CN116707628A

CN116707628A - Method and device for transmitting signals

Info

Publication number: CN116707628A
Application number: CN202210175621.8A
Authority: CN
Inventors: 周恩波; 李恭鹏; 顾堃
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2022-02-24
Filing date: 2022-02-24
Publication date: 2023-09-05
Also published as: WO2023160490A1

Abstract

The application provides a method and a device for transmitting signals, comprising the following steps: generating and transmitting a first optical signal; receiving a second optical signal comprising reflected and scattered signals of the first optical signal; converting the second optical signal into a first electrical signal; determining a first heterodyne frequency value of the first electrical signal; determining a second heterodyne frequency value based on the first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal; a third optical signal is generated and transmitted in accordance with the second heterodyne frequency value. The method provided by the application can be applied to the heterodyne coherent optical time domain reflectometer OTDR device, and by adaptively adjusting the input optical signals, the spatial resolution and dynamic range index of the OTDR system can be further improved on the premise of high dynamic range, the blind area distance can be improved, and the detection performance of the heterodyne coherent OTDR device can be further improved.

Description

Method and device for transmitting signals

Technical Field

The present application relates to the field of optical fiber testing and optical fiber sensing, and more particularly, to a method and apparatus for transmitting signals.

Background

The optical time domain reflectometer (Optical Time Domain Reflectometer, OTDR) is a fiber testing instrument commonly used in the technical field of fiber testing, and is manufactured according to the principles of Rayleigh back scattering (Rayleigh Backscattering, RBS) and Fresnel reflection (Fresnel Reflection, FR) of light. Correlation expansion applications of OTDR, e.g. phase-type optical time domain reflectometersBrillouin Optical Time Domain Reflectometry (BOTDR) and Raman Optical Time Domain Reflectometry (ROTDR) are fiber optic test instruments commonly used in the field of fiber optic sensing. In the following description the relevant OTDR includes all +.>All relevant extended applications of BOTDR and ROTDR.

The OTDR can analyze the uniformity, defects, fracture, joint coupling and other performances of the optical fiber by measuring the attenuation conditions of scattered optical signals and reflected optical signals along the axial direction of the optical fiber generated in the process of transmitting the optical signals in the optical fiber, and is an indispensable tool in the processes of optical cable construction, maintenance and monitoring the optical fiber loss. For example: optical fiber length detection, outage detection, joint position detection, attenuation coefficient detection, joint loss, optical fiber fault point positioning, loss of optical fibers along the length, vibration, temperature, stress distribution conditions and the like.

Currently, OTDR generally has two detection modes, i.e., direct detection and coherent detection, for scattered light signals and reflected light signals. The OTDR of the direct detection structure directly detects the signal intensity of the scattered light signal and the reflected light signal after mutual interference by the detector, and the OTDR can accurately acquire the position point of the disturbance signal and has a multi-point positioning function. The OTDR with the structure has the advantages of simple structure, easy pulse generation, short Signal processing time, low cost, and suitability for scenes with short sensing distance and low system Signal-to-Noise Ratio (SNR). However, the direct detection OTDR is limited by its principle, and does not use frequency and phase information of an optical carrier, and has poor detection sensitivity, dynamic Range (DR), dead Zone (DZ), and other indexes, which are difficult to be applied to long-distance optical fiber fault detection.

In order to further improve the detection sensitivity of the traditional OTDR device, a coherent detection technology is introduced into an OTDR system, local oscillation light, scattered light and reflected light are subjected to coherent demodulation, and the signal intensity after demodulation is far greater than the scattered light and reflected light signal intensity in the direct detection type OTDR system, so that the SNR value of the OTDR system is obviously improved, the OTDR can detect tiny scattered light and reflected light signals, and the dynamic range of the system is effectively increased. Currently, the common coherent detection OTDR technology may include two technical schemes of homodyne coherent reception and heterodyne coherent reception. In the OTDR device, there is a constraint relationship between the specification indexes. For example, in a non-ideal fiber link, the end reflection and large insertion loss of the fiber can cause a large dead zone in the OTDR curve. The dynamic range can be improved but the blind area can be cracked by adopting the detection pulse with larger energy, so that the measurement performance of the device is reduced, and the requirement of long-distance high-precision optical fiber detection is difficult to meet. Therefore, how to balance the dynamic range, spatial resolution and dead zone of the OTDR to realize high performance OTDR is a technical problem to be solved in the scheme design.

Disclosure of Invention

The embodiment of the application provides a method and a device for transmitting signals, which are used for adaptively adjusting input signals to adapt to detection requirements in different scenes, so that the detection performance of an OTDR device of a heterodyne coherent optical time domain reflectometer is improved.

In a first aspect, a method for transmitting signals is provided, applied in the field of optical fiber detection systems, the method comprising: generating and transmitting a first optical signal; receiving a second optical signal, the second optical signal comprising reflected and scattered signals of the first optical signal; converting the second optical signal into a first electrical signal; determining a first heterodyne frequency value of the first electrical signal; determining a second heterodyne frequency value from a first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal, wherein the eigenvalues of the first electrical signal include: power spectral density, signal-to-noise ratio, dynamic range, dead zone; a third optical signal is generated and transmitted in accordance with the second heterodyne frequency value.

Thus, according to the technical scheme provided by the application, the laser transmitting module in the OTDR device generates and transmits the first optical signal, reflects or scatters the second optical signal back through the tested optical fiber, converts the second optical signal into the first electric signal through the photoelectric detection unit in the receiving module, determines the first outer difference frequency value of the first electric signal, and the signal feedback control module determines the second outer difference frequency value according to the first outer difference frequency value of the first electric signal and one or more characteristic values of the first electric signal; the signal generation module generates a third optical signal according to the second heterodyne frequency value. By the technical scheme provided by the application, the heterodyne frequency of the optical signal input by the OTDR device can be adaptively adjusted to meet detection requirements under different scenes, and the spatial resolution and dynamic range index of the OTDR system can be further improved and the blind area distance can be improved on the premise of high dynamic range, so that the detection performance of the heterodyne coherent OTDR device can be improved.

With reference to the first aspect, in certain implementations of the first aspect, determining the second heterodyne frequency value from the first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal includes: converting the first electrical signal into a first digital signal; converting the first digital signal into a first time domain signal; converting the first time domain signal into a first frequency domain signal; the second difference frequency value is determined from one or more eigenvalues of the first frequency domain signal.

With reference to the first aspect, in certain implementations of the first aspect, determining the second heterodyne frequency value from the first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal includes: converting the first frequency domain signal into a second time domain signal; the second beat frequency value is determined from one or more eigenvalues of the second time domain signal.

With reference to the first aspect, in certain implementations of the first aspect, before determining the second heterodyne frequency value from the first heterodyne frequency value of the first electrical signal and the one or more eigenvalues of the first electrical signal, further includes: and judging the second outer difference frequency value, wherein the second outer difference frequency value is transmitted when the absolute value of the difference value between the first outer difference frequency value and the second outer difference frequency value of the first electric signal is larger than a judgment threshold value.

Therefore, in the application, when the absolute value of the difference value between the first heterodyne frequency value and the second heterodyne frequency is detected to be larger than a decision threshold value in the signal feedback control module, the heterodyne frequency value is adjusted to be the second heterodyne frequency value, otherwise, the adjustment is not performed, and the original first heterodyne frequency value is maintained. The magnitude of the absolute value of the first heterodyne frequency value and the absolute value of the second heterodyne frequency value of the first electric signal are judged with the judgment threshold, and the heterodyne frequency value can be adjusted in a threshold setting mode, so that the detection precision of the OTDR device is improved, and the detection requirements of heterodyne coherent OTDR devices under different scenes are met.

With reference to the first aspect, in certain implementations of the first aspect, generating and transmitting a third optical signal according to the second heterodyne frequency value includes: determining a second digital signal according to a second heterodyne frequency value, wherein the second digital signal has signal characteristics of the second heterodyne frequency value; converting the second digital signal into a second electrical signal; amplifying the second electric signal to obtain a third electric signal; the third electrical signal is converted into a third optical signal.

With reference to the first aspect, in certain implementations of the first aspect, a heterodyne frequency value of the first optical signal is not zero.

