CN1304814C - Self-mixed interference HeNe laser displacement transducer with direction recognition function - Google Patents
Self-mixed interference HeNe laser displacement transducer with direction recognition function Download PDFInfo
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- 238000006073 displacement reaction Methods 0.000 title claims abstract description 34
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- 239000000919 ceramic Substances 0.000 claims description 17
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Abstract
The present invention relates to a self-mixing interference He-Ne laser displacement transducer with the function of direction recognition, which belongs to the field of laser displacement measurement. The present invention is characterized in that the present invention is composed of a light source, a measuring part and a signal processing part, and has the advantage of compact structure. The present invention only has one interference passage. The light source uses a double longitudinal mode laser which can output two beams of orthogonal polarized light with different lighting intensity; in a measuring process, the two beams of the orthogonal polarized light output by a laser are detected so as to obtain two lighting intensity signals with reverse phase differences, and one period of the two lighting intensity signals is provided with two different equal light intensity points. The positive and the negative of the difference value of the two different equal light intensity points are different with the difference of the moving directions of objects, and direction judgment is realized hereby. The lighting intensity signal of each period corresponds to the displacement of a half of wavelength of the laser, namely that the resolution of a system is the half of the wavelength of the laser. The present invention has the advantages of compact and simple structure, and high performance-price ratio. The present invention is a self-mixing interference displacement transducer which can realize the direction judgment under the condition without needing controlling optical feedback levels.
Description
Technical field
The invention belongs to Laser Measuring shift technique field.
Background technology
Laser displacement sensor measure and metering field should in extensively, the self-mixed interference interferometer is studied extensive in recent years.Than traditional interferometer, that the self-mixed interference instrument has is simple in structure, aim at straightforward less demanding and advantage that cost performance is high.In the self-mixed interference instrument apparatus, light path system has only a laser instrument and extraneous reverberation or scattering thing (being object under test).The light of laser instrument output be reflected or scattering after, part light return laser light resonator cavity mixes the light intensity variation that causes laser instrument with light in the chamber.Outside object under test whenever moves the displacement of half optical wavelength, and the laser instrument light intensity changes a striped, and the shape of striped presents difformity because of the difference of feedback level.The fluctuation degree of depth of striped and traditional double beam interference system can compare.Laser instrument light intensity striped can be directly used in counting and realize displacement measurement this moment, and systemic resolution is a half wavelength.
The most research of self-mixed interference displacement measuring technology all concentrates on the self-mixed interference research in the semiconductor laser.Self-mixed interference phenomenon more complicated in the semiconductor laser can be divided into four kinds of light feedback levels according to the difference of feedback coefficient C:
A. very low light level feedback (C 1), feedback signal is a cosine waveform;
B. low light level feedback (0.1＜C＜1), feedback signal are class sawtooth wave waveform;
C. intermediate light feedback (1＜C＜4.6), feedback signal is a class sawtooth wave waveform, bistable state appears in laser instrument;
D. high light feedback (C＞4.6), feedback is strong excessively, can not be used for interferometry.
Under low light level feedback and intermediate light feedback level, the self-mixing interference of semiconductor laser is asymmetrical class sawtooth wave shape, and the vergence direction of sawtooth wave is relevant with the moving direction of exocoel reverberation.Consider the displacement of the corresponding exocoel reverberation of each periodic group sawtooth wave half wavelength simultaneously, so not only can utilize class sawtooth wave realization direction to discern but also can realize the measurement of displacement.Therefore semiconductor self-mixed interference system can realize using one road light signal realize declaring to purpose.Under intermediate light feedback level, sluggish phenomenon can appear in self-mixing interference, will bring error to counting.Therefore under low light level feedback level, can effectively realize displacement measurement for the self-mixed interference system that uses semiconductor laser, but the feedback level of laser instrument need be strict controlled in low light level feedback level.If light feedback level because of extraneous object under test surface reflection or scattering property improve or variation makes laser works in very low light level feedback level or intermediate light feedback level, system will because of self-mixing interference for the sinusoidal signal of symmetry can not realize declaring to or cause measuring error because of hysteresis phenomenon.
Summary of the invention
The object of the invention is to provide a kind of compact conformation, the cost performance height, can realize declaring to and need not to control the self-mixed interference displacement sensor of light feedback level.
