CN102353393B - Quadrature demodulation device for interference type photo-sensor based on pi/2 phase modulation - Google Patents
Quadrature demodulation device for interference type photo-sensor based on pi/2 phase modulation Download PDFInfo
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Abstract
The invention discloses a quadrature demodulation device for an interference type photo-sensor based on pi/2 phase modulation. In the device, light output by a laser is divided into a signal sensing light path and a reference light path through a 1*2 coupler; on the signal sensing light path, a sensing signal output is acquired by a phase sensitive device of a sensing head; on the reference light path, a reference signal output is acquired by a pi/2 phase modulator; the sensing signal output and the reference signal output are combined through a 2*1 light combiner, pass through a photoelectric detector and a low-noise amplifier sequentially and then are sampled by a digital signal processor; and the acquired data is divided into two paths according to odd-even positions and then is subjected to digital quadrature demodulation to acquired a sensing signal required to be demodulated. The device has the advantages of simple phase demodulation structure, simple and effective processing arithmetic, capability of effectively eliminating non-linear influences of devices and the like.
Description
Technical field
The present invention relates to the orthogonal demodulation device of interfere type optical sensor, relate in particular to a kind of orthogonal demodulation device of the interfere type optical sensor based on pi/2 phase modulation.
Background technology
Along with the fast development of modern science and technology, human society just changes to informationization from intense industrialization, and sensor, as a kind of important way of people's acquired information, has received people's concern more and more, becomes the forward of development of modern scientific technology.Fibre Optical Sensor has anti-electromagnetic interference (EMI), and volume is little, lightweight, spatial resolution advantages of higher, and it is easy to be designed to various shapes, is easy to realize Optical Fiber Transmission and remote remote measurement, is easy to form sensing network and realizes the measurement to multiple spot many reference amounts.
Interferometric optical fiber sensor and Techniques of Intensity Type Optical Fibre Sensors structure compared are complicated, but its sensitivity is very high, thereby become an important component part of Fibre Optical Sensor research.Interferometric optical fiber sensor is to utilize the effect of measurand to optical fiber, and while causing light through optical fiber, phase place changes to reach the object of detection.At present, the existing practical application that a plurality of interferometric optical fiber sensors is combined into systems array, the sensor-based system of intelligent, the functional form that also has that comprehensive optical fiber technology forms, but from practical application product, mainly concentrates on fibre optic accelerometer and optical fiber water and listens etc.
Fibre optic accelerometer is that the shock resistances such as vehicle, boats and ships, anti-vibration are measured, conventional important sensor in earthquake detection system, its ultimate principle is: at inertial space, the mass that quality is M is set, the inertial force producing while making acceleration movement with perception measured device and displacement, measure inertial force or displacement and can measure corresponding acceleration.Interferometric fiber optic accelerometer is by extraneous physical field, to carry out the phase place of the light wave that passes in the interference arm of modulation optical fiber interferometer, and interferometer is converted into light intensity variation phase place variation, can utilize photoelectric conversion technique and phase-detection technology to demodulate extraneous physical signalling to be measured.Fibre optic accelerometer is the new sensor that a kind of antijamming capability is strong, highly sensitive, dynamic range is wide, and the eighties is firm is subject to everybody attention once coming out.
Fibre optic hydrophone is divided into by principle: intensity type, interfere type and grating type optical fiber.Wherein phase interference type fibre optic hydrophone is to make according to the principle of interference of coherent light, thereby not only highly sensitive, and dynamic range is large.Generally believe at present, phase interference type fibre optic hydrophone is the most rising nautical receiving set.Because electromagnetic wave and light wave under water all can not long-distance communications, sound wave has been exactly main information carrier since device development under water, but traditional piezoelectric type nautical receiving set is all difficult to meet new requirement at aspects such as sensitivity and communications at present.Fibre optic hydrophone has that detection sensitivity is high, antijamming capability is strong, enough large dynamic range, round-the-clock real-time detection identification, system green end is lightweight and the arbitrariness of structure, and these technical characterstics make fibre optic hydrophone be enough to adapt to the needs of various sensings.
