CN109459072A - It is a kind of based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation - Google Patents
It is a kind of based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation Download PDFInfo
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- 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
Abstract
It is a kind of based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation, belong to photoelectron technical field.The coherent light time domain reflection meter includes narrow linewidth linearly polarized laser device, beam splitter, light intensity modulator, optical fiber circulator, polarization-maintaining sensor fibre, optical phase modulator, polarization-maintaining fiber coupler, balanced detector, signal processing circuit and square wave signal generator；The square wave signal generator generates periodic signal of square wave and inputs optical phase modulator, phase-shift keying (PSK) modulation is carried out with the phase to local oscillator light, simultaneously, under the action of square wave signal generator, the signal that signal processing circuit identification balanced detector is obtained in different additional phase delays, to carry out signal processing.Coherent light time domain reflection meter provided by the invention substantially reduces the bandwidth requirement of photodetection circuit, so that larger across hindering in photodetection circuit, thermal noise is smaller, to effectively increase received signal to noise ratio and the sensitivity of system.
Description
Technical field
The invention belongs to photoelectron technical fields, and in particular to when a kind of coherent light based on local oscillator light orthogonal phase modulation
Domain reflectometer.
Background technique
Optical time domain reflectometer (OTDR) is the backward Rayleigh scattering and Fresnel reflection principle according to light, using light in optical fiber
The back scattering that generates when middle propagation and reflected light obtain the device of the related optical information of device under test, can be used for measuring light
Fine decaying, splicing loss, positioning fiber failure point etc., and the sensing for parameters such as fiber optic temperature, vibration and stress, be into
Row optical fiber construction, maintenance and the powerful of monitoring.This technology was put forward for the first time in 1976 by Barnoski et al., at present
Until, it has been obtained in optical fiber sensing system using Rayleigh scattering, Raman scattering and the optical time domain reflection technology of Brillouin scattering
Extensive concern and research are arrived.
The working principle of traditional OTDR is that (Tian Guodong, the optical fiber test method based on OTDR technique inquire into hyundai electronics skill
Art, 2009,19 phases: 99-101): semiconductor light source output optical pulse under driving circuit modulation injects quilt by photo-coupler
Surveying optical fiber becomes incident light pulse；Incident light pulse can generate Rayleigh scattering light, most of Rayleigh scattering when transmitting in a fiber
Light will be decayed after being refracted into covering, wherein the back rayleigh scattering light contrary with light pulse propagation will be transmitted along optical fiber
To entering light port, oriented coupler incidence photodetector obtains measured physical quantity by the processing to photosignal.Tradition
The major defect of OTDR is: Rayleigh scattering light is very faint, and the signal-to-noise ratio that direct photodetection obtains is not high, limits entire system
The measurement distance and positioning accuracy of system.
Received signal to noise ratio can largely be improved using heterodyne detection technology, domestic and international researcher is opened in this respect
Extensive exploration and trial, such as Yuelan Lu (Yuelan Lu, Tao Zhu, Member, IEEE.Distributed are opened up
Vibration Sensor Based on Coherent Detection of Phase-OTDR[J].JOURNAL OF
LIGHTWAVE TECHNOLOGY, VOL.28, NO.22, NOVEMBER 15,2010.) it has developed a kind of heterodyne system OTDR and is used for
Vibrating sensing.Its working principle is that: by the output of one 1.55 μm of narrow-linewidth single frequency continuous wave laser through fiber coupler point
It is put wherein a branch of generate pulse laser through acousto-optic modulator shift frequency 200MHz and by modulation using Er-doped fiber at two beams
Big device (EDFA) amplifies, and filters out most of spontaneous emission light using optical fiber filter；Filtered pulsed light passes through light
The test optical fiber of fine circulator injection 1.2km, generates rear orientation light (signal light) in transmission process；Signal light passes through the ring of light
Injection fibre coupler after shape device is interfered, light in the another light beam (local oscillator light) wherein with the output of single-frequency continuous wave laser
The output of fine coupler accesses balanced detector, obtains the beat signal that frequency is 200MHz, is handled by follow-up data
Obtain the vibration information in test optical fiber.This method improves the signal-to-noise ratio of system by infradyne manner compared with direct detection
And sensitivity, still, due between signal light and local oscillator light there are biggish frequency difference (generally 100MHz~200MHz, herein
For 200MHz), need using the biggish photodetector of bandwidth, so that smaller across hindering in detection circuit, thermal noise is stronger, from
And limit system signal noise ratio and sensitivity.
