CN100476387C - System for detecting polarization maintaining optical fiber beat length - Google Patents

Abstract

The present invention discloses a detection system for detecting beat length of polarization-holding optic fibre. Said system includes the following several portions: wide-spectrum light source, fibre polarizer, Michelson interferometer, photoelectric detector, preamplification circuit, phase-locked amplifier, signal generator, computer and beat length detection device, etc. Besides, said invention also provides the working principle of said detection system and its operation method and steps.

Description

A kind of detection system to beat length of polarization maintaining optical fiber

Technical field

The present invention relates to a kind of long detection system of bat that is used to measure tested polarization maintaining optical fibre, this is clapped long detection system and is made up of hardware components and software section.

Background technology

Polarization maintaining optical fibre is to utilize the structural birefringence of waveguide or stress birefrin to realize what polarization kept.Extensively adopt stress application to realize birefringence now, promptly utilized a kind of thermal expansivity in optical fiber, to produce stress than quartzy big additional materials.When making the stress type polarization maintaining optical fibre, preform is to make by the both sides that the quartz pushrod of two high-concentration dopants (adopting boron, phosphorus or aluminium usually) are placed on the core district.Drawing optic fibre at high temperature, optical fiber pulls into these two highly doped rods of back and shrinks when cooling, but their thermal shrinking quantity is subjected to quartzy influence on every side, highly doped rod is under the pressure, the core region that makes light propagate the place by retroaction produces stress and exists an action of pulling stress along the axle of two highly doped rods, and this axle generally is called slow axis; And existing an action of compressive stress along the axle of quadrature with it, this axle generally is called fast axle.Fig. 1 is the sectional drawing of three kinds of polarization maintaining optical fibres commonly used, and 101 is the stressed zone among the figure, and 102 is fiber cores, and 103 is common covering.In " panda " type optical fiber of Fig. 1 (A), highly doped rod is round; In " knot " type optical fiber of Fig. 1 (B), highly doped regional shape resembles knot; In " ellipse " type optical fiber of Fig. 1 (C), the stress covering is oval.Because the stress of different directions is different, cause the equivalent refractive index n of profile of optic fibre directions X _EqxEquivalent refractive index n with the Y direction _EqyProduced equivalent refraction rate variance Δ n _b=n _Eqx-n _EqyIts directions X transmission is ${\mathrm{\β}}_x=\frac{2\mathrm{\π}{n}_{\mathrm{eqx}}}{\mathrm{\λ}},$ Y direction transmission is ${\mathrm{\β}}_y=\frac{2\mathrm{\π}{n}_{\mathrm{eqy}}}{\mathrm{\λ}},$ λ is the centre wavelength of the light wave that sends of light source.When this Shu Guang propagates, will evoke two transmission β in polarization maintaining optical fibre _xAnd β _yCommunication mode, when they transmit in optical fiber, because transmission is different, increase along with transmission range, its phase differential will increase, when the optical path difference of this phase differential correspondence during greater than the coherent length of used light source, these two patterns will lose the interference contrast, and this moment, corresponding Transmission Fibers length was defined as interferometer decoherence length.This optical path difference that is produced by the transmission difference will have influence on the application prospect of polarization maintaining optical fibre in optical-fibre communications and optical fiber sensing system.

Clap the long synchronous HE that is coupled into polarization maintaining optical fibre that is meant ₁₁ ^XMould and HE ₁₁ ^YWhen the phase difference variable of mould is 2 π, the distance that light is propagated in optical fiber $L_B=\frac{2\mathrm{\π}}{{\mathrm{\β}}_x-{\mathrm{\β}}_y},$ β x, β y are the propagation constant of pairwise orthogonal polarization mode.

