CN1308700C - Electro-optical modulation laser distance measuring method and device - Google Patents

Abstract

An electro-optical modulated laser ranging method and device, the method uses the polarization characteristics of laser as an information carrier to perform laser ranging: using the transverse electro-optical effect of a uniaxial crystal, in conjunction with a polarization beam splitter and a polarization analyzer, when a half-wave voltage is applied to the uniaxial crystal in a direction parallel to the optical axis, the characteristic of twisting the polarization direction of linear polarized light by 90° is utilized to extract a light pulse with a pulse width of the time t required for the laser to travel back and forth to the distance to be measured. The present invention overcomes the errors introduced by the photoelectric conversion process and the circuit system itself in the existing ranging method. The present invention has a simple structure, is easy to operate, is not affected by the environment, has strong anti-interference ability, and has a wide range of measuring distances. The closest distance that can be measured is a few meters. When the laser energy is high, the farthest distance that can be measured is 10 kilometers. The measurement accuracy is high, and the measurement accuracy can reach centimeter level.

Description

Electro-optic modulation laser ranging method and device

technical field

The invention relates to laser ranging, in particular to an electro-optical modulation laser ranging method and its device, which can be applied to many fields such as industrial and agricultural production, military affairs, communication, and remote sensing.

Background technique

The high-precision measurement of distance is one of the key technologies in many fields of national modernization. With the development of science and technology, the requirements for the range and accuracy of distance measurement are getting higher and higher. As an information carrier with extremely high monochromaticity, collimation, and coherence, laser has become the preferred tool for distance measurement. At present, the advanced range finders at home and abroad all use laser as the information carrier to improve the accuracy of distance measurement.

The prior art [1] (see Kozo Ohtani, Misuru Baba, A range finding approach by detecting the position and the incident angle of alight-stripe, IEEE Instru.and Mea.Techno.Conf.2002) is a geometric optics ranging method . The laser emits a laser beam that is reflected by the target and is received by the PSD or CCD, and then calculates the distance between the target and the detector based on the received spot position and the geometric positional relationship between the laser and the receiver. This method is mainly used in industrial surface profile measurement, 2D/3D surface reconstruction and positioning, etc. The relative accuracy of measurement is about 0.85%, and it can only measure a very short distance. As the distance increases, the accuracy drops sharply.

The prior art [2] (see Raimo Ahola, Risto Myllyla, A new method forming the time-of-flight in fast laser range finding, [J].Proc.SPIE vol.654, pp19-, 1986) is a Ranging method of light pulse time-of-flight. A pulse laser with a short duration is emitted by the pulse laser, which is called the main wave. After passing the distance L to be measured, it shoots to the target to be measured. The pulsed laser reflected by the target is called an echo. The echo returns to the distance meter and is received by the photoelectric detector. According to the time between the main wave signal and the echo signal Interval, that is, the round-trip time t from when the laser pulse is emitted from the laser to when it is reflected by the target, the distance to the target to be measured can be calculated, that is, L=ct/2, where c is the speed of light. This method requires not only a high-performance laser, but also a complex circuit processing system. First, part of the energy of the main wave light pulse is converted into an electrical pulse, and after shaping, the counter is triggered by a gating circuit to start counting the number of time pulses sent by the clock oscillator; then the echo signal is converted into an electrical pulse again by the detector after it arrives. After the signal undergoes the same electrical process, the counting of the time pulse signal is stopped, and the round-trip time t of the light pulse is determined by the number of time signal pulses. Many errors will be introduced in the process of converting optical signals into electrical signals and in the circuit processing system of electrical signals.

The prior art [3] (see Fujima I, Seta K, Matsumoto H and O'ishi T1988GHz traveling-wave optical modulator for precision distancemeasurement Proc. SPIE vol 889 pp 86-90) is a distance measurement using continuous laser phase information method. Phase laser ranging achieves ranging by measuring the phase difference of high-frequency modulation. The light source in the instrument emits continuous light, which is modulated by the modulator to become modulated light and shoots to the target. The light intensity of the modulated light changes periodically with time, and the sine wave modulation is used to measure the number of full cycles of the sine wave during the round trip of the light wave and less than one The phase of the periodic sine function can determine the interval t of the round-trip time of the light wave, and thus calculate the measured distance. This method still needs to convert the optical signal into an electrical signal and then process it through the circuit system. The phase difference between the emitted and received sine waves is compared by an electronic phase comparator, and an electrical device for precisely modulating the sinusoidal light intensity is also required.

