Phase noise compensation enhancement method and system for optical fiber optical frequency transmission

Abstract

The invention discloses a phase noise compensation enhancement method and system for optical fiber optical frequency transmission, and relates to the technical field of optical communication and signal processing. A local high-precision laser source is transmitted to a far end through an optical fiber and is subjected to frequency comparison with a far-end laser source in a beat frequency manner; measuring the beat frequency signal through a phase counter to obtain comparison data; a local compensation radio frequency signal and an uncompensated signal are acquired through a digital circuit, a measurement time interval of the two signals is set, then the signals are connected to a phase counter for measurement, and compensation deviation data can be obtained by subtracting the two measured phase signals. The phase noise suppression enhancement can be realized by subtracting the compensation deviation data from the comparison data, so that the phase control bandwidth of optical fiber optical frequency transmission is improved, and the signal transmission precision is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical communication and signal processing, and particularly relates to a method, system, device and medium for enhancing phase noise compensation in optical fiber optical frequency transfer. Background Art

[0002] Optical fiber optical frequency transfer is to transmit high-precision optical frequency signals through optical fibers to achieve remote transmission and comparison of frequency signals. It has advantages such as high precision, low loss, and anti-interference, and has important applications in fields such as high-precision time-frequency standards, optical communication, and scientific research. To ensure the accuracy of the transmitted signal, it is necessary to overcome the phase noise introduced by the optical fiber environment disturbance, such as temperature changes, vibration interference, etc.

[0003] The current optical fiber optical frequency transfer scheme is to compare the phase noise between the round-trip transmitted signal and the reference signal through the optical fiber interference method and compensate for the phase noise, so as to achieve high-fidelity optical frequency signal transmission. However, the inherent optical fiber delay in the optical frequency signal transmission process limits the phase-locked bandwidth and the noise suppression amplitude, and further limits the transmission accuracy. Although the multi-stage relay transmission method can be used to increase the system phase-locked bandwidth at present, the relay scheme greatly increases the system structure complexity and reduces the system reliability at the same time. As a result, the current solution limits the control bandwidth under the optical fiber delay, making the accuracy of the transmitted signal relatively low and difficult to be applied to high-precision optical fiber optical frequency transfer. Summary of the Invention

[0004] Embodiments of the present invention provide a method and system for enhancing phase noise compensation in optical fiber optical frequency transfer, which can solve the problem in the prior art that the current solution limits the control bandwidth under the optical fiber delay, resulting in relatively low accuracy of the transmitted signal and being difficult to be applied to high-precision optical fiber optical frequency transfer.

[0005] Embodiments of the present invention provide a method for enhancing phase noise compensation in optical fiber optical frequency transfer, including the following steps: The transmitting end splits the optical frequency signal into a first optical frequency signal and a second optical frequency signal, and the first optical frequency signal is transmitted to the receiving end through an optical fiber line; The receiving end splits the first optical frequency signal transmitted to the receiving end into a third optical frequency signal and a fourth optical frequency signal, the third optical frequency signal is output to the user end, and the fourth optical frequency signal returns to the transmitting end along the original path in reverse through a Faraday mirror; the transmitting end detects the beat signal of the second optical frequency signal and the fourth optical frequency signal, and demodulates the phase of the beat signal to obtain the optical fiber line phase noise signal; The transmitting end measures the phase of the optical fiber line phase noise signal and the first optical frequency signal, adjusts the measurement time interval of the optical fiber line phase noise signal and the first optical frequency signal during phase measurement, obtains the phases measured by the optical fiber line phase noise signal and the first optical frequency signal, and subtracts the phases measured by the optical fiber line phase noise signal and the first optical frequency signal to obtain phase noise deviation data; The receiving end measures the phase of the first optical frequency signal transmitted to the receiving end to obtain transmitted signal phase data, subtracts the phase noise deviation data from the transmitted signal phase data to perform phase noise compensation on the first optical frequency signal transmitted to the receiving end, obtains the first optical frequency signal after phase noise compensation, and outputs the split third optical frequency signal to the user end.

