CN101949685B - Fiber laser self-mixing interferometer and measurement method thereof - Google Patents
Fiber laser self-mixing interferometer and measurement method thereof Download PDFInfo
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Abstract
The invention discloses a fiber laser self-mixing interferometer and a measurement method thereof and belongs to the field of displacement precision measurement. The interferometer comprises a distributed feedback semiconductor laser, a polarization-maintaining fiber coupler, an intra-line polarizer, a single mode fiber, an electrooptical modulator, an fiber Bragg grating, a gradient refractive index lens, a test piece, an photoelectric detector, a data acquisition and processing system, a fiber holder, one-dimensional guide rails, two-dimensional precision translation platform, a microscope, a base, a support and a signal generator. The fiber Bragg grating and the test piece form a reference outer cavity and a measurement outer cavity with the exit end face of the laser respectively for generating a double outer cavity self-mixing interference phenomenon; and the data acquisition and processing system adopts a self-mixing signal obtained by analysis by orthogonal demodulation technology to calculate the displacement of the test piece. The structure of the fiber interferometer is very suitable for measuring the nanometer displacement and vibration of the micro machines and MEMS devices and is more practical.
Description
Technical field
The present invention relates to the displacement fine measuring instrument, relate to a kind of optical-fiber type self-mixed interference instrument and measuring method thereof of measuring micro-displacement particularly.
Background technology
The interferometry instrument system often is applied to the micro-displacement measurement in precision optical machinery, microelectronics and MEMS (micro electro mechanical system) fields such as (MEMS).For the microdisplacement measurement scope of sub-micron to micron (μ m), laser interferometry relies on advantages such as noncontact, high resolution and high measurement accuracy, has obtained widely and has used.Because therefore advantages such as that the semiconductor laser of optical fiber coupling output has is flexible, miniaturization and anti-electromagnetic interference (EMI) are applied in displacement transducer.For example, the MTI-2100 FotonicTM Sensor of U.S. MTI company series fiber optics displacement meter, error is 0.01 μ m ~ 0.1 μ m in 1 μ m ~ 10 μ m working ranges.With this series products is that the optical-fiber type micro-displacement interferometry apparatus of representative is based on feedback light intensity and the linear principle of tested distance, and the employing photonic crystal fiber relaxed the requirement to the testee reflectivity, has guaranteed measuring accuracy.But these measuring instruments need a lot of optical components and complicated optical signal detecting devices, thereby are difficult to make compact conformation, cheap measurement mechanism.
Traditional interference testing structure common configuration is huge, and the light path complexity is sensitive to collimation, and costs an arm and a leg, and therefore presses for simple, compact, stable more interference system.The laser self-mixing interference technology is a kind of novel relevant measurement technology, is applied to geometric measurement since the eighties.The self-mixing interference that the exterior resonant cavity that analysis is made of laser instrument and measured object surface produces can be determined the state of object, measuring distance, displacement and speed.The existing self-mixed interference that studies show that has several characteristics: interference signal is class cosine striped or sawtooth wave striped; The phse sensitivity of interfering is identical with conventional interference; Interference signal under the appropriateness light feedback level can carry out sensing to object of which movement.The laser self-mixing interference instrument also has the following advantages: simple and compact for structure, autocollimation is saved components and parts; Need not external photodetector; Testee can be coarse scattering surface.This shows that the laser self-mixing interference technology is better than the conventional interference technology in the part fields of measurement.
Summary of the invention
The purpose of this invention is to provide optical-fiber type laser self-mixing interference instrument, this instrument is a kind of fine measuring instrument that can observe micro-displacement.Another object of the present invention provides a kind of method of utilizing this optical-fiber type laser self-mixing interference instrument to carry out displacement measurement.
