CN101261322B - Dual Frequency He-Ne Laser Optical Feedback Rangefinder - Google Patents

Abstract

The invention relates to a light feedback telemeter for a double frequency He-Ne laser, belonging to the technical field of laser measurement. The telemeter comprises the double frequency He-Ne laser, an external cavity of laser feedback, a measurement circuit and a data processing system, wherein, the He-Ne laser comprises a gain tube, an antireflective window plate fixed on one end of the gain tube and a resonator; the resonator comprises a reflecting mirror of a first internal cavity fixed on the other end of the gain tube, a reflecting mirror of a second internal cavity fixed on the other end of the antireflective window plate, quartz crystal and a first piezoceramics. In the course of measuring, a second piezoceramics pushes the reflecting mirror of the external cavity of laser feedback to move from left to right along the laser axes so as to produce two lines of cross-polarized laser feedback signals and a phase difference exists between the two lines of cross-polarized laser feedback signals in direct proportion to the length of feedback external cavity. The telemeter is characterized by simple and compact structure as well as high performance.

Description

Dual Frequency He-Ne Laser Optical Feedback Rangefinder

technical field

The invention relates to a dual-frequency He-Ne laser optical feedback rangefinder, which belongs to the technical field of laser measurement.

Background technique

Self-mixing interference or light feedback refers to the phenomenon that in the laser application system, after the output light of the laser is reflected or scattered by external objects, part of the light is fed back into the laser and mixed with the light in the cavity to cause the output power of the laser to change. Conventional two-beam interference signals are similar.

Since self-mixing interference seriously affects the performance of lasers, researchers initially focused on how to eliminate or avoid the impact of optical feedback on laser systems. In 1963, King first reported the phenomenon of self-mixing interference. When a movable external mirror reflected the laser output light back to the laser resonator, the laser power fluctuated, and every time the external mirror moved by half the wavelength of the light wave, the laser power One fringe is varied, and the fluctuating depth of the fringe is comparable to that of a conventional two-beam interference system. This research has fundamentally changed people's concept of optical feedback, from passive elimination to active use, a lot of research has been carried out on optical feedback, and a series of results have been achieved. At present, laser self-mixing interference has been widely used in shape measurement, displacement and distance measurement, velocity and vibration measurement, etc.

The ranging technology based on laser feedback has the advantages of simple and compact structure, only one laser and one external reflector in the optical system, and high sensitivity. It has been rising since the 1980s, and the main research focuses on the optical feedback of semiconductor lasers. In 1986, G. Beheim et al. reported the optical feedback mode hopping ranging method. In the optical feedback LD, the injection current of the LD is continuously modulated, and the output power of the laser fluctuates due to mode hopping, and the number of mode hopping is proportional to the length of the external cavity. Based on this principle, the measurement of the length of the feedback external cavity is realized. However, the measurement accuracy of this method is limited by the modulation frequency of the injection current and the temperature drift effect of the LD, and the measurement speed is also limited by the modulation frequency of the injection current. F.Gouaux rebuilt the LD injection current by considering the thermal effect compensation, which greatly improved the resolution of the mode jump ranging. In 2002, Ho Khai Weng studied the mode-hopping ranging scheme in VCSEL, and achieved a measurement range of 0.2-0.6 meters, with a maximum relative error of less than 6%. Due to the large divergence angle of the semiconductor laser beam, the collimation and focusing system is indispensable in the feedback optical system, which limits its application range. Moreover, the temperature drift of the semiconductor laser is large, which seriously affects the accuracy of laser ranging.

Contents of the invention

The purpose of the present invention is to provide an optical feedback rangefinder with simple and compact structure, no need for collimation and focusing elements in the external cavity, simple signal processing and high cost performance.

In order to achieve the above object, the present invention adopts the following technical solutions. It contains four parts: dual-frequency He-Ne laser, laser feedback external cavity, measurement circuit and data processing system, wherein: A: dual-frequency He-Ne laser, the dual-frequency He-Ne laser contains:

The gain tube 2 is filled with a mixed gas of He and Ne;

An anti-reflection window 3; the anti-reflection window 3 is fixed at one end of the gain tube 2;

A resonant cavity, the resonant cavity includes:

A first cavity reflector 1, the first cavity reflector 1 is fixed at the other end of the gain tube 2;

The second intracavity reflector 4 is located at the other end of the above-mentioned anti-reflection window 3;

