CN103743392A - Gyroscope with single coupling device and dual-polarization optical fiber - Google Patents

Abstract

The invention provides a gyroscope with a single coupling device and a dual-polarization optical fiber. The gyroscope comprises a wide-spectrum light source, a polarization maintaining optical fiber, the coupling device, a polarization maintaining optical fiber ring and a photoelectric detector, wherein the output end of the wide spectrum light source is connected with the polarization maintaining optical fiber by a single-mode optical fiber; the polarization maintaining optical fiber is divided into two sections which are welded at a rotary angle of 45 degrees; the other end of the polarization maintaining optical fiber is connected with a first port of the coupling device; a third port and a fourth port of the coupling device are respectively coupled with two ports of the polarization maintaining optical fiber ring by single-mode optical fibers; a second port of the coupling device is coupled with the input end of the photoelectric detector by a single-mode optical fiber. According to the gyroscope, a polarizer and one coupling device in a smallest reciprocity structure are saved; the polarization maintaining optical fiber which is welded at the rotary angle of 45 degrees generates dual-polarization light to compensate a non-reciprocity error so that the cost is greatly reduced; meanwhile, the gyroscope has low noises and the good zero-polarization stability.

Description

A kind of unicoupler double polarizing light fiber gyroscope

Technical field

The invention belongs to gyroscope technical field, be specifically related to a kind of unicoupler double polarizing light fiber 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 the fields such as guidance, industry and the military precision measurement of aircraft and weapon.Early stage gyroscope is mechanical gyroscope, and mechanical gyroscope is to utilize the turning axle of high-speed rotary body to have the orienting device that keeps the such physical principle of trend of its direction and produce.For example, because mechanical gyroscope comprises movable part (high speed rotor), therefore, the high and precision of its complex structure, technological requirement has been subject to many-sided restriction.

In generation nineteen sixty, along with the appearance of laser, the research that utilizes laser to manufacture optical gyroscope develops rapidly.Optical gyroscope is based on Sagnac effect (Sagnac effect) and produced orienting device.Specifically, in the closed light path of rotating, the identical light of two bundle features being sent by same light source interferes respectively when (CW) direction is with counterclockwise (CCW) direction transmission clockwise, by detecting the phase differential of described two-beam or the variation of interference fringe, just can measure the rotational angular velocity of this closure light path.Above-mentioned phase differential is known as Sagnac phase shift φ _s, it is directly proportional to the rotational angular velocity Ω of closed light path:

${\mathrm{\φ}}_S=\frac{4\mathrm{\ωA}}{c^2}\mathrm{\Ω}$ Wherein, ω is light frequency to formula (1), 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, and its compact conformation, highly sensitive, good reliability and life-span are long.Within 1963, first generation optical gyroscope-lasergyro is come out.The primary element of lasergyro is ring laser.For example, lasergyro can comprise the triangular closed light path of being made by quartz, is provided with a he-ne laser tube, two catoptrons and a semitransparent mirror in this light path.The laser of the contrary transmission of two bundles of sending from he-ne laser tube reflects through two catoptrons respectively, then derives loop by semitransparent mirror, just can obtain the rotational angular velocity of closed light path by measuring the phase differential of 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.Adopt multiturn coil can strengthen Sagnac effect.In this case, Sagnac phase shift φ _sexpression formula be:

${\mathrm{\φ}}_S=2\mathrm{\π}\frac{\mathrm{LD}}{\mathrm{\λc}}\mathrm{\Ω}$ Formula (2) wherein, the length that L is optical fiber, D is fiber optic coils diameter, the wavelength that λ is light wave.

In order accurately to measure Sagnac effect, (be Sagnac phase shift φ _s), guarantee that described closed light path has reciprocity, guarantee that the light (calling CW light in the following text) transmitting along the clockwise direction of described closed light path and the light (calling CCW light in the following text) transmitting along the counter clockwise direction of described closed light path have identical pattern, polarization and phase delay, make the phase differential of CW light and CCW light only relevant with the rotational angular velocity of this closure light path, and irrelevant with transmission, thereby improve the accuracy of measuring.

