CN105157812A - Digital enhanced interference-based high-sensitivity quasi-distributed fiber bragg grating vibration sensor - Google Patents

Digital enhanced interference-based high-sensitivity quasi-distributed fiber bragg grating vibration sensor Download PDF

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CN105157812A
CN105157812A CN201510601605.0A CN201510601605A CN105157812A CN 105157812 A CN105157812 A CN 105157812A CN 201510601605 A CN201510601605 A CN 201510601605A CN 105157812 A CN105157812 A CN 105157812A
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卢斌
叶青
魏韦
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Optical Information Technology Co Ltd Is Sent In Nanjing
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Abstract

The invention discloses a digital enhanced interference-based high-sensitivity quasi-distributed fiber bragg grating vibration sensor, which comprises a narrow linewidth laser, a first fiber coupler, an electro-optic modulator, an acousto-optic modulator, a circulator, a weak reflection fiber bragg grating array, a second fiber coupler, a double-balanced detector, an arbitrary waveform generator, an electrical amplifier, n electrical delayers, n multipliers and a phase demodulator, wherein the output port of the narrow linewidth laser is connected with the input port of the first fiber coupler; the first output port of the first fiber coupler is connected with the light signal input end of the electro-optic modulator; the output port of the electro-optic modulator is connected with the light signal input port of the acousto-optic modulator; the light signal output port of the acousto-optic modulator is connected with the first port of the circulator; and the second port of the circulator is connected with the input port of the weak reflection fiber bragg grating array.

Description

The high sensitivity quasi-distributed fiber grating vibration transducer of interfering is strengthened based on numeral
Technical field
The present invention relates to numeral and strengthen interference optical fiber sensing technology, particularly a kind of high sensitivity quasi-distributed fiber grating vibration transducer strengthening interference based on numeral.
Background technology
It is strong that Fibre Optical Sensor has anti-electromagnetic interference capability, high sensitivity, and corrosion-resistant, explosion-proof, light path has flexibility, and distance sensing is long, is convenient to and the advantage such as fibre system is connected.In recent years, be widely used in rock gas, petroleum pipe line safety monitoring, bridge crack is monitored, the fields such as gas concentration detection, border security protection.Such as, but in the occasion of ask for something high sensitivity detection ability, the detection etc. of sound-detection, weak vibration, the sensitivity of Fibre Optical Sensor and signal to noise ratio (S/N ratio) are its restraining factors always.Therefore, the sensitivity and the signal to noise ratio (S/N ratio) that improve optical fiber sensing system are the task of top priority.
Since H.F.Taylor in 1993 proposes phase sensitive optical time domain reflectometer (Phasesensitiveopticaltimedomainreflectometry, hereinafter referred to as Phase-OTDR) since, substantially increase the sensitivity of Fibre Optical Sensor, specifically see [H.F.TaylorandE.E.Lee.Apparatusandmethodforfiberopticintr usionsensing.U.S.Patent5,1993:194847].
RobertM.Payton etc. propose in Phase-OTDR, apply pseudo-random sequence and carry out phase-modulation to continuous light, and carry out related operation at receiving end, demodulate phase information, improve sensitivity and the signal to noise ratio (S/N ratio) [RobertM.Payton.Naturalfiberspanreflectometerprovidingasp readvirtualsensingarraycapability.U.S.Patent, US7268863] of system.
The numeral that D.A.Shaddock etc. propose strengthens the concept of interference technique, utilize the correlation properties of pseudo-random code, effectively can suppress clutter noise, specifically see [DanielA.Shaddock, Digitallyenhancedheterodyneinterferometry.Opticsletters2 007,32 (22), 3355-3357.]