A quartz crystal 14 is located between the above-mentioned second inner cavity mirror 4 and the anti-reflection window 3, and both sides of the quartz crystal 14 are coated with an anti-reflection film;

The first piezoelectric ceramic 5 is fixed on the above-mentioned first inner cavity reflector 1. Under the action of the input voltage, the above-mentioned piezoelectric ceramic 5 pushes the above-mentioned first inner cavity reflector 1 to move left and right along the laser axis direction to change the laser frequency. ;

B: Laser feedback external cavity, the laser feedback external cavity contains:

The second piezoelectric ceramic 7 is fixed on the object to be measured;

The laser feedback external cavity reflector 6 is fixed on the above-mentioned second piezoelectric ceramic 7, and the laser feedback external cavity reflector 6 is driven by the second piezoelectric ceramic 7 to move along the axis of the laser, so that the incident light on the object to be measured The two orthogonally polarized lights are reflected back to the laser resonator cavity and mixed with the two orthogonally polarized lights in the cavity, causing the respective light intensity fluctuations of the two orthogonally polarized lights to generate laser feedback signals;

C: Measuring circuit, containing:

A polarizing beam splitter prism 8, located on one side of the first inner cavity mirror 1, for separating two orthogonally polarized lasers;

The first photodetector 9 and the second photodetector 10 respectively detect the feedback signals of the two orthogonally polarized lights separated by the polarization beam splitter prism 8;

D: data processing system, the data processing system includes:

Analog/digital converter 11, the input signal is respectively the laser feedback signal output by the first photodetector 9 and the second photodetector 10;

A digital/analog converter 12, the output of the digital/analog converter is connected to the input terminals of the first piezoelectric ceramic 5 and the second piezoelectric ceramic 7;

The computer 13 is connected with the output end of the analog-to-digital converter 11, reads the laser feedback signal, and processes the data to calculate the distance between the object to be measured and the light source. The input terminal of the digital/analog converter 12 is connected with the first piezoelectric ceramic 5 and the second piezoelectric ceramic 7, and the first piezoelectric ceramic 5 and the second piezoelectric ceramic 7 are controlled, respectively for realizing the control Laser frequency and generate laser feedback signal.

The quartz crystal 14 and the anti-reflection window 3 are replaced by an anti-reflection window 3 coated with an anti-reflection film on both sides and a stress applying device 15 clamped on the window, and the anti-reflection window 3 is fixed on the above-mentioned One end of the gain tube 2 close to the second inner cavity mirror 4;

The quartz crystal 14 and the anti-reflection window 3 are replaced by a quartz crystal wedge 16 coated with an anti-reflection film on both sides, and the quartz crystal wedge 16 is fixed on the end of the gain tube close to the second inner cavity mirror 4 .

The dual-frequency He-Ne laser optical feedback rangefinder provided by the present invention does not need a collimation and focusing system in the feedback external cavity, has a simple and compact structure, has the characteristics of simple signal processing and high cost performance.

Description of drawings

Figure 1: One of the implementation examples of the birefringent external cavity feedback displacement measurement system of the present invention

Figure 2: The second implementation example of the birefringent external cavity feedback displacement measurement system of the present invention

Figure 3: The third implementation example of the birefringent external cavity feedback displacement measurement system of the present invention

Figure 4: When the length of the external cavity is l=67.5mm, the feedback curve of two orthogonally polarized lights

Figure 5: When the length of the external cavity is l=135mm, the feedback curve of two orthogonally polarized lights

Figure 6: When the external cavity length l=202.5mm, the feedback curve of two orthogonally polarized light

Figure 7: When the length of the external cavity is l=270mm, the feedback curve of two orthogonally polarized lights

In the figure: 1. First inner cavity reflector, 2. Gain tube, 3. Antireflection window, 4. Second inner cavity reflector, 5. First piezoelectric ceramic, 6. Laser feedback external cavity reflector, 7. Second piezoelectric ceramic, 8. Polarizing beam splitter, 9. First photodetector, 10. Second photodetector, 11. Analog/digital converter, 12. Digital/analog converter, 13. Computer, 14. Quartz crystal, 15. Stress applying device, 16. Quartz crystal wedge.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing:

Embodiment one:

The experimental device of the present embodiment is shown in Figure 1, comprises the first cavity reflector 1, the second cavity reflector 4, gain tube 2, anti-reflection window 3, the first piezoelectric ceramic 5, quartz crystal 14 , a second piezoelectric ceramic 7, a laser feedback external cavity mirror 6, a polarization beam splitter prism 8, a first photodetector 9, a second photodetector 10 and a computer 13. In FIG. 1 , the reflectivity of the first inner cavity mirror 1 and the second inner cavity mirror 4 are 99.9% and 99.4% respectively, and the distance between them, that is, the length L of the laser cavity is 135 mm. There is a mixture of He and Ne in the gain tube 2, and the gas pressure ratio of He and Ne is 7:1. The anti-reflection window 3 is fixed at one end of the above-mentioned gain tube 2 . The first inner cavity reflector 1 , the gain tube 2 , the anti-reflection window 3 , and the second inner cavity reflector 4 jointly constitute a half-external-cavity 632.8nm He-Ne laser. The light source used in this embodiment is a dual-frequency laser. By placing a quartz crystal 14 in the cavity to generate a birefringence effect, the ordinary semi-external cavity He-Ne laser is made into an orthogonally polarized dual-frequency He-Ne laser. The first piezoelectric ceramic 5 is fixed on the above-mentioned first inner cavity reflector, and under the action of the input voltage, it pushes the above-mentioned first inner cavity reflector to move left and right along the laser axis direction, so that when there is no light feedback, the two positive Cross-polarized light has equal intensity. The reflectivity of the laser feedback external cavity reflector 6 is 30%, and the distance between the laser feedback external cavity reflector 6 and the second internal cavity reflector 4 is the length of the feedback external cavity, denoted as 1. The second piezoelectric ceramic 7 is fixed on the above-mentioned laser feedback external cavity reflector 6, and under the action of the input voltage, it pushes the above-mentioned laser feedback external cavity reflector 6 to move left and right along the laser axis direction to generate an optical feedback signal. The polarization beam splitter 8 separates two orthogonally polarized lasers from space, and the first photodetector 9 and the second photodetector 10 are two photodetectors; the analog/digital converter 11 converts the light received by the above photodetector The feedback signal is converted into a digital quantity; the output signal of the digital/analog converter 12 is used to control the first piezoelectric ceramic 5 and the second piezoelectric ceramic 7 respectively. The computer 13 realizes the control of the first piezoelectric ceramic 5 and the second piezoelectric ceramic 7 through the digital/analog converter 12 to generate a suitable optical feedback signal, realizes the collection of the optical feedback signal through the analog/digital converter 11, and finally passes Data analysis obtains the length of the laser feedback external cavity, that is, the distance to be measured l.

Principle of the present invention is as follows:

In the case of optical feedback for a single-mode He-Ne laser, the gain variation Δg per unit length is:

Δg=gg ₀ =-ξcos(4πvl/c), (1)

In the formula, g is the linear gain per unit length when there is light feedback, g ₀ is the linear gain per unit length when there is no light feedback, ξ is the laser feedback factor, v is the laser frequency, c is the speed of light in vacuum, l is the change of the laser feedback external cavity length.

Since the change of laser intensity during feedback is proportional to the change of linear gain, that is

I=I ₀ -kΔg, (2)

In the formula, I ₀ is the initial light intensity without feedback, and k is a constant.

Then under the condition of optical feedback, the light intensity of the two orthogonally polarized lights (ie o light and e light) of the laser is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&zeta;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&zeta;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, v _o and v _e are the frequencies of o light and e light, I _o0 is the initial light intensity of o light without feedback, I _e0 is the initial light intensity of e light without feedback, and ζ _o is the feedback factor of o light , ζ _e is the light feedback factor of e. Equation (3) shows that when the length l of the feedback external cavity changes by λ/2, the intensities of the two orthogonally polarized lights both fluctuate for one cycle, but there is a phase difference δ between them:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&zeta;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&zeta;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;vl</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; l</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;v</span>}}{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In the formula: Δv=v _o -v _e is the frequency difference between two orthogonally polarized lights, and Λ is the laser longitudinal mode interval. From formula (4), when the laser is selected, δ will be determined by the laser feedback external cavity length l (that is, the distance to be measured) and the frequency difference Δv. If Δv is smaller than the linewidth of the uniformly broadened gain curve (about 200MHz), the hole burning of the two orthogonal polarization modes will overlap, so the influence of mode competition must be considered, and the phase relationship between I _o and I _e will not only Only depending on formula (4), there will be a phenomenon that the intensity of one polarized light increases and the intensity of the other polarized light decreases. If Δv is larger than the linewidth of the uniformly broadened gain curve, the effect of mode competition can be neglected, and the phase relationship δ between I _o and I _e is uniquely determined by equation (4).

