CN115021849B - Optical fiber time synchronization device and method based on photoelectric combined time compensation - Google Patents

Abstract

An optical fiber time synchronization device and method based on photoelectric combination time compensation firstly adopts an optical frequency comb technology to obtain high-frequency optical-loaded microwave signals, then carries out transmission delay sensing on optical fibers through the optical-loaded microwave signals, phase jitter of the optical-loaded microwave signals is caused by delay change of the optical fibers, absolute phase difference information of the optical-loaded microwave signals can be obtained through phase detection on the optical-loaded microwave signals, and the optical-loaded microwave signals are divided into two paths. The first path of absolute phase difference is divided by the frequency of the light-carried microwave signal to obtain the delay variation of the optical fiber, and then an electric delay line device is adopted on an electric domain to carry out time compensation; the second absolute phase difference integrates the output voltage through a loop filter, and then time compensation is performed on the optical domain by driving an optical delay line device. The invention realizes high-precision measurement of optical fiber delay by utilizing a microwave photon technology, and adopts a time compensation mechanism combining an electric domain and an optical domain, thereby greatly improving the compensation precision and the compensation range of time synchronization and simultaneously having the advantage of quick response.

Description

Optical fiber time synchronization device and method based on photoelectric combined time compensation

Technical Field

The present invention relates to the field of time synchronization technology, and in particular to the field of optical fiber time synchronization technology based on photoelectric combined time compensation.

Background technique

With the rapid development of atomic clocks and modern communication technology, and relying on the advantages of optical fiber such as low loss, high bandwidth and anti-electromagnetic interference, the synchronization technology of time and frequency signals through optical fiber plays an increasingly important role in basic scientific research, global navigation systems, mobile communication networks and other fields. Due to changes in external temperature and pressure, the transmission delay of optical fiber changes, resulting in unstable signals after optical fiber transmission, and phase or time compensation is required to achieve signal synchronization. Time compensation for optical fiber delay changes mainly includes the following two aspects: compensation in the electrical domain through electrical devices and compensation in the optical domain through optical devices.

The first is the time compensation technology in the electrical domain. Depending on the transmission signal, compensation can be performed through voltage-controlled oscillators, electrical delay lines, and pulse delay devices. Voltage-controlled oscillators are often used for phase compensation of frequency signals. With the help of phase-locked loop technology, the phase error of the transmission signal is detected by the phase detector, and then the phase output of the voltage-controlled oscillator is controlled by loop filter integration to achieve compensation. Due to the limitation of input bandwidth, electrical delay lines and pulse delay devices are often used for compensation of low-frequency frequency signals and time signals. The transmission delay change information of the optical fiber is obtained by detecting the phase jitter or delay information of the signal, and then the signal is time-compensated or the pulse signal is delayed in the electrical domain to achieve signal synchronization. In the above method, the accuracy of time synchronization is affected by the low measurement accuracy of the optical fiber delay change. At the same time, the resolution limitation of commercial electrical delay lines and pulse delay devices further reduces the accuracy of time synchronization.

The second type is the time compensation technology in the optical domain. On the basis of the transmission optical fiber, part of the optical fiber is connected externally. Then, the information of the delay change of the transmission optical fiber is converted into an electrical signal to control the stretching of the external optical fiber to offset the delay change of the transmission optical fiber caused by the change of the external environment to achieve signal synchronization. The external optical fiber is generally wrapped around the piezoelectric ceramic and placed in a temperature control box. The information of the delay change caused by the transmission optical fiber can be fed back to control the piezoelectric ceramic to mechanically stretch the optical fiber, or the length of the optical fiber can be changed by controlling the temperature in the temperature control box. Due to the slow response speed of the optical delay line, the bandwidth of the control loop is limited, resulting in the inability to effectively compensate for fast jitter. Moreover, as the transmission distance increases, a longer external optical fiber is required for large-scale delay compensation. Not only is the compensation speed slower, but it also increases the power loss of the optical signal and deteriorates the signal-to-noise ratio of the signal.

Summary of the invention

In view of the defects in the prior art, the present invention provides an optical fiber time synchronization device and method based on photoelectric combined time compensation. First, the optical frequency comb technology is used to obtain a high-frequency optical microwave signal, and then the optical fiber is sensed for transmission delay through the optical microwave signal. The optical microwave signal sensed in the optical fiber is phase-detected with the reference signal using microwave photon technology, and then the absolute phase difference information of the optical microwave signal obtained by the phase detection is divided into two paths. The absolute phase difference of the first optical microwave signal is divided by the signal frequency to obtain the delay change of the optical fiber. Obviously, the higher the frequency of the optical microwave signal, the higher the measurement accuracy. Then, an electrical delay line is used for time compensation in the electrical domain; the absolute phase difference of the second optical microwave signal is integrated and output voltage is output through a loop filter, and then the optical delay line based on piezoelectric ceramics is driven and controlled to perform time compensation in the optical domain. The present invention first uses microwave photon technology to complete the high-precision measurement of optical fiber delay, and then uses a time compensation mechanism combining the electrical domain and the optical domain to achieve time synchronization, which greatly improves the compensation accuracy and compensation range of time, while also having the advantage of fast response.

