Optical fiber time service system based on gain switch laser regulation and control

Abstract

The invention discloses an optical fiber time service system based on gain switch laser regulation and control in the technical field of optical fiber time service. The optical fiber time service system comprises a central station, an optical fiber link and a terminal station. And the central station generates a coded pulse string with a determined time length by using a clock source signal to modulate the gain switch laser, and generates a laser pulse string to be injected into the optical fiber. The terminal station divides a received laser pulse into two parts, and one part is injected into a gain switch laser of the terminal station after being subjected to delay amplification, so that the working wavelength of the laser is locked with the laser of the central station; the other part is used for extracting the pulse per second generated by the central station and completing time interval measurement of the pulse per second of the terminal station and the pulse per second generated by the central station; the terminal station generates a time frequency and information coding pulse string, modulates a local gain switch laser to generate a laser pulse string, injects the laser pulse string into an optical fiber and returns the laser pulse string to the central station; and the central station and the terminal station use single-fiber single-wavelength bidirectional time transmission comparison to obtain a clock difference between the two stations, and finish servo regeneration of a time frequency signal at the terminal station.

Description

Technical Field

[0001] The invention belongs to the technical field of high-precision time and frequency synchronization, and in particular relates to an optical fiber timing system based on gain switch laser regulation and control and a realization method thereof. Background Art

[0002] At present, high-precision optical fiber time transfer systems usually use two technical systems: wavelength division multiplexing bidirectional transmission or time division multiplexing transmission. Wavelength division multiplexing transmission uses two different standard wavelengths to achieve bidirectional transmission of time and frequency signals in a single optical fiber. However, the dispersion coefficients of optical fibers for optical signals of different wavelengths are different, and different dispersion coefficients lead to different group velocities. The transmission delays of optical signals of different wavelengths on the round-trip link cannot be exactly the same. When the working wavelength interval increases, the accuracy of time transfer cannot be guaranteed due to the existence of this asymmetry of transmission delay.

[0003] Taking a distance of 100 km as an example, when commercial G.652 optical fiber is used for time transmission, since the dispersion coefficient D at 1550 nm is about 17 ps / (nm.km), a laser wavelength drift of ±0.1 nm will produce a timing error of about 340 ps. Although theoretical corrections can be made by estimating the dispersion value of standard single-mode optical fiber at a given synchronization distance, in actual applications, the center wavelength of the laser has random fluctuations during use (generally the commercial laser index is ±0.1 nm), and the dispersion value of commercial optical fiber itself fluctuates from different batches and in different environments. Therefore, as long as the timing system uses two different wavelengths for time transmission, the fiber dispersion and dispersion fluctuations and the random drift of the two laser wavelengths will lead to asymmetric deviations and deviation fluctuations in timing, and the timing error can reach hundreds of picoseconds at a distance of hundreds of kilometers.

[0004] Time division multiplexing transmission is a half-duplex working mode for the optical transmitters of the timing center station and the terminal station, and each station does not receive laser signals while sending signals. The advantage of this working mode is that the lasers of the center station and the terminal station can theoretically operate at the same wavelength, and the half-duplex working mode can avoid the interference of the backscattered light of the laser signal sent by the station in the optical fiber on the received signal. However, in the systems that have been reported, a more complex switching mechanism is usually required to ensure the optical isolation of the same wavelength transmission. More importantly, the lasers of the center station and the terminal station are still in an independent working state. It is difficult to avoid the deviation of the laser wavelengths of the two stations due to temperature drift and aging of the laser, which will still bring about the problem of dispersion asymmetry. Summary of the invention

[0005] The object of the present invention is to provide an optical fiber timing system based on gain switch laser regulation, which has the characteristics of high timing accuracy, low cost and easy compatibility with optical fiber links.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides an optical fiber timing system based on gain switch laser regulation, comprising a central station and a terminal station connected by optical fiber;

[0008] The central station is equipped with a central control module and a central gain switch laser; the terminal station is equipped with a delay amplifier, a terminal control module, and a terminal gain switch laser;

[0009] The information transmission and reception process from the central station to the terminal station includes:

