CN115900787B - Method and system for realizing spectrum domain reflectometer - Google Patents
Method and system for realizing spectrum domain reflectometerInfo
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- CN115900787B CN115900787B CN202211606823.XA CN202211606823A CN115900787B CN 115900787 B CN115900787 B CN 115900787B CN 202211606823 A CN202211606823 A CN 202211606823A CN 115900787 B CN115900787 B CN 115900787B
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Abstract
The invention provides a spectrum domain reflectometer system and an implementation method thereof, wherein the spectrum domain reflectometer system comprises a light source module, a signal processing module and a signal processing module, wherein the light source module generates a local light signal and a detection light signal with comb spectrum, the local light signal is directly connected with the coherent detection module, the detection light signal enters an optical fiber to be detected from the rear part of a passive light path module, a backscattering signal returned from the optical fiber to be detected enters the coherent detection module through the passive light path module, the backscattering signal enters the coherent detection module and is output into a sensing electric signal after being beaten with the local light, the other part of the backscattering signal directly enters the coherent detection module and is output into a reference electric signal after being beaten with the local light, and the sensing electric signal and the reference electric signal are input into the signal processing module for data demodulation, so that the intensity and phase distribution signal of the backscattering signal on an optical fiber link can be obtained.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a method and a system for realizing a spectrum domain reflectometer, and more particularly relates to a method and a system for detecting back scattering in an optical fiber and determining the intensity and the phase of the back scattering.
Background
Light reflectometry is a technique that is capable of detecting and locating backscattered light (e.g., rayleigh scattering) signals in an optical fiber. And the detection of the loss of the optical fiber link, the measurement of physical quantities such as environmental strain and temperature and the like are realized by analyzing the information of the intensity or the phase of the back scattering optical signals at different positions of the optical fiber.
According to the positioning principle of the backward scattered light signals, the existing optical reflectometer mainly comprises three types of optical time domain reflectometers, optical frequency domain reflectometers and optical coherence domain reflectometers.
The optical time domain reflectometer transmits detection pulses, receives back scattered light generated by the detection pulses, determines the position of scattering according to the time of returning the back scattered light, and has the advantages that the shorter the duration of the detection pulses is, the higher the spatial resolution is, but the worse the signal to noise ratio of the back scattered light is, the contradiction between the spatial resolution and the detection signal to noise ratio ensures that the spatial resolution of the reflectometer is not high, and is generally more than 1 meter;
The optical frequency domain reflectometer adopts a linear tuning light source and a coherent receiving mode, the scattered light signal and the local light are beaten, the time delay of the scattered light signal is mapped into the frequency of the beated signal, the spatial resolution of the scheme depends on the frequency tuning range of the light source and is not limited by the duration of the detected light, but the scheme needs a sweep frequency light source with high linearity and low phase noise, and the light source is very expensive.
The optical coherence domain reflectometer adopts low coherence light as a light source, and can observe interference signals only when the optical path of scattered light is the same as that of local light, so that high spatial resolution can be realized, but the measurement distance is generally short.
Patent document CN113014313a (application number: 201911328434.3) discloses an optical time domain reflectometer, which comprises a laser for emitting a detection light source, a modulator for converting the detection light source into a first pulse signal and a second pulse signal and for transmitting the first pulse signal to an optical fiber to be measured so that the optical fiber to be measured generates a reflected signal, a coupler for coupling the second pulse signal and the reflected signal of the optical fiber to be measured into an optical signal, a photoelectric conversion module for converting the optical signal into an electrical signal, and a programmable module for adjusting the detection light source emitted by the laser according to the electrical signal.
Patent document CN114964329a (application number: 202210559130.3) discloses a double-sideband optical frequency domain reflectometer, which comprises a modulation signal generating unit, a sensing signal receiving unit and a signal processing unit, wherein the modulation signal generating unit generates double-sideband detection light waves in an external modulation mode, the detection light waves are divided into two paths, one path is used as detection light to be input into an optical fiber to be detected, the other path is used as local light to be input into the sensing signal receiving unit, the optical fiber to be detected couples the change of external physical quantity to the detection light waves, and a backward rayleigh scattering signal generated by the optical fiber to be used as signal light to be transmitted back to the sensing signal receiving unit, the sensing signal receiving unit uses a frequency shift method or an IQ receiving method to divide two different beat signals generated by frequency sweeping of two sidebands from the double-sideband signal light, and the signal processing unit performs fourier transformation on the two different beat signals after time domain alignment according to the frequency sweep range, so as to obtain the intensity and phase information of rayleigh scattering on the optical fiber.
