CN102506916A - Distributed sensor network using weak reflection fiber Bragg grating (FBG) and precise positioning method of each FBG - Google Patents

Abstract

The invention relates to a distributed sensor network using weak reflection fiber Bragg gratings (FBGs) and a precise positioning method of each FBG. The sensor network comprises a weak reflection FBG array and a positioning system. The weak reflection FBG array consists of N groups of weak reflection FBGs which are serially connected in an optical path. Each weak reflection FBG group comprises M weak reflection FBGs which are sequentially arranged. The center wavelengths of all weak reflection FBGs in each FBG group are different. The positioning system comprises a tunable laser source, a detector and a calculation unit which are arranged at the initial end of the weak reflection FBG array, and a fully reflecting surface which is arranged at the terminal end of the weak reflection FBG array. A reference reflection point is arranged in the sensor network. The tunable laser source sequentially transmits optical pulses with corresponding wavelengths, obtains the direct reflecting time t<n> and t'<n> and the indirect reflecting time t<mi> and t'<mi> of the reference reflecting point and the weak reflection FBG with i reflecting wavelength being lambda<m> through the detector, and obtains the distance between any weak reflection FBG and the reference reflecting point according to the time. The distributed sensor network using the weak reflection FBGs and the precise positioning method of each FBG have the advantages that the space resolution in the distributed optical fiber sensor network can be improved and the quantity and distance of disturbed sensors are increased.

Description

Adopt the distributed sensing network of weak reflection FBG and the accurate positioning method of each FBG thereof

Technical field

The present invention relates to sensory field of optic fibre, be specifically related to adopt the distributed sensing network of weak reflection FBG and the accurate positioning method of each FBG thereof.

Background technology

FBG (Fiber Bragg Grating, Fiber Bragg Grating FBG) is a topmost senser element in the present distributing optical fiber sensing network.Because FBG has reflection wavelength is linear change with extraneous factors such as temperature, pulling force characteristic; Therefore; The skew of monitoring FBG reflection wavelength can be measured the variation that obtains external parameter, and its detectivity do not receive the influence of factors such as light source power fluctuation, bending loss of optical fiber and detector are aging, and has the self calibration characteristic; So, be fit to very much long-term safety monitoring.

Sensor location addressing and Wavelength demodulation are based on the difficult point of the distributing optical fiber sensing network of FBG.Usually have dual mode that FBG is positioned addressing at present: first kind is the wavelength-division mode, and the FBG that respectively the diverse location place is laid has nonoverlapping reflection wavelength window, can confirm the FBG that reflects according to the residing wavelength window of reflection wavelength; Second kind is time division way; Possibly there is overlapping situation in the wavelength window that is applicable to the FBG that lays; When a single wavelength light pulse is successively reflected at a plurality of weak reflection FBG place; Through the wavelength window of the earlier definite FBG of reflection wavelength, confirm the distance that lays of each FBG simultaneously through the time interval of back light pulse, thereby locate this FBG uniquely.

The distributed fiber grating sensing network of practicability adopts the wavelength-division addressing mode more at present, but the fl transmission loss of this method detection light is big, and reusable FBG number is also limited on the simple optical fiber.For improving the density that measurement point lays, realize the distributed sensing network of the long distance of high capacity, adopting the time-division addressing mode to combine weak reflection FBG is an effective way.Weak reflection FBG has narrow bandwidth, transonic periodic structure, only near the scope minimum centre wavelength is had very low reflectivity.When flashlight incident optical fibre core, only fainter a part of light is by the centre wavelength FBG reflection consistent with signal light wavelength, and remaining most of light continues transmission forward.

Typically as shown in Figure 1 based on the FBG distributed sensing network of time-division wavelength-division mixing addressing mode.Wherein transmitting terminal is a Wavelength tunable light source, and the time of Wavelength tunable light source transmission wavelength and switch is tunable, can send the rectangular light pulse.Optical circulator will be surveyed light and send into the FBG array, and reflected light is sent into detector.The FBG array is that a plurality of weak reflection FBG by the different wave length window gets up to constitute by the different polyphones of wavelength, repeats to lay after the weak reflection FBG of identical reflection windows keeps at a certain distance away.Photo-detector is then handled the light pulse sequence that returns, and confirms reflection wavelength and the reflection position of weak reflection FBG.

