CN101718563A - Phase-shift white light interferometry method based on 3*3 optical fiber coupler - Google Patents

Phase-shift white light interferometry method based on 3*3 optical fiber coupler Download PDF

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CN101718563A
CN101718563A CN200910249630A CN200910249630A CN101718563A CN 101718563 A CN101718563 A CN 101718563A CN 200910249630 A CN200910249630 A CN 200910249630A CN 200910249630 A CN200910249630 A CN 200910249630A CN 101718563 A CN101718563 A CN 101718563A
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interferometer
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phase
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phase information
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江毅
梁蓬娟
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Beijing Institute of Technology BIT
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Abstract

The invention relates to an optical fiber white light interferometry method, in particular to a phase-shift white light interferometry method based on a 3*3 optical fiber coupler, belonging to the technical field of optical fiber sensing. A 2*2 optical fiber coupler and a 3*3 optical fiber coupler form an optical fiber M-Z interferometer, and a wavelength scanning light is injected into the optical fiber M-Z interferometer. Magnitudes of three paths of output white light interference spectrum signals are equal, and an angle of 120 degrees is formed between every two paths of output white light interference spectrum signals on the phase. When the wavelength scanning light scans from Lambda 1 to Lambda 2, three paths of output signals I1, I2 and I3 are obtained, and Delta is demodulated through computing or constructing two paths of orthorhombic signals and utilizing a derivation cross multiplying method. The Delta is subjected to the unwrapping operation to demodulate linear phase information after computed. The absolute optical path difference of the interferometer can be computed by using the linear phase information. The invention can absolutely measure the optical path difference of the optical fiber interferometer with high precision and high speed.