Fig. 1 shows the minimum reciprocal structure of interferometric fiber optic gyroscope.As shown in Figure 1, this minimum reciprocal structure comprises light source, source ends coupling mechanism, the polarizer, ring end coupling mechanism, fiber optic loop and photodetector.Above-mentioned coupling mechanism can be realized the beam splitting of light beam and again converge.Light beam of light source is passing through after the polarizer, through encircling, end coupling mechanism is divided into CW light and CCW light transmits in fiber optic loop, this CW light and CCW light are held coupling mechanism again to converge by ring again after transmitting in fiber optic loop and are formed interference wave, and this interference wave enters photodetector finally by crossing source ends coupling mechanism.Ring end coupling mechanism has reciprocity, and the phase delay that it causes CW light and CCW light is identical.In addition, the polarizer is used for light wave to carry out polarization filtering, to guarantee that CW light and CCW light have identical polarization, thereby realizes polarization reciprocity.In fibre optic gyroscope, can adopt polarization maintaining optical fibre to guarantee polarization reciprocity.

Due to fiber optic loop when static the phase place of CW light and CCW light identical with amplitude, the therefore power P of interference light ₀for maximum.When fiber optic loop has rotation, interference light power P is the phase difference of rotating caused CW light and CCW light _sfunction P (φ _s)=P ₀(1+cos φ _s).In order to obtain high sensitivity, should give φ _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 in one end of fiber optic loop phase-modulator (for example, PZT phase-modulator), to the CW light transmitting in fiber optic loop and CCW light are carried out to phase-modulation, thereby make it when fiber optic loop is static, produce phase difference φ.

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

The technical requirement of the each precision grade of table 1.

Wherein, zero bias stability is to weigh the most important technical indicator of interferometric fiber optic gyroscope precision.Zero partial correlation noise comprises quantizing noise, angle random walk, speed random walk, rate ramp etc.

As mentioned above, in fibre optic gyroscope, the structural principle of two coupling mechanisms and a polarizer can be eliminated the nonreciprocal noise component causing of polarization, guarantees zero good bias stability, but has also caused the raising of cost.

Summary of the invention

The object of the invention is to, a kind of unicoupler double polarizing light fiber gyroscope is provided, this unicoupler double polarizing light fiber gyroscope has very low complexity, lower cost and higher precision and zero bias stability.

To achieve these goals, the invention provides a kind of unicoupler double polarizing light fiber gyroscope, it comprises wide spectrum light source, polarization maintaining optical fibre, coupling mechanism, polarization-maintaining fiber coil, and photodetector, wherein, the output terminal of wide spectrum light source is connected with polarization maintaining optical fibre by single-mode fiber, polarization maintaining optical fibre divides two sections and 45 ° of gyration weldings, the first port coupling of the polarization maintaining optical fibre other end and coupling mechanism, the 3rd port of coupling mechanism and the 4th port are coupled with two ports of polarization-maintaining fiber coil respectively by single-mode fiber, the second port of coupling mechanism is by the input end coupling of single-mode fiber and photodetector.

Preferably, described coupling mechanism is 3dB polarization-maintaining fiber coupler.

Preferably, in described polarization-maintaining fiber coil, be inserted with phase-modulator.Further preferably, described phase-modulator is PZT phase-modulator.

Preferably, the segment length of described two sections of polarization maintaining optical fibres is (L ₀, 2L ₀), wherein, L ₀=L _d/ Δ n, the refringence between the x axle of the birefringece crystal that Δ n is this polarization maintaining optical fibre and y axle 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, the spectrum width that Δ λ is described wide spectrum light source.

As mentioned above, the principle that the present invention is based on polarization error compensation has broken through the restriction of optical fibre gyro minimum reciprocal structure, unicoupler double polarizing light fiber gyroscope of the present invention does not need the polarizer, only need a coupling mechanism, greatly reduce the cost of structure, the cost of its structure is lower than the current optical fibre gyro structure of main flow on the market.Polarization maintaining optical fibre by 45 ° of weldings of two-part produces double polarizing light, can reach good nonreciprocal error compensation effect, realizes higher Gyro Precision and degree of stability.

Accompanying drawing explanation

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

Fig. 2 is the schematic diagram of the structure of the unicoupler double polarizing light fiber gyroscope described in one embodiment of the present of invention;

Fig. 3 is the principle schematic of 45 ° of weldings of two sections of polarization maintaining optical fibres;

Fig. 4 is the time domain data figure of the gyroscope Output speed value in Fig. 2;

Fig. 5 is the error analysis figure of the gyroscope Output speed data in Fig. 2; And

Fig. 6 is the linearity analysis figure of the gyroscope Output speed data in Fig. 2.

Embodiment

In the following description, for purposes of illustration, for the complete understanding to one or more embodiment is provided, many details have been set forth.But, clearly, also can in the situation that there is no these details, realize these embodiment.In other example, one or more embodiment for convenience of description, known structure and equipment illustrate with the form of block scheme.