[0010] The central control module controls the central gain switch laser to send a central laser pulse to the terminal station. The central laser pulse includes a clock source second pulse, a frequency signal, time information, and a second time interval between the clock source second pulse and the second pulse sent by the terminal station. The terminal station divides the central laser pulse sent by the central station into two parts, one part of the central laser pulse is sent to the terminal gain switch laser through the delay amplifier device, the working wavelength of the terminal gain switch laser is locked to the working wavelength of the central gain switch laser, and the other part of the central laser pulse is directly sent to the terminal control module;

[0011] The information transmission and reception process from the terminal station to the central station includes:

[0012] The terminal control module controls the terminal gain switch laser to send a terminal laser pulse to the central station, and the terminal laser pulse includes a second pulse of the terminal station, a frequency signal, time information, and a first time interval between the second pulse of the terminal station and the second pulse of the clock source. ;

[0013] The clock error is calculated through the interactive information between the central station and the terminal station, and the time of the servo clock in the terminal station is corrected according to the clock error to achieve time synchronization with the clock source.

[0014] Further, the central control module includes a central time measurement unit, a central control unit and a central optical receiver;

[0015] The central optical receiver is used to receive the terminal laser pulse, convert the terminal laser pulse into a photoelectric signal, and then send it to the central control unit;

[0016] The central time measurement unit is used to measure the second time interval between the second pulse sent by the terminal station and the second pulse sent by the clock source And sent to the central control unit;

[0017] The central control unit is used to extract the second pulse sent by the terminal station from the terminal laser pulse, and send the second pulse sent by the terminal station to the central time measurement unit; the central control unit is used to measure the time signal, frequency signal, time information and second time interval of the central station according to the time signal, frequency signal, time information and second time interval of the central station A center-coded pulse train is generated and sent to the center gain-switched laser.

[0018] Further, the terminal control module includes a servo clock, a terminal time measurement unit, a terminal control unit and a terminal optical receiver;

[0019] The terminal optical receiver is used to receive the central laser pulse, convert the central laser pulse into a photoelectric signal, and then send it to the terminal control unit;

[0020] The terminal control unit is used to extract the clock source second pulse in the central laser pulse and send the clock source second pulse to the terminal time measurement unit; the terminal control unit is used to extract the clock source second pulse from ... according to the second pulse, frequency signal, time information and first time interval of the terminal station. Generate a terminal coded pulse train; extract information from the central laser pulse to obtain a second time interval , according to the second time interval and the first time interval Calculate the clock difference between the central station and the terminal station, and send the clock difference to the terminal station servo clock;

[0021] The terminal time measurement unit measures a first time interval between a second pulse in the terminal station and a second pulse of a clock source , the first time interval Sending to the terminal control unit;

[0022] The servo clock is used to send the second pulse of the terminal station to the terminal time measurement unit, and send the second pulse, frequency signal and time information of the terminal station to the terminal control unit; the servo clock is used to receive the clock difference sent by the terminal control unit, and correct its own time according to the clock difference to achieve time synchronization with the clock source.

[0023] Furthermore, the central station is equipped with a central circulator; the central circulator is connected to a central optical receiver and a central gain switch laser through optical fiber; the terminal station is equipped with a terminal circulator; the terminal circulator is connected to a delay amplifier, a terminal optical receiver and a terminal gain switch laser through optical fiber; the central circulator is connected to the terminal circulator through optical fiber.

[0024] Furthermore, an injection control signal is provided at the end of the central laser pulse, and the time length of the central laser pulse is adjusted by the injection control signal, and the time length of the central laser pulse is less than the total round-trip delay from the central station to the terminal station; when the terminal coded pulse train modulates the terminal gain switch laser, the terminal gain switch laser is in the state of receiving the injection control signal in the central laser pulse sent by the central station.

[0025] Furthermore, when the center gain switch laser and the terminal gain switch laser are in pulse train modulation, the bias current is higher than the gain switch laser threshold; when the center gain switch laser and the terminal gain switch laser are in non-pulse train modulation, the bias current is lower than the gain switch laser threshold; when the central station and the terminal station receive laser pulses, the backscattered light power of the optical signal sent is at least 20dB lower than the received light power of the optical receiver.