[0006] Preferably, the obtaining of the phase noise deviation data includes: Set the phase of the optical fiber line phase noise signal to Set the phase of the second optical frequency signal to Set the phase of the first optical frequency signal to ; At t The phase of the transmitted signal received by the receiving end at the moment is , expressed as: ; Wherein: Represents the phase jitter introduced by the optical signal passing through the optical fiber line in the forward direction; Represents the time required for the optical frequency signal to pass through the optical fiber line once; Obtained by comparing the round-trip signal and the reference signal, expressed as: ; Wherein: Represents the phase jitter introduced by the optical signal passing through the optical fiber line in the reverse direction; Adjust the measurement time interval of the optical fiber line phase noise signal and the first optical frequency signal during phase measurement, and subtract the phases of the optical fiber line phase noise signal and the first optical frequency signal to obtain phase noise deviation data.

[0007] Preferably, the phase measurement of the transmitting end and the receiving end includes: Adopt the optical fiber time synchronization method to provide a unified time reference for the phase measurement devices of the transmitting end and the receiving end; Attach a time stamp during phase data acquisition and correct the timing deviation formed by the transmission delay through an algorithm.

[0008] Preferably, the path of the fourth optical frequency signal returning to the transmitting end along the original path through the Faraday mirror includes: The fourth optical frequency signal is reflected by the Faraday mirror. After reflection, the fourth optical frequency signal returns to the optical fiber line through the second beam splitter and is transmitted in the reverse direction to the transmitting end. Then, it is input through the second interface of the circulator and is directionally output to the detector through the third interface of the circulator.

[0009] Preferably, at the transmitting end, after the optical frequency signal is split into a first optical frequency signal and a second optical frequency signal by the first beam splitter, the first optical frequency signal is modulated by the first acousto-optic modulator and then transmitted to the receiving end through the optical fiber line. At the receiving end, the first optical frequency signal transmitted through the optical fiber line is modulated by the second acousto-optic modulator and then split into a third optical frequency signal and a fourth optical frequency signal by the second beam splitter.

[0010] Preferably, the process of the first acousto-optic modulator modulating the optical frequency signal includes: The radio frequency source RF1 and the radio frequency source RF2 respectively output drive signals with frequencies of f1 and f2, and f1 and f2 are not equal. Based on the drive signals with frequencies of f1 and f2, the phase noise compensation signal of the optical fiber line and the uncompensated phase noise signal of the optical fiber line are separated by the frequency division multiplexing method, and the phase noise compensation signal φ1 of the optical fiber line and the uncompensated phase noise signal of the optical fiber line are independently extracted.

[0011] An embodiment of the present invention further provides a phase noise compensation enhancement system for optical fiber optical frequency transfer, including: A signal modulation module, at the transmitting end, the optical frequency signal is split into a first optical frequency signal and a second optical frequency signal, and the first optical frequency signal is transmitted to the receiving end through the optical fiber line. At the receiving end, the first optical frequency signal transmitted to the receiving end is split into a third optical frequency signal and a fourth optical frequency signal. The third optical frequency signal is output to the user end, and the fourth optical frequency signal returns to the transmitting end in the reverse direction along the original path through the Faraday mirror; at the transmitting end, the beat signal of the second optical frequency signal and the fourth optical frequency signal is detected, and the beat signal is phase demodulated to obtain the phase noise signal of the optical fiber line. A modulation compensation module, at the transmitting end, the phase noise signal of the optical fiber line and the first optical frequency signal are phase measured, and the measurement time interval during the phase measurement of the phase noise signal of the optical fiber line and the first optical frequency signal is adjusted to obtain the phases measured for the phase noise signal of the optical fiber line and the first optical frequency signal. The difference between the phases measured for the phase noise signal of the optical fiber line and the first optical frequency signal is used to obtain the phase noise deviation data. At the receiving end, the first optical frequency signal transmitted to the receiving end is phase measured to obtain the phase data of the transmitted signal. The phase data of the transmitted signal is subtracted from the phase noise deviation data to perform phase noise compensation on the first optical frequency signal transmitted to the receiving end, obtaining the first optical frequency signal after phase noise compensation, and the split third optical frequency signal is output to the user end.