Since the frequency difference of the dual-frequency He-Ne laser used in the system is about 550MHz, which is far greater than the uniform broadening of the spectrum of the laser medium (about 200MHz), the phase difference between the two orthogonally polarized lights o and e is δ Nothing to do with mode competition. At this time, the phase difference δ between the two is proportional to the length l of the feedback external cavity, and the laser cavity length L, the frequency difference Δv of the two orthogonally polarized lights, and the laser longitudinal mode interval Λ are all determined. Therefore, Only by measuring the phase difference δ between the two orthogonally polarized o-lights and e-lights, the length l of the laser feedback external cavity can be easily calculated according to formula (4), which is the distance to be measured. Here it is the theoretical basis of the present invention.

即回馈外腔长l每变化2L，相位差变化2π。而实验得到的两正交偏振光的回馈信号之间的相位差δ范围为0～2π，因此，本系统的距离测量范围为2倍的激光谐振腔长，即2L。当然，通过调整激光器参数Δv和Λ，其测量范围还可以扩大。当首先知道待测物体在激光器若干个谐振腔长以外时，通过测量两正交偏振光回馈信号之间的相位差δ，再根据(4)式计算获得回馈外腔长度，从而确定待测物体的位置。Fig. 4 to Fig. 7 respectively show the experimental results of two orthogonally polarized light feedback signals under different external cavity lengths. It is found that as the length of the feedback external cavity changes from 67.5mm to 270mm, the phase difference between the two orthogonally polarized light feedback signals also changes from about 0.5π to 2π, and there is a linear relationship between the two. According to formula (4), when the length of the feedback external cavity is: l=67.5mm; l=135mm; l=202.5mm; l=270mm, the phase difference between the two orthogonally polarized light feedback signals obtained by theoretical calculation is respectively : δ=0.5π, δ=π, δ=1.5π, δ=2π. The theoretical calculation results are consistent with the experimental results. Therefore, the phenomenon that the phase difference δ between the two orthogonally polarized light feedback signals is proportional to the length l of the feedback external cavity can be used for distance measurement. According to (4), for specific parameters Δv and Λ, the period of the phase difference δ is

That is, when the length l of the external feedback cavity changes by 2L, the phase difference changes by 2π. The experimentally obtained phase difference δ between the feedback signals of the two orthogonally polarized lights ranges from 0 to 2π. Therefore, the distance measurement range of this system is twice the length of the laser resonator, that is, 2L. Of course, by adjusting the laser parameters Δv and Λ, the measurement range can also be expanded. When it is first known that the object to be measured is outside several resonant cavity lengths of the laser, by measuring the phase difference δ between the two orthogonally polarized light feedback signals, and then calculating the length of the external cavity of the feedback according to (4), the object to be measured can be determined s position.

Embodiment two:

As shown in FIG. 2 , the structure of this embodiment is basically the same as that of Embodiment 1, except that the antireflection window 3 and the quartz crystal 14 are different. In this embodiment, the quartz crystal 14 and the antireflection window 3 in the first embodiment are replaced by an antireflection window 3 coated with an antireflection film on both sides and a stress applying device 15 clamped on the window. The anti-reflection window 3 is a window with anti-reflection coatings on both sides, and is fixed at one end of the gain tube 2 . The stress applying device 15 among Fig. 2 is a reinforcing ring studded with screws, and it applies a stress to the anti-reflection window 3 along the axial direction of the vertical laser, due to the stress-birefringence effect of the anti-reflection window 3, a frequency is split into two frequencies. The first cavity reflector 1 , the gain tube 2 , the anti-reflection window 3 , the second cavity reflector 4 and the stress applying device 15 together constitute a dual-frequency He-Ne laser.

Embodiment three:

As shown in FIG. 3 , the structure of this embodiment is basically the same as that of Embodiment 1, except that the antireflection window 3 and the quartz crystal 14 are different. In this embodiment, the quartz crystal 14 and the anti-reflection window 3 in Embodiment 1 are replaced by a quartz crystal wedge 16 coated with an anti-reflection film on both sides, and the quartz crystal wedge 16 is fixed on the above-mentioned gain tube close to the second inner cavity reflector 4 at one end. Both sides of the quartz crystal wedge 16 are coated with anti-reflection coatings, and are fixed at one end of the gain tube 2 for frequency splitting. The first inner cavity mirror 1, the gain tube 2, the quartz crystal wedge 16 and the second inner cavity mirror 4 jointly constitute a dual-frequency He-Ne laser.