Prior technology [4] (see S F Collins, M M Murphy, K T V Grattan, et al. Asimple laser diode ranging scheme using an intensity modulated FMCW approach [J]. Meas. and Tech., 1993, 4: 1437-1439 ) is a ranging method using continuous laser frequency information. The principle of continuous wave FM laser ranging is to calculate the distance by emitting a continuously adjustable laser frequency and measuring the frequency of the received laser light reflected back from the target. There is a frequency drift between the received light and the emitted light due to chirp, so a beat frequency will be generated in the mixer, and this beat frequency is proportional to the distance to be measured. This method still needs to convert the optical signal into an electrical signal and then process it through the circuit system, and also needs to add an additional circuit system for adjusting the laser frequency.

Invention content:

The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies in the prior art, provide an electro-optical modulation laser ranging method and its device, avoid the introduction of complex circuit systems, and overcome the errors introduced by the photoelectric conversion process and circuit system.

Technical solution of the present invention is as follows:

An electro-optic modulation laser ranging method, characterized in that the polarization characteristics of the laser are used as the carrier of the distance information to be measured. , the uniaxial electro-optic crystal, the compensation crystal and the polarization analyzer, the light beam going back and forth between the uniaxial electro-optic crystal and the object to be measured is cut into a rectangular optical pulse with a pulse width t, then the uniaxial electro-optic crystal and the object to be measured The distance L between:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Vc</span>}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}$

where Vc is the speed of light in air.

The electro-optic modulation laser distance measuring device implementing the above-mentioned electro-optic modulation laser distance measurement method is characterized in that it consists of a laser that outputs a collimated continuous laser, and along the beam advancing direction are a polarization beam splitter, a uniaxial electro-optic crystal, a compensation crystal, Polarization analyzer, the uniaxial electro-optic crystal and its compensation crystal are cuboid LiNbO ₃ crystals of the same size, side length b>a=c, and the light passes through the crystal parallel to side b, and a pair of electrode sheets are closely attached to the On the two b×c planes of the uniaxial electro-optic crystal, the half-wave voltage is applied to the uniaxial electro-optic crystal through the electrode plate perpendicular to the side b, and the polarization direction of the polarization beam splitter and the polarization analyzer of the polarization analyzer The directions are parallel or perpendicular to each other, the optical axes of the uniaxial electro-optic crystal and the compensation crystal are placed perpendicular to each other, and the directions of the optical axes of the two are 45° to the polarization direction of the polarization beam splitter and the analysis direction of the polarization analyzer , and a detector is arranged in the echo reflection direction of the polarization beam splitter.

Technical effect of the present invention:

Compared with the prior art: the prior art [1] is a micro-short distance measurement method, with the increase of the measurement distance, the accuracy drops sharply, and it is not suitable for large-scale distance measurement; there is a widely used prior art [2] [3][4] need to transform the optical signal into an electrical signal to analyze and extract the distance information to be measured. Not only will redundant errors be introduced in the process of converting optical problems into electrical problems, but also Finally, the complexity of the device is greatly increased, and many electrical errors are introduced at the same time. Compared with the prior art, the present invention is simple in structure, easy to operate, not affected by the environment, strong in anti-interference ability, wide in range of measuring distance, the nearest distance of several meters can be measured, and in the case of high laser energy, the furthest Can measure the distance of 10 kilometers. The measurement accuracy is high and can reach centimeter-level measurement accuracy.

Description of drawings:

Fig. 1 is a schematic diagram of the basic idea of the present invention.

Fig. 2 is a structural schematic diagram of the principle of the present invention.

Fig. 3 is a schematic diagram of the structure and placement of each device in the present invention.

Detailed ways:

The present invention will be further described below in conjunction with drawings and embodiments.

