CN115900787A - Method and system for realizing spectral domain reflectometer - Google Patents
Method and system for realizing spectral domain reflectometer Download PDFInfo
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Abstract
The invention provides a spectral domain reflectometer system and an implementation method, comprising the following steps: the light source module generates a local light signal and a probe light signal with comb spectrum, the local light signal is directly connected with the coherent detection module, a part of the probe light signal enters the optical fiber to be detected after passing through the passive optical path module, a backward scattering signal returned from the optical fiber to be detected enters the coherent detection module through the passive optical path module, and outputs a sensing electrical signal after being subjected to beat frequency with the local light; the other part directly enters a coherent detection module, and outputs a reference electric signal after being subjected to beat frequency with local light; the sensing electric signal and the reference electric signal are input into the signal processing module for data demodulation, and the strength and phase distribution signal of the backscattering signal on the optical fiber link is 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 spectral domain reflectometer, and more particularly to a method and a system for detecting backscattering in an optical fiber and determining the intensity and the phase of the backscattering.
Background
Optical reflectometry is a technique capable of detecting and locating backscattered light (e.g., rayleigh scattering) signals in an optical fiber. The detection of the loss of the optical fiber link and the measurement of physical quantities such as environmental strain, temperature and the like are realized by analyzing the strength or phase information of the backward scattering optical signals at different positions of the optical fiber.
According to the positioning principle of the back scattering optical signals, the existing optical reflectometer mainly comprises three types of optical time domain reflectometer, optical frequency domain reflectometer and optical coherent domain reflectometer.
The optical time domain reflectometer emits a detection pulse, receives backward scattering light generated by the detection pulse, and determines the position of scattering according to the time of returning of the backward scattering light, wherein the shorter the duration of the detection pulse is, the higher the spatial resolution is, but the poorer the signal-to-noise ratio of the backward scattering light is, and the contradiction between the spatial resolution and the detection signal-to-noise ratio causes the spatial resolution of the reflectometer to be not high, generally greater than 1 meter;
the optical frequency domain reflectometer adopts a linear tuning light source and a coherent receiving mode to beat frequency of a scattered light signal and local light, and maps time delay of the scattered light signal into frequency of a beat frequency signal.
The optical coherence domain reflectometer adopts low coherence light as a light source, and only when the optical path of scattered light is the same as that of local light, interference signals can be observed, 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 includes: a laser for emitting a detection light source; the modulator is used for converting the detection light source into a first pulse signal and a second pulse signal and sending the first pulse signal to the optical fiber to be detected so that the optical fiber to be detected generates a reflection signal; the coupler is used for coupling the second pulse signal and the reflected signal of the optical fiber to be detected into an optical signal; the photoelectric conversion module is used for converting the optical signal into an electric signal; and the programmable module is used for adjusting the detection light source emitted by the laser according to the electric signal.
Patent document CN114964329A (application number: 202210559130.3) discloses a double-sideband optical frequency domain reflectometer, comprising: the device 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 and input into an optical fiber to be detected, the other path is used as local light and input into the sensing signal receiving unit, the optical fiber to be detected couples the change of external physical quantity onto the detection light waves, backward Rayleigh scattering signals generated by the change are used as signal light and are transmitted back to the sensing signal receiving unit, the sensing signal receiving unit divides two different beat frequency signals generated by two sideband frequency sweeps from the double-sideband signal light by using a frequency shift method or an IQ (orthogonal frequency division) receiving method, and the signal processing unit performs Fourier transform on the two different beat frequency signals after aligning in a time domain according to a frequency sweep range to obtain the strength and phase information of Rayleigh scattering on the optical fiber.
Patent document CN203617996U (application number: 201320800522.0) discloses a coherent optical time domain reflectometer apparatus, which is characterized in that: the device comprises a laser, an optical beam splitter, a pair of pulse generating devices, an optical circulator and a photoelectric detector. A coherent optical time domain reflectometry method is characterized in that: acquiring scattering/reflecting information of a tested device by adopting test pulse light, interfering local pulse light with optical signals scattered/reflected back, completely constructing reflected/scattered optical signals by adjusting respective repetition frequencies of the test pulse light and the local pulse light, and acquiring scattering/reflected light position information by photoelectric conversion and analog-to-digital conversion; the pulse widths of the test pulse light and the local pulse light are adaptive to the required spatial resolution, and the adjacent pulse distance is far larger than the pulse width.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a spectral domain reflectometer system and an implementation method.
