CN106500742A - A kind of phase sensitive optical time domain reflectometer phase demodulating system and phase demodulating method - Google Patents
A kind of phase sensitive optical time domain reflectometer phase demodulating system and phase demodulating method Download PDFInfo
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
- G01D5/35354—Sensor working in reflection
- G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
- G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
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Abstract
The present invention is that a kind of phase sensitive optical time domain reflectometer phase demodulating system and phase demodulating method, narrow linewidth laser connect fiber coupler, and big portion connects sensor fibre through circulator after modulating shift frequency for sensing soft exchange acousto-optic modulator.Fraction light is used as with reference to soft exchange Polarization Controller, 2 × 2 fiber couplers are accessed together with circulator is divided into two beam flashlights, a branch of first connect fiber delay line, two beams are respectively obtained the signal of telecommunication through photoelectric conversion module and are mixed with fc signals in electric frequency mixer, then each low-pass filtered device and analog-to-digital conversion module Access Control center.This method sense light and with reference to optical heterodyne relevant after be divided into two beam flashlights, send into control centre's reference light operation orthogonal to two beams through photoelectric conversion and the mixing of fc signals, filtering, analog digital conversion and obtain the phase demodulating for sensing optical signal.This invention removes the phase drift of extra electron noise and ambient temperature, noise when good stability increases detection range, can demodulate flashlight phase place change simultaneously.
Description
Technical field
The present invention relates to a kind of optical fiber sensing system, and in particular to a kind of phase sensitive optical time domain reflectometer (φ-OTDR)
Phase demodulating system and phase demodulating method.
Background technology
Optical time domain reflectometer OTDR (English names：Optical time-domain reflect meter) according to light
Back scattering and Fresnel inversion principle make, and the rear orientation light produced when propagated using light in a fiber is obtaining decay
Information, can be used to measure optical fiber attenuation, splicing loss, fiber failure point location and understands loss distribution feelings of the optical fiber along length
Condition etc., is requisite instrument in optical cable construction, maintenance and monitoring.General optical time domain reflectometer is based on optical fibre refractivity
Measurement, has been widely used for loss and the inflection point of loss, fusion point and the connection of detection optical fiber circuit in fiber optic communication,
But the event of static state can only be measured as time of measuring is longer.
Phase sensitive optical time domain reflectometer (φ-OTDR) technology can with the position of quick detection to intrusion behavior and type,
Just by extensive concern since appearance. φ-OTDR can apply to border, oil and gas pipes, oil well well logging, Traffic monitoring and emphasis area
The multiple fields such as domain intrusion detection.
Have the optical signal detection structure of two kinds of φ-OTDR at present, one kind be with highly sensitive detector direct detection after
To the strength signal of Rayleigh scattering light, although simple structure but detection range is limited.Another kind be using local light with auspicious backward
The relevant coherent detection structure of sharp scattered light, can demodulate strength signal and phase signal simultaneously, and greatly improve sensing letter
Number signal to noise ratio, extend detection range.There is the optical signal demodulation mode of three kinds of φ-OTDR coherent detections at present；3 × 3 bonders
Demodulation method, light zero balancing and digital coherent demodulation method.First two needs to introduce an interferometer structure, is easily subject to the shadow of environment
Ring, and thus introduce extra noise.Digital coherent demodulation method needs the data receiver of a large amount of high speeds and process, so price is high
Expensive, realize difficult.
Content of the invention
The purpose of the present invention is to design a kind of phase sensitive optical time domain reflectometer phase demodulating system and phase demodulating method,
Fiber coupler by larger for laser beam a branch of be allocated as sense light, modulation shift frequency fc sends into sensor fibre, less light beam conduct
Reference light, is coupled in bonder with the sense light returned through circulator, is further divided into two equal beam flashlights, wherein a branch of is prolonged
When, two beams are converted to the signal of telecommunication through identical photoelectric conversion module afterwards, and frequency mixer and signal generating module send respectively
Frequency is mixed for the sinusoidal signal of fc, then each low-pass filtered device and analog-to-digital conversion module send into control centre, obtain sense light
The phase demodulating result of signal.
