Laser wavelength automatic tracking method and system for optical fiber time transmission
阅读说明：本技术 一种用于光纤时间传递的激光波长自动跟踪方法及系统 (Laser wavelength automatic tracking method and system for optical fiber time transmission ) 是由 陈法喜 赵侃 李博 刘博� 郭新兴 刘涛 张首刚 于 2019-11-04 设计创作，主要内容包括：本发明公开了一种用于光纤时间传递的激光波长自动跟踪方法及系统,将跟踪光信号与参考光信号使用光电探测器进行拍频,拍频得到的信号经过分频器后采用频率测量单元进行测量,运算控制单元测得的频率值,计算跟踪光信号与参考光信号的波长差异,控制跟踪激光器的工作温度,使跟踪光信号的波长长期与参考光信号的波长保持高度一致。本发明采用激光波长高精度自动跟踪方法,可消除温度、老化等因素对双向激光波长差异的影响,能够极大提高双向传输时延的对称性,可提升长距离光纤时间传递准确度。(The invention discloses a laser wavelength automatic tracking method and a system for optical fiber time transmission, wherein a tracking optical signal and a reference optical signal are subjected to beat frequency by using a photoelectric detector, a signal obtained by beat frequency is measured by using a frequency measuring unit after passing through a frequency divider, a frequency value measured by a control unit is calculated, the wavelength difference between the tracking optical signal and the reference optical signal is calculated, and the working temperature of a tracking laser is controlled, so that the wavelength of the tracking optical signal is kept highly consistent with the wavelength of the reference optical signal for a long time. The invention adopts a high-precision automatic tracking method of laser wavelength, can eliminate the influence of factors such as temperature, aging and the like on the difference of the bidirectional laser wavelength, can greatly improve the symmetry of bidirectional transmission time delay, and can improve the time transmission accuracy of long-distance optical fibers.)
1. A method for laser wavelength automatic tracking for fiber optic time transfer, comprising:
step 1, performing beat frequency on a tracking light signal emitted by a tracking laser and a reference light signal emitted by a reference laser to obtain a beat frequency signal;
step 2, frequency division processing is carried out on the beat frequency signals obtained in the step 1, and processed signals are obtained;
step 3, measuring the processed signals obtained in the step 2 to obtain a frequency difference value delta f of the tracking optical signal and the reference optical signal;
step 4, calculating according to the frequency difference value delta f obtained in the step 3 to obtain a wavelength difference value delta lambda of the tracking optical signal and the reference optical signal;
wherein, the calculation formula is as follows,
where c is the speed of light in the experimental environment, λ1For reference, the wavelength, λ2Weighing the wavelength for tracking;
and 5, controlling the working temperature of the tracking light laser according to the wavelength difference delta lambda obtained in the step 4 to adjust the wavelength of the tracking laser, so that the difference of the bidirectional laser wavelength is kept within a preset threshold value, and the automatic tracking of the laser wavelength is realized.
2. The method according to claim 1, wherein the step 1 specifically comprises: and inputting a tracking light signal emitted by the tracking laser and a reference light signal emitted by the reference laser into the photoelectric detector through a beam combiner for beat frequency to obtain a beat frequency signal.
3. The method according to claim 2, wherein the step 2 specifically comprises: and (3) inputting the beat frequency signal output by the photoelectric detector in the step (1) into the N-time frequency divider to obtain a signal processed by the N-time frequency divider.
4. The method according to claim 3, wherein step 3 specifically comprises: inputting the obtained signal processed by the N-time frequency divider into a frequency measuring unit, and measuring the frequency difference delta f of the signal; and then inputting the frequency difference value delta f into an operation control unit, and calculating by the operation control unit to obtain a wavelength difference value delta lambda.
5. The method for automatically tracking laser wavelength in optical fiber time transfer according to claim 1, wherein in step 5, the relation expression of tracking laser working temperature and laser wavelength is,
the computational expression of E (T) is,
in the formula, T is the working temperature; e0To track the laser constants, a-5.405 x 10-4，b＝204。
6. The method according to claim 1, wherein in step 5, the laser tube of the tracking laser is controlled by high-precision digital temperature control method according to the obtained wavelength difference Δ λ, so that the operating temperature of the tracking laser is changed to ToutKeeping the difference of the bidirectional laser wavelengths within a preset threshold value;
wherein, ToutThe computational expression of (a) is as follows,
7. the method of claim 1 wherein the difference between the bidirectional laser wavelengths is less than or equal to 0.02 pm.