[0012] An embodiment of the present invention further provides an electronic device, including a memory and a processor; The memory is used to store a computer program; When the processor executes the computer program stored in the memory, the steps of a phase noise compensation enhancement method for fiber optic optical frequency transfer as described above are implemented.

[0013] An embodiment of the present invention further provides a computer-readable storage medium for storing a computer program, and when the computer program is executed by a processor, the steps of a phase noise compensation enhancement method for fiber optic optical frequency transfer as described above are implemented.

[0014] An embodiment of the present invention provides a phase noise compensation enhancement method and system for fiber optic optical frequency transfer. Compared with the prior art, the beneficial effects are as follows: In the present invention, the optical frequency signal at the sending end is split into a first optical frequency signal and a second optical frequency signal. The first optical frequency signal is transmitted to the receiving end through an optical fiber line; the first optical frequency signal transmitted to the receiving end is split into a third optical frequency signal and a fourth optical frequency signal. The third optical frequency signal is output to the user end, and the fourth optical frequency signal returns to the sending end along the original path through a Faraday mirror. The beat signal of the second optical frequency signal and the fourth optical frequency signal is detected by a detector, and the beat signal is phase-demodulated to obtain the phase noise signal of the optical fiber line; the phase of the phase noise signal of the optical fiber line and the first optical frequency signal is measured, and the measurement time interval of the phase noise signal of the optical fiber line and the uncompensated signal of the phase noise of the optical fiber line during phase measurement is adjusted, and the difference is obtained to get the phase noise compensation deviation data. Then, the phase data of the first optical frequency signal transmitted to the receiving end is subtracted by the phase noise compensation deviation data to achieve the phase noise compensation of the transmitted signal. In this process, because the phase noise compensation signal of the optical fiber line lags behind the uncompensated signal in the measurement time, that is, by setting the measurement time interval between the uncompensated signal and the compensated signal of the phase noise of the optical fiber line, the measurement time interval between the compensated signal and the uncompensated signal is set, and the optical fiber delay can be adjusted according to the actual situation, and the phase compensation deviation caused by the delay can be accurately eliminated in the later stage. This process does not require setting multiple relays for signal transmission, but directly compensates the signal, so as to improve the phase-locked bandwidth and noise suppression amplitude during the transmission of the optical frequency signal, and further improve the accuracy of the transmitted signal. Description of the Drawings

[0015] Figure 1 It is a flowchart of a phase noise compensation enhancement method for fiber optic optical frequency transfer provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of phase jitter caused by an optical fiber line in a phase noise compensation enhancement method for fiber optic optical frequency transfer provided by an embodiment of the present invention; Figure 3Schematic diagram of phase noise corresponding to phase jitter caused by an optical fiber line of a phase noise compensation enhancement method for optical fiber optical frequency transfer provided by an embodiment of the present invention. Detailed implementation manners