Patent document CN203617996U (application number 201320800522.0) discloses a coherent optical time domain reflectometer device, which is characterized by comprising a laser, an optical beam splitter, a pair of pulse generating devices, an optical circulator and a photodetector. A coherent light time domain reflection measurement method is characterized in that test pulse light is adopted to obtain scattering/reflection information of a device to be measured, local pulse light is adopted to interfere with scattered/reflected light signals, the respective repetition frequencies of the test pulse light and the local pulse light are adjusted to completely construct reflected/scattered light signals, and then photoelectric conversion and analog-to-digital conversion are carried out to obtain scattering/reflected light position information, pulse widths of the test pulse light and the local pulse light are adapted to required spatial resolution, and adjacent pulse distances are far larger than pulse widths.
Disclosure of Invention
In view of the defects in the prior art, the invention aims to provide a spectrum domain reflectometer system and an implementation method.
The spectrum domain reflectometer system comprises a light source module, a coherent detection module, a passive optical path module, a signal processing module and a signal processing module, wherein the light source module generates a local light signal and a detection light signal with comb spectrum, the local light signal is directly connected with the coherent detection module, a part of the detection light signal enters an optical fiber to be detected after passing through the passive optical path module, a back scattering signal returned from the optical fiber to be detected enters the coherent detection module through the passive optical path module and is subjected to beat frequency with the local light to output a sensing electric signal, the other part of the detection light signal directly enters the coherent detection module and is subjected to beat frequency with the local light to output a reference electric signal, and the sensing electric signal and the reference electric signal are both input into the signal processing module to be subjected to data demodulation to obtain the intensity and phase distribution signal of the back scattering signal on an optical fiber link.
Preferably, the light source module is Shan Guangshu light source module, and the light source module comprises a narrow linewidth laser light source or an optical frequency comb light source, a signal generator, a phase or intensity modulator, an acousto-optic modulator, a first coupler and an optical filter;
The narrow-linewidth laser light source is divided into a local light path and a detection light path by the first coupler, the local light path is input into the acousto-optic modulator to enable narrow-band laser to generate frequency shift to obtain a local optical signal, and the narrow-band laser corresponding to the detection light path is modulated in the phase or modulator by a periodic signal generated by the signal generator to generate a detection optical signal with a comb spectrum.
The optical frequency comb light source is divided into a local light path and a detection light path by the first coupler, the local light path is input into the optical filter and filtered to obtain a single-frequency comb tooth, so that a local optical signal is obtained, and the detection light path is the optical frequency comb light source and generates the optical signal with a comb spectrum.
Preferably, the light source module is a dual-light comb light source module, and two light frequency combs with small difference in repetition frequency are simultaneously generated to serve as local light and detection light respectively.
Preferably, the passive optical path module comprises a first coupler, a third coupler and an optical circulator;
The detection optical signal with the comb spectrum enters the first coupler to be divided into two paths, one path of optical signal with larger energy enters the optical circulator to be connected with the optical fiber to be detected, and the optical signal with smaller energy enters the fourth coupler; and returning a back scattering signal from the optical fiber to be tested to enter the second coupler, entering the third coupler by a local optical signal, entering the second coupler by a path of optical signal with higher beam splitting ratio, and entering the fourth coupler by a path of optical signal with smaller beam splitting ratio.
Preferably, the coherent detection module comprises a second coupler, a fourth coupler, a first balanced photoelectric detector and a second balanced photoelectric detector;
The local light and the detection light signals output by the passive light path module are subjected to beat frequency at the second coupler and the fourth coupler respectively, the generated beat frequency light signals are input into the first balance photoelectric detector and the second balance photoelectric detector respectively, the first balance photoelectric detector and the second balance photoelectric detector convert the beat frequency light signals into electric signals, and the sensing electric signals and the reference electric signals are output respectively.
