CN103558438A - System and method for reducing frequency of null drift of reflective optical fiber amperemeter - Google Patents

Abstract

The invention discloses a system for reducing the frequency of null drift of a reflective optical fiber amperemeter. The system for reducing the frequency of the null drift of the reflective optical fiber amperemeter comprises an SLD device and a PINFET device, wherein the SLD device and the PINFET device are connected with a lithium niobate Y-waveguide integrated optical device in a welding mode, and the lithium niobate Y-waveguide integrated optical device is used in a backward mode. The invention further discloses a method for reducing the frequency of the null drift of the reflective optical fiber amperemeter. The method for reducing the frequency of the null drift of the reflective optical fiber amperemeter comprises the steps that polarization characteristics of polarization devices in an optical path are shown through the Jones matrix, a normalization scale factor formula is obtained, the normalization scale factor reflects the proportional relation between an actual testing result and an ideal result, and as is shown by analysis, the larger the extinction ratio is, the closer the normalization impact factor is to one, namely, the smaller the introduced phase error is, and the lower the null drift of the system is. According to the system and method for reducing the frequency of the null drift of the reflective optical fiber amperemeter, due to the fact that a 3db coupler and a polarizer of an existing system are replaced by the lithium niobate Y-waveguide integrated optical device which is used in the backward mode, the polarization extinction ratio of the system is increased, influence caused by the polarization error of an all-fiber current transformer can be obviously reduced, the frequency of the null drift is reduced, and the bias stability of the system is improved.

Description

A kind of system and method that reduces the drift of reflection type optical fiber current meter

Technical field

The invention belongs to full optical-fiber current field of sensing technologies, relate to a kind of system and method that reduces the drift of reflection type optical fiber current meter.

Background technology

Reflection type optical fiber current meter, because of safe, large without hysteresis & saturation, measurement range, advantages of simple structure and simple, is subject to various countries researcher's attention.At present, because the optical device in real system is not completely desirable, there is crosstalking between polarized light in system, shows as other nonreciprocal phase shift of having introduced non-faraday's phase shift, and in no current situation, system output is non-vanishing, occurs zero drift phenomenon.For the large galvanometer of drift, cannot judge that its output is drift or has less electric current, becomes problem demanding prompt solution in industrialization process.

Solve drift problem, key is to eliminate the polarization error phenomenon of all-fiber current transformator.Polarization error problem for all-fiber current transformator, document [1] utilizes Jones matrix method, the error that each main polarizer of system is brought has been carried out emulation, [2] selective analysis the impact of four/wave plate, [3] have analyzed the impact on test of nonreciprocal phase shift that system external environmental factor brings.Yet, for the above document of polarization error of all-fiber current transformator, effective solution is not all proposed.

[1] Wang Xiaxiao, Zhang Chunxi. the polarization error research [J] of all-fiber current transformator. photon journal, 2007,362:320-323

[2] Jinhui Hao, Ping Huang, Xuyou Li.Polarization Errors Analysis of Waveplate in Sagnac Optical Fiber Current Sensor[J] .2011International Conference on Electronic & Mechanical Engineering and Information Technology(Hao Jin brightness, Huang Ping, polarization error analysis [J] .2011 electronics and mechanical engineering and the infotech international conference .238-241 of Li Xu friend .Sagnac type fibre optic current sensor wave plate)

[3] Wei Wang n, Xuefeng Wang, Junlei Xia.The Nonreciprocal Errors in Fiber Optic Current Sensors[J] .Optics & Laser Technology, 2011,43:1470-1474(Wang Wei etc. the nonreciprocal error [J] of fibre optic current sensor. optics and laser technology, 2011,43:1470-1474.)

Summary of the invention

The object of this invention is to provide a kind of system and method that reduces the drift of reflection type optical fiber current meter, solved the larger technical matters of common reflection type optical fiber current meter drift in prior art.

