CN102706340B - A kind of interferometric fiber optic gyroscope - Google Patents

Abstract

A kind of interferometric fiber optic gyroscope of the present invention, it comprises wide spectrum light source, source ends coupling mechanism, depolarizer before ring, ring end coupling mechanism, single-mode fiber ring, and photodetector, wherein, the output terminal of wide spectrum light source is coupled with the first port of source ends coupling mechanism by single-mode fiber, 3rd port of source ends coupling mechanism is by the coupled one end of depolarizer before single-mode fiber and ring, before ring, the other end of depolarizer is coupled by first port of single-mode fiber with ring end coupling mechanism, 3rd port of ring end coupling mechanism and the 4th port are coupled with two ports of single-mode fiber ring respectively by single-mode fiber, second port of source ends coupling mechanism is coupled with the input end of photodetector by single-mode fiber.This gyroscope arrangement eliminates the polarizer in gyroscope minimum reciprocal structure, is compensated and eliminates nonreciprocal error, thus greatly reduce cost, have lower noise and good bias instaility simultaneously by the decoherence between two polarization states and interference light intensity.

Description

A kind of interferometric fiber optic gyroscope

Technical field

The present invention relates to gyroscope field, specifically, relate to a kind of interferometric fiber optic gyroscope.

Background technology

Gyroscope is a kind of rotation sensor, for measuring the rotational angular velocity of its place carrier.Gyroscope is widely used in guidance, the field such as industry and military precision measurement of aircraft and weapon.Early stage gyroscope is mechanical gyroscope, and mechanical gyroscope is the such physical principle of trend and the orienting device that produces that utilize the turning axle of high-speed rotary body to have to keep its direction.Because mechanical gyroscope comprises movable part (such as high speed rotor), therefore, its complex structure, technological requirement are high and precision receives many-sided restriction.

In generation nineteen sixty, along with the appearance of laser, laser is utilized to develop rapidly to the research manufacturing optical gyroscope.Optical gyroscope is produced orienting device based on Sagnac effect (Sagnac effect).Specifically, in the closed light path of rotating, the light that the two bundle features sent by same light source are identical interferes along when clockwise (CW) direction and counterclockwise (CCW) direction transmission respectively, by the change of the phase differential or interference fringe that detect described two-beam, the rotational angular velocity of this closed light path just can be measured.Above-mentioned phase differential is referred to as Sagnac phase shift φ S, and it is directly proportional to the rotational angular velocity Ω of closed light path:

${\mathrm{\φ}}_S=\frac{4\mathrm{\ωA}}{c^2}\mathrm{\Ω}$ Formula (1)

Wherein, ω is the frequency of light, and c is the light velocity in vacuum, and A is the area that closed light path is enclosed.

Optical gyroscope does not have movable part, its compact conformation, highly sensitive, good reliability and the life-span long.Within 1963, first generation optical gyroscope-lasergyro is come out.The primary element of lasergyro is ring laser.Such as, lasergyro can comprise the triangular closed light path be made up of quartz, is provided with a he-ne laser tube, two catoptrons and a semitransparent mirror in this light path.The contrary laser transmitted of two bundles sent from he-ne laser tube reflects through two catoptrons respectively, then derives loop by semitransparent mirror, just can be obtained the rotational angular velocity of closed light path by the phase differential measuring this two-beam.

Within 1976, second generation optical gyroscope-fibre optic gyroscope occurs.Sensitivity and the degree of stability of fibre optic gyroscope are higher, cost and power consumption is lower and small volume.Fibre optic gyroscope is roughly divided into interferometric fiber optic gyroscope and resonant mode fibre optic gyroscope, at present, and being most widely used of interferometric fiber optic gyroscope.

In interferometric fiber optic gyroscope, the longer optical fiber of normal employing turns to multiturn coil to form closed light path.Multiturn coil is adopted to strengthen Sagnac effect.In this case, the expression formula of Sagnac phase shift φ S is:

${\mathrm{\φ}}_S=2\mathrm{\π}\frac{\mathrm{LD}}{\mathrm{\λc}}\mathrm{\Ω}$ Formula (2)

Wherein, L is the length of optical fiber, and D is fiber optic coils diameter, and λ is the wavelength of light wave.

In order to accurately measure Sagnac effect (i.e. Sagnac phase shift φ _s), ensure that described closed light path has reciprocity, namely ensure the light (calling CW light in the following text) that transmits along the clockwise direction of described closed light path and along the light (calling CCW light in the following text) that the counter clockwise direction of described closed light path is transmitted, there is identical pattern, polarization and phase delay, make CW light only relevant with the rotational angular velocity of this closed light path with the phase differential of CCW light, and irrelevant with transmission, thus improve the accuracy measured.

Fig. 1 shows the minimum reciprocal structure of interferometric fiber optic gyroscope.As shown in Figure 1, this minimum reciprocal structure comprises light source 10, source ends coupling mechanism 20, the polarizer 30, ring end coupling mechanism 40, fiber optic loop 50 and photodetector 60.Source ends coupling mechanism 20 and ring end coupling mechanism 40 can be X-coupler (i.e. four port coupler) or Y type coupling mechanism (i.e. three port coupler).Fig. 2 shows an example arrangement of X-type source ends coupling mechanism 20.As shown in Figure 2, X-type source ends coupling mechanism 20 comprises two optical fiber (first optical fiber 21 and the second optical fiber 22) leaning on very near.When light wave transmits from one end 21a of the first optical fiber 21 to the other end 21b of this optical fiber, in the coupled zone of two optical fiber, the fadout afterbody 11a of the bell basic mode 11 of this light wave extends to the fibre core of the second adjacent optical fiber 22, and optical mode is inspired in the second optical fiber 22, so, according to stiffness of coupling (distance of fibre core-fibre core) and the coupling length of described two optical fiber, the luminous power of one end 21a of the first optical fiber 21 just can be distributed between the other end 21b of the first optical fiber 21 and the other end 22b of the second optical fiber 22, preferably, described distribution ratio can be made to be 50:50(and 3dB).Similarly, from the light wave that the other end 21b of the first optical fiber 21 returns, also can one end 21a of light splitting to the first optical fiber 21 and one end 22a of the second optical fiber 22.As can be seen here, above-mentioned coupling mechanism can realize the beam splitting of light beam and again converge.