8. A laser wavelength automatic tracking system for fiber optic time transfer, comprising:
the photoelectric detector is used for carrying out beat frequency on a tracking light signal sent by the tracking laser and a reference light signal sent by the reference laser to obtain a beat frequency signal;
the frequency divider is used for carrying out frequency division processing on the beat frequency signal obtained by the photoelectric detector to obtain a processed signal;
the frequency measuring unit is used for measuring the processed signals obtained by the frequency divider to obtain a frequency difference value delta f of the tracking optical signal and the reference optical signal;
the operation control unit is used for calculating and obtaining the wavelength difference delta lambda of the tracking light signal and the reference light signal according to the frequency difference delta f obtained by the frequency measuring unit;
wherein, the calculation formula is as follows,
where c is the speed of light in the experimental environment, λ1For reference, the wavelength, λ2Weighing the wavelength for tracking;
and the precise temperature control unit is used for controlling the working temperature of the tracking light laser according to the wavelength difference delta lambda obtained by the operation control unit to adjust the wavelength of the tracking laser, so that the difference of the bidirectional laser wavelength is kept within a preset threshold value, and the automatic tracking of the laser wavelength is realized.
9. The automatic laser wavelength tracking system for optical fiber time transfer according to claim 8, wherein in the precise temperature control unit, the relation expression of the tracking laser working temperature and the laser wavelength is,
the computational expression of E (T) is,
in the formula, T is the working temperature; e0To track the laser constants, a-5.405 x 10-4，b＝204。
10. The automatic laser wavelength tracking system for optical fiber time transfer as claimed in claim 8, wherein the temperature of the laser tube of the tracking laser is controlled by high-precision digital temperature control in the precise temperature control unit, so that the operating temperature of the tracking laser is changed to ToutKeeping the difference of the bidirectional laser wavelengths within a preset threshold value;
wherein, ToutThe computational expression of (a) is as follows,
Technical Field
The invention belongs to the technical field of laser wavelength locking of optical fiber time transfer, and particularly relates to a laser wavelength automatic tracking method and system for optical fiber time transfer.
Background
The high-precision optical fiber time frequency transmission technology has become one of the key supporting technologies in the fields of aerospace, high-speed communication, geodetic surveying, precision metering, deep space exploration, gravitational wave exploration and the like due to the advantages of safety, reliability and stability. The asymmetry of the bidirectional transmission delay is one of the main factors influencing the accuracy and stability of long-distance optical fiber time transmission, and in order to improve the accuracy and stability of the optical fiber time transmission, a bidirectional same-fiber same-wave scheme is adopted at home and abroad at present to overcome the symmetry of the bidirectional transmission delay.
In practical applications, the bidirectional same-fiber same-wave scheme affects the accuracy of time transmission of the optical fiber due to the difference of bidirectional laser wavelength along with factors such as temperature and laser aging, and the effect is further increased along with the increase of transmission distance.
In order to ensure that the difference of the bidirectional laser wavelengths is controlled in a small enough range, laser wavelength locking methods such as atomic molecular spectroscopy, reference cavities and the like can be adopted, but the traditional methods are not only complicated in structure but also expensive, do not conform to the widely applied scene of optical fiber time transmission, are difficult to popularize and apply, and a high-precision laser wavelength locking method is urgently needed.
Disclosure of Invention
The invention aims to provide a laser wavelength automatic tracking method and a laser wavelength automatic tracking system for optical fiber time transfer aiming at the problem of time delay asymmetry caused by bidirectional laser wavelength difference in the actual optical fiber time transfer process so as to reduce the accuracy deviation of time transfer introduced by the bidirectional laser wavelength difference.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention relates to a laser wavelength automatic tracking method for optical fiber time transfer, which comprises the following steps:
step 1, performing beat frequency on a tracking light signal emitted by a tracking laser and a reference light signal emitted by a reference laser to obtain a beat frequency signal;
step 2, frequency division processing is carried out on the beat frequency signals obtained in the step 1, and processed signals are obtained;
step 3, measuring the processed signals obtained in the step 2 to obtain a frequency difference value delta f of the tracking optical signal and the reference optical signal;
step 4, calculating according to the frequency difference value delta f obtained in the step 3 to obtain a wavelength difference value delta lambda of the tracking optical signal and the reference optical signal;
wherein, the calculation formula is as follows,
where c is the speed of light in the experimental environment, λ1For reference, the wavelength, λ2Weighing the wavelength for tracking;
and 5, controlling the working temperature of the tracking light laser according to the wavelength difference delta lambda obtained in the step 4 to adjust the wavelength of the tracking laser, so that the difference of the bidirectional laser wavelength is kept within a preset threshold value, and the automatic tracking of the laser wavelength is realized.