According to the present invention there is provided a spectral domain reflectometry system, comprising: the light source module generates a local light signal and a probe light signal with comb spectrum, the local light signal is directly connected with the coherent detection module, a part of the probe light signal enters the optical fiber to be detected after passing through the passive optical path module, a backward scattering signal returned from the optical fiber to be detected enters the coherent detection module through the passive optical path module, and outputs a sensing electrical signal after being subjected to beat frequency with the local light; the other part directly enters a coherent detection module, and outputs a reference electric signal after being subjected to beat frequency with local light; the sensing electric signal and the reference electric signal are input into the signal processing module for data demodulation, and the strength and phase distribution signal of the backscattering signal on the optical fiber link is obtained.
Preferably, the light source module is a single optical comb light source module, and the light source module includes: the device comprises a narrow line width laser light source or light 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 through the first coupler; the local light path is input into the acousto-optic modulator to enable narrow-band laser to generate frequency shift, and a local optical signal is obtained; the narrow-band laser corresponding to the detection optical path is modulated by the periodic signal generated by the signal generator in the phase or modulator to generate a detection optical signal with a comb-shaped spectrum.
The optical frequency comb light source is divided into a local light path and a detection light path through the first coupler; the local optical path is input into the optical filter to be filtered to obtain a single-frequency comb tooth, and a local optical signal is obtained; the detection optical path is used for generating an optical signal with a comb spectrum for the optical frequency comb light source.
Preferably, the light source module is a dual-optical comb light source module, and two optical frequency combs with slightly different repetition frequencies are simultaneously generated and respectively used as the local light and the probe light.
Preferably, the passive optical circuit module comprises a first coupler, a third coupler and an optical circulator;
the detection optical signal with the comb spectrum enters the first coupler and is 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; returning a back scattering signal from the optical fiber to be tested to enter a second coupler; and the local optical signal enters the third coupler, the optical signal with higher beam splitting ratio enters the second coupler, and the optical signal with smaller beam splitting ratio enters the fourth coupler.
Preferably, the coherent detection module comprises: a second coupler, a fourth coupler, a first balanced photodetector, and a second balanced photodetector;
the local light and the detection light signals output by the passive optical path module are respectively subjected to beat frequency at the second coupler and the fourth coupler, and generated beat frequency light signals are respectively input into the first balanced photoelectric detector and the second balanced photoelectric detector; the first balanced photoelectric detector and the second balanced photoelectric detector convert beat frequency optical signals into electric signals and respectively output sensing electric signals and reference electric signals.
Preferably, the signal processing module includes: 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 reference electric signals are input into the digital signal processor for signal demodulation.
Preferably, in the signal processing module, the sensing electrical signal and the reference electrical signal are digitized by an analog-to-digital converter, then the frequency spectrums of the sensing electrical signal and the reference electrical signal are obtained by fourier transform, the phase of the frequency spectrum of the reference electrical signal is conjugated, the modulus value is reciprocal, then the reciprocal is multiplied by the frequency spectrum of the sensing electrical signal, and the inverse fourier transform is performed on the result, so that the strength and phase information of the back scattering signal on the optical fiber to be measured are obtained.
The implementation method of the spectral domain reflectometer provided by the invention comprises the following steps: the light source module generates a local light signal and a probe light signal with comb spectrum, the local light signal is directly connected with the coherent detection module, a part of the probe light signal enters the optical fiber to be detected after passing through the passive optical path module, a backward scattering signal returned from the optical fiber to be detected enters the coherent detection module through the passive optical path module, and outputs a sensing electrical signal after being subjected to beat frequency with the local light; the other part directly enters a coherent detection module, and outputs a reference electric signal after beat frequency with local light; the sensing electric signal and the reference electric signal are input into the signal processing module for data demodulation, and the strength and phase distribution signal of the backscattering signal on the optical fiber link is obtained.