The present invention provides an optical fiber time synchronization device based on photoelectric combined time compensation, characterized in that it comprises: an optical frequency comb generation module, a signal generation module, a phase detection module, an electrical delay line compensation module, an optical delay line compensation module, and a synchronization signal output module;

The optical frequency comb generation module generates an optical frequency comb signal which is divided into two paths through an optical coupler, wherein the first path of the optical frequency comb signal is used for optical fiber transmission delay perception and time synchronization, and the second path of the optical frequency comb signal is used as a local reference signal for phase detection of the returned optical microwave signal;

The signal generation module filters the first optical frequency comb signal to obtain three optical carriers, and the three optical carriers further generate optical microwave signals and optical time signals for optical fiber delay measurement;

The phase detection module performs phase error detection on the return optical microwave signal after the optical fiber is subjected to transmission delay sensing, and obtains absolute phase difference information of the optical microwave signal caused by the optical fiber delay variation;

The electrical delay line compensation module converts the absolute phase difference obtained by the phase detection module into phase-time, and then controls the output of the electrical delay line to perform time pre-compensation in the electrical domain;

The optical delay line compensation module integrates the absolute phase difference obtained by the phase detection module through a loop filter to output a voltage signal, and then drives the optical delay line to perform time pre-compensation in the optical domain;

The synchronization signal output module is used to obtain a time signal synchronized with a local clock standard source, and at the same time perform a secondary frequency shift on the optical microwave signal input from the optical fiber to avoid backward Rayleigh scattering noise.

Preferably, the optical frequency comb generation module comprises a fiber laser, a signal generator, and an optical frequency comb generator; wherein the optical signal output by the fiber laser is modulated by the optical frequency comb generator driven by the signal generator to generate an optical frequency comb signal, and then divided into the first optical frequency comb signal and the second optical frequency comb signal by an optical coupler.

Preferably, the signal generating module comprises a first circulator, a polarization-maintaining array waveguide grating, a first acousto-optic modulator, and a Mach-Zehnder modulator; wherein the first optical frequency comb signal enters port 1 of the first circulator, and then is output from port 2 of the first circulator and enters the polarization-maintaining array waveguide grating, and then three optical carriers are filtered out by the polarization-maintaining array waveguide grating, one of which is first up-converted by the first acousto-optic modulator, and then coupled with the other carrier by a 1×2 optical coupler to form an optically-carried microwave signal; the third optical carrier is modulated by a Mach-Zehnder modulator driven by an electrical delay line to generate an optically-carried time signal, and the optically-carried time signal is then coupled with the optically-carried microwave signal by an optical coupler and sequentially enters the optical delay line and the optical fiber.

Preferably, the synchronization signal output module comprises a second circulator, a wavelength division multiplexer, a second acousto-optic modulator, and a first balanced detector; wherein, after the light-carrying time signal is coupled with the light-carrying microwave signal, it is transmitted through the optical fiber and enters port 2 of the second circulator, and then enters the wavelength division multiplexer from port 3 of the second circulator to filter out the light-carrying time signal and the light-carrying microwave signal, wherein the filtered light-carrying microwave signal undergoes secondary frequency shift through the second acousto-optic modulator and enters port 1 of the second circulator, and then is output from port 2 of the second circulator, and then passes through the optical fiber, the optical delay line, the first acousto-optic modulator and the polarization-maintaining array waveguide grating in sequence and returns to port 2 of the first circulator, and finally outputs the return light-carrying microwave signal from port 3 of the first circulator and is transmitted back to the measurement end; the filtered light-carrying time signal is sent to the first balanced detector for photoelectric conversion, and a time signal synchronized with a local clock standard source can be obtained.

Preferably, the phase detection module includes a second balanced detector, a clock standard source, a phase detector, and a phase comparator; wherein the second optical frequency comb signal is used as a reference signal for phase detection of the returned optical microwave signal, and is optically mixed with the returned optical microwave signal in a 2×2 optical coupler; the mixed output signal is converted into an electrical signal by the second balanced photodetector, and then a phase jitter signal is generated by the phase detector, and then the generated phase jitter signal is compared with the frequency signal output by the clock standard source in the phase comparator to detect the absolute phase difference of the optical microwave signal caused by the change in optical fiber delay.