In a second aspect, an apparatus for transmitting signals is provided, applied in the field of optical fiber detection, including: the laser emission module is used for generating and sending a first optical signal; a receiving module for receiving a second optical signal comprising reflected and scattered signals of the first optical signal; the receiving module is also used for converting the second optical signal into a first electric signal; the signal feedback control module is used for determining a second outer difference frequency value according to a first outer difference frequency value of the first electric signal and one or more characteristic values of the first electric signal, wherein the characteristic values of the first electric signal comprise: power spectral density, signal-to-noise ratio, dynamic range, dead zone; and the signal generating module is used for generating and transmitting a third optical signal according to the second exogenous frequency value.

With reference to the second aspect, in certain implementations of the second aspect, the signal feedback control module includes: an analog-to-digital conversion unit for converting the first electrical signal into a first digital signal; a framing calculation unit, configured to convert the first digital signal into a first time domain signal; a time-frequency transformation calculation unit for converting the first time-domain signal into a first frequency-domain signal calculation unit for determining the second difference frequency value from one or more eigenvalues of the first frequency-domain signal.

With reference to the second aspect, in certain implementations of the second aspect, the signal feedback control module further includes: and the time-frequency inverse transformation unit is used for converting the first frequency domain signal into a second time domain signal.

With reference to the second aspect, in certain implementations of the second aspect, the signal feedback control module further includes: and the judging unit is used for judging the second external difference frequency value, wherein when the absolute value of the difference value between the first external difference frequency value and the second external difference frequency value of the first electric signal is larger than a judging threshold value, the second external difference frequency value is sent to the signal generating module.

With reference to the second aspect, in certain implementations of the second aspect, the signal generating module includes: a digital signal generation unit for determining a second digital signal according to a second heterodyne frequency value, wherein the second digital signal has signal characteristics of the second heterodyne frequency value; a first digital-to-analog conversion unit for converting the second digital signal into a second electrical signal; the signal amplifying unit is used for amplifying the second electric signal to obtain a third electric signal; and an electro-optical modulator for converting the third electrical signal into a third optical signal.

In a third aspect, there is provided a communication apparatus comprising: various modules or units for implementing the method of the first aspect or any of the possible implementations of the first aspect.

In a fourth aspect, the present application provides a computer readable storage medium having stored therein computer instructions which, when run on a computer, cause the method as in the first aspect or any one of the possible implementations of the first aspect to be performed.

In a fifth aspect, the present application provides a chip, comprising: a processor for calling and running a computer program from a memory, such that a communication device on which the chip is mounted performs the method as in the first aspect or any one of the possible implementations of the first aspect.

In a sixth aspect, the application provides a computer program product comprising computer program code which, when run on a computer, causes the method as in the first aspect or any one of the possible implementations of the first aspect to be performed.

Drawings

Fig. 1 is a schematic block diagram of a heterodyne coherent OTDR apparatus according to an embodiment of the present application.

Fig. 2 is a schematic diagram of an example of a signal feedback control module according to an embodiment of the present application.

Fig. 3 is a schematic diagram illustrating an example of a signal detection and calculation unit according to an embodiment of the present application.

Fig. 4 is a schematic structural diagram of an example of a signal generating module according to an embodiment of the present application.

Fig. 5 shows a schematic flow chart of an example of a method for adaptively adjusting a differential frequency value based on OTDR according to the present application.

Fig. 6 is a flowchart of a method for calculating an external differential frequency value in an OTDR system according to an embodiment of the present application.

FIG. 7 shows an example of the present applicationA flow chart of a method for dynamically adjusting a slip frequency value in a system.

Fig. 8 is a schematic block diagram of a communication device according to an embodiment of the present application.

Detailed Description

The technical scheme of the embodiment of the application can be applied to various distributed optical fiber testing technical fields based on OTDR and optical fiber sensing technical fields, such as: a plain optical time domain reflectometer (Optical Time Domain Reflectometry, OTDR), a polarization sensitive optical time domain reflectometer (Polarization Optical Time Domain Reflectometry, POTDR), a Phase sensitive optical time domain reflectometer (Phase-Sensitive Optical Time Domain Reflectometry, ) Brillouin optical time domain reflectometer (Brillouin Optical Time Domain Reflectometry, BOTDR), raman optical time domain reflectometer (Raman Optical Time Domain Reflectometry, ROTDR), etc., as embodiments of the present application are not limited in this regard.

The OTDR is an optoelectronic integrated instrument manufactured by utilizing scattering generated by an optical signal in an optical fiber to be tested, including Rayleigh scattering, brillouin scattering and Raman scattering, and Fresnel reflection generated by discontinuous points of the optical signal in the optical fiber. An OTDR is an optical fiber detection instrument for performing feature analysis, troubleshooting, and maintenance of an optical fiber link, and performs OTDR test by transmitting pulsed laser light in an optical fiber and analyzing it. The working principle of the OTDR is to analyze and obtain the transmission characteristics of the length, attenuation, faults and the like of the optical fiber by detecting the energy distribution curve of the back scattered light of the pulse laser on the optical fiber line with time or distance. When the light pulse propagates forwards along the optical fiber line, part of the light ring signal is scattered and reflected back, and the light signal is continuously sampled at high speed to obtain a curve reflecting the characteristics of the optical fiber such as attenuation, faults and the like.

For example, heterodyne coherent detection is commonly used in the field of fiber vibration sensing In the prior heterodyne coherent +.>The device mainly comprises a laser, a beam splitter, a modulator, a circulator, a tested optical fiber, a coupler, a photoelectric detector, a processing unit and the like. In the practical use process, the laser, the beam splitter, the modulator, the circulator, the coupler, the photoelectric detector and other corresponding power supplies, driving, circuit units and communication interfaces of the sensor can be integrated into the same sensing processing device, and the tested optical fibers are usually arranged in a sensing optical cable. The heterodyne coherent detection +.>The specific working principle of the device is as follows: the laser is used as a light source to generate continuous light which is divided into an upper path and a lower path by the light splitter, the lower path of light is used as local oscillation light to be sent to the coupler, the upper path of light is used as detection light which is modulated into light pulses by the modulator and is injected into the tested optical fiber through one port of the circulator, rayleigh back scattering light generated by the tested optical fiber is injected into the coupler through the other port of the circulator to be mixed with local oscillation light signals, the mixed light signals are injected into the photoelectric detector to be detected and output electric signals, and finally, data processing and result display are carried out by an analog-to-digital converter (ADC), a data acquisition card or an oscilloscope in the processing unit.

For example, compared with the traditional OTDR, the heterodyne coherent detection type OTDR device in the optical fiber testing field can effectively improve the sensitivity and dynamic range of detection, and can effectively avoid the problem of dead zones caused by saturation of the receiving end of the OTDR device due to reflection generated by characteristic points such as a movable connector and a mechanical connector in a tested optical fiber link. The dead zone may include an event dead zone and an attenuation dead zone, and when the OTDR technology is used for detecting the optical fiber link, due to the influence of the scattered light signal and the reflected light signal, it is difficult to detect or accurately locate an event point and a fault point in the optical fiber link within a certain distance or time, where the distance difficult to detect or accurately locate is the dead zone. Specifically, the event blind zone refers to the shortest distance that the OTDR can detect another continuous event after fresnel reflection occurs, that is, the distance between the start point of the reflection peak of the laser pulse and the saturation peak of the front-end receiver, and the event blind zone is the distance where the reflection level drops from the peak to 1.5 dB. The attenuation blind zone is the minimum distance from which the OTDR can accurately measure the loss of continuous non-reflection events after the Fresnel reflection occurs, namely the distance from the starting point of the reflection peak of the laser pulse to other identifiable event points, and is also called as an optical pulse attenuation blind zone. The attenuation dead zone is 0.5dB from when the reflection event occurs until the reflection drops to the backscatter level of the fiber. In addition, the attenuation blind zone is generally longer than the event blind zone.

At present, the OTDR technology can increase the dynamic range of the system by increasing the pulse width, so as to increase the measurement range of the OTDR device, but the dead zone of the laser pulse also increases continuously with the increase of the laser pulse width, so that the measurement dead zone is enlarged to cause the cracking of the test result.

In order to further improve the detection performance of the OTDR device, the embodiment of the application provides a heterodyne coherent detection type OTDR device. The heterodyne coherent detection type OTDR device is provided with a frequency self-adaptive adjusting module, wherein the frequency self-adaptive adjusting module comprises a signal feedback control module and a signal generating module, an optimal heterodyne frequency value of detected light is found and self-adaptively adjusted through a calculation and decision feedback method, and an optical signal corresponding to the optimal heterodyne frequency value is output, so that the heterodyne coherent detection type OTDR device with high performance is realized.