[0026] In a second aspect, the present invention provides a fiber timing method based on gain switch laser regulation, comprising:

[0027] The central station receives the terminal laser pulse and measures the second time interval between the second pulse in the terminal station and the second pulse of the clock source according to the terminal laser pulse. , generating a first transmitted central coded pulse string according to the clock source second pulse, the frequency signal and the time information; the time information in the central coded pulse string includes a second time interval , the second time interval in the first transmission of the center coded pulse train Set to discard mask; send the center coded pulse string to the center gain switch laser, convert the center coded pulse string into a center laser pulse and send it to the terminal station;

[0028] The terminal station receives the central laser pulse, divides the central laser pulse into two, and sends part of the central laser pulse to the terminal gain switch laser after delayed amplification. The working wavelength of the terminal gain switch laser locks the working wavelength of the central gain switch laser, and the other part of the central laser pulse is sent to the terminal control module; the second pulse in the terminal station and the second pulse of the clock source are measured according to the central laser pulse to obtain the first time interval , according to the second pulse, frequency signal, time information and first time interval of the terminal station generating a terminal coded pulse train, and modulating a terminal gain switch laser to convert the terminal coded pulse train into a terminal laser pulse;

[0029] The second time interval in the center code pulse train received by the terminal station When the mask is discarded, the time of the terminal station is prohibited from being corrected; otherwise, the information of the central laser pulse is extracted to obtain the second time interval , according to the second time interval and the first time interval Calculate the clock difference between the central station and the terminal station, and correct the time of the terminal station based on the clock difference.

[0030] Further, according to the first time interval between the second pulse in the terminal station and the second pulse of the clock source measured by the terminal station , including:

[0031]

[0032] In the formula, The time of the second pulse of the central station clock source; The time of the terminal station servo clock second pulse; It is the optical fiber transmission delay from the central station to the terminal station.

[0033] Further, according to the second time interval between the second pulse in the terminal station and the second pulse of the clock source measured by the central station The specific process includes:

[0034]

[0035] In the formula, The time of the second pulse of the central station clock source; The time of the terminal station servo clock second pulse; It is the optical fiber transmission delay from the terminal station to the central station.

[0036] Further, the terminal station and the first time interval Calculate the clock difference between the central station and the terminal station. The specific process includes:

[0037]

[0038] In the formula, is the clock difference between the central station and the terminal station, is the asymmetry residual between the central station and the terminal station.

[0039] Furthermore, the terminal station servo clock uses the clock difference And the servo control algorithm calibrates the time generated by itself in real time, thereby achieving time synchronization with the clock source.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention utilizes a single-fiber single-wavelength bidirectional transmission technology based on gain switch regulation to ensure the symmetry of the transmission delay of a bidirectional channel. Furthermore, due to the wavelength tracking characteristics of the terminal gain switch laser in the terminal station, when the wavelength of the central station laser drifts due to temperature, aging and other reasons, the symmetry of the bidirectional transmission delay can still be ensured. High-precision time transfer can be achieved in the existing optical fiber relay segment, and the invention has the advantages of high timing accuracy, low cost and easy compatibility with existing optical fiber links. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a structural diagram of the optical fiber timing system provided in this embodiment. DETAILED DESCRIPTION

[0043] The following is combined with Figure 1 The present invention is further described in the following examples, which are only used to more clearly illustrate the technical solution of the present invention and are not intended to limit the protection scope of the present invention.

[0044] It should be noted that in the description of the present invention, the directions or positional relationships indicated by the terms "front", "rear", "left", "right", "up", "down", "inside", "outside", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention rather than requiring the present invention to be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. The terms "front", "rear", "left", "right", "up", and "down" used in the description of the present invention refer to the directions in the accompanying drawings, and the terms "inside" and "outside" refer to the directions toward or away from the geometric center of a specific component, respectively.

[0045] like Figure 1 As shown, this embodiment provides an optical fiber timing system based on gain switch laser regulation, including a central station and a terminal station connected by optical fiber. The central station is equipped with a central time measurement unit, a central control unit, a central optical receiver and the central gain switch laser; the terminal station is equipped with a delay amplifier, a servo clock, a terminal time measurement unit, a terminal control unit, a terminal optical receiver and a terminal gain switch laser.