The technical solution adopted in the present invention is, a kind of system that reduces the drift of reflection type optical fiber current meter, comprise SLD device, PINFET device, SLD device, PINFET device is connected with the mode of lithium niobate Y waveguide integrated optical device by welding, lithium niobate Y waveguide integrated optical device is swung to use, the light that SLD device sends becomes linearly polarized light through lithium niobate Y waveguide integrated optical device, by 45 ° of fusion points, a branch of linearly polarized light becomes the orthogonal linearly polarized light of two bundles, along X-axis and the Y-axis of polarization maintaining optical fibre, propagate respectively, after quarter wave plate, two bunch polarized lights change respectively left circularly polarized light and right-circularly polarized light into, by sensor fibre, be transferred to sensor fibre end, sensor fibre end is provided with catoptron.By mirror polarization state, be there is upset and returned by original optical path in left circularly polarized light and right-circularly polarized light, when left circularly polarized light and right-circularly polarized light pass through sensor fibre, because electric current produces the Faraday effect in magnetic field, make to produce faraday between the transmission phase place of left circularly polarized light and right-circularly polarized light and differ; Simultaneously, the polarization state upset being produced by catoptron the process of returning by original optical path, the phase differential that Faraday effect is produced doubles, when reaching quarter wave plate place, left circularly polarized light and right-circularly polarized light change mutually orthogonal linearly polarized light into, two bunch polarized lights interfere, and measure by PINFET device.

The invention also discloses a kind of method that reduces the drift of reflection type optical fiber current meter, its feature is: comprise,

The in the situation that at the polarizer, in undesirable and supposing the system, other devices being desirable device, available following Jones matrix represents the polarization characteristic of each polarizer in light path

(1) optical fiber polarizer P $G_p=\left[\begin{array}{cc}1& 0\\ 0& \mathrm{\ϵ}\end{array}\right]$

Wherein, ε represents electric vector amplitude ratio separately in extinction axis and light transmission shaft direction, uses T=-10log ε ²represent extinction ratio

(2) 45 ° of fusion point S (3) phase-modulator Z

$G_s=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& -1\\ 1& 1\end{array}\right]G_{\mathrm{Zin}}=\left[\begin{array}{cc}1& 0\\ 0& e^{\mathrm{i\ψ}(t-\mathrm{\τ})}\end{array}\right]G_{\mathrm{Zout}}=\left[\begin{array}{cc}1& 0\\ 0& e^{\mathrm{i\ψ}\left(t\right)}\end{array}\right]$

ψ in formula (t-τ) represents the t-τ phase modulation of phase-modulator constantly, and ψ (t) represents the t phase modulation of phase-modulation constantly

(4) four/wave plate R (5) Faraday devices

$G_{\mathrm{Rin}}=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& i\\ i& 1\end{array}\right]G_{\mathrm{Rout}}=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& -i\\ -i& 1\end{array}\right]G_{\mathrm{Fin}}=\left[\begin{array}{cc}\cos \mathrm{\θ}& \sin \mathrm{\θ}\\ -\sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]G_{\mathrm{Fout}}=\left[\begin{array}{cc}\cos \mathrm{\θ}& -\sin \mathrm{\θ}\\ \sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]$

Wherein, θ=VNI, V represents Verdet constant, and N is the sensor fibre number of turn, and I is tested electric current

(6) end reflector M $G_M=\left[\begin{array}{cc}1& 0\\ 0& -1\end{array}\right]$

The expression formula E of output light vector _out=G _pg _sg _zoutg _routg _foutg _mg _fing _ring _zing _sg _pe _in

Wherein, E _infor input light, be expressed as $E_{\mathrm{in}}=\left[\begin{array}{c}1\\ 1\end{array}\right]$

Output intensity

I _out＝0.5[(1+ε ²) ²+(ε ²-1) ²cos(Δφ+4θ)] ①

Wherein Δ φ=ψ (t-τ)-ψ (t), represents that the non-reciprocal phase of introducing due to phase-modulation is poor for open loop demodulation scheme, and the phase differential after demodulation is:

Normalization scaling factor

Normalization scaling factor has reflected the proportionate relationship of actual test result and desired result, and extinction ratio is larger, and normalization factor of influence is more tending towards 1, and the phase error of introducing is less, and the drift of system is lower.