A kind of phase sensitive optical time domain reflectometer phase demodulating system designed by the present invention includes that LASER Light Source, acousto-optic are adjusted
Device processed and sensor fibre connect through optical fiber successively, and signal driver connects acousto-optic modulator through holding wire；The laser light of the present invention
Source is narrow linewidth laser, and narrow linewidth laser connects fiber coupler, and the splitting ratio of fiber coupler is (9:1)～(7:3), greatly
Part light is that sensing soft exchange acousto-optic modulator, acousto-optic modulator are modulated after simultaneously shift frequency fc through circulator and sense light to which
Fine connection.Fraction light is terminated 2 × 2 as soft exchange Polarization Controller, the output of Polarization Controller is referred to by fiber coupler
One input of fiber coupler, the other end of circulator access 2 × 2 fiber couplers another inputs, the light after coupling
It is divided into two beam flashlights, wherein light beam first connects fiber delay line, and two-beam is respectively connected to No. one, No. two photoelectric conversion modules,
The signal of telecommunication of conversion respectively enters frequency mixer, and the frequency that signal generating module sends also is respectively connected to one for the sinusoidal signal of fc
Number, No. two electric frequency mixers, the signal of telecommunication mixing with the conversion of two beam flashlights, then respectively through No. one, No. two low pass filters and No. one,
No. two analog-to-digital conversion module Access Control centers.No. one of the two beams flashlight, No. two photoelectric conversion modules, No. one, No. two
Electric frequency mixer, No. one, No. two low pass filters and No. one, No. two analog-to-digital conversion module specifications parameters are identical.
The narrow linewidth laser connects image intensifer and optical fiber filter incoming fiber optic bonder again.
The acousto-optic modulator is followed by image intensifer and optical fiber filter accesses circulator again.
Described acousto-optic modulator is changed to frequency shifter and electrooptic modulator, fiber coupler light splitting mostly as sensing
Soft exchange frequency shifter, signal driver access electrooptic modulator, and frequency shifter connects electrooptic modulator, electrooptic modulator connection annular
Device.
Described acousto-optic modulator is changed to electrooptic modulator, fiber coupler light splitting mostly as sensing soft exchange electricity
Photomodulator, electrooptic modulator connects circulator；The fraction of fiber coupler light splitting connects frequency shifter and connects Polarization Controller again.
The fiber delay line can be used the optical fiber of one section of long L instead and replace, L=(c × π)/(2n × fc), and in formula, c is vacuum
In the light velocity, n for optical fiber refractive index.
Described No. one, No. two photoelectric conversion modules be that PIN is managed or avalanche diode.
The control centre is computer, and digital signal processor, in field programmable gate array (FPGA) and industrial computer
Any one.
Phase demodulating method using the phase sensitive optical time domain reflectometer phase demodulating system of present invention design is as follows：Narrow
The laser beam that live width laser instrument sends is divided into two parts by fiber coupler, and fraction light is as local reference light through Polarization Control
Device carries out Polarization Control, and major part after acousto-optic modulator is modulated simultaneously shift frequency fc enters sensor fibre through circulator, dissipates
The sensing optical signal for being emitted back towards accesses 2 × 2 fiber couplers through circulator, and the local reference light after Polarization Control also accesses 2 × 2
Fiber coupler, the two carry out being divided into two beam flashlights after heterodyne is relevant, after a branch of time delay through fiber delay line, two beam flashlights
Phase pi/2 formed orthogonal.Two beam flashlights respectively carry out photoelectric conversion through photoelectric conversion module, the signal of telecommunication difference for obtaining
The frequency sent by electric frequency mixer and signal generating module is mixed for the sinusoidal signal of fc, and the signal of telecommunication for obtaining leads to respectively
Cross low pass filter filtering, filter heterodyne frequency signal and its higher harmonic components, then respectively be converted into counting through modulus module
Word signal, sends into control centre, and control centre receives the conversion signal of the orthogonal flashlight of two beams and carries out differential multiplication cross phase
Subtract (DCM) operation, obtain the phase demodulating for sensing optical signal.