Clap the important parameter that the polarization maintaining optical fibre mode birefringence is weighed in long conduct, because the variation of the kind of polarization maintaining optical fibre and size brings great difficulty for the measurement of clapping length, and all there are some problems in original measuring method.At present, the measuring method of polarization maintaining optical fibre mainly contains three kinds:

1.kaminow I P Polarization in Optical Fibers IEEE J QuantumElectronics.1981; 17 (1); The measuring principle of disclosed Rayleigh scattering method (X is in 150～220 papers, and tested optical fiber is advanced in the optically-coupled that high power laser sends, and measures bat length by observing the spacing bright, dark fringe that the cycle changes on the tested optical fiber.Though this kind method equipment is simple, and is convenient and easy, can only measure visible light, and owing to be range estimation, spatial resolution is low.

2.Takada K.precision Measurement of model Birefringence of HighlyBirefringent Fibers by periodic lateral Force.Appl optics.1985; 24 (24); Disclosed in 4387～4391 papers is the dynamic pressure method, and this method external force in addition periodically on tested optical fiber makes external force move along fiber axis and makes the cyclical variation of output polarization state, claps long thereby measure optical fiber.The method equipment needed thereby is simple, but measurement result is relevant with the optical fiber laying state, so measuring accuracy is not high.

3. disclosed in the Magnetooptic Modulation measuring light communication technology Vol.21 No.1 paper of peaceful ancient cooking vessel Polarization Maintaining Optical Fiber Beat length is Magnetooptic Modulation, this method is that alternating magnetic field is moved along fiber axis, because the Faraday effect of fiber optic materials makes the output polarization state of light be cyclical variation, it is long that the one-period of this variation is the bat of optical fiber.The method surveying instrument cost is low, and measuring method is simple, but the long minimum value of the bat of institute's energy measurement be subjected to add the influence of magnetic field magnetic gap width.

Summary of the invention

The purpose of this invention is to provide a kind of detection system long to the bat of polarization maintaining optical fibre, the long detection system of this bat is handled by the interference light intensity signal of gathering is carried out the rectangular scanning method, extract two peak values of interference signal, thereby obtain the compensation optical path difference corresponding and measure the range information that mirror moves, and the centre wavelength of the light wave that sends according to described displacement, polarization maintaining optical fibre length to be measured and wide spectrum light source calculates the bat long value of polarization maintaining optical fibre to be measured with peak value.

A kind of detection system of the present invention to beat length of polarization maintaining optical fiber, comprise computing machine and be stored in the computing machine interior long pick-up unit of bat, wide spectrum light source, the optical fiber polarizer, photodetector, Michelson interferometer, signal generator and lock-in amplifier that the long pick-up unit of described bat comprises data acquisition unit, peak picking unit and claps the long unit that resolves;

Described Michelson interferometer comprises coupled lens, analyzer, spectroscope, reference mirror and measurement mirror, coupled lens, analyzer, spectroscope, reference mirror and measurement mirror are installed in respectively on the erecting bed, erecting bed is provided with line slideway translation stage, universal stage and support, measuring mirror is installed on the line slideway translation stage, analyzer is installed on the universal stage, and coupled lens, spectroscope and reference mirror are separately fixed on separately the support; The back fixation of reference mirror has piezoelectric ceramic actuator;

Be connected with A/D capture card and gpib interface card on the described computing machine, be connected with on the A/D capture card and be used for preceding discharge road that the light intensity signal of photodetector output is handled, be connected with lock-in amplifier on the gpib interface card, be connected with on the RS232 serial ports A of computing machine and be used to drive the motor of measuring the line slideway translation stage that mirror moves horizontally, be connected with the motor of the universal stage that is used to drive the analyzer rotation on another RS232 serial ports B of computing machine;

Wide spectrum light source and the optical fiber polarizer adopt optical fiber to be connected, and the tail optical fiber of wide spectrum light source and the optical fiber polarizer go into fine single mode welding, an end of the tail optical fiber of the optical fiber polarizer and polarization maintaining optical fibre to be measured is 45 ° of weldings;