The present invention is characterised in that it contains:
The Lights section, it is the laser instrument of two longitudinal modes, its output is the polarized light of two different bundle quadratures of light intensity;
Measure portion, it comprises piezoelectric ceramics and is combined in the exocoel catoptron as object under test on the described piezoelectric ceramics; The incident beam of described exocoel catoptron is two bundle quadrature and the different polarized lights of light intensity of the laser instrument output of above-mentioned pair of longitudinal mode; When the exocoel catoptron when the direction of the main beam of above-mentioned double-longitudinal-mode laser output is moved, after mixing, pairwise orthogonal polarized light in the reflected light of described exocoel catoptron and the above-mentioned double-longitudinal-mode laser resonator cavity causes pairwise orthogonal polarized light intensity variations in the laser instrument, the light intensity curve variation tendency of pairwise orthogonal polarized light is opposite, and occurred two different isocandela points in the light intensity curve striped of the above-mentioned pairwise orthogonal polarized light in one-period, the positive and negative direction of motion because of described exocoel catoptron of described isocandela point difference is different;
Signal processing comprises:
The Wollaston prism is positioned at the tail light output end of the laser instrument of described pair of longitudinal mode, and the input optical signal of described prism is the polarized light of two bundle quadratures;
Photodetector, totally two, all be positioned at the opposite side of described Wollaston prism, two input signals of described photodetector are respectively the polarized lights of two bundle quadratures of separated described Wollaston prism output;
Signal processing apparatus, it is a computing machine or single-chip microcomputer, it is gathered the output signal of described two photodetectors and carries out real-time signal Processing, identifies the positive and negative of two isocandela point differences in the above-mentioned one-period striped, and displacement measurement is shown.
It is simple to the invention provides a kind of compact conformation, the cost performance height, can realize declaring to and need not to control the self-mixed interference displacement sensor of light feedback level, see Fig. 1.
Description of drawings
One of Fig. 1 self-mixed interference displacement sensor embodiment of the present invention.
Two of Fig. 2 self-mixed interference displacement sensor embodiment of the present invention.
Three of Fig. 3 self-mixed interference displacement sensor embodiment of the present invention.
The polarized light light intensity of two bundle quadratures is with Piezoelectric Ceramic change in voltage curve map in Fig. 4 (a) light regeneration processes; Two isocandela point synoptic diagram when (b) Piezoelectric Ceramic voltage rises; Two isocandela point synoptic diagram when (c) Piezoelectric Ceramic voltage descends.
Two light intensity are with Piezoelectric Ceramic change in voltage curve map in the birefringence double-frequency laser of Fig. 5 450MHz frequency difference
The polarized light light intensity of Fig. 6 (a) two bundle quadratures is with Piezoelectric Ceramic change in voltage curve map; (b) the displacement curve figure after electronic fine-grained.
Embodiment
Example 1 of the present invention as shown in Figure 1,1 is the tail light outgoing mirror of HeNe laser instrument, its reflectivity is generally 99.8%, 2 is the gain tube of laser instrument, and inside is filled with the mixed gas of HeNe, and 3 is the anti-reflection window of laser instrument, 4 is the main beam outgoing mirror of laser instrument, and reflectivity is generally 98%.1,2,3 and 4 have formed the main body of a HeNe laser instrument jointly, and the chamber is long to be 126mm, long by the fine setting laser chamber, can export two linear orthogonal polarized lights so that this laser instrument is a double-longitudinal-mode laser.5 is the exocoel catoptron, and in actual applications, this catoptron is an object under test.6 are used for driving catoptron 5 moving along radiation direction for piezoelectric ceramics.5 and 6 two elements have been formed the exocoel of self-mixed interference system, and the chamber is long to be 290mm.The tail light of laser instrument through Wollaston prism 7 be divided into two the bundle quadratures polarized light, two the bundle quadratures polarized lights survey by detector 8 and 9 respectively, gained two photosignals are handled by computing machine 12.Computing machine 12 realizes collecting the function that signals collecting, fringe count, direction identification and measurement result show by the mode of software programming.Total system can be divided into three parts: 11 for measure portion is the exocoel of self-mixed interference system, and 12 is signal processing, and 13 is the Lights section.