Description

Phase-shift white light interferometry method based on 3 * 3 fiber couplers
Technical field
The present invention relates to the optical fiber white light interference measuring method, particularly, belong to technical field of optical fiber sensing based on the phase-shift white light interferometry method of 3 * 3 fiber couplers.
Background technology
Interferometric optical fiber sensor as Fabry-Perot (Fabry-Perot, method amber), Mach-Zehnder (Mach-Zehnder), Michelson (Michelson), Sagnac (Sagnac) etc., has very high measurement sensitivity, is widely used.To be measured, as strain, temperature, displacement or pressure etc., act on the interferometer, cause the variation of interferometer optical path difference, from the output interference signal of interferometer, demodulate optical path difference, thereby realize measurement measurand.
Interferometry is to measure a lot of parameters (as temperature, pressure, strain etc.) very important a kind of method, an arm that often uses interferometer is as reference light (not through containing the environment of required measurement parameter), another arm is as flashlight (through containing the environment of required measurement parameter), demodulate the phase differential between two arms, need just can obtain the parameter of measurement.Therefore the demodulation techniques of interference signal are the core technologies of optical fibre interference art.Interfere demodulation techniques mainly to be divided into relative measurement technology and absolute measurement technology.The relative measurement technology can only measuring-signal variable quantity, not energy measurement static state or tempolabile signal, and absolute measurement can be measured the optical path difference of interferometer, thereby can measure static state and tempolabile signal.
Optical fiber white light interference mensuration (WLI) is generally used in absolute measurement.Traditional white light interferometric method uses scanning interferometer to compensate light path, but such system stability is poor, and resolution is low.The spectral domain white light interferometric method utilizes wideband light source or wavelength-swept source, surveys the output white-light spectrum of sensing interferometer, by two optical path differences that wavelength comes the absolute measurement interferometer of phase phasic difference 2 π in the spectrum.If use broadband light to inject interferometer, then survey the white-light spectrum of interferometer with spectroanalysis instrument; If use wavelength scanning light to inject interferometer, then just can obtain the white-light spectrum of interferometer with a photodiode.Reported some spectral domain white light interferometric methods at present, (Yijiang can get a sinusoidal signal such as the Fourier transform white light interferometric method
Figure G2009102496301D0000021
2 times the 2 road signal can obtain a cosine signal divided by coefficient 3 after deducting 1 and 3 road signal sums
Figure G2009102496301D0000022
With top resulting g 1Signal phase differs 90 °; With g 1And g 2Negate cosine can obtain the phase information of interferometer after these two-way orthogonal signal were divided by δ = arctg ( - 3 I 1 - I 3 2 I 2 - I 1 - I 3 ) .
4) extract phase information δ in the step 3 and obtain by the arc tangent algorithm, phase range exists
Figure G2009102496301D0000024
Between, discontinuous.In order to obtain continuous phase information, need separate the parcel computing to phase place.Method is: all multiply by 2 for earlier the phase information δ that demodulates, its range expansion between [π, π], is carried out phase place again and separated the parcel computing, and then divided by 2, return to original linear phase information
Figure G2009102496301D0000025
According to linear phase information
Figure G2009102496301D0000026
And the differential relationship between the wavelength
Figure G2009102496301D0000027
The optical path difference D of interferometer just can directly obtain by following formula:
Figure G2009102496301D0000028
Aforesaid phase-shift white light interferometry method based on 3 * 3 fiber couplers, also can realize by following method:
Method two, the specific implementation step is as follows:
A) with method one in step 1) and 2) identical;
B) 1 and 3 two-way in three road interference signals that obtain among the step a are carried out following processing and can get a sinusoidal signal
Figure G2009102496301D0000029
2 times the 2 road signal can obtain a cosine signal divided by coefficient 3 after deducting 1 and 3 road signal sums
Figure G2009102496301D00000210
With top resulting g 1Signal phase differs 90 °; Respectively to g 1And g 2Can get g after the differentiate 1=b (λ) δ ' cos δ, g 2The b of '=-(λ) δ ' is sin δ (t); With g 1, g 2, g 1" Fourier Transform White_Light Interferometry for theMeasurement of Fiber_Optic Extrinsic Fabry_PerotInterferometric Sensors; " Opt Lett., Vol.33, NO.16), software demodulation method (Yijiang, " Wavelength_scanning white-light interferometrywith a 3*3coupler based interferometer; " OptLett., Vol.20, NO.2), these method measuring accuracy height, dynamic range is big, but the algorithm more complicated is measured a time and is about 130us.
Summary of the invention
The objective of the invention is for better solve fast, the problem of efficient demodulated interferential instrument absolute light path difference, the method that proposes a kind of simple high speed is come measuring optical fiber interferometer absolute light path difference, have precision height, speed fast, can absolute measurement etc. advantage.
Phase-shift white light interferometry method based on 3 * 3 fiber couplers of the present invention is achieved through the following technical solutions:
Method one, the specific implementation step is as follows:
1) uses one 2 * 2 coupling mechanism and one 3 * 3 coupling mechanism and constitute optical fiber M-Z interferometer; Wavelength scanning light is incided interferometer, make the output terminal of interferometer obtain three road white light interference spectrum.
2) as if 3 * 3 coupling mechanism symmetries, three road output terminals of interferometer are mutually 120 °.Three road interference signals of definition 3 * 3 coupling mechanisms output are:
Figure G2009102496301D0000031
Wherein, be 1 road signal during definition K=1, be 2 road signals during K=2, during K=3 3 road signals, the bias light (being direct current signal) that a (λ) introduces for the light source light spectrum profile, b (λ) is the contrast of interference fringe, linear phase information
Figure G2009102496301D0000032
(the m value is an integer in the formula, and-π≤δ≤π), D is the optical path difference between interferometer two arms.
3) 1 and 3 two-way in three road interference signals that obtain in the step 2 are following processing g 2Subtract each other again after the ' multiplication cross and obtain x=g 2g 1'-g 1g 2'=b 2(λ) (sin 2δ+cos 2δ) δ '=b 2(λ) δ '; With g 1And g 2Addition gets y=b respectively square 2(λ); X obtains after divided by y