The technical scheme that the present invention is adopted for its technical matters of solution is: optical-fiber type laser self-mixing interference instrument comprises distributed feedback semiconductor laser, polarization-maintaining fiber coupler, the polarizer in the line, single-mode fiber, electrooptic modulator, fiber grating, gradient-index lens, test specimen, photodetector, data Collection ﹠ Processing System, fibre holder, the one dimension guide rail, the accurate translation stage of two dimension, microscope, base, support and signal generator, described one dimension guide rail, the accurate translation stage of two dimension, test specimen is fixed on the center of base successively, described support is fixed on the both sides of base, described microscope and fibre holder are contained on the support, described single-mode fiber connects laser instrument successively, polarization-maintaining fiber coupler, the polarizer in the line, electrooptic modulator, fiber grating and gradient-index lens, and fix by fibre holder, the output terminal of described signal generator is connected with described electrooptic modulator.
Wherein, data Collection ﹠ Processing System comprises amplifier, wave filter, analog to digital conversion circuit, computer data processing unit and display terminal, amplifier input terminal is connected with the output terminal of photodetector, the output terminal of amplifier is connected with the input end of wave filter, the output terminal of wave filter is connected with the input end of analog to digital conversion circuit, and the output terminal of analog to digital conversion circuit is connected by the input end of USB interface with computer data processing unit and display terminal; Analog to digital conversion circuit comprises A/D conversion card and synchronized sampling circuit; Electrooptic modulator can adopt the waveguide type electro-optic crystal.
Measure micro-displacement in order to utilize above-mentioned optical-fiber type laser self-mixing interference instrument, measuring method of the present invention mainly may further comprise the steps: distributed feedback semiconductor laser sends single longitudinal mode light and transmits via single-mode fiber, and the polarizer makes electrooptic modulator carry out the modulation of pure phase position to laser beam in the line; The cosine signal that signal generator sends appropriate frequency drives electrooptic modulator, cause the cosine phase modulation of laser beam, light part after modulated is through the resonator cavity of fiber grating reflected back laser instrument, another part feeds back in the laser cavity after being reflected by test specimen, produce double exocoel self-mixed interference phenomenon, detect by photodetector from the mixed signal light intensity; Utilize data Collection ﹠ Processing System to the output signal of photodetector amplify with Filtering Processing after, carry out analog to digital conversion; In each modulation period, digital sampled signal is carried out 4 integral operationes of time, result to signal integration carries out linear combination calculating again, the result who is only comprised the sinusoidal component and the cosine component of quadrature, ratio by these two components obtains arctan function then, draws phase value; According to phase place
And the relation between the self-mixed interference instrument external cavity length
Just can calculate the displacement of test specimen
L
Self-mixing interference effect occurs in the resonator cavity of laser instrument, can export light intensity and spectral characteristic by modulated laser by changing parameters such as exocoel equivalent cavity length and feedback intensity, and the photodetector that connects coupling mechanism one end is finished the detection of optical interference signals.The detection optical feedback causes the intensity and the phase change of signal, determines the micro-displacement of object.Under the condition of weak optical feedback, self-mixing interference is a sinusoidal variations, and the displacement of the every change half-wavelength of external cavity length is from mixed signal fluctuation one-period, the analytical approach of tradition self-mixing interference is mostly used striped peak value counting method, and the displacement measurement precision is only in λ/2.The present invention adopts electrooptic modulator that the output light of laser instrument is carried out the position and modulates mutually, part light feeds back to the resonator cavity of laser instrument as reference light via the fiber grating reflection, another part light transmission fiber grating focuses on the test specimen through behind the gradient-index lens, reflection or scattered light are as the resonator cavity of measuring light by former road return laser light device, feedback light is carried the information of exterior object, mix back generation self-mixed interference mutually with the light in the laser cavity, the light intensity of interference signal is detected by photodetector and is converted to digital signal through the A/D change-over circuit, adopt the quadrature demodulation technology analysis from mixed signal by data processing unit at last, at last by display terminal output result.
