CN103018747A - Laser self-mixing distance measuring system based on uncollimated feedback external cavity - Google Patents

Abstract

The invention discloses a laser self-mixing distance measuring system based on an uncollimated feedback external cavity. The laser self-mixing distance measuring system comprises a total-internal cavity He-Ne double-longitudinal mode laser device, an uncollimated feedback external cavity, a signal detecting-processing and frequency stabilizing system. The total-internal cavity He-Ne double-longitudinal mode laser device outputs polarized orthorhombic laser from both ends of the laser device; the laser output from one end is incident to the uncollimated feedback external cavity; an incident beam reciprocates for a plurality of times in the feedback external cavity and then returns to the laser device to form high-order feedback; a frequency stabilizing system controls the power-on time of a resistance wire wound on the surface of the laser device and stabilizes the frequency of the laser device; and the laser output from the other end of the laser device is received by a photoelectric detector after being split by a Wollaston prism and analyzed by a signal processing unit, and then measurement results are output. On the premise of simplifying the structure of the laser device, the distance measuring system adopts the uncollimated external cavity feedback to increase the resolution ratio of the distance measuring system and utilizes the isocandela frequency stabilizing system to ensure the measurement precision, thereby improving the performance of an instrument and expanding the application field of the instrument.

Description

Based on the laser of non-collimation feedback exocoel from the hybrid ranging system

Technical field

The invention belongs to the laser ranging technique field, relate to a kind of range measurement system, especially a kind of laser based on non-collimation feedback exocoel is from the hybrid ranging system.

Background technology

Laser self-mixing interference, claim again laser feedback, its ultimate principle is: the output light of laser instrument is reflected back laser gain pipe by external reflection face, carry out self-mixed interference with the light field in the laserresonator, and the loss of modulated laser, make the output intensity generating period variation of laser instrument, just can obtain the information of external reflection face by the demodulation output intensity.Only have an optical channel based on the range measurement system of laser feedback, have simple in structure, compact, easy collimation, cost performance advantages of higher.According to the difference of feedback mode, laser feedback can be divided into collimation exocoel feedback and the feedback of non-collimation exocoel etc.Wherein, the feedback mirror of antiradar reflectivity is generally adopted in the feedback of collimation exocoel, and its optical resolution is lower, is generally λ/2, and for the helium-neon laser of 632.8nm wavelength, the resolution of displacement measurement is 316.4nm.

(application number: 200510011514.8) the multiple laser physics phenomenons such as comprehensive utilization Zeeman birefringence effect, laser self-mixing interference, dynamic Laser modulation successfully are transformed into a distance measuring sensor with a common two-frequency laser to Chinese patent " based on the laser feedback stadimeter of Zeeman birefringence double-frequency laser ".The agent structure of this invention is the external mirror of a Zeeman birefringence double-frequency He-Ne laser instrument and dynamic modulation, and external mirror is fixed on the testee.When external mirror during with certain amplitude back and forth movement, the output intensity of laser instrument has the different intensity modulation degree of depth in different positions, obtain the distance of testee according to the difference of the intensity modulation degree of depth.The method has range capability, but resolution and precision are not high, and Zeeman birefringence double-frequency laser complex structure.Chinese patent " double frequency HeNe laser optical feedback distance measuring apparatus " (application number: 200810104260.8), utilize the self-mixing effect of half inner chamber birefringence double-frequency laser and the method for phase demodulation to realize the feedback range observation, its optical resolution is λ/2, but to place birefringence element in the half inner chamber birefringence double-frequency laser chamber, be subject to easily the impact of the factors such as temperature, and there are not frequency stabilization system, measuring accuracy to be difficult to guarantee; Simultaneously, the optical resolution of the method is difficult to further raising.Because the restriction on the principle, above-mentioned two kinds of feedback distance-finding methods all exist laser structure complicated, optical resolution is low, does not have the deficiencies such as frequency stabilization system and precision are low.

Summary of the invention

The object of the invention is to overcome the shortcoming of above-mentioned prior art, provide a kind of laser based on non-collimation feedback exocoel from the hybrid ranging system, this range measurement system is on the basis of simplifying laser structure, adopt non-collimation exocoel feedback to improve the resolution of range measurement system, and utilize the isocandela frequency stabilization system to guarantee measuring accuracy, thereby improve instrument performance and widen its application.