In general, the signal intensity returned in optical fiber is larger, and the signal to noise ratio (S/N ratio) of system is higher.What utilize in Phase-OTDR is that Rayleigh scattering light carries out sensing, and the strength ratio of Rayleigh scattering light is lower, has considerable restraint for the sensitivity and signal to noise ratio (S/N ratio) improving system.And by introducing reflection spot in a fiber, the light signal strength be reflected back can improve greatly.Based on this, reflected signal in optical fiber can be extracted in order to try as transducing signal, and strengthen interference technique with numeral and be combined, improve the sensitivity of system.But it is very crucial for how adding quasi-distributed reflection spot in a fiber.Someone adopts experiment when utilizing the cascade of fiber connector to carry out several reflection spot as reflection spot, and by the reference point of connector above as adjacent connector below, obtains the phase information between connector.Reflectivity such as the APC of fiber connector is ~ 1%, UPC emissivity ~ 4%, and connector position about has the loss of 0.4dB.If multiple connector level be linked togather, the signal intensity be reflected back after only several reflection spot can be caused all very low, even detect less than, cannot meet in quasi-distributed sensor-based system the requirement that a lot of sensing is counted at all.Numeral strengthens in interference technique, due to the their cross correlation of pseudo-random code, requires that the signal intensity that each weak reflection spot is reflected back is basically identical, to improve signal to noise ratio (S/N ratio).Before and after the signal intensity that each connector position is reflected back, difference is too large, greatly can reduce signal to noise ratio (S/N ratio).Further, connector has the shortcomings such as poor stability, volume be large in engineer applied.Therefore, need a kind of weak reflectivity, low-loss, be easy to integrated sensory reflex point, and preferably can realize the reflectivity adjustable of reflection spot, suitable with the signal intensity making front and back reflection spot be reflected back as far as possible.
Summary of the invention
The object of the invention is to, overcome that the sensitivity of above-mentioned existing fiber sensor-based system is low, the deficiency of poor signal to noise, propose a kind ofly to strengthen the high sensitivity quasi-distributed fiber grating sensor of interfering based on numeral.Adopt the array of weak reflectivity fiber grating cascade, the signal of collection is the signal reflected in grating, and signal intensity is large, and signal to noise ratio (S/N ratio) is high.Adopt numeral to strengthen interference technique in system, utilize the their cross correlation of pseudo-random code, remove the impact of clutter noise, improve the signal to noise ratio (S/N ratio) of system.
Technical solution of the present invention is as follows: a kind of high sensitivity quasi-distributed fiber grating vibration transducer strengthening interference based on numeral, it is characterized in that comprising narrow linewidth laser (1), first fiber coupler (2), electrooptic modulator (3), acousto-optic modulator (4), circulator (5), weak reflectivity optical fiber optical grating array (6), weak reflectivity optical fiber optical grating array is by weak reflective gratings 1, grating 2 grating m cascade forms, second fiber coupler (7), two balanced detector (8), AWG (Arbitrary Waveform Generator) (9), electrical amplifier (10), n electricity chronotron: electricity chronotron 1 (11), electrical delay device 2 (12) electricity chronotron n (13), n multiplier: multiplier 1 (14), multiplier 2 (15) multiplier n (16), phase demodulator (17), the output port of described narrow linewidth laser (1) is connected with the input port of described the first fiber coupler (2), first output port of the first fiber coupler (2) is connected with the optical signal input of described electrooptic modulator (3), described electrooptic modulator (3) output port is connected with the optical signal input mouth of described acousto-optic modulator (4), the light signal output end mouth of described acousto-optic modulator (4) is connected with described circulator (5) first port, second port of described circulator (5) is connected with the input port of weak reflectivity optical fiber optical grating array (6), 3rd port of described circulator (5) is connected with the first input end of described the second fiber coupler (7), second output port of the first fiber coupler (2) is connected with the second input port of the second fiber coupler (7), two output ports of the second fiber coupler (7) are connected with two input ports of two balanced detector (8), the output port of described pair of balanced detector (8) simultaneously with multiplier 1 (14), multiplier 2 (15) the first input end mouth of multiplier n (16) is connected, first output port of described AWG (Arbitrary Waveform Generator) (9) is connected with the input port of described electrical amplifier (10), the output port of described electrical amplifier (10) is connected with the radio-frequency (RF) signal input end mouth of electrooptic modulator (3), second output port of AWG (Arbitrary Waveform Generator) (9) is connected with described n electricity chronotron input port parallel connection simultaneously, the output port of n described electricity chronotron is connected with the second input port of a corresponding n multiplier respectively, the output port of n multiplier is connected with multiple input ports of phase demodulator (17) respectively.