Preferably, when the light source module is a single optical comb light source module, the light source module includes: the device comprises a narrow linewidth laser light source, a pulse generator, a phase modulator, an acousto-optic modulator and a first coupler;
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 is input into the acousto-optic modulator to enable narrow-band laser to generate frequency shift to obtain a local optical signal; narrow-band laser corresponding to the detection optical path is modulated by the pulse generated by the pulse generator in the phase modulator to generate a detection optical signal with a comb spectrum;
when the light source module is a dual optical comb light source module, the light source module includes: the device comprises a narrow-linewidth laser light source, a pulse generator, a first phase modulator, a second phase modulator, a first coupler, a first optical filter and a second optical filter;
the narrow linewidth laser light source is equally divided into a local light path and a detection light path through the first coupler; the local optical path and the detection optical path are respectively input into the first phase modulator and the second phase modulator, and the first phase modulator and the second phase modulator are respectively modulated by different sequences generated by the pulse generator; the output optical signal of the first phase modulator enters the first optical filter for filtering processing to obtain an optical comb signal in a required frequency range, and the optical comb signal is output as a detection optical signal; and the output light of the second phase modulator enters the second optical filter for filtering processing to obtain an optical comb signal in a required frequency range, and the optical comb signal is output as a local optical signal.
Preferably, the passive optical circuit module comprises a second coupler, a fourth coupler and an optical circulator;
the detection optical signal with the comb spectrum enters the second coupler to respectively obtain an optical signal with 90% of energy and an optical signal with 10% of energy; an optical signal with 90% of energy enters the optical circulator to be connected with the optical fiber to be tested, and an optical signal with 10% of energy enters the fifth coupler; returning a back scattering signal from the optical fiber to be tested to enter a third coupler; the local optical signal with the comb spectrum enters the fourth coupler to respectively obtain an optical signal with 90% of energy and an optical signal with 10% of energy; an optical signal with energy of 90% enters the third coupler, and an optical signal with energy of 10% enters the fifth coupler;
the coherent detection module includes: a third coupler, a fifth coupler, a first balanced photodetector, and a second balanced photodetector;
the local light and the detection light signals output by the passive optical path module are respectively subjected to beat frequency at the third coupler and the fifth coupler, and generated beat frequency light signals are respectively input to the first balanced photoelectric detector and the second balanced photoelectric detector; the first balanced photoelectric detector and the second balanced photoelectric detector convert beat frequency optical signals into electric signals and respectively output sensing electric signals and reference electric signals;
the signal processing module includes: a data acquisition card and a digital signal processor;
the method comprises the following steps of collecting and storing input sensing electric signals and reference electric signals through a data collection card, and inputting the collected sensing electric signals and reference electric signals into a digital signal processor for signal demodulation;
in the signal processing module, the sensing electrical signal and the reference electrical signal are digitized by an analog-to-digital converter, frequency spectrums of the sensing electrical signal and the reference electrical signal are respectively obtained by Fourier transform, the phase of the frequency spectrum of the reference electrical signal is conjugated, the modulus is inverted, the frequency spectrum of the sensing electrical signal is multiplied, the result is subjected to inverse Fourier transform, and the strength and the phase information of the backscattering signal on the optical fiber to be measured are obtained.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention utilizes the technical characteristics of continuous light and frequency spectrum sampling, breaks through the contradiction between the spatial resolution and the detection signal-to-noise ratio, and realizes the technical effects of higher spatial resolution and dynamic range;
2. according to the invention, through the technical characteristics of a non-sweep frequency light source (namely, an optical comb), the non-linearity of sweep frequency is avoided, the complexity of the system is greatly simplified, and the stable and accurate technical effect of the system performance is ensured;
3. the invention realizes the technical effect that the signal can be observed without adjusting the coherent length under the condition of not compensating the phase noise and as long as the optical path difference between the detection path and the reference path does not exceed the coherent length of the light source by using the technical characteristics of the coherent light source.
4. The invention avoids a series of problems caused by the non-linearity of the frequency sweep light source, and reduces the cost of optical frequency domain reflection and the system complexity; compared with an optical time domain reflectometer and an optical coherent domain reflectometer, the optical coherent domain reflectometer has high positioning precision and signal-to-noise ratio and longer measurable distance.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
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: the device comprises a light source module 1, a light coupler 2, an optical circulator 3, a second coupler 4, a third coupler 5, a fourth coupler 6, a first balanced detector 7, a second balanced detector 8, a data acquisition card 9 and a signal processing unit 10.
In fig. 2: 1-narrow linewidth laser source, 2-optical coupler, 3-signal generator, 4-modulator, 5-modulator.
In FIG. 3: 1-optical frequency comb laser source, 2-optical coupler and 3-optical filter.
In fig. 4: 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 invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the invention.