The present invention has following beneficial effect: distributed feedback semiconductor (DFB) laser instrument that adopt (1) is simultaneously as system source and displacement measurement sensor, replace free space to make the intrinsic difficulty that optical interference circuit can reduce the long-armed Installation And Calibration of interferometer with optical fiber, and can make interferometer have flexible and miniaturization; (2) the present invention's instrument error in 0 μ m ~ 10 μ m working ranges is 0.01 μ m, and the interference probe of optical-fiber type is not subjected to the influence of electromagnetic interference (EMI), and is applicable to polytype body surface; (3) the dual exocoel feedback arrangement of Ti Chuing dramatically the filtering interferometer be subjected to the influence of variation of ambient temperature, optical frequency fluctuation and extraneous vibration; (4) this fibre optic interferometer structure is applicable to the nano-grade displacement of micromechanics and MEMS device and the measurement of vibration very much, more near practicability.
Description of drawings
Fig. 1 is the structural drawing of optical-fiber type laser self-mixing interference instrument of the present invention.
Fig. 2 is the structural drawing of data Collection ﹠ Processing System in the interferometer of the present invention.
Fig. 3 is to the software processes process flow diagram of signal in the measuring method of the present invention.
Specific embodiment
Below in conjunction with drawings and Examples, the present invention is described in further details.
As Fig. 1, the interference probe of measuring nano-grade displacement and vibration in apparatus of the present invention is connected in Distributed Feedback Laser 1, polarization-maintaining fiber coupler 2, the line polarizer 3, electrooptic modulator 5, fiber grating 6 and gradient-index lens 7 successively by single-mode fiber 4 and forms; Interfere probe over against test specimen 8, the port of polarization-maintaining fiber coupler 2 connects optical fiber photodetector 9 and data Collection ﹠ Processing System 10.One dimension guide rail 12 is fixed on the center of base 15, on base 15, be fixed with support 16, the microscope 14 that is positioned on the support 16 is used for observing and adjusting the fibre-optical probe position, and fibre holder 11 is used for fixing fibre-optical probe, and signal generator 17 is connected with electrooptic modulator 5.Test specimen 8 is fixed on the two-dimentional accurate translation stage 13.Distributed Feedback Laser 1 is selected JW3101(centre wavelength 1550nm for use, peak power-8.7dBm, line width is 0.15nm), photodetector 9 is selected DET01CFC(wavelength coverage 800nm ~ 1700nm, bandwidth 2GHz for use), electrooptic modulator 5 adopts lithium niobate phase modulator LPM-001(operation wavelength 1550nm, half-wave voltage 3.5V, bandwidth〉2.5GHz), the centre wavelength of fiber grating 6 is 1549.94nm, three dB bandwidth is 0.012nm.Adopt the MEMS device as test specimen 8(catoptron), purpose is the light intensity for Control and Feedback light, makes system works under the condition of weak optical feedback.
Utilize optical system to produce the implementation method of self-mixed interference, Displacement Measurement in conjunction with Fig. 1 explanation.Two end faces of laser instrument 1 resonator cavity have constituted built in laser cavity, and fiber grating 6, test specimen 8 constitute with reference to exocoel with the outgoing end face of laser resonant cavity respectively and measure exocoel.Send single longitudinal mode light via single-mode fiber 4 transmission, by coupling mechanism 2 beam split of 50:50 by Distributed Feedback Laser 1.One end makes 5 pairs of laser beam of electrooptic modulator carry out the modulation of pure phase position via the polarizer 3 output polarization directions and the consistent linearly polarized light of electrooptic modulator 5 major axes orientations.Light part after modulated is through the resonator cavity of fiber grating 6 reflected back laser instruments 1, another part feeds back in the laser cavity after by test specimen 8 reflection or scattering, produce double exocoel self-mixed interference phenomenon, the result of self-mixed interference makes that radiative amplitude and frequency are modulated.The output intensity fluctuation one-period of laser instrument changes optical wavelength half corresponding to the equivalent measurement external cavity length, λ/2.Utilize the phase place of quadrature demodulation technology restituted signal, the relation by phase place and displacement calculates displacement again.Because the signal phase error that temperature variation produces is identical to two exocoels, when the interference signal phase place of utilizing reference light and measuring light is found the solution displacement, temperature-induced variations will be used as common-mode signal and weed out, so use the influence that system is produced with reference to exocoel energy filtering disturbance.