Preferably, the electrical delay line compensation module includes a microprocessor and an electrical delay line; wherein, the microprocessor calculates the delay change of the optical fiber based on the absolute phase difference obtained by the phase comparator and divides it by the frequency of the optically-carried microwave signal, and at the same time, the time signal output by the clock standard source is sent to the electrical delay line, and then the microprocessor controls the electrical delay line in real time according to the obtained optical fiber delay to perform time compensation in the electrical domain.

Preferably, the optical delay line compensation module includes a loop filter and an optical delay line; wherein the loop filter integrates the absolute phase difference obtained by the phase comparator, and the voltage signal generated by the integration is used to drive the optical delay line to perform time compensation in the optical domain.

The present invention also provides an optical fiber time synchronization method based on photoelectric combined time compensation, characterized in that it comprises the following steps:

Step 1, generating a first optical frequency comb signal for optical fiber transmission delay perception and time synchronization, and a second optical frequency comb signal used as a local reference;

Step 2, filtering the first optical frequency comb signal to obtain three optical carriers, one of which is first up-converted and then coupled with another carrier to generate an optical microwave signal for optical fiber delay measurement; the third optical carrier is modulated by a Mach-Zehnder modulator driven by an electrical delay line to generate an optical time signal, and the optical time signal is then coupled with the optical microwave signal and enters the optical delay line and the optical fiber in sequence;

Step 3, the light-carrying microwave signal and the light-carrying time signal coupled into the optical fiber transmission then enter the second circulator and the wavelength division multiplexer in sequence to filter out the light-carrying time signal and the light-carrying microwave signal, wherein the filtered light-carrying microwave signal is output through the second circulator after secondary frequency shift, and then is transmitted back to the measurement end along the same link to obtain the returned light-carrying microwave signal;

Step 4: the second optical frequency comb signal is used as a reference signal for phase detection of the returned optical microwave signal, and is optically mixed with the returned optical microwave signal through an optical coupler; the mixed output signal is converted into an electrical signal through a second balanced photodetector, and then a phase jitter signal is generated through a phase detector, and then the generated phase jitter signal is compared with the frequency signal output by the clock standard source in a phase comparator to detect the absolute phase difference of the optical microwave signal caused by the change of optical fiber delay;

Step 5, the microprocessor calculates the delay change of the optical fiber according to the absolute phase difference obtained by the phase comparator, and at the same time, the time signal output by the clock standard source is sent to the electrical delay line, and then the microprocessor controls the electrical delay line in real time according to the obtained optical fiber delay to perform time compensation in the electrical domain;

Step 6: The loop filter integrates the absolute phase difference obtained by the phase comparator, and the voltage signal generated by the integration is used to drive the optical delay line based on piezoelectric ceramics to perform time compensation in the optical domain;

Step 7: The optical time signal filtered out by the wavelength division multiplexer is sent to the first balanced detector for photoelectric conversion, so as to obtain a time signal synchronized with the local clock standard source.

Preferably, the clock standard source can output frequency signals and time signals of different frequencies that are phase-synchronized.

Preferably, the signal generator is phase-synchronized with the clock standard source.

Preferably, the first AOM driving signal is provided by a frequency signal output by a clock standard source.

Preferably, the signal generator is a microwave signal generator.

Preferably, the phase detector is composed of a bandpass filter and a mixer.

Preferably, the phase comparator has a built-in programmable frequency divider.

The optical fiber time synchronization device and method based on optoelectronic combined time compensation provided by the present invention obtains high-precision optical fiber delay changes based on microwave photonic technology, and then uses an electrical delay line to perform time compensation on the time signal in the electrical domain, and uses an optical delay line to perform time compensation in the optical domain. The optoelectronic combined time compensation method greatly improves the time compensation accuracy and compensation range, while also having the advantage of rapid response.

Compared with the prior art, the present invention has the following beneficial effects:

1. Obtain high-frequency light-carrying microwave signals by using optical frequency comb technology, and then obtain the fiber delay variation based on the relationship between the signal phase jitter and the fiber delay variation. The higher the frequency of the light-carrying microwave signal, the higher the accuracy of the fiber delay variation measurement.