When a port of X-coupler is free end, it is just equivalent to Y type coupling mechanism.Fig. 3 a shows four ports of X-coupler, and Fig. 3 b and 3c respectively illustrates three ports closing road type Y type coupling mechanism and shunt type Y type coupling mechanism.Below with reference to Fig. 3 a-3c, Uniform Name is carried out to the port of coupling mechanism so that censure.

As shown in Figure 3 a, one end of the first optical fiber in X-coupler and the other end are called the first port one and the 3rd port 3 of this coupling mechanism, one end of the second optical fiber in X-coupler and the other end are called the second port 2 and the 4th port 4 of this coupling mechanism.As shown in Figure 3 b, the left end two-port of closing road type Y type coupling mechanism is called the first port one and second port 2 of this coupling mechanism, the right-hand member port closing road type Y type coupling mechanism is called the 3rd port 3 of this coupling mechanism.As shown in Figure 3 c, left end port of shunt type Y type coupling mechanism is called the first port one of this coupling mechanism, right-hand member two ports of shunt type Y type coupling mechanism is called the 3rd port 3 and the 4th port 4 of this coupling mechanism.

Referring again to Fig. 1, light beam of light source is after passing through the polarizer 30, CW light is divided into and CCW light transmits in fiber optic loop 50 through ring end coupling mechanism 40, this CW light and CCW light are again converged by ring end coupling mechanism 40 and are formed interference wave again after transmitting in fiber optic loop 50, and this interference wave eventually passes source ends coupling mechanism 20 and enters photodetector 60.Ring end coupling mechanism 40 has reciprocity, and the phase delay that it causes CW light and CCW light is identical.In addition, the polarizer 30 is used for carrying out polarization filtering to light wave, to ensure that CW light and CCW light have identical polarization, thus realizes polarization reciprocity.In fibre optic gyroscope, polarization maintaining optical fibre can be adopted to ensure polarization reciprocity.

Due to fiber optic loop static time CW light identical with amplitude with the phase place of CCW light, the therefore power P of interference light ₀for maximum.When fiber optic loop has rotation, the CW light of interference light power P caused by rotation and the phase difference of CCW light _sfunction P (φ _s)=P ₀(1+cos φ _s).In order to obtain high sensitivity, φ should be given _sapply a bias Δ φ, make system works near the non-vanishing point of luminous power slope: P (φ _s)=P ₀[1+cos (φ _s+ Δ φ)].For this reason, need to add phase-modulator (such as, PZT phase-modulator) in one end of fiber optic loop 50, to carry out phase-modulation to the CW light transmitted in fiber optic loop 50 and CCW light, thus make it produce phase difference φ when fiber optic loop 50 is static.Fig. 4 is the interferometric fiber optic gyroscope with reciprocity phase-modulation-demodulating equipment.In the fibre optic gyroscope shown in Fig. 4, except comprising the minimum reciprocal structure shown in Fig. 1, being also included in phase-modulator 70, the Target to enlarge device 80 increased in photodetector 60 one end that fiber optic loop 50 one end increases and providing the signal generator 90 of same modulation-demodulation signal for phase-modulator 70 and Target to enlarge device 80.

Interferometric fiber optic gyroscope needs to have divided different precision grades according to its application, and table 1 shows the technical requirement of each precision grade.

Table 1

Wherein, bias instaility is the most important technical indicator weighing interferometric fiber optic gyroscope precision.Zero partial correlation noise then comprises quantizing noise, angle random walk, speed random walk, rate ramp etc.

As mentioned above, in fibre optic gyroscope, the polarizer or had partially and protect bias can device can eliminate the nonreciprocal noise component caused of polarization, ensure good bias instaility, but also result in the raising of cost.In addition, adopt polarization maintaining optical fibre to be an effective means of the polarization reciprocity ensureing optical fibre gyro structure, but in engineer applied, polarization maintaining optical fibre gyro still exist that cost is high, polarization maintaining optical fibre to bending sensitivity to problems such as magnetic-field-sensitives.Therefore, people also been proposed depolarized scheme, adopt depolarizer and single-mode fiber to build the optical fibre gyro structure of lower cost.But in existing polarization maintaining optical fibre gyro and fiber-op-tic depolarized gyros, all will arrange the polarizer before fiber optic loop, or be provided with the Y waveguide integrated optical circuit of inclined function, these all result in the raising of cost.Such as present market price, the price of the polarizer is about 3000 yuan/, the price of Y waveguide integrated optical circuit is about 6000 yuan/, the price of polarization maintaining optical fibre is about 20 yuan/meter (and in actual gyro, the length of fiber optic loop is 100 ~ 2000 meters), the price of polarization-maintaining coupler is about 1000 ~ 2000 yuan, therefore, the cost of polarization maintaining optical fibre gyro want tens thousand of unit/, and fiber-op-tic depolarized gyros is owing to using the device such as Y waveguide, cost also up to ten thousand/.

Summary of the invention

The object of the invention is to, provide a kind of interferometric fiber optic gyroscope, this interferometric fiber optic gyroscope has very low cost and higher precision and bias instaility.

