CN108566259B - Phase jitter compensation method and compensation system - Google Patents
Phase jitter compensation method and compensation system Download PDFInfo
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- CN108566259B CN108566259B CN201810407664.8A CN201810407664A CN108566259B CN 108566259 B CN108566259 B CN 108566259B CN 201810407664 A CN201810407664 A CN 201810407664A CN 108566259 B CN108566259 B CN 108566259B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- 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
- H04B10/25—Arrangements specific to fibre transmission
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- 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
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
- H04B10/616—Details of the electronic signal processing in coherent optical receivers
- H04B10/6165—Estimation of the phase of the received optical signal, phase error estimation or phase error correction
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Abstract
The invention provides a phase jitter compensation method and a phase jitter compensation system, wherein a pilot signal is introduced for back and forth transmission to sense phase jitter caused by external environment change, mapping of a single phase error correction unit and each channel in a distributed system is realized by switching of an optical switch, and phase error compensation of the distributed system is realized by phase error correction; the phase error correction method comprises the steps of extracting a phase error by using a phase discrimination unit and controlling the optical adjustable delay line by combining a proportional-integral amplification algorithm. Compared with the prior art, the method is not only suitable for time-frequency ultra-stable transmission in the civil field, but also suitable for solving the problems of clock synchronization and stable transmission of time-varying signals in a large-array electronic information system due to the advantages of broadband property, multi-channel distribution and the like.
Description
Technical Field
The invention relates to a phase jitter compensation method and a phase jitter compensation system, and relates to the field of radio and optical communication.
Background
High quality frequency sources are the core of modern electronic systems, and promote the development of many fields, such as navigation, high-speed communication, astronomical observation, aerospace measurement and control, phased array radar and the like. Taking radar application as an example, radar measures the distance, speed and direction of a target by emitting radio waves to collide with the target and reflecting the radio waves, and if the radio signals are too noisy, the electric signal changes caused by some small movements or size changes of the target are not enough to be distinguished from the noise, and then the noise of a frequency source severely limits the resolution of radar detection. Similarly, in the aerospace measurement and control application, due to the limitation of the volume and energy consumption of the spacecraft, the power of the transmitted signal is very limited, so that the signal received by the ground measurement and control antenna is very weak, and if the frequency source signal at the antenna is over-noisy, the downlink signal sent back by the spacecraft is submerged, and the sensitivity of the aerospace measurement and control is seriously influenced. Since the last century, jet propulsion laboratories in the united states designed stable time and frequency transmission systems for the national aerospace administration (NASA) deep space exploration network (DSN). The DSNs are distributed at three places, each several tens of kilometres from the generation of the high stability frequency source, at 120 degree longitude intervals. If time-frequency synchronization is not carried out, the antennas in the DSN network cannot be coordinated, so that the deep space detection capability is lost.
In recent decades, China has made continuous progress in the fields of aviation, aerospace and the like. The success of Chang' e I to III marks that China has started to advance to the deep space exploration field, and the exploration tasks of more remote asteroids and other planets are also in the planning demonstration, which puts higher requirements on the exploration resolution and sensitivity of the aerospace measurement and control system in China. While the quality of frequency source generation is higher and higher with the development of atomic frequency standard, the stability of transmission and distribution method based on traditional electricity is far lower than that of atomic clock, and this contradiction makes the transmission of frequency signal through optical fiber a promising solution.
In particular, there are many methods for compensating for the phase jitter of signals based on optical means. The National Institute of Standards and Technology (NIST) and the United states institute of celestial physics (JILA) of the university of Colorado realize the short-circuit stability of a high-precision frequency signal transmission system reaching 3 multiplied by 10 for the first time based on a mode-locked laser by changing the compensation mode of an optical path-14The length stability is 8 multiplied by 10-15. In 2007, NIST and JILA cooperated again, it was first proposed to use an optical frequency comb to transmit both RF and optical frequency standards, and the femtosecond optical frequency comb stability at 32km optical fiber distance transmission reached 10-17(Steady to seconds) and 10-19(stable in the sky). Similar fiber frequencies were reported in the same year by the large-scale millimeter wave array project of actama, co-established in the united states, canada, europe and japanThe phase-stable transmission technique is characterized by that it utilizes the comparison of round-trip transmission signal and untransmitted signal to obtain error signal, and uses said error signal to control two optical fibre squeezers with quick change and slow change to compensate phase jitter of link circuit so as to implement that the second stability is 2X10-12Stable transmission of (2). A2010 France physical laser laboratory realizes high-precision frequency transmission of 9.5GHz signals in 86km suburban communication network optical fiber links by a technical means of feeding back fast-varying error signals to piezoelectric ceramics (PZT), and obtains the signal stability of 1.5 multiplied by 10 seconds-15And Rizhao 10-18The stability of (2). Two antiparallel communication optical fiber links of 2012 German Max-Planck research realize 920km optical frequency phase-stable transmission, and the second stability reaches 5 multiplied by 10-15。
The above schemes have advantages and are also used in different application fields, wherein the compensation precision of the round-trip signal transmission scheme is high and is widely concerned and researched. However, the prior art schemes mostly come at the cost of high delay, small bandwidth and known frequency, and it is difficult to support the wdm system and the distributed system. Therefore, the research of the signal phase jitter compensation method suitable for the distributed system has great significance and application value in civil and military-civil integrated electronic information systems.