The basic idea of the present invention is shown in Figure 1. The laser emits a beam of highly collimated continuous laser light, which returns along the original path after encountering the object to be measured. At this time, if a reflector at an angle of 45° to the light propagation direction can be inserted "instantaneously" at the light source end, so that the reflective surface faces the object to be measured, then the light emitted by the laser is cut off at this time, and the light reflected back by the object to be measured The light is also cut off and reflected to the other direction by the reflector at the same time. The beams cut off at both ends form a rectangular light pulse with a pulse width of t, which is the time when the light starts from the reflector to the object to be measured and reflects back to the reflector again. required time. The light pulse is received by the detector, and the time t is obtained, then the distance to be measured can be L=vct/2, where Vc is the propagation speed of light in the air. The present invention realizes the above-mentioned function of "instantaneously" inserting the reflector.

The basic structure of the present invention is shown in Figures 2 and 3. As can be seen from the figures, the electro-optic modulation laser distance measuring device for implementing the electro-optic modulation laser distance measurement method in the present invention consists of a laser 1 outputting a collimated continuous laser , followed by a polarization beam splitter 2, a uniaxial electro-optic crystal 3, a compensation crystal 5, and a polarization analyzer 6 along the beam advancing direction, and the uniaxial electro-optic crystal 3 and its compensation crystal ₅ are cuboid LiNbO crystals of the same size, Side length b>a=c, and make the light pass through the crystal parallel to side b, a pair of electrode sheets 4 are close to the two b×c planes of the uniaxial electro-optic crystal 3, and the half-wave voltage passes through the electrode sheet 4 perpendicular to Side b is added on the uniaxial electro-optic crystal 3, the polarization direction of the polarization beam splitter 2 and the polarization analyzer 6 are parallel to each other or perpendicular to each other, the optical axis of the uniaxial electro-optic crystal 3 and the compensation crystal 5 Place them perpendicular to each other, and make the optical axis directions of the two and the polarization direction of the polarization beam splitter 2 and the polarization analysis direction of the polarization analyzer 6 respectively be 45°, and a detector is arranged in the echo reflection direction of the polarization beam splitter 2 8.

The continuous wave laser 1 used as the light source should have higher energy to meet the requirement of longer distance measurement.

Said polarizing beam splitter 2 has two functions: the first is to change the original outgoing light A emitted by the laser 1 into linearly polarized light B whose polarization direction is parallel to the polarization direction of the polarizer; When the polarization direction of the reflected linearly polarized return light F is perpendicular to the polarization direction of the polarizer, the return light F is reflected and deviated from the original optical path for detection. Based on the above reasons, the polarizing beam splitter 2 should use a polarizing beam splitter structure made of crystal material, such as a Glan prism. The polarizing beam splitter 2 is placed next to the laser 1 at the light output end of the laser 1, so that the original outgoing light A is vertically incident on its surface. The polarization direction 2C of the polarizing beam splitter 2 is along the coordinate x' direction in Fig. 3, when random polarized light A enters it, it is divided into two beams of light B and W1 whose polarization directions are perpendicular to each other, and polarized along the polarization direction x' The linearly polarized light B passes through the polarizing beam splitter 2 along the original optical path, and the linearly polarized light W1 polarized along the y' direction becomes useless light, which deviates from the original optical path and exits. At the same time, when the polarization direction of the return light F reflected by the object to be measured is parallel to the polarization direction x' of the polarization beam splitter 2, the return light F passes through the polarization beam splitter 2 along the original optical path, and when the polarization direction of the return light F is parallel to the polarization direction x' When vertical, the return light F is reflected by the polarization beam splitter 2 out of the original optical path and enters the detector 8 .