The light that is penetrated by wide spectrum light source enters the optical fiber polarizer after polarization maintaining optical fibre to be measured incides in the Michelson interferometer, after photodetector receives the light wave of Michelson interferometer output, and the output intensity signal was given preceding discharge road after it was carried out the interference signal conversion processing of light wave, the output intensity voltage signal was given lock-in amplifier after the current/voltage conversion process was carried out to described light intensity signal in the preceding road of discharging, and lock-in amplifier carries out exporting modulation signal to the long pick-up unit of bat in the computing machine after the demodulation process to the described optical intensity voltage signal of reception with by the sinusoidal wave pulse that signal generator is exported; The motor of line slideway translation stage drives described measurement mirror and moves after receiving by the drive signal of computing machine output, and moving distance information is fed back to the long pick-up unit of bat in the computing machine; The long pick-up unit of described bat resolves to the described modulation signal that receives and described moving distance information that to handle the bat that obtains polarization maintaining optical fibre to be measured long.

The long detection system of the bat of described polarization maintaining optical fibre, it is clapped long pick-up unit and the described modulation signal that receives and described moving distance information is resolved to handle be to obtain and store the interference light intensity signal V of lock-in amplifier output and the displacement signal Z of measurement mirror according to (A) in data acquisition unit; (B) in the peak picking unit, adopt the rectangular scanning method that the interference light intensity signal in the described data acquisition unit is carried out peak picking, obtain the secondary peak of interference light intensity signal and the alternate position spike Z=Z of main peak ₁-Z ₀, Z ₁The position of expression time peak-to-peak value correspondence, Z ₀The position of expression main peak peak value; (C) clapping the long long formula of employing bat in the unit of resolving $L_B=\frac{\mathrm{\λl}}{2Z}$ Calculate the bat long value that obtains polarization maintaining optical fibre to be measured, λ represents the centre wavelength of the light wave that wide spectrum light source sends, and l represents the length of polarization maintaining optical fibre to be measured, and Z represents the alternate position spike of the secondary peak and the main peak of interference light intensity signal.

The advantage that the present invention claps long detection system is: (1) the present invention adopts rectangular scanning to the picking up of peak value, and the peak value after picking up merged with compensation optical path difference information resolves, and has improved effectively and has clapped long measuring accuracy (reaching 0.01mm); (2) the present invention adopts modulation-demodulation technique to reduce the influence to signal of various noises and environment, signal to noise ratio (S/N ratio) height; (3) precise guide rail of the present invention is by driven by servomotor, and the vibration noise in measuring the mirror moving process is little, measuring speed is high; (4) reference mirror adopts prism of corner cube with measuring mirror, guarantees the parallel after reflection outgoing of incident ray on it; (5) simple, all types polarization maintaining optical fibre of measuring method of the present invention all can be measured.

Description of drawings

Fig. 1 is the sectional drawing of polarization maintaining optical fibre.

Fig. 2 is the structured flowchart that the present invention claps long detection system.

Fig. 3 is the annexation synoptic diagram of computing machine and part hardware.

Fig. 4 is the schematic diagram on preceding discharge road.

Fig. 5 is the schematic diagram of power-switching circuit.

Fig. 6 is the pick up curve map of rectangular scanning of the present invention to peak value.

Fig. 7 is the interference signal figure that the present invention detects acquisition.

Fig. 8 is the interface synoptic diagram that the present invention claps long pick-up unit.

Fig. 9 is that peak signal of the present invention is picked up process flow diagram.

Among the figure: 1. the wide spectrum light source 2. optical fiber polarizers 3. polarization maintaining optical fibre 4. coupled lens 5. analyzers 6. spectroscopes 7. reference mirrors 8. to be measured are measured mirror 9. photodetectors 10. piezoelectric ceramic actuators 11. preceding discharge road 12. signal generators, 13. lock-in amplifiers, 14. computing machines

Embodiment

The present invention is described in further detail below in conjunction with accompanying drawing.

