CN101555989A - Safety monitoring system based on distributed optical fiber - Google Patents

Abstract

The invention discloses a safety monitoring system based on distributed optical fiber, comprising a transmitted and received light signal processing module 100, a light delay component 101 and a loop optical fiber part 102 which are formed into a double-variant-type optical fiber Sagnac interferometer. The transmitted and received light signal processing module 1 comprises a computer 1, a light source driver 2, a light source 3, a polarization remover 4, a detector 10 and a circuit processing board 11 with a detector. The light delay component 2 comprises a 3*3 optical fiber coupler 5, a short fiber 6, a long fiber 7 and a 2*1 coupler 8. The loop optical fiber part 102 relates to induction optical fibers 9 of two cases, i.e. vibration and impact act on the two optical fibers in a loop or on one optical fiber in the loop. A single system is additionally provided with a light switch to perform multi-channel periodic route-inspection measurement and monitor large-area vibration. The remote intelligent monitoring can be realized through the networking of a plurality of monitoring systems.

Description

Safety monitoring system based on distribution type fiber-optic

Technical field

The present invention discloses a kind of safety monitoring system based on distribution type fiber-optic, and the distributed measurement that relate to vibration, impacts belongs to the safety precautions technical field.

Background technique

The safety of maintain infrastructure is a basic demand of social stability, rapid economic development.Infrastructure such as communication optical cable, high-voltage fence, oil transport pipeline, gas pipeline, bridge, dam, building are carried out safety monitoring, to determine health, maintenance needs, life-span and other characteristic, be not only these facilities and realize the guarantee of technical function, the effective means of avoiding causing heavy economic losses especially, maintaining social stability and develop.

The being perfectly safe property of optical fiber information transmission is broken in recent years, eavesdropping incident at the land lightguide cable link has report repeatly, and Central Intelligence Agency's submarine optical fiber cable eavesdropping plan that related media discloses more causes the abundant attention of people to the submarine optical fiber cable information transmission safety.How in time to find and accurately a kind of especially challenge of these accidents of location.

Along with the development of pipeline transport industry, various pipeline transport safety monitoring technologies are also in continuous development, and present existing pipe safety production monitoring technology mainly contains two classes.One: the monitoring technology after the pipe leakage incident takes place, this technology mainly contains " tube fluid mechanical state detection technique ".Tube fluid mechanical state detection technique is to gather signals such as the flow of fluid in the pipeline, temperature and pressure in real time, carry out pipeline leakage testing and location, this technology is subjected to the effects limit such as performance of fluid characteristics, delivery technology and test instrument in the pipeline, sensitivity and Location accuracy to line leakage are lower, and this class technology comprises: pressure gradient method, negative pressure wave method, flow equilibrium method.They are two years old, prevention monitoring technology before the pipeline damage incident takes place, pipeline damage early warning technology just, existing such technology mainly is " technology of acoustic wave monitoring " at present, this technology is to utilize sound wave along the pipeline transmission principle, an active transducer is being installed every about 1km, picking up pipeline sound signal along the line is analyzed, determine event property, and then the incident of destroying pipeline found in advance, but each sensing means must be equipped with a cover power supply unit and a communicator, not only increases the investment and the maintenance cost of equipment, and these facilities are also destroyed easily itself, and device can not normally be moved.

Along with the development of optical fiber sensing technology, the long-distance distributed optical fiber sensory technique also begins to be applied to pipeline leakage testing and communication optical cable safety monitoring, mainly contains scattering method and optical interferometry behind the light.Scattering method utilizes the influence of external event to optical fiber transmission property based on Rayleigh, Raman, Brillouin, polarization theory behind the light, judges local external force, temperature variation by astigmatism strong variation the in back in the detection and localization optical fiber, and then can assess the safe condition of pipeline.For pipeline, distribution type fiber-optic temperature and stress monitoring technology are the positions that the medium that utilizes the nonlinear characteristics of optical fiber (Raman effect and brillouin effect) to gather pipe leakage is in real time determined leakage point to the temperature effect and the impact stress of optical fiber, and this technology is subjected to the distance limit of the structure of optical cable and optical cable and leakage point and influences monitoring effect.