Figure G2009102496301D0000041
To demodulating phase information δ behind the z integration;
C) the phase information δ that obtains among the step b is carried out phase place and separate the parcel computing, recover original linear phase information
Figure G2009102496301D0000042
Linear phase information
Figure G2009102496301D0000043
Be that optical source wavelength is from λ 1Scan λ 2The phase change of caused interferometer is according to the differential relationship between phase place and the wavelength
Figure G2009102496301D0000044
The optical path difference D of interferometer just can directly obtain by (2) formula:
Realized the purpose of absolute measurement optical path difference by above-mentioned two kinds of methods.
Beneficial effect:
The phase-shift white light interferometry art based on 3 * 3 coupling mechanisms that the inventive method proposed has highly sensitive, the precision height, and characteristics such as dynamic range is big, and algorithm is simple, and speed is fast satisfy the requirement of high speed absolute measurement.
Description of drawings
Fig. 1 is applied to a specific embodiments measuring based on the white light scanning interferometer of 3 * 3 coupling mechanisms for the inventive method;
Fig. 2 is a road in three road white light interference spectral signals;
Fig. 3 is used for the spectrum of etalon of tuning wavelength;
Fig. 4 comes out with the linear phase information of wavelength variations for method one demodulation
Figure G2009102496301D0000046
Fig. 5 is the I that constructs 1-I 3And 2I 2-I 1-I 3The Li Sarutu of two-way orthogonal signal;
The linear phase information that Fig. 6 comes out for the method two demodulation
Figure G2009102496301D0000047
The phase place that Fig. 7 demodulates for two kinds of methods of the present invention and the comparison of fourier transformation white light interferometric method;
Among the figure, 1-wideband light source, 2-optoisolator, the humorous method amber of 3-optical-fibre adjustable wave filter, 4-2 * 2 coupling mechanisms, 5-elasticity post, 6-3 * 3 coupling mechanisms, 7-photodetector, 8-signals collecting and disposal system, 9-saw-toothed wave generator, 10-method amber etalon, 11-fiber grating, 12-photodetector.
Specific embodiments
The present invention will be further described below in conjunction with drawings and Examples.
Measuring method of the present invention is verified by experiment.Fig. 1 is one of the inventive method and implements schematic diagram, in conjunction with the measurement of optical path difference between two arms of Mach-Zehnder interferometer the inventive method described.
The light that wideband light source 1 sends is input to the humorous method amber of optical-fibre adjustable wave filter 3 through optoisolator 2, the humorous method amber of optical-fibre adjustable wave filter 3 is output wavelength scanning narrow band light under the driving of saw-toothed wave generator 9, the length scanning narrow band light is divided into two-way by 2 * 2 coupling mechanisms 4, wherein one road light is by method amber etalon 10, fiber grating 11, photodetector 12 is in order to the transmission spectrum of probe method amber etalon 10 and fiber grating 11; Other one road light beam is gone into interferometer; In the interferometer, one road light is as reference light, another road is as flashlight (light that includes information to be measured), two-way light interferes at 3 * 3 coupling mechanisms, 6 places, the interference signal of three tunnel outputs is converted into electric signal through photodetector 7, signals collecting and disposal system 8 are used for gathering the output signal of detector 7 and detector 12, and handle, and control saw-toothed wave generator 9 output drive signals simultaneously.
In Fig. 1 example, wideband light source 1 is the ASE light source, and spectral range covers from 1525nm to 1565nm, and free spectral range (FSR) width of the humorous method amber of optical-fibre adjustable wave filter 3 is 65nm, and fineness is 200, so bandwidth is 0.325nm; The free spectrum sector width of method amber etalon 10 is 0.8nm (100GHz), and fineness is 14, and the wavelength thermal stability of method amber etalon 10 is less than 0.7GHz from 0 ℃ to 70 ℃ variation; The centre wavelength that bandwidth is 0.7nm is that the fiber grating 11 of 1535.027nm is connected in series to method amber etalon 10 back, a peak wavelength of method amber etalon 10 output pectination spectrum is used for erasing, as the wavelength mark, and this peak wavelength of being erased is exactly 11 centre wavelengths of fiber grating.The interference signal that method amber etalon 10 is used for collecting is converted into wavelength domain from time domain, and then replaces heavy expensive spectroanalysis instrument.
The amplitude of three road white light interference spectrum of gathering equates that phase place differs 120 ° mutually.Wherein one tunnel white-light spectrum as shown in Figure 2, in fact exactly the white-light fringe that superposeed on the profile of ASE light source is so in processing signals, do normalized to interference signal earlier, remove the influence of light source profile, reduce the error that light source fluctuation brings measurement.During wavelength calibration, chosen that the segment signal between the 1525.649nm and these two transmission peak value points of 1564.676nm carries out wavelength calibration to interference signal on the method amber etalon 10, the output signal of method amber etalon 10 as shown in Figure 3, the start-stop wavelength of having determined length scanning simultaneously is 1525.649nm and 1564.676nm.
Utilize two kinds of above-mentioned methods to carry out phase demodulating then respectively.Utilize phase information that method one demodulation comes out as shown in Figure 4.Utilize method two, the Li Sarutu of the two-way orthogonal signal that construct as shown in Figure 5, the two paths of signals of Huo Deing is a quadrature as can be seen from Figure, the phase information that demodulation is come out as shown in Figure 6.
" Fourier transform white light interference art " (number of patent application: 200710177837.3) compare with propositions such as Jiang Yi, the phase place that three kinds of scheme demodulation are come out changes as shown in Figure 7 with scanning wavelength, use formula (2), the absolute light path difference of the interferometer that can calculate is 2996.19um, moves a time to be about 30us.As seen the result that measures of the result that obtains of the method that proposes of the application and other method is identical, but travelling speed has but improved four or five times than other method far away, is easier to realize the real time high-speed Testing requirement.