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

Fig. 2 is the schematic diagram of the structure of the unicoupler double polarizing light fiber gyroscope described in one embodiment of the present of invention.As shown in Figure 2, unicoupler double polarizing light fiber gyroscope of the present invention comprises: wide spectrum light source, polarization maintaining optical fibre, coupling mechanism, phase-modulator, polarization-maintaining fiber coil and photodetector.Wide spectrum light source can adopt the wide spectrum light source generally adopting in interference type optical fiber gyroscope, for example, 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 is connected by the polarization maintaining optical fibre of 45 ° of weldings of single-mode fiber and two-part.The other end of this polarization maintaining optical fibre is connected with the first port of coupling mechanism, preferably, uses the polarization-maintaining fiber coupler that splitting ratio is 50:50, i.e. 3dB polarization-maintaining fiber coupler.

Fig. 3 is the principle schematic of 45 ° of weldings of described two sections of polarization maintaining optical fibres.The segment length of described two sections of polarization maintaining optical fibres is (L ₀, 2L ₀), wherein, L ₀=L _d/ Δ n, the refringence between the x axle of the birefringece crystal that Δ n is this polarization maintaining optical fibre and y axle 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, the spectrum width that Δ λ is described wide spectrum light source.During welding, the main shaft angle of two sections of optical fiber is 45 °.The light wave of light source can become double polarizing light after by this part polarization maintaining optical fibre.

In Fig. 2, the 3rd port of coupling mechanism and the 4th port are coupled to axle with two ports of polarization-maintaining fiber coil respectively.The second port of coupling mechanism is by the input end coupling of single-mode fiber and photodetector.Preferably, photodetector can adopt for example semiconductor PIN optical diode.

As mentioned above, the present invention utilizes double polarizing light to avoid using the polarizer in existing fiber gyroscope, and has realized the compensation effect (will describe in detail) of phase error below.In addition the said fibre optic gyroscope of the present invention only need to use a coupling mechanism, and unlike using two coupling mechanisms in existing fiber gyro, therefore the cost of fibre optic gyroscope of the present invention has reduced widely.

The polarization maintaining optical fibre of two sections of 45 ° of weldings can produce light intensity and equate and two separate polarization states, and it has nonreciprocity, but can eliminate the impact that nonreciprocity brings by error compensation.Below by theoretical analysis, this point is described.

Definition C point place, between polarization maintaining optical fibre section and coupling mechanism, the polarization degree at some place is d, the normalization light field of inputting like this polarization-maintaining fiber coil is:

$E_C=\left[\begin{array}{c}\sqrt{1+d/2}{e}^{-\mathrm{j\Δ\β}{L}_0}\\ \sqrt{(1-d)/2}\end{array}\right]e^{{\mathrm{j\ω}}_{0}t}$ Formula (3)

Wherein, Δ β is the poor of propagation constant between polarization maintaining optical fibre diaxon, length L ₀eliminated the coherence between two polarization states.The degree of polarization of light wave is d, and span is ﹣ 1～1.D=﹣ 1 represents y direction linear polarization, and d=0 represents the sizes such as the amplitude of x direction and y direction, and d=1 represents x direction linear polarization.

Use symbol M _cWrepresent that the light wave of transmission clockwise passes total transmission matrix of coupling mechanism and fiber optic loop, uses symbol M _cCWrepresent that the light wave of transmission counterclockwise, through total transmission matrix of coupling mechanism and fiber optic loop, has:

$M_{\mathrm{CW}}=\left[\begin{array}{cc}{C}_1& C_2\\ C_3& C_4\end{array}\right]$ Formula (4)

$M_{\mathrm{CCW}}=\left[\begin{array}{cc}{C}_1& C_3\\ C_2& C_4\end{array}\right]$ Formula (5)

Can calculate thus the interference light wave that close echo forms:

$E_{\mathrm{CW}}+E_{\mathrm{CCW}}=M_{\mathrm{CW}}{E}_C{e}^{\mathrm{i\φ}}+M_{\mathrm{CCW}}{E}_C$ Formula (6)

Wherein non-reciprocal phase φ=φ _s+ Δ φ (t) has comprised Sagnac phase difference _sphase bias Δ φ (t) with modulator introducing.In formula, the concrete form of each is as follows