The objective of the invention is to solve by the following technical programs:

This laser based on non-collimation feedback exocoel is from the hybrid ranging system, comprises that full inner chamber He-Ne double-longitudinal-mode laser, non-collimation feedback exocoel, acquisition of signal process and frequency stabilization system four parts, wherein:

(A) described full inner chamber He-Ne double-longitudinal-mode laser comprises:

Laser gain pipe, in fill He, Ne mixed gas;

Resonator cavity comprises:

The first inner chamber catoptron is positioned at an end of described laser gain pipe, is concave mirror, and it is towards concave surface plating reflectance coating of laser gain pipe, outside surface plating anti-reflection film;

The second inner chamber catoptron is fixed on the other end of described laser gain pipe, is flat mirror, and it is towards plane plating reflectance coating of laser gain pipe, outside surface plating anti-reflection film;

(B) described non-collimation feedback exocoel comprises:

Catoptron is concave mirror, and towards the concave surface plating reflectance coating of full inner chamber He-Ne double-longitudinal-mode laser, the other end is plated film not, and the surface of described catoptron and laser axis be θ in an angle;

Piezoelectric ceramics, the outside of light direction is inputted on the edge that is fixed on above-mentioned catoptron, and under the effect of input voltage, described piezoelectric ceramics promotes catoptron along the left and right movement of laser axis direction;

(C) described acquisition of signal is processed and is comprised:

Polarization splitting prism is positioned at the outside of the first inner chamber catoptron, and the laser of output is divided into X-direction, the Y-direction light intensity cosine component that two-way has phasic difference in the space;

Photodetector, totally two, be positioned at the light exit side of described polarization splitting prism, survey respectively X-direction and two light intensity cosine components of Y-direction of described polarization splitting prism output;

Filtering and amplifying circuit, be positioned at the rear end of above-mentioned photodetector, the signal output part of two photodetectors is connected to respectively the signal input part of filtering and amplifying circuit, described filtering and amplifying circuit is converted to digital quantity with the light feedback signal that photodetector receives, and signal is carried out filtering, amplifies and process;

Phase discriminator, the output terminal of connection filtering and amplifying circuit carries out phase demodulation to the two-way class cosine signal after amplifying;

The CPLD module, the output terminal of connection phase discriminator is finished shaping, filtering to digital signal, and is had the signal of phasic difference to calculate to above-mentioned two-way, draws the laser feedback external cavity length;

(D) described frequency stabilization system comprises:

Resistance wire is wrapped on the shell of laser gain pipe;

Frequency stabilization circuit, with the difference signal of X-direction, the Y-direction two-way light intensity amplitude control signal as frequency stabilization, the time that the controlling resistance silk heats full inner chamber He-Ne double-longitudinal-mode laser, thus realize stable double longitudinal mode laser output.

The volume ratio of the He that fills in the above-mentioned laser gain pipe, Ne mixed gas is 7:1.

Above-mentioned resistance wire is thin copper wire, and resistance is 15 Europe.

Above-mentioned filtering and amplifying circuit is connected with frequency stabilization circuit.

Above-mentioned photodetector is the PIN photodetector.

The present invention has following beneficial effect:

The present invention adopts non-collimation exocoel feedback to improve the resolution of range measurement system, and utilize the isocandela frequency stabilization system, a kind of non-collimation exocoel double longitudinal mode laser feedback range measurement system is provided, the full inner chamber He-Ne double-longitudinal-mode laser of this system is laser of output polarization quadrature all at its two ends, wherein the laser of end output incides the non-collimation feedback exocoel that is comprised of plane mirror and concave mirror, two catoptrons all are coated with high reflection film, incident beam repeatedly comes and goes in the feedback exocoel, and then turn back in the laser instrument, form the high-order feedback; Frequency stabilization system control is wrapped in the conduction time of laser instrument surface resistance silk, adopts the method for isocandela frequency stabilization that laser instrument is carried out frequency stabilization, guarantees stable double longitudinal mode laser output; The laser of laser instrument other end output is received by photodetector after the Wollaston prism light splitting, and is analyzed by signal processing unit, the output measurement result.The present invention is simple in structure, and it is for helium-neon laser, system optics resolution nanometer scale.This system has resolution height, simple in structure, the characteristics such as precision is high and cost is low.