To achieve these goals, the invention provides a kind of interferometric fiber optic gyroscope, it comprises wide spectrum light source, source ends coupling mechanism, depolarizer before ring, ring end coupling mechanism, single-mode fiber ring, and photodetector, wherein, the output terminal of wide spectrum light source is coupled with the first port of source ends coupling mechanism by single-mode fiber, 3rd port of source ends coupling mechanism is by the coupled one end of depolarizer before single-mode fiber and ring, before ring, the other end of depolarizer is coupled by first port of single-mode fiber with ring end coupling mechanism, 3rd port of ring end coupling mechanism and the 4th port are coupled with two ports of single-mode fiber ring respectively by single-mode fiber, second port of source ends coupling mechanism is coupled with the input end of photodetector by single-mode fiber.

Preferably, described source ends coupling mechanism and/or described ring end coupling mechanism can be 3dB fiber coupler.

Preferably, PZT phase-modulator can be inserted with in described single-mode fiber ring.

Preferably, light source depolarizer can be inserted with at the output terminal of above-mentioned wide spectrum light source.Further preferably, described light source depolarizer can be the two-part Lyot depolarizer of polarization maintaining optical fibre making.Especially, the segment length of described two-part Lyot depolarizer can be (L ₀, 2L ₀), wherein, L ₀=L _d/ Δ n, Δ n are the refringence between the x-axis of the birefringece crystal of this polarization maintaining optical fibre and y-axis or between x ' axle and y ' axle, for the decoherence length of described wide spectrum light source, λ ₀for the centre wavelength of described wide spectrum light source, Δ λ is the spectrum width of described wide spectrum light source.

In addition, preferably, depolarizer in first ring can be inserted with at the 3rd port of described ring end coupling mechanism, and/or depolarizer in the second ring can be inserted with at the 4th port of described ring end coupling mechanism.Further preferably, before described ring, in depolarizer and/or described first ring, in depolarizer and/or described second ring, depolarizer can for the two-part Lyot depolarizer made by polarization maintaining optical fibre.

Preferably, be inserted with light source depolarizer at the output terminal of described wide spectrum light source, be inserted with depolarizer in first ring at the 3rd port of described ring end coupling mechanism, and be inserted with depolarizer in the second ring at the 4th port of described ring end coupling mechanism.Before described light source depolarizer, described ring, in depolarizer, described first ring, in depolarizer and described second ring, depolarizer is the two-part Lyot depolarizer made by polarization maintaining optical fibre.The segment length of described light source depolarizer is (L ₀, 2L ₀), before described ring, in depolarizer, described first ring, in depolarizer and described second ring, the segment length of depolarizer is taken as the one arrangement of { (1L, 2L), (4L, 8L), (16L, 32L) } respectively, L ₀be constant with L.Especially, length L meets Δ nL=Δ n ₀l _sMF+ L ₀, Δ n is the refringence between the x-axis of the birefringece crystal of the polarization maintaining optical fibre making described depolarizer and y-axis or between x ' axle and y ' axle, Δ n ₀for the specific refractivity of the birefringece crystal of described single-mode fiber ring, L _sMFfor the fiber lengths of this single-mode fiber ring, and L ₀for the first paragraph length of described two-part light source depolarizer, and

${\mathrm{\Δn}}_0=0.25n_{\mathrm{eff}}^2(P_{11}-P_{12})(1+v){\left(\frac{a}{r}\right)}^2=0.0927{\left(\frac{a}{r}\right)}^2$

N _efffor the equivalent refractive index of the optical fiber in described single-mode fiber ring, P11 and P12 is the elasto-optical coefficient of the optical fiber in described single-mode fiber ring, v is the Poisson's coefficient of the optical fiber in described single-mode fiber ring, a and r is respectively the core diameter of the optical fiber in described single-mode fiber ring and the bending radius of described single-mode fiber ring.

As mentioned above, the principle that the present invention is based on polarization error compensation breaches the restriction of optical fibre gyro minimum reciprocal structure, interferometric fiber optic gyroscope of the present invention does not need the polarizer and the inclined device of any guarantor, greatly reduce the cost of structure, the cost of its structure is lower than optical fibre gyro structures all on the market at present.Good nonreciprocal error compensation effect can be reached by depolarizer in depolarizer, ring before light source depolarizer, ring, realize higher Gyro Precision and degree of stability.

In order to realize above-mentioned and relevant object, will describe in detail and the feature particularly pointed out in the claims after one or more aspect of the present invention comprises.Explanation below and accompanying drawing describe some illustrative aspects of the present invention in detail.But what these aspects indicated is only some modes that can use in the various modes of principle of the present invention.In addition, the present invention is intended to comprise all these aspects and their equivalent.

Accompanying drawing explanation

By reference to the content below in conjunction with the description of the drawings and claims, and understand more comprehensively along with to of the present invention, other object of the present invention and result will be understood and easy to understand more.In the accompanying drawings:

Fig. 1 is the schematic diagram of the minimum reciprocal structure of interferometric fiber optic gyroscope;

Fig. 2 is the schematic diagram of an example arrangement of X-type source ends coupling mechanism;

Fig. 3 a is the schematic diagram of four ports of X-coupler;

The schematic diagram of three ports of Fig. 3 b Shi He road type Y type coupling mechanism;

Fig. 3 c is the schematic diagram of three ports of type Y type coupling mechanism along separate routes;

Fig. 4 is the schematic diagram of the interferometric fiber optic gyroscope with reciprocity phase-modulation-demodulating equipment;

Fig. 5 is the schematic diagram of the structure of interferometric fiber optic gyroscope described in one embodiment of the present of invention;

Fig. 6 is the principle schematic of Lyot depolarizer;

Fig. 7 is the structural representation of the Lyot depolarizer made by polarization maintaining optical fibre;

Fig. 8 is the schematic diagram of the approximate model structure of interferometric fiber optic gyroscope in Fig. 5;

Fig. 9 is the schematic diagram of the structure of interferometric fiber optic gyroscope described in an alternative embodiment of the invention;

Figure 10 is the time domain data figure of the gyroscope Output speed value in Fig. 9; And

Figure 11 is the error analysis figure of the gyroscope Output speed data in Fig. 9.