Disclosure of Invention
The invention provides a phase jitter compensation method which has the characteristics of no need of obtaining frequency information of transmission signals and suitability for phase error compensation of a distributed system.
The phase jitter compensation method provided by the invention comprises the following steps of introducing a pilot signal to carry out round-trip transmission to sense phase jitter brought by external environment change, realizing mapping between a single phase error correction unit and each channel in a distributed system by switching of an optical switch, and realizing phase error compensation of the distributed system by phase error correction; the phase error correction method comprises the steps of extracting a phase error by using a phase discrimination unit, and controlling an optical adjustable delay line by combining a proportional-integral-amplification (PID) algorithm;
the specific method adopting the proportional-integral amplification algorithm comprises the following steps: first stageInitialising respective parameters, including a current sampling period TsThe previous time T-1Phase error of (1), T-1A time T before the time-2Phase error and scale and coefficient at time; and reflecting the error at the current moment through proportional control, and proportionally adjusting towards the direction of reducing the error.
The specific method adopting the proportional-integral amplification algorithm comprises the following steps: and initializing integral coefficients, and continuously accumulating system errors through integral control to eliminate steady-state errors of the system.
The specific method adopting the proportional-integral amplification algorithm comprises the following steps: the coefficient of the differential is initialized, overshoot is reduced through differential control, oscillation is overcome, the stability of the system is improved, the response speed of the system is accelerated, and therefore the deviation is restrained from changing to any direction.
A phase jitter compensation system, adapted to the phase jitter compensation method, comprising: comprises an optical frequency signal input unit 101, a first optical amplifier 102, a 1 XN optical power divider 103, N first optical circulators 104 which are connected in sequence1～104NN photo-tunable delay lines 1051～105NN sections of optical fiber 1061～106NN second optical circulators 1071～107NN adjustable optical attenuators 1081～108NN first optical wavelength division multiplexers 1101～110NAnd N second optical amplifiers 1111～111N(ii) a The 1 × N optical power splitter 103 is respectively connected with N first optical circulators 1041～104NConnecting; the N first optical circulators 1041～104NN photo-tunable delay lines 1051～105NN sections of optical fiber 1061～106NN second optical circulators 1071～107NN adjustable optical attenuators 1081～108NN first optical wavelength division multiplexers 1101～110NAnd N second optical amplifiers 1111～111NThe N signal lines are formed by sequentially connecting the N signal lines in a one-to-one correspondence manner; the N second optical amplifiers 1111～111NAnd N second optical circulators 1071～107NAre connected in a one-to-one correspondence manner; also included are N second wavelength division demultiplexers 1121～112NSignal input terminal and N first optical circulators 1041～104NThe signal output ends are connected with the phase error correction unit 114 through the Nx 1 optical switch 113; the phase error correction unit 114 is connected to the N photo-tunable delay lines 105 respectively1～105NConnecting; the N first optical wavelength division multiplexers 1101～110NAnd each is connected with M optical signal input units 10911～109MM；
After the optical pilot signal 101 passes through the first optical amplifier 102, the optical power divider 103 of 1 × N divides the signal into N channels of signals with average power, and then passes through the corresponding N first optical circulators 1041～104NInto N optically tunable delay lines (105)1～105N) Performing phase precompensation; the pilot signals after pre-compensation enter respective optical fibers for transmission; the transmitted signals pass through a second optical circulator and an adjustable optical attenuator and then enter the optical wavelength division multiplexer together with the M optical signals at the far ends of different places; the multiplexed optical signals are subjected to power amplification by the corresponding second optical amplifier and then enter the optical fiber again for transmission; the transmitted multi-channel signals and pilot signals enter an optical adjustable delay line together for phase compensation, and then channel separation is carried out through a first optical circulator and a second wavelength division demultiplexer; finally, the separated N pilot signals pass through the nx1 optical switch 113 and then enter the phase error correction unit 114 for error extraction, and the error value is fed back to the corresponding optical tunable delay line for phase error compensation, thereby realizing real-time phase jitter compensation of the M optical signals.
