CN101487723B - Optical fiber distributed perturbation sensor based on Sagnac interferometer - Google Patents

Abstract

The invention discloses an optical fiber distributed disturbance sensor based on a Sagnac interferometer. A Sagnac interferometer is used to couple a support arm, and a delay optical fiber ring is attached at the same time, that is, a single Sagnac interferometer A delay fiber ring is superimposed in the instrument to form two Sagnac interferometers of different lengths. Through the propagation of optical pulses in the interferometer, the time division multiplexing of two Sagnac interferometers of different lengths is realized, and according to The amplitude of the output signals of the two Sagnac interferometers is used to calculate the position of the disturbance point and realize the distributed sensing of the disturbance. The system of the invention has low cost, simple structure and good stability.

Description

Optical fiber distributed perturbation sensor based on Sagnac interferometer

Technical field

The present invention relates to a kind of Fibre Optical Sensor, relate in particular to a kind of optical fiber distributed perturbation sensor based on Sagnac interferometer.

Background technology

Fibre Optical Sensor is because its anti-electromagnetic interference (EMI), volume is little, in light weight, susceptibility is high, be easy to networking, particularly can realize good characteristics such as distributed measurement, has widely in industry, civilian and military field and uses.Wherein, optical fiber distributed perturbation sensor is all significant in fields such as perimeter alarm, oil pipeline monitoring and acoustic emission monitor(ing)s.

At present, according to the difference of principle of work, optical fibre distribution type sensor mainly is divided into four kinds of forms such as interferometer type, grating type optical fiber, optical time domain reflectometer type, intensity modulation type and scatter-type.

Wherein, the interferometer type distributed sensor has to be realized that principle is simple, highly sensitive, device cost is low, is suitable for good characteristic such as long-distance sensing, has become the main technical schemes of optical fiber distributed perturbation sensor.The scheme of existing interferometer type optical fibre distribution type sensor mainly contains two Mach Zehnder types, single Sagnac type, two Sagnac type, Sagnac+Michaelson, Sagnac+Mach Zehnder type, dual wavelength Sagnac type, various ways such as double modulation frequency Sagnac type.

As shown in Figure 1, existing Sagnac interferometer comprises the Lights section, photodetector, coupling mechanism 1, sensor fibre, after light process coupling mechanism 1 beam split that the Lights section sends, be divided into two-way light respectively clockwise and propagate along sensor fibre counterclockwise, and two-way light interferes at coupling mechanism 1 place, receives interference signal by photodetector.

In the prior art, in time domain, realize Sagnac interferometer to the time become the location of disturbance, can pass through two Sagnac interferometers, or while two operation wavelengths, or a Sagnac interferometer that is operated in two modulating frequencies is simultaneously realized.

There is following shortcoming at least in above-mentioned prior art:

Need to adopt two light sources and detector, and the devices such as modulator that need practical wavelength division multiplexer and different frequency, the hardware cost of system and the complicacy and the less stable of structure increased.

Summary of the invention

The purpose of this invention is to provide that a kind of system cost is low, simple in structure, the optical fiber distributed perturbation sensor based on Sagnac interferometer of good stability.

The objective of the invention is to be achieved through the following technical solutions:

Optical fiber distributed perturbation sensor based on Sagnac interferometer of the present invention, comprise Sagnac interferometer, it is characterized in that, on the sensor fibre of described Sagnac interferometer, be coupled out a support arm, and on this support arm, optical delay devices is set, form two Sagnac interferometers, wherein, light wave in first Sagnac interferometer is propagated along former sensor fibre, without described optical delay devices; Light wave in second Sagnac interferometer is propagated in former sensor fibre, and through described optical delay devices;

Feed light to Sagnac interferometer, light wave is propagated in first Sagnac interferometer and second Sagnac interferometer respectively;

According to the phase differential of two Sagnac interferometer output signals, calculate the position Δ L of disturbance point by following formula:

In the formula, ω is the angular frequency of disturbing signal; L ₁Length for sensor fibre; L ₂=L ₁+ L _D, L _DEquivalent length for the optical delay devices on the support arm; C is the light velocity; It is the phase differential of two interferometer output signals.

As seen from the above technical solution provided by the invention, optical fiber distributed perturbation sensor based on Sagnac interferometer of the present invention, because by a Sagnac interferometer, be coupled out a support arm, additional simultaneously optical delay devices, the Sagnac interferometer of two different lengths of formation, by the propagation of light in interferometer, according to the phase differential of two Sagnac interferometer output signals, calculate the position of disturbance point, realize distributed sensing to disturbance.System cost is low, simple in structure, good stability.