Preferably, the signal processing module comprises a data acquisition card and a digital signal processor;
The data acquisition card is used for acquiring and storing the input sensing electric signals and the reference electric signals, and the acquired sensing electric signals and the acquired reference electric signals are input into the digital signal processor for signal demodulation.
Preferably, in the signal processing module, the sensing electric signal and the reference electric signal are digitized by using an analog-to-digital converter, then the frequency spectrums of the sensing electric signal and the reference electric signal are obtained respectively by using fourier transformation, the frequency spectrums of the reference electric signal are subjected to phase conjugation, the modulus value is inverted, and then multiplied by the frequency spectrums of the sensing electric signal, and the result is subjected to inverse fourier transformation to obtain the intensity and phase information of the back scattering signal on the optical fiber to be detected.
The invention provides an implementation method of a spectrum domain reflectometer, which comprises the steps that a light source module generates a local light signal and a detection light signal with comb spectrum, the local light signal is directly connected with a coherent detection module, the detection light signal enters an optical fiber to be detected from the rear part of a passive optical path module, a back scattering signal returned from the optical fiber to be detected enters the coherent detection module through the passive optical path module, the back scattering signal enters the coherent detection module from the passive optical path module, the back scattering signal is output after being beaten with the local light, the other part of the back scattering signal directly enters the coherent detection module, a reference electric signal is output after being beaten with the local light, and the sensing electric signal and the reference electric signal are input into a signal processing module for data demodulation, so that the intensity and phase distribution signal of the back scattering signal on an optical fiber link are obtained.
Preferably, when the light source module is Shan Guangshu light source modules, the light source module comprises a narrow linewidth laser light source, a pulse generator, a phase modulator, an acousto-optic modulator and a first coupler;
The narrow-line-width laser light source is divided into a local light path and a detection light path by the first coupler, wherein the local light path is input into the acousto-optic modulator to enable narrow-band laser to generate frequency shift to obtain a local optical signal;
When the light source module is a double-light comb light source module, the light source module comprises a narrow linewidth laser light source, a pulse generator, a first phase modulator, a second phase modulator, a first coupler, a first light filter and a second light filter;
The narrow linewidth laser light source is divided into a local light path and a detection light path through the first coupler, the local light path and the detection light path are respectively input into the first phase modulator and the second phase modulator, the first phase modulator and the second phase modulator are respectively modulated by different sequences generated by the pulse generator, an output light signal of the first phase modulator enters the first optical filter to be subjected to filtering processing to obtain an optical comb signal in a required frequency range and is output as a detection light signal, and an output light of the second phase modulator enters the second optical filter to be subjected to filtering processing to obtain an optical comb signal in the required frequency range and is output as a local light signal.
Preferably, the passive optical path module comprises a second coupler, a fourth coupler and an optical circulator;
The optical signal with the energy of 90% is connected with an optical fiber to be tested, the optical signal with the energy of 10% is connected with a fifth coupler, a backward scattered signal is returned from the optical fiber to be tested and enters the third coupler, the local optical signal with the comb spectrum enters the fourth coupler to respectively obtain the optical signal with the energy of 90% and the optical signal with the energy of 10%, the optical signal with the energy of 90% enters the third coupler, and the optical signal with the energy of 10% enters the fifth coupler;
the coherent detection module comprises a third coupler, a fifth coupler, a first balanced photoelectric detector and a second balanced photoelectric detector;
The local light and the detection light signals output by the passive light path module are subjected to beat frequency at the third coupler and the fifth coupler respectively, and the generated beat frequency light signals are input into the first balance photoelectric detector and the second balance photoelectric detector respectively;
the signal processing module comprises a data acquisition card and a digital signal processor;
The input sensing electric signals and reference electric signals are acquired and stored through a data acquisition card, and the acquired sensing electric signals and reference electric signals are input into a digital signal processor for signal demodulation;
In the signal processing module, the sensing electric signal and the reference electric signal are digitized by using an analog-to-digital converter, then the frequency spectrums of the sensing electric signal and the reference electric signal are obtained by using Fourier transformation, the frequency spectrums of the reference electric signal are subjected to phase conjugation, the modulus value is inverted, and then multiplied by the frequency spectrums of the sensing electric signal, and the result is subjected to Fourier inverse transformation to obtain the intensity and phase information of the back scattering signal on the optical fiber to be detected.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention breaks through the contradiction between the spatial resolution and the detection signal-to-noise ratio by utilizing the technical characteristics of continuous light and spectrum sampling, and realizes the technical effects of higher spatial resolution and dynamic range;
2. the invention realizes the technical effects of avoiding the nonlinearity of sweep frequency, greatly simplifying the complexity of the system and ensuring the stability and the accuracy of the system performance through the technical characteristics of a non-sweep frequency light source (namely an optical comb);
3. by using the technical characteristics of the coherent light source, the invention realizes the technical effect that the signal can be observed without adjusting the coherence length as long as the optical path difference between the detection path and the reference path does not exceed the coherence length of the light source under the condition of not compensating phase noise.