Compared with the prior art, the method is not only suitable for time-frequency ultra-stable transmission in the civil field, but also suitable for solving the problems of clock synchronization and stable transmission of time-varying signals in a large-array electronic information system due to the advantages of broadband property, multi-channel distribution and the like.
Drawings
Fig. 1 is a schematic structural diagram of a phase jitter compensation system according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a phase error correction unit according to an embodiment of the present invention.
FIG. 3 is a schematic diagram of a principle of a proportional-integral-amplification algorithm according to an embodiment of the present invention.
FIG. 4 is a schematic flow chart of a proportional-integral-amplification algorithm according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of a typical daily air temperature change trend in accordance with one embodiment of the present invention.
Fig. 6 is a diagram showing the results of phase jitter of signal transmission at the frequency points of 12GHz and 18GHz in the embodiment shown in fig. 5, wherein (a) and (b) respectively show waveforms of input signals; (c) and (d) a waveform representation after transmission through the optical fiber; (e) and (f) are enlargements of the details of fig. 6(c) and 6(d), respectively.
FIG. 7 is a diagram showing the phase jitter compensation results of 12GHz and 18GHz signals in the embodiment shown in FIG. 5, wherein (a) and (b) respectively show waveforms after phase jitter compensation; (c) and (d) are enlargements of the details of fig. 7(a) and 7(b), respectively; (e) and (f) represents the phase stability.
Fig. 8 shows the phase jitter results of the broadband signal fiber transmission in the embodiment shown in fig. 5, (a) shows the two-tone signal input waveforms with frequencies of 10GHz and 14GHz, (b) shows the two-tone signal input waveforms with frequencies of 14GHz and 18GHz, (c) and (d) show the waveforms of the two input signals after fiber transmission, respectively, and (e) and (f) are the amplification of the details of fig. 8(c) and 8(d), respectively.
Fig. 9 shows the result of the phase jitter compensation of the wideband signal in the embodiment shown in fig. 5.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Any feature disclosed in this specification (including any accompanying drawings) may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.
The phase jitter compensation method provided by the invention comprises the following steps of introducing a pilot signal to carry out round-trip transmission to sense phase jitter brought by external environment change, realizing mapping between a single phase error correction unit and each channel in a distributed system by switching of an optical switch, and realizing phase error compensation of the distributed system by phase error correction; the phase error correction method comprises the steps of extracting a phase error by using a phase discrimination unit, and controlling an optical adjustable delay line by combining a proportional-integral-amplification (PID) algorithm;
the specific method adopting the proportional-integral amplification algorithm comprises the following steps: initializing various parameters, including the current sampling period TsThe previous time T-1Phase error of (1), T-1A time T before the time-2Phase error and scale and coefficient at time; and reflecting the error at the current moment through proportional control, and proportionally adjusting towards the direction of reducing the error.
Multiple optical signals with different wavelengths are transmitted in an optical fiber and subjected to external environment changes to introduce phase changes. If the phase variation is a fixed value, the performance of the optical coherent reception is not affected. However, due to the existence of various uncertain factors such as material defects, temperature changes, and stress changes, the amount of change in the signal phase tends to fluctuate and be unpredictable. This not only results in an increase in phase noise, but also destroys the original relative phase difference between the channels. The invention introduces the pilot signal to carry out the round-trip transmission, extracts the phase error by utilizing the phase discriminator and the PID algorithm by extracting the phase jitter variable quantity of the pilot signal as the reference, converts the information into the analog signal and sends the analog signal to the optical adjustable delay line, and realizes the real-time compensation of the phase jitter of the transmission signal.
The method of the invention comprises the following characteristics: 1) the accurate compensation of the phase jitter can be realized without acquiring the frequency of the transmission signal; 2) the extremely high time and frequency transmission stability can be realized; 3) the method is suitable for distributed systems and wavelength division multiplexing systems; 4) and broadband real-time phase jitter compensation can be realized. Generally speaking, the long-distance distributed transmission of broadband signals is particularly important in a plurality of fields and various electronic information systems, so that the method is suitable for solving the problem of time-frequency ultra-stable transmission in the civil field, is also suitable for stable transmission of signal synchronization and time-varying signals in applications such as deep space exploration and gravitational wave exploration based on a large array, and has great significance and application value in the application field of military and civil integration.