[0016] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following describes the detailed implementation manners of the present invention with reference to the accompanying drawings. Many specific details are set forth in the following description to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0017] See Figure 1 , an embodiment of the present invention provides a phase noise compensation enhancement method for optical fiber optical frequency transfer. After the optical frequency signal output by the laser passes through the beam splitter 1, it is divided into two beams of signals. One beam is connected to the circulator interface 1 and output from the circulator interface 2, and then passes through the acousto-optic modulator 1 (AOM1). The function of the acousto-optic modulator 1 is to modulate the optical frequency signal, and the modulation signal is provided by two radio frequency sources (RF1 and RF2 respectively); the optical frequency signal output by the AOM1 reaches the signal receiving end through the optical fiber line. First, it passes through the acousto-optic modulator 2 (AOM2). The optical frequency signal output by the acousto-optic modulator is divided into two beams by the beam splitter 2. One beam is output to the user, and the other beam is connected to the Faraday mirror. The Faraday mirror reversely returns the transmitted signal along the original transmission path to the sending end. After the reverse optical frequency signal is output to the circulator at the sending end, it is input from the circulator interface 2 and output from the circulator interface 3, and is input to the detector together with the output light of the beam splitter 1. The detector detects the beat frequency signal of the two beams of light. The beat frequency signal frequency is the sum of the modulation frequencies of the AOM1 and the AOM2. Since the AOM1 has two radio frequency drives with different frequencies, the detector detects two frequency signals. One of the frequency signals is filtered and phase demodulated through a filter and a demodulator to obtain the optical fiber line phase noise compensation signal, and this noise compensation signal is fed back to the radio frequency drive 1 to achieve optical fiber line noise compensation.

[0018] Denote the phase of the compensation signal provided by the radio frequency drive 1 as , the other frequency signal detected by the detector carries the uncompensated optical fiber noise, and denote its phase as , and denote the phase of the transmitted signal obtained at the receiving end as ; it can be known that at t moment, the phase of the received signal can be expressed as . Through the optical fiber noise compensation method described above, it can be obtained that: .

[0019] Where: represents the phase jitter introduced when the optical signal passes through the optical fiber line in the forward direction; represents the time required for the optical frequency signal to pass through the optical fiber line once; is obtained by comparing the round-trip signal and the reference signal, and can be expressed as , where represents the phase jitter introduced when the optical signal passes through the optical fiber line in the reverse direction.

[0020] From the expression, it can be seen that relative to the transmitted signal, the compensation signal lags behind the noise signal in time, thus limiting the noise suppression bandwidth.

[0021] In the present invention, by filtering the other output signal of the detector through a filter at the transmitting end, the filtered signal and the compensation signal are together sent to a measuring device for phase measurement, and the time interval between the two is reasonably adjusted, and the difference between the two can obtain the phase noise compensation deviation data; at the receiving end, the phase of the transmitted signal is also measured by a phase measuring device to obtain the transmitted signal phase data, and then the phase noise deviation data obtained at the local end is subtracted through post-processing, so as to further reduce the signal noise, thereby improving the control bandwidth and the optical frequency signal transmission accuracy; through derivation, it can be known that when the time interval difference between the phase of the compensation signal measured at the local end and the phase of the uncompensated signal is 1.5 , the phase control bandwidth has a maximum value; at the same time, in order to ensure that the time scales of the phase data obtained at the transmitting end and the receiving end are consistent, the phase measuring devices on both sides can be time-synchronized.

[0022] The current optical fiber optical frequency transfer technology mainly focuses on the compensation of real-time optical fiber phase noise. However, due to the limitation of optical fiber delay, the optical fiber phase noise cannot be completely compensated; the present invention measures the phase compensation deviation caused by the delay locally and further eliminates these deviations through post-processing, thereby improving the phase control bandwidth of optical fiber optical frequency transfer and further improving the transfer accuracy; the present invention will provide a high-precision optical frequency transfer means for fields such as long-distance optical fiber optical frequency comparison and precision spectroscopic measurement; by setting the measurement time interval between the local compensation signal and the uncompensated signal, the signal phase control bandwidth and the phase noise suppression ratio will be effectively improved compared with the prior art, thereby improving the signal transmission accuracy.