The function of the uniaxial electro-optic crystal 3 is: combined with the compensation crystal 5, when a half-wave voltage V is applied to the uniaxial electro-optic crystal 3, the polarization direction of the linearly polarized light passing through the uniaxial electro-optic crystal 3 and the compensation crystal 5 in turn The angle is twisted by 90° so that the polarization directions of the linearly polarized light C emitted from the compensation crystal 5 and the linearly polarized light B incident from the uniaxial electro-optic crystal 3 are perpendicular to each other. The uniaxial electro-optic crystal 3 should be a uniaxial crystal with transverse electro-optic modulation properties, such as lithium niobate, lithium tantalate, etc., whose shape is a cuboid and whose geometric dimensions are a×b×c, where b>c. There is no strict requirement between a and b, because the laser spot is circular, from the aspect of size reduction and material saving, a=b should be made. The half-wave voltage V applied on the uniaxial electro-optic crystal 3 is proportional to the crystal size ratio a/b. Therefore, to obtain a lower half-wave voltage V, the minimum side length should be selected to allow the laser spot to pass through the ab plane smoothly Under the condition of a, try to make b>a, but at the same time, the crystal side length b is limited by the maximum length of the obtained crystal. The cuboid uniaxial electro-optic crystal 3 is placed in such a direction that the side length b is parallel to the coordinate axis z direction, the side length a is parallel to the y direction, and the side length c is parallel to the x direction, so that the linearly polarized light B is perpendicularly incident on the two a×c planes. The crystal axis direction 3C is selected along the coordinate axis y direction, placed at an angle of 45° to the crystal axis direction 2C of the polarizing beam splitter 2, and perpendicular to the two b×c planes of the uniaxial electro-optic crystal 3. A pair of electrode sheets 4 are respectively pasted on the two b×c planes of the uniaxial electro-optic crystal 3 , and the size is preferably just to cover the two b×c planes. When a voltage is applied to the electrode sheet 4, the direction of the electric field in the crystal is parallel to the direction of the crystal axis 3C.

The compensation crystal 5 plays the role of assisting the uniaxial electro-optic crystal 3 to complete the modulation of polarized light: first, it plays the role of temperature compensation, and the refractive index of the crystal is relatively sensitive to the influence of temperature, especially when light passes through a long crystal path , small changes in the refractive index will have a great impact on the phase difference of the output o-light and e-light; second, it works together with the uniaxial electro-optic crystal 3, so that when no voltage is applied to the uniaxial electro-optic crystal 3, the o-light, e-light The optical path difference of light passing through these two crystals is zero. To accomplish the above functions, the compensating crystal 5 should be made of the same material as the uniaxial electro-optic crystal 3 and have a similar cuboid shape, with a geometric dimension of a'×b'×c', and the length of its long side must be strictly the same as that of the electro-optic crystal. Etc., that is, b'=b, the requirements for the short side lengths a' and c' are relatively loose, and it is enough to ensure that the laser beam passes through smoothly. Considering the same factors as the uniaxial electro-optic crystal 3, it is better to take a'=c'. To make the optical axis direction 5C of the compensation crystal 5 and the optical axis direction 3C of the uniaxial electro-optic crystal 3 be placed perpendicular to each other, that is, the direction 5C should be placed along the direction of the coordinate x axis, while the laser beam is vertically passed through its two a'× c' plane.

Said polarizing analyzer 6 plays the role of only allowing the polarized light whose polarization direction is parallel to its analyzing direction to pass through, and blocking the passing of the polarized light whose polarization direction is perpendicular to its analyzing direction. Standard polarization analyzer, no special requirements for its structure. There are two ways to place the analyzer optical axis of the polarization analyzer 6, such as the direction of the solid line 6C and the direction of the dotted line 6C' in Figure 3, and the direction 6C is parallel to the polarization direction 2C of the polarization beam splitter 2, that is, to the coordinate axis x' In the same direction, the direction 6C' is perpendicular to the polarization direction 2C of the polarization beam splitter 2, that is, it is in the same direction as the coordinate axis y', and the directions 6C and 6C' are perpendicular to each other and respectively to the optical axis direction 3C of the uniaxial electro-optic crystal 3 and the compensation crystal The optical axis direction 5C of 5 forms an included angle of 45°.