When instrument is interfered in debugging, open photodetector 9 and Distributed Feedback Laser 1 successively, because this laser works wavelength is 1550nm, shoot laser is an invisible light, should wear safety goggles during practical operation.Cooperate the use of microscope 14, fiber end face and the vertical range between the test specimen 8 that adjusting has gradient-index lens 7 are 3 ~ 5 millimeters, guarantee that shoot laser focuses on the test specimen 8, luminous energy after test specimen 8 scatterings feeds back in the laser cavity, the self-mixed interference phenomenon takes place, when regulating the outgoing fiber end face, photodetector 9 has tangible fluctuation signal to produce.Signalization generator 17, make its output cosine voltage signal, the voltage peak-to-peak value is 1.5V, frequency is 1KHz, this signal is used to drive electrooptic modulator 5, and this moment, photodetector 9 output signals presented stable periodic near sinusoidal ripple signal, improves the frequency of signal generator 17 output cosine voltage signals, can find obviously to increase from the vibration frequency of mixed signal, the fluctuation striped becomes close.
The signal processing circuitry of self-mixed interference is described in conjunction with Fig. 2.System comprises that photodetector 9 is used to detect self-mixing interference, its output signal is connected to the input end of amplifier 18, amplifier is actual to be low noise operational amplifier, amplifies primary signal and noise is produced certain inhibiting effect under the distortionless condition of assurance signal.The output of amplifier 18 is connected to the input end of wave filter 19, and wave filter is removed the noise of sudden change to carrying out noise reduction process from mixed signal after amplifying.System also comprises signal analog to digital conversion circuit 20, and these parts are made up of A/D conversion card and synchronized sampling circuit, and its input end is received the output terminal of wave filter 19, and its output terminal is connected to computer data processing unit and display terminal 21 by USB interface.Through synchronized sampling and A/D conversion, become digital signal from mixed signal.Produce Synchronous Sampling Pulse from the negative edge starting point in each cycle of cosine modulation signal.The enlargement factor of resonance-amplifier 18 is 40 ~ 60, and according to the sample frequency and the precision of measured signal frequency and existing A/D conversion card, selects sampled point, for example selects 512 or 1024 sampled points.For the medium and low frequency signal, choose sample frequency 〉=1 MHz of A/D conversion card, precision 〉=16 bit.The digital signal of adopting is coupled to computing machine, handles in real time with computing machine.
Utilize the programming development platform of LabVIEW, programme, generate the graphic user interface that shows, analyzes and control, finish computer interface control, data acquisition, analysis and calculating as system software.Signal processing flow figure in conjunction with Fig. 3, the step of extracting signal phase with the quadrature demodulation principle is described: behind the LabVIEW software startup, initialization A/D changes card, utilize the start and stop of DAQ Assistant module controls A/D conversion, sample frequency can be provided with as required flexibly, when the data of preserving reach 1024, begin to carry out data processing, otherwise continue sampling.The negative edge starting point in each cycle of cosine modulation signal can produce Synchronous Sampling Pulse, and sampling pulse is the one-period of modulation signal at interval.(1) at each modulation signal period T (T=1/
f m ) in, with sampling obtain from mixed signal according to the time sequencing timeslice that to be divided into 4 length be T/4, respectively the self-mixing interference in each timeslice is carried out integral operation to the time.The integral result of each timeslice
C i Can be expressed as
, wherein
i=1,2,3,4; (2) according to Theoretical Calculation, calculate by 4 integral results in each modulation period being carried out linear combination, can obtain:
, wherein
A, H x , H y Be constant coefficient, thereby
So,
Be proportional to the sinusoidal component and the cosine component of test specimen phase place respectively; (3) ratio of calculating sinusoidal component and cosine component, then phase place
Can obtain by following relational expression:
, according to the relation between phase place and the self-mixed interference instrument external cavity length
Displacement that just can calculation testing piece
L(4) to handling according to the method described above in each modulation period from mixed signal, the displacement waveform of the test specimen of reconstruct in real time.