The heterodyne coherent detection type OTDR device of the present application is further described with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present application, and are not intended to limit the scope of the present application.

Fig. 1 is a schematic block diagram of a heterodyne coherent OTDR apparatus according to an embodiment of the present application. As can be seen from fig. 1, the heterodyne coherent adaptive heterodyne frequency OTDR apparatus 100 includes a laser emitting module 110, a beam splitter 120, a frequency adaptive adjustment module 130, a circulator 140, a receiving module 160, and a processing module 170. The frequency self-adaptive adjusting module can comprise a signal feedback control module and a signal generating module.

Optionally, the heterodyne coherent OTDR device may further include a fiber 150 under test.

It should be appreciated that in embodiments of the present application, the laser emitting module 110 may include a narrow linewidth laser (Narrow Linewidth Laser, NLL), a distributed bragg grating (Distributed Feedback, DFB) laser, and an integrated tunable laser (Integrated Tunable Laser Assembly, ITLA), as various laser sources, which are not limited in this embodiment of the present application.

An output of the laser emitting module 110 is connected to an input of the beam splitter 120. The laser emitting module 110 is configured to output a continuous optical signal to an input end of the optical splitter 120.

In one implementation, the continuous optical signal generated via the laser emitting module 110 may be the first optical signal.

Optionally, the splitter 120 includes two output ports and one input port. The input port of the optical splitter 120 is connected to the output port of the laser emission module 110, and the output port of the optical splitter 120 is connected to the input ports of the receiving module 160 and the frequency adaptive adjustment module 130, respectively.

The optical splitter 120 is configured to split the continuous optical signal input by the laser emission module 110 into two paths, wherein the first path is used as a detection optical signal to be output to the frequency adaptive adjustment module 130, and the second path is used as a local oscillation optical signal to be output to the receiving module 160.

In one implementation, the first optical signal separated by the optical splitter 120 may be the second optical signal as the detected optical signal, and the third optical signal may be the local oscillator optical signal.

The frequency adaptation module 130 may include a signal feedback control module and a signal generation module.

Optionally, the frequency adaptive adjustment module 130 is connected to the optical splitter 120, the circulator 140, the receiving module 160, and the processing module 170, respectively.

The frequency adaptive adjustment module 130 is configured to modulate the probe optical signal sent by the optical splitter 120 into a pulse optical signal and send the pulse optical signal to the first port of the circulator 140, and generate an adjusted optical signal according to the electrical signal sent by the receiving module 160 and send the adjusted optical signal to the first port of the circulator 140.

In one implementation, the pulse optical signal generated by the frequency adaptive adjustment module 130 after modulating the detection optical signal, i.e., the second optical signal, sent by the optical splitter 120 may be a fourth optical signal, and the adjusted optical signal generated by the frequency adaptive adjustment module 130 according to the heterodyne frequency value of the first electrical signal sent by the receiving module 160 and one or more characteristic values of the first electrical signal may be an eighth optical signal.

Optionally, the heterodyne coherent OTDR module provided in an embodiment of the present application may further include a erbium doped fiber amplifier, where the erbium doped fiber amplifier is configured to amplify and input the pulse optical signal after having been modulated to the first port of the circulator 140.

The bait-doped amplifier may be connected to the frequency adaptive adjustment module 130 and the first port of the circulator 140.

The circulator 140 includes a first port, a second port, and a third port.

Optionally, a circulator 140 is disposed at a port of the optical fiber to be tested, so as to distinguish an incident signal from a reflected signal, and the pulse laser signal output by the frequency adaptive adjustment module 130 is injected onto the optical fiber to be tested for detection, and the rayleigh back-scattered optical signal reflected on the optical fiber to be tested is received by the receiving module 160 through the circulator 140. Alternatively, the circulator 140 may be connected to the frequency adaptive modulation module 130, the measured optical fiber 150, and the receiving module 160, respectively. Specifically, a first port of the circulator 140 is connected to the output end of the frequency adaptive adjustment module 130, a second port of the circulator 140 is connected to the measured optical fiber 150, and a third port of the circulator 140 is connected to the receiving module 160.

The circulator 140 is configured to input the optical signal generated by the frequency adaptive adjustment module 130 from the first port of the circulator 140 and output the optical signal from the second port of the circulator 140 onto the optical fiber 150; and is further configured to receive the rayleigh backscattered light signal reflected from the measured optical fiber from the second port of the circulator 140 and output the rayleigh backscattered light signal to the receiving module 160 through the third port of the circulator 140.

Rayleigh backscattering is understood to mean that rayleigh scattering occurs in the optical fiber medium, the rayleigh scattering power of the optical fiber is distributed throughout the optical fiber space, and the scattering direction includes forward and backward scattering along the optical fiber axis in all directions, wherein rayleigh backscattering is scattering along the optical fiber axis backward direction in the optical fiber.

In one implementation, the probe optical signal output from the second port of the circulator 140 may be a fifth optical signal, and the rayleigh backscattered optical signal output from the third port of the circulator 140 may be a sixth optical signal.

The receiving module 160 may include a coupler 161 and a photodetector 162.

In one implementation, the receiving module 160 is configured to couple the rayleigh backscattered optical signal output from the third port of the circulator 140 and the local oscillator optical signal output from the optical splitter 120 into a seventh optical signal, and convert the seventh optical signal into the first electrical signal for output through the photodetector.

Optionally, a coupler 161 is connected to the third port of the circulator 140 and the photodetector 162, respectively.

And a coupler 161, configured to couple the rayleigh back-scattered optical signal output from the third port of the circulator 140 and the local oscillation optical signal input from the optical splitter 120 to generate a heterodyne optical signal.

In one implementation, the coupler 161 may couple the sixth optical signal input to the third port of the circulator 140 with the third optical signal input to the optical splitter 120 to generate a seventh optical signal.

Optionally, the receiving module 160 within the heterodyne correlation OTDR device 100 further comprises an optical filter.

Alternatively, the optical filter may be connected to the coupler 161 and the photodetector 162, respectively.

The optical filter is used for filtering the optical signal output by the coupler 161 and outputting the filtered optical signal to the photodetector 162.

For example, the optical filter may filter the seventh optical signal generated by the coupler 161 and output the filtered seventh optical signal to the photodetector 162.

Alternatively, the photodetector 162 may be connected with the frequency adaptation module 130, the coupler 161, and the frequency adaptation module 130, respectively.

The photodetector 162 is configured to convert an input optical signal into an electrical signal and send the electrical signal to the frequency adaptive adjustment module 130.

In one implementation, the photodetector 162 may convert the seventh optical signal generated by the coupler 161 into the first electrical signal.

Optionally, heterodyne coherent OTDR device 100 further comprises a low noise amplifier, which may be connected to receiving module 170 and frequency adaptation module 130, respectively.

The low noise amplifier is configured to amplify the weak electrical signal filtered by the low pass filter and output the amplified weak electrical signal to the processing module 170.

In one implementation, the low noise amplifier is configured to low-pass filter and amplify a second electrical signal output by the frequency adaptive adjustment module 130, and output the second electrical signal to the processing module 170, where the second electrical signal is an electrical signal determined by feedback from the frequency adaptive adjustment module 130.

The processing module 170 includes a data acquisition card and an oscilloscope, and the processing module 170 is connected with the frequency adaptive adjustment module 130.

The processing module 170 is configured to convert the electrical signal input by the frequency adaptive adjustment module 130 into a digital signal and process the digital signal.

The data acquisition card is used for converting an input electric signal into a digital signal and analyzing and acquiring the data.

And the oscilloscope is used for displaying the electric signals determined by the photoelectric detector.

In one implementation, the processing module 170 may convert the electrical signal output by the frequency adaptive adjustment module 130 into a digital signal and perform data processing. It should be appreciated that the electrical signal is an electrical signal determined by the frequency adaptation module 130.

In one implementation, the oscilloscope may display the electrical signal determined by the frequency adaptation module 130.

Optionally, the heterodyne coherent OTDR device 100 may further include an optical fiber 150, where the optical fiber 150 is connected to the second port of the circulator 140.

An optical fiber 150 for transmitting the probe optical signal output from the second port of the circulator 140, and for transmitting the rayleigh backscattered optical signal generated by reflection on the optical fiber 150 to the third port of the circulator 140.