[0046] The working process of the optical fiber timing system is as follows:

[0047] (1) Time and frequency information sent by the timing center:

[0048] The clock source second pulse signal, 10MHz frequency signal and time information (for example: the time information in this embodiment includes year, month, day, hour, minute and second) are sent to the central control unit to generate a central coded pulse train TIM-S of a certain time length. The central coded pulse train TIM-S contains a second pulse and its head indication, a frequency signal, a time information code and an injection control signal for the terminal station gain switch laser to remain locked when sending signals. The total time length of the central coded pulse train TIM-S is preferably to ensure the complete transmission of time and frequency information and support terminal station detection and wavelength injection locking. The total time length of the central coded pulse train TIM-S should be less than the total round-trip delay of the optical fiber link. The central coded pulse train TIM-S modulates the central gain switch laser operating at a stable wavelength (such as the standard wavelength of the wavelength division multiplexing system) to generate a central laser pulse train, and injects the central laser pulse into the optical fiber channel through the central optical ring type device. During the period when the central coded pulse train TIM-S modulates the central gain switch laser, the bias current I of the gain switch laser B During the period without pulse train modulation, the bias current I B Below the threshold, the central gain switch laser is not in the stimulated radiation state, ensuring that during the reception of the optical pulse sent by the terminal station, the backscattered optical power of the optical signal sent by the central station is at least 20dB lower than the optical power of the terminal laser pulse reaching the central optical receiver.

[0049] (2) Terminal station wavelength locking and time measurement:

[0050] After the laser pulse string sent by the central station reaches the terminal station, the central laser pulse is divided into two. A part of the central laser pulse is injected into the terminal gain switch laser after delayed amplification. The delay amount can not only ensure that the working wavelength of the terminal gain switch laser is locked to the working wavelength of the central station gain switch laser, but also ensure that the terminal gain switch laser does not affect the normal reception of the time and frequency information in the central laser pulse sent by the central station when sending signals. The terminal gain switch laser adopts a low-isolation package and its lasing working wavelength is close to the wavelength of the central gain switch laser. Under the action of the central station optical pulse injection locking, the wavelength of the terminal gain switch laser is equal to that of the central gain switch laser. The other part of the central laser pulse completes the photoelectric conversion to obtain the central coded pulse string TI M-S , the center coded pulse train TI M-S The terminal control unit sent to the terminal station restores the second pulse, frequency and time information in the central station. The terminal control unit will restore the second pulse 1PPS M-S The time is sent to the terminal time measurement module, which measures the 1PPS pulse in the terminal station and the 1PPS pulse in the clock source. M-S The time difference TIV is sent back to the terminal control unit and expressed as:

[0051]

[0052] In the formula, The time of the second pulse of the central station clock source; The time of the terminal station servo clock second pulse; It is the optical fiber transmission delay from the central station to the terminal station; is the time interval between the second pulse in the terminal station and the second pulse of the clock source, recorded as the first time interval .

[0053] (3) Terminal station time and frequency information transmission:

[0054] After the central laser pulse sent by the central station is completely received, the terminal control unit of the terminal station uses the second pulse signal, frequency signal, time information of the servo clock in the terminal station and the first time interval measured by the station Generate terminal code pulse train TI S-M , while increasing the bias current I of the injection gain-opening laser B Greater than the threshold. Terminal coding pulse string TI S-M The time length should be the minimum time length to ensure the stable operation of the terminal gain switch laser and the transmission of second pulses, time difference data and management information. S-M When modulating the terminal gain switch laser, the terminal gain switch laser just receives the injection control signal with a relatively stable level at the end of the central laser pulse sent by the central station. At this time, modulating the terminal gain switch laser can not only ensure wavelength locking, but also avoid the influence of the injected optical signal on the modulated transmission signal. The terminal laser pulse generated by modulation is injected into the optical fiber channel through the terminal optical ring type device. During the period without pulse train modulation, the terminal gain switch laser bias current I B Below the threshold, it is ensured that during the reception of the central laser pulse sent by the central station, the optical power of the backscattered optical signal of the terminal laser pulse sent by the terminal station is more than 20dB lower than the optical power of the central laser pulse reaching the terminal optical receiver.