See also shown in Figure 2, the present invention is a kind of detection system to beat length of polarization maintaining optical fiber, is made up of wide spectrum light source 1, the optical fiber polarizer 2, photodetector 9, Michelson interferometer, signal generator 12, lock-in amplifier 13, computing machine and the long pick-up unit of bat that is stored in the computing machine.Described Michelson interferometer comprises coupled lens 4, analyzer 5, spectroscope 6, reference mirror 7 and measures mirror 8, the light path of these five mirrors is closed: (A) light through coupled lens 4 couplings incides on the analyzer 5, incides on the spectroscope 6 through the light behind the analyzer 5; (B) incide transmittance on the spectroscope 6 to reference mirror 7, the light of reference mirror 7 reflected backs reflexes on the photosurface of photodetector 9 through spectroscope 6; (C) light that incides on the spectroscope 6 reflexes on the measurement mirror 8, and the light of measuring mirror 8 reflected backs is transmitted on the photosurface of photodetector 9 through spectroscope 6; This two-beam is vertical with the photosurface of photodetector 9, photodetector 9 output is that (spectroscope 6 is located at the center for the interference light intensity signal of this two-beam, analyzer 5 is placed in the dead ahead of spectroscope 6, coupled lens 4 is placed in the back of analyzer 5, the top of spectroscope 6 is placed and is measured mirror 8, reference mirror 7 is placed in the dead astern of spectroscope 6, and coupled lens 4, analyzer 5, spectroscope 6 and reference mirror 7 are placed on the same horizontal line, measures mirror 8 and spectroscope 6).These five mirrors are installed in respectively on the erecting bed, erecting bed is provided with line slideway translation stage, universal stage and support, measuring mirror 8 is installed on the line slideway translation stage model TSA200 platform of Chinese light (employing stand upright), analyzer 5 is installed on the universal stage automatically controlled universal stage of RSA of Chinese light (employing stand upright), and coupled lens 4, spectroscope 6 and reference mirror 7 these three mirrors are separately fixed on separately the support.The back fixation of reference mirror 7 has piezoelectric ceramics (brilliant rich electronics corporation produces, and model is XZT 500G), and the sine wave of signal generator 12 outputs is used to control the driving output of piezoelectric ceramics.

See also shown in Figure 3, be connected with A/D capture card and gpib interface card on the described computing machine, be connected with on the A/D capture card and be used for preceding discharge road 11 that the light intensity signal of photodetector 9 output is handled, be connected with lock-in amplifier 13 on the gpib interface card, be connected with on the RS232 serial ports A of computing machine and be used to drive the motor of measuring the line slideway translation stage that mirror 8 moves horizontally, be connected with the motor of the universal stage that is used to drive analyzer 5 rotations on another RS232 serial ports B of computing machine.

In the present invention, the input end on preceding discharge road 11 receives the light intensity signal by photodetector 9 outputs, the capacitor C 4 of carrying out light intensity signal output voltage signal after the first low noise operational amplifier A1 carries out the current/voltage conversion process exporting to after voltage amplification is handled for the second low noise operational amplifier A2 to be connected between lock-in amplifier 13, the first low noise operational amplifier A1 and the second low noise operational amplifier A2 plays the AC coupling to input signal.Preceding discharge road 11 is amplification feeble signal circuit of a routine, and its circuit principle structure as shown in Figure 4.For the present invention control provide-5V ,+5V ,+circuit of 1.5V electric signal is conventional power-switching circuit structure, as shown in Figure 5, so locate not elaborate.