Description of drawings

Fig. 1: based on the laser of non-collimation feedback exocoel from the hybrid ranging system schematic;

Fig. 2: non-collimation exocoel high-order feedback intensity modulation curve;

Fig. 3: during the long L=110mm of feedback exocoel, the phase curve of two adjacent longitudinal modes;

Fig. 4: during the long L=112mm of feedback exocoel, the phase curve of two adjacent longitudinal modes;

Fig. 5: during the long L=114mm of feedback exocoel, the phase curve of two adjacent longitudinal modes.

Wherein: 1 is piezoelectric ceramics; 2 is catoptron; 3 is the second inner chamber catoptron; 4 is laser gain pipe; 5 is resistance wire; 6 is the first inner chamber catoptron; 7 is polarization splitting prism; 8,9 is photodetector; 10 is filtering and amplifying circuit; 11 is phase discriminator; 12 is the CPLD module; 13 is frequency stabilization circuit.

Embodiment

Below in conjunction with accompanying drawing the present invention is done and to describe in further detail:

Referring to Fig. 1, this kind of the present invention from the hybrid ranging system, comprises that full inner chamber He-Ne double-longitudinal-mode laser, non-collimation feedback exocoel, acquisition of signal process and frequency stabilization system four parts based on the laser of non-collimation feedback exocoel, below each several part is elaborated:

(A) full inner chamber He-Ne double-longitudinal-mode laser

Full inner chamber He-Ne double-longitudinal-mode laser comprises laser gain pipe 4, resonator cavity, and wherein resonator cavity comprises the first inner chamber catoptron 6 and the second inner chamber catoptron 3.

Fill He, Ne mixed gas in the laser gain pipe 4, two kinds of gas volumes are than being 7:1.The first inner chamber catoptron 6 is positioned at an end of laser gain pipe 4, is concave mirror, and it is towards the concave surface plating reflectance coating of laser gain pipe 4, outside surface plating anti-reflection film; The second inner chamber catoptron 3 is fixed on the other end of laser gain pipe 4, is flat mirror, and it is towards the plane plating reflectance coating of laser gain pipe 4, outside surface plating anti-reflection film.

(B) non-collimation feedback exocoel

Non-collimation feedback exocoel comprises catoptron 2 and piezoelectric ceramics 1(PZT).Wherein catoptron 2 is the concave mirror of high reflectance, and towards the concave surface plating reflectance coating of full inner chamber He-Ne double-longitudinal-mode laser, the other end is plated film not, and the surface of catoptron 2 and laser axis be θ in an angle.Piezoelectric ceramics 1 is fixed on the outside along the input light direction of above-mentioned catoptron 2, and under the effect of input voltage, piezoelectric ceramics 1 promotes catoptron 2 along the left and right movement of laser axis direction.

(C) acquisition of signal is processed

The acquisition of signal processing section comprises polarization splitting prism 7, photodetector and filtering and amplifying circuit 10, phase discriminator 11 and CPLD module 12.Wherein:

Polarization splitting prism 7 is positioned at the outside of the first inner chamber catoptron 6, and the laser of output is divided into X-direction, the Y-direction light intensity cosine component that two-way has phasic difference in the space;

Totally two of photodetectors such as the photodetector 8 and 9 among Fig. 1, are positioned at the light exit side of polarization splitting prism 7, respectively X-direction and two light intensity cosine components of Y-direction of 7 outputs of detecting polarization Amici prism;

Filtering and amplifying circuit 10 is positioned at above-mentioned photodetector 8,9 rear end, two photodetectors are the PIN photodetector, the signal output part of two photodetectors is connected to respectively the signal input part of filtering and amplifying circuit 10, described filtering and amplifying circuit 10 is converted to digital quantity with the light feedback signal that photodetector receives, and signal is carried out filtering, amplifies and process.

