CN102353393A - 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 has received people's attention more and more as a kind of important way of people's acquired information, becomes the forward of development of modern scientific technology.Fibre Optical Sensor has anti-electromagnetic interference (EMI), and volume is little, and is in light weight, the spatial resolution advantages of higher, and it is easy to be designed to different shape, is easy to realize Optical Fiber Transmission and remote remote measurement, is easy to constitute sensing network and realizes the measurement to the 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 phase place changes and reaches the purpose of detection when causing light through optical fiber.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 has also that comprehensive optical fiber technology constitutes, but from the practical application product mainly concentrates on fibre optic accelerometer and optical fiber water and listens etc.
Fibre optic accelerometer is that shock resistances such as vehicle, boats and ships, anti-vibration are measured; The important sensor of using always in the earthquake detection system; Its ultimate principle is: at inertial space the mass that quality is M is set; Inertial force that produces when making acceleration movement with the perception measured device and displacement are measured inertial force or displacement and can be measured relevant acceleration.Interferometric fiber optic accelerometer is the phase place of coming the light wave that passes in the interference arm of modulation optical fiber interferometer through extraneous physical field; And interferometer is converted into the light intensity variation to phase change, can utilize photoelectric conversion technique and phase-detection technology to demodulate extraneous physical signalling to be measured.Fibre optic accelerometer is the novel sensor spare that a kind of antijamming capability is strong, highly sensitive, dynamic range is wide, the firm attention that receives everybody the coming out eighties.
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 process according to the principle of interference of coherent light, thereby not only highly sensitive, and dynamic range is big.Generally believe that at present phase interference type fibre optic hydrophone is the most rising nautical receiving set.Because electromagnetic wave and light wave all can not long-distance communications under water, sound wave has been exactly the main information carrier since device development under water, but present traditional piezoelectric type nautical receiving set all is difficult to satisfy new requirement at aspects such as sensitivity and information transmission.Fibre optic hydrophone have detection sensitivity height, antijamming capability strong, enough big dynamic range, all-weather real-time survey discern, system's green end is in light weight and the arbitrariness of structure, 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; Through light source frequency is carried out high frequency modulated; Thereby in interferometer, introduce the phase modulated signal significantly of a certain frequency outside the detection signal bandwidth; Make institute's detection signal become these sidebands of carrier wave significantly; The mode of carrying out coherent detection and differential-multiplication cross with the carrier wave of carrier wave self and two frequencys multiplication is separated the interchange transducing signal and the drift of low frequency random phase of fibre optic interferometer respectively, obtains stable transducing signal output through Hi-pass filter again.But this method has two defectives, the one, have association amplitude modulation phenomenon in the time of to light source frequency modulation, and cause the restituted signal distortion; Two is that the carrier wave of two frequencys multiplication is multiplied each other by carrier wave self and obtains, and phase place is asynchronous with self, also can bring the distortion of demodulation.
3 * 3 coupling mechanism demodulation principle are that mach zhender can get three road interference signals of 120 ° of phase phasic differences successively, thereby can not occur signal blanking phenomenon simultaneously after interfering two arm signals to synthesize through 3 * 3 coupling mechanisms.Operations such as demodulating algorithm only need carry out addition to this three road signal, subtracts each other, multiplies each other, differential, integration, filtering just can obtain required transducing signal at last.This method can use simple device to realize the signal demodulation; But it also exists defective; At first 3 * 3 coupling mechanisms are because principles such as manufacturing process three tunnel output light signal sizes can not be equal fully; The photodetector responsiveness that three road interference signals are surveyed also can not be just the same in addition; And these unbalancednesss will exert an influence to last demodulation result, cause distorted signals.Other 3 * 3 coupling mechanism demodulation methods need be handled 3 road signals, and the Processing Algorithm relative complex influences the net result integrality.
The heterodyne demodulation method need not used modulated light source, in interferometer reference arm, adds heterodyne modulator usually, makes reference arm produce frequency displacement, thereby makes two arms form frequency difference, interferes the back just can obtain by the heterodyne signal of photodetector response like this.Heterodyne signal by photodetection output is divided into identical two-way, with heterodyne modulation signal and the signal mixing of heterodyne modulation signal behind phase-shift circuit, carries out the demodulation of transducing signal through demodulator circuits such as low-pass filtering, differential more respectively.The advantage of heterodyne demodulation method is to avoid the association AM interference; Shortcoming is the heterodyne modulation signal phase-shift circuit that needs with accurate; Phase place in case fixing just can not be regulated along with the variation of heterodyne modulation signal, and has problems such as intrinsic electronics phase drift and noise are serious.