[0055] (4) Central station time difference measurement and feedback:

[0056] After the central station receives the terminal laser pulse string sent by the terminal station, it is injected into the optical receiver through the central optical ring type device to complete the photoelectric conversion, and the recovered terminal coded pulse string TI S-M The central control unit extracts the pulse per second signal 1PPS transmitted from the terminal station to the central station. S-M , the central time measurement unit completes the time difference measurement with the central station clock source second pulse, and the expression formula is:

[0057]

[0058] In the formula, The time of the second pulse of the central station clock source; The time of the terminal station servo clock second pulse; It is the optical fiber transmission delay from the terminal station to the central station; is the time interval between the second pulse in the terminal station and the second pulse of the clock source, recorded as the second time interval .

[0059] The second time interval Included in the central coded pulse train TI sent to the terminal station M-S The central station uses the second time interval The center coded pulse train TI M-S The central gain switching laser is modulated to generate a central laser pulse of a determined time length, and the central laser pulse is injected into the optical fiber channel through the central optical ring type device.

[0060] (5) Terminal station time and frequency servo regeneration:

[0061] The terminal station receives the central station including the second time interval The central laser pulse is sent to the terminal control unit after photoelectric conversion by the terminal optical ring type device and the terminal optical receiver. The terminal control unit extracts the second time interval sent by the central station Combined with the first time interval measured by the terminal station , and because the terminal gain switch laser works in the injection locked state, the wavelength of the bidirectional transmission light is the same, so the transmission delay from the central station to the terminal station is Optical fiber transmission delay from terminal station to central station Equal, that is, The terminal control unit can then use the two-way time comparison method to calculate the clock difference between the terminal station servo clock and the central station clock source, expressed as: ;In the formula, is the clock difference between the central station and the terminal station, The asymmetric residual between the central station and the terminal station. The terminal station servo clock implements time calibration based on the clock difference and the corresponding clock servo algorithm to achieve high-precision time and frequency synchronization with the clock source.

[0062] In this embodiment, single-fiber single-wavelength bidirectional transmission technology based on gain switch control is used to ensure the complete symmetry of the bidirectional transmission channel. Due to the wavelength tracking characteristics of the terminal gain switch laser in the terminal station, the drift and aging of the central station laser have no effect on the timing accuracy. High-precision time transfer can be achieved in the existing optical fiber relay segment. It has the advantages of high timing accuracy, low cost and easy compatibility with existing optical fiber links.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fiber timing system based on gain-switched laser control, characterized in that: Includes central stations and terminal stations connected by optical fiber; The central station is equipped with a central control module and a central gain switch laser; The terminal station is equipped with a time delay amplifier, a terminal control module and a terminal gain switch laser; The information transmission and reception process from the central station to the terminal station includes: The central control module controls the central gain switch laser to send a central laser pulse to the terminal station. The central laser pulse includes a clock source second pulse, a frequency signal, time information and a second time interval measured by the central control module. The terminal station divides the central laser pulse sent by the central station into two parts, one part of the central laser pulse is sent to the terminal gain switch laser through the delay amplifier device, so that the working wavelength of the terminal gain switch laser is locked to the working wavelength of the central gain switch laser, and the other part of the central laser pulse is directly sent to the terminal control module; The information transmission and reception process from the terminal station to the central station includes: The terminal control module controls the terminal gain switch laser to send a terminal laser pulse to the central station, and the terminal laser pulse includes a second pulse, a frequency signal, time information and a first time interval of the terminal station. , the central control module in the central station receives and processes the terminal laser pulses; The central station and the terminal station exchange information to calculate the clock difference, and the terminal station corrects the time of the servo clock in the station according to the clock difference to achieve time synchronization with the clock source.

2. The optical fiber timing system according to claim 1, characterized in that: The central control module includes a central time measurement unit, a central control unit and a central optical receiver; The central optical receiver is used to receive the terminal laser pulse, convert the terminal laser pulse into a photoelectric signal, and then send it to the central control unit; The central control unit is used to extract the second pulse sent by the terminal station from the terminal laser pulse, and send the second pulse sent by the terminal station to the central time measurement unit; the ... generating a center coded pulse train and sending it to a center gain switching laser to generate a center laser pulse; The central time measurement unit is used to measure the second time interval between the second pulse sent by the terminal station and the second pulse sent by the clock source , the second time interval Sent to the central control unit.