Summary of the invention
It is an object of the present invention to which it is high, high sensitivity to propose a kind of signal-to-noise ratio for defect existing for background technique
Based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation.
To achieve the above object, The technical solution adopted by the invention is as follows:
It is a kind of based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation, including narrow linewidth linearly polarized laser device 1,
Beam splitter 2, light intensity modulator 3, optical fiber circulator 4, polarization-maintaining sensor fibre 5-1, optical phase modulator 6, polarization maintaining optical fibre coupling
Clutch 7, balanced detector 8, signal processing circuit 9 and square wave signal generator 10；
The narrow linewidth linearly polarized laser device is connected by optical fiber with the input terminal of beam splitter, and two of beam splitter are defeated
Exit port is separately connected the input terminal of light intensity modulator and the input terminal of optical phase modulator；The output end of light intensity modulator
The pulse laser input port of optical fiber circulator is connected, the duplex port of optical fiber circulator connects polarization-maintaining sensor fibre, fiber optic loop
One input port of the signal optical output port connection polarization-maintaining fiber coupler of shape device；The output port of optical phase modulator connects
Another input port of polarization-maintaining fiber coupler is connect, two output ports of polarization-maintaining fiber coupler connect balanced detector；
The output port of balanced detector accesses signal processing circuit；The output port of the square wave signal generator connects light phase tune
Device processed and signal processing circuit；
The square wave signal generator generates periodic signal of square wave and inputs optical phase modulator, with the phase to local oscillator light
Phase-shift keying (PSK) modulation is carried out, meanwhile, under the action of square wave signal generator, signal processing circuit identifies balanced detector not
Signal (the V that same additional phase delay (0 ° and 90 °) obtainsaAnd Vb), to carry out signal processing；When local oscillator light is in low level
After optical phase modulator and polarization-maintaining fiber coupler, the voltage V of balanced detector outputa∝ESELOcos(Δωt+Δ
φ), wherein Δ ω is the difference of the angular frequency of signal light and local oscillator light, and Δ φ is the difference of the initial phase of signal light and local oscillator light, ES
For the amplitude of signal light field, ELOFor the amplitude of local oscillator light field, t is the time-parameters of entire signal；When local oscillator light is in pi/2 level
After optical phase modulator and polarization-maintaining fiber coupler, the voltage V of balanced detector outputb∝ESELOsin(Δωt+Δ
φ)；The voltage signal entering signal processing circuit of balanced detector output, signal processing circuit by voltage respectively square again
Summation, obtains signal V=Va 2+Vb 2∝ISILO, ISFor the intensity of signal light, ILOFor the intensity of local oscillator light；It is strong due to local oscillator light
Degree is constant, so that the demodulation to signal light intensity can be realized.
Further, the amplitude for the square-wave signal that the square wave signal generator generates be optical phase modulator voltage π/
2, duty ratio 50%.
Further, Δ ω is mainly determined by laser frequency drift rate, usually less than 1kHz.
Further, single mode sensor fibre substitution can be used in the polarization-maintaining sensor fibre, to reduce system cost；Work as use
When single mode sensor fibre, it must add between the signal optical output port of optical fiber circulator and the input port of polarization-maintaining fiber coupler
Add optical fiber polarization controller, the signal light polarization direction for being input to polarization-maintaining fiber coupler adjusted by optical fiber polarization controller,
It is consistent the polarization direction of local oscillator light and signal light.