Description of drawings

Fig. 1 is the structure principle chart of Sagnac interferometer in the prior art;

Fig. 2 is the structure principle chart of Sagnac interferometer among the present invention.

Embodiment

Optical fiber distributed perturbation sensor based on Sagnac interferometer of the present invention, its preferable embodiment as shown in Figure 2, comprise Sagnac interferometer, on the sensor fibre of described Sagnac interferometer, be coupled out a support arm, and on this support arm, optical delay devices is set, form two Sagnac interferometers.Can be coupled out described support arm by two coupling mechanisms are set on the sensor fibre of described Sagnac interferometer, also can be coupled out support arm by other beam split or coupled apparatus.

Wherein, the light wave of first Sagnac interferometer is propagated along former sensor fibre, without described support arm; The light wave of second Sagnac interferometer is propagated along former sensor fibre through described support arm.

Feed light to Sagnac interferometer, light wave is propagated in first Sagnac interferometer and second Sagnac interferometer respectively;

According to the phase differential of two Sagnac interferometer output signals, calculate the position Δ L of disturbance point by following formula:

In the formula, ω is the angular frequency of disturbing signal; L ₁Length for sensor fibre; L ₂=L ₁+ L _D, L _DEquivalent length for the optical delay devices on the support arm; C is the light velocity; It is the phase differential of two interferometer output signals.

Described optical delay devices can also can be other optical time delay unit spare for postponing fiber optic loop.

The length of described delay fiber optic loop can equal the length of described sensor fibre, also can select other length for use.

Described Sagnac interferometer comprises the Lights section, and the light that described the Lights section sends is pulsed light.The Lights section can comprise light-pulse generator or continuous light source and pulse-modulator etc.

Can adopt time-division multiplex technology that the output signal of two Sagnac interferometers is distinguished.

Optical fiber distributed perturbation sensor based on Sagnac interferometer of the present invention, adopt a Sagnac interferometer, be coupled out a support arm, additional simultaneously one postpones fiber optic loop, promptly one of stack postpones fiber optic loop in single Sagnac interferometer, form two different length Sagnac interferometers, by the propagation of light pulse in interferometer, realize the time division multiplex of two different length Sagnac interferometers, by two time-multiplexed Sagnac interferometer output signals, from the time-multiplexed interference signal of two-way, calculate the disturbance location, realize distributed sensing disturbance.

The present invention has realized time-division multiplex technology in the distributed perturbation sensor of traditional Sagnac interferometer, position by time multiplexing signal.System cost is low, simple in structure, good stability.

Below by specific embodiment the present invention is carried out detail analysis:

As shown in Figure 2, in traditional Sagnac interferometer, having superposeed one postpones fiber optic loop, has formed two Sagnac interferometers.The light path of first interferometer is directly to get back to coupling mechanism 1 by sensor fibre by coupling mechanism 1; Optical routing coupling mechanism 1 beginning of second interferometer via coupling mechanism 2, postpones fiber optic loop and coupling mechanism 3, gets back to coupling mechanism 1 at last.

Referring to Fig. 1,, suppose that disturbance is to have the cosine form for Sagnac interferometer:

In the formula,

With ω be respectively the amplitude and the angular frequency of disturbing signal, disturbing signal is meant time varying signal.

Disturbing signal acts in the Sagnac interferometer, can cause phase modulation (PM), at perturbation action point not under the situation of Sagnac fiber optic loop mid point, there is time delay in the phase modulation (PM) of the disturbing signal of two-way light wave wherein clockwise and that counterclockwise propagate, cause when interfering, there is following phase differential in the two-way light wave:

In the formula,

Be that Δ τ is the delay inequality of phase modulation (PM) in the two-way light wave transmissions that disturbance causes, and in Sagnac interferometer, has along the phase differential of two-way light wave clockwise and that counterclockwise propagate:

Δτ＝n(L-2ΔL)/c (3)

In the formula, n is the optical fiber effective refractive index, and L is the length of Sagnac interferometer, and c is the light velocity, and Δ L is the distance of disturbance location apart from coupling mechanism 1.

Again as shown in Figure 2, postpone two Sagnac interferometers that fiber optic loop forms later on for stack, just the length difference is respectively L ₁And L ₂, and L ₂=L ₁+ L _D, L wherein _DBe the length that postpones fiber optic loop.For two Sagnac interferometers, its phase differential is respectively:

As following formula, φ _Int1(t) show as one with

Be amplitude, ω is the cycle,

A sine wave for initial phase; While φ _Int2(t) show as one with $2{\mathrm{\φ}}_0\sin [\mathrm{\ω}\frac{(L_2-2(L_1-\mathrm{\ΔL}))}{c}/2]$ Be amplitude, ω is the cycle,

A sine wave for initial phase.

