are provided:
thereby realizing one-way phase difference constancy.
3. The optical fiber phase synchronization system based on optical active compensation as claimed in claim 1, wherein the optical delay line (18) is composed of a fast-changing optical fiber delay line based on PZT stretching principle and a slow-changing optical fiber delay line based on temperature variation principle in series, so as to adapt to the requirement of fast, accurate and wide-range delay compensation.
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| US10826265B2 (en) * | 2018-09-18 | 2020-11-03 | Korea Advanced Institute Of Science And Technology | Optical frequency stabilizer using optical fiber delay line, and method for generating stable optical frequency signal |
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