Limit to but above-mentioned scheme based on the addressing of Wave time division hybrid mode exists necessarily: the spatial resolution of distributed sensing network is limited, has the measurement blind area, can crosstalk because of repeatedly reflecting to bring when reflecting FBG a little less than using.For overcoming the problems referred to above, improve system performance when improving the capacity of system, must improve existing distributed sensing network and signal processing mode.

Summary of the invention

Defective to existing in the prior art the objective of the invention is to, and a kind of distributed sensing network of weak reflection FBG and accurate positioning method of FBG thereof of adopting is provided; End at weak reflection FBG array is provided with fully reflecting surface; Top at weak reflection FBG array passes through to analyze Time Domain Reflectometry information, obtains the exact position of each weak reflection FBG, thereby has improved the spatial resolution of distributing optical fiber sensing network; Do not measure the blind area, avoid repeatedly reflecting to bring crosstalking.

For reaching above purpose; The invention provides a kind of distributed sensing network that adopts weak reflection FBG; Comprise weak reflection FBG array and positioning system, the said weak FBG array that reflects is made up of the weak reflection of the N group FBG that is connected in the light path, comprises the weak reflection FBG that the individual order successively of M is provided with in each said FBG group; And the foveal reflex wavelength of M said weak reflection FBG in each FBG group is all inequality; N>=2, M>=2, said positioning system comprises tunable laser source, detector and the computing unit that is arranged on weak reflection FBG array top; And the fully reflecting surface that is arranged on weak reflection FBG array end; Said light path is provided with reference reflection point, and said tunable laser source is launched and said reference reflection point and the identical light pulse of weak reflection FBG centre wavelength to be scanned successively, and said detector is surveyed direct reflection interval of the t of said reference reflection point_nWith indirect reference time t '_n, and direct reflection interval of the t of each said weak reflection FBG_MiWith indirect reference time t '_Mi, the light pulse that the said indirect reference time is respective wavelength sees through said reference reflection point or corresponding said weak reflection FBG and through fully reflecting surface, reference reflection point or weak reflection FBG, fully reflecting surface time of reflected back detector once more; Said computing unit is according to computing formula

Obtaining i reflection wavelength is λ_mWeak reflection FBG and reference reflection point between apart from d_Mi-d_n, i=1 ..., N; In the formula, d_MiBe that i reflection wavelength is λ_mWeak reflection FBG to the distance at said weak reflection FBG array top, d_nBe the distance of said reference reflection point to said weak reflection FBG array top, c is the light velocity.

In the above-mentioned distributed sensing network, said reference reflection point is to reflect the fibre junction point on FBG or the light path a little less than any in the said weak reflection FBG array.

In the above-mentioned distributed sensing network; Said detector by the intensity of corresponding weak reflection FBG reflection in N the FBG group and time of arrival successively, obtains in N the FBG group direct reflection interval and indirect reference time that each reflects FBG a little less than corresponding according to the light pulse of a certain wavelength.

The present invention also provides the accurate positioning method of each weak reflection FBG in a kind of distributed sensing network that adopts weak reflection FBG, may further comprise the steps:

A10, fully reflecting surface is set, and chooses reference reflection point at the end of weak reflection FBG array;

A20, a little less than the top of said weak reflection FBG array emission wavelength successively equals in reference reflection point and the every group of said FBG group each reflection FBG central wavelength lambda_mLight pulse, and write down direct reflection interval of the t of said reference reflection point_nWith indirect reference time t '_n, and i reflection wavelength is λ_mDirect reflection interval of the t of corresponding said weak reflection FBG_MiWith indirect reference time t '_Mi, i=1 ..., N, the light pulse that the said indirect reference time is respective wavelength sees through said reference reflection point or said FBG and through fully reflecting surface, reference reflection point or weak reflection FBG, fully reflecting surface time of reflected back detector once more;

A30, utilize formula

Obtaining i reflection wavelength is λ_mCorresponding weak reflection FBG and reference reflection point between apart from d_Mi-d_nIn the formula, d_MiBe that i reflection wavelength is λ_mWeak reflection FBG to the distance at said weak reflection FBG array top, d_nBe the distance of said reference reflection point to said weak reflection FBG array top, c is the light velocity.

In said method, said reference reflection point is to reflect the fibre junction point on FBG or the light path a little less than any in the said weak reflection FBG array.

In said method, in steps A 20, utilize detector to be λ according to wavelength_mLight pulse by the intensity of corresponding weak reflection FBG reflection in the said weak reflection FBG group and time of arrival successively, obtaining the foveal reflex wavelength is λ_mDirect reflection interval and indirect reference time of each weak reflection FBG.

