CN1313836C - Electro-optic modulation pulse laser distance measurer - Google Patents

Abstract

The present invention relates to an electro-optic modulation pulse laser rangefinder which comprises a linear polarizing short pulse lasing light emitter and elements which are arranged in the output light direction of the lasing light emitter, such as a polarizing light isolator, a second polarizing beam splitter, an electro-optic modulation crystal, a spectroscope and a 1/8 wave plate; a third polarizing beam splitter is arranged in the direction of sampling light emitted from the spectroscope. The electro-optic modulation crystal is a cube, the lengthwise direction of the cube coincides with the output light direction, the crystal axis is perpendicular to the output light direction; a pair of electrode pieces are pasted on the electro-optic modulation crystal and are connected with the electrodes of a sine alternating power supply. A first CCD detector and a second CCD detector which have the same performance are respectively arranged in the transmitted light direction and the reflected light direction of the third polarizing beam splitter; a third CCD detector and a fourthly CCD detector are respectively arranged in the reflected light directions of. the second polarizing beam splitter and the polarizing light isolator The rangefinder of the present invention has the advantages of simplified equipment and improved distance-measuring length and precision.

Description

Electro-optic modulation pulse laser distance measurer

Technical field

The present invention relates to laser ranging, is a kind of electro-optic modulation pulse laser distance measurer, can be applicable to numerous areas such as industrial and agricultural production, military affairs, communication, remote sensing.

Background technology

The high-acruracy survey of the information of adjusting the distance is one of gordian technique of modernization of the country construction numerous areas.Along with development of science and technology, the scope and the accuracy requirement of the measurement of adjusting the distance are more and more higher.Laser has become the first-selected instrument of range observation as the information carrier with high monochromaticity, collimation, coherence.Advanced both at home and abroad at present distance mearuring equipment all utilizes laser to improve the degree of accuracy of range finding as information carrier.

Formerly technology [1] is (referring to Kozo Ohtani, Misuru Baba, A rangefinding approach bydetecting the position and the incident angle of a light-stripe, IEEE Instru.andMea.Techno.Conf.2002) be a kind of distance-finding method of geometrical optics.The laser instrument emission of lasering beam is received by PSD or CCD behind target reflection, according to facula position that receives and the geometry site between laser instrument and the receiver, calculates the distance between target and the detector then.This method is mainly used in industrial face type profile measurement, the type reconstruct of 2D/3D face and location etc., and measuring relative accuracy is about 0.85%, can only survey very short distance.Along with the increase of distance, precision sharply descends.

Formerly technology [2] is (referring to Raimo Ahola, Risto Myllyla, A new method for measuringthe time-of-flight in fast laser range finding, [J] .Proc.SPIE vol.654,1986) be a kind of distance-finding method that utilizes the light pulse flight time.Send very short pulse laser of a duration by pulsed laser, be referred to as main ripple.Through directive measured target behind the testing distance L, the pulse laser of being returned by target reflection is referred to as echo, echo is received by photodetector after returning stadimeter, according to the time interval between main ripple signal and the echoed signal, being laser pulse is transmitted into τ two-way time that returned by target reflection from laser instrument, just can calculate the distance of target to be measured.This method remove to need needs complicated processing of circuit system, is electric pulse with the Conversion of energy of the main glistening light of waves pulse of part, and shaping is after the gating circuit flip-flop number, and the time pulse number that begins clock oscillator is sent is counted; Be detected device after echoed signal arrives then and be converted into electric signal once more, the electricity processing procedure through same stops the counting to time pulse signal, determines light pulse t two-way time by the number of time tick.In being converted into the processing of circuit system of the process of electric signal and electric signal, light signal all can introduce some errors.

Formerly technology [3] is (referring to Fujima I, Seta K, Matsumoto H and O ' ishi T 1988 GHztraveling-wave optical modulator for precision distance measurement Proc.SPIEvol 889) be a kind of distance-finding method that utilizes the continuous laser phase information.Phase laser distance is realized range finding by measuring the high frequency modulated phase differential.Light source in the instrument sends continuous light, by becoming light modulated directive target after the modulators modulate, the light intensity of the light modulated cycle of intercropping at any time changes, adopt sine wave modulation, the phase place of the sinusoidal wave complete cycle issue in the mensuration light wave two-way process and the sine function of not enough one-period, just can determine the interval τ of the two-way time of light wave, thereby calculate testing distance.This method still needs light signal is converted into electric signal after Circuits System is handled, and is relatively launched and accepted the phase differential of sine wave by the electronics phase comparator.Because be the continuous light range finding, finite energy, finding range are difficult to reach more than 1 km.