Phase discriminator 11 connects the output terminal of filtering and amplifying circuit 10, and the two-way class cosine signal after amplifying is carried out phase demodulation.

CPLD module 12 comprises CPLD chip and peripheral circuit, and it connects the output terminal of phase discriminator 11, finishes shaping, filtering to digital signal, and has the signal of phasic difference to calculate to above-mentioned two-way, draws the laser feedback external cavity length.

In addition, the present invention also can arrange all the other signal processing circuits in the acquisition of signal processing section, comprises interrelated counting and digital display circuit, and the measurement result of displacement is counted and shown.

(D) frequency stabilization system

Comprise resistance wire 5 and frequency stabilization circuit 13.Wherein resistance wire 5 is wrapped on the shell of laser gain pipe 4.Filtering and amplifying circuit 10 is connected with frequency stabilization circuit 13, frequency stabilization circuit 13 is with the difference signal of X-direction, the Y-direction two-way light intensity amplitude control signal as frequency stabilization, the time that 5 pairs of full inner chamber He-Ne double-longitudinal-mode lasers of controlling resistance silk heat, thus realize stable double longitudinal mode laser output.

Piezoelectric ceramics 1 of the present invention and catoptron 2 have formed non-collimation exocoel feedback part.The second inner chamber catoptron 3, laser gain pipe 4 and the first inner chamber catoptron 6 have formed the double-longitudinal-mode laser of full inner chamber jointly, and whole chamber is long to be 200mm.Principle of work of the present invention is as follows:

The non-collimation exocoel high-order feedback of He-Ne double-longitudinal-mode laser, (curve of cyclical fluctuations of laser intensity can have for two-way the class cosine signal of phasic difference not only to have the position phase tuning characteristic of He-Ne birefringence double-frequency laser collimation exocoel feedback, measurement target feedback mirror is when different feedback exocoel positions, has different phasic differences), and the laser tuning curve has higher density, can reach tens times when collimating feedback, so have higher optical resolution.Simultaneously, owing to adopted the full intracavity laser of frequency stabilization, so also have the measuring accuracy of simpler structure and Geng Gao, its ultimate principle is as follows:

Double longitudinal mode laser by full intracavity laser generation, because the existence of laser instrument residual stress, the laser of adjacent two longitudinal modes will have the polarization state of quadrature, can be referred to as the ⊥ polarized light and || polarized light, in the situation of light feedback, laser light field can be divided into two parts.The one, the inner chamber propagation field of light beam after the laser inner chamber comes and goes a week, the 2nd, light beam comes and goes the propagation field that n Zhou Houzai turns back to laser resonant cavity at exocoel.The inner chamber propagation field with come and go the propagation field stack of n after week at the feedback exocoel, form self-mixed interference, since light at exocoel through Multi reflection, turn back to that light in the resonator cavity become a little less than, the oscillating condition of cross polarization double-longitudinal-mode laser is under low light level feedback condition:

$r_1{r}_{\mathrm{eff}}^{\⊥}\exp \left[(g_{\⊥}-{\mathrm{\α}}_{\⊥})L\right]\exp \left(i{\mathrm{\ω}}_{\⊥}{\mathrm{\τ}}_c\right)=1$

（1）

$r_1{r}_{\mathrm{eff}}^{\left|\right|}\exp \left[(g_{\left|\right|}-{\mathrm{\α}}_{\left|\right|})L\right]\exp \left(i{\mathrm{\ω}}_{\left|\right|}{\mathrm{\τ}}_c\right)=1$

In the formula:

With Represent respectively the ⊥ polarized light and || the equivalent cavity reflection coefficient of polarized light, ω _⊥And ω _||Be _⊥Polarized light and || the optics angular frequency of polarized light, τ _cTo be light beam come and go time in a week at inner chamber to=2L/c, and c is the light velocity in the vacuum, and L is that the feedback exocoel is long, i.e. distance between feedback catoptron and laser instrument the second inner chamber catoptron.Because the angle of inclination of exocoel catoptron is very little, so can obtain $r_{\mathrm{eff}}^{\&perp;}=r_2[1+\mathrm{\&zeta;exp}\left(i{\mathrm{\&omega;}}_{\&perp;}\mathrm{n\&tau;}\right)]$ With $r_{\mathrm{eff}}^{\left|\right|}=r_2[1+\mathrm{\&zeta;exp}\left(i{\mathrm{\&omega;}}_{\left|\right|}\mathrm{n\&tau;}\right)],$ Wherein $\mathrm{\&zeta;}=(1-{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00002468808100011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2^2){\mathrm{<figure-callout\; id="3"\; label="r"\; filenames="HDA00002468808100011.png"\; state="\{\{state\}\}">r</figure-callout>}}_3/{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00002468808100011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2$ Represent the light feedback factor, to be light beam come and go time in a week at exocoel to τ=2l/c, and n is the number of times (being defined as order) that light comes and goes at exocoel.Under the laser feedback condition, what laser threshold gained is changed to

ΔG _⊥=ζ′cos(ω _⊥nτ) （2）

ΔG _||=ζ′cos(ω _||nτ)

Wherein ζ ' is the laser feedback factor.Because the variation ratio of laser intensity is in Δ G _⊥With Δ G _||So under light feedback condition, the output intensity of two crossed polarized lights can be expressed as:

I _⊥=I _⊥0+ζ _⊥cos(ω _⊥nτ) （3）

I _||=I _||0+ζ _||cos(ω _||nτ)

In the formula: I _{⊥ 0}And I _{|| 0}The output intensity of two crossed polarized lights when being unglazed feedback, ζ _⊥And ζ _||It is the laser feedback factor.(3) formula shows that when the light feedback was arranged, the output intensity of two crossed polarized lights was all modulated, and waveform is similar to cosine, if the ⊥ polarized light and || the initial light intensity of polarized light equates that they will have identical depth of modulation.For simplicity, (3) formula is rewritten as:

$I_{\&perp;}=I_{\&perp;0}+{\mathrm{\&zeta;}}_{\&perp;}\cos \left(\frac{4\mathrm{\&pi;}}{c}n{v}_{\&perp;}l\right)$

（4）

$I_{\left|\right|}=I_{\left|\right|0}+{\mathrm{\&zeta;}}_{\left|\right|}\cos \left(\frac{4\mathrm{\&pi;}}{c}n{v}_{\left|\right|}l\right)$

In the formula: v _⊥And v _||Be the ⊥ polarized light and || the optical frequency of polarized light.(4) formula shows when the long l of exocoel changes λ/2n, two polarization light intensities one-period that all fluctuates, but have a phasic difference δ between them, for double-longitudinal-mode laser, phasic difference δ can be expressed as

$\mathrm{\&delta;}=2\mathrm{\&pi;n}\frac{l}{L}---\left(5\right)$

Known that by (5) formula after laser instrument and feedback order were determined, the δ frequency difference was determined by the long L of feedback exocoel, so just can obtain the distance of measurement target feedback mirror by measurement phasic difference δ.

During measurement, exocoel catoptron 2 is in the long position of certain exocoel, the triangle wave voltage of piezoelectric ceramics 1 drives catoptron along the to-and-fro movement of laser axis, the feedback signal that PIN photodetector 8,9 obtains through the laser intensity curve after the filter amplification circuit 10 as shown in Figure 2, PZT is the driving voltage curve of piezoelectric ceramics, I _⊥And I _||Be respectively the intensity modulation curve of adjacent longitudinal mode, they are very close high-order frequency multiplication striped, and its optical fine can reach λ/50, are tens times of collimation feedback distance measuring apparatus; Simultaneously, the depth of modulation of two stripeds is basic identical, and all has cosine characteristic.Fig. 3, Fig. 4 and Fig. 5 are respectively that feedback exocoel catoptron is 110mm in exocoel length, when 112mm and 114mm, and the phase curve between two adjacent longitudinal mode feedback fringes (amplitude of two adjacent longitudinal mode feedback fringes is not both for the ease of observing among Fig. 2).Can find out from Fig. 3 ~ Fig. 5, when the exocoel catoptron when different distance (feedback exocoel long), has different phasic differences between the pairwise orthogonal polarization feedback fringe of adjacent longitudinal mode, through recording the phasic difference value between two feedback fringes behind the phase discriminator 11, size according to this phasic difference value, it is long to utilize formula (5) just can obtain exocoel catoptron feedback exocoel, thereby obtains the position of measured target, and the result is presented at counting and display unit 12.When measuring, frequency stabilization circuit 13 guarantees two longitudinal modes of laser instrument stable output.This range measurement system have the resolution height, simple in structure, precision is high and low cost and other advantages.