Because the proportional control can not completely eliminate the steady-state error, as an implementation mode of the invention, a specific method adopting a proportional-integral amplification algorithm comprises the following steps: and initializing integral coefficients, and continuously accumulating system errors through integral control to eliminate steady-state errors of the system.
As an embodiment of the present invention, a specific method using a proportional-integral amplification algorithm includes: the coefficient of the differential is initialized, overshoot is reduced through differential control, oscillation is overcome, the stability of the system is improved, the response speed of the system is accelerated, and therefore the deviation is restrained from changing to any direction.
A phase jitter compensation system, as shown in fig. 1, suitable for the phase jitter compensation method, includes an optical frequency guide signal input unit 101, a first optical amplifier 102, a 1 × N optical power splitter 103, and N first optical circulators 104 connected in sequence1～104NN photo-tunable delay lines 1051～105NN sections of optical fiber 1061～106NN second optical circulators 1071～107NN adjustable optical attenuators 1081～108NN first optical wavelength division multiplexers 1101～110NAnd N second optical amplifiers 1111～111N(ii) a The 1 × N optical power splitter 103 is respectively connected with N first optical circulators 1041～104NConnecting; the N first optical circulators 1041～104NN photo-tunable delay lines 1051～105NN sections of optical fiber 1061～106NN second optical circulators 1071～107NN adjustable optical attenuators 1081～108NN first optical wavelength division multiplexers 1101～110NAnd N second light amplifiersAmplifier 1111～111NThe N signal lines are formed by sequentially connecting the N signal lines in a one-to-one correspondence manner; the N second optical amplifiers 1111～111NAnd N second optical circulators 1071～107NAre connected in a one-to-one correspondence manner; also included are N second wavelength division demultiplexers 1121～112NSignal input terminal and N first optical circulators 1041～104NThe signal output ends are connected with the phase error correction unit 114 through the Nx 1 optical switch 113; the phase error correction unit 114 is connected to the N photo-tunable delay lines 105 respectively1～105NConnecting; the N first optical wavelength division multiplexers 1101～110NAnd each is connected with M optical signal input units 10911～109NM(ii) a N and M are both natural numbers more than or equal to 2;
the optical pilot signal passes through the first optical amplifier 102, is divided into N channels of signals by the 1 × N optical power divider 103, and then passes through the corresponding N first optical circulators 1041～104NInto N optically tunable delay lines (105)1～105N) Performing phase precompensation; the pilot signals after pre-compensation enter respective optical fibers for transmission; the transmitted signals pass through a second optical circulator and an adjustable optical attenuator and then enter the optical wavelength division multiplexer together with remote multi-channel M optical signals located at different places; the multiplexed optical signals are subjected to power amplification by the corresponding second optical amplifier and then enter the optical fiber again for transmission; the transmitted multi-channel signals and pilot signals enter an optical adjustable delay line together for phase compensation, and then channel separation is carried out through a first optical circulator and a second wavelength division demultiplexer; finally, the separated N pilot signals pass through the nx1 optical switch 113 and then enter the phase error correction unit 114 for error extraction, and the error value is fed back to the corresponding optical tunable delay line for phase error compensation, thereby realizing real-time phase jitter compensation of the multi-channel M optical signals.
The invention aims at the civil and military-civil integrated electronic information system, can solve civil ultra-stable time-frequency transmission (such as time service center), and can also be combined with a wavelength division multiplexing means to solve the synchronization problem in a large-array electronic information system. Compared with the traditional phase jitter compensation technology, the method has the advantages of real-time phase jitter compensation by adopting a pilot frequency round-trip transmission technology, broadband phase jitter compensation by adopting an optical adjustable delay technology, mapping between a single phase correction unit and a plurality of channels in a distributed system by switching of an optical switch, low cost and high compatibility with the existing system by combining a wavelength division multiplexing technology.
The multichannel M signals may be in the same wavelength and wavelength division multiplexing form, the input M optical signals include intensity modulation, phase modulation, polarization modulation, quadrature amplitude modulation, and other formats, the formats include digital signals, narrowband analog signals, and wideband analog signals, and the frequency may be known or unknown.
For further similar explanation, two distributed nodes are taken, each node having two optical input signals, i.e., N-M-2. First, a pilot signal of 1GHz is applied to the laser through a modulator (here, an intensity modulator is taken as an example), and the wavelength is 194.4 THz. Suppose the phase of the optical pilot signal is phiref(t), the optical pilot signal passes through the first optical amplifier 102, the power divider 103 and the first optical circulator 1041～1042Into the electrically controlled tunable optical delay line 1051～1052After that, the phase becomes:
φDi(t)＝φref(t)+φcori(t) (1)
wherein i is 1, 2; phi is acori(t)＝-ωref·τcoriThe phase introduced for the optical delay line; omegarefIs the pilot signal angular frequency; tau iscoriIs an optical delay line delay.