The signal demodulation techniques of existing interfere type optical sensor are mainly PGC demodulation method, 3 * 3 coupling mechanism demodulation methods and heterodyne demodulation method etc.
The principle of PGC demodulation is to adopt uneven interferometer, by light source frequency is carried out to high frequency modulated, thereby in interferometer, introduce the significantly phase modulated signal of a certain frequency outside detection signal bandwidth, make institute's detection signal become these significantly sidebands of carrier wave, with the carrier wave of carrier wave self and two frequencys multiplication, carry out respectively interchange transducing signal and the drift of low frequency random phase of the separated fibre optic interferometer of mode of coherent detection and differential-multiplication cross, then by Hi-pass filter, obtain stable transducing signal and export.But this method has two defects, the one, in the time of to light source frequency modulation, have association amplitude modulated phenomenon, cause restituted signal distortion; Two is that the carrier wave of two frequencys multiplication is multiplied each other and obtained by carrier wave self, and phase place is asynchronous with self, also can bring the distortion of demodulation.
3 * 3 coupling mechanism demodulation principle are that Mach Zehnder interferometry two arm signals, after 3 * 3 coupling mechanisms are synthetic, can obtain the 120 ° tri-road interference signals of phase phasic difference successively, thereby can not occur signal blanking phenomenon simultaneously.Demodulating algorithm only needs the operations such as Dui Zhe tri-road signals are added, subtract each other, multiply each other, differential, integration, filtering, finally just can obtain required transducing signal.This method can be used simple device to realize signal demodulation, but it also exists defect, first 3 * 3 coupling mechanisms are because the principles such as manufacturing process three road output optical signal sizes can not be completely equal, in addition the photodetector responsiveness that Dui San road interference signal is surveyed also can not be just the same, and these unbalancednesss will exert an influence to last demodulation result, cause distorted signals.Other 3 * 3 coupling mechanism demodulation methods need to be processed 3 road signals, and Processing Algorithm relative complex, affects net result integrality.
Heterodyne demodulation method does not need to use modulated light source, conventionally in interferometer reference arm, adds heterodyne modulator, makes reference arm produce frequency displacement, thereby makes two arms form frequency difference, the heterodyne signal that just can obtain being responded by photodetector after interfering like this.The heterodyne signal of being exported by photodetection is divided into identical two-way, the signal mixing after phase-shift circuit with heterodyne modulation signal and heterodyne modulation signal respectively, then through demodulator circuits such as low-pass filtering, differential, carry out the demodulation of transducing signal.The advantage of heterodyne demodulation method is to avoid association AM interference, shortcoming is need to be with accurate heterodyne modulation signal phase-shift circuit, once phase place is fixing, just can not regulate along with the variation of heterodyne modulation signal, and have intrinsic electronics phase drift and the problem such as noise is serious.
Summary of the invention
In order to overcome the deficiency of background technology, the object of the present invention is to provide a kind of orthogonal demodulation device of the interfere type optical sensor based on pi/2 phase modulation.Can effectively eliminate association amplitude modulation impact, eliminate phase amplitude unbalanced factor, reduce the use of components and parts, reduce the factor impacts such as non-linear, realize accurately adjustable phase quadrature quadrature demodulation.
The technical solution used in the present invention is:
Laser instrument output optical signal is divided into two-way after 1 * 2 coupling mechanism light splitting, one tunnel connects sensing head and obtains transducing signal output, another road connects phase-modulator and obtains reference path output, transducing signal output and reference path output obtain the interference light signal of sensing light path and reference path after 2 * 1 optical combiners, interference light signal is input to photodetector and obtains interfering electric signal, then by digital signal processor, is being input to the data sampling of realizing interference electric signal under the square-wave signal external trigger of phase-modulator after low noise amplifier amplifies.