Formerly technology [4] is (referring to S F Collins, M M Murphy, K T V Grattan, etal.A simple laserdiode ranging scheme using an intensity modulated FMCW approach[J] .Meas.andTech., 1993,4) be a kind of distance-finding method that utilizes the continuous laser frequency information.The FM-CW laser ranging principle is by launching the continuously adjustable laser of a frequency, receives through the return frequency of laser of target reflection by measurement and calculates distance.Receive light and have frequency drift owing to warbling with emission light, so will produce beat frequency in frequency mixer, this beat frequency is directly proportional with testing distance.This method still needs light signal is converted into electric signal after Circuits System is handled, but also needs to increase the additional circuitry of regulating laser frequency.Finding range also is far smaller than the distance-finding method of pulsed light.

Summary of the invention

The technical problem to be solved in the present invention is to overcome the deficiency of above-mentioned technology formerly, and a kind of electro-optic modulation pulse laser distance measurer is provided, and with simplification device, improves the distance and the precision of range finding.

Ultimate principle of the present invention:

Formerly technology [2] is present domestic and international topmost distance-finding method, and principle of the present invention is identical with its basic ideas, all is to adopt the round required flight time of testing distance of measurement pulse laser to find range.But apparatus of the present invention are utilized crystal current luminous effect change modulates pulsed light in time, and utilize the method for modulated pulsed light photon number ratio on two orthogonal polarization orientation to determine the flight time, thereby can improve distance measuring precision greatly.

Concrete technical solution of the present invention is as follows:

A kind of electro-optic modulation pulse laser distance measurer, it is characterized in that comprising a linear polarization short-pulse laser light source, along the output light direction of this pulsed laser light source, be polarized light isolator, second polarising beam splitter, transverse electric optical modulation uniaxial crystal, spectroscope and 1/8 wave plate successively; The sampling light direction that reflects from spectroscope has the 3rd polarising beam splitter; Described transverse electric optical modulation uniaxial crystal is a rectangular parallelepiped, its length direction is consistent with the output light direction, its crystallographic axis is perpendicular to the output light direction, transverse electric optical modulation uniaxial crystal be parallel to optical propagation direction arbitraryly post the pair of electrodes sheet on to the plane and link to each other with the electrode of a sinusoidal alternating power supply; The light direction that sees through of described the 3rd polarising beam splitter is respectively equipped with the first identical ccd detector of performance and second ccd detector with the reflected light direction, and the reflected light direction of described second polarising beam splitter and polarized light isolator is respectively equipped with the 3rd identical ccd detector of performance and the 4th ccd detector.

Described polarized light isolator is made up of first polarising beam splitter and magnetic polarization apparatus, and the one way optical activity of this magnetic polarization apparatus is π/4, and correspondingly the printing opacity optical axis direction of first polarising beam splitter and second polarising beam splitter is at 45.

Described the 3rd polarising beam splitter, second polarising beam splitter and first polarising beam splitter all are that Glan prism constitutes.

Described electrode slice size is identical with two planes that are parallel to optical propagation direction of transverse electric optical modulation uniaxial crystal and be attached to respectively on these two planes.

The performance of described first ccd detector and second ccd detector is identical, and the performance of the 3rd ccd detector and the 4th ccd detector is identical.

Description of drawings

Fig. 1 is the synoptic diagram of apparatus of the present invention.

Fig. 2 is the concrete displacement structure synoptic diagram of each parts of apparatus of the present invention.

Fig. 3 is that voltage waveform among the present invention, pulsed light outgoing moment value function waveform and pulsed light reflect value function waveform corresponding relation synoptic diagram constantly.

Embodiment

The invention will be further described below in conjunction with drawings and Examples, but should not limit protection scope of the present invention with this.