In the long detection system of bat of the present invention, wide spectrum light source 1 is connected with the optical fiber polarizer 2 employing optical fiber, and the tail optical fiber of wide spectrum light source 1 and the optical fiber polarizer 2 go into fine single mode welding, an end of the tail optical fiber of the optical fiber polarizer 2 and polarization maintaining optical fibre to be measured is 45 ° of weldings.The light that is penetrated by wide spectrum light source 1 enters the optical fiber polarizer 2 after polarization maintaining optical fibre to be measured 3 incides in the Michelson interferometer, after photodetector 9 receives the light wave of Michelson interferometer output, and to discharge road 11 before the output intensity signal is exported to after its interference signal conversion processing through carrying out light wave, before the described light intensity signal of the discharge 11 pairs of receptions in road carry out after the current/voltage conversion process output intensity voltage signal and give lock-in amplifier 13, the described optical intensity voltage signal of 13 pairs of receptions of lock-in amplifier and carry out output modulation signal after the demodulation process by the sinusoidal wave pulse of signal generator 12 outputs and give the long pick-up unit of bat in the computing machine 14; The motor of line slideway translation stage drives described measurement mirror 8 and moves after receiving by the drive signal of computing machine output, and moving distance information is fed back to the long pick-up unit of bat in the computing machine 14; The long pick-up unit of described bat resolves to the described modulation signal that receives and described moving distance information that to handle the bat that obtains polarization maintaining optical fibre 3 to be measured long.

In the present invention, clapping long pick-up unit comprises data acquisition unit, peak picking unit and claps the long unit that resolves.The long pick-up unit of described bat resolves to the described modulation signal that receives and described moving distance information that to handle be foundation:

(A) obtain and store the interference light intensity signal V of lock-in amplifier 13 outputs and the displacement signal Z of measurement mirror 8 in the data acquisition unit.

(B) in the peak picking unit, adopt the rectangular scanning method that the interference light intensity signal in the described data acquisition unit is carried out peak picking, obtain the secondary peak of interference light intensity signal and the alternate position spike Z=Z of main peak ₁-Z ₀, Z ₁The position of expression time peak-to-peak value correspondence, Z ₀The position of expression main peak peak value.

The peak picking curve as shown in Figure 6, among the figure, mobile search rectangle method is the pick-up method to data local peaking, it is simple, efficient is high, the peak picking instrument of famous data processing software Origin just is based on this algorithm.This method is by setting the rectangle width W and judge height H, search data maximal value in the scope of rectangle width W, when this maximal value all greater than the data value of rectangle two ends correspondence, and when judging height H, think that this value is a data local peaking.By constantly moving this rectangle, just can detect the local peaking of different pieces of information section then.Because comprised many small peaks in the envelope diagram of interference signal, search parameter is incorrect, probably these small peaks is found, and in the present invention, the inventor chooses the peak value of an envelope diagram and imports as parameter.Therefore, in X arrived between the rectangle region of X+W, the maximal value of data was P1, and in X+W arrived between the rectangle region of X+2W, the maximal value of data was P2, and in X+2W arrived between the rectangle region of X+3W, the maximal value of data was P3.Preset height is H.The corresponding data value in X place is a, the corresponding data value in X+W place is b, at first between the rectangle region of X+W, search data maximal value P1 at X, if P1＞a, P1＞b and P1＞H, then P1 is the peak value of this data segment, in like manner can search the peak value P2 of X+2W to X+3W, and X+2W is to the peak value P3 of X+3W.As seen, because that width W and height H are chosen is different, may search a plurality of signal peaks, and for clapping the long data that detect, signal envelope peak value P2 is only and needs, and therefore will constantly change width W and height H is searched for.

(C) clapping the long long formula of employing bat in the unit of resolving $L_B=\frac{\mathrm{\λl}}{2Z}$ Calculate the bat long value that obtains polarization maintaining optical fibre 3 to be measured, λ represents the centre wavelength of the light wave that wide spectrum light source 1 sends, and l represents the length of polarization maintaining optical fibre 3 to be measured, and Z represents the alternate position spike of the secondary peak and the main peak of interference light intensity signal.

See also shown in Figure 8, in the present invention, be stored in the long continuous coverage interface of bat (software section) in the computing machine be used for to the hardware components of the long detection system of bat of the present invention's design gather in real time, measure, control, resolve, the demodulation process of correlativity such as output.