Example 1
The invention provides a spectral domain reflectometer method and a system aiming at the defects of the existing reflectometer in performance indexes and device cost, can realize distributed measurement on a sensing element to be measured by utilizing a detection optical signal with comb-shaped spectrum without frequency sweep, can realize high spatial resolution, avoids adverse effects caused by frequency sweep nonlinearity, and simplifies the system structure.
As shown in FIG. 1, the present invention discloses a system for realizing spectral domain reflectometry by using a single optical comb, comprising: light source module, passive optical path module, coherent detection module and signal processing module, wherein: the output of the light source module is divided into a detection light path and a local light path, and the detection light path and the local light path are respectively input into the first coupler 2 and the third coupler 5; the first coupler 2 divides an incident detection light path into two parts, one part with larger energy enters the port 1 of the optical circulator 3 and is output to the optical fiber to be detected through the port 2, and Rayleigh back scattering light generated by the optical fiber to be detected is input into the optical circulator 3 through the port 2 of the optical circulator 3 and is input into the second coupler 4 through the port 3; a lower part of the energy is input to the fourth coupler 6. The local light is divided into two parts with equal energy through the third coupler 5 and is respectively input into the second coupler 4 and the fourth coupler 6. The local light and the detection light signals are subjected to beat frequency at the second coupler 4 and the fourth coupler 6, and the generated beat frequency light signals are respectively input into a first balanced photoelectric detector 7 and a second balanced photoelectric detector 8; the balanced photoelectric detector converts the beat frequency optical signal into an electric signal, and the electric signal is input into the data acquisition card 9 for subsequent signal processing and data demodulation to obtain the intensity and phase of backward astigmatism.
The passive optical circuit module comprises: a first coupler 2, a third coupler 5 and an optical circulator 3, wherein the first coupler 2 is a 90.
The coherent detection module comprises a second coupler 4, a fourth coupler 6, a first balanced detector 7 and a second balanced detector 8. The second coupler 4 and the fourth coupler 6 are both 50 couplers.
The bandwidths of the first balanced detector 7 and the second balanced detector 8 are both 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 electrical signals, and inputs the original data into the signal processing unit 10 for data demodulation.
The sampling rate f of the data acquisition card 9 c Resolution is 8bit for 1 GHz.
The specific steps of this example are as follows:
step 1: starting the laser to make the light source module in working state, recording the optical power signals detected by the two balance detectors, and obtaining a detection light receiving signal I from the output electric signal of the first balance detector 1 (t) Fourier transform is performed to obtain frequency domain information I of the probe electrical signal 1 (f)。
Step 2: after obtaining the signals received by the first and the second balanced detectors, the output signal I of the second balanced detector is 2 (t) carrying out Fourier transform to obtain frequency domain information I 2 (f) Is shown by 1 (f) Multiplication by
Then divided by I 1 (f) And I 2 (f) The product of the magnitude, i.e. < >>
Wherein denotes conjugation.
And step 3: then, inverse fourier transform is performed on R (f), so as to obtain a rayleigh reflectance curve, i.e., { R (t) = IFFT (R (f)) }. The position of a point on the optical fiber to be measured is
Wherein: c is the speed of light in vacuum, n isEffective refractive index of optical fiber, f c The system sampling rate is given in hertz (Hz), and k is the index value corresponding to the point.
And 4, step 4: the spatial resolution is obtained by amplification at the position of the reflection peak. The spatial resolution of this embodiment is determined by the frequency coverage of the detecting optical-frequency comb, i.e.
Where B is the optical comb frequency coverage bandwidth and the actual spatial resolution is defined by the full width at half maximum of the reflection peak.
Example 2
Preferably, the line width of the narrow-line width laser source is less than 1kHz;
the coupler is a 50;
the modulator is a phase or intensity modulator,
the specific steps of this example are as follows:
step 1: firstly, pre-programmed data is loaded into a signal generator 3, an output signal is accessed into a phase or intensity modulator 4, a laser 1 is started, the output optical signal is divided into two parts with equal energy through a first coupler 2, one part enters the phase or intensity modulator 4, and the other part 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 optical signals of a detection path and a local path and are connected to a subsequent optical system.
Example 3
The optical filter is a tunable optical filter.