See also Fig. 1 and Fig. 2 earlier, as seen from the figure, the formation of electro-optic modulation pulse laser distance measurer of the present invention, comprising a linear polarization short-pulse laser light source 1 (being called for short light source 1), along the output light direction of this pulsed laser light source 1, is polarized light isolator 2 successively, second polarising beam splitter 3, the electrooptical modulation crystal 4, spectroscope 6,1/8 wave plates 10; The sampling light direction that reflects from spectroscope 6 has the 3rd polarising beam splitter 7; Described electrooptical modulation crystal 4 is a rectangular parallelepiped, and its length direction is consistent with the output light direction, and its crystallographic axis hangs down as for the output light direction, posts pair of electrodes sheet 5 and link to each other with the electrode of a sinusoidal alternating power supply (not shown) on the electrooptical modulation crystal 4; Described the 3rd polarising beam splitter 7 see through light direction and the reflected light direction is respectively equipped with first ccd detector 8 and second ccd detector 9, the reflected light direction of described second polarising beam splitter 3 and polarized light isolator 2 is respectively equipped with the 3rd ccd detector 12 and the 4th ccd detector 13.

Described polarized light isolator 2 is made up of first polarising beam splitter 21 and magnetic polarization apparatus 22, and the one way optical activity of this magnetic polarization apparatus 22 is π/4, and correspondingly the printing opacity optical axis direction of first polarising beam splitter 21 and second polarising beam splitter 3 is at 45.

Described the 3rd polarising beam splitter 7, second polarising beam splitter 3 and first polarising beam splitter 21 all are made of Glan prism.

Described electrode slice 5 sizes are identical with the b * c plane of electrooptical modulation crystal 4 and be attached to respectively on two b of this electrooptical modulation crystal 4 * c plane.

The performance of described first ccd detector 8 and second ccd detector 9 is identical, and the performance of the 3rd ccd detector 12 and the 4th ccd detector 13 is identical.

Make linear polarization pulse laser A polarization direction that light source sends along coordinate x ' direction among Fig. 2.

Described polarized light isolator 2 is made up of first polarising beam splitter 21 and magnetic polarization apparatus 22, it act as: make the linearly polarized laser that light source 1 sends can only one way propagation, be to propagate along direction from left to right shown in Fig. 1 and Fig. 2, and when light returns light source 1 from right to left, the blocking-up light path, and reflect it in the 4th ccd detector 13.Optoisolator 2 can be selected the structure shown in Fig. 2 for use, be made up of first polarising beam splitter 21 and a magnetic polarization apparatus 22: 21C is depicted as coordinate x ' direction among the printing opacity optical axis direction of first polarising beam splitter 21 such as Fig. 2, be that it is to the transmittance along x ' direction polarization, to light reflection along y ' direction polarization, select the Glan prism structure for use, to the no specific (special) requirements of its size, guarantee printing opacity, reflective getting final product.The pulsed light A along x ' direction polarization that light source 1 sends can pass through first polarising beam splitter 21 from left to right smoothly, runs into magnetic polarization apparatus 22; The effect of magnetic polarization apparatus 22 is under the control of certain magnetic field size and Orientation, makes the polarization direction of the linearly polarized light that passes through reverse a certain angle towards a direction.Here, we make the linearly polarized light by it rotate 45 ° in direction observation from left to right towards counter clockwise direction.Like this, when propagating from left to right, behind the polarized light isolator of being made up of first polarising beam splitter 21 and magnetic polarization apparatus 22 2, the polarization direction becomes the linearly polarized light B of polarization direction along coordinate y along the linear polarization pulsed light A of x ' axle; And when light is propagated from right to left, the linear polarization pulsed light L identical with linear polarization pulsed light B polarization direction rotates 45 ° once more through magnetic polarization apparatus 22 rear polarizer directions, become direction along coordinate y ', thereby reflected original optical path by first polarising beam splitter 21, enter into the 4th ccd detector 13, finish the light path buffer action.