Claims (6)
1. optical-fiber type laser self-mixing interference instrument, it is characterized in that: described interferometer comprises distributed feedback semiconductor laser (1), polarization-maintaining fiber coupler (2), the polarizer (3) in the line, single-mode fiber (4), electrooptic modulator (5), fiber grating (6), gradient-index lens (7), test specimen (8), photodetector (9), data Collection ﹠ Processing System (10), fibre holder (11), one dimension guide rail (12), two dimension accurate translation stage (13), microscope (14), base (15), support (16) and signal generator (17), described one dimension guide rail (12), two dimension accurate translation stage (13), test specimen (8) is fixed on the center of described base (15) successively, described support (16) is fixed on the both sides of described base (15), described microscope (14) and fibre holder (11) are contained on the described support (16), described single-mode fiber (4) connects described laser instrument (1) successively, polarization-maintaining fiber coupler (2), the polarizer (3) in the line, electrooptic modulator (5), fiber grating (6) and gradient-index lens (7), and fixing by described fibre holder (11), the output terminal of described signal generator (17) is connected with described electrooptic modulator (5).
2. optical-fiber type laser self-mixing interference instrument according to claim 1, it is characterized in that: described data Collection ﹠ Processing System (10) comprises amplifier (18), wave filter (19), analog to digital conversion circuit (20), computer data processing unit and display terminal (21), the input end of described amplifier (18) is connected with the output terminal of photodetector (9), the output terminal of described amplifier (18) is connected with the input end of wave filter (19), the output terminal of described wave filter (19) is connected with the input end of analog to digital conversion circuit (20), and the output terminal of analog-digital conversion circuit as described (20) is connected with the input end of computer data processing unit with display terminal (21) by USB interface.
3. optical-fiber type laser self-mixing interference instrument according to claim 2 is characterized in that: analog to digital conversion circuit (20) comprises A/D conversion card and synchronized sampling circuit.
4. according to the described optical-fiber type laser self-mixing interference of one of claim 1 to 3 instrument, it is characterized in that: electrooptic modulator (5) adopts the waveguide type electro-optic crystal.
5. utilize the measuring method of optical-fiber type laser self-mixing interference instrument as claimed in claim 1, it is characterized in that mainly may further comprise the steps:
Distributed feedback semiconductor laser (1) sends single longitudinal mode light via single-mode fiber (4) transmission, and the polarizer (3) makes electrooptic modulator (5) carry out the modulation of pure phase position to laser beam in the line;
The cosine signal that signal generator (17) sends appropriate frequency drives electrooptic modulator (5), cause the cosine phase modulation of laser beam, light part after modulated is through the resonator cavity of fiber grating (6) reflected back laser instrument (1), another part feeds back in the resonator cavity after being reflected by test specimen (8), produce double exocoel self-mixed interference phenomenon, detect by photodetector (9) from the mixed signal light intensity;
Utilize data Collection ﹠ Processing System (10) to the output signal of photodetector (9) amplify with Filtering Processing after, carry out analog to digital conversion;
In each modulation period, digital sampled signal is carried out 4 integral operationes of time, result to signal integration carries out linear combination calculating again, the result who is only comprised the sinusoidal component and the cosine component of quadrature, ratio by these two components obtains arctan function then, draws phase value;
According to phase place
And the relation between the self-mixed interference instrument external cavity length
Just can calculate the displacement of test specimen
L,
λOutput light-wave wavelength for laser instrument.