It is provided by the invention it is a kind of based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation in, the narrow linewidth
Linearly polarized laser device generates the single-frequency laser of narrow linewidth, linear polarization, is divided into two bundles laser by beam splitter, wherein light beam
Polarization-maintaining fiber coupler is inputted after optical phase modulator as local oscillator light, another light beam input light intensity modulator will be continuous
Laser Modulation inputs polarization-maintaining sensor fibre at pulse laser, by optical fiber circulator；Due to the Rayleigh scattering of optical fiber itself, there is portion
Sub-signal light can return to optical fiber circulator, and the scattering that the optical power that different moments return represents the sensor fibre of different location is special
Property；The echo optical signal of scattering is after optical fiber circulator, coherent superposition, output two in polarization-maintaining fiber coupler with local oscillator light
Road phase difference is respectively the coherent light signal of 0 ° and 180 °, is balanced detector reception；
The square wave signal generator generates periodic signal of square wave and inputs optical phase modulator, with the phase to local oscillator light
Progress phase-shift keying (PSK) modulation, pi/2 of the amplitude of the square-wave signal for optical phase modulator voltage, duty ratio 50%, meanwhile,
Square wave signal generator gives signal processing circuit one trigger action, and signal processing circuit is identified and is existed from balanced detector
Obtained signal (the V of different additional phase delays (0 ° and 90 °)aAnd Vb), to carry out signal processing；When local oscillator light is in low electricity
Usually by optical phase modulator, additional phase delay is 0 °, the photoelectric signal voltage V of balanced detector outputa∝
ESELOCos (Δ ω t+ Δ φ), wherein VaFor the output voltage of local oscillator light balanced detector in low level, Δ ω is signal
The difference ω of the angular frequency of light and local oscillator lightS-ωLO, for stabilized light source, the difference on the frequency of two-beam is typically small, mainly by laser
Frequency drift rate determines that usually less than 1kHz, Δ φ are the difference φ of the initial phase of signal light and local oscillator lightS-φLO, ES(signal
Light) and ELO(local oscillator light) is respectively the amplitude of signal light field Yu local oscillator light field, and t is the time-parameters of entire signal；When local oscillator light
In pi/2 level by optical phase modulator, additional phase delay is 90 °, the photoelectric signal voltage of balanced detector output
Vb∝ESELOSin (Δ ω t+ Δ φ), VbFor the output voltage of local oscillator light balanced detector in pi/2 level；Balanced detector is defeated
Voltage signal entering signal processing circuit out, signal processing circuit is by half period (additive phase preceding in each modulation period
Delay is 0 °) voltage signal and second half of the cycle (additional phase delay is 90 °) voltage signal, square sum again respectively,
Obtain signal V=Va 2+Vb 2∝ISILO, ISAnd ILOThe respectively intensity of signal light and local oscillator light, since the intensity of local oscillator light is permanent
Fixed, so that the demodulation to signal light intensity can be realized.
Compared with prior art, the invention has the benefit that
The present invention provides a kind of based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation, using nearly homodyne phase
Dry detection method, in optical signal receiving end, signal light and local oscillator light have approximately uniform frequency (frequency difference is generally kHz magnitude,
Determined by laser frequency drift), the square-wave signal that square wave signal generator of the present invention generates carries out phase-shift keying (PSK) to the phase of local oscillator light
(PSK) it modulates, phase takes 0 and pi/2, and the voltage by receiving former and later two detectable signals in the period to one carries out quadratic sum
Operation can recover the intensity of echo-signal.Coherent light time domain reflection meter provided by the invention with based on acousto-optic frequency shifters
Heterodyne detection technology is compared, and (usual low 1~2 order of magnitude) is substantially reduced to the bandwidth requirement of photodetection circuit, so that light
Larger across hindering in electrical resistivity survey slowdown monitoring circuit, thermal noise is smaller, to effectively increase received signal to noise ratio and the sensitivity of system.