Described second polarising beam splitter 3 is identical with first polarising beam splitter, 21 effects in the polarized light isolator 2, it is different just to place the orientation: its printing opacity optical axis direction is placed along coordinate y direction shown in 3C among Fig. 2, be that it is to the transmittance along y direction polarization, to the light reflection along x direction polarization.That propagates so from left to right can be smoothly becomes pulsed light C with the polarization direction by second polarising beam splitter 3 along the pulsed light B of y direction polarization; And the light J that propagates from right to left comprises x and two kinds of polarized components of y, and then it is divided into two parts after through second polarising beam splitter 3: pass second polarising beam splitter 3 along the linearly polarized light L of y direction polarization and continue to propagate along original optical path; Departed from original optical path by 3 reflections of second polarising beam splitter and enter in the 3rd ccd detector 12 along the linearly polarized light K of x direction polarization.

Said electrooptical modulation crystal 4 plays transverse electric optical modulation effect in conjunction with pair of electrodes sheet 5: because the birefringence effect of electro-optic crystal 4, when the vertical crystallographic axis 4C of light and vertical plane a * c incide in the electrooptical modulation crystal 4, be divided into along the polarization direction of same light path co-propagate orthogonal ordinary light o light and unusual light e light, o light vertical optical axis 4C polarization wherein, e parallel light optical axis 4C polarization.Because the refractive index n of 4 pairs of o light of electrical modulation luminescent crystal and e light _oAnd n _eDifference causes o light and e light velocity of propagation difference to some extent in crystal, and like this, just there are certain phase difference Γ in o light and e light when going out the electrooptical modulation crystal 4, make the two close light beam change into incident before different polarization states.When parallel optical axis 4C direction added certain voltage V on electro-optic crystal 4 by electrode slice 5, because an electrooptical effect of electrooptical modulation crystal 4, to change its refractive index to o light and e light be n to crystal under electric field action _o' and n _e', so just on o light that goes out crystal and e light, added certain phase difference, make o light and e light phase difference become Γ ', control effect thereby play by the polarization state of electrooptical modulation crystal 4 light beam by the size of control voltage V.When the present invention requires linear polarization pulse laser C through the electrooptical modulation crystal 4, modulated by the voltage of sinusoidal alternating in time, thus can be according to the accurately anti-moment value of releasing pulse through the electrooptical modulation crystal 4 of the polarization state that goes out crystal afterpulse light D.For reaching above-mentioned requirements, the electrooptical modulation crystal 4 should be selected the uniaxial crystal with transverse electric optical modulation performance for use, and as lithium niobate, lithium tantalate etc., its shape is a rectangular parallelepiped, and physical dimension is a * b * c.Wherein concern between a and the b and concrete size and the making alive peak swing value V of institute _mAnd required phase differential Γ is relevant, does not have between a and the c and is strict with, because laser facula is circular, considers from the aspect that reduces size and economical with materials, should get a=c.Make the crystalline axis direction 4C of electrooptical modulation crystal 4 and the polarization direction of linear polarization pulsed light C be the 45 placement, i.e. optical axis 4C direction parallel coordinates y ' axle.Make side length b be parallel to coordinate axis z direction, the parallel y ' direction of length of side a, the parallel x ' direction of length of side c impinges perpendicularly on two a * c face light C.Pair of electrodes sheet 5 is attached to respectively on two b * c plane of electrooptical modulation crystal 4, and size is good just to cover two b * c plane.Like this, when making alive on electrode slice 5, the direction of an electric field in the electrooptical modulation crystal 4 is parallel to crystallographic axis 4C direction.

Described spectroscope 6 works to extract a part of sampled light: when by the light pulse D process spectroscope 6 after the modulation of electrooptical modulation crystal 4, most of energy sees through this spectroscope 6 and becomes pulsed light H along the original optical path propagation, and the fraction energy is reflexed to by it becomes sampled light pulse E in the 3rd polarising beam splitter 7; Therefore the loss of fraction energy also can be arranged when reflected light pulse I is through spectroscope 6 simultaneously.Outgoing pulse light light intensity is very big, the sampled light of therefore only getting very little part energy just can guarantee that first ccd detector 8 surveys, so should make the reflectivity of spectroscope 6 as far as possible little, get about 1% and get final product, can guarantee that so also faint reflected light pulse energy reduces the loss.Spectroscope 6 and the angle at 45 of light path are from left to right placed.