Embodiment

In the following description, for purposes of illustration, in order to provide the complete understanding to one or more embodiment, many details have been set forth.But, clearly, also these embodiments can be realized when there is no these details.In other example, one or more embodiment for convenience of description, known structure and equipment illustrate in block form an.

Below with reference to accompanying drawings each embodiment of the present invention is described in detail.

Fig. 5 is the schematic diagram of the structure of interferometric fiber optic gyroscope described in one embodiment of the present of invention.As shown in Figure 5, interferometric fiber optic gyroscope of the present invention comprises: depolarizer 35, ring end coupling mechanism 40, single-mode fiber ring 50 and photodetector 60 before wide spectrum light source 10, source ends coupling mechanism 20, ring.Wide spectrum light source 10 can adopt the wide spectrum light source generally adopted in interference type optical fiber gyroscope, such as, can adopt ASE wide spectrum light source, and its centre wavelength is 1550nm, and spectrum width is 40nm.The output terminal of wide spectrum light source 10 is coupled with the first port one of source ends coupling mechanism 20 by single-mode fiber.Source ends coupling mechanism 20 can be X-coupler or Y type coupling mechanism, preferably, uses the fiber coupler that splitting ratio is 50:50, i.e. 3dB fiber coupler.

3rd port 3 of source ends coupling mechanism 20 is by the coupled one end of depolarizer 35 before single-mode fiber and ring, and before ring, the other end of depolarizer 35 is coupled by first port one of single-mode fiber with ring end coupling mechanism 40.Depolarizer is a kind of device polarized light being become nonpolarized light, and specifically, depolarizer is used for a branch of linearly polarized light to become that intensity is identical, the direction of vibration vertically and mutual linearly polarized light that is superimposed of incoherent two bundles mutually.That is, the result of the two bunch polarized light non-coherent addition leached from two orthogonal polarizers respectively can be equivalent to from depolarizer light out.Depolarizer has a lot of type, the principle of the Lyot depolarizer that makes a brief explanation below.

Fig. 6 is the principle schematic of Lyot depolarizer.As shown in Figure 6, Lyot depolarizer comprises two birefringece crystals of the same race, and its thickness is respectively L and 2L, its main shaft x and x ' angle at 45 °.If the refringence that (that is to say between x ' axle and y ' axle) between the x-axis of this birefringece crystal and y-axis is Δ n, the decoherence length L of light source _dbe less than Δ nL, then light wave train A is divided into the mutually vertical and mutual incoherent wave train B of two bundles after by first crystal unevenly.Every Shu Bolie B is decomposed equably after by second piece of crystal again, finally forms four wave train C at output terminal, and the light intensity of these wave trains on two polarization directions is equal and irrelevant mutually, namely forms depolarized light.

Utilize the birefringence effect of polarization maintaining optical fibre, Lyot depolarizer can be made by two sections of polarization maintaining optical fibres.Fig. 7 shows the structure of the Lyot depolarizer made by polarization maintaining optical fibre.As shown in Figure 7, two sections of polarization maintaining optical fibres at main shaft x and x ' angle at 45 ° form Lyot depolarizer by welding, and its depolarized mechanism is identical with the depolarized mechanism of birefringece crystal.Preferably, the depolarizer adopted in the present invention can be the Lyot depolarizer made of polarization maintaining optical fibre.The cost of this depolarizer is only the cost of same length polarization maintaining optical fibre, well below the polarizer in traditional fiber gyro and the cost protecting inclined device.

Referring again to Fig. 5, the 3rd port 3 of ring end coupling mechanism 40 and the 4th port 4 are coupled with two ports of single-mode fiber ring 50 respectively by single-mode fiber.Ring end coupling mechanism 40 can be X-coupler or Y type coupling mechanism, and preferably, the splitting ratio of ring end coupling mechanism 40 is 50:50, and namely ring end coupling mechanism 40 is 3dB fiber coupler.

The expression formula of the specific refractivity of the birefringece crystal of the single-mode fiber ring 50 used in embodiments of the invention is as follows:

${\mathrm{\Δn}}_0=0.25n_{\mathrm{eff}}^2(P_{11}-P_{12})(1+v){\left(\frac{a}{r}\right)}^2=0.0927{\left(\frac{a}{r}\right)}^2$ Formula (3)

Wherein, n _efffor the equivalent refractive index (n of silica fibre _eff=0.146), P11 and P12 is the elasto-optical coefficient (P11=0.12, P12=0.27) of quartz, and v is Poisson's coefficient (v=0.16), a is optical fiber core diameter, and r is the bending radius of fiber optic loop.In this example, the fiber lengths L of single-mode fiber ring _sMF=2100m, optical fiber core diameter is a=1253 μm, and the bending radius of ring is r=7cm.

In addition, the second port 2 of source ends coupling mechanism 20 is coupled by the input end of single-mode fiber with photodetector 60.Preferably, photodetector 60 can adopt such as semiconductor PIN optical diode.

As mentioned above, before the present invention utilizes ring, depolarizer 35 replaces the polarizer 30 in existing interferometric fiber optic gyroscope, and achieves the compensation effect (will be described in detail later) of phase error, and therefore the cost of fibre optic gyroscope of the present invention greatly reduces.

