CN104634256A - Fiber laser single-wave self-mixing interference displacement measuring system - Google Patents

Abstract

The invention discloses a fiber laser single-wave self-mixing interference displacement measuring system, and belongs to the technical field of optical measuring. The system comprises a pumping source, a laser device, five optical fiber gratings, three optical fiber isolators, two detectors, an Er-doped fiber, piezoelectric ceramic, a 3dB coupler, a circulator, a collimating mirror, a wavelength division multiplexer, a variable optical attenuator, a signal processing circuit, a feedback control circuit, an A/D (analog to digital) conversion card, a computer and result output. A pair of optical fiber gratings with the same reflection wavelength is used as a laser resonator mirror to generate single-wavelength laser; the single-wavelength laser is projected to a measured object surface, reflected or scattered back to a laser cavity through a measured object to generate self-mixing interference with light in the cavity, so that displacement measuring with nano-scale resolution is realized. The system can measure a low-reflectivity object due to an amplifying effect of a gain medium in the laser cavity; output wavelength of the laser device is stabilized through feedback control, so that the measuring precision is greatly improved; the fiber laser device is not only a sensor, but also an interferometer, is simple in structure and easy to carry.

Description

A kind of optical-fiber laser list ripple self-mixed interference displacement measuring system

Technical field

The present invention relates to field of optical measurements, particularly relate to a kind of optical-fiber laser list ripple self-mixed interference displacement measuring system.

Background technology

The document that existing technology is therewith close has following two:

[1] D.P.Hand, T.A.Carolan, J.S.Barton, and J.D.C.Jones. " Profile measurement of optically rough surfaces by fiber-optic interferometry ", Opt.Lett., Vol.18, No.16,1993, P.1361-1363. (Optics Letters (optics letter), 18th volume, the 16th phase, P.1361-1363)

The know-why of document [1] as shown in Figure 1.

The light that semiconductor laser sends is after faraday isolator and optical fiber three-dB coupler, arrive measuring head, measuring head is a Feisuo interferometer, part light is by fiber end face reflection conduct reference light, another part light, after GRIN Lens focuses on, projects on measured surface, is reflected come back in system and interfere with reference light by measured surface, interference signal is detected by detector, and the phase decision of interference signal is in the longitudinally height of measured surface measured point; Change the drive current of this laser instrument to change the glow frequency of laser instrument, with the light of four kinds of different frequencies, same point is measured, obtain four interference signals, because incident light wave frequency is different, the position of four interference signals is just different mutually, regulates drive current, make the phase differential pi/2 of adjacent two interference signals, by following formula, the optical path difference D of this point can be demodulated, namely complete the measurement of single-point:

$D=\frac{c}{4\mathrm{\πv}}{\tan }^{-1}\left(\frac{I_4-I_2}{I_1-I_3}\right)$

I _n(n=1,2,3,4) are the intensity of n-th interference signal, and c is the light velocity, and ν is incident light frequency.

Stepper motor drives measuring head transversal scanning measured surface again, namely completes the measurement to measured surface.

[2] Dejiao Lin, Xiangqian Jiang, Fang Xie, Wei Zhang, Lin Zhang and Ian Bennion. " High stability multiplexed fibre interferometer and its application on absolute displacement measurement and on-line surface metrology ", Optics Express, Vol.12, Issue 23,2004, P.5729-5734. (Optics Express (optics is express), 2004,12nd volume, the 23rd phase, P.5729-5734)

The technical schematic diagram of document [2] as shown in Figure 2.

This system comprises the Michelson interferometer that two light paths almost overlap.A Michelson interferometer utilizes the fiber grating on gage beam and reference mirror to form as catoptron, for completing steady operation; Another Michelson interferometer utilizes measurement mirror and reference mirror to form as catoptron, for completing surveying work.Because the reference arm of two interferometers shares a catoptron, the reference arm light path of two interferometers overlaps completely, again because the gage beam of two interferometers almost overlaps, so an interferometer stabilizes, and another interferometer also just stabilizes.