In the present invention, clap long pick-up unit and carry out peak value and pick up mode automatically for (seeing also shown in Figure 9): by continuous change rectangle width W with judge height H, the data peak value is searched for.Will search a series of peak values at every turn, when a series of peak values that search satisfy following condition, think that these peak values are peak values of clapping long detection signal envelope diagram.The peak point number of search equals desired number, can tentatively get rid of inappropriate Search Results by this condition.A series of peak values of search are about the peak-peak symmetry.This condition utilizes the symmetry of interference signal further to get rid of asymmetric Search Results.Distance between the peak value that searches is greater than the white light source coherent length.This condition shows, when main peak and time peak separation during less than the white light source coherent length, because the light intensity stack, its peak point can not be asked for exactly.This condition has also been got rid of the situation that searches near the small peak of main peak value simultaneously.Show that by experiment this method can be automatic accurate searches multiple coupled some interference data peak value.

In the present invention, the angle of polarization maintaining optical fibre 3 stress axiss to be measured and the optical fiber polarizer 2 and analyzer 4 is respectively α, β, and the amplitude that incident light passes the optical fiber polarizer 2 is E _A, the component that passes behind the polarization maintaining optical fibre 3 to be measured is:

$\left\{\begin{array}{c}{E}_S=E_A\cos \mathrm{\α}\\ E_F=E_A\sin \mathrm{\α}\·e^{j{\mathrm{\δ}}_f}\end{array}\right.\text{---}\left(1\right)$

E _SRepresent the amplitude on the slow axis of polarization maintaining optical fibre 3 to be measured, E _FRepresent the amplitude on the fast axle of polarization maintaining optical fibre 3 to be measured, δ _fRepresent the phase differential after two polarization modes transmit in polarization maintaining optical fibre 3 to be measured.

Light is by behind the analyzer 4, two components the projection that sees through direction and be:

$E_B=(\sin \mathrm{\α}\sin \mathrm{\β}\·e^{j{\mathrm{\δ}}_f}+\cos \mathrm{\α}\cos \mathrm{\β})\·E_A---\left(2\right)$

During test, set α=β=45 °, then following formula is:

$E_B=\frac{1}{2}(e^{j{\mathrm{\δ}}_f}+1)\·E_A---\left(3\right)$

Light is injected the measurement mirror 8 and the reference mirror 7 of Michelson interferometer respectively through spectroscope 6.If reference mirror 7 is Z with the alternate position spike of measuring mirror 8, then be from reference mirror 7 and the light wave electric field that measurement mirror 8 reflexes to photodetector 9:

$E_D=\frac{1}{2}(E_B+E_B\·e^{j{\mathrm{\δ}}_m})---\left(4\right)$

δ _mThe compensation of phase that expression is introduced by Michelson interferometer,

Then the light intensity of photodetector 9 receptions is:

$I=\frac{{\mathrm{<figure-callout\; id="2"\; label="E\; A"\; filenames="C20061000828400131.png,C20061000828400142.png"\; state="\{\{state\}\}">E</figure-callout>}}_A^{}}{8}\&CenterDot;(2+2\cos \left({\mathrm{\&delta;}}_f\right)+2\cos \left({\mathrm{\&delta;}}_m\right)+$

(5)

$({\mathrm{\&delta;}}_f+{\mathrm{\&delta;}}_m)\text{+cos}({\text{\&delta;}}_f-{\mathrm{\&delta;}}_m))$

In above-mentioned derivation, do not consider the influence of light source spectrum width, in this system, adopted the SLD light source of wide range, establishing its coherence function is γ (δ), then following formula should be rewritten as:

$I=\frac{{\mathrm{<figure-callout\; id="2"\; label="E\; A"\; filenames="C20061000828400131.png,C20061000828400142.png"\; state="\{\{state\}\}">E</figure-callout>}}_A^{}}{8}\&CenterDot;(2+2\mathrm{\&gamma;}\left({\mathrm{\&delta;}}_f\right)\&CenterDot;\cos \left({\mathrm{\&delta;}}_f\right)+2\mathrm{\&gamma;}\left({\mathrm{\&delta;}}_m\right)\&CenterDot;\cos \left({\mathrm{\&delta;}}_m\right)+$