The method for sensing of the sensor that utilizes of the present invention is: utilize AWG (Arbitrary Waveform Generator) to produce pseudo-random sequence, pseudo-random sequence is after amplifier, be used for driving electrooptic modulator, electrooptic modulator carries out phase-modulation to the laser of narrow linewidth laser, after pscudo-random codc modulation, light signal is through weak reflectivity optical fiber optical grating array, the time that the light signal that different weak reflectivity fiber grating reflection spot place reflects arrives receiving end is different, pseudo-random code coefficient of autocorrelation is utilized to be 1, cross-correlation coefficient is about the feature of 0, the signal received is carried out related operation with the local pseudo-random code through specific delays (consistent with the two-way time that flashlight arrives for measurement point), just can obtain the reflected signal of certain point interested, and the signal (comprising noise) of other point is suppressed, signal after related operation is again through phase demodulating, obtain the phase information of each reflection spot, the phase information at two adjacent reflection spot places carries out difference, just can obtain the vibration on the sensor fibre between two reflection spots, the transducing signals such as sound.Be the signal of reflection spot due to what adopt in sensing, and have employed the mode of pseudo-random sequence phase-modulation demodulation, greatly can improve the signal to noise ratio (S/N ratio) of system.
Adopt by weak reflective gratings 1, grating 2 ..., grating m cascade forms weak reflectivity optical fiber optical grating array, the signal reflected by described grating array is as transducing signal.
The refractive index of each the weak reflective gratings in weak reflectivity optical fiber optical grating array is through design: the refractive index of each weak reflective gratings increases gradually with distance, ensures that the optical signal magnitude reflected is basically identical, improves signal to noise ratio (S/N ratio).
Described narrow linewidth laser is RIO narrow linewidth laser, and centre wavelength is 1550nm, and live width is about 2.5kHz, also can adopt the laser instrument of the narrow linewidth of other kind.
Inclined fiber coupler protected by the first described fiber coupler, and 1550nm wave band, port 2X2, splitting ratio is 9:1, also can adopt the slightly differentiated fiber coupler of splitting ratio.
The second described fiber coupler is general single mode fiber, 1550 wave bands, port 2X2, and splitting ratio is 1:1, also can adopt the slightly differentiated fiber coupler of splitting ratio.
Described electrooptic modulator is JDSUAPE phase-modulator, 1550 wave bands, and bandwidth is 10GHz, and half-wave voltage is about 4.8v, carries out 0 or π phase-modulation, also can adopt the phase-modulator of other types by pseudo-random code to light signal.
Described acousto-optic modulator, wave band 1550nm, acousto-optic side-play amount 160MHz, be make local oscillator light produce the difference on the frequency of 160MHz with detection light, exporting light is still continuous light, also can adopt other acousto-optic modulator.
Described optical fiber circulator, is three port single-mode fiber circulators, also can adopts the way of incoming fiber optic coupling mechanism and isolator, play the scheme being equal to optical fiber circulator effect.
Described two balanced detector are high speed detector light signal being converted to electric signal, and wave band 1550nm, three dB bandwidth 40kHz-800MHz also can adopt other to meet two balanced detector of system performance.
Described low-pass filter, the radio-frequency component of main filtering electric signal.
Described multiplier is multiplication (relevant) computing realizing electric signal and pseudo-random sequence.
Described analog to digital converter, is mainly converted to digital signal by analog electrical signal.
Described AWG (Arbitrary Waveform Generator) is prepared by programmable logic device (PLD), realizes the generation of pseudo-random sequence, and to digital signal processing, realizes the phase demodulating of digital signal.
Described amplifier, mainly realizes the amplification to pseudo-random sequence, enables pseudo-random sequence drive electrooptic modulator to realize 0 or π phase-modulation.
Described electricity chronotron is to make local pseudo-random sequence postpone, consistent with the pseudo-random sequence phase place of the signal that reflection spot reflects.
Described phase demodulator can be the hardware module of the phase demodulating that can realize signal, also can be through the software demodulation after analog to digital converter+computing machine host computer.
Beneficial effect of the present invention:
1, adopt numeral to strengthen interference technique, sense light is through the continuous light of pscudo-random codc modulation, and the signal received is carried out related operation with local through the pseudo-random sequence of phase delay by receiving end, then carries out phase demodulating.Due to the correlation properties of pseudo-random code, clutter noise and intersymbol interference can be suppressed, improve signal to noise ratio (S/N ratio).