The invention has the beneficial effects as follows: reasonable in design of the present invention, by swinging to, use lithium niobate Y waveguide integrated optical device to replace 3db coupling mechanism and the polarizer in existing system, improved the polarization extinction ratio of system, can obviously reduce the impact of all-fiber current transformator polarization error, reduce drift, improve system zero bias stability.

Accompanying drawing explanation

Fig. 1 is reflection type optical fiber current meter systems block diagram in prior art;

Fig. 2 is that the present invention swings to use Y waveguide structural system block diagram;

Fig. 3 is the schematic diagram that is related to of normalization scaling factor of the present invention and extinction ratio;

Fig. 4 is system polarization coupled illustraton of model of the present invention;

Fig. 5 is system polarization state evolution of the present invention;

Fig. 6 is the long-term drift test result of the present invention figure;

Wherein: SLD interface 1, PINFET interface 2,3,45 ° of fusion points 4 of lithium niobate Y waveguide integrated optical device, phase-modulator 5, quarter wave plate 6, catoptron 7, the polarizer 8, Coupling point Q9, polarizer N10,3db coupling mechanism 11.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

As shown in Figure 1: this reflection type optical fiber current meter, comprise SLD device 1, PINFET device 2, the light that SLD device 1 sends is through 3db coupling mechanism 11, after the polarizer 8, become linearly polarized light again, by 45 ° of fusion points 4, through phase-modulator 5, a branch of linearly polarized light becomes the orthogonal linearly polarized light of two bundles, along X-axis and the Y-axis of polarization maintaining optical fibre, propagate respectively, after quarter wave plate 6, two bunch polarized lights change respectively left circularly polarized light and right-circularly polarized light into, when left circularly polarized light and right-circularly polarized light pass through sensor fibre, because electric current produces the Faraday effect in magnetic field, between left circularly polarized light and right-circularly polarized light, producing faraday differs, left circularly polarized light and right-circularly polarized light are transferred to sensor fibre end, sensor fibre end is provided with catoptron 7, effect due to catoptron 7, there is upset and return by original optical path in left circularly polarized light and right-hand circular polarization polarization state, while again passing through sensor fibre, the phase differential producing due to Faraday effect doubles, reach quarter wave plate 6 place's left circularly polarized lights and right-circularly polarized light and change mutually orthogonal linearly polarized light into, two bunch polarized lights interfere at the polarizer 8 places.

As shown in Figure 2: a kind of system that reduces the drift of reflection type optical fiber current meter of the present invention, comprise SLD device 1, PINFET device 2, SLD device 1, PINFET device 2 is connected with the mode of lithium niobate Y waveguide integrated optical device 3 by welding, lithium niobate Y waveguide integrated optical device 3 is swung to use, the light that SLD device 1 sends becomes linearly polarized light through lithium niobate Y waveguide integrated optical device 3, by 45 ° of fusion points 4, a branch of linearly polarized light becomes the orthogonal linearly polarized light of two bundles, along X-axis and the Y-axis of polarization maintaining optical fibre, propagate respectively, after quarter wave plate 6, two bunch polarized lights change respectively left circularly polarized light and right-circularly polarized light into, left circularly polarized light and right-circularly polarized light are transferred to sensor fibre end by sensor fibre, sensor fibre end is provided with catoptron 7.By mirror polarization state, be there is upset and returned by original optical path in left circularly polarized light and right-circularly polarized light, when left circularly polarized light and right-circularly polarized light pass through sensor fibre, because electric current produces the Faraday effect in magnetic field, make to produce faraday between the transmission phase place of left circularly polarized light and right-circularly polarized light and differ; Simultaneously, the polarization state upset being produced by catoptron the process of returning by original optical path, the phase differential that Faraday effect is produced doubles, when reaching quarter wave plate 6 place, left circularly polarized light and right-circularly polarized light change mutually orthogonal linearly polarized light into, two bunch polarized lights interfere, and measure by PINFET device 2.