4. The invention avoids a series of problems caused by the nonlinearity of the sweep frequency light source, reduces the cost and the system complexity of the reflection of the optical frequency domain, and has high positioning precision, high signal-to-noise ratio and longer measurable distance compared with an optical time domain reflectometer and an optical coherence domain reflectometer.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
fig. 1 is a system block diagram of a spectral domain reflectometer scheme.
FIG. 2 is a block diagram of a single frequency laser source as a single optical comb light source.
FIG. 3 is a block diagram of an optical frequency comb as a single optical comb light source.
Fig. 4 is a dual optical comb light source module.
In FIG. 1, a 1-light source module, a 2-optical coupler, a 3-optical circulator, a 4-second coupler, a 5-third coupler, a 6-fourth coupler, a 7-first balance detector, an 8-second balance detector, a 9-data acquisition card and a 10-signal processing unit are shown.
In FIG. 2, a 1-narrow linewidth laser source, a 2-optocoupler, a 3-signal generator, a 4-modulator, and a 5-modulator.
In FIG. 3, a 1-optical frequency comb laser source, a 2-optical coupler, and a 3-optical filter.
In FIG. 4, a 1-double optical comb laser source.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
Example 1
Aiming at the defects of the existing reflectometer in performance index and device cost, the invention provides a spectral domain reflectometer method and a system, which can realize distributed measurement of a sensing element to be measured without frequency sweep by utilizing a detection light signal with comb spectrum, can realize high spatial resolution, avoid adverse effects caused by frequency sweep nonlinearity and simplify the system structure.
The invention discloses a spectrum domain reflectometer system realized by utilizing a single optical comb, which comprises a light source module, a passive light path module, a coherent detection module and a signal processing module, wherein the output of the light source module is divided into a detection light path and a local light path and is respectively input into a first coupler 2 and a third coupler 5, the first coupler 2 divides an incident detection light path into two parts, one part with larger energy enters a No. 1 port of an optical circulator 3 and is output to an optical fiber to be detected through a 2 port, the Rayleigh back scattered light generated by the optical fiber to be detected is input into the optical circulator 3 through the 2 port of the optical circulator 3 and is input into a second coupler 4 through the 3 port, and the other part with lower energy is input into a fourth coupler 6. The local light is split into two equal energy parts by the third coupler 5 and is input to the second coupler 4 and the fourth coupler 6, respectively. The local light and the detection light signals are subjected to beat frequency at the second coupler 4 and the fourth coupler 6, the generated beat frequency light signals are respectively input into the first balance photoelectric detector 7 and the second balance photoelectric detector 8, the balance photoelectric detectors convert the beat frequency light signals into electric signals and input into the data acquisition card 9 for subsequent signal processing and data demodulation, and the intensity and the phase of the backward astigmatism are obtained.
The passive optical path module comprises a first coupler 2, a third coupler 5 and an optical circulator 3, wherein the first coupler 2 is a 90:10 optical fiber coupler, 90% of output ports are 1 port, 10% of output ports are 2 ports, and the third coupler 5 is a 50:50 coupler.
The coherent detection module comprises a second coupler 4, a fourth coupler 6, a first balance detector 7 and a second balance detector 8. The second coupler 4 and the fourth coupler 6 are both 50:50 couplers.
The bandwidths of the first balance detector 7 and the second balance detector 8 are 1.6GHz.
The signal processing module comprises a data acquisition card 9 and a signal processing unit 10.
The data acquisition card 9 samples the input electric signal and inputs the original data into the signal processing unit 10 for data demodulation.