That optical interferometry has is highly sensitive, dynamic range big, response is fast, transmission distance is long, can satisfy long distance, microvibration detection requirement.Continuous wave laser is used in Chinese invention patent applications 200410020046.6,200410040282.4,200610113044.0,200510023104.5,200610090594.5 etc., present low-power incident problem, when monitoring distance surpasses 20 kms use general single mode fiber, because the restriction of excited Brillouin threshold value, incident power is no more than 2 milliwatts, has superiority in the monitoring of moderate distance length.Utilize principle of interference to make up length and need extremely exacting terms apart from monitoring system.Mach-Zehnder interferometer and Michelson interferometer since light propagate on two different light arms, cause the independence of polarization of light from phase modulation, cross-phase modulation, the polarization state of interference optical field presents unpredictable problem, the error that just is difficult to accomplish decimeter grade when mounted at two optical fiber that reach km up to a hundred in addition, this can need the laser of narrow live width could guarantee to interfere.The Chinese invention patent 200710051004.2 of our application uses a modification Sagnac interferometer to constitute safety monitoring system of long-distance pipeline, article two, sense line, enable advantageously that standby optical fiber is feasible on its pipeline, but adopt two branch road demodulation to suppress noise, its cost is higher.

Summary of the invention

The objective of the invention is to adopt two modification optical fiber Sagnac interferometers, the demodulation of single channel coherent optical pulse ratio constitutes safety monitoring system cheaply, realizes long apart from microvibration, impulse detection and location.In order to achieve the above object, the following technological scheme that the present invention adopts: comprise transmitting and receiving optical signal puocessing module 100, light delay parts 101, loopback fiber part 102 constitutes a two modification optical fiber Sagnac interferometer; Transmit and receive that optical signal puocessing module 1 comprises computer 1, light source drive 2, light source 3, removes inclined to one side device 4, the processing of circuit plate 11 of prober 10, band prober; Light delay parts 2 comprise 3 * 3 Fiber Optic Coupler 5, short fiber 6, long optic fiber 7 and 2 * 1 Couplers 8; Loopback fiber part 102 relates to the sensor fibre 9 of two kinds of situations: vibration, percussion are in the loop on two optical fiber (as shown in Figure 1) or in the loop on optical fiber (as shown in Figure 2).

Working principle of the present invention: as shown in Figure 1, computer 1 control light source drive 2 makes light source 3 by certain frequency emission light pulse, and pulsewidth is less than 10ps, and photoderm power is less than the stimulated Raman scattering threshold value.Pulse is by removing inclined to one side device 4 inputs 3 * 3 Couplers 5, go the effect of inclined to one side device 4 to avoid the influence of light source polarization, preferred coupled device 5 merit proportions by subtraction are 1: 1: 1, the light pulse that is divided into three beams equivalent is respectively at short fiber 13, long optic fiber 14 and sensor fibre 9 are counterclockwise propagated, two-beam pulse input coupler 8 wherein, preferred coupled device 8 merit proportions by subtraction are 1: 1, the two light pulse amounts of contracting 1/2 output to propagate in the direction of the clock in the sensor fibre 9 and reach Coupler 5, the light pulse that light pulse input coupler 8 components of propagating are equal is counterclockwise being grown respectively, short fiber 7, propagate in 6 and reach Coupler 5, there are and have only experience two light pulses the longest and the shortest correspondence to interfere, the coherent pulse of two sequencings of output, they continue to propagate priority and are converted to electrical signal by photodetector, be converted to digital signal by processing of circuit plate 11 again, handle by computer 5, calculate vibration position on the sense line.Advantageously two priorities coherent optical pulse that reaches and the coherent optical pulses that next time, two priorities reached can not mix, and the frequency of light source 7 emission light pulses is smaller or equal to c/ (n _EffL), c is a light speed in a vacuum, n _EffBe the optical fiber effective refractive index, short fiber 13 length are L ₁Km, long optic fiber 14 length are L ₂Km, L=L ₂-L ₁Advantageously each light pulse of returning of the complete conversion of prober, the A/D sampling retention time, the A/D sample frequency was greater than the light source repetition frequency greater than pulsewidth.The digital signal of this two coherent optical pulses conversion separated as ratio transfer to suppress light source fluctuation.The oscillation function that oscillating point D produces among Fig. 1 is made as φ (t), shortest path, the phase difference φ that longest path is clockwise and light pulse that propagate counterclockwise produces at Coupler 5 _m, m=1,2 are expressed as:

Δφ _m＝φ(t+τ _m+T)+φ(t+τ _m)-φ(t)-φ(t+T)-2π/3 (1)