A kind of method that reduces the drift of reflection type optical fiber current meter of the present invention, its feature is: comprises,

The in the situation that at the polarizer, in undesirable and supposing the system, other devices being desirable device, available following Jones matrix represents the polarization characteristic of each polarizer in light path

(1) optical fiber polarizer P $G_p=\left[\begin{array}{cc}1& 0\\ 0& \mathrm{\ϵ}\end{array}\right]$

Wherein, ε represents electric vector amplitude ratio separately in extinction axis and light transmission shaft direction, uses T=-10log ε ²represent extinction ratio

(2) 45 ° of fusion point S (3) phase-modulator Z

$G_s=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& -1\\ 1& 1\end{array}\right]G_{\mathrm{Zin}}=\left[\begin{array}{cc}1& 0\\ 0& e^{\mathrm{i\ψ}(t-\mathrm{\τ})}\end{array}\right]G_{\mathrm{Zout}}=\left[\begin{array}{cc}1& 0\\ 0& e^{\mathrm{i\ψ}\left(t\right)}\end{array}\right]$

ψ in formula (t-τ) represents the t-τ phase modulation of phase-modulator constantly, and ψ (t) represents the t phase modulation of phase-modulation constantly

(4) four/wave plate R (5) Faraday devices

$G_{\mathrm{Rin}}=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& i\\ i& 1\end{array}\right]G_{\mathrm{Rout}}=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& -i\\ -i& 1\end{array}\right]G_{\mathrm{Fin}}=\left[\begin{array}{cc}\cos \mathrm{\θ}& \sin \mathrm{\θ}\\ -\sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]G_{\mathrm{Fout}}=\left[\begin{array}{cc}\cos \mathrm{\θ}& -\sin \mathrm{\θ}\\ \sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]$

Wherein, θ=VNI, V represents Verdet constant, and N is the sensor fibre number of turn, and I is tested electric current

(6) end reflector M $G_M=\left[\begin{array}{cc}1& 0\\ 0& -1\end{array}\right]$

The expression formula E of output light vector _out=G _pg _sg _zoutg _routg _foutg _mg _fing _ring _zing _sg _pe _in

Wherein, E _infor input light, be expressed as $E_{\mathrm{in}}=\left[\begin{array}{c}1\\ 1\end{array}\right]$

Output intensity

I _out＝0.5[(1+ε ²) ²+(ε ²-1) ²cos(Δφ+4θ)] ①

Wherein Δ φ=ψ (t-τ)-ψ (t), represents that the non-reciprocal phase of introducing due to phase-modulation is poor for open loop demodulation scheme, and the phase differential after demodulation is:

Normalization scaling factor

Normalization scaling factor has reflected the proportionate relationship of actual test result and desired result, and extinction ratio is larger, and normalization factor of influence is more tending towards 1, and the phase error of introducing is less, and the drift of system is lower.

As shown in Figure 3, transverse axis is extinction ratio, and simulation result shows that extinction ratio is larger, and normalization factor of influence is more tending towards 1, and the phase error of introducing is less, and the drift of system is lower.