Compared with prior art, the phase demodulating system of phase sensitive optical time domain reflectometer of the invention and phase demodulating side
The advantage of method is：Eliminate Electric phase-shift element the extra electron noise for being brought and the phase place that variation of ambient temperature causes to float
Move, make position sensitivity optical time domain reflectometer (φ-OTDR) system that there is more preferable noise when stability, increase detection range, and
The phase place change of flashlight is demodulated simultaneously can.
Description of the drawings
Fig. 1 is the structural representation of this phase sensitive optical time domain reflectometer phase demodulating system embodiment 1；
Fig. 2 is the structural representation of this phase sensitive optical time domain reflectometer phase demodulating system embodiment 2；
Fig. 3 is the structural representation of this phase sensitive optical time domain reflectometer phase demodulating system embodiment 3.
Figure internal label is：
1st, narrow linewidth laser, 2, fiber coupler, 3, acousto-optic modulator, 4, signal driver, 5, circulator, 6, No. one
Photoelectric conversion module, 7, signal generating module, 8, electric frequency mixer, 9, sensor fibre/optical cable, 10, low pass filter
11st, an analog-to-digital conversion module, 12, control centre, 13, No. two analog-to-digital conversion modules, 14, No. two low pass filters, 15, No. two
Electric frequency mixer, 16, No. two photoelectric conversion modules, 17, fiber delay line, 18,2 × 2 fiber couplers, 19, Polarization Controller,
20th, electrooptic modulator, 21, frequency shifter.
Specific embodiment
Below in conjunction with the accompanying drawings present disclosure is described in further detail.
This phase sensitive optical time domain reflectometer phase demodulating system embodiment 1
This phase sensitive optical time domain reflectometer (φ-OTDR) phase demodulating system embodiment 1 is as shown in figure 1, wavelength is C ripples
The narrow linewidth laser 1 of section connects fiber coupler 2, and the splitting ratio of fiber coupler 2 is
90:10.Used as sensing soft exchange acousto-optic modulator 3, signal driver 4 connects acousto-optic modulator 3, sound to 90% light
The sense lights of the access of photomodulator 3 pairs be modulated and shift frequency fc after connect through circulator 5 and sensor fibre 9.
Fiber coupler 2 is using 10% light as with reference to soft exchange Polarization Controller 19, the outfan of Polarization Controller 19
Connect 2 × 2 fiber coupler, 18 1 inputs, the other end of circulator 5 accesses 2 × 2 fiber coupler 18 another input,
Light after coupling is divided into two beam flashlights, and wherein light beam first connects fiber delay line 17, and two-beam respectively accesses No. one, No. two photoelectricity
Modular converter 6,16, the signal of telecommunication of conversion respectively enter No. one, No. two electric frequency mixers 8,15, the frequency that signal generating module 7 sends
Rate is also respectively connected to two electric frequency mixers 8,15 for the sinusoidal signal of fc, the signal of telecommunication mixing with the conversion of two beam flashlights, then respectively
Through No. one, No. two low pass filters 10,14 and No. one, No. two analog-to-digital conversion modules 11,13 Access Control centers 12；Two beam
No. one of flashlight, No. two photoelectric conversion modules 6,16, No. one, No. two electric frequency mixers 8,15, No. two low pass filters
10th, 14 is identical with the specifications parameter of No. one, No. two analog-to-digital conversion module 11,13.
Image intensifer and optical fiber filter incoming fiber optic bonder 2 again can be connected in this example after narrow linewidth laser 1.
Image intensifer can be connect after this example acousto-optic modulator 3 and optical fiber filter accesses circulator 5 again.