In one implementation, the fifth optical signal output from the second port of the circulator 140 may be transmitted on the optical fiber 150, and the sixth optical signal reflected or scattered back on the optical fiber may be output to the receiving module 160 through the third port of the circulator 140. It should be understood that the optical signal output by the second port of the circulator 140 may be the first detected optical signal after the optical signal emitted by the laser emitting module 110 is modulated, or may be the detected optical signal after the optical signal is processed by the frequency adaptive adjustment module 130.

Next, the working principle of the heterodyne correlation OTDR device will be explained in detail by taking the trend of signals between different modules and devices as an example.

In one implementation, the continuous optical signal generated by the laser emitting module 110 may be sent as a first optical signal to the input of the optical splitter 120; the optical splitter 120 divides the first optical signal input by the laser emission module 110 into two paths, the first path of detection optical signal can be a second optical signal and output to the input end of the frequency adaptive adjustment module 130, and the second path of local oscillation optical signal can be a third optical signal and output to the receiving module 160; the pulse optical signal obtained after the frequency adaptive adjustment module 130 modulates the second optical signal sent by the optical splitter 120 may be a fourth optical signal, and the frequency adaptive adjustment module 130 may further determine a second heterodyne frequency value according to the first heterodyne frequency value of the first electrical signal sent by the receiving module 160 and one or more characteristic values of the first electrical signal, and the adjusted optical signal generated according to the second heterodyne frequency value may be a seventh optical signal; the fourth optical signal is input through the first port of the circulator 140, the fifth optical signal is output from the second port of the circulator 140 to the measured optical fiber 150, and the reflected or scattered signal generated by reflection on the measured optical fiber 150, that is, the sixth optical signal, can be output from the third port of the circulator 140 to the receiving module 160; the coupler 161 in the receiving module 160 can couple the third optical signal and the sixth optical signal, generate a seventh optical signal after mixing, generate a first electrical signal after modulating by the photodetector 162, and send the first electrical signal to the frequency adaptive adjusting module 130; the frequency adaptation adjustment module 130 determines a second external difference frequency value from the external difference value of the first electrical signal and one or more eigenvalues of the first external difference value, and generates a seventh optical signal from the second external difference frequency value. If the absolute value of the difference value between the first outer difference frequency value and the second outer difference frequency value is larger than the judgment threshold value, the second outer difference frequency value is sent; when the absolute value of the difference between the first and second heterodyne frequency values of the first electrical signal is less than or equal to the decision threshold, the first heterodyne frequency value of the first electrical signal is retained, and the first electrical signal is output to the signal processing module 170.

In order to explain the working principle of the signal feedback control module 200 in the adaptive adjustment module 130 in detail, fig. 2 is a schematic diagram of an example of the signal feedback control module according to an embodiment of the present application. Fig. 2 is a schematic diagram of a signal feedback control module 200 in a frequency adaptive adjustment module 130 in a heterodyne coherent OTDR device according to an embodiment of the present application. The signal feedback control module 200 includes a signal detection and calculation unit 1200.

Alternatively, the signal detection unit 1200 is connected to the reception module 160, the signal generation module, and the signal processing module, respectively.

In one implementation, the signal detection and calculation unit 1200 is configured to calculate the second heterodyne frequency value by using the first heterodyne frequency value of the first electrical signal transmitted by the receiving module 160 and one or more characteristic values of the first electrical signal.

Illustratively, the characteristic values of the electrical signals received by the signal detection and computation unit 1200 include: power spectral density (Power Spectral density, PSD), signal-to-Noise Ratio (SNR), dynamic Range (DR), dead Zone (DZ), and the like.

In one implementation, the signal detection and calculation unit 1200 may calculate the second difference frequency value by extracting the first difference frequency value and the SNR value in the first electrical signal sent by the receiving module 160.

Optionally, the signal feedback control module 200 may further include a decision unit 1300. The decision unit comprises two outputs and an input.

In one implementation, an input of the decision unit 1300 is connected to an output of the signal detection and calculation unit 1200, and an output of the decision unit 1300 is connected to inputs of the signal generation module 300 and the signal processing module 170, respectively.

The decision unit 1300 is used for deciding the heterodyne frequency value calculated by the signal detection and calculation unit 1200.

In one implementation, the decision unit 1300 may receive the second difference frequency value transmitted by the signal detection and calculation unit 1200 and make a decision on it. If the absolute value of the difference between the first and second heterodyne frequency values of the first electrical signal is greater than a decision threshold, the second heterodyne frequency value is sent to the signal generation module 300 for processing; if the absolute value of the difference between the first heterodyne frequency value and the second heterodyne frequency value of the first electrical signal is less than or equal to the decision threshold, the first heterodyne frequency value of the first electrical signal is used as the heterodyne frequency value to be output, and the first electrical signal is output to the processing module 170.

It should be understood that the above decision threshold may be set according to actual requirements, for example, the decision threshold may be set to 1MHz, which is not limited by the present application.

The structural principle of the signal detecting and calculating unit 1200 in the signal feedback control module 200 will be described in detail with reference to fig. 3. Fig. 3 is a schematic diagram of a signal detection and calculation unit 1200 in a signal feedback control unit 1300 according to an embodiment of the present application. As shown in fig. 3, the signal detection and calculation unit 1200 includes an analog-to-digital conversion unit 1201, a framing calculation unit 1202, a time-frequency conversion calculation unit 1203, and a calculation unit 1207. The signal detection and calculation unit 1200 may further include a down-conversion calculation unit 1204, a filtering unit 1205, and an inverse time-frequency transform unit 1206.

The analog-to-digital conversion unit 1201 is connected to the output of the receiving module 160 and the input of the framing calculation unit 1202, respectively. The analog-to-digital conversion unit 1201 is configured to convert an analog electrical signal input from the receiving module 160 into a digital signal.

In one implementation, the analog-to-digital conversion unit 1201 acquires the first electrical signal sent by the receiving module 160 and converts it into a digital signal Et (i) of length N, where i=1, 2, … N.

The framing calculation unit 1202 is connected to the output of the analog-to-digital conversion unit 1201 and the input of the time-frequency transformation calculation unit 1203, respectively. The framing calculation unit 1202 is configured to divide an input digital signal into different sets of time domain signals with the same length.

In one implementation, the framing calculation unit 1202 receives the digital signal Et (i) sent by the analog-to-digital conversion unit 1201, and divides the digital signal Et (i) into K groups of time domain signals with lengths M, where the lengths of the time domain signals in each group are equal and keep the same as the pulse period. The digital time domain signal of the j-th group is Et (j, l), where j=1, 2, …, K, l=1, 2, …, M, and n=k×m.

The time-frequency transformation calculation unit 1203 is connected to the output of the framing calculation unit 1202 and the input of the down-conversion calculation unit 1204, respectively. The time-frequency transformation calculation unit 1203 is configured to convert the time domain signal obtained by the processing of the framing calculation unit 1202 into a frequency domain signal.

In one implementation, the time-frequency transformation calculation unit 1203 receives the j-th set of time-domain signals sent by the framing calculation unit 1202 and converts them into frequency-domain signals Ef (j, l), where l=1, 2, …, M. It should be appreciated that the manner of time-frequency transformation may be a fourier transform calculation, i.e. ef=f (Et). Let j=1, 2, …, K in turn, i.e. perform this step K times, K sets of frequency domain signals Ef (j, l) with lengths M are obtained, where j=1, 2, …, K, l=1, 2, …, M, and n=k×m.

Optionally, the signal detection and calculation unit 1200 further comprises a down-conversion calculation unit 1204. The down-conversion calculation unit 1204 is connected to an output terminal of the time-frequency conversion calculation unit 1203 and an inlet terminal of the filtering unit 1205, respectively. The down-conversion computing unit 1204 is configured to convert the frequency domain signal obtained by the time-frequency conversion computing unit into a frequency domain signal after down-conversion.

In one implementation, the down-conversion calculating unit 1204 may convert the frequency domain signal Ef (j, l) obtained by the time-frequency transforming unit 1203 into a down-converted frequency domain signal ef_ddc (j, l), where l=1, 2, …, M. Let j=1, 2, …, K sequentially, i.e. perform this step K times, K sets of frequency domain signals ef_ddc (j, l) with lengths M can be obtained, where j=1, 2, …, K, l=1, 2, …, M, and n=k×m.