The invention has the further improvement that the step 1 specifically comprises the following steps: and inputting a tracking light signal emitted by the tracking laser and a reference light signal emitted by the reference laser into the photoelectric detector through a beam combiner for beat frequency to obtain a beat frequency signal.
The invention has the further improvement that the step 2 specifically comprises the following steps: and (3) inputting the beat frequency signal output by the photoelectric detector in the step (1) into the N-time frequency divider to obtain a signal processed by the N-time frequency divider.
The invention has the further improvement that the step 3 specifically comprises the following steps: inputting the obtained signal processed by the N-time frequency divider into a frequency measuring unit, and measuring the frequency difference delta f of the signal; and then inputting the frequency difference value delta f into an operation control unit, and calculating by the operation control unit to obtain a wavelength difference value delta lambda.
In step 5, the relation expression of the tracking laser working temperature and the laser wavelength is as follows,
the computational expression of E (T) is,
in the formula, T is the working temperature; e0To track the laser constants, a-5.405 x 10-4，b＝204。
The further improvement of the invention is that in step 5, the laser tube of the tracking laser is controlled by adopting a high-precision digital temperature control method according to the obtained wavelength difference delta lambda, so that the working temperature of the tracking laser is changed to ToutKeeping the difference of the bidirectional laser wavelengths within a preset threshold value;
wherein, ToutThe computational expression of (a) is as follows,
the invention is further improved in that the difference of the bidirectional laser wavelengths can be less than or equal to 0.02 pm.
The invention relates to a laser wavelength automatic tracking system for optical fiber time transfer, which comprises:
the photoelectric detector is used for carrying out beat frequency on a tracking light signal sent by the tracking laser and a reference light signal sent by the reference laser to obtain a beat frequency signal;
the frequency divider is used for carrying out frequency division processing on the beat frequency signal obtained by the photoelectric detector to obtain a processed signal;
the frequency measuring unit is used for measuring the processed signals obtained by the frequency divider to obtain a frequency difference value delta f of the tracking optical signal and the reference optical signal;
the operation control unit is used for calculating and obtaining the wavelength difference delta lambda of the tracking light signal and the reference light signal according to the frequency difference delta f obtained by the frequency measuring unit;
wherein, the calculation formula is as follows,
where c is the speed of light in the experimental environment, λ1For reference, the wavelength, λ2Weighing the wavelength for tracking;
and the precise temperature control unit is used for controlling the working temperature of the tracking light laser according to the wavelength difference delta lambda obtained by the operation control unit to adjust the wavelength of the tracking laser, so that the difference of the bidirectional laser wavelength is kept within a preset threshold value, and the automatic tracking of the laser wavelength is realized.
The further improvement of the invention is that in the precise temperature control unit, the relational expression of the tracking laser working temperature and the laser wavelength is as follows,
the computational expression of E (T) is,
in the formula, T is the working temperature; e0To track the laser constants, a-5.405 x 10-4，b＝204。
The invention is further improved in that in the precise temperature control unit, a high-precision digital temperature control method is adopted to control the temperature of the laser tube of the tracking laser, so that the working temperature of the tracking laser is changed to ToutKeeping the difference of the bidirectional laser wavelengths within a preset threshold value;
wherein, ToutThe computational expression of (a) is as follows,
compared with the prior art, the invention has the following beneficial effects:
the high-precision automatic tracking method for the laser wavelength can reduce the accuracy deviation of time transfer caused by the difference of the two-way laser wavelength. The invention uses a photoelectric detector to beat the frequency of the tracking light signal and the reference light signal, the frequency measuring unit is used to measure the signals obtained by beat frequency after the signals pass through the frequency divider, the wavelength difference between the tracking light signal and the reference light signal is calculated by calculating the frequency value measured by the control unit, the working temperature of the tracking laser is controlled, and the wavelength of the tracking light signal can keep highly consistent with the wavelength of the reference light signal for a long time. The invention adopts a high-precision automatic tracking method of laser wavelength, can eliminate the influence of factors such as temperature, aging and the like on the difference of the bidirectional laser wavelength, and can greatly improve the symmetry of bidirectional transmission time delay, thereby improving the accuracy of long-distance optical fiber time transmission and prolonging the time transmission distance; meanwhile, the invention can reduce the cost, simplify the structure and is beneficial to wide application in practical engineering.