This example fiber delay line 17 can be changed to the optical fiber of one section of long L, L=(c × π)/(2n × fc), and in formula, c is in vacuum
The light velocity, n for optical fiber refractive index.
No. one, No. two photoelectric conversion modules 6,19 of this example are that PIN is managed or avalanche diode.
This example control centre 12 be computer, digital signal processor, in field programmable gate array and industrial computer appoint
A kind of.
Phase sensitive optical time domain reflectometer phase demodulating system embodiment 2
This phase sensitive optical time domain reflectometer phase demodulating system embodiment 2 as shown in Fig. 2 with above-mentioned phase demodulating system
2 structure of embodiment is similar, but the acousto-optic modulator 3 in embodiment 1 is changed to frequency shifter 21 and electrooptic modulator 20, signal driver
4 access electrooptic modulator 20, and 90% conduct of 2 light splitting of fiber coupler senses soft exchange frequency shifter 21, and frequency shifter 21 connects electricity
Photomodulator 20, electrooptic modulator 20 connect circulator 5.Phase sensitive optical time domain reflectometer phase demodulating system embodiment 3
This phase sensitive optical time domain reflectometer phase demodulating system embodiment 3 as shown in figure 3, with above-mentioned phase demodulating system
1 structure of embodiment is similar, but the acousto-optic modulator 3 in embodiment 1 is changed to electrooptic modulator 20,2 light splitting of fiber coupler
90%, as sensing soft exchange electrooptic modulator 20, reconnects circulator 5；The 10% of 2 light splitting of fiber coupler is used as sense light
Frequency shifter 21 is accessed, then connects Polarization Controller 19.
The phase demodulating embodiment of the method 1 of phase sensitive optical time domain reflectometer phase demodulating system
This phase demodulating embodiment of the method 1 is in above-mentioned phase sensitive optical time domain reflectometer phase demodulating system embodiment 1
Carry out.
The laser beam that narrow linewidth laser 1 sends is divided into two parts by fiber coupler 2, and fraction light is used as local reference
Light carries out Polarization Control through Polarization Controller 19, and major part is after acousto-optic modulator 3 is modulated simultaneously shift frequency fc through circulator 5
Sensor fibre 9 is entered, the sensing optical signal that scattering is returned accesses 2 × 2 fiber couplers 18 through circulator 5, after Polarization Control
Local reference light also accesses 2 × 2 fiber couplers 18, and the two carries out being divided into two beam flashlights after heterodyne is relevant, a branch of through optical fiber
After 17 time delay of delay line, the phase pi/2 of two beam flashlights forms orthogonal；Two beam signals are respectively through No. one, No. two opto-electronic conversion
Module 6,16 carries out photoelectric conversion, and the signal of telecommunication for obtaining is respectively by No. one, No. two electric frequency mixers 8,15 and signal generating module 7
The frequency for sending is mixed for the sinusoidal signal of fc, and the signal of telecommunication for obtaining passes through No. one, No. two low pass filters 10,14 respectively
Filtering, heterodyne frequency signal and its higher harmonic components are filtered, then respectively through No. one, 11,13 turns of No. two analog-to-digital conversion modules
Change digital signal into, send into control centre 12, control centre 12 receives the orthogonal signal of two beams and carries out differential multiplication cross
Phase reducing, obtains the phase demodulating for sensing optical signal.
The phase demodulating embodiment of the method 2 of phase sensitive optical time domain reflectometer phase demodulating system
This phase demodulating embodiment of the method 2 is in above-mentioned phase sensitive optical time domain reflectometer phase demodulating system embodiment 2
Carry out.The present embodiment 2 is similar to above-mentioned phase demodulating embodiment of the method 1, and simply the first of sense light on frequency shifter 21 completes to move
Frequency fc, enters back into electrooptic modulator 20 and completes signal modulation.