The pilot signal, which has undergone preliminary phase correction, enters the optical fiber 1061～1062Transmitting to the direction of the remote node and passing through the second optical circulator 1071～1072An adjustable attenuator 1081～1082And then wavelength division multiplexing is carried out with the remote multipath optical signals. Assuming that the lengths of the two optical fibers are the same, but the length variation of the two optical fibers is delta t under the disturbance of the external environmentiThen the phases of the pilot signals in the two fiber channels become
φfiberi(t)＝φref(t)+φcori(t)+φτ(t)+φΔi(t) (2)
Wherein tau isFIs a fixed delay of the optical fiber, phiτ(t)＝-ωref·τFIs the fixed phase difference of the fiber with respect to the pilot signal; phi is aΔi(t)＝-ωref·ΔtiThe phase jitter is caused by the disturbance of the pilot signal by the optical fiber, and the power of the pilot signal adjusted by the optical attenuator is the same as the power of the transmission signal.
The multiplexed signals still maintain their respective phase information, and are passed through a second optical circulator 107 after being pre-compensated for power1～1072Re-entering the optical fiber 1061～1062And (4) transmitting. When the signals are returned to the pilot side again, the phase of the respective signals in the transmission path changes as shown in Table 1, where φij(t) is the initial phase of the signal for the jth channel in the i distributed remote nodes, φτij(t)＝-ωij·τFIs the fixed phase difference, phi, of the fiber with respect to each frequency signalΔij(t)＝-ωij·ΔtiThe phase jitter generated after each wavelength channel passes through the optical fiber.
TABLE 1 phase change after signal fiber transmission
Then, the two multiplexed signals are phase-corrected by respective tunable optical delay lines, and the phase of each wavelength channel is shown in table 2.
TABLE 2 phase corrected for each wavelength channel
Will phicori(t)、φτij(t) and phiΔijThe expressions of (t) are respectively substituted into the table above, and the phase relationship of 4 channels can be obtained:
φFij＝φij(t)+φτij(t)+ωi(-τcori-Δti)(3)
where i is 1,2, j is 1,2, representing the jth channel in the ith distributed node, phiFijIndicating the phase of the signal after transmission through the fiber. Middle phi of the above formulaij(t)+φτij(t) is a fixed amount and does not vary with the change of the external environment, and therefore, only needs to satisfy
-τcori-Δti＝C (4)
Wherein C is a constant, the delay of the whole link can be stabilized. Due to Δ tiWill vary randomly due to environmental factors and therefore will pass through the first optical circulator 104 in the system1～1042And a second demultiplexer 1121～1122And pilot frequency extraction is carried out, the pilot frequency is sent to a phase error correction unit 114 through an optical switch (113) to estimate the variation of the optical fiber delay jitter, synchronous adjustment of the optical adjustable delay line 105 is realized through a PID algorithm based on the variation, and finally real-time compensation of the multi-channel broadband signal phase jitter is realized. Since the change speed of the external temperature is far less than the switching speed of the optical switch, the compensation value of the phase jitter at the moment can be considered to be the same as that at the next moment for each channel, so that the mapping of a single phase correction unit and a plurality of optical fiber channels in a distributed system is realized.
In the system, the pilot signal keeps a continuous working state, and no matter whether the channel has signal transmission or not, the system can sense the change of the external environment in real time through the analysis of the pilot signal, so that the relevant parameters can be obtained uninterruptedly. Once a signal to be transmitted appears in the channel, when the signal is transmitted to the pilot frequency unit end through the optical fiber, the phase of the transmitted signal can be corrected in real time through the currently acquired jitter parameters.