As shown in Figure 4: suppose at 45 ° of fusion point 4l of distance ₁after length, have a polarization coupled point Q9, all devices after polarization coupled point Q9 are regarded polarizer N10 as, part after polarization coupled point Q9, and length is designated as l ₂.Because the polarizer 8 extinction ratios are undesirable, input light wave becomes along the axial light wave A1 of printing opacity with along the axial A of delustring after the polarizer 8 ₂, after 45 ° of fusion points 4, this two-beam wavelength-division is not decomposed into the vertical light wave A in polarization direction ₁₁, A ₁₂and A ₂₁, A ₂₂, this four bundles light wave continues to propagate, through polarization coupled point Q9 and polarizer N10.Process for simplifying the analysis, there is the situation of polarization coupled while only considering light wave for the first time through polarization coupled point Q9 in us, and does not consider the polarization coupled of return course.When light wave returns to 45 ° of fusion points 4 again, can be divided three classes like this, be respectively there is not any coupling but the key light ripple of polarization state upset to A ₁₁, A ₁₂and A ₂₁, A ₂₂, by light wave A ₁₁, A ₁₂be coupled to respectively coupling light wave after orthogonal polarization axes to A ₁₁₂, A ₁₂₁, by light wave A ₂₁, A ₂₂be coupled to respectively coupling light wave after orthogonal polarization axes to A ₂₁₂, A ₂₂₁.These 4 pairs of light waves are decomposed into 16 bundle light waves after 45 ° of fusion points 4.

As shown in Figure 5: all light waves arrive polarizer place and interfere situation as follows:

By key light ripple to A ₁₁, A ₁₂and A ₂₁, A ₂₂the light wave that decomposition obtains is to A _1k1, A _2k1and A _1k2, A _2k2(k=1,2), produce main interference signal, and the non-reciprocal phase that interference phase difference is only partly introduced for sensing head is poor.

Coupling light wave is to A ₁₁₂, A ₁₂₁because having experienced polarization coupled one time, after whole transmitting procedure, its light path is not identical, and the phase shift of this two-beam is respectively

β in formula _xfor polarization maintaining optical fibre X polarization axle propagation constant, β _yfor polarization maintaining optical fibre Y polarization axle propagation constant.Poor being expressed as of non-reciprocal phase between two-beam ripple

By formula, 6. known, 45 ° of fusing points of Coupling point distance are nearer, and the nonreciprocal of generation differs just less.Light wave A ₁₁₂, A ₁₂₁after 45 ° of fusing points, be decomposed into A _1i1, A _1i2(i=12,21), light wave A _1i1with A _1k1polarization direction is identical, A _1i2with A _1k2polarization direction is identical, between them, interferes, and total phase error is proportional to ε.In like manner, coupling light wave A ₂₁₂, A ₂₂₁through 45 ° of fusing points, the phase error that introduce with corresponding main wave interference the interference of the light wave after decomposition and they is also proportional to ε.

As shown in Figure 6: in experimentation, we use light source for 1310nmSLD, PINFET model is MFT915, and lock-in amplifier is SR830, gathers respectively the drift data of two cover systems by data collecting card, every system testing 3 hours, Fig. 6 is the long-term drift test result that experiment obtains, and by experiment with computing data, can obtain, and system drift drops to 1.58A from 11.1A, utilize Y waveguide structure obviously to reduce drift, improved reflection type optical fiber current meter output stability.

Drift problem for reflection type optical fiber current meter, first the derived relational expression of reflection type optical fiber current meter systems polarizer extinction ratio and normalization scaling factor of the present invention, then analyzed the impact of extinction ratio on polarization interference, shown that on this basis raising extinction ratio can lower drift, improves the conclusion of system stability.The experimental system of finally having built two kinds of structures, found through experiments, and swings to and uses after Y waveguide, and system drift is reduced to 1.58A from 11.1A, and this result has been verified theoretical correctness effectively.

Reasonable in design of the present invention, by swinging to 3db coupling mechanism 11 and the polarizer 8 that uses lithium niobate Y waveguide integrated optical device 3 to replace in existing system, improved the polarization extinction ratio of system, can obviously reduce the impact of all-fiber current transformator polarization error, reduce drift, improve system zero bias stability.