Oscillating point D is made as x from the distal-most end distance, and the time between light comes and goes at these 2 in the formula (1) is T, T=2 _NeffX/c, τ _m=n _EffL _m/ c, t are the moment that Coupler 5 beam splitting light pulses take the lead in reaching oscillating point D.If the fourier transform of φ (t) is F (ω), get by the linear behavio(u)r of fourier transform

(2)

Trap point is in the formula (2) , promptly

ωT＝2kπ-π，ωτ _m≠2kπ，m＝1，2 (3)

K is a natural number in the following formula (3), and eigen frequency is:

$f_{\mathrm{null}}=\frac{2k-1}{2T}=\frac{(2k-1)c}{{4n}_{\mathrm{eff}}x},f_{\mathrm{null}}\≠\frac{\mathrm{kc}}{n_{\mathrm{eff}}{L}_m},m=\mathrm{1,2}---\left(4\right)$

Obviously, as x＞0.25L ₂The time, any k is just had $f_{\mathrm{null}}\≠\frac{\mathrm{kc}}{n_{\mathrm{eff}}{L}_m},$ M=1,2, that is to say that native system has the monitoring blind area, length is 0.25L ₂With eigen frequency f _NullPairing fiber lengths x is: $x=\frac{(2k-1)c}{4n_{\mathrm{eff}}{f}_{\mathrm{null}}}---\left(5\right)$

Because formula (1) is similar fully with formula (2) frequency space, their photosignal does to carry out fourier transform again after the ratio can obtain The above results equally, and can calculate the oscillation function image of oscillating point generation.

The oscillation function that oscillating point D produces among Fig. 2 is made as φ (t), shortest path, the phase difference φ that longest path is clockwise and light pulse that propagate counterclockwise produces at Coupler 5 ₃, Δ φ ₄Be expressed as:

Δφ _m+2＝φ(t+τ _m-T ₀)-φ(t+T ₀)-2π/3，m＝1，2 (6)

Oscillating point D is made as x from the distal-most end distance, and the one-way time that light passes through between these 2 in the formula (6) is T ₀, T ₀=n _EffX/c, t are that Coupler 5 beam splitting light pulses are propagated the moment that reaches distal-most end counterclockwise.If the fourier transform of φ (t) is F (ω), get by the linear behavio(u)r of fourier transform

Falling into humorous wave point in the formula (7) is

, promptly

ω(2T ₀-τ _m)＝2kπ，m＝1，2 (8)

K is a natural number in the following formula (8), and eigen frequency is:

$f_{\mathrm{null}}=\frac{k}{2T_0-{\mathrm{\τ}}_m}=\frac{\mathrm{kc}}{n_{\mathrm{eff}}(2x-L_m)},m=\mathrm{1,2}---\left(9\right)$

This structure does not have the monitoring blind area, but humorous wave point position difference in the spectrum space that front and back are set up respectively for twice, their photosignal is done to carry out also difference of the humorous wave point of fourier transform position again after the ratio, calculates the position, oscillating point respectively, averages and reduces uncertainty.

Single detection system installs optical switch additional, carries out the multichannel cycle and patrols and examines measurement, the monitor large-area oscillation phenomenon.A plurality of monitoring system networkings realize the long-distance intelligent monitoring.

Advantage of the present invention:

1., be widely used: promptly can be applicable to the safety monitoring of pipeline, can be applied to large-area safety monitoring again.

2., detection sensitivity height, monitoring distance are far away: adopt and go inclined to one side device to avoid the influence of light source polarization, the frequency that light source 7 emission light pulses are set is smaller or equal to c/ (n _EffL), make two priorities coherent optical pulse that reaches and the coherent optical pulse that next time, two priorities reached not to mix, system signal noise ratio is guaranteed; Be set greater than pulsewidth the A/D sampling retention time, the A/D sample frequency is greater than the light source repetition frequency, and each coherent optical pulse that returns of the complete conversion of prober makes the undistorted phenomenon of electrical signal.The priority coherent optical pulse that returns is independently set up spectrum space separately and is determined that vibration position and they do to set up spectrum space again after the ratio and determine the position, can also set up the functional image of vibration thus.Single detection system installs optical switch additional, carries out the multichannel cycle and patrols and examines measurement, the oscillation phenomenon of monitor large-area.

3., Location accuracy height: adopt short-pulse laser, can obtain positioning error in theory less than 2m less than 10ns.

Accompanying drawing and description of drawings

Fig. 1 oscillating point of the present invention acts on two system construction drawings on the optical fiber wire;

Fig. 2 oscillating point of the present invention acts on a system construction drawing on the optical fiber wire;

The sequential chart of the photosignal that Fig. 3 the present invention gathers;

The oscillation function image that Fig. 4 the present invention obtains;

The spectrogram that counterclockwise, clockwise light pulse is interfered between Fig. 5 longest path of the present invention.