[0023] The present invention can be used for remote optical frequency comparison. A high-precision local laser source is transmitted to the remote end through an optical fiber and beat with the remote laser source for frequency comparison. The beat frequency signal is measured by a phase counter to obtain comparison data. The local compensated RF signal and the uncompensated signal are collected by a digital circuit, and the measurement time interval of the two signals is set. Then the signals are connected to the phase counter for measurement. By subtracting the two measured phase signals according to the method of the present invention, the compensation deviation data can be obtained. At the same time, considering that the optical fiber delay is τ, the beat frequency signal obtained at the remote end is delayed by 0.5τ through a delay optical fiber and then counted by the phase counter. By subtracting the deviation data from the comparison data, the phase noise suppression can be enhanced, thereby improving the comparison accuracy.

[0024] The present invention simulates the traditional noise compensation scheme of optical fiber optical frequency transfer and the phase noise compensation enhancement method proposed by the present invention through Matlab software. A 500-km optical fiber optical frequency transfer simulation model is established according to the optical fiber phase noise and delay characteristics. By calculating and compensating the compensation deviation data, it is verified that the phase noise compensation enhancement method proposed by the present invention can effectively suppress the residual noise and further improve the transfer accuracy. As Figure 2 shown in the schematic diagram of phase jitter caused by the optical fiber line, as Figure 3 shown in the schematic diagram of the phase noise corresponding to the phase jitter caused by the optical fiber line. The black line is the uncompensated optical fiber phase noise, the red line is the phase noise after compensation by the traditional scheme, and the blue line is the phase noise after compensation by the method proposed by the present invention. It can be seen that the phase noise is further suppressed, and the phase suppression bandwidth is also increased.

[0025] The above embodiments merely represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent shall be subject to the appended claims.

Claims

1. A method for enhancing phase noise compensation in optical fiber optical frequency transfer, characterized in that Including the following steps: The transmitting end splits the optical frequency signal into a first optical frequency signal and a second optical frequency signal, and the first optical frequency signal is transmitted to the receiving end through an optical fiber line; The receiving end splits the first optical frequency signal transmitted to the receiving end into a third optical frequency signal and a fourth optical frequency signal. The third optical frequency signal is output to the user end, and the fourth optical frequency signal returns to the transmitting end along the original path in reverse through a Faraday mirror; the transmitting end detects the beat signal of the second optical frequency signal and the fourth optical frequency signal, demodulates the phase of the beat signal, and obtains the phase noise signal of the optical fiber line; The transmitting end measures the phases of the optical fiber line phase noise signal and the first optical frequency signal, adjusts the measurement time interval of the optical fiber line phase noise signal and the first optical frequency signal during phase measurement, obtains the phases measured by the optical fiber line phase noise signal and the first optical frequency signal, and subtracts the phases measured by the optical fiber line phase noise signal and the first optical frequency signal to obtain the phase noise deviation data; The receiving end measures the phase of the first optical frequency signal transmitted to the receiving end to obtain the transmitted signal phase data, subtracts the phase noise deviation data from the transmitted signal phase data to perform phase noise compensation on the first optical frequency signal transmitted to the receiving end, obtains the first optical frequency signal after phase noise compensation, and outputs the split third optical frequency signal to the user end.

2. The phase noise compensation enhancement method for optical fiber optical frequency transfer according to claim 1, wherein The obtaining of the phase noise deviation data includes: Set the phase of the phase noise signal of the optical fiber line to , set the phase of the second optical frequency signal to , set the phase of the first optical frequency signal to ; At t the moment, the phase of the transmitted signal received by the receiving end is , expressed as: ； Wherein: represents the phase jitter introduced when the optical signal passes through the optical fiber line in the forward direction; represents the time required for the optical frequency signal to pass through the optical fiber line once; Obtained by comparing the round-trip signal and the reference signal, expressed as: ； Wherein: represents the phase jitter introduced by the optical signal passing backward through the optical fiber line; Adjusting the measurement time interval of the optical fiber line phase noise signal and the first optical frequency signal during phase measurement, and subtracting the phases of the optical fiber line phase noise signal and the first optical frequency signal to obtain the phase noise deviation data.