Said the 3rd polarising beam splitter 7 is identical with the firstth polarising beam splitter 21 effects in second polarising beam splitter 3 and the polarized light isolator 2, the placement orientation is different: its printing opacity optical axis direction is placed along coordinate z direction shown in 7C among Fig. 2, be that it is to the transmittance along z direction polarization, to the light reflection along x direction polarization.So as shown in Figure 2, the sampled light E of Chuan Boing comprises x and two kinds of polarized components of z because modulated by electro-optic crystal 4 from top to bottom, and then it is divided into two parts after through the 3rd polarising beam splitter 7: pass the 3rd polarising beam splitter 7 along the linear polarization pulsed light F of z direction polarization and continue to spread in first ccd detector 8 along original optical path; Departed from original optical path by 7 reflections of the 3rd polarising beam splitter and enter in second ccd detector 9 along the linear polarization pulsed light G of x direction polarization.

Described first ccd detector 8, second ccd detector 9, the 3rd ccd detector 12, the 4th ccd detector 13 receive linear polarization pulsed light F, G, K and M respectively, survey the relative value size (ratio that promptly comprises photon number) of its energy.Because the measurement of testing distance L is only relevant with F, G two pulse energy ratios and K, M two pulse energy ratios among the present invention, and it is irrelevant with their concrete size, so first ccd detector 8 and second ccd detector 9 must be selected the duplicate CCD of performance respectively for use, the 3rd ccd detector 12 and the 4th ccd detector 13 must be selected the duplicate CCD of performance respectively for use, otherwise can influence distance measuring precision.

Said 1/8 wave plate 10 plays a part to regulate phasic difference: the fast axle 10C of 1/8 wave plate 10 is placed along y ' direction of principal axis as shown in Figure 2, behind outgoing pulse H process wave plate 10, increase the phasic difference of π/4 between o light and the e light, when H is reflected once more through 1/8 wave plate 10 by object under test 11, can on original basis, continue to increase the phasic difference of π/4 again.Like this, when the H outgoing and reflect twice through 1/8 wave plate 10 after, with regard to many phasic differences of pi/2, become the light echo pulse I that arrives the electrooptical modulation crystal 4 between its o, e two beam split.Regulate mutually by such position, can simplify the energy distribution curve after light echo pulse I is modulated by the electrooptical modulation crystal 4.

Range measurement principle of the present invention is summarized as follows: add the sinusoidal alternating voltage of a certain size and frequency on the electrooptical modulation crystal 4, the refractive index of electrooptical modulation crystal 4 is carried out periodic modulation.Make the short-pulse laser of linear polarization accept modulation back outgoing, determine the moment value of emergent light according to the ratio size of sampling light E energy on two orthogonal polarization orientation through the electrooptical modulation crystal 4; Emergent light is modulated by the electrooptical modulation crystal 4 after by object under test 11 reflected backs once more, according to being obtained the moment value that pulse laser returns by the ratio size of the reflected light J energy on two corresponding polarization directions after the modulation for the second time.According to outgoing with return constantly difference and can try to achieve light pulse and come and go the required flight time τ of testing distance L, according to formula

$L=c*\frac{\mathrm{\τ}}{2}---\left(1\right)$

Can draw the size of testing distance L, wherein c is the aerial velocity of propagation of light.

With reference to Fig. 1, Fig. 2 and Fig. 3, the concrete ranging process of apparatus of the present invention is as follows: by light source 1 send along the linear polarization pulse laser A of coordinate x ' direction polarization through behind the optoisolator 2, become along the linear polarization pulsed light B of coordinate y direction polarization, light B becomes linear polarization pulsed light C with the polarization direction by second polarising beam splitter 3 smoothly, the crystallographic axis 4C direction of the polarization direction of C and electrooptical modulation crystal 4 is 45 ° of angles, enters that to be divided into amplitude behind the crystal identical, the polarization direction is vertical mutually, o light and e light (the vertical crystallographic axis 4C of o light polarization along the same optical path propagation, e parallel light crystallographic axis 4C polarization).Electro-optic crystal 4 is own different with the e optical index to o light, simultaneously on the electrooptical modulation crystal 4 added sinusoidal alternating voltage also refractive index change, like this, just have a phasic difference between o light behind the pulsed light C process electrooptical modulation crystal 4 and the e light, its polarization mode of closing light D is cyclical variation with the moment value difference that pulsed light C passes through the electrooptical modulation crystal 4.Pulsed D is reflected into through spectroscope 6 back part energy and is sampling light pulse E, E is divided into two parts after through first polarising beam splitter 7: wherein the energy along coordinate z direction polarization becomes pulsed light F, enter ccd detector 8, energy along coordinate x direction polarization becomes pulsed light G, enters ccd detector 9.On the electrooptical modulation crystal 4, add sinusoidal alternating voltage V=V _mSin (cot) (V _mVoltage maximum value, ω is the angular frequency of sinusoidal voltage) situation under, the energy that detector 8,9 receives is respectively:

E ₈＝E _E(1+cos(ΔΦ+Msin(ωt))

(2)

E ₉＝E _E(1-cos(ΔΦ+Msin(ωt))

(3)

E in the formula _EBe the gross energy of sampled light pulse E, ΔΦ is the phasic difference that crystal itself produces, the phasic difference that Msin (ω t) produces for the alternating voltage modulation, and ΔΦ and M can be expressed as:

$\mathrm{\Δ\Φ}=\frac{2\mathrm{\πb}}{\mathrm{\λ}}(n_o-n_e);$ $M=\frac{\mathrm{\πb}{V}_m}{\mathrm{\λa}}({n_o}^3{r}_{13}-{n_e}^3{r}_{33})$

(4)

A, b are two length of side length of rectangular parallelepiped electrooptical modulation crystal 4 in the formula, and λ is an optical maser wavelength, V _mBe institute's making alive amplitude maximum, n _o, n _eBe respectively the intrinsic refractive index of crystal, r to o light, e light ₁₃, r ₃₃Two respective components for the crystal electrooptical coefficient.We get ratio r 1 (t)=E ₉/ (E ₈+ E ₉), then:

r1(t)＝1/2(1-cos(ΔΦ+Msin(ωt)))

(5)

Obtain r1 (t) by the ratio between two first ccd detectors 8, second ccd detector 9, can try to achieve the moment value t1 that emergent light pulse C passes crystal 4 according to formula (5).Here it is noted that because formula (5) is the function of the nested sin of cos more complicated is so the functional digraph of multiple complexity can occur when ΔΦ and M get different value.Here we get the simplest situation, make ΔΦ=2k π+pi/2, the M=pi/2, and like this, formula (5) is reduced to:

$r1\left(t\right)=1/2(1-\cos (\frac{\mathrm{\π}}{2}+\frac{\mathrm{\π}}{2}\sin \left(\mathrm{\ωt}\right)))=1/2(1+\sin \left(\frac{\mathrm{\π}}{2}\sin \left(\mathrm{\ωt}\right)\right))$

(6)

Function (6) graph of a correspondence is shown in Fig. 3 intermediate curve, and the coordinate transverse axis is ω t.The top curve is sinusoidal alternating voltage V among Fig. 3 _mThe figure of sin (ω t), the coordinate transverse axis is ω t.

Pulsed light D is except little energy is sampled, overwhelming majority energy passes spectroscope 6 becomes final outgoing pulse H, H increases directive object under test 11 after π/4 phasic differences through 1/8 wave plate 10, after being returned by the object under test surface reflection once more by 1/8 wave plate 10, on original basis, increase π/4 phasic differences again, except the minute quantity energy by spectroscope 6 reflection losses, most energy pass spectroscope becomes light echo pulse I.Light echo pulse I can be carried out the modulation second time by crystal through the electrooptical modulation crystal 4, become the pulsed light J that comprises testing distance information, J finishes the leaching process of information subsequently successively through second polarising beam splitter 3 and first polarising beam splitter 21: because the printing opacity optical axis direction of second polarization beam apparatus 3 is along y, light J is divided into two-beam during through second polarization beam apparatus 3, and wherein the polarization direction is reflected in the 3rd ccd detector 12 along the linear polarization pulsed light K of x; The polarization direction along the linear polarization pulsed light H of y by behind second polarization beam apparatus 3, become the linear polarization pulsed light L of polarization direction by magnetic polarization apparatus 22 along y ', the L polarization direction is just vertical with the printing opacity optical axis 21C direction of first polarising beam splitter 21, is therefore reflexed in the 4th ccd detector 13 by it.According to ratio r 2 (the t)=E between the 3rd ccd detector 12 and the 4th ccd detector 13 ₁₂/ (E ₁₂+ E ₁₃) just can try to achieve the moment value t2 of light echo pulse I by the electrooptical modulation crystal 4.We have drawn the moment value t1 of outgoing pulse light C by the electrooptical modulation crystal 4 by the ratio r 1 (t) between first ccd detector 8 and second ccd detector 9 according to formula (6) front, also will add the phasic difference pi/2 through 10 increases of 1/8 wave plate simultaneously twice, we obtain formula:

$r2\left(t\right)=1/2(1-\cos (\frac{3\mathrm{\π}}{2}+\frac{\mathrm{\π}}{2}\sin \left(\mathrm{\ωt}1\right)+\frac{\mathrm{\π}}{2}\sin \left(\mathrm{\ωt}\right)))$

(7)

Will be by r2 (t)=E ₁₂/ (E ₁₂+ E ₁₃) in r2 (t) the value substitution formula (7) that obtains, we just can try to achieve the moment value t2 of light echo by the electrooptical modulation crystal 4.Again in the difference τ between t1 and t2 generation, just can be tried to achieve the size of testing distance L as formula (1).Because when t1, t2 appear at function r1 (t), r2 (t) rate of curve maximum, the moment value t1 that tries to achieve, t2 error minimum, in order to obtain the maximal accuracy of testing distance L, we should regulate the moment and the frequency of light source 1 emission pulse laser, and the moment that makes pulsed light C arrive the electrooptical modulation crystal 4 appears at r1 (t) slope of a curve maximum: promptly near b, the d in Fig. 3 intermediate curve, the f point.After supposing that we regulate distance measuring equipment, order is worth the b point place (shown in the * symbol) that t1 just appears at Fig. 3 intermediate curve constantly, i.e. ω t1=π place, and then light echo pulse I can further be reduced to through the formula (7) in the crystal 4 moment:

$r2\left(t\right)=1/2(1-\sin \left(\frac{\mathrm{\π}}{2}\sin \left(\mathrm{\ωt}\right)\right))$

(8)

The curve map of function (8) is shown in lower curve among Fig. 3, and horizontal ordinate is ω t.Simultaneously in order to reduce error as far as possible, we also will be adjusted at the angular frequency that adds sinusoidal voltage on the electro-optic crystal 4 according to the size of estimation testing distance L, make the moment be worth t2 and appear near the slope maximum (b ' of lower curve, d ', f ' locate among Fig. 3) of curve r2 (t).Suppose that t2 just appears at d ' and locates (in the curve shown in left side * number), pulsed light flight time τ=t2-t1=π/ω then, the angular frequency value of sinusoidal voltage that substitution adds just can obtain τ, and then tries to achieve the size of testing distance L according to formula (1).

Compare with technology formerly: formerly technology [1] is little short-range measuring method, and along with the increase of measuring distance, precision sharply descends.Formerly technology [3] [4] is the continuous light range finding, and laser energy is limited, and finding range is limited greatly.The ingenious size of utilizing the accuracy method mensuration laser pulse flight time of photon number ratio of the present invention, distance accuracy only depends on the statistical error that two detectors receive photon number ratio, guaranteeing under the wide prerequisite of pulsed light flight time distance-finding method measurement range, improved the accuracy of range finding greatly, simultaneously also avoid having introduced complicated Circuits System, than formerly technology [2] precision is higher, install also simpler.