The two placement structures of the polarizing analyzer 6 correspond to the two operating methods of the present invention, and the first operating method is placed according to the analyzing direction 6C. In this case, at first no voltage is applied to the pair of electrode sheets 4 of the uniaxial electro-optic crystal 3, at this moment, the random polarized light A emitted by the laser 1 is first vertically incident on the polarization beam splitter 2, and the polarization beam splitter 2 will The light beam A is divided into two parts: the unwanted light W1 that is transformed into a polarization direction perpendicular to the polarization direction 2C is emitted away from the original optical path; the linearly polarized light B that is transformed into a polarization direction parallel to the polarization direction 2C is emitted along the original optical path. The beam B polarized along the 2C direction then passes through the uniaxial electro-optic crystal 3 perpendicular to the two a×c planes and the compensation crystal 5 perpendicular to the two a′×c′ planes. Due to the birefringence of the crystal, the linearly polarized light B whose polarization direction and crystal axis direction 3C form an angle of 45° enters the uniaxial electro-optic crystal 3 and is divided into ordinary light o light and extraordinary light e light with equal energy. The optical axis is incident, and the o-light and e-light whose polarization directions are perpendicular to each other propagate along the original optical path without separation, wherein the polarization direction of the o-light is parallel to the optical axis direction 3C of the uniaxial electro-optic crystal 3, and the e-light is perpendicular to the optical axis direction 3C. The crystal has different refractive indexes for o-light and e-light, and the different refractive indexes lead to an optical path difference between the two beams o-light and e-light on the same path after the beam B passes through the uniaxial electro-optic crystal 3, so that the two A phase difference Γ is generated between the same beams, and its specific value depends on the side length b of the electro-optic crystal. The two light beams o light and e light then enter the compensation crystal 5. Under the action of the compensation crystal 5, since its optical axis direction 5C and the uniaxial electro-optic crystal 3 optical axis direction 3C are perpendicular to each other, the two in the uniaxial electro-optic crystal 3 After the split o light and e light enter the compensation crystal 5, the o split light in the original uniaxial electro-optic crystal 3 becomes the e split light relative to the compensation crystal 5, and the e split light in the original uniaxial electro-optic crystal 3 becomes relative to the compensation crystal 5 In this way, the two split lights produce a phase difference Г' after passing through the compensation crystal 5, and because the side length b'=b, this phase difference Г' and the phase difference of the two split lights after passing through the uniaxial electro-optic crystal 3 Γ is equal in size and opposite in sign, that is, Γ=-Г', therefore, when the linearly polarized light B passes through the uniaxial electro-optic crystal 3 and the compensation crystal 5 in sequence, the phase difference between the two split lights with equal amplitude is zero, After exiting the two crystals, the polarization characteristics of the synthesized light remain unchanged, and become linearly polarized light C with the same polarization direction as B. Since the polarization direction of C is parallel to the polarization analysis direction 6C of the polarization analyzer 6 , the linearly polarized light C can pass through the polarization analyzer 6 without being affected and become the final outgoing light D. The outgoing light D passes through a distance L to be measured and irradiates the surface of the object 7 to be measured and is reflected back to become the reflected light E. The polarization state of the returned light E remains unchanged when it emerges from the polarization analyzer 6, along the coordinate x 'direction polarization, so after going through the reverse change process from beam B to beam D, the polarization state remains unchanged and becomes linearly polarized light F polarized along the coordinate axis x', which enters the polarization beam splitter 2. The polarizing direction of the polarizing beam splitter 2 is along the coordinate axis x' and parallel to the polarizing direction of F, so that F can pass through the polarizing beam splitter 2 smoothly and become useless light W2. To sum up, the original outgoing light A from the laser 1 passes through each device 2, 3, 4, 5, 6 in turn, reaches the surface of the object 7 to be measured and reflects back, and then passes through the devices 6, 5, 4, 3, 2 again. In the whole process of becoming unwanted light W2, except that random polarized light A separates unwanted light W1 in polarization beam splitter 2, other light beams B, C, D, E, F, W2 are the same as polarization beam splitter 2, polarization Linearly polarized light polarized parallel to the optical axis of the analyzer 3, during their transmission, it is as if no mirror is inserted in Figure 1, and the devices 2, 3, 4, 5, and 6 are transparent to the transmission of light Same. This is the state of preparation before ranging.