Detailed description of the invention
Fig. 1 is the knot based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation that the embodiment of the present invention 1 provides
Structure schematic diagram；
Fig. 2 be it is provided by the invention based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation in, fiber annular
The concrete structure schematic diagram of device；
Fig. 3 be it is provided by the invention based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation in, light phase tune
The modulation waveform figure of device processed；
Fig. 4 is that the signal processing provided by the invention based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation is former
Reason figure；
Fig. 5 is the knot based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation that the embodiment of the present invention 2 provides
Structure schematic diagram；
In figure, 1. narrow linewidth linearly polarized laser devices, 2. beam splitters, 3. light intensity modulators, 4. optical fiber circulators, 5-1.
Polarization-maintaining sensor fibre, 5-2. single mode sensor fibre, 6. optical phase modulators, 7. polarization-maintaining fiber couplers, 8. balanced detectors, 9.
Signal processing circuit, 10. square wave signal generators, 11. optical fiber polarization controllers.
Specific embodiment
With reference to the accompanying drawings and examples, technical solution of the present invention is described in detail.
Embodiment 1
As shown in Figure 1, the coherent light time domain reflection based on local oscillator light orthogonal phase modulation provided for the embodiment of the present invention 1
The structural schematic diagram of meter；Wherein, narrow linewidth linearly polarized laser device 1 is inclined using U.S. Ethernal company ETH series narrow linewidth line
Shake optical fiber laser, and line width can reach within 400Hz.The narrow-linewidth laser of the output of narrow linewidth linearly polarized laser device 1 1550nm
Light beam is divided into two bundles by light beam by beam splitter 2, and wherein light beam enters light intensity modulator 3, generates arteries and veins by modulation
Impulse light is inputted from the pulse laser input port of optical fiber circulator 4；Then pass through the duplex port of optical fiber circulator 4, input
Polarization-maintaining sensor fibre 5-1 scatters the echo optical signal of generation in polarization-maintaining sensor fibre 5-1, and enters the double of fiber optical circulator 4
Work port is exported from signal optical output port；The another light beam exported from beam splitter 2 inputs optical phase modulator 6, Jing Guangxiang
The echo optical signal that the local oscillator light and scattering that position modulator 6 exports generate is respectively from two input terminals of polarization-maintaining fiber coupler 7
Mouth input, local oscillator light and the signal light coherent superposition in polarization-maintaining fiber coupler 7, output two-way phase difference is respectively 0 ° and 180 °
Coherent light signal, be balanced detector 8 reception；The square wave signal generator 10 generates periodic signal of square wave and input light phase
Position modulator 6 carries out phase-shift keying (PSK) modulation with the phase to local oscillator light；The output end connection signal of balanced detector 8 handles electricity
Road 9, while square wave signal generator 10 also regard periodic signal of square wave input signal processing circuit 9 as synchronization signal.
As shown in Fig. 2, for it is provided by the invention based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation in, light
The concrete structure schematic diagram of fine circulator；As shown in Figure 2, the optical fiber circulator includes three ports: pulse laser input terminal
Mouth, duplex port and signal optical output port.Fiber optic loop is entered from pulse laser input port by the pulse laser that modulation is formed
It after shape device 4, is exported from duplex port, duplex port is entered by the signal light that fibre scattering generates, and from signal optical output port
Output.