The phase demodulating embodiment of the method 3 of phase sensitive optical time domain reflectometer phase demodulating system
This phase demodulating embodiment of the method 3 is in above-mentioned phase sensitive optical time domain reflectometer phase demodulating system embodiment 3
Carry out.The present embodiment 3 is similar to above-mentioned phase demodulating embodiment of the method 1, but sense light does not carry out shift frequency, simply in Electro-optical Modulation
Device 20 completes to modulate.Reference light then first completes shift frequency fc on frequency shifter 21, enters back into the process after Polarization Controller 19.
Above-described embodiment, only the purpose of the present invention, technical scheme and beneficial effect are further described are concrete
Individual example, the present invention are not limited to this.All any modifications that is made within the scope of disclosure of the invention, equivalent, change
Enter, be all contained within protection scope of the present invention.
Claims (10)
1. a kind of phase sensitive optical time domain reflectometer phase demodulating system, including LASER Light Source, acousto-optic modulator and sensor fibre
Connect through optical fiber successively, signal driver connects acousto-optic modulator through holding wire；It is characterized in that：
The LASER Light Source is narrow linewidth laser (1), and narrow linewidth laser (1) connects fiber coupler (2), fiber coupler
(2) splitting ratio is (9:1)～(7:3), used as sensing soft exchange acousto-optic modulator (3), acousto-optic modulator (3) is right for most of light
Which connects through circulator (5) and sensor fibre (9) after being modulated simultaneously shift frequency fc；Fiber coupler (2) using fraction light as
With reference to soft exchange Polarization Controller (19), the output of Polarization Controller (19) terminates (18) inputs of 2 × 2 fiber coupler
2 × 2 fiber couplers (18) another input is accessed at end, the other end of circulator (5), and the light after coupling is divided into two beam signals
Light, wherein light beam first connect fiber delay line (17), and two-beam respectively accesses No. one, No. two photoelectric conversion modules (6,16), conversion
The signal of telecommunication respectively enter No. one, No. two electric frequency mixers (8,15), sinusoidal letter of the frequency that signal generating module (7) sends for fc
Number be also respectively connected to two electric frequency mixers (8,15), the signal of telecommunication mixing with the conversion of two beam flashlights, then respectively through No. one, No. two low
Bandpass filter (10,14) and No. one, No. two analog-to-digital conversion module (11,13) Access Control centers (12)；The two beams flashlight
No. one, No. two photoelectric conversion modules (6,16), No. one, No. two electric frequency mixers (8,15), No. one, No. two low pass filters (10,
14) specifications parameter of with No. one, No. two analog-to-digital conversion module (11,13) is identical.
2. phase sensitive optical time domain reflectometer phase demodulating system according to claim 1, it is characterised in that：
Narrow linewidth laser (1) connects image intensifer and optical fiber filter incoming fiber optic bonder (2) again.
3. phase sensitive optical time domain reflectometer phase demodulating system according to claim 1, it is characterised in that：
Acousto-optic modulator (3) are followed by image intensifer and optical fiber filter accesses circulator (5) again.
4. phase sensitive optical time domain reflectometer phase demodulating system according to claim 1, it is characterised in that：
Described acousto-optic modulator (3) is changed to frequency shifter (21) and electrooptic modulator (20), fiber coupler (2) light splitting
Mostly as sensing soft exchange frequency shifter (21), signal driver (4) accesses electrooptic modulator (20), and frequency shifter (21) connects
Electrooptic modulator (20), electrooptic modulator (20) connection circulator (5).
5. phase sensitive optical time domain reflectometer phase demodulating system according to claim 1, it is characterised in that：
Fiber delay line (17) are changed to the optical fiber of one section of long L, L=(c × π)/(2n × fc), and in formula, c is the light in vacuum
Speed, refractive indexs of the n for optical fiber.
6. phase sensitive optical time domain reflectometer phase demodulating system according to claim 1, it is characterised in that：
Described No. one, No. two photoelectric conversion modules (6,19) be that PIN is managed or avalanche diode.
7. phase sensitive optical time domain reflectometer phase demodulating system according to claim 1, it is characterised in that：
Described control centre (12) are computer, and digital signal processor is arbitrary in field programmable gate array and industrial computer
Kind.