The principle of the invention is as follows.The feedback coefficient C of self-mixed interference system can followingly represent:
R wherein
2And R
sBe respectively the reflectivity of main beam outgoing mirror 4 and exocoel catoptron 5; τ and τ
cBeing respectively light beam advances a time back and forth at exocoel and inner chamber; B is the live width gain coefficient.The reflectivity R of main beam outgoing mirror 4
2=0.98 is almost 1, no matter makes exocoel catoptron 5 reflectivity R
sHow changing, feedback coefficient C will be much smaller than 1, so use the self-mixed interference system of the long HeNe laser instrument of short cavity to belong to very low light level feedback level.The light intensity of the polarized light (two longitudinal modes) of two bundle quadratures can be expressed as in following pair of longitudinal mode HeNe laser instrument of low light level feedback level very:
I
//＝I
//0[1+mcos()] (2)
I
⊥＝I
⊥0[1+mcos(+Δ)] (3)
I
//And I
⊥Represent directional light and the vertical light light intensity when the light feedback exists respectively, and I
// 0And I
⊥ 0Then represent directional light and the vertical light light intensity when unglazed feedback respectively.M is the index of modulation of light feedback.=4 π l/ λ are light beam at the exocoel caused back and forth phase differential of advancing, and wherein l is an external cavity length.The phase differential of Δ for causing because of the mode competition between two light, relatively fiercer for two longitudinal mode HeNe laser instrument two intermodes competitions, experimental result shows that phase differential is about 180 degree between the light intensity curve of the polarized light of two bundle quadratures.Therefore the Δ of system for the application gets π, and formula 3 can be expressed as:
I
⊥＝I
⊥0[1-mcos()] (4)
Therefore after laserresonator is returned in the polarized light feedback simultaneously of two of two longitudinal mode HeNe laser instrument outputs being restrainted quadratures, can directly obtain two opposite light intensity curves of phase place, for example shown in Fig. 4 (a).Last figure is the polarized light light intensity curve of two bundle quadratures among Fig. 4 (a), and the curve of punctuating is that directional light feedback curve real point curve map then is vertical light feedback curve.Figure below is the triangular wave drive signal of piezoelectric ceramics among Fig. 4 (a).Because two longitudinal mode initial strength differences, the two institute's competitive edge that shows in the light feedback is also different, stronger mould is in strong position than strong mode and makes that the light intensity of more weak mould is zero near its light intensity maximal value the time, the horizontal linear part on corresponding the light intensity curve.Stronger mould is near its light intensity minimum value the time, more weak mould show its competitive edge, its light intensity curve shows as the bulge of a pulsed, it is all very fast that intensity rises and descends.Two light intensity curves have two isocandela points, and the light intensity level of these two somes height is different.When the driving voltage of piezoelectric ceramics 5 rose, the isocandela point on the left side was higher than the isocandela point on the right, shown in Fig. 4 (b).And when the driving voltage of piezoelectric ceramics 5 descended, the isocandela point on the left side was lower than the isocandela point on the right, shown in Fig. 4 (c).Fig. 5 has then provided two light intensity curve figure in the birefringence double-frequency laser of 450MHz frequency difference.Than Fig. 4, two isocandela level point differences among Fig. 5 in the two light intensity curve one-periods are more obvious.Therefore the positive and negative direction that can represent the piezoelectric ceramics telescopic variation of two isocandela point differences about, thus can realize identification to the object under test direction.Therefore only need in the process of signals collecting, second isocandela point place in the one-period signal counts, the two isocandela point differences that depend on two light intensity signals of adding deduct of counting positive and negative, for example get the isocandela point hour counter that isocandela point when the left side is higher than the right and add 1, and subtract 1 when the isocandela point hour counter of the isocandela point on the left side on the right of being lower than.For example shown in Figure 6, Fig. 6 (a) and Fig. 6 (b) are two sets of curves that obtain simultaneously, and the last figure of Fig. 6 (a) is double-longitudinal-mode laser two polarized light light intensity curve figure, and figure below is a Piezoelectric Ceramic voltage.Fig. 6 (b) then is displacement curve figure.Each step among the displacement curve figure is represented the displacement of λ/2=316.4nm.As shown in Figure 6, when the driving voltage of piezoelectric ceramics 5 rises, the step of a rising will appear along with the appearance of a light intensity curve striped in displacement curve, and when the driving voltage of piezoelectric ceramics 5 descends, displacement curve then will occur the step of a decline along with the appearance of a light intensity curve striped.Displacement among Fig. 5 (b) can reflect the variation of movement of objects direction, also can count along with the appearance of striped simultaneously.So the application's displacement transducer can realize declaring to, simultaneity factor resolution is λ/2=316.4nm.
The structural representation of example 2 of the present invention as shown in Figure 2.1-10 among totally ten elements and Fig. 1 1-10 totally ten elements are identical, so locate no longer to repeat to introduce.14 for placing the crystalline quartz of laser resonant cavity, and a longitudinal mode splitting that can make the laser instrument of a single longitudinal mode is two mutually perpendicular longitudinal modes in polarization direction.The use of crystalline quartz can be implemented in the output that realizes two longitudinal modes in the long single longitudinal mode laser of a short cavity, and the chamber that has reduced laser instrument is long.