Fig. 8 is the schematic diagram of the approximate model structure of interferometric fiber optic gyroscope in Fig. 5.Wherein, circulator 351 and circulator 352 make the incident light wave in respective place light path branch and return light wave along different path transmission, polarization divides the function of/bundling device (PBS/C) 353 to be: realize polarization coupling from left to right, and the incident light wave in the Liang Ge light path branch of namely transmitting from left to right is polarized x-axis and y-axis respectively and mutually exports after superposition; Realize polarization beam splitting from right to left, namely the x component in light wave that returns transmitted from right to left is exported by a port (i.e. inclined port x-axis) of PBS/C 353 left end, and the y component in this light wave is exported by another port (i.e. inclined port y-axis) of PBS/C 353 left end.Before ring in Fig. 5 the function of depolarizer 35 be just equivalent to two-way light wave in Fig. 8 by PBS/C rise respectively be biased to x-axis and y-axis after stack up, but before ring, depolarizer 35 does not have Insertion Loss, and PBS/C has Insertion Loss.Delay line 354 in Fig. 8 is used for the decoherence function of depolarizer 35 before equivalent ring, in addition, nonreciprocal error is all comprised in the testing result of photodetector 355 and photodetector 356, but the result of its summation makes error cancel out each other, thus obtaining Low Noise Stable output, this summed result is equivalent to the direct Output rusults of the photodetector 60 in Fig. 5.The result of experiment test shows, above equivalent model can simulate actual fibre optic gyroscope completely, and its bias instaility all reaches 10 ^-2degree/hour magnitude, namely reach the requirement of inert stage and Tactics-level.

Before ring, depolarizer 35 can produce two equal and separate polarization states of light intensity, and it has nonreciprocity, but eliminates the impact that brings of nonreciprocity by error compensation.Below by theoretical analysis, this point is described.

Before ring, the x direction of depolarizer 35 and y direction are played the Jones matrix of two inclined equivalent polarizers and are:

$P_x=\left[\begin{array}{cc}1& 0\\ 0& {\mathrm{\ϵ}}_1\end{array}\right]$ Formula (4)

$P_y=\left[\begin{array}{cc}{\mathrm{\ϵ}}_2& 0\\ 0& 1\end{array}\right]$ Formula (5)

Wherein, the imperfection that inclined imperfection is equivalent to depolarizer decoherence is played.Time desirable, ε ₁=ε ₂=0.

Before entering ring, the degree of polarization of the light wave of depolarizer 35 is d, and its span is ﹣ 1 ~ 1.D=﹣ 1 represents y direction linear polarization, and d=0 represents the sizes such as the amplitude in x direction and y direction, and d=1 represents x direction linear polarization.The normalization amplitude now inputting light wave is

$E_{\mathrm{IN}}=\left[\begin{array}{c}\sqrt{(1+d)/2}\\ \sqrt{(1-d)/2}\end{array}\right]$ Formula (6)

Use symbol T _cwrepresent the total transmission matrix of the light wave of clockwise transmission through coupling mechanism 35 before ring, use symbol T _ccwrepresent the total transmission matrix of the light wave of counterclockwise transmission through coupling mechanism 35 before ring, then have:

$T_{\mathrm{cw}}=\left[\begin{array}{cc}{C}_1& -C_2\\ C_3& C_4\end{array}\right]$ Formula (7)

$T_{\mathrm{ccw}}=\left[\begin{array}{cc}{C}_1& -C_3\\ C_2& C_4\end{array}\right]$ Formula (8)

Each matrix element of above-mentioned transmission matrix has following relation:

< C ₁c ₂ ^*>=< C ₃c ₄ ^*> ≠ < C ₁c ₃ ^*>=< C ₂c ₄ ^*> formula (9)

| C ₁c ₂|=| C ₃c ₄| ≠ | C ₁c ₃|=| C ₂c ₄| formula (10)

φ ₁₂=φ ₃₄≠ φ ₁₃=φ ₂₄, φ ₂₃≠ O formula (11)

Wherein, φ ₁₂, φ ₃₄, φ ₁₃, φ ₂₄, φ ₂₃be respectively < C ₁c ₂ ^*the phase place of >, < C ₃c ₄ ^*the phase place of >, < C ₁c ₃ ^*the phase place of >, < C ₂c ₄ ^*the phase place of >, < C ₂c ₃ ^*the phase place of >.The interference light wave of the incident wave of x direction polarization and the close echo formation of x direction polarization can be calculated thus:

$E_{\mathrm{CWx}}+E_{\mathrm{CCWx}}=P_x{T}_{\mathrm{cw}}{P}_x{E}_{\mathrm{IN}}{e}^{{\mathrm{i\&phi;}}_S}+P_x{T}_{\mathrm{ccw}}{P}_x{E}_{\mathrm{IN}}$ Formula (12)

The light intensity I of the interference wave of the incident wave of x direction polarization and the close echo formation of x direction polarization can be obtained further _xx=| E _cWx+ E _cCWx| ², cast out wherein irrelevant with phase place DC component and high-order a small amount of, obtain after only retaining the component relevant to interference:

$\begin{array}{c}{I}_{\mathrm{xx}}=2{\left|C_1\right|}^2(1+d){\cos \mathrm{\&phi;}}_S+{2\mathrm{\&epsiv;}}_1\sqrt{1-d^2}\left[\right|C_1{C}_3|(-{\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{13}+{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{13})\\ +\left|C_2{C}_1\right|(-{\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{12}-{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{12})]\end{array}$ Formula (13)

In like manner, the light intensity component relevant to interference that can obtain the incident wave of y direction polarization and the close echo (this is nonreciprocal composition, can bring comparatively big error) of x direction polarization is:

$\begin{array}{c}{I}_{\mathrm{yx}}=2(1-d)\left|C_2{C}_3\right|({\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{23}-{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{23})+2{\mathrm{\&epsiv;}}_2\sqrt{1-d^2}\left[\right|C_1{C}_3|(-{\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{13}\\ +{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{13})+|C_2{C}_1\left|(-{\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{12}-{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{12})\right]\end{array}$ Formula (14)