2. Use electrical delay line and optical delay line to perform time compensation in the electrical domain and optical domain respectively. The combination of optoelectronics can improve the accuracy and compensation range of time compensation, and has the characteristics of fast response;

3. The implementation method is simple. The time compensation values in the electrical domain and the optical domain are obtained through the absolute phase difference of the light-carrying microwave signal, which can meet the application requirements in the fields of optical communication, optical fiber sensing, microwave photonics, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

FIG1 is a structural block diagram of an optical fiber time synchronization device based on photoelectric combined time compensation according to an embodiment of the present invention;

FIG2 is an electrical connection diagram of an optical fiber time synchronization device based on optoelectronic combined time compensation according to an embodiment of the present invention;

In the figure:

101-fiber laser; 102-optical frequency comb generator; 103-signal generator;

104-a first circulator; 105-a polarization-maintaining array waveguide grating; 106-a first acousto-optic modulator;

107-Mach-Zehnder modulator; 108-optical delay line; 109-second circulator;

110-wavelength division multiplexer; 111-first balanced detector; 112-second acousto-optic modulator;

113 - a second balanced detector; 114 - a phase detector; 115 - a clock standard source;

116-phase comparator; 117-microprocessor; 118-electric delay line;

119 loop filter;

FIG3 is a flow chart of a method for optical fiber time synchronization based on optoelectronic combined time compensation according to another embodiment of the present invention;

FIG4 shows the delay variation of the synchronization time signal with and without time compensation using the time compensation of the present invention on a 40 km optical fiber;

FIG5 is a diagram showing the delay variation of the synchronous time signal using the time compensation of the present invention and the time compensation using only the electrical delay line device on a 40 km optical fiber;

Detailed ways

The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings:

FIG1 is a block diagram of a fiber optic time synchronization device based on optoelectronic combined time compensation according to an embodiment of the present invention, comprising: an optical frequency comb generation module, a signal generation module, a phase detection module, an electrical delay line compensation module, an optical delay line compensation module and a synchronization signal output module.

Referring to FIG1 , the present invention provides an optical fiber time synchronization device based on optoelectronic combined time compensation, characterized in that it includes: an optical frequency comb generation module, a signal generation module, a phase detection module, an electrical delay line compensation module, an optical delay line compensation module, and a synchronization signal output module;

The optical frequency comb generation module generates an optical frequency comb signal which is divided into two paths through an optical coupler, wherein the first path of the optical frequency comb signal is used for optical fiber transmission delay perception and time synchronization, and the second path of the optical frequency comb signal is used as a local reference signal for phase detection of the returned optical microwave signal;

The signal generation module filters the first optical frequency comb signal to obtain three optical carriers, and the three optical carriers further generate optical microwave signals and optical time signals for optical fiber delay measurement;

The phase detection module performs phase error detection on the return optical microwave signal after the optical fiber is subjected to transmission delay sensing, and obtains absolute phase difference information of the optical microwave signal caused by the optical fiber delay change;

The electrical delay line compensation module converts the absolute phase difference obtained by the phase detection module into phase-time, and then controls the output of the electrical delay line to perform time pre-compensation in the electrical domain;

The optical delay line compensation module integrates the absolute phase difference obtained by the phase detection module through a loop filter to output a voltage signal, and then drives the optical delay line to perform time pre-compensation in the optical domain;

The synchronization signal output module is used to obtain a time signal synchronized with a local clock standard source, and at the same time perform a secondary frequency shift on the optical microwave signal input from the optical fiber to avoid backward Rayleigh scattering noise.

Fig. 2 is an electrical connection diagram of the optical fiber time synchronization device based on optoelectronic combined time compensation in this embodiment. The frequency of the optical microwave signal in this embodiment can be selected through different output channels of the polarization-maintaining array waveguide grating. The larger the frequency interval between the two optical carriers (the frequency of the optical microwave signal), the higher the accuracy of the optical fiber delay change measurement. The polarization-maintaining array waveguide grating can also be replaced by an optical bandpass filter.

In a preferred embodiment, referring to Fig. 2, an electrical connection diagram of an optical fiber time synchronization device based on optoelectronic combined time compensation according to an embodiment of the present invention is provided. The optical frequency comb generation module comprises an optical fiber laser 101, a signal generator 103, and an optical frequency comb generator 102; the optical signal output by the optical fiber laser 101 is modulated by the optical frequency comb generator 102 driven by the signal generator 103 to generate an optical frequency comb signal, which is then divided into the first optical frequency comb signal and the second optical frequency comb signal by an optical coupler.

In a preferred embodiment, the signal generation module includes a first circulator 104, a polarization-maintaining array waveguide grating 105, a first acousto-optic modulator 106, and a Mach-Zehnder modulator 107; wherein the first optical frequency comb signal enters port 1 of the first circulator 104, and then is output from port 2 of the first circulator 104 to enter the polarization-maintaining array waveguide grating 105, and then three optical carriers are filtered out by the polarization-maintaining array waveguide grating 105, one of which is first up-converted by the first acousto-optic modulator 106, and then coupled with the other optical carrier through a 1×2 optical coupler to form an optically-carried microwave signal; the third optical carrier is modulated by the Mach-Zehnder modulator 107 driven by the electrical delay line 118 to generate an optically-carried time signal, and the optically-carried time signal is then coupled with the optically-carried microwave signal through a 1×2 optical coupler and sequentially enters the optical delay line 108 and the optical fiber.