3. The optical fiber timing system according to claim 2, characterized in that: The terminal control module includes a servo clock, a terminal time measurement unit, a terminal control unit and a terminal optical receiver; The terminal optical receiver is used to receive the central laser pulse, convert the central laser pulse into a photoelectric signal, and then send it to the terminal control unit; The terminal control unit is used to extract the clock source second pulse in the central laser pulse and send the clock source second pulse to the terminal time measurement unit; the terminal control unit is used to extract the clock source second pulse from ... according to the second pulse, frequency signal, time information and first time interval of the terminal station. Generate a terminal coded pulse string and send it to the terminal gain switch laser to generate a terminal laser pulse; the terminal control unit is used to extract information from the central laser pulse to obtain a second time interval , according to the second time interval and the first time interval Calculate the clock difference between the central station and the terminal station, and send the clock difference to the terminal station servo clock; The terminal time measurement unit is used to measure the first time interval between the second pulse in the terminal station and the second pulse of the clock source , the first time interval Sending to the terminal control unit; The servo clock is used to send the terminal station second pulse to the terminal time measurement unit, and send the terminal station second pulse, frequency signal and time information to the terminal control unit; the servo clock is used to receive the clock difference sent by the terminal control unit, and correct its own time according to the clock difference to achieve time synchronization with the clock source.

4. The optical fiber timing system according to claim 3, characterized in that: The central station is equipped with a central circulator; the central circulator is connected to a central optical receiver and a central gain switch laser through optical fiber; the terminal station is equipped with a terminal circulator; the terminal circulator is connected to a delay amplifier, a terminal optical receiver and a terminal gain switch laser through optical fiber; the central circulator is connected to the terminal circulator through optical fiber.

5. The optical fiber timing system according to claim 1, characterized in that: An injection control signal is provided at the end of the central laser pulse, and the time length of the central laser pulse is adjusted by injecting the control signal, and the time length of the central laser pulse is less than the total round-trip delay from the central station to the terminal station; When the terminal coded pulse train modulates the terminal gain switch laser, the terminal gain switch laser receives the injection control signal in the central laser pulse sent by the central station.

6. The optical fiber timing system according to claim 1, characterized in that: When the center gain switch laser and the terminal gain switch laser are in pulse train modulation, the bias current is higher than the gain switch laser threshold; when the center gain switch laser and the terminal gain switch laser are in non-pulse train modulation, the bias current is lower than the gain switch laser threshold; when the central station and the terminal station receive laser pulses, the backscattered light power of the optical signal sent is at least 20dB lower than the received light power of the optical receiver.

7. The timing execution method of the optical fiber timing system according to any one of claims 1 to 6, characterized in that: include: The central station receives the terminal laser pulse and measures the second time interval between the second pulse in the terminal station and the second pulse of the clock source according to the terminal laser pulse. , based on the second pulse of the clock source, the frequency signal, the time information and the second time interval Generate a center coded pulse train; send the center coded pulse train to a center gain switch laser, and the center gain switch laser converts the center coded pulse train into a center laser pulse and sends it to a terminal station; The terminal station receives the central laser pulse and divides it into two parts. After delayed amplification, part of the central laser pulse is sent to the terminal gain switch laser, so that the working wavelength of the terminal gain switch laser is locked to the working wavelength of the central gain switch laser. The other part of the central laser pulse is sent to the terminal control unit to measure the first time interval between the second pulse in the terminal station and the second pulse of the clock source. , according to the second pulse, frequency signal, time information and first time interval of the terminal station Generate a terminal coded pulse string; convert the terminal coded pulse string into a terminal laser pulse; the terminal station extracts information from the central laser pulse to obtain a second time interval , according to the second time interval and the first time interval Calculate the clock difference between the central station and the terminal station, and correct the time of the terminal station servo clock based on the clock difference, so as to achieve time synchronization with the clock source.

Images