Described digital signal processor comprises parity packet module, two differential modules, two modules that multiply each other, subtraction block, integration module and low-pass filtering modules, from low noise amplifier, (signal of input is triggered by square-wave signal through parity packet module, obtain the orthogonal signal that two groups of pi/2s differ, again these two groups of orthogonal signal are input to respectively the output of the first differential module and the second differential module again with differential before data cross enter first module and second module that multiplies each other that multiplies each other and realize multiplication cross, first the multiply each other module output of module and second of multiplying each other enters and in subtraction block, subtracts each other processing, again after processing in integration module, random phase by the relative low frequency of low-pass filtering module filtering changes, obtain the transducing signal of required demodulation, finally realized whole demodulating process.
Described phase-modulator is after amplitude is 1/2nd half-wave voltage square-wave frequency modulation, and light phase amplitude of variation is pi/2.
Described phase-modulator modulated square wave signal frequency f is greater than transducing signal highest frequency more than 10 times.
The phase-modulation speed of described phase-modulator is more than 10MHz.
Described laser instrument is narrow linewidth laser, and the phase sensitive device on described sensing head is optical fibre vibration sensor, fibre optic hydrophone, fibre optic gyroscope or phase sensitive formula current/voltage sensor.
The reception bandwidth of described photodetector is greater than 10 times of modulated square wave signal frequency f.
The sample frequency of described digital signal processor is set to 2Nf, and N is integer.
Compare with background technology, beneficial effect of the present invention is:
The present invention can be the Digital Square-Wave phase-modulated signal of 1/2nd half-wave voltages by input peak-to-peak value, the phase place of instantaneous change interference signal, make to have between neighbouring sample point pi/2 phase poor, and because changing, phase-modulator phase modulation far faster than transducing signal, changes and random phase offset variation, two adjacent groups signal can be regarded synchronization sampled signal as, the interference signal that two groups of pi/2s that obtain thus differ finally can be realized quadrature demodulation by digital demodulation algorithm and process, and eliminates random phase and changes the impact that demodulation result is brought.With the comparison of PGC demodulating equipment, this device can be eliminated association amplitude modulation impact, has reduced frequency mixer and low-pass filter and has used, thereby reduced active device non-linear effects, has improved output signal-to-noise ratio.With 3 * 3 demodulating equipment comparisons, the impact that this device does not exist each road detectable signal imbalance of 3 * 3 coupling mechanisms to cause more, and can reduce photodetector usage quantity and simplify subsequent demodulation algorithm calculation step, restituted signal is improved.With the comparison of heterodyne demodulation device, this device, equally without using frequency mixer, wave filter, reduces non-linear; And can replace phase shifting device to realize the accurate modulation of phase place with phase-modulator, phase modulation amplitude can change by changing phase-modulator square wave amplitude.
Accompanying drawing explanation
Fig. 1 is this pi/2 phase modulation-demodulation device schematic diagram.
Fig. 2 is DSP internal data processing flow chart.
Fig. 3 is digital signal processor demodulation result oscillogram.
In figure: 101, laser instrument, 102,1 * 2 coupling mechanism, 103, phase-modulator, 104, sensing head, 105,2 * 1 optical combiners, 106, photodetector, 107, low noise amplifier, 108, digital signal processor, 201, parity packet module, 202, differential module, 203, differential module, 204, module multiplies each other, 205, the module that multiplies each other, 206, subtraction block, 207, integration module, 208, low pass filtered glass module.
Embodiment
Below in conjunction with drawings and Examples, the present invention is further illustrated.
As shown in Figure 1, laser instrument 101 output optical signals are divided into two-way after 1 * 2 coupling mechanism 102 light splitting, one tunnel connects sensing head 104 and obtains transducing signal output, another road connects phase-modulator 103 and obtains reference path output, transducing signal output and reference path output obtain the interference light signal of sensing light path and reference path after 2 * 1 optical combiners 105, interference light signal is input to photodetector 106 and obtains interfering electric signal, after amplifying, low noise amplifier 107 is being input to by digital signal processor 108 data sampling of realizing interference electric signal under the square-wave signal external trigger of phase-modulator 103 again.