$E_{\mathrm{CW}}=M_{\mathrm{CW}}{E}_C{e}^{\mathrm{j\φ}}=\left[\begin{array}{c}{C}_1\sqrt{(1+d)/2}{e}^{-\mathrm{j\Δ\βL}}+C_2\sqrt{(1-d)/2}\\ C_3\sqrt{(1+d)/2}{e}^{-\mathrm{j\Δ\βL}}+C_4\sqrt{(1-d)/2}\end{array}\right]e^{{\mathrm{j\ω}}_{0}t}{e}^{\mathrm{j\φ}}$ Formula (7)

$E_{\mathrm{CCW}}=M_{\mathrm{CCW}}{E}_C=\left[\begin{array}{c}{C}_1\sqrt{(1+d)/2}{e}^{{-\mathrm{j\&Delta;\&beta;<figure-callout\; id="0"\; label="L"\; filenames="HDA0000453579860000022.png"\; state="\{\{state\}\}">L</figure-callout>}}_0}+C_3\sqrt{(1-d)/2}\\ C_2\sqrt{(1+d)/2}{e}^{{-\mathrm{j\&Delta;\&beta;<figure-callout\; id="0"\; label="L"\; filenames="HDA0000453579860000022.png"\; state="\{\{state\}\}">L</figure-callout>}}_0}+C_4\sqrt{(1-d)/2}\end{array}\right]e^{{\mathrm{j\&omega;}}_{0}t}$ Formula (8)

For the clear principle that obtains interpretation errors compensation, we calculate respectively x polarized component and y polarized component in obtained interference light ripple.Wherein the interference light intensity of x polarized component is

$\begin{array}{c}{I}_x=<{|E_{\mathrm{CWx}}+E_{\mathrm{CCWx}}|}^2>\\ =I_{x0}+{\left|C_1\right|}^2(1+d)\cos \mathrm{\&phi;}+(1-d)\left|C_2{C}_3\right|\mathrm{\&Gamma;}\left(z_{23}\right)\cos \mathrm{\&phi;}\cos {\mathrm{\&phi;}}_{23}\\ -(1-d)\left|C_2{C}_3\right|\mathrm{\&Gamma;}\left(z_{23}\right)\sin \mathrm{\&phi;}\sin {\mathrm{\&phi;}}_{23}\end{array}$ Formula (9)

Write one with the DC component of phase-independent and weak coherent term in this step and be incorporated to I _x0, cast out high-order in a small amount.Wherein φ ₂₃and z ₂₃respectively C ₂c ₃ ^*phase place and birefringence time delay, Γ (z) is the coherence degree function of light source.

In order to analyze the error of obtained signal, we can be write as the result of formula (9) form of following equivalence

$I_x=I_{x0}+q_x\cos \mathrm{\&phi;}+p_x\sin \mathrm{\&phi;}=I_{x0}+\sqrt{p_x^2+q_x^2}\cos (\mathrm{\&phi;}-{\mathrm{\&phi;}}_{\mathrm{err}}^x)$ Formula (10)

P _x=-(1-d) | C ₂c ₃| Γ (z ₂₃) sin φ ₂₃formula (11)

Q _x=(1+d) | C ₁| ²+ (1-d) | C ₂c ₃| Γ (z ₂₃) cos φ ₂₃formula (12)

Wherein represented the size of the phase error of the nonreciprocal introducing of x direction polarization.

Similarly, we can obtain the interference light intensity I of y direction _ywith the phase error in signal

${\mathrm{\&phi;}}_{\mathrm{err}}^y=\arctan (p_y/q_y).$

formula (10) p _y=(1+d) | C ₂c ₃| Γ (z ₂₃) sin φ ₂₃formula (11) q _y=(1-d) | C ₄| ²+ (1+d) | C ₂c ₃| Γ (z ₂₃) cos φ ₂₃formula (12)

Finally, two composition I _x, I _ythe form of the total light intensity of interference light obtaining after stack can be expressed as DC component (DC) and add interference correlated components:

$\begin{array}{c}{I}_x+I_y=I_{x0}+I_{y0}+(q_x+q_y)\cos {\mathrm{\&phi;}}_s+(p_x+p_y)\sin {\mathrm{\&phi;}}_s\\ =I_0+\cos (\mathrm{\&phi;}-{\mathrm{\&phi;}}_{\mathrm{err}})\end{array}$ Formula (13)

The error that polarization nonreciprocity is introduced is:

$\begin{array}{c}{\mathrm{\&phi;}}_{\mathrm{err}}=\arctan \left(\frac{p_x+p_y}{q_x+q_y}\right)\\ =\arctan \frac{2d\left|C_2{C}_3\right|\mathrm{\&Gamma;}\left(z_{23}\right)\sin {\mathrm{\&phi;}}_{23}}{{\left|C_1\right|}^2(1+d)+{C_4|}^2(1-d)+2\left|C_2{C}_3\right|\mathrm{\&Gamma;}\left(z_{23}\right)\cos {\mathrm{\&phi;}}_{23}}\end{array}$ Formula (14)