Summary of the invention
In order to overcome disadvantages 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 influence, eliminate the phase amplitude unbalanced factor, reduce the use of components and parts, reduce factor affecting such as non-linear, realize the phase quadrature quadrature demodulation of accurate and adjustable.
The technical scheme that the present invention adopts is:
Laser instrument output light signal is divided into two-way after 1 * 2 coupler splitting; One the tunnel connects sensing head 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 behind 2 * 1 optical combiners; Interference light signal is input to photodetector and obtains interfering electric signal, amplifies the back through low noise amplifier again and is being input to the data sampling of realizing interfering electric signal under the square-wave signal external trigger of phase-modulator by digital signal processor.
Said digital signal processor includes a parity grouping module, two differential modules, two multiplication modules, subtraction module, integration module and low pass filter module; from a low noise amplifier (the input signal by the parity packet module by the square wave signal triggered, we get two π / 2 away from the quadrature signal, then the two quadrature signals which are input to the first module and the second differential output of the differential module and the differential data before re-entering the first multiplication block and the cross-section two cross-multiplication multiplication module, the first module and the second multiplication output of the multiplication block into the subtractor module for subtraction process, and then processed in the module integration, through the low-pass filter module relative to the low frequency random phase filter change, to give the desired sensor signal demodulated, and finally achieved the demodulation process.
Described phase-modulator is after amplitude is 1/2nd half-wave voltage square-wave frequency modulation, and the light phase amplitude of variation is a pi/2.
Described phase-modulator modulated square wave signal frequency f is greater than the transducing signal highest frequency more than 10 times.
The phase modulation (PM) speed of described phase-modulator is more than 10MHz.
Described laser instrument is a narrow linewidth laser, and the phase sensitive device on the described sensing head is optical fibre vibration sensor, fibre optic hydrophone, fibre optic gyroscope or phase sensitive formula current/voltage sensor etc.
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 an 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 through the input peak-to-peak value; The phase place of instantaneous change interference signal; Make that to have pi/2 phase between the neighbouring sample point poor; And, the phase-modulator phase modulation far changes and the random phase offset variation faster than transducing signal because changing; The two adjacent groups signal can be regarded the synchronization sampled signal as; The interference signal that two groups of pi/2s that obtain thus differ can be realized the quadrature demodulation processing at last through the digital demodulation algorithm, eliminates random phase and changes the influence that demodulation result is brought.Compare with the PGC demodulating equipment, this device can be eliminated association amplitude modulation influence, has reduced frequency mixer and low-pass filter and has used, thereby reduced the active device non-linear effects, has improved output signal-to-noise ratio.Compare with 3 * 3 demodulating equipments, the influence that this device does not exist each road detectable signal imbalance of 3 * 3 coupling mechanisms to cause more, and can reduce the photodetector usage quantity and simplify subsequent demodulation algorithm calculation step, restituted signal is improved.Compare with the heterodyne demodulation device, this device need not to use frequency mixer, wave filter equally, reduces non-linear; And can replace phase shifting device to realize the accurate modulation of phase place with phase-modulator, the phase modulation amplitude can change through changing the phase-modulator square wave amplitude.
Description of drawings
Fig. 1 is this pi/2 phase modulation-demodulation device schematic diagram.
Fig. 2 is a DSP internal data processing flow chart.
Fig. 3 is a digital signal processor demodulation result oscillogram.
Among the 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, the parity packet module; 202, differential module, 203, the 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
The present invention is further illustrated below in conjunction with accompanying drawing and embodiment.
As shown in Figure 1; Laser instrument 101 output optical signals are divided into two-way after 102 beam split of 1 * 2 coupler; One the tunnel connects sensing head 104 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 behind 2 * 1 optical combiners 105; Interference light signal is input to photodetector 106 and obtains interfering the signal of telecommunication, amplifies the back through low-noise amplifier 107 again and is being input to the data sampling of realizing interfering the signal of telecommunication under the square-wave signal external trigger of phase-modulator 103 by digital signal processor 108.