Sending wavelength by semiconductor laser is λ ₀light after two three-dB couplers, be divided into two-way, a road is reflected by fiber grating, the reflection of the referenced catoptron in another road.Two-way reflected light again meets and interferes after three-dB coupler, interference signal is after circulator, reflected by another fiber grating, again through circulator, then device detection is detected, the signal that this detector detects regulates the length of the reference arm of fibre optic interferometer through servo circuit process rear drive piezoelectric ceramic tube, make two of stable interferometer to interfere arm to be in quadrature (phase differential is pi/2) all the time, thus realize the object stablizing this interferometer.

The wavelength X that tunable laser sends _mvariable light is divided into two-way after two optical fiber three-dB couplers, one tunnel is reflected by measurement mirror again and is again got back in interferometer after optical fiber self-focus lens, another road is reflected by reference mirror again and is again got back in interferometer after optical fiber self-focus lens, two-way light meets after three-dB coupler, form interference signal, this interference signal, after circulator and fiber grating, is detected device detection, more namely measures the displacement of measuring mirror through phase analysis.

Above-mentioned two prior art Problems existing and deficiency are:

1, be difficult to measure the object of antiradar reflectivity.

2, measurement result is by the impact of light source spectral drift, and measuring accuracy is difficult to improve.

Summary of the invention

The fiber grating (FBG) that the present invention utilizes a pair reflection wavelength identical forms laserresonator as laser mirror, 980nm light source is as pumping source, Er-doped fiber is as gain media, the Single wavelength laser meeting condition of resonance produces reflection through measured object, feed back in laser cavity with light self-mixed interference in chamber, process single wave interference signal, realize the displacement measurement to testee.Laser cavity has amplification to feedback light, so native system can be measured the object of antiradar reflectivity.Utilize the optical maser wavelength of FEEDBACK CONTROL stable fiber laser instrument, and temperature compensation is done to fiber grating, improve system rejection to disturbance, be applicable to on-line measurement.Fiber laser is sensor and interferometer, and all-fiber light path is without the need to regulating, simple and compact for structure, is easy to carry about with one.

The present invention is achieved by the following technical solutions.

A kind of optical-fiber laser list ripple self-mixed interference displacement measuring system, by 980nm pumping source S1,1310nm semiconductor laser L1, three fibre optic isolaters I1, I2, I3, Er-doped fiber F1, five fiber grating FBG ₁₁, FBG ₁₂, FBG ₂₁, FBG ₂₂, FBG ₂₃, three-dB coupler N1, piezoelectric ceramics PZT, variable optical attenuator VOA, collimating mirror G1, circulator H1, two detectors PD1, PD2, wavelength division multiplexer WDM, signal processing circuit B1, feedback control circuit B2, A/D transition card B3, computing machine B4 and Output rusults B5 forms; The light that 980nm light source S1 and 1310nm semiconductor laser L1 sends is coupled and arrives fiber grating FBG after fibre optic isolater I1 and I2, wavelength division multiplexer WDM and three-dB coupler N1 ₂₁.Fiber grating FBG ₂₁and FBG ₂₂bragg wavelength be 1310nm laser wavelength, therefore 980nm pump light is through fiber grating FBG ₂₁arrive the FBG of next-door neighbour ₁₁.FBG ₁₁, FBG ₁₂bragg wavelength identical and at 1550nm wave band, therefore form two laser mirrors, FBG ₁₁and FBG ₁₂between be Er-doped fiber F1, the light stimulus being subject to 980nm light source S1 produces 1550nm wave band fluorescence, meets laser cavity condition of resonance and at FBG ₁₁and FBG ₁₂wave resonance in reflectance spectrum, produces laser when gain is greater than loss, and at laser cavity mid-variable attenuator VOA regulation loss to regulate Er-doped fiber gain spectral shape, realize stablizing single longitudinal mode and export, Output of laser is through FBG ₁₂with the FBG of next-door neighbour ₂₂, via 1310nm isolator I3 and collimating mirror G1, directive measured object, and penetrated by measured object anti-(faling apart) and feed back to light self-mixed interference in laser cavity and chamber, interference signal is via FBG ₁₁, FBG ₂₁, arrive three-dB coupler N1.One road signal arrives isolator I1 and I2, because the effect of I1 and I2 can not have an impact to 980nm pumping source S1 and 1310nm semiconductor laser L1 via wavelength division multiplexer WDM; Another road signal arrives FBG through circulator H1 ₂₃, because FBG ₂₃bragg wavelength is 1310nm laser wavelength, light therethrough FBG ₂₃be detected device PD1 to detect.Feedback light, containing measured object displacement signal, so the signal that PD1 obtains is after the program in signal processing circuit B1, A/D transition card B3 and computing machine B4 is for data processing, obtains displacement measurement, exports B5 export by result.