The initial phase of Sagnac interferometer 1 is expressed as

The initial phase of Sagnac interferometer 2 is expressed as

Then the phase differential of two phase signals is

$=\mathrm{\ω}\frac{(L_2-3L_1+4\mathrm{\ΔL})}{2c}$

When making L ₂=3L ₁The time,

From (9) formula, as can be known, from the phase signal of two Sagnac interferometers, can solve the position Δ L of disturbing signal.The luminous power of two interferometer signals that receive in photodetector is respectively:

At known input optical power P ₀Condition under, can obtain P ₀₁And P ₀₂

$P_{01}={10}^{-\frac{\mathrm{\α}{L}_s}{10}}\frac{P_0}{2}---\left(12\right)$

$P_{02}={10}^{-\frac{\mathrm{\α}(L_S+L_D)}{10}}\frac{P_0}{2}---\left(13\right)$

Wherein, α is the loss factor of optical fiber.

By solving phase signal (extracting its phase signal from power signal has several different methods, and the present invention is not specifically related to extracting method) in power signal (10) and (11), the delay difference that calculates two phase signals can realize the location.

Distinguish the signal of first and second Sagnac interferometers, can adopt time-multiplexed mode, promptly the output terminal at wide spectrum light source increases a modulator or photoswitch, the continuous light wave that light source is sent becomes pulsed light wave, and the frequency of pulse can be selected according to the length of first Sagnac interferometer and the length of delay fiber optic loop.

Postpone time delay device such as fiber optic loop among the present invention and play time-lag action; Modulator or photoswitch play the continuous light wave that wide spectrum light source is sent and carry out pulse modulated effect, its objective is the realization light pulse, also can use light-pulse generator etc.; Coupling mechanism 1,2,3 all is in order to realize beam split and coupling, also can to use circulator, beam splitter etc., playing beam splitting and coupling.

In Sagnac interferometer, adopt time-division multiplex technology by ring retard; Utilize the differentiation of light pulse realization to the signal of the Sagnac interferometer of two different lengths; On measuring-signal peak-to-peak value basis, carry out location algorithm.System architecture is simple, and device is little to the influence of system performance; Reduce cost, avoided the use of a plurality of expensive device; Highly sensitive.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.

Claims (5)

1. a kind of optical fiber distributed disturbance sensor based on Sagnac interferometer, comprises Sagnac interferometer, it is characterized in that, on the sensing fiber of described Sagnac interferometer, couple out an arm, And an optical delay device is set on the arm to form two Sagnac interferometers, wherein the light wave in the first Sagnac interferometer propagates along the original sensing fiber without passing through the optical delay device; the second The light waves in the two Sagnac interferometers propagate in the original sensing fiber and pass through the optical delay device; Pass light into the Sagnac interferometer, and the light waves propagate in the first Sagnac interferometer and the second Sagnac interferometer respectively; According to the phase difference of the output signals of the two Sagnac interferometers, the position ΔL of the disturbance point is calculated by the following formula:

In the formula, ω is the angular frequency of the disturbance signal; L ₁ is the length of the sensing fiber; L ₂ = L ₁ + L _D , L _D is the equivalent length of the optical delay device on the arm; c is the speed of light;

is the phase difference of the output signals of the two interferometers; The optical delay device is a delay fiber ring; The length of the delay fiber ring is equal to the length of the original sensing fiber. 2. the optical fiber distributed disturbance sensor based on Sagnac interferometer according to claim 1, is characterized in that, by setting two couplers on the sensing fiber of described Sagnac interferometer to couple out all the aforementioned arm. 3. The optical fiber distributed disturbance sensor based on Sagnac interferometer according to claim 1, characterized in that, the Sagnac interferometer comprises a light source part, and the light emitted by the light source part is pulsed light. 4. The optical fiber distributed disturbance sensor based on Sagnac interferometer according to claim 3, characterized in that, the light source part comprises a pulsed light source or a continuous light source and a pulse modulator. 5. according to claim 3 or 4 described fiber optic distributed disturbance sensor based on Sagnac interferometer realizes the method for disturbance localization, it is characterized in that, adopt time division multiplexing technique to describe two Sagnac interferometers The output signal is distinguished.

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