Optionally, the signal detection and calculation unit 1200 further comprises a filtering unit 1205. The filtering unit 1205 is connected to the output of the down-conversion calculating unit 1204 and the input of the calculating unit 1207, respectively. The filtering unit 1205 is configured to filter the frequency domain signal obtained by the down-conversion calculating unit.

In one implementation, the filtering unit 1205 may receive the frequency domain signal ef_dcc (j, l) obtained by the down-conversion calculating unit 1204, and perform filtering processing on the frequency domain signal ef_dcc to filter out-of-band noise, where the filtered frequency domain signal is h×ef_ddc, and H is a filtering function.

Optionally, the signal detection and calculation unit 1200 further includes a time-frequency inverse transform unit 1206. The inverse time-frequency transform unit 1206 may be connected to an output of the filtering unit 1205 and an input of the calculating unit 1207. The time-frequency inverse transformation unit is used for transforming the time-frequency signal obtained by the framing calculation unit 1202 into a frequency domain signal; and may also be used to convert the frequency domain signal filtered by the filtering unit 1205 into a frequency domain signal.

In one implementation, the inverse time-frequency transform unit 1206 may receive the j-th set of frequency domain signals h×ef_ddc filtered by the filtering unit 1205 and convert the j-th set of frequency domain signals h×ef_ddc into the time domain signals E't (j, l), where l=1, 2, …, M. The inverse time-frequency transform may be calculated by inverse fourier transform, that is, ef=f-1 (Et).

The calculation unit 1207 is connected to the output of the filtering unit 1205 and the input of the decision unit 1300, respectively. The calculation unit 1207 is configured to calculate a second difference frequency value for one or more eigenvalues in the frequency domain signal filtered by the filtering unit or the frequency domain signal output by the inverse time-frequency transformation unit 1206.

In one implementation, the calculating unit 1207 receives the frequency domain signal h×ef_ddc filtered by the filtering unit 1205, and determines a second differential frequency value Δf' =function (Δf, PSD, SNR, …) according to at least one index of the frequency domain signal, where the index includes: PSD, SNR, DR, DZ of the frequency domain signal, etc.

Optionally, the calculating unit 1207 may further receive the time domain signal E't (j, l) converted by the inverse time-frequency transforming unit 1206, and determine a second difference frequency value Δf' =function (Δf, PSD, SNR, …) according to one or more characteristic values of the frequency domain signal, where the characteristic values of the frequency domain signal include: PSD, SNR, DR, DZ of the frequency domain signal, etc.

The structural principle of the signal generating module 400 in the frequency adaptive adjusting module 130 will be described in detail with reference to fig. 4. Fig. 4 is a schematic structural diagram of a signal generating module 400 in a heterodyne coherent OTDR device according to an embodiment of the present application. As shown in fig. 4, the signal generation module 400 includes a digital signal generation unit 4010, a first digital-to-analog conversion unit 4011, a signal amplification unit 4012, a signal coupling unit 4013, and an electro-optical modulator 4014. The signal generating module 400 may further include a photo detection unit 4015, a bias voltage monitor control unit 4016, and an optical pulse generating unit 4017.

The digital signal generation unit 4010 is connected to an output terminal of the signal feedback control unit 1300 and an input terminal of the first digital-to-analog conversion unit 4011, respectively. The digital signal generation unit 4010 is configured to generate a digital signal according to the heterodyne frequency value input from the feedback control unit 1300.

In one implementation, the digital signal generation unit 4010 receives the second offset frequency value provided by the signal feedback control unit 1300, and the digital signal generation unit 4010 determines a first digital signal according to the second offset frequency value and sends the first digital signal to the first digital-to-analog conversion unit 4011.

The first digital-to-analog conversion unit 4011 is connected to an output terminal of the digital signal generation unit 4010 and an input terminal of the signal amplification unit 4012, respectively. The first digital-to-analog conversion unit 4011 is used to convert an input digital signal into an analog electrical signal.

In one implementation, the first digital-to-analog conversion unit 4011 converts the first digital signal generated by the digital signal generation unit 4010 into the second electrical signal.

The signal amplifying unit 4012 is connected to an output end of the first digital-to-analog conversion unit 4011 and an input end of the signal coupling unit 4013, respectively. The signal amplification unit 4012 is configured to amplify an input analog electric signal.

In one implementation, the signal amplifying unit 4012 may amplify the second electrical signal generated by the first digital-to-analog conversion unit 4011 and generate the third electrical signal.

The signal coupling unit 4013 is connected to an input terminal of the electro-optical modulator 4014, an output terminal of the signal amplifying unit 4012, and an output terminal of the bias voltage monitor control unit 4016, respectively. The signal coupling unit 4013 is configured to press and input the amplified analog electric signal and the bias circuit into the electro-optical modulator 4014.

The electro-optical modulator 4014 is connected to a first port of the optical splitter 110, an output terminal of the signal coupling unit 3013, and an input terminal of the optical pulse generating unit 4017, respectively. The electro-optical modulator 4014 is configured to modulate an input analog electrical signal onto an optical carrier, and output the modulated analog electrical signal as an optical signal to an optical pulse generation unit.

In one implementation, the electro-optical modulator 4014 may modulate the second optical signal and output the second optical signal to the optical pulse generating unit, and the electro-optical modulator 4014 may further convert the third electrical signal input from the signal coupling unit 4013 into the eighth optical signal.

Alternatively, the Electro-Optic Modulator 4014 may comprise a replacement Modulator such as an Acousto-Optic Modulator (AOM), a semiconductor optical amplifier (Semiconductor Optical Amplifier, SOA), an Electro-absorption Modulator (Electro-Absorption Modulator, EAM), a Mach-zehnder Modulator (Mach-Zehnder Modulator, MZM), etc., as the application is not limited in this regard.

Optionally, the signal generating module 400 further includes an optical pulse generating unit 4017. The optical pulse generation unit 4017 is connected to an output terminal of the electro-optical modulator 4014, and is configured to process an optical signal input from the electro-optical modulator 4014 and generate a pulsed optical signal.

The light pulse generation unit 4017 may generate one pulse signal in one test period, or a plurality of repeated pulse signals of a fixed pulse width and duty ratio in one test period, for example.

Optionally, the signal generating module 400 further includes a photo detection unit 4015.

The photo-detection unit 4015 is connected to an input end of the bias voltage monitor control unit 4016 and an output end of the electro-optical modulator 4014, respectively, and the photo-detection unit 3015 is used for detecting the modulated optical signal.

In one implementation, the photo-detection unit 4015 may detect the second optical signal or the eighth optical signal output by the electro-optical modulator 4014.

Optionally, the signal generating module 400 further includes a bias voltage monitor 4016.

The bias voltage monitor control unit 4016 is connected to an input terminal of the signal coupling unit 4013 and an output terminal of the photoelectric detection unit 4015, respectively. The bias voltage monitor control unit 4016 is configured to feed back a bias voltage according to a detection result of the photoelectric detection unit 4015, and lock the bias voltage.

In one implementation, the bias voltage monitor control unit 4016 may determine the bias voltage according to the detection result of the photoelectric detection unit 4015 on the second optical signal or the eighth optical signal output by the electro-optical modulator 4014, and is further configured to lock the bias voltage.

Fig. 5 shows a schematic flow chart of a method for transmitting signals according to the present application.

S501, a first optical signal is generated and transmitted.

Alternatively, the first optical signal may be used to indicate a continuous optical signal generated by the laser emitting module, and may also be used to indicate a continuous optical signal generated by the frequency adaptive adjustment module according to the heterodyne frequency value of the last electrical signal and one or more eigenvalues of the electrical signal.

In one implementation, a continuous optical signal generated by the laser emitting module is input through the first port of the circulator and output from the third port of the circulator onto the optical fiber under test.

S502, a second optical signal is received, the second optical signal comprising a reflected and scattered signal of the first optical signal.

Specifically, the second optical signal may be used to indicate an electrical signal generated by mixing and modulating a local oscillator optical signal generated by the optical splitter and an optical signal output by the third port of the circulator when the laser transmitting module transmits laser for the first time. The second optical signal can also be used for indicating an optical signal generated and sent by the signal generating module in the frequency self-adaptive adjustment process after the optical signal reflected or scattered back by the optical fiber link to be detected and the local oscillation optical signal generated by the optical splitter are subjected to frequency mixing processing.

Specifically, the second optical signal is used for indicating an optical signal generated after the optical signal reflected or scattered back by the first optical signal on the tested optical fiber is coupled with the local oscillation optical signal separated by the first optical signal through the optical splitter.