FBG ₂₁and FBG ₂₂form F-P interferometer two catoptron, in F-P interferometric cavity, Optical Fiber Winding is on piezoelectric ceramics PZT, after system is entered in the optically-coupled sent from 1310nm semiconductor laser L1, acts on FBG ₂₁and FBG ₂₂for in the F-P interferometer of catoptron, interference signal is extremely similar to the signal of two-beam interference, after three-dB coupler (N1), one tunnel arrives isolator I1 and I2, because the effect of I1 and I2 can not have an impact to 980nm pumping source S1 and 1310nm semiconductor laser L1 via wavelength division multiplexer WDM; Another road signal arrives FBG through circulator H1 ₂₃, because FBG ₂₃reflectivity reaches 100%, and flashlight is by FBG ₂₃be detected device PD2 after reflection to detect, the signal obtained is after feedback control circuit B2 process, its output signal is added on piezoelectric ceramics PZT, drives piezoelectric ceramics PZT to regulate fiber lengths in F-P interferometric cavity, makes F-P interferometer be stabilized in orthogonal points (phase differential ), namely stabilize F-P interferometric cavity long.Reason FBG ₁₁and FBG ₁₂the laser cavity of composition is in this F-P interferometric cavity, and laser mirror FBG ₁₁and FBG ₁₂next-door neighbour F-P interferometer reflection mirror FBG ₂₁and FBG ₂₂, so laser cavity looks stable, make substrate with minus thermal-expansion coefficient in the present system simultaneously, fiber grating FBG is bonded on substrate and do temperature compensation, the bragg wavelength of FBG is stablized, thus the wavelength stabilized laser that laser cavity is exported.

Further, preferably, the fiber grating FBG that a pair reflection wavelength is identical is utilized ₁₁and FBG ₁₂as laser mirror, Er-doped fiber F1, as gain media, produces 1550nm Single wavelength laser, projects on testee, reflect or be scattered back laser cavity, with light self-mixed interference in laser cavity, obtain interference signal and realize displacement measurement through testee.

Further, as a kind of preferred version, the signal utilizing PD2 to detect is after feedback control circuit B2 process, and output signal drives piezoelectric ceramics PZT, regulates fiber grating FBG ₂₁and FBG ₂₂fiber lengths in the F-P interferometric cavity of composition, stabilize F-P interferometric cavity long, indirect stabilization laser chamber is long, makes substrate with minus thermal-expansion coefficient simultaneously, being bonded at by light grating on substrate makes fiber grating bragg wavelength stablize do temperature compensation, makes laser cavity produce wavelength stabilized laser.

Beneficial effect of the present invention mainly contains four:

1. the fiber grating that the present invention utilizes a pair reflection wavelength identical produces Single wavelength laser projection on measured surface as laser mirror, be reflected back in laser cavity through measured object, in feedback light and chamber, light produces self-mixed interference, thus realizes the displacement measurement that resolution is nanometer scale.

2. the present invention utilizes the gain media in the laser cavity of fiber laser to have amplification to the light that measured object feeds back in chamber, realizes the measurement to antiradar reflectivity object.

3. the present invention utilizes the chamber of the method stable fiber laser instrument of feedback control compensation light path long, with the wavelength of this stable laser output light-wave or frequency, greatly improves the measuring accuracy of measurement result.