6. the measuring method of optical-fiber type laser self-mixing interference instrument according to claim 5 is characterized in that: electrooptic modulator (5) adopts the waveguide type electro-optic crystal.
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| CN103337776B (en) * | 2013-06-09 | 2015-07-15 | 安徽大学 | All-optical fiber type self-mixing distance measuring system of laser |
| TWI479119B (en) * | 2014-03-06 | 2015-04-01 | Nat Univ Chung Hsing | Optical measuring device and optical measuring method |
| CN104535535B (en) * | 2015-01-16 | 2018-01-19 | 厦门大学 | A kind of apparatus for measuring refractive index and method based on self-mixed interference |
| CN104713473B (en) * | 2015-03-17 | 2017-10-10 | 南京师范大学 | Laser mixes grating interferometer and its measuring method certainly |
| EP3401634A1 (en) * | 2017-05-12 | 2018-11-14 | Taylor Hobson Limited | Distance measuring assembly for determining the distance to an object |
| CN110631511B (en) * | 2018-05-18 | 2021-01-05 | 安徽大学 | Right-angle prism type angle sensing measurement device and method based on multi-longitudinal-mode self-mixing effect |
| CN110161669A (en) * | 2019-06-12 | 2019-08-23 | 中国科学院自动化研究所 | Based on analog video signal in body fluorescence microscopy lens head and fluorescence microscope |
| CN110631484B (en) * | 2019-11-04 | 2021-04-06 | 南京师范大学 | Three-dimensional displacement measurement system and method based on laser self-mixing grating interference |
| CN112433221B (en) * | 2020-12-15 | 2023-06-27 | 深圳市中图仪器股份有限公司 | Absolute distance measuring device based on polarization modulation |
| CN113483671B (en) * | 2021-05-11 | 2023-03-28 | 岭南师范学院 | Real-time orthogonal laser self-mixing interference displacement measuring instrument and displacement reconstruction method |
| CN113566897B (en) * | 2021-08-16 | 2024-03-22 | 安徽至博光电科技股份有限公司 | Temperature and vibration measurement system and method |
| CN114396893B (en) * | 2021-11-12 | 2023-02-14 | 中国科学院西安光学精密机械研究所 | Optical fiber transmission type passive angular displacement measuring device based on graded index lens |
| CN114353930A (en) * | 2021-12-22 | 2022-04-15 | 西安工程大学 | Micro-displacement detection device and method for enhancing self-mixing interference by intra-cavity interference |
| CN116878394B (en) * | 2023-08-02 | 2024-04-19 | 哈尔滨工业大学 | Interference displacement measurement system and method for polarized light phase modulation of microprobe |
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| DE4400680C2 (en) * | 1994-01-12 | 1995-11-02 | Kayser Threde Gmbh | Device for determining changes in distance of an object |
| CN2537958Y (en) * | 2002-04-30 | 2003-02-26 | 延边大学 | Semiconductor laser self mixing frequency interference sensor |
| CN1165744C (en) * | 2002-05-13 | 2004-09-08 | 南京师范大学 | Micro displacement self-mixing interference measurer and its signal controller and measuring method |
| CN1166914C (en) * | 2002-05-31 | 2004-09-15 | 清华大学 | Frequency-dividing self-mixing feedback-type non-contact He-Ne laser micrometer |
| US7619744B2 (en) * | 2004-04-29 | 2009-11-17 | Koninklijke Philips Electronics N.V. | Movement sensor |
| CN1259541C (en) * | 2005-01-21 | 2006-06-14 | 清华大学 | Self-mixed interference displacement sensor based on two-way laser |
| CN101706579A (en) * | 2009-11-17 | 2010-05-12 | 中国工程物理研究院电子工程研究所 | MEMS dynamic tester based on self-mixing effect of diode laser |
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