2, adopt weak reflectivity optical fiber optical grating array (by weak reflective gratings 1, grating 2 ..., grating n cascade forms), with reflected signal as transducing signal, signal intensity is high, larger than scattered signal intensity in optical fiber, signal to noise ratio (S/N ratio) is high, can realize the measurement of the information such as sound, vibration.
3, in weak reflectivity optical fiber optical grating array, the reflectivity of each grating can differentiation design, and the intensity of the signal that each optical grating reflection is returned is basically identical, improves signal to noise ratio (S/N ratio) further.
Accompanying drawing explanation
Fig. 1 the present invention is based on numeral to strengthen the high sensitivity quasi-distributed fiber grating vibration transducer structured flowchart of interfering;
Fig. 2 be in weak reflectivity optical fiber optical grating array each grating be reflection differences alienation design before and after performance comparison.
Embodiment
Below in conjunction with embodiment and accompanying drawing, the invention will be further described, but should not limit the scope of the invention with this.
First please refer to Fig. 1, Fig. 1 strengthens the high sensitivity quasi-distributed fiber grating vibration transducer one-piece construction block diagram of interfering based on numeral.As seen from Figure 1, its formation of high sensitivity quasi-distributed fiber grating vibration transducer that the present invention is based on numeral enhancing interference comprises narrow linewidth laser 1, first fiber coupler 2, electrooptic modulator 3, acousto-optic modulator 4, circulator 5, weak reflectivity optical fiber optical grating array 6 is (by weak reflective gratings 1, grating 2 grating n cascade forms), second fiber coupler 7, two balanced detector 8, AWG (Arbitrary Waveform Generator) 9, electrical amplifier 10, electricity chronotron 111, electrical delay device 212 electricity chronotron n13, multiplier 114, multiplier 215 multiplier n16, phase demodulator 17, it is characterized in that the output port of described narrow linewidth laser 1 is connected with the input port of the first described fiber coupler 2, first output port of this first fiber coupler 2 is connected with described electrooptic modulator 3 optical signal input, described electrooptic modulator 3 output port is connected with the optical signal input mouth of described acousto-optic modulator 4, the light signal output end mouth of described acousto-optic modulator 4 is connected with described circulator 5 first port, second port of this circulator 5 is connected with the input port of weak reflectivity optical fiber optical grating array 6, 3rd port of this circulator 5 is connected with the first input end of the second described fiber coupler 7, second output port of the first fiber coupler 2 is connected with the second input port of the second fiber coupler 7, two output ports of the second fiber coupler 7 are connected with two input ports of two balanced detector 8, the output port of this pair of balanced detector 8 simultaneously with multiplier 114, multiplier 215 the first input end mouth of multiplier n16 is connected, first output port of described AWG (Arbitrary Waveform Generator) 9 is connected with the input port of described electrical amplifier 10, the output port of described electrical amplifier 10 is connected with the radio-frequency (RF) signal input end mouth of electrooptic modulator 3, the second output port of AWG (Arbitrary Waveform Generator) 9 simultaneously with described electricity chronotron 111, electrical delay device 212 the input port of electricity chronotron n13 is connected, described electricity chronotron 111, electrical delay device 212 the output port of electricity chronotron n13 respectively with multiplier 114, multiplier 215 second input port of multiplier n16 is connected, multiplier 114, multiplier 215 the output port of multiplier n16 is connected with multiple input ports of phase demodulator respectively.
The ultimate principle of apparatus of the present invention is as follows:
The first, the light signal that narrow linewidth laser exports is divided into detection light and local oscillator light through the first fiber coupler, and detection light is through electrooptic modulator, and pseudo-random code drives electrooptic modulator to carry out phase-modulation to input continuous laser.0 corresponding modulating phase place 0 of pseudo-code, 1 corresponding modulating phase place π of pseudo-code.Light after modulation, after acousto-optic modulator, produces certain frequency displacement.
The second, the light signal after producing frequency displacement injects weak reflectivity optical fiber optical grating array by circulator, supposes that the position of adjacent two fiber gratings is respectively l 1and l 2, then the sensor fibre length between these two gratings is Δ l=l 2-l 1.The time that detection light signal comes and goes each fiber grating is respectively t 1=2nl 1/ c, t 2=2nl 2/ c, in formula, c is the light velocity, and n is optical fibre refractivity.The light phase difference signal that between adjacent gratings, measured signal produces is Δ φ (t)=4 π n (t) Δ l (t)/c.