In a preferred embodiment, the synchronization signal output module includes a second circulator 109, a wavelength division multiplexer 110, a second acousto-optic modulator 112, and a first balanced detector 111; wherein, after the light-carrying time signal is coupled with the light-carrying microwave signal, it is transmitted through the optical fiber and enters port 2 of the second circulator 109, and then enters the wavelength division multiplexer 110 from port 3 of the second circulator 109 to filter out the light-carrying time signal and the light-carrying microwave signal, wherein the filtered light-carrying microwave signal undergoes secondary frequency shift through the second acousto-optic modulator 112 and enters port 1 of the second circulator 109, and then is output from port 2 of the second circulator 109, and then returns to port 2 of the first circulator 104 through the optical fiber, the optical delay line, the first acousto-optic modulator 106, and the polarization-maintaining arrayed waveguide grating 105 in sequence, and finally outputs the return light-carrying microwave signal from port 3 of the first circulator 104 to the measurement end; the filtered light-carrying time signal is sent to the first balanced detector 111, and a time signal synchronized with a local clock standard source can be obtained.

In a preferred embodiment, the phase detection module includes a second balanced detector 113, a clock standard source 115, a phase detector 114, and a phase comparator 116; wherein the second optical frequency comb signal is used as a reference signal for phase detection of the returned optical microwave signal, and is optically mixed with the returned optical microwave signal in a 2×2 optical coupler; the mixed output signal is converted into an electrical signal by the second balanced photodetector 113, and then a phase jitter signal is generated by the phase detector 114, and then the generated phase jitter signal is compared with the frequency signal output by the clock standard source 115 in the phase comparator 116 to detect the absolute phase difference of the optical microwave signal caused by the change in optical fiber delay.

In a preferred embodiment, the electrical delay line compensation module includes a microprocessor 117 and an electrical delay line device 118; wherein the microprocessor 117 calculates the delay change of the optical fiber based on the absolute phase difference obtained by the phase comparator 116 and divides it by the frequency of the optically-carried microwave signal, and at the same time, the time signal output by the clock standard source 115 is sent to the electrical delay line device 118, and then the microprocessor 117 controls the electrical delay line device 118 in real time according to the obtained optical fiber delay to perform time compensation in the electrical domain.

In a preferred embodiment, the optical delay line compensation module includes a loop filter 119 and an optical delay line device 108; wherein the loop filter 119 integrates the absolute phase difference obtained by the phase comparator 116, and the voltage signal generated by the integration is used to drive the optical delay line device 108 to perform time compensation in the optical domain.

In a preferred embodiment, the signal generator 103 can be a microwave signal generator, the clock standard source 115 has output ports with different frequency references and output ports for time signals, and all output signals are phase synchronized; the phase detector 114 has a built-in bandpass filter and a mixer; the phase comparator 116 has a built-in programmable divider.

Another embodiment of the present invention further provides a method for optical fiber time synchronization based on photoelectric combined time compensation, as shown in FIG3 , which is a flow chart of the method for optical fiber time synchronization based on photoelectric combined time compensation in this embodiment. A method for optical fiber time synchronization based on photoelectric combined time compensation is characterized in that it comprises the following steps:

Step 1: Generate a first optical frequency comb signal for optical fiber transmission delay perception and time synchronization, and a second optical frequency comb signal used as a local reference.

Specifically, in this step, the local oscillator optical signal generated by the fiber laser 101 is modulated by the optical frequency comb generator 102 driven by the signal generator 103 to generate an optical frequency comb signal, including a first optical frequency comb signal for optical fiber transmission delay perception and time synchronization, and a second optical frequency comb signal used as a local reference;

Furthermore, the signal generator 103 and the clock standard source 115 are phase synchronized;

Step 2, filtering the first optical frequency comb signal to obtain three optical carriers, one of which is first up-converted and then coupled with another optical carrier to generate an optical microwave signal for optical fiber delay measurement; the third optical carrier is modulated by a Mach-Zehnder modulator driven by an electrical delay line to generate an optical time signal, and the optical time signal is then coupled with the optical microwave signal and enters the optical delay line and the optical fiber in sequence.