As shown in Figure 2, described digital signal processor 108 comprises parity packet module 201, two differential modules 202,203, two multiply each other module 204,205, subtraction block 206, integration module 207 and low-pass filtering modules 208, from the signal of low noise amplifier 107 inputs, through parity packet module 201, by square-wave signal, triggered, obtain the orthogonal signal that two groups of pi/2s differ, again these two groups of orthogonal signal are input to respectively the first differential module 202 and the output of the second differential module 203 again with differential before data cross enter first module 204 and second module 205 that multiplies each other that multiplies each other and realize multiplication cross, first module 204 and second module 205 output of multiplying each other of multiplying each other enters in subtraction block 206 and subtracts each other processing, again after processing in integration module 207, random phase by the relative low frequency of low-pass filtering module 208 filtering changes, obtain the transducing signal of required demodulation, finally realized whole demodulating process.
Described phase-modulator 103 is after amplitude is 1/2nd half-wave voltage square-wave frequency modulation, and light phase amplitude of variation is pi/2.
Described phase-modulator 103 modulated square wave signal frequency f are greater than transducing signal highest frequency more than 10 times
The phase-modulation speed of described phase-modulator 103 is more than 10MHz.
Described laser instrument is narrow linewidth laser, can effectively reduce the impact of phase noise on demodulation result, improves output signal-to-noise ratio.Phase sensitive device on described sensing head 104 is optical fibre vibration sensor, fibre optic hydrophone, fibre optic gyroscope or phase sensitive formula current/voltage sensor.
The reception bandwidth of described photodetector 106 is greater than 10 times of modulated square wave signal frequency f, to guarantee to detect the higher hamonic wave amount that obtains square-wave signal.
The sample frequency of described digital signal processor 108 is set to 2Nf, and N is integer.And adjust sampling time delay, make sample in the intermediate point moment position of phase-modulation square-wave signal low and high level.
Suppose that laser instrument 101 outputs to light intensity in signal arm and reference arm through 1 * 2 coupling mechanism 102 couplings and is respectively E
1, E
2;
Suppose that transducing signal processed is 4.5KHz sinusoidal signal
s(t)＝Acos(2π×4500×t)
Suppose that pi/2 phase-modulated signal frequency f is that 100KHz has:
Through the phase sensitive device of sensing head 104, obtaining transducing signal is output as:
Through pi/2 phase modulator 103, obtaining reference path is output as:
for the drift of two-way random phase.
Therefore photodetector 106 output signals can be expressed as:
Wherein
As shown in Figure 2, this signal will be collected by digital signal processor 108 the concrete output waveform of photodetector 106 after low noise amplifier 107 amplifies.The data sampling frequency that DSP is set is the twice (being made as 200kHz herein) with reference to frequency modulating signal, and time that sampling delay makes to interfere the sampled data of electric signal is set to be corresponded respectively to reference to the intermediate point of square-wave signal modulation low and high level position constantly, impact demodulation result being brought to eliminate square wave rising edge and negative edge.If 0 carries out first sampling constantly, N sampled point time can be expressed as:
Ignore DC component influence, N sampled data of digital signal processor corresponds to:
Due to S (N) with
the relative N of variation be a gradual process, therefore have:
Image data is carried out to parity packet, and even number set can be expressed as:
Odd number group can be expressed as:
Visible after above-mentioned packet transaction, two groups of group signal I of resulting odd even
1and I (N)
2(N) differ as pi/2, utilize them can carry out quadrature demodulation.
DSP internal processes as shown in Figure 2, first sampling the data obtained is processed through parity packet module 201, obtain the orthogonal signal that two groups of pi/2s differ, then these two groups of orthogonal signal be input to respectively in differential module 202,203 and processed, by continuous signal, can be expressed as:
Differential module 202,203 Output rusults again with differential before data cross enter the module 204,205 that multiplies each other, realize multiplication cross process:
Two multiplier module 204,205 outputs enter in subtraction block 206 subtracts each other processing, obtains:
After processing in integration module 207, be again:
Random phase by the relative low frequency of low-pass filtering module 208 filtering changes, and finally obtains:
Hereto, realized whole demodulating process.Its demodulation result as shown in Figure 3.