4. in the present invention, fiber laser self integrates sensor and interferometer, and all-fiber light path, without the need to regulating, to be simple and compact for structurely easy to carry about with one.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of prior art document [1];

Fig. 2 is the schematic diagram of prior art document [2];

Fig. 3 is principle of the invention figure.

Embodiment

Below in conjunction with accompanying drawing 3 and embodiment, the invention will be further described.

As shown in Figure 3, a kind of optical-fiber laser list ripple self-mixed interference displacement measuring system, by 980nm pumping source S1,1310nm semiconductor laser L1, three fibre optic isolaters I1, I2, I3, Er-doped fiber F1, five fiber grating FBG ₁₁, FBG ₁₂, FBG ₂₁, FBG ₂₂, FBG ₂₃, three-dB coupler N1, piezoelectric ceramics PZT, variable optical attenuator VOA, collimating mirror G1, circulator H1, two detector PD1 and PD2, wavelength division multiplexer WDM, signal processing circuit B1, feedback control circuit B2, A/D transition card B3, computing machine B4 and Output rusults B5 forms.The fiber grating FBG that this measuring system utilizes a pair reflection wavelength identical ₁₁and FBG ₁₂as laser mirror, Er-doped fiber as gain media, the laser list ripple sent through measured object feed back in chamber with light self-mixed interference in chamber, the interference signal of generation obtains measured object displacement measurement after demodulation.Fiber grating FBG in system ₁₁, FBG ₁₂bragg wavelength is identical and at 1550nm wave band, fiber grating FBG ₂₁, FBG ₂₂and FBG ₂₃bragg wavelength identical, and be 1310nm semiconductor laser wavelength.FBG ₁₁and FBG ₁₂between be Er-doped fiber, FBG ₁₁reflectivity is 95%, FBG ₁₂reflectivity is 5%, FBG ₂₁and FBG ₂₂reflectivity be 4%, FBG ₂₃reflectivity be 100%.

The light that 980nm light source S1 and 1310nm semiconductor laser L1 sends is coupled and arrives fiber grating FBG after fibre optic isolater I1 and I2, wavelength division multiplexer WDM and three-dB coupler N1 ₂₁.Fiber grating FBG ₂₁and FBG ₂₂bragg wavelength be 1310nm laser wavelength, therefore 980nm pump light is through fiber grating FBG ₂₁arrive the FBG of next-door neighbour ₁₁.FBG ₁₁, FBG ₁₂bragg wavelength identical and at 1550nm wave band, therefore form two laser mirrors, FBG ₁₁and FBG ₁₂between be Er-doped fiber F1, the light stimulus being subject to 980nm light source S1 produces 1550nm wave band fluorescence, meets laser cavity condition of resonance and at FBG ₁₁, FBG ₁₂wave resonance in reflectance spectrum, produces laser when gain is greater than loss, and at laser cavity mid-variable attenuator VOA regulation loss to regulate Er-doped fiber gain spectral shape, realize stablizing single longitudinal mode and export, Output of laser is through FBG ₁₂with the FBG of next-door neighbour ₂₂, via 1310nm isolator I3 and collimating mirror G1, directive measured object, and penetrated by measured object anti-(faling apart) and feed back to light self-mixed interference in laser cavity and chamber, interference signal is via FBG ₁₁, FBG ₂₁, arrive three-dB coupler N1.One road signal arrives isolator I1 and I2, because the effect of I1 and I2 can not have an impact to 980nm pumping source S1 and 1310nm semiconductor laser L1 via wavelength division multiplexer WDM; Another road signal arrives FBG through circulator H1 ₂₂, because FBG ₂₂bragg wavelength is 1310nm laser wavelength, light therethrough FBG ₂₃be detected device PD1 to detect.Feedback light, containing measured object displacement signal, so the signal that PD1 obtains is after the program in signal processing circuit B1, A/D transition card B3 and computing machine B4 is for data processing, obtains displacement measurement, exports B5 export by result.