Shown in Figure 2, said digital signal processor 108 includes a parity grouping module 201, the two differential modules 202 and 203, two multiplication modules 204 and 205, a subtraction module 206, credit module 207 and low pass filter module 208 ; from the low-noise amplifier 107 via the parity packet signal input module 201 is triggered by a square wave signal obtained under the two π / 2 away from the quadrature signal, then the two quadrature signals which are input to the first module 202 and the differential The second output of the differential module 203 then the differential data before crossing into the first and second multiplication block 204 for cross multiplication multiplication module 205, a first multiplication block 204 and the second multiplication block 205 outputs the subtraction module 206 into the for subtraction process, and then processed by the integrator module 207, through the low-pass filter module 208 filters relatively low phase change random, sensing the desired demodulated signals, and finally achieved the demodulation process.
Described phase-modulator 103 is after amplitude is 1/2nd half-wave voltage square-wave frequency modulation, and the light phase amplitude of variation is a pi/2.
Described phase-modulator 103 modulated square wave signal frequency f are greater than the transducing signal highest frequency more than 10 times
The phase modulation (PM) speed of described phase-modulator 103 is more than 10MHz.
Described laser instrument is a narrow linewidth laser, can effectively reduce the influence of phase noise to demodulation result, improves output signal-to-noise ratio.Phase sensitive device on the 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 the detecting 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 an integer.And adjustment sampling time-delay, make sampling optimization in the intermediate point moment position of phase modulation (PM) square-wave signal high-low level.
Suppose that laser instrument 101 outputs to through 102 couplings of 1 * 2 coupling mechanism that light intensity is respectively E in signal arm and the reference arm
1, E
2
Suppose that the system transducing signal is the 4.5KHz sinusoidal signal
s(t)＝Acos(2π×4500×t)
Suppose that pi/2 phase-modulated signal frequency f is that 100KHz has:
Then obtaining transducing signal through the phase sensitive device of sensing head 104 is output as:
Obtaining reference path through pi/2 phase modulator 103 is output as:
Therefore photodetector 106 output signals can be expressed as:
Wherein
Ignore the DC component influence, N sampled data of digital signal processor corresponds to:
Since S (N) with
change relatively slowly varying N is a process and therefore are:
Image data is carried out parity packet, and then even sets can be expressed as:
Odd number group can be expressed as:
It is thus clear that through after the above-mentioned packet transaction, two groups of group signals of resultant odd even I
1(N) and I
2(N) differ and be pi/2, utilize them can carry out quadrature demodulation.
The DSP internal processes as shown in Figure 2; Sampling gained data are at first handled through parity packet module 201; Obtain the orthogonal signal that two groups of pi/2s differ, again these two groups of orthogonal signal be input to respectively in the differential module 202,203 and handle, can be expressed as with continuous signal:
Differential module 202,203 output results again with differential before data cross get into the module 204,205 that multiplies each other, realize the multiplication cross process:
204,205 outputs of two multiplier modules get in the subtraction block 206 subtracts each other processing, obtains:
After in integration module 207, handling again be:
Random phase through the relative low frequency of low-pass filtering module 208 filterings changes, and obtains at last:
Hereto, realized whole demodulating process.Its demodulation result as shown in Figure 3.
The above; Only be the preferable embodiment of the present invention; But protection scope of the present invention is not limited thereto; Any technician who is familiar with the present technique field is in the technical scope that the present invention discloses; The variation that can expect easily or replacement (as changing square wave frequency and sample frequency etc.) all should be encompassed within protection scope of the present invention.
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| CN104698214A (en) * | 2013-12-10 | 2015-06-10 | 上海鸣志自动控制设备有限公司 | Modulated type photoelectric speed sensor sensitive in phase position |
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| CN110646020A (en) * | 2019-10-30 | 2020-01-03 | 电子科技大学中山学院 | Optical fiber interference device and method |
| CN113419341A (en) * | 2021-06-22 | 2021-09-21 | 中国人民解放军国防科技大学 | Method and device for complex reconstruction of optical fiber interferometer light field |
| CN114061732A (en) * | 2021-10-08 | 2022-02-18 | 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 |
| 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 |
| CN114440947A (en) * | 2021-12-22 | 2022-05-06 | 北京自动化控制设备研究所 | Interference signal phase demodulation method and system based on 3 x 3 coupler |
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