The specific steps of this example are as follows:
and starting the laser 1, dividing an output optical signal into two parts with equal energy through the first coupler 2, directly outputting one part as a detection path signal to be connected to a subsequent optical path, enabling the other part to enter the optical filter 3, adjusting the central frequency of the optical filter 3, selecting a comb tooth at one frequency as a local path optical signal, and connecting the local path optical signal to a subsequent optical system.
Example 4
The double-optical comb light source can be generated by an electro-optical modulation or mode-locked laser;
the specific steps of this example are as follows:
the double-optical comb light source is in a working state and is connected to a subsequent optical system.
Those skilled in the art will appreciate that, in addition to implementing the systems, apparatus, and various modules thereof provided by the present invention in purely computer readable program code, the same procedures can be implemented entirely by logically programming method steps such that the systems, apparatus, and various modules thereof are provided in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system, the apparatus, and the modules thereof provided by the present invention may be considered as a hardware component, and the modules included in the system, the apparatus, and the modules for implementing various programs may also be considered as structures in the hardware component; modules for performing various functions may also be considered to be both software programs for performing the methods and structures within hardware components.
The foregoing description has described specific embodiments of the present invention. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (10)
1. A spectral domain reflectometry system, comprising: the light source module generates a local light signal and a probe light signal with comb spectrum, the local light signal is directly connected with the coherent detection module, a part of the probe light signal enters the optical fiber to be detected after passing through the passive optical path module, a backward scattering signal returned from the optical fiber to be detected enters the coherent detection module through the passive optical path module, and outputs a sensing electrical signal after being subjected to beat frequency with the local light; the other part directly enters a coherent detection module, and outputs a reference electric signal after beat frequency with local light; the sensing electric signal and the reference electric signal are input into the signal processing module for data demodulation, and the strength and phase distribution signal of the backscattering signal on the optical fiber link is obtained.
2. The spectro-domain reflectometry system of claim 1 wherein the light source module is a single comb light source module, said light source module comprising: the device comprises a narrow-linewidth laser light source or light frequency comb light source, a signal generator, a phase or intensity modulator, an acousto-optic modulator, a first coupler and a 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 is input into the acousto-optic modulator to enable narrow-band laser to generate frequency shift, and a local optical signal is obtained; the narrow-band laser corresponding to the detection optical path is modulated by the periodic signal generated by the signal generator in the phase or modulator to generate a detection optical signal with a comb-shaped spectrum.
The optical frequency comb light source is divided into a local light path and a detection light path through the first coupler; the local optical path is input into the optical filter to be filtered to obtain a single-frequency comb tooth, and a local optical signal is obtained; the detection optical path is used for generating an optical signal with a comb spectrum for the optical frequency comb light source.
3. The spectral domain reflectometry system of claim 1 wherein the light source module is a dual optical comb light source module that simultaneously generates two optical frequency combs with slightly different repetition frequencies as the local light and the probe light, respectively.
4. A spectral domain reflectometry system as in claims 1 to 3, wherein the passive optical module comprises a first coupler, a third coupler and an optical circulator;
the detection optical signal with the comb spectrum enters the first coupler and is 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; returning a back scattering signal from the optical fiber to be tested to enter a second coupler; and the local optical signal enters the third coupler, the optical signal with higher beam splitting ratio enters the second coupler, and the optical signal with smaller beam splitting ratio enters the fourth coupler.
5. The spectral domain reflectometry system of claim 1, wherein the coherent detection module comprises: a second coupler, a fourth coupler, a first balanced photodetector, and a second balanced photodetector;
the local light and the detection light signals output by the passive optical path module are respectively subjected to beat frequency at the second coupler and the fourth coupler, and generated beat frequency light signals are respectively input into the first balanced photoelectric detector and the second balanced photoelectric detector; the first balanced photoelectric detector and the second balanced photoelectric detector convert beat frequency optical signals into electric signals and respectively output sensing electric signals and reference electric signals.
6. The spectral domain reflectometry system of claim 1, wherein 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 signal and the reference electric signal, and inputting the acquired sensing electric signal and the reference electric signal into the digital signal processor for signal demodulation.
7. The spectral domain reflectometry system of claim 6, wherein in the signal processing module, the sensing electrical signal and the reference electrical signal are digitized by an analog-to-digital converter, then the frequency spectrums of the sensing electrical signal and the reference electrical signal are obtained by fourier transform, the frequency spectrum of the reference electrical signal is subjected to phase conjugation, the modulus is subjected to reciprocal, then the reciprocal is multiplied by the frequency spectrum of the sensing electrical signal, and the result is subjected to inverse fourier transform to obtain the strength and phase information of the backscattered signal on the optical fiber to be measured.