Fig. 2 is a schematic diagram of a phase error correction unit according to the present invention, which is a core part of a multi-channel phase jitter compensation scheme suitable for a distributed system. Because the structure of the system multiplexes different wavelength signals together by wavelength division multiplexing and then the signals enter the optical fiber for transmission, the effect of delay change caused by the optical fiber on each channel is approximately equal, and meanwhile, a phase-stabilizing module system does not comprise a wavelength sensitive device, so the scheme can be well combined with a multi-channel transmission system. The input to the phase error correction unit is the pilot signal in the wavelength demultiplexer (1 GHz for example), which carries 2 times the fiber jitter after transmission over the round-trip fiber. The compensation idea is as follows: firstly, converting an optical frequency guide signal into a microwave pilot signal through a photoelectric detector, mixing the microwave pilot signal with a reference Local Oscillator (LO) of 300MHz, and obtaining a down-conversion signal through a filter if the phase of the LO is 0:
A1＝sin[(ωref-ωLO)t+φref(t)+2φτ(t)+2φcor(t)+2φΔ(t)](5)
wherein ω isrefAnd ωLORespectively, the pilot signal frequency and the reference local oscillator signal frequency, phiref、φτ、φcorAnd phiΔRespectively representing the original pilot signal phase, the fixed phase difference of the optical fiber relative to the pilot signal, the phase introduced by the delay compensation unit and the phase jitter of the pilot signal caused by the optical fiber disturbance.
Then, the down-conversion signal and the original pilot signal are up-converted to make the coefficient of the pilot signal phase the same as the coefficient of the optical fiber caused jitter, and the mixed signal is:
A2＝sin[(2ωref-ωLO)t+2φref(t)+2φτ(t)+2φcor(t)+2φΔ(t)](6)
the reference local oscillator is introduced to reduce the harmonic component of the pilot frequency mixed with the return signal, so that the signal needs to be mixed with the reference local oscillator again to eliminate the local oscillator frequency component:
A3＝sin[2ωref+2φref(t)+2φτ(t)+2φcor(t)+2φΔ(t)](7)
it should be noted that all coefficients in equation (7) are 2, so in order to compensate for the phase jitter of the far-end received signal transmission, the coefficients need to be eliminated, i.e. obtained by using a frequency divider:
A4＝sin[ωref+φref(t)+φτ(t)+φcor(t)+φΔ(t)](8)
obviously, the above equation is phase-discriminated from the original pilot signal, so that the phase error variation can be obtained:
A5＝φτ(t)+φcor(t)+φΔ(t) (9)
a proportional-integral amplifier (PID) is controlled by this component and then converted to an analog signal by a digital-to-analog conversion module. This analog signal is used to control the driving of the fiber delay line to achieve delay and phase stabilization.
As shown in fig. 3 and 4, the input and output of the PID algorithm module are respectively a phase discriminator and an optical tunable delay line, and the operating principle thereof is as follows: and (c) carrying out phase detection on the reference source r (t) with stable frequency and the actual output signal stream c (t) to extract the phase deviation e (t). Wherein, the reference source frequency is 1GHz, and the output signal flow and the phase deviation satisfy the formulas (8) and (9). Then, the proportion (P), integral (I) and differential (D) of the deviation are linearly combined to form a control quantity, and the optical adjustable delay line is controlled according to the control law that
Wherein, KpIs a proportionality coefficient, TITo integrate the time constant, TDU (t) is the derivative time constant, and u (t) is the output of the controller. The principle of the PID algorithm is to adjust Kp、TIAnd TDThree parameters stabilize the system.
FIG. 4 is a detailed flow chart of the PID algorithm. Firstly, the parameters used in the algorithm are initialized and set, including the sampling period TsAnd the previous time T-1Phase error (typically of0) (ii) a Then, adjusting a proper proportional coefficient, an integral time constant and a differential time constant to enable the PID to work in an optimal state; then, based on the currently inputted phase error signal e (t), the error accumulation e from the start time to the current time is calculatedIThe function of the analog integration is shown in equation (11).
eI＝eT0+eT-1+…e(t) (11)
Thirdly, the phase jitter difference e from the previous moment is calculated according to the currently input phase error signalDTo simulate the derivative function as shown in equation (12).
eD＝e(t)-eT-1(12)
Finally, the calculated amount is substituted into the formula (13) to obtain the PID control amount u (t), and the input signal (108) can be controlled by the PID control amount u (t) to control the optical adjustable delay line1～108N) Compensation of phase jitter.
u(t)＝Kp×[e(t)+(Ts/Ti)×eI+(TD/Ts)×ed](13)
Because the algorithm speed of the PID is far greater than the signal phase jitter change caused by the environment, the optical signal corrected by the formula (13) enters the phase discriminator to extract the phase error, and the new error value is used as the error of the current moment and enters the PID algorithm module to carry out integral, differential and proportional operations, so that the control quantity is continuously corrected, and the real-time correction and compensation of the phase jitter are realized.