Three, the light signal reflected through each fiber grating and local oscillator photo-beat frequently after, enter two balanced detector and carry out heterodyne reception, light signal is converted into electric signal.
Four, local pseudo-random sequence is through chronotron time delay t respectively 1, t 2, t nafter, carry out multiplication (relevant) computing to the signal that detector exports.T 1, t 2, t ncorresponding detection light signal comes and goes FBG1, FBG2 respectively ..., FBGn time.Coefficient of autocorrelation due to pseudo-random sequence is 1, and cross-correlation coefficient is 0.Therefore, each fiber grating reflection spot FBG1, FBG2 is obtained after the local pseudo-random sequence after specific time delay and the signal correction computing be reflected back ..., the signal that is reflected back of FBGn.
Five, the simulating signal that obtains of related operation, after analog to digital converter is converted to digital signal, access phase demodulation modules, carries out phase demodulating, such as, adopts the mode of quadrature phase demodulation.Demodulate FBG1, FBG2 in sensor array ..., FBGn place light signal phase information be then the light phase at adjacent two grating places carries out difference, just can obtain the phase perturbation signal on sensor fibre in adjacent two sections of gratings
Six, in addition, if the reflectivity of each grating is identical, then along with the increase of distance sensing, the signal intensity be reflected back can reduce gradually.If the intensity of reflected signal is widely different, the signal to noise ratio (S/N ratio) of meeting influential system.Can by realizing the refringence alienation design of fiber grating, fiber grating refractive index is increased gradually, the intensity of the signal that each optical grating reflection is returned is basically identical, further raising signal to noise ratio (S/N ratio), Fig. 2 is that other condition setting is consistent, the relation of the emulation of signal to noise ratio (S/N ratio) and grating number when just the refractive index of sensing grating is different: a kind of situation is each fiber grating reflectivity is all 1% (signal intensity be reflected back reduces gradually), it is another kind of that for each fiber grating refringence alienation design, (refractive index increases gradually, the signal intensity that each optical grating reflection returns is about 1% of incident intensity more).Visible, the refractive index of fiber grating carry out the signal to noise ratio (S/N ratio) after differentiation design more consistent than each grating refractive index when signal to noise ratio (S/N ratio) high, and grating number is more, and signal to noise ratio (S/N ratio) difference is more obvious.
Above technical scheme can realize a kind of high sensitivity quasi-distributed fiber grating vibration transducer strengthening interference based on numeral.Although describe in detail the present invention with reference to above-mentioned specific embodiment, should be appreciated that the present invention is not limited to disclosed embodiment and embodiment, for this professional domain technician, various change can be carried out to its form and details.The form of such as fiber laser can be replaced by other narrow-linewidth single frequency laser instrument; The service band of laser instrument can replace with other wave band; Circulator can substitute with coupling mechanism; Phase demodulating device also can be the digital signal processor of other kinds, as computing machine, single-chip microcomputer etc.Institute it should be understood that and the foregoing is only instantiation of the present invention, is not limited to the present invention, and all any amendments done within the spirit and principles in the present invention, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (10)

1. the high sensitivity quasi-distributed fiber grating vibration transducer strengthening to interfere based on numeral, it is characterized in that comprising narrow linewidth laser (1), first fiber coupler (2), electrooptic modulator (3), acousto-optic modulator (4), circulator (5), weak reflectivity optical fiber optical grating array (6), weak reflectivity optical fiber optical grating array is by weak reflective gratings 1, grating 2 grating m cascade forms, second fiber coupler (7), two balanced detector (8), AWG (Arbitrary Waveform Generator) (9), electrical amplifier (10), n electricity chronotron: electricity chronotron 1 (11), electrical delay device 2 (12) electricity chronotron n (13), n multiplier: multiplier 1 (14), multiplier 2 (15) multiplier n (16), phase demodulator (17), the output port of described narrow linewidth laser (1) is connected with the input port of described the first fiber coupler (2), first output port of the first fiber coupler (2) is connected with the optical signal input of described electrooptic modulator (3), described electrooptic modulator (3) output port is connected with the optical signal input mouth of described acousto-optic modulator (4), the light signal output end mouth of described acousto-optic modulator (4) is connected with described circulator (5) first port, second port of described circulator (5) is connected with the input port of weak reflectivity optical fiber optical grating array (6), 3rd port of described circulator (5) is connected with the first input end of described the second fiber coupler (7), second output port of the first fiber coupler (2) is connected with the second input port of the second fiber coupler (7), two output ports of the second fiber coupler (7) are connected with two input ports of two balanced detector (8), the output port of described pair of balanced detector (8) simultaneously with multiplier 1 (14), multiplier 2 (15) the first input end mouth of multiplier n (16) is connected, first output port of described AWG (Arbitrary Waveform Generator) (9) is connected with the input port of described electrical amplifier (10), the output port of described electrical amplifier (10) is connected with the radio-frequency (RF) signal input end mouth of electrooptic modulator (3), second output port of AWG (Arbitrary Waveform Generator) (9) is connected with described n electricity chronotron input port parallel connection simultaneously, the output port of n described electricity chronotron is connected with the second input port of a corresponding n multiplier respectively, the output port of n multiplier is connected with multiple input ports of phase demodulator (17) respectively.