FBG ₂₁and FBG ₂₂become F-P interferometer two catoptron, in F-P interferometric cavity, Optical Fiber Winding is on piezoelectric ceramics PZT, after system is entered in the optically-coupled sent from 1310nm semiconductor laser L1, acts on FBG ₂₁and FBG ₂₂for in the F-P interferometer of catoptron, interference signal is extremely similar to the signal of two-beam interference, after three-dB coupler, a road arrives isolator I1 and I2, because the effect of I1 and I2 can not have an impact to 980nm pumping source S1 and 1310nm semiconductor laser L1 via wavelength division multiplexer WDM; Another road signal arrives FBG through circulator H1 ₂₂, because FBG ₂₃reflectivity reaches 100%, and flashlight is by FBG ₂₃be detected device PD2 after reflection to detect, the signal obtained is after feedback control circuit B2 process, its output signal is added on piezoelectric ceramics PZT, drives piezoelectric ceramics PZT to regulate fiber lengths in F-P interferometric cavity, makes F-P interferometer be stabilized in orthogonal points (phase differential ), namely stabilize F-P interferometric cavity long.Reason FBG ₁₁and FBG ₁₂the laser cavity of composition is in this F-P interferometric cavity, and laser mirror FBG ₁₁and FBG ₁₂next-door neighbour F-P interferometer reflection mirror FBG ₂₁and FBG ₂₂, so laser cavity looks stable, make substrate with minus thermal-expansion coefficient in the present system simultaneously, fiber grating FBG is bonded on substrate and do temperature compensation, the bragg wavelength of FBG is stablized, thus the wavelength stabilized laser that laser cavity is exported.

Displacement h causes phase change A φ:

$\mathrm{\Δ\φ}=4\mathrm{\π}\frac{\mathrm{\Δh}}{\mathrm{\λ}}---\left(1\right)$

Have $\mathrm{\Δh}=\frac{\mathrm{\Δ\φ}\×\mathrm{\λ}}{4\mathrm{\π}}---\left(2\right)$

Because of phase ambiguity, Δ φ < π is had to retrain,

So $\mathrm{\&Delta;}{h}_{\max }=\frac{\mathrm{\&lambda;}}{4}---\left(3\right)$

Phase measurement resolution reaches 0.01 °, λ at 1550nm wave band, so Δ h resolution is better than 0.1nm.

Realization in order to demonstrate the invention; describe above-mentioned instantiation; but other changes of the present invention and amendment; it will be apparent to those skilled in the art that, in the present invention without any amendment/change within the scope of the essence of disclosure and cardinal rule or imitate conversion all to belong to claims of the present invention.

Claims (4)