The sampling rate f c = 1GHz of the data acquisition card 9, and the resolution is 8 bits.
The specific steps of this embodiment are as follows:
Step 1, turning on a laser to enable a light source module to be in a working state, recording optical power signals detected by two balance detectors, obtaining a detection light receiving signal I 1 (t) by an output electric signal of a first balance detector, and carrying out Fourier transformation on the detection light receiving signal I 1 (t) to obtain frequency domain information I 1 (f) of a detection path electric signal.
Step 2, after obtaining the signals received by the first and second balance detectors, performing Fourier transform on the output signal I 2 (t) of the second balance detector to obtain frequency domain information I 2 (f), and multiplying I 1 (f)Then divided by the product of I 1 (f) and I 2 (f), i.eWherein represents conjugation.
And 3, performing inverse Fourier transform on R (f) to obtain a Rayleigh reflectivity curve, namely { R (t) =IFFT (R (f)) }. The position of a certain point on the optical fiber to be measured isWhere c is the speed of light in vacuum, n is the effective refractive index of the fiber, f c is the system sampling rate in hertz (Hz), and k is the index value corresponding to that point.
And 4, amplifying and acquiring the spatial resolution at the position of the reflection peak. The spatial resolution of the present embodiment is determined by the frequency coverage of the probe optical frequency comb, i.eWherein B is the frequency coverage bandwidth of the optical comb, and the actual spatial resolution is defined by the full width at half maximum of the reflection peak.
Example 2
Embodiment 2 is one implementation of a single optical comb system light source module. As shown in fig. 2, the present embodiment includes a narrow linewidth laser source 1, a first coupler 2, a signal generator 3, a modulator 4, and an acousto-optic modulator 5.
Preferably, the line width of the narrow line width laser source is smaller than 1kHz;
The coupler is a 50:50 optical fiber coupler;
the modulator is a phase or intensity modulator,
The specific steps of this embodiment are as follows:
Step 1, firstly, pre-written data are loaded into a signal generator 3, an output signal is connected into a phase or intensity modulator 4, a laser 1 is started, an output optical signal is divided into two parts with equal energy through a first coupler 2, one part of the output optical signal enters the phase or intensity modulator 4, and the other part of the output optical signal enters an acousto-optic modulator 5. The outputs of the phase or intensity modulator 4 and the acousto-optic modulator 5 are respectively used as a detection path and a local path optical signal, and are connected into a subsequent optical system.
Example 3
Embodiment 3 is one implementation of a single optical comb system light source module. As shown in fig. 3, the present embodiment includes an optical frequency comb laser source 1, a first coupler 2, and an optical filter 3.
The optical filter is a tunable optical filter.
The specific steps of this embodiment are as follows:
The laser 1 is started, an output optical signal is divided into two parts with equal energy through the first coupler 2, one part is directly used as a detection path signal output to be connected into a subsequent optical path, the other part enters the optical filter 3, the center frequency of the optical filter 3 is adjusted, and comb teeth at one frequency are selected to be used as local path optical signals to be connected into a subsequent optical system.
Example 4
Embodiment 4 is one implementation of a dual optical comb system light source module. As shown in fig. 4, the present embodiment includes a double optical comb light source 1.
The double-optical comb light source can be generated by an electro-optical modulation or mode-locking laser;
the specific steps of this embodiment are as follows:
The double-optical comb light source is in a working state and is connected with a subsequent optical system.
Those skilled in the art will appreciate that the systems, apparatus, and their respective modules provided herein may be implemented entirely by logic programming of method steps such that the systems, apparatus, and their respective modules are implemented as logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers, etc., in addition to the systems, apparatus, and their respective modules being implemented as pure computer readable program code. Therefore, the system, the device and the respective modules thereof provided by the invention can be regarded as a hardware component, and the modules for realizing various programs included therein can be regarded as a structure in the hardware component, and the modules for realizing various functions can be regarded as a structure in the hardware component as well as a software program for realizing the method.
The foregoing describes specific embodiments of the present application. It is to be understood that the application is not limited to the particular embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without affecting the spirit of the application. The embodiments of the application and the features of the embodiments may be combined with each other arbitrarily without conflict.
Claims (6)
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