Light source 1 is chosen the high power pulsed laser diode of wavelength 905nm, an additional polarization polarizer produces the standard lines polarized laser beam, first polarising beam splitter 21, second polarising beam splitter 3 and Di Di three polarising beam splitters 7 are selected the Glan prism of same structure and size for use, magnetic polarization apparatus 22 is selected Faraday rotator spare for use, and the electrooptical modulation crystal 4 is selected rectangular structure LiNbO for use ₃Crystal, crystal constant are n _o=2.300, n _e=2.208, r ₁₃=8.6*10 ^-12M/V, r ₃₃=31*10 ^-12M/V, after cutting and polishing is made the required size crystal 4, possible side length b has slight error to cause intrinsic phase differential ΔΦ and requirement to disagree, can recompense by correspondingly additional certain electrostatic field on electrode slice 5 this moment, make that its crystallographic axis is a coordinate y axle, electrode slice 5 adopts electric plating method to make on a pair of organic glass sheet, then it is fixedly clamped at LiNbO ₃On two b of crystal * c plane, prevent crystal in the electrooptical modulation process in coordinate y direction of principal axis generation deformation, 1/8 wave plate, 10 selection standard devices.Each device is chosen suitable volume size and putting position, guarantee laser facula can be fully when shining these apparatus surfaces by and energy does not leak, mutual placement is close in the unoccupied place of not leaving a blank of should trying one's best between each installs simultaneously.On electrode slice 5, add sinusoidal alternating electric voltage frequency adjustable size, in order to obtain best distance accuracy, should make outgoing pulse and return pulse and appear at respectively near r1 (t) and r2 (t) the slope of a curve maximum through moment value t1, the t2 of electrooptical modulation crystal 4, for fear of the situation that the corresponding a plurality of t2 values of a r2 (t) value occur (as two ordinate values that the * symbol is corresponding identical in Fig. 3 lower curve), when measuring, should estimate the size of testing distance L, regulate the sinusoidal voltage period T, make it come and go the required time τ of testing distance L greater than pulse.

Structure as shown in Figure 1, 2.Light source is selected the high power pulsed laser diode of wavelength 905nm for use.Use rectangular structure LiNbO ₃Crystal is made the electrooptical modulation crystal 4, get intrinsic phasic difference ΔΦ=pi/2, the modulation additional bit differ maximal value M=pi/2, choose crystal and be of a size of a * b * c=0.2 * 3.4 * 0.2cm ³, pair of electrodes sheet 5 sizes are as the criterion with two b * c plane that just covers the electrooptical modulation crystal 4, sinusoidal alternating voltage peak swing V that add this moment _m(aspect ratio is a/b=1 to=117.5V: 17).Through probationary certificate, stadimeter of the present invention has been simplified device, has improved the distance and the precision of range finding.

Claims (5)

1, a kind of electro-optic modulation pulse laser distance measurer, it is characterized in that comprising a linear polarization short-pulse laser light source (1), output light direction along this pulsed laser light source (1), be polarized light isolator (2) successively, second polarising beam splitter (3), transverse electric optical modulation uniaxial crystal (4), spectroscope (6), 1/8 wave plate (10); The sampling light direction that reflects from spectroscope (6) has the 3rd polarising beam splitter (7); Described electrooptical modulation uniaxial crystal (4) is a rectangular parallelepiped, its length direction is consistent with the output light direction, its crystallographic axis is perpendicular to the output light direction, transverse electric optical modulation uniaxial crystal (4) be parallel to optical propagation direction arbitraryly post pair of electrodes sheet (5) on to relative plane and link to each other with the electrode of a sinusoidal alternating power supply; The light direction that sees through of described the 3rd polarising beam splitter (7) is respectively equipped with identical first ccd detector (8) of performance and second ccd detector (9) with the reflected light direction, and the reflected light direction of described second polarising beam splitter (3) and polarized light isolator (2) is respectively equipped with identical the 3rd ccd detector (12) of performance and the 4th ccd detector (13).

2, electrooptical modulation polarization laser stadimeter according to claim 1, it is characterized in that described polarized light isolator (2) is made up of first polarising beam splitter (21) and magnetic polarization apparatus (22), the one way optical activity of this magnetic polarization apparatus (22) is π/4, and correspondingly the printing opacity optical axis direction of first polarising beam splitter (21) and second polarising beam splitter (3) is at 45.

3, electrooptical modulation polarization laser stadimeter according to claim 1 is characterized in that described the 3rd polarising beam splitter (7), second polarising beam splitter (3) and first polarising beam splitter (21) all are Glan prisms.

4, electrooptical modulation polarization laser stadimeter according to claim 1, what it is characterized in that described electrode slice (5) size and transverse electric optical modulation uniaxial crystal (4) is described arbitrary identical and be attached to respectively on these two planes to relative plane.

5, electrooptical modulation polarization laser stadimeter according to claim 1, the performance that it is characterized in that described first ccd detector (8) and second ccd detector (9) is identical, and the performance of the 3rd ccd detector (12) and the 4th ccd detector (13) is identical.

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