The present invention can significantly increase quantity and the distance that sensor lays.Measuring and calculating theoretically, the foveal reflex consistent wavelength, reflectivity is that 1% weak reflection FBG can connect after 210 times still that intensity still can detect and distinguish the reflection at the different weak FBG of reflection place greater than Rayleigh scattering, specifically advantage is following:

(1) distance between the reflection FBG a little less than each has been amplified 4 times with the relation of reflected impulse mistiming, precision is higher.Owing to the relative distance of only measuring weak reflection FBG, be adapted at closely interior identification and differentiate different reflective informations.

(2) calculate the relative distance between each weak reflection FBG according to formula

, eliminated fully on the principle because light path is not isometric or reason errors caused such as processor time-delay.Therefore can tunable laser source be separated with detector on the light path, tunable laser source is multiplexing in multichannel measurement, also can ignore processing time-delay fixing on the circuit.

(3) because the sets of being returned by total reflection has suffered main luminous power, the corresponding outstanding especially spike of the reflective power meeting of monitoring, light pulse is surveyed elapsed-time standards t from being transmitted into_D, t_DReflected impulse constantly can be used as reference marker, two reflected signal t of reflection FBG a little less than any_MiAnd t '_MiAlways satisfy t '_Mi-t_D=t_D-t_Mi, can be used as the reliable basis of perception reflex signal with this, each splicing point is surveyed in difference all has the fixing reflection of relative position under the wavelength, therefore also can be used as reference.

(4), there is not the blind area of measurement with respect to the distance measuring method that adopts OTDR (Optical Time Domain Reflectometer, optical time domain reflectometer).

Description of drawings

Fig. 1 is the FBG distributed sensing network system schematic diagram that mixes addressing mode in the background technology based on the time-division wavelength-division;

A kind of embodiment synoptic diagram of the distributed sensing network of the weak reflection of Fig. 2 employing provided by the invention FBG;

Fig. 3 is the intensity of reflected light distribution plan in time of each reflection spot in the accurate positioning method of each weak reflection FBG in the distributed sensing network provided by the invention;

Fig. 4 is the accurate positioning method process flow diagram of weak reflection FBG in the distributed sensing network provided by the invention.

Embodiment

Below in conjunction with accompanying drawing and specific embodiment the present invention is done further explain.

As shown in Figures 2 and 3; Adopt the distributed sensing network of weak reflection FBG to comprise weak reflection FBG array and positioning system; The FBG array is formed (N>=2) by the weak reflection of the N group FBG that is connected in the light path; Every group of weak reflection FBG group includes M weak reflection FBG (M>=2) that is disposed in order successively, and the central wavelength lambda of M weak reflection FBG_mAll inequality (m=1 ..., M).

Positioning system comprises tunable laser source, detector and the computing unit that is arranged on FBG array top, and is arranged on the terminal fully reflecting surface of FBG array.

Be provided with reference reflection point in the light path of distributed sensing network; Reference reflection point can be selected any the weak reflection FBG in the FBG array; Because any splicing point on the fibre circuit all has the fixing reflection of relative position under different wave length; Therefore, reference reflection point also can be selected any splicing point on the fibre circuit.

Tunable laser source reflects the FBG central wavelength lambda a little less than each successively in weak reflection FBG array emission and reference reflection point and each FBG group_mThe light pulse that wavelength is identical, wavelength X_mDetermined that each FBG group is λ at the foveal reflex wavelength only_mSingle weak reflection FBG place reflect, N FBG group just has N and reflects FBG a little less than individual and reflect like this.Referring to Fig. 2, this N weak reflection FBG is owing to the distance to transmitting terminal is different, therefore again; Also have the time of arrival of reflection light pulse successively; Like this, when detector receives reflection light pulse, can distinguish direct reflection interval of the t that identifies reference reflection point according to time of arrival and light intensity_nWith indirect reference time t '_n, and i reflection wavelength is λ_mDirect reflection interval of the t of corresponding weak reflection FBG_MiAnd indirect reference time t '_Mi, i=1 ..., M.Directly reflection interval t_nOr t_MiBe meant the time that the light pulse of being sent by tunable laser source is experienced by reference reflection point or the direct reflected back detector of weak reflection FBG, indirect reference time t '_nOr t '_MiBe meant that the light pulse of being sent by tunable laser source sees through corresponding reference reflection point or weak reflection FBG and successively through fully reflecting surface, reference reflection point or weak reflection FBG, fully reflecting surface time of reflected back detector once more.