Further, the temperature change in one day is taken as an example for explanation, and the temperature change trend is shown in fig. 5. The temperature variation function in the day is a cosine curve and in the night is a straight line, and the temperature difference between day and night is about 10 ℃. The temperature coefficient of a typical single mode fiber is 6.7392x10-4/° c, and thus the maximum delay jitter induced by the fiber is up to 35ps (126.1 ° phase jitter with respect to a signal having a frequency of 10 GHz). It can be seen that the phase relation of the original signal can be greatly destroyed by the temperature change in one day, but fig. 4 shows that the phase change belongs to a slow process relative to the signal transmission frequency.
As shown in fig. 6, in the experiment, the phase change amount of the optical signal induced by the temperature change is determined in fig. 5, and the time parameter is simulated by the simulation times in the experiment and takes a value of 100. When no phase stabilization is performed, no matter the frequency of the transmitted signal is 12GHz or 18GHz, the phase of the signal generates obvious jitter along with the change of the external environment. The phase jitter introduced by the 12GHz and 18GHz signals after transmission through the fiber was 86.4 deg. and 129.6 deg., respectively, when subjected to the same environmental changes (as shown in fig. 5). But the delay jitter is the same and is 20 ps.
As shown in fig. 7, when the phase jitter correction unit normally operates, the signal phase of each frequency signal transmitted through the optical fiber maintains the same value regardless of the change of the external environment. Taking the channel with the optical carrier frequency of 193.2THz as an example, in the same long simulation time, the peak-to-peak value of the delay variation of the link signal before the phase jitter compensation is 20ps (as shown in fig. 6), and after the delay jitter of the link is stabilized, the waveform diagrams of the frequency signals are shown in fig. 7(a) - (d), so that the delay jitter is well suppressed. Meanwhile, as can be seen from fig. 7(e) and 7(f), the peak-to-peak value of the compensated delay jitter is suppressed within 5ps (the phase jitter after compensation of 12GHz and 18GHz signals is 21.6 ° and 32.4 °, respectively). In practical application, even after the delay jitter of the optical fiber link is compensated, the residual delay jitter still exists in the signal, and the residual delay jitter is caused by the factors such as the change of the environmental temperature, the vibration and the like of the optical and electronic devices outside the compensation loop. In the simulation, the residual phase jitter is mainly caused by the imperfect phase design of the filter.
As shown in fig. 8, two frequencies are superimposed to simulate the phase-stable transmission of a wideband signal, the input signal frequency combination is shown in fig. 8, and other simulation parameters are similar to those of single-frequency-point signal transmission.
As can be seen from fig. 7, the wideband signal is not a standard positive or residual wave, and it is difficult to describe the phase change within a certain time by using a certain phase jitter value, so that the present application uses the delay jitter instead of the phase jitter more accurately. Before phase stabilization, the signal phase still has serious jitter, and the peak-to-peak value of delay jitter is up to 20 ps.
As shown in fig. 9, after phase jitter compensation is performed by using the same algorithm, the peak-to-peak value of jitter is reduced from 20ps to within 4ps, and phase-stable transmission of wideband (multi-frequency) signals is successfully achieved. Considering the case where the phase jitter is the largest (transmission frequency is 18GHz), the phase jitter is compensated to decrease from 130 ° to 26 °.
It can be observed from the above experimental results that the present invention utilizes the pilot signal to perform round-trip transmission to sense the phase jitter introduced by the external environment, realizes the mapping of a single phase correction unit and a plurality of optical fiber channels in the distributed system through the optical switch, and finally successfully realizes the phase jitter real-time compensation scheme of the broadband signal based on the phase discriminator and the PID algorithm. The scheme is not only suitable for time-frequency ultra-stable transmission in the civil field, but also suitable for solving the problems of clock synchronization and stable transmission of time-varying signals in a large-array electronic information system due to the advantages of the broadband property, the multi-channel distributed type and the like.