Optionally, the second optical signal is further used for indicating an optical signal preset in the OTDR device.

S503, converting the second optical signal into a first electrical signal;

in one implementation, a photodetector in the receiving module converts the second optical signal into a first electrical signal.

S504, determining a first heterodyne frequency value of the first electrical signal.

In one implementation, the signal feedback control module obtains a first electrical signal sent by the receiving module and determines a heterodyne frequency value of the first electrical signal.

S505, determining a second heterodyne frequency value according to the first heterodyne frequency value of the first electrical signal and one or more characteristic values of the first electrical signal.

Alternatively, the first electrical signal may be used to indicate the electrical signal sent by the receiving module to the frequency adaptive adjustment module.

In one implementation, the signal feedback control module determines the second heterodyne frequency value based on a first heterodyne frequency value of a first electrical signal and one or more heterodyne frequency values of the first electrical signal.

The signal feedback control module comprises a signal detection and calculation unit.

Specifically, the signal detection and calculation unit determines the second heterodyne frequency value based on a first heterodyne frequency value of a first electrical signal and one or more eigenvalues of the first electrical signal. Wherein the characteristic value of the first electrical signal includes: PSD, SNR, DR, DZ, etc.

Specifically, in the embodiment of the present application, the signal detection and calculation unit may include an analog-to-digital conversion unit, a framing calculation unit, a time-frequency conversion calculation unit, a down-conversion calculation unit, a filtering unit, and a calculation unit.

In one implementation, the first electrical signal is described in detail with respect to its orientation between different units. The analog-to-digital conversion unit receives the first electric signal sent by the receiving module and converts the first electric signal into a digital signal Et (i) with the length of N, wherein i=1, 2, … N; the framing calculation unit receives the digital signal Et (i) sent by the analog-to-digital conversion unit, and divides the digital signal Et (i) into K groups of time domain signals with the length of M, wherein the length of each group of time domain signals is equal, and the time domain signals are kept the same as the pulse period. The digital time domain signal of the j-th group is Et (j, l), where j=1, 2, …, K, l=1, 2, …, M, and n=k×m; the time-frequency transformation calculating unit receives the j-th group of time-domain signals sent by the framing calculating unit and converts the j-th group of time-domain signals into frequency-domain signals Ef (j, l), wherein l=1, 2, …, M. It should be appreciated that the manner of time-frequency transformation may be a fourier transform calculation, i.e. ef=f (Et). Let j=1, 2, …, K in turn, i.e. perform this step K times, K sets of frequency domain signals Ef (j, l) with lengths M are obtained, where j=1, 2, …, K, l=1, 2, …, M, and n=k×m.

Optionally, the signal detection and calculation unit further comprises a down-conversion calculation unit. The signal detection and calculation unit may convert the frequency domain signal Ef (j, l) obtained by the time-frequency conversion unit into a frequency domain signal ef_ddc (j, l) after down-conversion, where l=1, 2, …, M. Let j=1, 2, …, K sequentially, i.e. perform this step K times, K sets of frequency domain signals ef_ddc (j, l) with lengths M can be obtained, where j=1, 2, …, K, l=1, 2, …, M, and n=k×m.

Optionally, the signal detection and calculation unit further comprises a filtering unit. The filtering unit can receive the frequency domain signal ef_dcc (j, l) obtained by the down-conversion calculating unit, and carries out filtering treatment on the frequency domain signal ef_dcc (j, l) to filter out-of-band noise, wherein the filtered frequency domain signal is H×ef_DDC, and H is a filtering function; the calculating unit receives the frequency domain signal h×ef_ddc filtered by the filtering unit, and determines a second outer difference frequency value Δf' =function (Δf, PSD, SNR, …) according to at least one index of the frequency domain signal, where the index includes: PSD, SNR, DR, DZ of the frequency domain signal, etc.

Optionally, the signal detection and calculation unit further comprises a time-frequency inverse transformation unit. The time-frequency inverse transformation unit can be connected with the output end of the filtering unit and the input end of the calculating unit. The time-frequency inverse transformation unit is used for converting the time-frequency signal obtained by the framing calculation unit into a frequency-domain signal.

In one implementation, the inverse time-frequency transformation unit may receive the j-th set of frequency domain signals h×ef_ddc filtered by the filtering unit and convert the j-th set of frequency domain signals h×ef_ddc into time domain signals E't (j, l), where l=1, 2, …, M. The inverse time-frequency transform may be calculated by inverse fourier transform, i.e., ef=f-1 (Et); the calculating unit may receive the time domain signal E't (j, l) converted by the inverse time-frequency transforming unit, and determine a second differential frequency value Δf' =function (Δf, PSD, SNR, …) according to at least one index of the frequency domain signal, where the index includes: PSD, SNR, DR, DZ of the frequency domain signal, etc.

Optionally, the feedback control module further comprises a decision unit. The decision is used for deciding the second outer difference frequency value calculated by the signal detection and calculation unit.

In one implementation, the decision unit may receive the second differential frequency value sent by the signal detection and calculation unit and make a decision on it. If the absolute value of the difference value between the first outer difference frequency value and the second outer difference frequency value of the first electric signal is larger than the judgment threshold value, the second outer difference frequency value is sent to the signal generation module for processing; if the absolute value of the difference value between the first outer difference frequency value and the second outer difference frequency value of the first electric signal is smaller than or equal to the judgment threshold value, the first outer difference frequency value of the first electric signal is reserved, and the first electric signal is output to the processing module for processing.

It should be understood that the above decision threshold may be set according to actual scene requirements, for example, the decision threshold may be set to 1MHz, which is not limited by the present application.

S506, generating a third optical signal according to the second heterodyne frequency value.

In one implementation, the third optical signal is used to instruct the signal generating module to generate the third optical signal according to the second differential frequency value sent by the signal feedback control module.

The signal generating module may include a digital signal generating unit, a first digital-to-analog converting unit, a signal amplifying unit, a signal coupling unit, and a modulating unit.

Optionally, the signal generating module may further include the photo detection unit and a bias voltage monitoring unit.

In one implementation, the digital signal generating unit receives a second external difference frequency value sent by the signal feedback control module, determines a second digital signal according to the second external difference frequency value, and sends the second digital signal to the first digital-to-analog conversion unit, wherein the second digital signal has a signal characteristic of the second external difference frequency value; the first digital-to-analog conversion unit receives the first digital signal sent by the digital signal generation unit and converts the first digital signal into a second electric signal; the signal amplifying unit receives the second electric signal generated by the first digital-to-analog conversion unit, amplifies the analog electric signal and generates a third electric signal; the signal coupling unit receives the third electric signal amplified by the signal amplifying unit, and inputs the analog electric signal and the bias circuit into the photoelectric modulation unit; the modulation unit receives the third electric signal input by the signal coupling unit and converts the third electric signal into a third optical signal.

Optionally, the photoelectric detection unit may detect an optical signal output by the modulation unit; the bias voltage monitoring unit is used for feeding back bias voltage aiming at the detection structure of the photoelectric detection unit and locking the bias voltage.

Fig. 6 is a flowchart of a method for calculating a differential frequency value in an OTDR system according to an embodiment of the present application. The method comprises the following steps as shown in fig. 6:

s601, setting an initial differential frequency value Deltaf ₀ 。

By way of example, and not limitation, the initial heterodyne frequency value of an embodiment of the present application may be 10MHz.

S602, the differential frequency value delta f is gradually increased at a fixed frequency.

In one implementation, the outer difference frequency values are stepped up at a fixed frequency and a set number of pulses is sent at each outer difference frequency value Δf for its corresponding time domain signal E _t Acquisition and recording followed by conversion into a frequency domain signal E by Fourier transformation _f 。

By way of example and not limitation, the fixed frequency of stepping in embodiments of the present application may be set to 30MHz and the number of pulses may be set to 4096.

S603, when the heterodyne frequency value delta f is greater than the threshold value, stopping adjusting the heterodyne frequency value.

In particular, the threshold may be BW _6dB The BW is _6dB This is the analog bandwidth value at 6dB at the receiving end, which corresponds to 25% of the peak power.

It should be understood that the above threshold may be set according to actual requirements, which is not limited in this embodiment of the present application.

S604, corresponding SNR values under different heterodyne frequency values are calculated.