Similarly, the incident wave of y direction polarization is respectively to interfering the light intensity component relevant to interference of relevant light intensity component and the incident wave of x direction polarization and the close echo (this is nonreciprocal composition, can bring comparatively big error) of y direction polarization with the close echo of y direction polarization:

$\begin{array}{c}{I}_{\mathrm{yy}}=2{\left|C_4\right|}^2(1-d){\cos \mathrm{\&phi;}}_S+{2\mathrm{\&epsiv;}}_2\sqrt{1-d^2}\left[\right|C_4{C}_2|({\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{24}+{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{24})\\ +\left|C_3{C}_4\right|(-{\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{34}-{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{34})]\end{array}$ Formula (15)

$\begin{array}{c}{I}_{\mathrm{xy}}=2(1+d)\left|C_3{C}_2\right|({\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{23}-{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{23})+2{\mathrm{\&epsiv;}}_1\sqrt{1-d^2}\left[\right|C_4{C}_2|({\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{24}\\ +{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{24})+|C_3{C}_4\left|({\cos \mathrm{\&phi;}}_S{\cos \mathrm{\&phi;}}_{34}-{\sin \mathrm{\&phi;}}_S{\sin \mathrm{\&phi;}}_{34})\right]\end{array}$ Formula (16)

Finally, four composition I _xx, I _yx, I _xyand I _yythe form of the total light intensity of the interference light obtained after superposition can be expressed as DC component (DC) and add interference correlated components:

DC+qcos φ _s+ psin φ _s=DC+cos (φ _s-φ _err) formula (17)

The error that polarization nonreciprocity is introduced is:

${\mathrm{\&phi;}}_{\mathrm{err}}=\arctan \left(\frac{p}{q}\right)$ Formula (18)

Wherein, p=p _x+ p _y; q=q _x+ q _y

$P_x=-2(1-d)\left|C_2{C}_3\right|{\sin \mathrm{\&phi;}}_{23}+{2\mathrm{\&epsiv;}}_1\sqrt{1-d^2}\left(\right|C_1{C}_3|{\sin \mathrm{\&phi;}}_{13}-|C_1{C}_2\left|{\sin \mathrm{\&phi;}}_{12}\right)$ Formula (19)

$+{2\mathrm{\&epsiv;}}_2\sqrt{1-d^2}\left[\right|C_1{C}_3|{\sin \mathrm{\&phi;}}_{13}-|C_1{C}_2\left|{\sin \mathrm{\&phi;}}_{12}\right)]$

$P_y=2(1+d)\left|C_3{C}_2\right|{\sin \mathrm{\&phi;}}_{23}+{2\mathrm{\&epsiv;}}_2\sqrt{1-d^2}\left(\right|C_2{C}_4|{\sin \mathrm{\&phi;}}_{24}-|C_3{C}_4\left|{\sin \mathrm{\&phi;}}_{34}\right)$ Formula (20)

$+{2\mathrm{\&epsiv;}}_1\sqrt{1-d^2}\left(\right|C_2{C}_4|{\sin \mathrm{\&phi;}}_{24}-|C_3{C}_4\left|{\sin \mathrm{\&phi;}}_{34}\right)$

$q_x=2\left|{C_1|}^2(1+d){-2\mathrm{\&epsiv;}}_1\sqrt{1-d^2}\right[\left(\right|C_1{C}_3|{\sin \mathrm{\&phi;}}_{13}+|C_2{C}_1\left|{\sin \mathrm{\&phi;}}_{12}\right)$ Formula (21)

$+2(1-d)\left|C_2{C}_3\right|{\cos \mathrm{\&phi;}}_{23}-{2\mathrm{\&epsiv;}}_2\sqrt{1-d^2}\left(\right|C_1{C}_3|{\cos \mathrm{\&phi;}}_{13}+|C_2{C}_1\left|{\cos \mathrm{\&phi;}}_{12}\right)$

$q_y=2\left|{C_4|}^2(1-d){+2\mathrm{\&epsiv;}}_2\sqrt{1-d^2}\right[\left(\right|C_4{C}_2|{\sin \mathrm{\&phi;}}_{24}+|C_3{C}_4\left|{\sin \mathrm{\&phi;}}_{34}\right)$ Formula (22)

$+2(1+d)\left|C_2{C}_2\right|{\cos \mathrm{\&phi;}}_{23}+{2\mathrm{\&epsiv;}}_1\sqrt{1-d^2}\left(\right|C_4{C}_2|{\cos \mathrm{\&phi;}}_{24}+|C_3{C}_4\left|{\cos \mathrm{\&phi;}}_{34}\right)$

Obviously, p=p _x+ p _ymore be bordering on zero, then error is less.P _xand p _ysection 1 be the main source of error, item be below the single order of error in a small amount.According to formula (19) and formula (20) visible, when the miter angle of depolarizer before ring 35 is desirable, d=0, the main error of Section 1 can be offset completely, namely eliminates by the method for error compensation the impact that nonreciprocity brings.Like this, the polarizer can be saved and protect inclined device, and the error that depolarizer can be used but to eliminate nonreciprocity cause.

Fig. 9 is the schematic diagram of the structure of interferometric fiber optic gyroscope described in an alternative embodiment of the invention.As shown in Figure 9, interferometric fiber optic gyroscope of the present invention can also comprise the phase-modulator 70 be inserted in single-mode fiber ring 50.An example of phase-modulator 70 is PZT phase-modulators.Phase-modulator 70 contributes to improving the sensitivity of measuring, and its principle describes existing above, here just no longer repeats.