Claims (4)
1. A phase jitter compensation method comprises the steps that pilot signals are introduced to carry out round-trip transmission to sense phase jitter caused by external environment changes, mapping of a single phase error correction unit and each channel in a distributed system is achieved by switching of an optical switch, and phase error compensation of the distributed system is achieved through phase error correction; the phase error correction method comprises the steps of extracting a phase error by using a phase discrimination unit, and controlling the optical adjustable delay line by combining a proportional-integral amplification algorithm;
the specific method adopting the proportional-integral amplification algorithm comprises the following steps: initializing various parameters, including the current sampling period TsThe previous time T-1Phase error of (1), T-1A time T before the time-2Phase error and scale and coefficient at time; reflecting the error of the current moment through proportional control, and proportionally adjusting towards the direction of reducing the error;
the specific method comprises the following steps: after passing through the first optical amplifier 1, the optical pilot signal is divided into N paths of signals by the 1 × N optical power divider 1, and then enters N optical adjustable delay lines through corresponding N first optical circulators to perform phase precompensation; the pilot signals after pre-compensation enter respective optical fibers for transmission; the transmitted signals pass through a second optical circulator and an adjustable optical attenuator and then enter the optical wavelength division multiplexer together with remote multi-channel M optical signals located at different places; the multiplexed optical signals are subjected to power amplification by the corresponding second optical amplifier and then enter the optical fiber again for transmission; the transmitted multi-channel signals and pilot signals enter an optical adjustable delay line together for phase compensation, and then channel separation is carried out through a first optical circulator and a second wavelength division demultiplexer; and finally, the separated N pilot signals enter a phase error correction unit for error extraction after passing through an Nx 1 optical switch, and the error value is fed back to a corresponding optical adjustable delay line for phase error compensation, so that the real-time phase jitter compensation of the multi-channel M optical signals is realized.
2. The phase jitter compensation method of claim 1, wherein the specific method using the proportional-integral-amplification algorithm further comprises: and initializing integral coefficients, and continuously accumulating system errors through integral control to eliminate steady-state errors of the system.
3. The phase jitter compensation method of claim 2, wherein the specific method using the proportional-integral-amplification algorithm further comprises: the coefficient of the differential is initialized, overshoot is reduced through differential control, oscillation is overcome, the stability of the system is improved, the response speed of the system is accelerated, and therefore the deviation is restrained from changing to any direction.
4. A phase jitter compensation system adapted to the phase jitter compensation method of any one of claims 1 to 3, wherein: comprises an optical frequency signal input unit (101), a first optical amplifier (102), a 1 XN optical power divider (103) and N first optical circulators (104) which are connected in sequence1～104N) N photo-tunable delay lines (105)1～105N) N sections of optical fiber (106)1～106N) N second optical circulators (107)1～107N) N variable optical attenuators (108)1～108N) N first optical wavelength division multiplexers (110)1～110N) And N second optical amplifiers (111)1～111N) (ii) a The 1 XN optical power splitter (103) is respectively connected with N first optical circulators (104)1～104N) Connecting; the N first optical circulators (104)1～104N) N photo-tunable delay lines (105)1～105N) N sections of optical fiber (106)1～106N) N second optical circulators (107)1～107N) N variable optical attenuators (108)1～108N) N first optical wavelength division multiplexers (110)1～110N) And N second optical amplifiers (111)1～111N) The N signal lines are formed by sequentially connecting the N signal lines in a one-to-one correspondence manner; the N second optical amplifiers (111)1～111N) And N second optical circulators (107)1～107N) Are connected in a one-to-one correspondence manner; also included are N second wavelength division demultiplexers (112)1～112N) A signal input terminal and N first optical circulators (104)1～104N) The signal output ends are connected with a phase error correction unit (114) through Nx 1 optical switches (113); the phase error correction unit (114) is in turn connected to the N optically tunable delay lines (105) respectively1～105N) Connecting; the N first optical wavelength division multiplexers (110)1～110N) And each is connected with M optical signal input units (109)11～109MM)；
The optical frequency signal (101) passes through a first optical amplifier (102), then is subjected to average power division by a 1 XN optical power divider (103) to obtain N-path signals, and then passes through corresponding N first optical circulators (104)1～104N) Into N optically tunable delay lines (105)1～105N) Performing phase precompensation; the pilot signals after pre-compensation enter respective optical fibers for transmission; the transmitted signals pass through a second optical circulator and an adjustable optical attenuator and then enter the optical wavelength division multiplexer together with the M optical signals at the far ends of different places; the multiplexed optical signals are subjected to power amplification by the corresponding second optical amplifier and then enter the optical fiber again for transmission; the transmitted multi-channel signal and the pilot signal enter the optical adjustable delay togetherThe line carries out phase compensation, and then channel separation is carried out through a first optical circulator and a second wavelength division demultiplexer; and finally, the separated N pilot signals enter a phase error correction unit (114) for error extraction after passing through an Nx 1 optical switch (113), and the error value is fed back to a corresponding optical adjustable delay line for phase error compensation, so that the real-time phase jitter compensation of the M optical signals is realized.
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| CN104486026A (en) * | 2014-11-28 | 2015-04-01 | 中国电子科技集团公司第二十九研究所 | Multi-path microwave phase stable transmission method and device |
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| CN104486026A (en) * | 2014-11-28 | 2015-04-01 | 中国电子科技集团公司第二十九研究所 | Multi-path microwave phase stable transmission method and device |
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