Specifically, in this step, the first optical frequency comb signal enters port 1 of the first circulator 104, and then outputs from port 2 to enter the polarization-maintaining array waveguide grating 105. The polarization-maintaining array grating 105 filters out three optical carriers, one of which is first up-converted by the first acousto-optic modulator 106, and then coupled with the other optical carrier through a 1×2 optical coupler to form an optically-carried microwave signal for optical fiber delay measurement; the third optical carrier is modulated by the Mach-Zehnder modulator 107 driven by the electrical delay line 118 to generate an optically-carried time signal, and the optically-carried time signal is then coupled with the optically-carried microwave signal through an optical coupler, and then enters the optical delay line 108 and the optical fiber in sequence.

Furthermore, the driving circuit of the first acousto-optic modulator 106 is provided by a clock standard source 115 to ensure the phase synchronization of the optically-carried microwave signal, and the time signal output by the clock standard source 115 is sent to an electrical delay line 118 to ensure the phase synchronization of the time signal.

Step 3, the optical microwave signal and the optical time signal coupled into the optical fiber transmission then enter the second circulator and the wavelength division multiplexer in turn, and then filter out the optical time signal and the optical microwave signal, wherein the filtered optical microwave signal is output through the second circulator after secondary frequency shift, and then is transmitted back to the measurement end along the same link to obtain the returned optical microwave signal.

Specifically, in this step, the light-carrying microwave signal and the light-carrying time signal enter port 2 of the second circulator 109 after being transmitted through the optical fiber, and then enter the wavelength division multiplexer 110 from port 3 of the second circulator 109 to filter out the light-carrying time signal and the light-carrying microwave signal, wherein the filtered light-carrying microwave signal undergoes secondary frequency shift through the second acousto-optic modulator 112 and enters port 1 of the second circulator 109, and then is output from port 2 of the second circulator 109, and then passes through the optical fiber, the optical delay line 108, the first acousto-optic modulator 106 and the polarization-maintaining array waveguide grating 105 in sequence to enter port 2 of the first circulator 104, and finally outputs the return light-carrying microwave signal from port 3 of the first circulator 104 to be transmitted back to the measurement end.

Step 4: The second optical frequency comb signal is used as a reference signal for phase detection of the returned optical microwave signal, and is optically mixed with the returned optical microwave signal through an optical coupler; the mixed output signal is converted into an electrical signal through a second balanced photodetector, and then a phase jitter signal is generated through a phase detector, and then the generated phase jitter signal is compared with the frequency signal output by the clock standard source in a phase comparator to detect the absolute phase difference of the optical microwave signal caused by the change in optical fiber delay.

Specifically, in this step, the second optical frequency comb signal is used as a reference signal for phase detection of the returned optical microwave signal, and is mixed with the returned optical microwave signal in a 2×2 optical coupler; the mixed output signal is converted into an electrical signal by a second balanced photodetector 113, and then a phase jitter signal is generated by a phase detector 114, and then the generated phase jitter signal is compared with the frequency signal output by the clock standard source 115 in a phase comparator 116 to detect the absolute phase difference of the optical microwave signal caused by the change in optical fiber delay.

Furthermore, the phase detector 114 first performs bandpass filtering on the electrical signal and then performs electrical mixing, and then filters and outputs a difference frequency signal with phase jitter information of the optically-carried microwave signal;

Furthermore, the phase comparator 116 has a built-in programmable frequency divider to ensure that the same-frequency phase comparison can be performed between signals of different frequencies;

Step 5, the microprocessor calculates the delay change of the optical fiber based on the absolute phase difference obtained by the phase comparator, and at the same time, the time signal output by the clock standard source is sent to the electrical delay line. Then the microprocessor controls the electrical delay line in real time according to the obtained optical fiber delay to perform time compensation in the electrical domain.

Specifically, in this step, the microprocessor 117 calculates the delay change of the optical fiber based on the absolute phase difference obtained by the phase comparator 116 and divides it by the frequency of the optically-carried microwave signal. At the same time, the time signal output by the clock standard source 115 is sent to the electrical delay line 118. Then, the microprocessor 117 controls the electrical delay line 118 in real time according to the obtained optical fiber delay to perform time compensation in the electrical domain.

Step 6: The loop filter integrates the absolute phase difference obtained by the phase comparator, and the voltage signal generated by the integration is used to drive the optical delay line based on piezoelectric ceramics to perform time compensation in the optical domain;

Specifically, in this step, the loop filter 119 integrates the absolute phase difference obtained by the phase comparator 116, and the voltage signal generated by the integration is used to drive the piezoelectric ceramic-based optical delay line device 108 to perform time compensation in the optical domain.