Wherein the initial offset frequency value Δf ₀ The corresponding SNR value is SNR ₀ 。

S606, selecting the heterodyne frequency value Deltaf with the largest value meeting the SNR threshold as the heterodyne frequency value Deltaf of the output ₁ 。

In one implementation, the Δf ₁ The SNR values of (2) satisfy: SNR is greater than or equal to SNR ₀ -Δ ₀ (dB), wherein Δ ₀ =1.5 (dB), and the heterodyne frequency value with the largest value is selected as the heterodyne frequency value of the output under the above conditions.

According to the technical scheme provided by the application, the method for calculating the output heterodyne frequency value by adopting the heterodyne frequency value gradually increasing in the OTDR system can achieve the optimal system performance under the limit of the simulation bandwidth of the current equipment by adaptively optimizing the heterodyne frequency value, can effectively improve the anti-optical fiber link reflection capability, reduce the influence of an attenuation blind area, and can balance the dynamic range and the attenuation blind area of the OTDR system.

FIG. 7 is a schematic diagram of an embodiment of the present application A flow chart of dynamic adjustment of the heterodyne frequency value of the system. As shown in fig. 7, the method for dynamically adjusting heterodyne frequency values includes:

s701, initializingThe system.

S702, under the initial condition, calculating an initial outer difference frequency value A.

S703, detecting SNR values at different distances on the tested optical fiber under the initial heterodyne frequency value.

S704, if the SNR value is smaller than the SNR threshold, the heterodyne frequency value A is required to be adjusted, the adjusted heterodyne frequency value B is input to S703, and the SNR value corresponding to the adjusted heterodyne frequency value B is calculated again.

Exemplary, if SNR < SNR _th The heterodyne frequency value a is to be adjusted, and the heterodyne frequency value B may be Δf '=a×Δf, where Δf' is the adjusted heterodyne frequency value, Δf is the heterodyne frequency value before adjustment, and a is a constant coefficient.

It should be understood that the SNR threshold may be set according to actual requirements, which is not limited in the embodiment of the present application.

S705, if the SNR value is equal to or higher than the SNR threshold, thenThe system delays back to S703 and again detects SNR values over all distances at the heterodyne frequency value.

Exemplary if SNR is ≡SNR _th Will thenAfter the system delays for 100ms, the system returns to S703, and the SNR values at different detection distances under the heterodyne frequency value are calculated again.

It should be appreciated that, under the initial heterodyne frequency values described above,the system detects SNR values over all distances, and it is difficult to separate the useful signal from the signal when the fading point at a distance is below the phase Jie Diaomen limit, i.e., when the signal-to-noise ratio of the signal is below a threshold value, and the useful signal can be separated when the signal-to-noise ratio of the signal is above the threshold value. If the SNR value at a certain distance is lower than the demodulation threshold value for a long time, a coherent attenuation blind zone is easily formed in a specific area, so that +.>The measurement accuracy of the system is reduced, severely reduced +.>Detection performance of the system.

The method is characterized in that a series of blind spots caused by saturation of the receiving end of an OTDR system due to reflection generated by characteristic points such as a movable connector, a mechanical connector and the like in an OTDR distributed optical fiber link are called blind spots. The distance from the starting point of the laser pulse reflection peak to other identifiable time points is called an optical pulse attenuation blind zone.

To raise upThe method for adaptively adjusting the heterodyne frequency value is adopted to adjust the heterodyne frequency value which is lower than the phase demodulation threshold, so that the measurement accuracy of the distance is improved, and the phenomenon that dead zones occur is avoided Influence->Detection performance of the system. However, at the same time, the SNR value at the distance adjacent to the position will be lower than the demodulation threshold value due to the variation of the heterodyne frequency value, multiple dynamic adjustment is required to change the heterodyne frequency value at different distances, so as to avoid the long-term attenuation blind area limit of the specific distance>The detection accuracy of the system.

According to the technical scheme provided by the application, inThe adaptive adjustment of the external difference frequency value is realized in the system in a decision feedback mode, so that the situation that the phase cannot be demodulated because the specific distance is on the coherent attenuation point for a long time can be avoided, namely, the coherent attenuation blind area formed at the specific distance can be effectively avoided, and the coherent attenuation blind area is improved>All-fiber link performance of the system and further promote the +.>Detection performance of the system.

The embodiment of the method for adaptively adjusting the differential frequency value based on the optical time domain reflectometer OTDR of the present application is described in detail above with reference to fig. 1 to 7, and the device side for adaptively adjusting the differential frequency value based on the optical time domain reflectometer OTDR of the present application is described in detail below with reference to fig. 8. It should be understood that the description of the apparatus-side embodiment corresponds to the description of the method-side embodiment, and thus, a part not described in detail may be referred to the foregoing method-side embodiment.

Fig. 8 is a schematic block diagram of a communication device according to an embodiment of the present application. As shown in fig. 8, the communication device may include: a receiving unit 810, a transmitting unit 820 and a processing unit 830.

It should be understood that the communication device 800 may include means for performing the various methods of the method 500 of fig. 5. And, each element in the communication device 800 and the other operations and/or functions described above are each for implementing a corresponding flow of the method 500 in fig. 5.

Illustratively, the transmitting unit 810 is configured to transmit the first optical signal.

The transmitting unit 810 is further configured to transmit the third optical signal.

And a receiving unit 820 for receiving a second optical signal, wherein the second optical signal includes the reflected and scattered signals of the first optical signal.

A processing unit 830 for converting the second optical signal into a first electrical signal.

The processing unit 830 is further configured to determine a second heterodyne frequency value according to the first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal, wherein the eigenvalues of the first electrical signal include: power spectral density, signal to noise ratio, dynamic range, dead zone.

Optionally, the processing unit 830 is further configured to generate a third optical signal according to the second heterodyne frequency value.

Optionally, the processing unit 830 is further configured to convert the first electrical signal into a first digital signal, where the first electrical signal is convertible into a digital signal Et (i) of length N, where i=1, 2, … N; converting the first digital signal into a first time domain signal, wherein the first time domain signal is K groups of time domain signals with the length of M, the length of each group of time domain signals is equal, and the length of the first time domain signal is kept the same as the pulse period; converting the first time domain signal into a first frequency domain signal, wherein the first frequency domain signal is obtained by carrying out Fourier transform calculation on the first time domain signal; converting the first frequency domain signal into a second frequency domain signal after the down-conversion processing; filtering the second frequency domain signal to obtain a third frequency domain signal; and determining a second difference frequency value from one or more eigenvalues of the third frequency domain signal.

Optionally, the processing unit 830 is further configured to convert the third frequency domain signal into a second time domain signal; and determining a second difference frequency value of the second signal based on one or more characteristics of the second time domain signal.

Optionally, the processing unit 830 is further configured to determine a second heterodyne frequency value based on the first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal, wherein the second heterodyne frequency value is transmitted when an absolute value of a difference between the first and second heterodyne frequency values of the first electrical signal is greater than a decision threshold.

Optionally, the processing unit 830 is further configured to determine a second digital signal according to the second heterodyne frequency value, wherein the second digital signal has a signal characteristic of the second heterodyne frequency value; converting the second digital signal into a second electrical signal; amplifying the second electric signal to obtain a third electric signal; inputting the third electric signal and the bias circuit into the photoelectric modulation unit; the third electrical signal is converted into a third optical signal.

Optionally, the processing unit 830 is further configured to detect a third optical signal; and determining the bias voltage according to the detection result of the third optical signal, and locking the bias voltage to fix the adjusted second offset frequency value.

It should also be appreciated that the processing unit 830 in the communication device 800 may be implemented by at least one processor.

It should also be appreciated that the processing unit 830 in the communication device 800 may be implemented by a processor, microprocessor, integrated circuit, or the like integrated on the chip or system-on-chip.

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

It will be clear to those skilled in the art that, for convenience and brevity of description, specific working procedures of the above-described systems, apparatuses and units may refer to corresponding procedures in the foregoing method embodiments, and are not repeated herein.

In the several embodiments provided by the present application, it should be understood that the disclosed apparatus and method may be implemented in other manners. For example, the apparatus embodiments described above are merely illustrative, and for example, the division of the units is merely a logical function division, and there may be additional divisions when actually implemented, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted or not performed. Alternatively, the coupling or direct coupling or communication connection shown or discussed with each other may be an indirect coupling or communication connection via some interfaces, devices or units, which may be in electrical, mechanical or other form.