(6)

$\mathrm{\&gamma;}({\mathrm{\&delta;}}_f+{\mathrm{\&delta;}}_m)\&CenterDot;\cos ({\mathrm{\&delta;}}_f+{\mathrm{\&delta;}}_m)+\mathrm{\&gamma;}({\mathrm{\&delta;}}_f-{\mathrm{\&delta;}}_m)\&CenterDot;\cos ({\mathrm{\&delta;}}_f-{\mathrm{\&delta;}}_m))$

Because l when test _f＞＞l _d, l _dThe decoherence length of expression wide spectrum light source 1, so γ (δ _f)=0, then following formula should be rewritten as:

$I=\frac{{\mathrm{<figure-callout\; id="2"\; label="E\; A"\; filenames="C20061000828400131.png,C20061000828400142.png"\; state="\{\{state\}\}">E</figure-callout>}}_A^{}}{8}\&CenterDot;(2+2\mathrm{\&gamma;}\left({\mathrm{\&delta;}}_m\right)\&CenterDot;\cos \left({\mathrm{\&delta;}}_m\right)+\mathrm{\&gamma;}({\mathrm{\&delta;}}_f+{\mathrm{\&delta;}}_m)\&CenterDot;\cos ({\mathrm{\&delta;}}_f+{\mathrm{\&delta;}}_m)+$

(7)

$\mathrm{\&gamma;}({\mathrm{\&delta;}}_f-{\mathrm{\&delta;}}_m)\&CenterDot;\cos ({\mathrm{\&delta;}}_f-{\mathrm{\&delta;}}_m))$

δ when Michelson interferometer two arms equate _m=0 occurs interfering main peak, comes compensation of phase difference δ by traverse measurement mirror 8 _f, promptly | δ _m|=| δ _f|, in the symmetria bilateralis of main peak interference peaks appears two times, as shown in Figure 7.

The distance and position difference Z that obtains main peak and arbitrary secondary peak by peak picking calculates by following formula and claps length

$L_B=\frac{\mathrm{\&lambda;l}}{2Z}---\left(8\right)$

L is the length of polarization maintaining optical fibre 3 to be measured in the formula, and Z is that the secondary peak and the distance and position between the main peak of interference light intensity signal is poor, and λ is the centre wavelength of the light wave that sends of wide spectrum light source 1.

Claims (3)

1, a kind of detection system to beat length of polarization maintaining optical fiber, comprise computing machine, wide spectrum light source (1), the optical fiber polarizer (2), photodetector (9), Michelson interferometer, signal generator (12), lock-in amplifier (13), it is characterized in that: also comprise the long pick-up unit of bat that is stored in the computing machine; The long pick-up unit of described bat comprises data acquisition unit, peak picking unit and claps the long unit that resolves;

Described Michelson interferometer comprises coupled lens (4), analyzer (5), spectroscope (6), reference mirror (7) and measures mirror (8), coupled lens (4), analyzer (5), spectroscope (6), reference mirror (7) and measurement mirror (8) are installed in respectively on the erecting bed, erecting bed is provided with line slideway translation stage, universal stage and support, measuring mirror (8) is installed on the line slideway translation stage, analyzer (5) is installed on the universal stage, and coupled lens (4), spectroscope (6) and reference mirror (7) are separately fixed on separately the support; The back fixation of reference mirror (7) has piezoelectric ceramic actuator (10);

Be connected with A/D capture card and gpib interface card on the described computing machine, be connected with on the A/D capture card and be used for preceding discharge road (11) that the light intensity signal of photodetector (9) output is handled, be connected with lock-in amplifier (13) on the gpib interface card, be connected with the motor that is used for drive measuring the line slideway translation stage that mirror (8) moves horizontally on the RS232 serial ports A of computing machine, be connected with the motor of the universal stage that is used to drive analyzer (5) rotation on another RS232 serial ports B of computing machine;