1. an optical-fiber laser list ripple self-mixed interference displacement measuring system, it is characterized in that by 980nm pumping source (S1), 1310nm semiconductor laser (L1), three fibre optic isolaters (I1, I2, I3), Er-doped fiber (F1), five fiber grating (FBG ₁₁, FBG ₁₂, FBG ₂₁, FBG ₂₂, FBG ₂₃), three-dB coupler (N1), piezoelectric ceramics (PZT), variable optical attenuator (VOA), collimating mirror (G1), circulator (H1), two detectors (PD1, PD2), wavelength division multiplexer (WDM), signal processing circuit (B1), feedback control circuit (B2), A/D transition card (B3), computing machine (B4) and Output rusults (B5) composition; The light that 980nm light source (S1) and 1310nm semiconductor laser (L1) send is coupled and arrives fiber grating (FBG after fibre optic isolater (I1, I2), wavelength division multiplexer (WDM) and three-dB coupler (N1) ₂₁); Fiber grating (FBG ₂₁) and fiber grating (FBG ₂₂) bragg wavelength be 1310nm laser wavelength, therefore 980nm pump light is through fiber grating (FBG ₂₁) arrive the fiber grating (FBG be close to ₁₁); Two fiber grating (FBG ₁₁, FBG ₁₂) bragg wavelength identical and at 1550nm wave band, therefore form two laser mirrors, two fiber grating (FBG ₁₁, FBG ₁₂) between be Er-doped fiber (F1), the light stimulus being subject to 980nm light source (S1) produces 1550nm wave band fluorescence, meets laser cavity condition of resonance and at fiber grating (FBG ₁₁, FBG ₁₂) wave resonance in reflectance spectrum, produce laser, through fiber grating (FBG when gain is greater than loss ₁₂) and next-door neighbour fiber grating (FBG ₂₂), via 1310nm isolator (I3) and collimating mirror (G1), directive measured object, and penetrated by measured object anti-(faling apart) and feed back to light self-mixed interference in laser cavity and chamber, interference signal is via fiber grating (FBG ₁₁, FBG ₂₁), arrive three-dB coupler (N1); One road signal arrives isolator (I1, I2) via wavelength division multiplexer (WDM), because the effect of isolator (I1, I2) can not have an impact to 980nm pumping source (S1) and 1310nm semiconductor laser (L1); Another road signal arrives fiber grating (FBG through circulator (H1) ₂₂), because fiber grating (FBG ₂₃) bragg wavelength is 1310nm laser wavelength, light therethrough fiber grating (FBG ₂₃) be detected device (PD1) detection; Feedback light is containing measured object displacement signal, so the signal that detector (PD1) obtains is after the program in signal processing circuit (B1), A/D transition card (B3) and computing machine (B4) is for data processing, obtain displacement measurement, export (B5) by result and export; Fiber grating (FBG ₂₁, FBG ₂₂) forming F-P interferometer two catoptron, in F-P interferometric cavity, Optical Fiber Winding is on piezoelectric ceramics (PZT), after system is entered in the optically-coupled sent from 1310nm semiconductor laser (L1), acts on fiber grating (FBG ₂₁, FBG ₂₂) in the F-P interferometer of catoptron, interference signal is extremely similar to the signal of two-beam interference, after three-dB coupler (N1), one tunnel arrives isolator (I1, I2) via wavelength division multiplexer (WDM), because the effect of isolator (I1, I2) can not have an impact to 980nm pumping source (S1) and 1310nm semiconductor laser (L1); Another road signal arrives fiber grating (FBG through circulator (H1) ₂₃), because fiber grating (FBG ₂₃) reflectivity reaches 100%, flashlight is by fiber grating (FBG ₂₃) be detected device (PD2) detection after reflection, the signal obtained is after feedback control circuit (B2) process, its output signal drives piezoelectric ceramics (PZT), regulate fiber lengths in F-P interferometric cavity, make F-P interferometer be stabilized in orthogonal points (phase differential ), namely F-P interferometric cavity is stabilized long, also stablized so laser cavity is long, make substrate with minus thermal-expansion coefficient in the present system simultaneously, being bonded at by fiber grating (FBG) on substrate makes its bragg wavelength stablize do temperature compensation, thus the wavelength stabilized laser that laser cavity is exported.

2. a kind of optical-fiber laser list ripple self-mixed interference displacement measuring system according to claim 1, is characterized in that: utilize the fiber grating (FBG that a pair reflection wavelength is identical ₁₁, FBG ₁₂) produce Single wavelength laser as laser mirror, project on testee, reflect through measured object or be scattered back in laser cavity, with light self-mixed interference in chamber, realizing the displacement measurement that resolution is nanometer scale.

3. a kind of optical-fiber laser list ripple self-mixed interference displacement measuring system according to claim 1, it is characterized in that: the signal utilizing detector (PD2) to detect is after feedback control circuit (B2) process, output signal drives piezoelectric ceramics (PZT), regulate fiber lengths in F-P interferometric cavity, stablize F-P interferometric cavity long, namely stabilize wavelength or the frequency of laser instrument output light-wave, greatly improve the measuring accuracy of measurement result.

4. a kind of optical-fiber laser list ripple self-mixed interference displacement measuring system according to claim 1, is characterized in that: fiber laser self integrates sensor and interferometer, and all-fiber light path is without the need to regulating.