As shown in figure 3, for it is provided by the invention based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation in, light
The modulation waveform figure of phase-modulator；Phase-shift keying (PSK) modulation is carried out to the phase of local oscillator light, taking the amplitude of square-wave signal is light phase
The pi/2 voltage of position modulator, square-wave signal duty ratio are 50%.Pass through optical phase modulator when local oscillator light is in low level,
Additional phase delay is 0 °, the photoelectric signal voltage V of balanced detector outputa∝ESELOCos (Δ ω t+ Δ φ), wherein VaFor
The output voltage of local oscillator light balanced detector in low level, Δ ω are the difference ω of the angular frequency of signal light and local oscillator lightS-ωLO,
For stabilized light source, the difference on the frequency of two-beam is typically small, is mainly determined by laser frequency drift rate, usually less than 1kHz,
Δ φ is the difference φ of the initial phase of signal light and local oscillator lightS-φLO, ES(signal light) and ELO(local oscillator light) is respectively signal light field
With the amplitude of local oscillator light field, t is the time-parameters of entire signal；Pass through optical phase modulator when local oscillator light is in pi/2 level,
Additional phase delay is 90 °, the photoelectric signal voltage V of balanced detector outputb∝ESELOSin (Δ ω t+ Δ φ), VbFor local oscillator
The output voltage of light balanced detector in pi/2 level.The selection of the cycle T of modulated signal, depends primarily on to positioning accuracy
Requirement.Such as positioning accuracy is required to reach 100m, then T should be taken as 100m × 2/c=0.667 μ s, and wherein c is the light velocity, modulation
Frequency is 1.5MHz.Since modulating frequency is much larger than the line width (hundred Hz magnitudes) of narrow linewidth linearly polarized laser device 1, at one
In modulation period, phase change caused by the phase noise of laser itself is negligible；As long as by sensing parameter (temperature, vibration
Dynamic, stress, loss etc.) change frequency be less than modulating frequency (be herein 1.5MHz), can be carried out normal sensing measurement,
And the condition is typically satisfiable.
As shown in figure 4, being the letter provided by the invention based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation
Number handling principle figure；In signal processing circuit 9, by half period preceding in each modulation period (additional phase delay is 0 °)
Voltage signal VanWith the voltage signal V of second half of the cycle (additional phase delay is 90 °)bn(n indicates n-th of period), puts down respectively
Side sums again, obtained signal Wn=Van 2+Vbn 2∝ISILO, n=1,2,3 ..., ISAnd ILORespectively signal light and local oscillator light
Intensity, since the intensity of local oscillator light is constant, so that the demodulation to signal light intensity can be realized.
In the present embodiment, the detective bandwidth of balanced detector 8 is 3~5 times of phase modulation frequency, at this time can be completeer
Whole recovers signal light intensity.According to the 100m positioning accuracy being mentioned above, phase modulation frequency is 1.5MHz at this time, then
Detective bandwidth can be taken as 4.5~7.5MHz.As a comparison, using the heterodyne detection mode in background technique, detective bandwidth reaches
To 100MHz or more.
Therefore, provided by the invention based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation, to photodetection
The bandwidth requirement of circuit substantially reduces (usual low 1~2 order of magnitude), can be used in photodetection circuit biggish across resistance, heat
Noise is smaller, to improve system received signal to noise ratio and sensitivity.In conjunction with the highly sensitive advantage of coherent detection, the present invention is more suitable
For requiring monitoring distance high and lower to positioning accuracy request situation.
Embodiment 2
As shown in figure 5, the coherent light time domain reflection based on local oscillator light orthogonal phase modulation provided for the embodiment of the present invention 2
The structural schematic diagram of meter；In example 2, the polarization-maintaining sensor fibre 5-1 in embodiment 1 is replaced with into single mode sensor fibre 5-2,
And optical fiber polarisation control is added between the signal optical output port of optical fiber circulator and the input port of polarization-maintaining fiber coupler
Device 11.Adjusted by optical fiber polarization controller 11 and be input to the signal light polarization direction of polarization-maintaining fiber coupler 7, make local oscillator light and
The polarization direction of signal light is consistent, and can correctly demodulate signal light intensity at this time, while using single mode sensor fibre 5-2
System cost can be significantly reduced.