Wide spectrum light source (1) and the optical fiber polarizer (2) adopt optical fiber to be connected, and the tail optical fiber of wide spectrum light source (1) and the optical fiber polarizer (2) go into fine single mode welding, the tail optical fiber of the optical fiber polarizer (2) and an end of polarization maintaining optical fibre to be measured are 45 ° of weldings;

The light that is penetrated by wide spectrum light source (1) enters the optical fiber polarizer (2) after polarization maintaining optical fibre to be measured (3) incides in the Michelson interferometer, after photodetector (9) receives the light wave of Michelson interferometer output, and the output intensity signal was given preceding discharge road (11) after it was carried out the interference signal conversion processing of light wave, the output intensity voltage signal was given lock-in amplifier (13) after the current/voltage conversion process was carried out to described light intensity signal in the preceding road (11) of discharging, and lock-in amplifier (13) carries out exporting modulation signal to the long pick-up unit of bat in the computing machine (14) after the demodulation process to the described optical intensity voltage signal of reception with by the sinusoidal wave pulse that signal generator (12) is exported; The motor of line slideway translation stage drives described measurement mirror (8) and moves after receiving by the drive signal of computing machine output, and moving distance information is fed back to the long pick-up unit of bat in the computing machine (14); The long pick-up unit of described bat resolves to the described modulation signal that receives and described moving distance information that to handle the bat that obtains polarization maintaining optical fibre to be measured (3) long;

The long pick-up unit of described bat resolves to the described modulation signal that receives and described moving distance information that to handle be to obtain and store the interference light intensity signal V of lock-in amplifier (13) output and the displacement signal Z of measurement mirror (8) according to (A) in data acquisition unit; (B) in the peak picking unit, adopt mobile search rectangle method that the interference light intensity signal in the described data acquisition unit is carried out peak picking, obtain the secondary peak of interference light intensity signal and the alternate position spike Z=Z of main peak ₁-Z ₀, Z ₁The position of expression time peak-to-peak value correspondence, Z ₀The position of expression main peak peak value; (C) clapping the long long formula of employing bat in the unit of resolving $L_B=\frac{\mathrm{\&lambda;l}}{2Z}$ Calculate the bat long value that obtains polarization maintaining optical fibre to be measured (3), λ represents the centre wavelength of the light wave that wide spectrum light source (1) sends, and l represents the length of polarization maintaining optical fibre to be measured (3), and Z represents the alternate position spike of the secondary peak and the main peak of interference light intensity signal.

2, a kind of detection system according to claim 1 to beat length of polarization maintaining optical fiber, it is characterized in that: the light path of described Michelson interferometer is closed and is: (A) light through coupled lens (4) coupling incides on the analyzer (5), incides on the spectroscope (6) through the light behind the analyzer (5); (B) transmittance of inciding on the spectroscope (6) is arrived on the reference mirror (7), and the light of reference mirror (7) reflected back reflexes on the photosurface of photodetector (9) through spectroscope (6); (C) light that incides on the spectroscope (6) reflexes on the measurement mirror (8), and the light of measuring mirror (8) reflected back is transmitted on the photosurface of photodetector (9) through spectroscope (6).

3, a kind of detection system according to claim 1 to beat length of polarization maintaining optical fiber, it is characterized in that: the input end on discharge road (11) receives the light intensity signal by photodetector (9) output before described, light intensity signal output voltage signal after first low noise operational amplifier (A1) carries out the current/voltage conversion process carries out exporting to lock-in amplifier (13) after voltage amplification is handled for second low noise operational amplifier (A2), is connected electric capacity (C4) between first low noise operational amplifier (A1) and second low noise operational amplifier (A2) and plays AC coupling to input signal.

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