In addition, as shown in Figure 9, interferometric fiber optic gyroscope of the present invention can also comprise: in the first ring of the light source depolarizer 36 being inserted in the output terminal of wide spectrum light source 10 and/or the 3rd port 3 being inserted in ring end coupling mechanism 40 depolarizer 37 and/or be inserted in ring end coupling mechanism 40 the 4th port 4 the second ring in depolarizer 38.

Light source depolarizer 36, for carrying out depolarized to wide spectrum light source 10, in other words, when the miter angle of depolarizer before ring 35 is undesirable, can be undertaken depolarized to realize d=0 by light source depolarizer 36 pairs of wide spectrum light sources 10.Light source depolarizer 36 is preferably the two-part Lyot depolarizer made of polarization maintaining optical fibre, see Fig. 7.The segment length of this Lyot depolarizer is designated as (L ₀, 2L ₀), first paragraph length L ₀need to ensure Δ nL ₀be more than or equal to the decoherence length L of light source _d, second segment length is 2L ₀.Such as, L can be had ₀=L _d/ Δ n, wherein, Δ n is the refringence that (that is to say between x ' axle and y ' axle) between the x-axis of the birefringece crystal of this polarization maintaining optical fibre and y-axis, for the decoherence length of wide spectrum light source 10, here, λ ₀for the centre wavelength of wide spectrum light source 10, Δ λ is the spectrum width of wide spectrum light source 10.Such as, preferred to use ASE wide spectrum light source, its centre wavelength 1550nm, spectrum width 40nm in an example, the decoherence length that therefore can calculate light source is 34.3 μm, the first paragraph length L of light source depolarizer ₀for 6.86cm.In order to ensure depolarized effect, L can be got ₀=10cm, the total length of optical fiber that therefore light source depolarizer uses is L ₀+ 2L ₀=30cm.

In first ring, in depolarizer 37 and/or the second ring, the effect of depolarizer 38 changes coefficient C in above-mentioned transmission matrix ₁, C ₂, C ₃, C ₄, thus reduce the coherence of nonreciprocal composition, namely reduce the amplitude of interfering time error.Error compensation and error span reduction are worked in coordination and can be realized best effect.If depolarizer 35 is completely desirable before ring, so, depolarizer in ring, nonreciprocal error also can be eliminated by the method compensated completely.Preferably, before ring, in depolarizer 35 and/or described first ring, in depolarizer 37 and/or described second ring, depolarizer 38 can for the two-part Lyot depolarizer made by polarization maintaining optical fibre.

In one embodiment of the invention, as shown in Figure 9, be inserted with light source depolarizer 36 at the output terminal of wide spectrum light source 10, be inserted with depolarizer 37 in first ring at the 3rd port 3 of ring end coupling mechanism 40, and be inserted with depolarizer 38 in the second ring at the 4th port 4 of ring end coupling mechanism 40.Before light source depolarizer 36, ring, in depolarizer 35, first ring, in depolarizer 37 and the second ring, depolarizer 38 can for the two-part Lyot depolarizer made by polarization maintaining optical fibre.The segment length of light source depolarizer 36 is (L ₀, 2L ₀), L ₀for constant.Completely depolarized in order to ensure, the relation of the length demand fulfillment length multiplication of six sections of polarization maintaining optical fibres before ring in depolarizer 35, first ring in depolarizer 37 and the second ring in these three depolarizers of depolarizer 38.Preferably, the segment length of described three depolarizers is respectively the one arrangement of { (1L, 2L), (4L, 8L), (16L, 32L) }, and wherein, L is constant.That is, the segment length of these three depolarizers can be respectively (1L, 2L), (4L, 8L), (16L, 32L), and the position of these three depolarizers can exchange between two.

In the above-described embodiment, length L needs to ensure that Δ nL can offset the parasitic birefringence in single-mode fiber ring 50 completely, namely has: Δ nL>=Δ n ₀l _sMF+ L ₀, such as, Δ nL=Δ n ₀l _sMF+ L ₀, wherein, the refringence of (that is to say between x ' axle and y ' axle) between the x-axis of the birefringece crystal of the polarization maintaining optical fibre that Δ n uses for the described depolarizer of making and y-axis, Δ n ₀for the specific refractivity of the birefringece crystal of single-mode fiber ring 50, calculated by formula (3), L _sMFfor the length of single-mode fiber ring 50, L ₀for the first paragraph length of light source depolarizer 36.Such as, in an example, the length L of single-mode fiber ring 50 _sMF=2100m, core diameter is 1253 μm, and the bending radius of ring is 7cm, calculates length L=1.25+0.1=1.35m thus.In order to ensure depolarized effect, L=1.5m can be adopted.Depolarizer 35 before such ring, depolarizer 37 in first ring, in the second ring, the optical fiber total length of depolarizer 38 is respectively L+2L=4.5m, 4L+8L=18m, 16L+32L=72m.For the long L of shorter fiber optic loop _sMF, the optical fiber total length proportional reduction approx of described depolarizer.

Figure 10 shows the time domain data figure of the gyrostatic Output speed value in Fig. 9.Wherein, experiment measuring is to liking rotational-angular velocity of the earth, and on the surface level of laboratory dimension (north latitude 40.0 degree), theoretical value to be measured is 9.67 degree/hour, and data output gap is about 0.118 second, test duration length 1 hour.Visual data stable output, migration is all very little with drift.

Figure 11 shows the error analysis figure of gyrostatic Output speed data in Fig. 9.According to this figure, obtain gyro error parameter be: quantizing noise coefficient Q=8.6 × 10 ^-8rad, angle random walk bias instaility B=2.1 × 10 ^-2°/h, speed random walk K=4.9 × 10 ^-2°/h ^3/2, rate ramp B=4.5 × 10 ^-1°/h ².