Step 7: The optical time signal filtered out by the wavelength division multiplexer is sent to the first balanced detector for photoelectric conversion to obtain a time signal synchronized with a local clock standard source.

Specifically, in this step, the optical time signal filtered out by the wavelength division multiplexer 110 is sent to the first balanced detector 111, and a time signal synchronized with the local clock standard source can be obtained after demodulation.

Figure 4 shows the delay variation of the synchronous time signal on a 40km optical fiber using the time compensation method of the present invention and without time compensation. Without time compensation, the delay variation of the time signal is as high as 2ns, while after time compensation, the delay variation is within ±20ps. This experiment can verify the effectiveness of the time compensation method based on photoelectric combination of the present invention.

Figure 5 shows the delay variation of the synchronization time signal under two conditions: the method of combining optoelectronic time compensation of the present invention and the method of only using the electric delay line device for time compensation on a 40km optical fiber. The jitter of the time compensation method using only the electric delay line device is about 100ps, and the root mean square synchronization jitter error is about 23ps, while the jitter of the time compensation method using the present invention is about 40ps, and the root mean square synchronization jitter error is about 6ps. It can be found that compared with the compensation method using only the electric delay line device, the compensation accuracy of the present invention is improved by about 4 times.

The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims (10)

1. An optical fiber time synchronization device based on optoelectronic combined time compensation, characterized in that it includes: an optical frequency comb generation module, a signal generation module, a phase detection module, an electrical delay line compensation module, an optical delay line compensation module, and a synchronization signal output module; The optical frequency comb generation module generates an optical frequency comb signal which is divided into two paths through an optical coupler, wherein the first path of the optical frequency comb signal is used for optical fiber transmission delay measurement and time synchronization, and the second path of the optical frequency comb signal is used as a local reference signal for phase detection of the returned optical microwave signal; The signal generation module filters the first optical frequency comb signal to obtain three optical carriers, and the three optical carriers further generate optical microwave signals and optical time signals for optical fiber delay measurement; The phase detection module performs phase error detection on the return optical microwave signal after the optical fiber is subjected to transmission delay sensing, and obtains absolute phase difference information of the optical microwave signal caused by the optical fiber delay change; The electrical delay line compensation module converts the absolute phase difference obtained by the phase detection module into phase-time, and then controls the output of the electrical delay line to perform time pre-compensation in the electrical domain; The optical delay line compensation module integrates the absolute phase difference obtained by the phase detection module through a loop filter to output a voltage signal, and then drives the optical delay line to perform time pre-compensation in the optical domain; The synchronization signal output module is used to obtain a time signal synchronized with a local clock standard source, and at the same time perform a secondary frequency shift on the optical microwave signal input from the optical fiber to avoid backward Rayleigh scattering noise. 2. According to claim 1, a fiber optic time synchronization device based on optoelectronic time compensation is characterized in that the optical frequency comb generation module includes a fiber laser, a signal generator, and an optical frequency comb generator; wherein the optical signal output by the fiber laser is modulated by the optical frequency comb generator driven by the signal generator to generate an optical frequency comb signal, and then divided into the first optical frequency comb signal and the second optical frequency comb signal by an optical coupler. 3. An optical fiber time synchronization device based on optoelectronic time compensation according to claim 1 or 2, characterized in that the signal generation module includes a first circulator, a polarization-maintaining array waveguide grating, a first acousto-optic modulator, and a Mach-Zehnder modulator; wherein the first optical frequency comb signal enters the first circulator port 1, and then is output from the first circulator port 2 to enter the polarization-maintaining array waveguide grating, and then three optical carriers are filtered out by the polarization-maintaining array waveguide grating, one of which is first up-converted by the first acousto-optic modulator, and then coupled with the other carrier through a 1×2 optical coupler to form an optical microwave signal; the third optical carrier is modulated by the Mach-Zehnder modulator driven by the electrical delay line to generate an optical time signal, and the optical time signal is then coupled with the optical microwave signal by an optical coupler and enters the optical delay line and the optical fiber in sequence. 4. The optical fiber time synchronization device based on photoelectric combined time compensation according to claim 3 is characterized in that the synchronization signal output module comprises a second circulator, a wavelength division multiplexer, a second acousto-optic modulator, and a first balanced detector; wherein the optical time signal is coupled with the optical microwave signal and then transmitted through the optical fiber into port 2 of the second circulator, and then enters the wavelength division multiplexer from port 3 of the second circulator to filter out the optical time signal and the optical microwave signal, wherein the filtered optical microwave signal undergoes secondary frequency shift through the second acousto-optic modulator and enters port 1 of the second circulator, and then is output from port 2 of the second circulator, and then passes through the optical fiber, the optical delay line, the first acousto-optic modulator and the polarization-maintaining array waveguide grating in sequence and returns to port 2 of the first circulator, and finally outputs the return optical microwave signal from port 3 of the first circulator to the measurement end; the filtered optical time signal is sent to the first balanced detector for photoelectric conversion, and a time signal synchronized with a local clock standard source can be obtained. 