The structural representation of example 3 of the present invention as shown in Figure 3.1-10 totally ten elements still with Fig. 1 in 1-10 totally ten elements are identical, so locate also no longer to repeat to introduce.15 is mechanical type stress bringing device, it applies a stress along the direction perpendicular to laser gain tube axis to anti-reflection window, make anti-reflection window generation birefringence effect, can be so that a longitudinal mode splitting of the laser instrument of a single longitudinal mode be two mutually perpendicular longitudinal modes in polarization direction.Stress to apply the chamber that also can reduce laser instrument long, be implemented in the output that realizes two longitudinal modes in the long single longitudinal mode laser of a short cavity.
The designed self-mixed interference displacement sensor of the present invention is by light source, and 3 parts of measure portion and signal Processing are formed.Its system source is used is the two longitudinal mode HeNe laser instruments that can export neither with the crossed polarized light of light intensity.In measuring process, the polarized lights of two bundle quadratures of laser instrument output are surveyed can obtain the opposite light intensity signal of two-way phase differential, two different isocandela points are arranged in the two light intensity signal one-periods.The positive and negative difference because of the movement of objects direction of two isocandela point differences is different, can realize in view of the above declaring to.The displacement of the corresponding λ of the light intensity signal in each cycle/2, promptly the resolution of system is half laser wavelength.The application's displacement transducer is that a kind of compact conformation is simply compact, the cost performance height, and can be implemented in realize under the condition that need not to control light feedback level declaring to self-mixed interference displacement sensor.
Claims (1)
1, the self-mixed interference HeNe laser displacement transducer that has direction recognition function, this displacement transducer comprise light source, measurement and three parts of signal Processing, it is characterized in that it contains:
The Lights section, it is the laser instrument of two longitudinal modes, its output is the polarized light of two different bundle quadratures of initial light intensity;
Measure portion, it comprises piezoelectric ceramics and is combined in the exocoel catoptron as object under test on the described piezoelectric ceramics; The incident beam of described exocoel catoptron is two bundle quadrature and the different polarized lights of light intensity of the laser instrument output of above-mentioned pair of longitudinal mode; When the exocoel catoptron when the direction of the main beam of above-mentioned double-longitudinal-mode laser output is moved, after mixing, pairwise orthogonal polarized light in the reflected light of described exocoel catoptron and the above-mentioned double-longitudinal-mode laser resonator cavity causes pairwise orthogonal polarized light intensity variations in the laser instrument, this light intensity curve variation tendency is opposite, and occurred two different isocandela points in the light intensity curve striped of the mixed pairwise orthogonal polarized light of this in one-period, the positive and negative direction of motion because of described exocoel catoptron of described isocandela point difference is different;
Signal processing comprises:
The Wollaston prism is positioned at the tail light output end of the laser instrument of described pair of longitudinal mode, and the input optical signal of described prism is the polarized light of two bundle quadratures;
Photodetector, totally two, all be positioned at the opposite side of described Wollaston prism, two input signals of described photodetector are respectively the polarized lights of two bundle quadratures of separated described Wollaston prism output;
Signal processing apparatus, it is a computing machine or single-chip microcomputer, it is gathered the output signal of described two photodetectors and carries out real-time signal Processing, identifies the positive and negative of two isocandela point differences in the above-mentioned one-period striped, and displacement measurement is shown.
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| CN100386596C (en) * | 2006-06-07 | 2008-05-07 | 清华大学 | Laser feed-back displacement sensor based on frequency locked double-frequency laser |
| CN103115705B (en) * | 2013-01-19 | 2015-01-21 | 清华大学 | Stress and double refraction measurement instrument and measurement method based on cross-polarization solid laser |
| CN104713473B (en) * | 2015-03-17 | 2017-10-10 | 南京师范大学 | Laser mixes grating interferometer and its measuring method certainly |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60306A (en) * | 1983-06-16 | 1985-01-05 | Agency Of Ind Science & Technol | Range finding method using composite wavelength method |
| EP0408747A1 (en) * | 1988-02-19 | 1991-01-23 | Kitamura Machinery Co., Ltd. | Length measuring method by using laser beams |
| CN1547293A (en) * | 2003-11-28 | 2004-11-17 | 清华大学 | Displacement self-sensing HeNe laser system with cats eye as endoscope |
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2005
- 2005-02-25 CN CNB2005100113585A patent/CN1304814C/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60306A (en) * | 1983-06-16 | 1985-01-05 | Agency Of Ind Science & Technol | Range finding method using composite wavelength method |
| EP0408747A1 (en) * | 1988-02-19 | 1991-01-23 | Kitamura Machinery Co., Ltd. | Length measuring method by using laser beams |
| CN1547293A (en) * | 2003-11-28 | 2004-11-17 | 清华大学 | Displacement self-sensing HeNe laser system with cats eye as endoscope |
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