Computing unit is according to formula

Obtain a little less than in the of any one between reflection FBG and the reference reflection point apart from d_Mi-d_nIn the formula, d_MiBe that i reflection wavelength is λ_mCorresponding weak reflection FBG to the distance at weak reflection FBG array top, d_nBe the distance of reference reflection point to weak reflection FBG array top, c is the light velocity.

Through changing the λ of tunable laser source emission light pulse_m, just can obtain in the FBG array exact position of each weak reflection FBG.

As shown in Figure 4, the accurate positioning method of each weak reflection FBG may further comprise the steps in the distributed sensing network provided by the invention:

A10, at the end of weak reflection FBG array fully reflecting surface is set, and in the FBG array, chooses reference reflection point, reference reflection point can reflect FBG for a little less than in the FBG array any, also can be any splicing point on the fibre circuit.

A20, be λ at the top emission wavelength of weak reflection FBG array_mDetecting optical pulses, λ_mIdentical with the centre wavelength of reflection FBG a little less than in reference reflection point and each FBG group each, intensity and the reflection interval surveying and write down this reflection light pulse through detector;

Intensity through reflection light pulse and the time that successively arrives, identify direct reflection interval of the t of reference reflection point_nWith indirect reference time t '_n, and i reflection wavelength is λ_mDirect reflection interval of the t of corresponding weak reflection FBG_MiWith indirect reference time t '_MiBecause the sets of being returned by total reflection has suffered main luminous power, the corresponding outstanding especially spike of the reflective power meeting of monitoring, light pulse is surveyed elapsed-time standards t from being transmitted into_D, t_DReflected impulse constantly can be used as reference marker, and i reflection wavelength is λ_mTwo reflected signal t of corresponding weak reflection FBG_MiAnd t '_MiAlways satisfy t '_Mi-t_D=t_D-t_Mi, can be used as the reliable basis of perception reflex signal with this.According to the time of the arrival of reflection light pulse and the intensity of reflection light pulse; Identify the direct reflection light pulse and the time of arrival of each reflection spot, and the reflection light pulse and the time of arrival thereof of process tunable laser source-fully reflecting surface-weak reflection FBG-fully reflecting surface-detector.

A30, utilizationCalculate between the arbitrarily weak reflection FBG apart from d_Mi-d_n

The calculating principle of aforementioned calculation formula is following:

When tunable laser source is operated in single wavelength following time; Because the foveal reflex wavelength of each weak reflection FBG is different; Only equal the weak reflection FBG place generating unit sub reflector of incident wavelength at the foveal reflex wavelength; And the weak equal transmission in reflection FBG place of all the other different emission, so can ignore the weak reflection FBG that other do not reflect this moment.Suppose that incident light and reflection wavelength all are λ_m, the light incidence point is D to the distance of terminal fully reflecting surface, the light incidence point is d to the distance of n weak reflection FBG_n(referring to Fig. 3).Detector converts probe current to after receiving reflection light pulse, can think roughly that the size of probe current is proportional to the size of intensity of reflected light, and the time that the priority time that photocurrent produces arrives corresponding to light pulse.Ignore by twice of weak reflection FBG reflection and above situation, the light pulse of two types of concentration of energy is arranged: from inciding the direct reflected light detector by weak reflection FBG, consuming time therebetween is t_nThrough the reflected impulse of tunable laser source-fully reflecting surface-weak reflection FBG-fully reflecting surface-detector route, consuming time therebetween is t '_nSuppose that light pulse is t from being back into exit point to the circuit delay that is received machine detection experience_x, the definition light velocity is c, then has:

$t_n=\frac{2*d_n}{c}+t_x,$

$t_n^{\&prime;}=\frac{4*D-2*d_n}{c}+t_x,$

$t_n^{\&prime;}-t_n=\frac{4*D-4*d_n}{c}.$

In like manner, have for m weak reflection FBG:

$t_m^{\&prime;}-t_m=\frac{4*D-4*d_m}{c},$

$(t_n^{\&prime;}-t_n)-(t_m^{\&prime;}-t_m)=\frac{4*(d_m-d_n)}{c},$

Distance between the then weak arbitrarily reflection FBG:

$d_m-d_n=\frac{c*(t_n^{\&prime;}+t_m-t_n-t_m^{\&prime;})}{4}.$

The present invention is not limited to above-mentioned embodiment, for those skilled in the art, under the prerequisite that does not break away from the principle of the invention, can also make some improvement and retouching, and these improvement and retouching also are regarded as within protection scope of the present invention.The content of not doing in this instructions to describe in detail belongs to this area professional and technical personnel's known prior art.