5. According to claim 4, a fiber optic time synchronization device based on optoelectronic time compensation is characterized in that the phase detection module includes a second balanced detector, a clock standard source, a phase detector, and a phase comparator; wherein the second optical frequency comb signal is used as a reference signal for phase detection of the returned optical microwave signal, and is optically mixed with the returned optical microwave signal in a 2×2 optical coupler; the mixed output signal is converted into an electrical signal by the second balanced detector, and then a phase jitter signal is generated by the phase detector, and then the generated phase jitter signal is compared with the frequency signal output by the clock standard source in the phase comparator to detect the absolute phase difference of the optical microwave signal caused by the change in optical fiber delay. 6. According to claim 5, a fiber optic time synchronization device based on optoelectronic time compensation is characterized in that the electrical delay line compensation module includes a microprocessor and an electrical delay line; wherein the microprocessor calculates the delay change of the optical fiber based on the absolute phase difference obtained by the phase comparator and divides it by the frequency of the optical microwave signal, and at the same time, the time signal output by the clock standard source is sent to the electrical delay line, and then the microprocessor controls the electrical delay line in real time according to the obtained optical fiber delay to perform time compensation in the electrical domain. 7. According to claim 5, a fiber optic time synchronization device based on optoelectronic combined time compensation is characterized in that the optical delay line compensation module includes a loop filter and an optical delay line; wherein the loop filter integrates the absolute phase difference obtained by the phase comparator, and the voltage signal generated by the integration is used to drive the optical delay line to perform time compensation in the optical domain. 8. A method for optical fiber time synchronization based on photoelectric combined time compensation, characterized in that it comprises the following steps: Step 1, generating a first optical frequency comb signal for optical fiber transmission delay perception and time synchronization, and a second optical frequency comb signal used as a local reference; Step 2, filtering the first optical frequency comb signal to obtain three optical carriers, one of which is first up-converted and then coupled with another carrier to generate an optical microwave signal for optical fiber delay measurement; the third optical carrier is modulated by a Mach-Zehnder modulator driven by an electrical delay line to generate an optical time signal, and the optical time signal is then coupled with the optical microwave signal and enters the optical delay line and the optical fiber in sequence; Step 3, the light-carrying microwave signal and the light-carrying time signal coupled into the optical fiber transmission then enter the second circulator and the wavelength division multiplexer in sequence, and then filter out the light-carrying time signal and the light-carrying microwave signal, wherein the filtered light-carrying microwave signal is output through the second circulator after secondary frequency shift, and then is transmitted back to the measurement end along the same link to obtain the returned light-carrying microwave signal; Step 4: The second optical frequency comb signal is used as a reference signal for phase detection of the returned optical microwave signal, and is optically mixed with the returned optical microwave signal through an optical coupler; the mixed output signal is converted into an electrical signal through a second balanced detector, and then a phase jitter signal is generated through a phase detector, and then the generated phase jitter signal is compared with the frequency signal output by the clock standard source in a phase comparator to detect the absolute phase difference of the optical microwave signal caused by the change of optical fiber delay; Step 5, the microprocessor calculates the delay change of the optical fiber according to the absolute phase difference obtained by the phase comparator, and at the same time, the time signal output by the clock standard source is sent to the electrical delay line, and then the microprocessor controls the electrical delay line in real time according to the obtained optical fiber delay to perform time compensation in the electrical domain; Step 6: The loop filter integrates the absolute phase difference obtained by the phase comparator, and the voltage signal generated by the integration is used to drive the optical delay line based on piezoelectric ceramics to perform time compensation in the optical domain; Step 7: The optical time signal filtered out by the wavelength division multiplexer is sent to a first balanced detector for photoelectric conversion to obtain a time signal synchronized with a local clock standard source. 9. According to claim 8, a fiber optic time synchronization method based on optoelectronic combined time compensation is characterized in that the clock standard source can output frequency signals and time signals of different frequencies with phase synchronization; the signal generator and the clock standard source are phase synchronized; and the first acousto-optic modulator driving signal is provided by the frequency signal output by the clock standard source. 10. The optical fiber time synchronization method based on optoelectronic combined time compensation according to claim 9 is characterized in that the signal generator adopts a microwave signal generator, the phase detector is composed of a bandpass filter and a mixer; and the phase comparator has a built-in programmable divider.