Claims (2)

1.) a kind of phase-shift white light interferometry method based on 3 * 3 fiber couplers is characterized in that the specific implementation step is as follows:
1) uses one 2 * 2 coupling mechanism and one 3 * 3 coupling mechanism and constitute optical fiber M-Z interferometer; Wavelength scanning light is incided interferometer, make the output terminal of interferometer obtain three road white light interference spectrum;
2) as if 3 * 3 coupling mechanism symmetries, three road output terminals of interferometer are mutually 120 °, and three road interference signals of definition 3 * 3 coupling mechanisms output are:
k＝1，2，3
Wherein, be 1 road signal during definition K=1, be 2 road signals during K=2, during K=3 3 road signals, the bias light that a (λ) introduces for the light source light spectrum profile is a direct current signal, b (λ) is the contrast of interference fringe, linear phase information
Figure F2009102496301C0000012
The m value is an integer in the formula, and-π≤δ≤π, D are the optical path differences between interferometer two arms;
3) with step 2) in 1 and 3 two-way in three road interference signals that obtain do following processing and can get a sinusoidal signal
Figure F2009102496301C0000013
2 times the 2 road signal can obtain a cosine signal divided by coefficient 3 after deducting 1 and 3 road signal sums With top resulting g 1Signal phase differs 90 °; With g 1And g 2Negate cosine can obtain the phase information of interferometer after these two-way orthogonal signal were divided by
Figure F2009102496301C0000015
4) extract phase information δ in the step 3) and obtain by the arc tangent algorithm, phase range exists
Figure F2009102496301C0000016
Between, discontinuous; In order to obtain continuous phase information, need separate the parcel computing to phase place, method is: all multiply by 2 for earlier the phase information δ that demodulates, its range expansion between [π, π], is carried out phase place again and separated the parcel computing, and then, return to original linear phase information divided by 2
Figure F2009102496301C0000021
According to linear phase information
Figure F2009102496301C0000022
And the differential relationship between the wavelength
Figure F2009102496301C0000023
The optical path difference D of interferometer just can directly obtain by following formula:
2. a kind of phase-shift white light interferometry method based on 3 * 3 fiber couplers according to claim 1 is characterized in that also can realizing by following method:
A) preceding two steps are with 1 of claim 1) and 2);
B) 1 and 3 two-way in three road interference signals that obtain in the step a) are carried out following processing and can get a sinusoidal signal
Figure F2009102496301C0000025
2 times the 2 road signal can obtain a cosine signal divided by coefficient 3 after deducting 1 and 3 road signal sums
Figure F2009102496301C0000026
With top resulting g 1Signal phase differs 90 °; Respectively to g 1And g 2Can get g after the differentiate 1'=b (λ) δ ' cos δ, g 2The b of '=-(λ) δ ' is sin δ (t); With g 1, g 2, g 1', g 2Subtract each other again after the ' multiplication cross and obtain x=g 2g 1'-g 1g 2'=b 2(λ) (sin 2δ+cos 2δ) δ '=b 2(λ) δ '; With g 1And g 2Addition gets y=b respectively square 2(λ); X obtains after divided by y
Figure F2009102496301C0000027
To demodulating phase information δ behind the z integration;
C) the phase information δ that obtains in the step b) is carried out phase place and separate the parcel computing, recover original linear phase information
Figure F2009102496301C0000028
According to the differential relationship between phase place and the wavelength
Figure F2009102496301C0000029
The optical path difference D of interferometer is
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