In the inclined gyro of traditional guarantor and De-FOG, if remove the polarizer, its zero inclined instability can reach tens ~ up to a hundred °/h.For described complete depolarized type interferometric fiber optic gyroscope of the present invention, can according to the parameter of theoretical reasonable design four Lyot depolarizer above, thus almost Perfect ground compensates the noise that causes of nonreciprocal problem and drift, its result and have the gyroscope structure of the polarizer suitable.In addition, owing to containing circular component hardly in depolarized light, Faraday effect can reduce greatly.The drift caused due to Faraday effect can reduce greatly, and therefore, the present invention has extra advantage relative to the inclined structure of guarantor.

For complete depolarized type interferometric fiber optic gyroscope provided by the invention, four depolarizers use polarization maintaining optical fibre length altogether only to need tens meters, the price of single-mode optical-fibre coupler is lower than 50 yuan/, single-mode fiber price about 0.2 yuan/meter, if add light source and detector, gyrostatic cost of the present invention is altogether about 3000 ~ 5000 yuan/.This is relative to optical fibre gyro existing on market, and cost greatly reduces.

Although disclosed content shows exemplary embodiment of the present invention above, it should be noted that under the prerequisite not deviating from the scope of the present invention that claim limits, can multiple change and amendment be carried out.According to the structure of inventive embodiments described herein, the element of claim can substitute with the element of any function equivalent.Therefore, protection scope of the present invention should be determined by the content of appending claims.

Claims (9)

1. an interferometric fiber optic gyroscope, comprise depolarizer, ring end coupling mechanism, single-mode fiber ring and photodetector before wide spectrum light source, source ends coupling mechanism, ring, wherein, the output terminal of wide spectrum light source is coupled with the first port of source ends coupling mechanism by single-mode fiber, 3rd port of source ends coupling mechanism is by the coupled one end of depolarizer before single-mode fiber and ring, before ring, the other end of depolarizer is coupled by first port of single-mode fiber with ring end coupling mechanism, wherein

Before described ring, depolarizer carries out depolarized to the light sent from described source ends coupling mechanism, and produces two equal and separate polarization states of light intensity, is compensated eliminate nonreciprocal error by the decoherence between two polarization states and interference light intensity;

3rd port of ring end coupling mechanism and the 4th port are coupled with two ports of single-mode fiber ring respectively by single-mode fiber, and the second port of source ends coupling mechanism is coupled with the input end of photodetector by single-mode fiber; Wherein,

Be inserted with depolarizer in first ring at the 3rd port of described ring end coupling mechanism, and be inserted with depolarizer in the second ring at the 4th port of described ring end coupling mechanism; Before light source depolarizer, described ring, in depolarizer, described first ring, in depolarizer and described second ring, depolarizer is the two-part Lyot depolarizer made by polarization maintaining optical fibre; And the segment length of described light source depolarizer is (L ₀, 2L ₀), before described ring, in depolarizer, described first ring, in depolarizer and described second ring, the segment length of depolarizer is taken as { (1L, 2L) respectively, (4L, 8L), (16L, any one arrangement 32L) } in six kinds of fully intermeshing carrying out of three groups of data, wherein, L ₀be constant with L.

2. interferometric fiber optic gyroscope according to claim 1, wherein, described source ends coupling mechanism and/or described ring end coupling mechanism are 3dB fiber coupler.

3. interferometric fiber optic gyroscope according to claim 1, wherein, is inserted with PZT phase-modulator in described single-mode fiber ring.

4. the interferometric fiber optic gyroscope according to claim 1 or 3, wherein, is inserted with light source depolarizer at the output terminal of described wide spectrum light source.

5. interferometric fiber optic gyroscope according to claim 4, wherein, described light source depolarizer is the two-part Lyot depolarizer that polarization maintaining optical fibre makes.

6. interferometric fiber optic gyroscope according to claim 5, wherein, the segment length of described two-part Lyot depolarizer is (L ₀, 2L ₀), wherein, L ₀=L _d/ Δ n, Δ n are the refringence between the x-axis of the birefringece crystal of this polarization maintaining optical fibre and y-axis or between x ' axle and y ' axle, for the decoherence length of described wide spectrum light source, λ ₀for the centre wavelength of described wide spectrum light source, Δ λ is the spectrum width of described wide spectrum light source.

7. the interferometric fiber optic gyroscope according to claim 1 or 3, wherein, is inserted with depolarizer in first ring at the 3rd port of described ring end coupling mechanism, or is inserted with depolarizer in the second ring at the 4th port of described ring end coupling mechanism.

8. interferometric fiber optic gyroscope according to claim 7, wherein, before described ring, in depolarizer or described first ring, in depolarizer or described second ring, depolarizer is the two-part Lyot depolarizer made by polarization maintaining optical fibre.

9. interferometric fiber optic gyroscope according to claim 1, wherein, length L meets Δ nL=Δ n ₀l _sMF+ L ₀, the refringence between the x-axis of the birefringece crystal of the polarization maintaining optical fibre that Δ n uses for the described depolarizer of making and y-axis or between x ' axle and y ' axle, Δ n ₀for the specific refractivity of the birefringece crystal of described single-mode fiber ring, L _sMFfor the fiber lengths of described single-mode fiber ring, and L ₀for the first paragraph length of described two-part light source depolarizer, and

$\mathrm{\&Delta;}{n}_0=0.25n_{\mathrm{eff}}^2(P_{11}-P_{12})(1+v){\left(\frac{a}{r}\right)}^2=0.0927{\left(\frac{a}{r}\right)}^2$

N _efffor the equivalent refractive index of the optical fiber in described single-mode fiber ring, P11 and P12 is the elasto-optical coefficient of the optical fiber in described single-mode fiber ring, ν is the Poisson's coefficient of the optical fiber in described single-mode fiber ring, a and r is respectively the core diameter of the optical fiber in described single-mode fiber ring and the bending radius of described single-mode fiber ring.