Specific embodiment described herein is only to the explanation for example of the present invention's spirit.Those skilled in the art can make various modifications or supplement or adopt similar mode to substitute described specific embodiment, but can't depart from spirit of the present invention or surmount the defined scope of appended claims.

Claims (2)

1. a system that reduces the drift of reflection type optical fiber current meter, comprise SLD device (1), PINFET device (2), it is characterized in that: described SLD device (1), PINFET device (2) is connected with the mode of lithium niobate Y waveguide integrated optical device (3) by welding, lithium niobate Y waveguide integrated optical device (3) is swung to use, the light that SLD device (1) sends becomes linearly polarized light through lithium niobate Y waveguide integrated optical device (3), by 45 ° of fusion points (4), a branch of linearly polarized light becomes the orthogonal linearly polarized light of two bundles, along X-axis and the Y-axis of polarization maintaining optical fibre, propagate respectively, after quarter wave plate (6), two bunch polarized lights change respectively left circularly polarized light and right-circularly polarized light into, by sensor fibre, be transferred to sensor fibre end, sensor fibre end is provided with catoptron.

2. reduce a method for reflection type optical fiber current meter drift, its feature is: comprise,

The in the situation that at the polarizer, in undesirable and supposing the system, other devices being desirable device, available following Jones matrix represents the polarization characteristic of each polarizer in light path

(1) optical fiber polarizer P $G_p=\left[\begin{array}{cc}1& 0\\ 0& \mathrm{\ϵ}\end{array}\right]$

Wherein, ε represents electric vector amplitude ratio separately in extinction axis and light transmission shaft direction, uses T=-10log ε ²represent extinction ratio

(2) 45 ° of fusion point S (3) phase-modulator Z

$G_s=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& -1\\ 1& 1\end{array}\right]G_{\mathrm{Zin}}=\left[\begin{array}{cc}1& 0\\ 0& e^{\mathrm{i\ψ}(t-\mathrm{\τ})}\end{array}\right]G_{\mathrm{Zout}}=\left[\begin{array}{cc}1& 0\\ 0& e^{\mathrm{i\ψ}\left(t\right)}\end{array}\right]$

ψ in formula (t-τ) represents the t-τ phase modulation of phase-modulator constantly, and ψ (t) represents the t phase modulation of phase-modulation constantly

(4) four/wave plate R (5) Faraday devices

$G_{\mathrm{Rin}}=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& i\\ i& 1\end{array}\right]G_{\mathrm{Rout}}=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& -i\\ -i& 1\end{array}\right]G_{\mathrm{Fin}}=\left[\begin{array}{cc}\cos \mathrm{\θ}& \sin \mathrm{\θ}\\ -\sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]G_{\mathrm{Fout}}=\left[\begin{array}{cc}\cos \mathrm{\θ}& -\sin \mathrm{\θ}\\ \sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]$

Wherein, θ=VNI, V represents Verdet constant, and N is the sensor fibre number of turn, and I is tested electric current

(6) end reflector M $G_M=\left[\begin{array}{cc}1& 0\\ 0& -1\end{array}\right]$

The expression formula E of output light vector _out=G _pg _sg _zoutg _routg _foutg _mg _fing _ring _zing _sg _pe _in

Wherein, E _infor input light, be expressed as $E_{\mathrm{in}}=\left[\begin{array}{c}1\\ 1\end{array}\right]$

Output intensity

I _out＝0.5[(1+ε ²) ²+(ε ²-1) ²cos(Δφ+4θ)] ①

Wherein Δ φ=ψ (t-τ)-ψ (t), represents that the non-reciprocal phase of introducing due to phase-modulation is poor for open loop demodulation scheme, and the phase differential after demodulation is:

Normalization scaling factor

Normalization scaling factor has reflected the proportionate relationship of actual test result and desired result, and extinction ratio is larger, and normalization factor of influence is more tending towards 1, and the phase error of introducing is less, and the drift of system is lower.

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