It is provided by the invention it is a kind of based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation in, narrow linewidth line is inclined
The laser that laser generates that shakes has good coherence, the sensitivity that can be effectively lifted in follow-up signal optical detection；Light point
Laser beam is divided into two beams by beam device, local oscillator light has not only been provided, but also provide signal light, with source laser in polarization-maintaining fiber coupler
In can carry out efficient photomixing (interference)；Light intensity modulator is modulated optical signal, to form signal pulse；Optical fiber
Circulator has good isolation, and the back scattering optical echo that ensure that the optical signal of input and polarization-maintaining sensor fibre generate is believed
Number crosstalk does not occur；Polarization-maintaining fiber coupler forms signal light and local oscillator light wherein photomixing (interference), exports two-way phase
Potential difference is respectively the coherent light signal of 0 ° and 180 °, is conducive to be balanced detection；Balanced detector can significantly inhibit local oscillator and swash
The influence of the intensity noise of light improves received signal to noise ratio.
Claims (3)
1. it is a kind of based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation, including narrow linewidth linearly polarized laser device (1),
Beam splitter (2), light intensity modulator (3), optical fiber circulator (4), polarization-maintaining sensor fibre (5-1), optical phase modulator (6),
Polarization-maintaining fiber coupler (7), balanced detector (8), signal processing circuit (9) and square wave signal generator (10)；
The narrow linewidth linearly polarized laser device is connected with the input terminal of beam splitter, and two output ports of beam splitter connect respectively
Connect the input terminal of light intensity modulator and the input terminal of optical phase modulator；The output end of light intensity modulator connects fiber annular
The duplex port of the pulse laser input port of device, optical fiber circulator connects polarization-maintaining sensor fibre, the signal light of optical fiber circulator
One input port of output port connection polarization-maintaining fiber coupler；The output port of optical phase modulator connects polarization maintaining optical fibre coupling
Two output ports of another input port of clutch, polarization-maintaining fiber coupler connect balanced detector；Balanced detector
Output port accesses signal processing circuit；At the output port connection optical phase modulator and signal of the square wave signal generator
Manage circuit；
The square wave signal generator generates periodic signal of square wave and inputs optical phase modulator, is carried out with the phase to local oscillator light
Phase-shift keying (PSK) modulation；After passing through optical phase modulator and polarization-maintaining fiber coupler when local oscillator light is in low level, balanced detector
The voltage V of outputa∝ESELOCos (Δ ω t+ Δ φ), wherein Δ ω is the difference of the angular frequency of signal light and local oscillator light, Δ φ
For the difference of signal light and the initial phase of local oscillator light, ESFor the amplitude of signal light field, ELOFor the amplitude of local oscillator light field；When local oscillator light exists
After passing through optical phase modulator and polarization-maintaining fiber coupler when pi/2 level, the voltage V of balanced detector outputb∝ESELOsin
(Δωt+Δφ)；The voltage signal entering signal processing circuit of balanced detector output, signal processing circuit pass through to voltage
It square sums again respectively, obtains signal V=Va 2+Vb 2∝ISILO, ISFor the intensity of signal light, ILOFor the intensity of local oscillator light.
2. according to claim 1 based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation, which is characterized in that
The amplitude for the square-wave signal that the square wave signal generator generates is the pi/2 of optical phase modulator voltage, duty ratio 50%.
3. according to claim 1 based on the coherent light time domain reflection of local oscillator light orthogonal phase modulation, which is characterized in that
The polarization-maintaining sensor fibre is substituted using single mode sensor fibre, and in the signal optical output port and polarization maintaining optical fibre of optical fiber circulator
Optical fiber polarization controller is added between the input port of coupler.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110455324A (en) * | 2019-08-20 | 2019-11-15 | 电子科技大学 | A kind of quasi-distributed sensor-based system of high-repetition-rate and its implementation based on CP- Φ OTDR |
| CN110535461A (en) * | 2019-08-01 | 2019-12-03 | 上海大学 | A kind of heterodyne detection device based on optical injection-locked and Optical phase-locked loop |
| CN111412936A (en) * | 2020-03-10 | 2020-07-14 | 天津大学 | Full-digital orthogonal phase shift pulse COTDR sensing device and method |
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| CN111412936B (en) * | 2020-03-10 | 2021-08-06 | 天津大学 | Full-digital orthogonal phase shift pulse COTDR sensing device and method |
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