2. sensor carries out the method for sensing according to claim 1, AWG (Arbitrary Waveform Generator) is utilized to produce pseudo-random sequence, pseudo-random sequence is after amplifier, be used for driving electrooptic modulator, electrooptic modulator carries out phase-modulation to the laser of narrow linewidth laser, after pscudo-random codc modulation, light signal is through weak reflectivity optical fiber optical grating array, the time that the light signal that different weak reflectivity fiber grating reflection spot place reflects arrives receiving end is different, pseudo-random code coefficient of autocorrelation is utilized to be 1, cross-correlation coefficient is about the feature of 0, the signal received is carried out related operation with the local pseudo-random code namely arrived with flashlight through specific delays for the two-way time of measurement point is consistent, just obtain the reflected signal of certain point interested, and the signal (comprising noise) of other point is suppressed, signal after related operation is again through phase demodulating, obtain the phase information of each reflection spot, the phase information at two adjacent reflection spot places carries out difference, just can obtain the vibration on the sensor fibre between two reflection spots, sound sensor signal.
3. method according to claim 2, is characterized in that adopting by weak reflective gratings 1, grating 2 ..., grating m cascade weak reflectivity optical fiber optical grating array, the signal reflected by described grating array is as transducing signal.
4. method according to claim 2, it is characterized in that the refractive index of each the weak reflective gratings in weak reflectivity optical fiber optical grating array is through design: the refractive index of each weak reflective gratings increases gradually with distance, ensure that the optical signal magnitude reflected is basically identical, improve signal to noise ratio (S/N ratio).
5. method according to claim 2, described narrow linewidth laser is narrow cable and wide optical fiber laser, and centre wavelength is 1550nm, and live width is 2.5kHz, also can adopt the laser instrument of the narrow linewidth of other kind; The first described fiber coupler is general single mode fiber, 1550nm wave band, and splitting ratio is 9:1; The second described fiber coupler is general single mode fiber, and 1550nm wave band splitting ratio is 1:1.
6. method according to claim 2, described electrooptic modulator is the phase-modulator with higher bandwidth, carries out 0 or π phase-modulation by pseudo-random code to light signal.
7. method according to claim 2, described acousto-optic modulator makes local oscillator light produce the difference on the frequency of tens MHz with detection light, and exporting light is still continuous light.
8. method according to claim 2, described described AWG (Arbitrary Waveform Generator) is prepared by programmable logic device (PLD), realizes the generation of pseudo-random sequence, and to digital signal processing, realizes the phase demodulating of digital signal; Described two balanced detector are high speed detector light signal being converted to electric signal; Described multiplier is multiplication (relevant) computing realizing electric signal and pseudo-random sequence.
9. method according to claim 2, described electricity chronotron is to make local pseudo-random sequence postpone, consistent with the pseudo-random sequence phase place of the signal that reflection spot reflects.Described amplifier, mainly realizes the amplification to pseudo-random sequence, enables pseudo-random sequence drive electrooptic modulator to realize 0 or π phase-modulation.
10. method according to claim 2, described phase demodulator is the hardware module of the phase demodulating that can realize signal, or the software demodulation after analog to digital converter+computing machine host computer.
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