The invention adopts a high-precision automatic tracking method of laser wavelength, can realize long-term automatic tracking of laser wavelength, and enables bidirectional laser wavelength in an optical fiber time transmission system to be consistent and always superior to 0.02 pm; therefore, the accuracy error introduced over a 1 kilometre fibre link would theoretically be less than 0.2 ps.
The system can reduce the accuracy deviation of time transmission introduced by bidirectional laser wavelength difference, can improve the accuracy of long-distance optical fiber time transmission, and can prolong the time transmission distance.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below; it is obvious that the drawings in the following description are some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
Fig. 1 is a schematic block diagram of an automatic laser wavelength tracking system applied to optical fiber time transfer according to an embodiment of the present invention.
Detailed Description
In order to make the purpose, technical effect and technical solution of the embodiments of the present invention clearer, the following clearly and completely describes the technical solution of the embodiments of the present invention with reference to the drawings in the embodiments of the present invention; it is to be understood that the described embodiments are only some of the embodiments of the present invention. Other embodiments, which can be derived by one of ordinary skill in the art from the disclosed embodiments without inventive faculty, are intended to be within the scope of the invention.
The embodiment of the invention provides a laser wavelength automatic tracking method applied to optical fiber time transmission, which specifically comprises the following steps:
step 1, tracking the optical signal (with wavelength of lambda) emitted by the laser2) With an optical signal (of wavelength λ) from a reference laser1) Inputting the signals into a photoelectric detector through a beam combiner for beat frequency;
step 2: inputting beat frequency signals output by the photoelectric detector in the step 1 into an N-time frequency divider;
and step 3: inputting the signal which passes through the N-time frequency divider in the step 2 into a frequency measuring unit, and measuring a frequency value delta f of the signal;
and 4, step 4: sending the frequency value delta f measured by the frequency measuring unit in the step 3 to an operation control unit;
and 5: the operation control unit is shown as formula (1) according to the frequency-wavelength relation:
where c is the speed of light in the experimental environment, since the reference optical scale wavelength λ is known1And tracking optical scale wavelength lambda2The actual reference wavelength is denoted as λ1' then the actual value of the reference optical frequency is
Step 6: the relationship between the frequency difference and the wavelength difference can be derived from the relationship between the frequency and the wavelength
and 7: the wavelength of the tracking light laser is controlled by controlling the working temperature of the laser, and the relation between the working temperature of the laser and the wavelength of the laser is shown in formula (3):
in formula (3), T is temperature, and E (T) can be expressed clearly by formula (4):
in the formula, E0As laser constant, a-5.405 x 10-4，b＝204。
The operation control unit controls the temperature of the laser tube of the tracking laser by adopting a high-precision digital temperature control method according to the wavelength difference delta lambda data calculated in the step 6, so that the working temperature of the tracking laser is changed to ToutThe calculation relationship is shown in formula (5).
Therefore, the bidirectional laser wavelength is kept consistent, and the automatic tracking of the laser wavelength is realized.
The invention adopts a high-precision automatic tracking method of laser wavelength, can realize long-term automatic tracking of laser wavelength, and enables the bidirectional laser wavelength in the optical fiber time transmission system to be consistent and to be superior to 0.02pm all the time, so that the accuracy error introduced on an optical fiber link of 1 kilometre is theoretically less than 0.2 ps. The invention eliminates the influence of factors such as temperature, aging and the like on the difference of the bidirectional laser wavelengths, and reduces the accuracy deviation of time transfer introduced by the difference of the bidirectional laser wavelengths, thereby improving the accuracy of the time transfer of the optical fiber, prolonging the distance of the time transfer, reducing the cost and greatly promoting the wide application in the practical engineering. The invention can keep the difference of bidirectional laser wavelength within the range of sub-picosecond magnitude, and realize automatic tracking of laser wavelength.
Referring to fig. 1, fig. 1 is a schematic diagram of high-precision automatic tracking of laser wavelength; the system of the embodiment of the invention comprises the laser LD1Laser LD2The device comprises a photoelectric detector, a frequency divider, a frequency measuring unit, an operation control unit and a precise temperature control circuit.
By LD1As the laser signal of LD2Reference light of laser, realizing LD by loop2Wavelength tracking LD1Of (c) is measured.