The dual-frequency He-Ne laser optical feedback rangefinder designed by the present invention is composed of a dual-frequency He-Ne laser, a laser feedback external cavity, a measurement circuit and a data processing system. During the measurement process, the feedback mirror moves left and right along the laser axis to generate laser feedback signals. There is a phase difference between the feedback signals of the two orthogonally polarized lights, and the phase difference is proportional to the length of the feedback external cavity. The present invention utilizes this characteristic to determine the position of the external cavity reflector so as to realize distance measurement. The optical feedback rangefinder designed by the invention has the characteristics of simple and compact structure, simple signal processing and high cost performance.

Claims (3)

1. double frequency He-Ne laser optical feedback distance measuring apparatus is characterized in that: contain double frequency He-Ne laser, laser feedback exocoel, metering circuit and four parts of data handling system, wherein:

A: double frequency He-Ne laser, described double frequency He-Ne laser contains:

Gain tube (2), inside are filled with He, Ne mixed gas;

Anti-reflection window (3); Described anti-reflection window (3) is fixed on an end of described gain tube (2);

Resonator cavity, described resonator cavity comprises:

The first inner chamber catoptron (1), the described first inner chamber catoptron (1) is fixed on the other end of described gain tube (2);

The second inner chamber catoptron (4) is positioned at the other end of above-mentioned anti-reflection window (3);

Quartz crystal (14) is positioned between above-mentioned second inner chamber catoptron (4) and the anti-reflection window (3), and this quartz crystal (14) two sides all is coated with anti-reflection film;

First piezoelectric ceramics (5) is fixed on the above-mentioned first inner chamber catoptron (1), and under the input voltage effect, above-mentioned piezoelectric ceramics (5) promotes the above-mentioned first inner chamber catoptron (1) along laser axis direction move left and right, changes laser frequency;

B: the laser feedback exocoel, described laser feedback exocoel contains:

Second piezoelectric ceramics (7) is fixed on the object under test;

Laser feedback exocoel catoptron (6), reflectivity is 30%, be fixed on above-mentioned second piezoelectric ceramics (7), described laser feedback exocoel catoptron (6) is driven by second piezoelectric ceramics (7) and moves along the laser axis direction, making the pairwise orthogonal polarized light that incides on the object under test be reflected back toward laser resonant cavity mixes with pairwise orthogonal polarized light in the chamber respectively, cause the light-intensity variation separately of pairwise orthogonal polarized light, produce the laser feedback signal;

C: metering circuit, contain:

Polarization splitting prism (8) is positioned at a side of the above-mentioned first inner chamber catoptron (1), is used for the laser of pairwise orthogonal polarization separately;

First photodetector (9), second photodetector (10) are surveyed the feedback signal of the pairwise orthogonal polarized light that described polarization splitting prism (8) separated respectively;

D: data handling system, described data handling system comprises:

A/D converter (11), input signal are respectively the laser feedback signal of first photodetector (9) and second photodetector (10) output;

D/A (12), the output of this D/A links to each other with the input end of described first piezoelectric ceramics (5), second piezoelectric ceramics (7);

Computing machine (13), link to each other with the output terminal of described A/D converter (11), read the laser feedback signal, and deal with data, calculate the distance of object under test apart from light source, simultaneously, link to each other with the input end of described D/A (12), the output terminal of D/A (12) links to each other with second piezoelectric ceramics (7) with first piezoelectric ceramics (5).

2. double frequency He-Ne laser optical feedback distance measuring apparatus according to claim 1, it is characterized in that: described quartz crystal (14) and anti-reflection window (3) all are coated with the anti-reflection window (3) of anti-reflection film by a two sides and the stress bringing device (15) that is clipped on this window is replaced, and this anti-reflection window (3) is fixed on the end of above-mentioned gain tube (2) near the second inner chamber catoptron (4).

3. double frequency He-Ne laser optical feedback distance measuring apparatus according to claim 1, it is characterized in that: described quartz crystal (14) and anti-reflection window (3) are replaced by the quartz crystal wedge (16) that a two sides all is coated with anti-reflection film, and this quartz crystal wedge (16) is fixed in the end of above-mentioned gain tube near the second inner chamber catoptron (4).

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