Claims (5)

1. One kind based on the laser of non-collimation feedback exocoel from the hybrid ranging system, comprise that full inner chamber He-Ne double-longitudinal-mode laser, non-collimation feedback exocoel, acquisition of signal process and frequency stabilization system four parts, it is characterized in that:

   (A) described full inner chamber He-Ne double-longitudinal-mode laser comprises:

   Laser gain pipe (4), in fill He, Ne mixed gas;

   Resonator cavity comprises:

   The first inner chamber catoptron (6) is positioned at an end of described laser gain pipe (4), is concave mirror, and it is towards concave surface plating reflectance coating of laser gain pipe (4), outside surface plating anti-reflection film;

   The second inner chamber catoptron (3) is fixed on the other end of described laser gain pipe (4), is flat mirror, and it is towards plane plating reflectance coating of laser gain pipe (4), outside surface plating anti-reflection film;

   (B) described non-collimation feedback exocoel comprises:

   Catoptron (2) is concave mirror, and towards the concave surface plating reflectance coating of full inner chamber He-Ne double-longitudinal-mode laser, the other end is plated film not, and the surface of described catoptron (2) and laser axis be θ in an angle;

   Piezoelectric ceramics (1), the outside of light direction is inputted on the edge that is fixed on above-mentioned catoptron (2), and under the effect of input voltage, described piezoelectric ceramics (1) promotes catoptron (2) along the left and right movement of laser axis direction;

   (C) described acquisition of signal is processed and is comprised:

   Polarization splitting prism (7) is positioned at the outside of the first inner chamber catoptron (6), and the laser of output is divided into X-direction, the Y-direction light intensity cosine component that two-way has phasic difference in the space;

   Photodetector, totally two, be positioned at the light exit side of described polarization splitting prism (7), survey respectively X-direction and two light intensity cosine components of Y-direction of described polarization splitting prism (7) output;

   Filtering and amplifying circuit (10), be positioned at the rear end of above-mentioned photodetector, the signal output part of two photodetectors is connected to respectively the signal input part of filtering and amplifying circuit (10), described filtering and amplifying circuit (10) is converted to digital quantity with the light feedback signal that photodetector receives, and signal is carried out filtering, amplifies and process;

   Phase discriminator (11), the output terminal of connection filtering and amplifying circuit (10) carries out phase demodulation to the two-way class cosine signal after amplifying;

   CPLD module (12), the output terminal of connection phase discriminator (11) is finished shaping, filtering to digital signal, and is had the signal of phasic difference to calculate to above-mentioned two-way, draws the laser feedback external cavity length;

   (D) described frequency stabilization system comprises:

   Resistance wire (5) is wrapped on the shell of laser gain pipe (4);

   Frequency stabilization circuit (13), with the difference signal of X-direction, the Y-direction two-way light intensity amplitude control signal as frequency stabilization, the time that controlling resistance silk (5) heats full inner chamber He-Ne double-longitudinal-mode laser, thus realize stable double longitudinal mode laser output.
2. 2. the laser based on non-collimation feedback exocoel according to claim 1 is characterized in that from the hybrid ranging system fill He, Ne mixed gas in the described laser gain pipe (4), volume ratio is 7:1.
3. 3. the laser based on non-collimation feedback exocoel according to claim 1 is characterized in that from the hybrid ranging system described resistance wire (5) is thin copper wire, and resistance is 15 Europe.
4. 4. the laser based on non-collimation feedback exocoel according to claim 1 is characterized in that from the hybrid ranging system described filtering and amplifying circuit (10) is connected with frequency stabilization circuit (13).
5. 5. the laser based on non-collimation feedback exocoel according to claim 1 is characterized in that from the hybrid ranging system described photodetector is the PIN photodetector.

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