8. phase sensitive optical time domain reflectometer phase demodulating system according to claim 1, it is characterised in that：
Described acousto-optic modulator (3) is changed to electrooptic modulator (20), and signal driver (4) accesses electrooptic modulator (20), electricity
Photomodulator (20) connection circulator (5)；Fiber coupler (2) light splitting mostly as sensing soft exchange electrooptic modulator
(20), the fraction of fiber coupler (2) light splitting connects frequency shifter (21) and connects Polarization Controller (19) again.
9. using the phase place solution of the phase sensitive optical time domain reflectometer phase demodulating system any one of claim 1 to 7
Tune method, it is characterised in that：
The laser beam that narrow linewidth laser (1) sends is divided into two parts by fiber coupler (2), and fraction light is used as local reference
Light carries out Polarization Control through Polarization Controller (19), and major part is after acousto-optic modulator (3) is modulated simultaneously shift frequency fc through ring
Shape device (5) enters sensor fibre (9), and the sensing optical signal that scattering is returned accesses 2 × 2 fiber couplers (18) through circulator (5),
Local reference light after Polarization Control also accesses 2 × 2 fiber couplers (18), and the two carries out being divided into two beam signals after heterodyne is relevant
Light, a branch of through fiber delay line (17) time delay after, the phase pi/2 of two beam flashlights forms orthogonal；Two beam flashlights are respectively passed through
No. one, No. two photoelectric conversion modules (6,16) carry out photoelectric conversion, the signal of telecommunication for obtaining is respectively by No. one, No. two electric frequency mixers
The frequency that (8,15) are sent with signal generating module (7) is mixed for the sinusoidal signal of fc, and the signal of telecommunication for obtaining passes through respectively
No. one, the filtering of No. two low pass filters (10,14), filter heterodyne frequency signal and its higher harmonic components, then respectively through one
Number, No. two analog-to-digital conversion modules (11,13) be converted into digital signal, send into control centre (12), control centre (12) receives two
The conversion signal of the orthogonal flashlight of beam carries out differential multiplication cross phase reducing, obtains the phase demodulating for sensing optical signal.
10. the phase demodulating method of phase sensitive optical time domain reflectometer phase demodulating system according to claim 9, its are special
Levy and be：
Described acousto-optic modulator (3) is changed to electrooptic modulator (20), in the reference path that fiber coupler (2) is separated connects shifting
Frequency device (21) connects Polarization Controller (19) again；
The fraction light that fiber coupler (2) is separated first enters polarization control after frequency shifter (21) shift frequency fc as local reference light
Device (19) processed carry out Polarization Control, and most of light that fiber coupler (2) is separated is after electrooptic modulator (20) is modulated
Sensor fibre (9) is entered through circulator (5), the sensing optical signal that scattering is returned accesses 2 × 2 fiber couplers through circulator (5)
(18).
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| CN107389106A (en) * | 2017-08-30 | 2017-11-24 | 中国电子科技集团公司第三十四研究所 | A kind of φ OTDR quadrature phase demodulations system and phase demodulating method |
| CN110045357A (en) * | 2019-03-07 | 2019-07-23 | 南京合太光电科技有限公司 | A kind of linear FM signal generation device |
| CN110793558A (en) * | 2019-11-26 | 2020-02-14 | 南京大学 | Coherent detection type phi-OTDR system and self-checking method |
| CN111355485A (en) * | 2019-09-29 | 2020-06-30 | 西安空间无线电技术研究所 | System and method for eliminating phase drift of delay line |
| US10756820B2 (en) | 2018-05-21 | 2020-08-25 | Zhejiang Jericore Technologies Co., Ltd. | Phase analog coherent demodulation system and method for phase sensitive optical time domain reflectometry |
| CN113447112A (en) * | 2021-06-18 | 2021-09-28 | 天津大学 | Reflected light-based high-frequency vibration sensing system and high-frequency signal demodulation method |
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