3. An enhanced method for phase noise compensation in optical fiber optical frequency transfer according to claim 1, characterized in that, The phase measurement of the transmitting end and the receiving end includes: Adopting an optical fiber time synchronization method to provide a unified time reference for the phase measurement devices of the transmitting end and the receiving end; Adding a time stamp during phase data acquisition, and correcting the timing deviation formed by the transmission delay through an algorithm.

4. A method for enhancing phase noise compensation in optical fiber optical frequency transfer according to claim 1, characterized in that, The path for the fourth optical frequency signal to return to the transmitting end along the original path through the Faraday mirror includes: The fourth optical frequency signal is reflected by the Faraday mirror, and the reflected fourth optical frequency signal returns to the optical fiber line through a second beam splitter, is transmitted in reverse to the transmitting end, and is input through the second interface of the circulator and is directionally output to the detector through the third interface of the circulator.

5. According to the method for enhancing phase noise compensation of optical fiber optical frequency transfer described in claim 1, characterized in that At the transmitting end, after the optical frequency signal is split into a first optical frequency signal and a second optical frequency signal by a first beam splitter, the first optical frequency signal is modulated by a first acousto-optic modulator and then transmitted to the receiving end through an optical fiber line; At the receiving end, the first optical frequency signal transmitted through the optical fiber line is modulated by a second acousto-optic modulator and then split into a third optical frequency signal and a fourth optical frequency signal by a second beam splitter.

6. An enhanced method for phase noise compensation in optical fiber optical frequency transfer according to claim 5, characterized in that The process of the first acousto-optic modulator modulating the optical frequency signal includes: The RF source RF1 and the RF source RF2 respectively output drive signals with frequencies of f1 and f2, and f1 and f2 are not equal; Based on the drive signals with frequencies of f1 and f2, the optical fiber line phase noise compensation signal and the uncompensated optical fiber line phase noise signal are separated by a frequency division multiplexing method, and the optical fiber line phase noise compensation signal φ1 and the uncompensated optical fiber line phase noise signal are independently extracted.

7. An enhanced system for phase noise compensation in optical fiber optical frequency transfer, characterized in that, Including: A signal modulation module, at the transmitting end, an optical frequency signal is split into a first optical frequency signal and a second optical frequency signal, and the first optical frequency signal is transmitted to the receiving end through an optical fiber line; At the receiving end, the first optical frequency signal transmitted to the receiving end is split into a third optical frequency signal and a fourth optical frequency signal, the third optical frequency signal is output to the user end, and the fourth optical frequency signal is reversely returned to the transmitting end along the original path through a Faraday mirror; at the transmitting end, by detecting the beat signal of the second optical frequency signal and the fourth optical frequency signal, the beat signal is phase demodulated to obtain the phase noise signal of the optical fiber line; A modulation compensation module, at the transmitting end, the phase of the phase noise signal of the optical fiber line and the first optical frequency signal is measured, and the measurement time interval of the phase noise signal of the optical fiber line and the first optical frequency signal during phase measurement is adjusted to obtain the phases measured of the phase noise signal of the optical fiber line and the first optical frequency signal, and the difference between the phases measured of the phase noise signal of the optical fiber line and the first optical frequency signal is taken to obtain phase noise deviation data; At the receiving end, the phase of the first optical frequency signal transmitted to the receiving end is measured to obtain the phase data of the transmitted signal, and the phase data of the transmitted signal is subtracted by the phase noise deviation data to perform phase noise compensation on the first optical frequency signal transmitted to the receiving end, obtaining the first optical frequency signal after phase noise compensation, and outputting the split third optical frequency signal to the user end.

8. An electronic device, characterized in that, It includes: A memory and a processor; The memory is used for storing a computer program; The processor, when executing the computer program stored in the memory, implements the steps of a method for enhancing phase noise compensation of optical fiber optical frequency transfer according to any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that, For storing a computer program, when the computer program is executed by a processor, it implements the steps of a method for enhancing phase noise compensation of optical fiber optical frequency transfer according to any one of claims 1 to 6.

Images