The photoelectric detector is used for carrying out beat frequency on a tracking light signal sent by the tracking laser and a reference light signal sent by the reference laser to obtain a beat frequency signal;
the frequency divider is used for carrying out frequency division processing on the beat frequency signal obtained by the photoelectric detector to obtain a processed signal;
the frequency measuring unit is used for measuring the processed signals obtained by the frequency divider to obtain a frequency difference value delta f of the tracking optical signal and the reference optical signal;
the operation control unit is used for calculating and obtaining the wavelength difference delta lambda of the tracking light signal and the reference light signal according to the frequency difference delta f obtained by the frequency measuring unit;
wherein, the calculation formula is as follows,
where c is the speed of light in the experimental environment, λ1For reference, the wavelength, λ2Weighing the wavelength for tracking;
and the precise temperature control unit is used for controlling the working temperature of the tracking light laser according to the wavelength difference delta lambda obtained by the operation control unit to adjust the wavelength of the tracking laser, so that the bidirectional laser wavelength is kept consistent, and the automatic tracking of the laser wavelength is realized.
The embodiment of the invention comprises the following specific implementation steps:
step 1: to track the optical signal (with wavelength lambda) emitted by the laser21542.94nm) and a reference laser emitting an optical signal having a wavelength λ11542.94nm) are input into the photoelectric detector together through a beam combiner to carry out beat frequency;
step 2: inputting beat frequency signals output by the photoelectric detector in the step 1 into a 10-time frequency divider;
and step 3: inputting the signal which passes through the frequency divider of 10 times in the step 2 into a frequency measuring unit, and measuring the frequency of the signal;
and 4, step 4: sending the frequency value delta f measured by the frequency measuring unit in the step 3 to an operation control unit;
and 5: the operation control unit is shown as formula (1) according to the frequency-wavelength relation:
where c is the speed of light in the experimental environment, since the reference light is known to weigh the wavelength λ1And tracking optical scale wavelength lambda2The actual reference wavelength is denoted as λ1' then the actual value of the reference optical frequency is
Step 6: the relationship between the frequency difference and the wavelength difference can be derived from the relationship between the frequency and the wavelengthThe difference between the measured nominal wavelength and the actual wavelength was about 8pm, so it can be considered that1'λ2'＝λ1λ2Therefore, the calculation formula of the frequency difference and the wavelength difference is shown in formula (2):
and 7: the wavelength of the tracking light laser is controlled by controlling the working temperature of the laser, and the relation between the working temperature of the laser and the wavelength of the laser is shown in formula (3):
in formula (3), T is temperature, and E (T) can be expressed clearly by formula (4):
in the formula, E0As laser constant, a-5.405 x 10-4，b＝204。
The operation control unit controls the temperature of the laser tube of the tracking laser by adopting a high-precision digital temperature control method according to the wavelength difference delta lambda data calculated in the step 6, so that the working temperature of the tracking laser is changed to ToutThe calculation relationship is shown in formula (5).
Thereby keeping the bidirectional laser wavelength consistent.
Therefore, automatic tracking of laser wavelength is achieved. The maximum difference between the wavelengths of the tracking and reference light was 0.015pm after 24 hours of continuous testing.
In summary, the present invention provides a method and a system for high-precision automatic tracking of laser wavelength, aiming at the problem of asymmetry of time delay caused by bidirectional laser wavelength difference in the actual optical fiber time transmission process, so as to reduce the accuracy deviation of time transmission caused by bidirectional laser wavelength difference. The invention uses a photoelectric detector to beat the frequency of a tracking light signal and a reference light signal, a frequency measuring unit is used to measure the signals obtained by beating the frequency after the signals pass through a frequency divider, the frequency value measured by a control unit is calculated, the wavelength difference between the tracking light signal and the reference light signal is calculated, and the working temperature of a tracking laser is controlled, so that the wavelength of the tracking light signal is kept highly consistent with the wavelength of the reference light signal for a long time. The invention adopts a high-precision automatic tracking method of laser wavelength, eliminates the influence of factors such as temperature, aging and the like on the difference of the bidirectional laser wavelength, greatly improves the symmetry of bidirectional transmission delay, and improves the time transmission accuracy of long-distance optical fibers; meanwhile, the cost is reduced, the structure is simplified, and the method is favorable for wide application in practical engineering. The invention adopts a high-precision automatic tracking method of laser wavelength, can realize long-term automatic tracking of laser wavelength, and enables the bidirectional laser wavelength in the optical fiber time transmission system to be consistent and to be superior to 0.02pm all the time, so that the accuracy error introduced on an optical fiber link of 1 kilometre is theoretically less than 0.2 ps.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can make modifications and equivalents to the embodiments of the present invention without departing from the spirit and scope of the present invention, which is set forth in the claims of the present application.
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