Visible, when light splitting is uniform (d=0), I _xand I _yin the phase error large opposite sign such as just, now final phase error is zero.While being d=0, φ _err=0.This has just illustrated that the optical fibre gyro structure in the present invention can effectively reduce the error of the nonreciprocal introducing of polarization, thereby does not need two coupling mechanisms to carry out strict guarantee reciprocity, only with a coupling mechanism, also can obtain stable angular velocity detection result.

Fig. 4 shows the time domain data figure of the gyrostatic Output speed value in Fig. 2.Wherein, experiment measuring to as if rotational-angular velocity of the earth, on the surface level of laboratory dimension (north latitude 40.0 is spent), theoretical value to be measured be 9.67 degree/hour, data output gap is about 0.12 second, test duration length 2 hours.Visual data stable output, migration and drift are all very little.

Fig. 5 shows the error analysis figure of gyrostatic Output speed data in Fig. 2.According to this figure, the error parameter of the gyro that obtains is: quantizing noise coefficient Q=8.6 × 10 ^-8rad, angle random walk zero bias stability B=2.3 × 10 ^-2О/h, speed random walk K=5.3 × 10 ^-2О/h ^3/2, rate ramp R=1.5 × 10 ^-1О/h ².

Fig. 6 is the linearity analysis figure of the gyroscope Output speed data in Fig. 2.This figure is the deviational survey result based on earth rotation, shows that input and output have the good linearity.Wherein input and output have a fixing deviation to be about 2024 О/h.This deviation is introduced by coupling mechanism nonreciprocity, is individual not temporal evolution droop, can eliminate by simply doing poor mode, does not affect the precision and stability of gyro.

In the inclined to one side gyro of traditional guarantor and De-FOG, if remove the polarizer, its zero inclined to one side instability can reach tens～О/h up to a hundred.For described unicoupler double polarizing light fiber gyroscope of the present invention, the noise and the drift that can the nonreciprocal problem of almost Perfect ground compensation cause, its result and have the gyroscope structure of the polarizer suitable.In addition, unicoupler double polarizing light fiber gyroscope of the present invention only needs a coupling mechanism, and lower than the inclined to one side gyro of traditional guarantor and De-FOG structure complexity, cost is lower.

Although disclosed content shows exemplary embodiment of the present invention above, it should be noted that under the prerequisite of scope of the present invention that does not deviate from claim restriction, can carry out multiple change and modification.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 (7)

1. a unicoupler double polarizing light fiber gyroscope, it is characterized in that, comprise wide spectrum light source, polarization maintaining optical fibre, coupling mechanism, polarization-maintaining fiber coil, and photodetector, wherein, the output terminal of wide spectrum light source is connected with polarization maintaining optical fibre by single-mode fiber, polarization maintaining optical fibre is divided into two sections and 45 ° of gyration weldings, the first port coupling of the polarization maintaining optical fibre other end and coupling mechanism, the 3rd port of coupling mechanism and the 4th port are coupled with two ports of polarization-maintaining fiber coil respectively by single-mode fiber, the second port of coupling mechanism is by the input end coupling of single-mode fiber and photodetector.

2. unicoupler double polarizing light fiber gyroscope according to claim 1, is characterized in that, described coupling mechanism is 3dB polarization-maintaining fiber coupler.

3. unicoupler double polarizing light fiber gyroscope according to claim 1, is characterized in that, in described polarization-maintaining fiber coil, is inserted with phase-modulator.

4. unicoupler double polarizing light fiber gyroscope according to claim 3, is characterized in that, described phase-modulator is PZT phase-modulator.

5. unicoupler double polarizing light fiber gyroscope according to claim 1, is characterized in that, the segment length of described two sections of polarization maintaining optical fibres is (L ₀, 2L ₀), wherein, L ₀=L _d/ Δ n, the refringence between the x axle of the birefringece crystal that Δ n is this polarization maintaining optical fibre and y axle 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, the spectrum width that Δ λ is described wide spectrum light source.

6. unicoupler double polarizing light fiber gyroscope according to claim 1, is characterized in that, described wide spectrum light source adopts ASE wide spectrum light source.

7. unicoupler double polarizing light fiber gyroscope according to claim 1, is characterized in that, described photodetector adopts semiconductor PIN optical diode.

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