Claims (6)

1. adopt the distributed sensing network of weak reflection FBG; Comprise weak reflection FBG array and positioning system, said weak reflection FBG array is made up of N the weak reflection FBG that is connected in the light path, comprises M weak reflection FBG that is disposed in order successively in each said FBG group; And the foveal reflex wavelength of M said weak reflection FBG in each FBG group is all inequality; N >=2, M >=2 is characterized in that: said positioning system comprises:

Tunable laser source is arranged on the top of said weak reflection FBG array, and said light path is provided with reference reflection point, and said tunable laser source is launched and said reference reflection point and the identical light pulse of weak reflection FBG centre wavelength to be scanned successively;

Fully reflecting surface is arranged on the end of said weak reflection FBG array;

Detector is arranged on the top of said weak reflection FBG array, surveys direct reflection interval of the t of said reference reflection point_nWith indirect reference time t '_n, and direct reflection interval of the t of each said weak reflection FBG_MiAnd indirect reference time t '_Mi, the light pulse that the said indirect reference time is respective wavelength sees through said reference reflection point or corresponding said weak reflection FBG and through fully reflecting surface, reference reflection point or weak reflection FBG, fully reflecting surface time of reflected back detector once more;

Computing unit is arranged on the top of said FBG array, according to computing formula

Obtain that reflection wavelength is λ in the i group_mWeak reflection FBG and reference reflection point between apart from d_Mi-d_n, i=1 ..., N; In the formula, d_MiBe that reflection wavelength is λ in the i group_mWeak reflection FBG to the distance at said weak reflection FBG array top, d_nBe the distance of said reference reflection point to said weak reflection FBG array top, c is the light velocity.

2. the distributed sensing network of the weak reflection of employing as claimed in claim 1 FBG is characterized in that: said reference reflection point is to reflect the fibre junction point on FBG or the light path a little less than any in the said weak reflection FBG array.

3. the distributed sensing network of the weak reflection of employing as claimed in claim 1 FBG; It is characterized in that: said detector by the intensity of corresponding weak reflection FBG reflection in N the FBG group and time of arrival successively, obtains in N the FBG group direct reflection interval and indirect reference time that each reflects FBG a little less than corresponding according to the light pulse of a certain wavelength.

4. the accurate positioning method of each weak reflection FBG in the distributed sensing network of reflection FBG is characterized in that a little less than adopting, and may further comprise the steps:

A10, fully reflecting surface is set, and chooses reference reflection point at the end of weak reflection FBG array;

A20, in the top of weak reflection FBG array emission successively and reference reflection point and every group of said weak reflection FBG group, reflect the identical light pulse λ of FBG centre wavelength a little less than each_m, and write down direct reflection interval of the t of said reference reflection point_nWith indirect reference time t '_n, and i reflection wavelength is λ_mDirect reflection interval of the t of said weak reflection FBG_MiWith indirect reference time t '_Mi, the light pulse that the said indirect reference time is respective wavelength sees through corresponding said reference reflection point or said weak reflection FBG and through fully reflecting surface, reference reflection point or weak reflection FBG, fully reflecting surface time of reflected back detector once more;

A30, utilize formula

Obtaining any i reflection wavelength is λ_mSaid weak reflection FBG and reference reflection point between apart from d_Mi-d_n, i=1 ..., N; In the formula, d_MiBe that i reflection wavelength is λ_mWeak reflection FBG to the distance at said weak reflection FBG array top, d_nBe the distance of said reference reflection point to said weak reflection FBG array top, c is the light velocity.

5. method as claimed in claim 4 is characterized in that: said reference reflection point is to reflect the fibre junction point on FBG or the light path a little less than any in the said weak reflection FBG array.

6. method as claimed in claim 4 is characterized in that: in steps A 20, detector is according to wavelength X_mLight pulse by the intensity of corresponding weak reflection FBG reflection in the said weak reflection FBG array and time of arrival successively, obtaining the foveal reflex wavelength is λ_mDirect reflection interval and indirect reference time of each weak reflection FBG.

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