When distance measurement is required, a half-wave voltage V is applied to a pair of electrode sheets 4 of the uniaxial electro-optic crystal 3 . The reason why it is called a half-wave voltage is because under the action of this voltage, due to the transverse electro-optic effect of the crystal, the o-light and e-light passing through the uniaxial electro-optic crystal 3 on the vertical crystal axis 3C will be on the basis of the original phase difference Г Add a phase difference π. The size V of the half-wave voltage depends on the laser wavelength, the material of the crystal and the side length ratio a/b, and the size is:

where n is the laser wavelength, n _o and n _e are the ordinary and extraordinary light refractive indices of the uniaxial electro-optic crystal 3 respectively, and r ₁₃ and r ₃₃ are the two corresponding components of the electro-optic coefficient of the crystal. When a half-wave voltage V is applied to the uniaxial electro-optic crystal 3, a phase difference π is added between the o-light and e-light of the same direction and equal amplitude passing through the uniaxial electro-optic crystal 3 and the compensation crystal 5, at this time For the linearly polarized light B polarized along the coordinate axis x', the uniaxial electro-optic crystal 3 and the compensation crystal 5 act together as a 1/2 wave plate, and B passes through the uniaxial electro-optic crystal in turn 3 and the compensation crystal 5, the polarization direction is twisted at an angle of 90° to become linearly polarized light C polarized along the coordinate axis y' direction. The polarization direction of the light C and the polarization analyzer 6C are perpendicular to each other, so after the half-wave voltage is applied, the beam C emitted from the compensation crystal 5 cannot pass through the polarization analyzer 6, so that the original smooth outgoing beam is The a'×c' plane facing the polarization analyzer 6 from the compensation crystal 5 is truncated. While applying the half-wave voltage, let’s look at the return light E reflected by the object 7 that has been emitted before: the return light E that was originally polarized along the coordinate axis x’ direction passes through the compensation crystal 5 and the single axis in turn. After the electro-optic crystal 3 exits, it becomes the linearly polarized return light F whose polarization direction is perpendicular to the original and polarized along the coordinate axis y' direction. When encountering the polarization beam splitter 2, due to the polarization direction of F and the polarization of the polarization beam splitter The directions are perpendicular to each other, and the return light F cannot pass along the original optical path, and is reflected by the polarizing beam splitter 2 that simultaneously acts as a polarization splitter to the receiving detector 8 on one side, so that the originally smooth reflected return light is also directed from the uniaxial electro-optic crystal 3 The polarizing beam splitter 2 cuts off at the a×c plane. To sum up, when the half-wave voltage V is applied to the uniaxial electro-optic crystal 3, the devices 2, 3, 4, 5, and 6 play the role of "instantly" inserting a reflector in the optical path in Figure 1: The original optical path between the laser 1 and the object 7 to be measured is cut off, and the cut-off beam segment CDEF is reflected to the detector 8 to form a rectangular light pulse G to be measured. By measuring the pulse width t of the light pulse G, the distance to be measured L can be obtained:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Vc</span>}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

where Vc is the speed of light in air.

When the polarization analysis direction of the polarization analyzer 6 is placed according to the 6C' direction indicated by the dotted line in Fig. 3, and other devices are inconveniently positioned, it corresponds to the second operation method of the present invention. Under this operation method, the state of applying the half-wave voltage V to the pair of electrode sheets 4 of the uniaxial electro-optic crystal 3 is the preparation state before ranging. At this time, the linearly polarized light B whose polarization direction forms an angle of 45° with the crystal axis 3C of the uniaxial electro-optic crystal 3 passes through the uniaxial electro-optic crystal 3 and the compensation crystal 5 sequentially, and the polarization direction is twisted by 90° to become linearly polarized light C, which is linearly polarized The polarization direction of the light C is just parallel to the polarization analysis direction 6C' of the polarization analyzer 6 at this time, so it can pass through the polarization analyzer 6 smoothly to become the final outgoing light D. The return light E reflected by the object 7 to be measured passes through the polarization analyzer 6 and then passes through the compensation crystal 5 and the uniaxial electro-optic crystal 3 in sequence, and its polarization direction is twisted 90° again to become the polarization direction and the polarization of the polarization beam splitter 2 The linearly polarized light F parallel to the direction 2C, the light F smoothly passes through the polarizing beam splitter 2 and becomes useless light W2. It can be seen that when a voltage is applied to the uniaxial electro-optic crystal 3, the devices 2, 3, 4, 5, and 6 are transparent to the propagation of the laser light B, C, D, E, F, and W2. When distance measurement is required, the half-wave voltage V applied to the uniaxial electro-optic crystal 3 is removed, and the devices 2, 3, 4, 5, and 6 are like reflectors inserted "instantly" in the optical path of Fig. 1 Similarly, the outgoing optical path is cut off from the a'×c' plane where the compensation crystal 5 faces the polarization analyzer 6, and the reflected light path is cut off from the a×c plane where the uniaxial electro-optic crystal 3 faces the polarizing beam splitter 2 truncate, and at the same time reflect the truncated beam segment C-D-E-F to the detector 8 to form a rectangular light pulse G to be measured.