The above; it is only preferably embodiment of the present invention; but protection scope of the present invention is not limited to this; anyly be familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement (as changed square wave frequency and sample frequency etc.), within all should being encompassed in protection scope of the present invention.
Claims (7)
1. the orthogonal demodulation device of the interfere type optical sensor based on pi/2 phase modulation, it is characterized in that: laser instrument (101) output optical signal is divided into two-way after 1 * 2 coupling mechanism (102) light splitting, one tunnel connects sensing head (104) and obtains transducing signal output, another road connects phase-modulator (103) and obtains reference path output, transducing signal output and reference path output obtain the interference light signal of sensing light path and reference path after 2 * 1 optical combiners (105), interference light signal is input to photodetector (106) and obtains interfering electric signal, after amplifying, under the square-wave signal external trigger that is input to phase-modulator (103), realized by low noise amplifier (107) again the data sampling of interfering electric signal by digital signal processor (108),
Described phase-modulator (103) is after amplitude is 1/2nd half-wave voltage square-wave frequency modulation, and light phase amplitude of variation is pi/2.
2. the orthogonal demodulation device of a kind of interfere type optical sensor based on pi/2 phase modulation according to claim 1, it is characterized in that: described digital signal processor (108) comprises parity packet module (201), two differential modules (202,203), two modules that multiply each other (204,205), subtraction block (206), integration module (207) and low-pass filtering module (208), from the signal of low noise amplifier (107) input through parity packet module (201) by square-wave signal external trigger, obtain the orthogonal signal that two groups of pi/2s differ, again these two groups of orthogonal signal are input to respectively the output of the first differential module (202) and the second differential module (203) again with differential before data cross enter first module (204) and second module (205) that multiplies each other that multiplies each other and realize multiplication cross, first multiply each other module (205) output of module (204) and second of multiplying each other enters in subtraction block (206) and subtracts each other processing, again after processing in integration module (207), random phase by the relative low frequency of low-pass filtering module (208) filtering changes, obtain the transducing signal of required demodulation, finally realized whole demodulating process.
3. the orthogonal demodulation device of a kind of interfere type optical sensor based on pi/2 phase modulation according to claim 1, is characterized in that: described phase-modulator (103) modulated square wave signal frequency f is greater than transducing signal highest frequency more than 10 times.
4. the orthogonal demodulation device of a kind of interfere type optical sensor based on pi/2 phase modulation according to claim 1, is characterized in that: the phase-modulation speed of described phase-modulator (103) is more than 10MHz.
5. the orthogonal demodulation device of a kind of interfere type optical sensor based on pi/2 phase modulation according to claim 1, it is characterized in that: described laser instrument is narrow linewidth laser, the phase sensitive device on described sensing head (104) is optical fibre vibration sensor, fibre optic hydrophone, fibre optic gyroscope or phase sensitive formula current/voltage sensor.
6. the orthogonal demodulation device of a kind of interfere type optical sensor based on pi/2 phase modulation according to claim 1, is characterized in that: the reception bandwidth of described photodetector (106) is greater than 10 times of modulated square wave signal frequency f.
7. the orthogonal demodulation device of a kind of interfere type optical sensor based on pi/2 phase modulation according to claim 1, is characterized in that: the sample frequency of described digital signal processor (108) is set to 2Nf, and N is integer.
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| CN110646020B (en) * | 2019-10-30 | 2023-01-24 | 电子科技大学中山学院 | Optical fiber interference device and method |
| CN113419341B (en) * | 2021-06-22 | 2022-11-18 | 中国人民解放军国防科技大学 | Method and device for reconstructing optical field of optical fiber interferometer in complex manner |
| CN114061732B (en) * | 2021-10-08 | 2024-04-09 | 上海船舶电子设备研究所(中国船舶重工集团公司第七二六研究所) | One-dimensional optical fiber vector hydrophone structure |
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Granted publication date: 20140820 Termination date: 20160701 |