8. A method for implementing a spectral domain reflectometer, comprising: the light source module generates a local light signal and a probe light signal with comb spectrum, the local light signal is directly connected with the coherent detection module, a part of the probe light signal enters the optical fiber to be detected after passing through the passive optical path module, a backward scattering signal returned from the optical fiber to be detected enters the coherent detection module through the passive optical path module, and outputs a sensing electrical signal after being subjected to beat frequency with the local light; the other part directly enters a coherent detection module, and outputs a reference electric signal after beat frequency with local light; the sensing electric signal and the reference electric signal are input into the signal processing module for data demodulation, and the strength and phase distribution signal of the backscattering signal on the optical fiber link is obtained.
9. The method of claim 8, wherein when the light source module is a single optical comb light source module, the light source module comprises: the device comprises a narrow-linewidth laser light source, a pulse generator, a phase modulator, an acousto-optic modulator and a first coupler;
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 is input into the acousto-optic modulator to enable narrow-band laser to generate frequency shift, and a local optical signal is obtained; narrow-band laser corresponding to the detection optical path is modulated by the pulse generated by the pulse generator in the phase modulator to generate a detection optical signal with a comb spectrum;
when the light source module is a dual optical comb light source module, the light source module includes: the device comprises a narrow linewidth laser light source, a pulse generator, a first phase modulator, a second phase modulator, a first coupler, a first optical filter and a second optical 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 optical path and the detection optical path are respectively input into the first phase modulator and the second phase modulator, and the first phase modulator and the second phase modulator are respectively modulated by different sequences generated by the pulse generator; the output optical signal of the first phase modulator enters the first optical filter for filtering processing to obtain an optical comb signal in a required frequency range, and the optical comb signal is output as a detection optical signal; and the output light of the second phase modulator enters the second optical filter for filtering processing to obtain an optical comb signal in a required frequency range, and the optical comb signal is output as a local optical signal.
10. The method of claim 8, wherein the passive optical module comprises a second coupler, a fourth coupler, and an optical circulator;
the detection optical signal with the comb spectrum enters the second coupler to respectively obtain an optical signal with 90% of energy and an optical signal with 10% of energy; the optical signal with the energy of 90% enters the optical circulator to be connected with the optical fiber to be tested, and the optical signal with the energy of 10% enters the fifth coupler; returning a back scattering signal from the optical fiber to be tested to enter a third coupler; the local optical signal with the comb spectrum enters the fourth coupler to obtain an optical signal with 90% of energy and an optical signal with 10% of energy respectively; an optical signal with energy of 90% enters the third coupler, and an optical signal with energy of 10% enters the fifth coupler;
the coherent detection module includes: a third coupler, a fifth coupler, a first balanced photodetector, and a second balanced photodetector;
the local light and the detection light signals output by the passive optical path module are respectively subjected to beat frequency at the third coupler and the fifth coupler, and generated beat frequency light signals are respectively input into the first balanced photoelectric detector and the second balanced photoelectric detector; the first balance photoelectric detector and the second balance photoelectric detector convert beat frequency optical signals into electric signals and respectively output sensing electric signals and reference electric signals;
the signal processing module includes: a data acquisition card and a digital signal processor;
the method comprises the following steps of collecting and storing input sensing electric signals and reference electric signals through a data collection card, and inputting the collected sensing electric signals and reference electric signals into a digital signal processor for signal demodulation;
in the signal processing module, the sensing electrical signal and the reference electrical signal are digitized by an analog-to-digital converter, frequency spectrums of the sensing electrical signal and the reference electrical signal are respectively obtained by Fourier transform, the phase of the frequency spectrum of the reference electrical signal is conjugated, the modulus is inverted, the frequency spectrum of the sensing electrical signal is multiplied, the result is subjected to inverse Fourier transform, and the strength and the phase information of the backscattering signal on the optical fiber to be measured are obtained.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116337777A (en) * | 2023-05-29 | 2023-06-27 | 之江实验室 | Broadband photoacoustic spectrum measurement system and method based on single optical comb |
| CN116337777B (en) * | 2023-05-29 | 2023-08-29 | 之江实验室 | Broadband photoacoustic spectrum measurement system and method based on single optical comb |
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