Laser 1 selects a He-Ne laser with a wavelength of 632.8nm, polarizing beam splitter 2 selects a Glan prism, and both uniaxial electro-optic crystal 3 and compensation crystal 5 select lithium niobate LiNbO ₃ of the same size, so that the optical axis of uniaxial electro-optic crystal 3 is the coordinate y-axis, and the optical axis of the compensation crystal 3 is the coordinate x-axis. Devices 2, 3, 5, and 6 should be selected with appropriate volumes to ensure that the laser spot can completely pass through when it irradiates the surface of these devices without energy leakage. The devices 2, 3, 4, 5, 6 should be placed close to each other without leaving any gaps. When the laser wavelength is 632.8nm, the two principal refractive indices of LiNbO ₃ crystal are _no =2.2864 and _ne =2.2024.

example 1:

The structure shown in Figure 3. The dimensions of the uniaxial electro-optic crystal 3 and the compensation crystal 5 are a×b×c=a’×b’×c’=0.2×3.4×0.2cm ³ , and the size of a pair of electrode pieces is just enough to cover both sides of the uniaxial electro-optic crystal 3. A b×c plane shall prevail, at this time the half-wave voltage V=235V (the aspect ratio is a/b=1:17).

Claims (2)

1, a kind of electro light modulation laser distance measuring method, it is characterized in that utilizing the carrier of the polarization characteristic of laser as testing distance information, when the parallel optical axis direction adds half-wave voltage on the single shaft electro-optic crystal, the effect of the polarizing beam splitter in light path, single shaft electro-optic crystal, compensated crystal and polarization analyzer, with travelling to and fro between that light beam between single shaft electro-optic crystal and the object under test blocks to pulsewidth is the rectangular light pulse of t, the then distance L between single shaft electro-optic crystal and the object under test:

$L=\mathrm{Vc}*\frac{t}{2}$

Wherein Vc is the aerial speed of light.

2, a kind of electro light modulation laser distance measuring device of implementing the described electro light modulation laser distance measuring method of claim 1, be characterised in that its formation: the laser instrument (1) that comprises an output collimation continuous laser, along the light beam working direction is polarizing beam splitter (2), single shaft electro-optic crystal (3), compensated crystal (5), polarization analyzer (6) successively, and described single shaft electro-optic crystal (3) and compensated crystal (5) thereof are selected onesize rectangular parallelepiped LiNbO for use ₃Crystal, side length b＞a=c, and make parallel light b limit pass through crystal, pair of electrodes sheet (4) is close on the two b * c plane of described single shaft electro-optic crystal (3), half-wave voltage is added on the single shaft electro-optic crystal (3) perpendicular to the b limit by electrode slice (4), the folk prescription that rises of described polarizing beam splitter (2) is parallel to each other or vertical mutually to the analyzing direction with polarization analyzer (6), the vertical placement mutually of the optical axis of single shaft electro-optic crystal (3) and compensated crystal (5), and the optical axis direction that makes the two all and polarizing beam splitter (2) rise folk prescription to, polarization analyzer (6) analyzing direction is respectively at 45, in the echo reflection direction of polarizing beam splitter (2) detector (8) is set.

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