As used in this specification, the terms "component," "module," "system," and the like are intended to refer to a computer-related entity, either hardware, firmware, a combination of hardware and software, or software in execution. For example, a component may be, but is not limited to being, a process running on a processor, an object, an executable, a thread of execution, a program, and/or a computer. By way of illustration, both an application running on a computing device and the computing device can be a component. One or more components may reside within a process and/or thread of execution and a component may be localized on one computer and/or distributed between 2 or more computers. Furthermore, these components can execute from various computer readable media having various data structures stored thereon. The components may communicate by way of local and/or remote processes such as in accordance with a signal having one or more data packets (e.g., data from two components interacting with one another in a local system, distributed system, and/or across a network such as the internet with other systems by way of the signal).

It is to be appreciated that the processor in embodiments of the application may be a central processing unit (Central Processing Unit, CPU), other general purpose processor, digital signal processor (Digital Signal Processor, DSP), application specific integrated circuit (Application Specific Integrated Circuit, ASIC), field programmable gate array (Field Programmable Gate Array, FPGA) or other programmable logic device, transistor logic device, hardware components, or any combination thereof. The general purpose processor may be a microprocessor, but in the alternative, it may be any conventional processor.

The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in the embodiments of the present application may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit.

The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution, in the form of a software product stored in a storage medium, comprising several instructions for causing a computer device (which may be a personal computer, a server, a network device, etc.) to perform all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (Random Access Memory, RAM), a magnetic disk, or an optical disk, or other various media capable of storing program codes.

In various embodiments of the application, where no special description or logic conflict exists, terms and/or descriptions between the various embodiments are consistent and may reference each other, and features of the various embodiments may be combined to form new embodiments based on their inherent logic.

It should be understood that, in the embodiment of the present application, the numbers "first" and "second" … are merely for distinguishing different objects, for example, for distinguishing different network devices, and are not limited to the scope of the embodiment of the present application, but the embodiment of the present application is not limited thereto.

In the present application, "for indicating" may include for direct indication and for indirect indication. When describing that certain indication information is used for indicating A, the indication information may be included to directly indicate A or indirectly indicate A, and does not represent that the indication information is necessarily carried with A.

The specific indication means may be any of various existing indication means, such as, but not limited to, the above indication means, various combinations thereof, and the like. Specific details of various indications may be referred to the prior art and are not described herein. As can be seen from the above, for example, when multiple pieces of information of the same type need to be indicated, different manners of indication of different pieces of information may occur. In a specific implementation process, a required indication mode can be selected according to specific needs, and the selected indication mode is not limited in the embodiment of the present application, so that the indication mode according to the embodiment of the present application is understood to cover various methods that can enable a party to be indicated to learn information to be indicated.

It should also be understood that, in various embodiments of the present application, the sequence numbers of the foregoing processes do not mean the order of execution, and the order of execution of the processes should be determined by the functions and internal logic thereof, and should not constitute any limitation on the implementation process of the embodiments of the present application.

It should also be understood that, in the present application, "when …", "if" and "if" all refer to the corresponding processing that the network element will make under some objective condition, and are not limited in time, nor do they require that the network element must have a judging action when implemented, nor are other limitations meant to be present.

It should also be understood that in embodiments of the present application, "B corresponding to A" means that B is associated with A from which B may be determined. It should also be understood that determining B from a does not mean determining B from a alone, but may also determine B from a and/or other information.

It should also be understood that the term "and/or" is merely one association relationship describing the associated object, and means that three relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.

Items appearing in the present application that are similar to "include one or more of the following: the meaning of the expressions a, B, and C "generally means that the item may be any one of the following unless otherwise specified: a, A is as follows; b, a step of preparing a composite material; c, performing operation; a and B; a and C; b and C; a, B and C; a and A; a, A and A; a, A and B; a, a and C, a, B and B; a, C and C; b and B, B and C, C and C; c, C and C, and other combinations of a, B and C. The above is an optional entry for the item exemplified by 3 elements a, B and C, when expressed as "the item includes at least one of the following: a, B, … …, and X ", i.e. when there are more elements in the expression, then the entry to which the item is applicable can also be obtained according to the rules described above.

It will be appreciated that the various numerical numbers referred to in the embodiments of the present application are merely for ease of description and are not intended to limit the scope of the embodiments of the present application. The sequence number of each process does not mean the sequence of the execution sequence, and the execution sequence of each process should be determined according to the function and the internal logic.

The foregoing is merely illustrative of the present application, and the present application is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A method of transmitting a signal, comprising:

generating and transmitting a first optical signal;

receiving a second optical signal, the second optical signal comprising reflected and scattered signals of the first optical signal;

converting the second optical signal into a first electrical signal;

determining a first heterodyne frequency value of the first electrical signal;

determining a second heterodyne frequency value from a first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal, wherein the eigenvalues of the first electrical signal include: power spectral density, signal-to-noise ratio, dynamic range, dead zone;

and generating and transmitting a third optical signal according to the second heterodyne frequency value.

2. The method of claim 1, wherein the determining a second heterodyne frequency value from the first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal comprises:

converting the first electrical signal into a first digital signal;

converting the first digital signal into a first time domain signal;

converting the first time domain signal into a first frequency domain signal;

the second difference frequency value is determined from one or more eigenvalues of the first frequency domain signal.

3. The method of claim 2, wherein the determining a second heterodyne frequency value from the first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal further comprises:

converting the first frequency domain signal into a second time domain signal;

the second exogenous frequency value is determined from one or more characteristic values of the second time-domain signal.

4. A method according to claim 3, further comprising, prior to said determining a second heterodyne frequency value from a first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal:

and judging the second outer difference frequency value, wherein the second outer difference frequency value is sent when the absolute value of the difference value between the first outer difference frequency value and the second outer difference frequency value of the first electric signal is larger than a judging threshold value.

5. A method according to any of claims 1-3, wherein said generating and transmitting a third optical signal in accordance with said second heterodyne frequency value comprises:

determining a second digital signal according to the second heterodyne frequency value, wherein the second digital signal has signal characteristics of the second heterodyne frequency value;

Converting the second digital signal into a second electrical signal;

amplifying the second electric signal to obtain a third electric signal;

converting the third electrical signal into the third optical signal.

6. The method of any of claims 1-5, wherein the heterodyne frequency value of the first optical signal is non-zero.

7. An apparatus for transmitting a signal, comprising:

the laser emission module is used for generating and sending a first optical signal;

a receiving module for receiving a second optical signal comprising reflected and scattered signals of the first optical signal;

the receiving module is further configured to convert the second optical signal into a first electrical signal;

the signal feedback control module is used for determining a first heterodyne frequency value of the first electric signal;

the signal feedback control module is further configured to determine a second heterodyne frequency value according to the first heterodyne frequency value of the first electrical signal and one or more eigenvalues of the first electrical signal, wherein the eigenvalues of the first electrical signal include: power spectral density, signal-to-noise ratio, dynamic range, dead zone;

and the signal generating module is used for generating and transmitting a third optical signal according to the second differential frequency value.

8. The apparatus of claim 7, wherein the signal feedback control module comprises:

the analog-to-digital conversion unit is used for converting the first electric signal into a first digital signal;

the framing calculation unit is used for converting the first digital signal into a first time domain signal;

a time-frequency transformation calculation unit, configured to convert the first time-domain signal into a first frequency-domain signal;

a calculation unit for determining the second difference frequency value from one or more eigenvalues of the first frequency domain signal.

9. The apparatus of claim 8, wherein the signal feedback control module further comprises:

and the time-frequency inverse transformation unit is used for converting the first frequency domain signal into a second time domain signal.

10. The apparatus of claim 9, wherein the signal feedback control module further comprises:

and the judging unit is used for judging the second outer difference frequency value, wherein when the absolute value of the difference value between the first outer difference frequency value and the second outer difference frequency value of the first electric signal is larger than a judging threshold value, the second outer difference frequency value is sent.

11. The apparatus according to any one of claims 7-10, wherein the signal generation module comprises:

A digital signal generating unit for determining a second digital signal according to the second exogenous frequency value, wherein the second digital signal has the signal characteristics of the second exogenous frequency value;

a first digital-to-analog conversion unit for converting the second digital signal into a second electrical signal;

the signal amplifying unit is used for amplifying the second electric signal to obtain a third electric signal;

and an electro-optic modulator for converting the third electrical signal into the third optical signal.

12. A chip, comprising: a processor for calling and running a computer program from a memory, causing a communication device on which the chip is mounted to perform the method of any one of claims 1 to 6.