The repeated use of reference number is intended to represent identical or similar feature of the present invention or element in this specification of the present invention and the accompanying drawing.

Embodiment

For the purpose of summarizing the present invention, this paper has described some aspect of the present invention, advantage and novel feature.Should be appreciated that, need not realize all these advantages by any one specific embodiment according to the present invention.Therefore, the invention is not restricted to disclosed any specific embodiment.

Embodiments of the invention are as follows:

1, embodiment 1 safety monitoring optic telecommunication cable, this example is an experimental prototype, it constitutes as shown in Figure 1.Thick connecting line is an optical fiber among the figure, is provided by optical cable company of Chengdu Zhongzhu, and thin connecting line is an electric wire.Computer 1 is the PC104 system, the processing of circuit plate 11 of light source drive 2, band prober is that 1 1MHz12bitA/D chip, 1 PIN prober, drive circuit, processing circuit, buffer area are integrated in the integrated circuit board, finish by our making in laboratory, light source 3 also is homemade optical fibre laser, 980nm pump erbium-doped optical fiber output 1550nm light pulse, live width 8nm, pulsewidth 6.5ns, peak power 5W, repetition frequency 100kHz, be coiled in the integrated circuit board upper strata, integrated circuit board inserts in the slot of PC104 system.Coupler and go inclined to one side device 4 to provide by Shanghai writing brush space company; Systems soft ware is worked out by our laboratory, comprises system drive, collection, analysis, demonstration storage.Computer 1 control light source drive 2 makes light source 3 by 100kHz repetition frequency emission light pulse.Pulse is by removing inclined to one side device 4 inputs 3 * 3 Couplers 5, the light pulse that is divided into three beams equivalent is respectively at short fiber 6, long optic fiber 7 and sensor fibre 9 are counterclockwise propagated, two-beam pulse input coupler 8 wherein, this two light pulses amount of contracting 1/2 outputs to propagate in the direction of the clock in the sensor fibre 9 and reaches Coupler 5, the light pulse that light pulse input coupler 8 components of propagating are equal is counterclockwise being grown respectively, short fiber 7, propagate in 6 and reach Coupler 5, there are and have only experience two light pulses the longest and the shortest correspondence to interfere, the coherent pulse of two sequencings of output, they continue to propagate priority and are converted to electrical signal by photodetector, be converted to digital signal by processing of circuit plate 11 again, handle by computer 5, calculate vibration position on the sense line.Long optic fiber 7 long 2km and short fiber 6 long 1km in the experiment, single line optical fiber 3 length are 241km, the actual monitoring distance is (241-1)/2=120km.Among the embodiment, the position of vibration in sensor fibre is from distal-most end x=100km, the sequential chart of the photosignal of the collection among the embodiment as shown in Figure 3, between the longest path counterclockwise, clockwise the light pulse damaged situation of frequency spectrum of interfering as shown in Figure 5, first trap dot frequency f _Null=499.5Hz position is corresponding to x=100.1km, second trap dot frequency 1501.6Hz position is corresponding to x=99.89km, the 3rd trap dot frequency 2502.3Hz position is corresponding to x=99.908km, the 4th trap dot frequency 3491.4Hz position is corresponding to x=100.246km, average out to x=100.036km, average uncertainty are 0.036%.The oscillation function image that obtains as shown in Figure 4.

Native system not only is applicable to the safety precaution and the early warning of pipeline, also is applicable to the safety precaution and the early warning of other critical facility and important area, such as: bridge, dam, boundary line, facilities such as building and key activities district and regional safety protection and strick precaution early warning.

Claims (8)

1, a kind of safety monitoring method based on distribution type fiber-optic, utilization optical fiber Sagnac principle of interference, Distributed localization vibration, shock point is characterized in that vibration, shock point are x, T from the distal-most end distance ₁=n _EffX/c, T ₂=2 _NeffX/c, satisfy between optical signal spectrum Ξ that obtains and vibration, the impact frequency spectrum Θ:

Perhaps

Wherein

Be the angular frequency of vibration, impact, τ ₁, τ ₂Be the time of light wave through fibre delay line, τ ₁=2n _EffL/c, τ ₂=n _EffL/c.

2, press the safety monitoring system based on distribution type fiber-optic of the described method of claim 1, it is characterized in that: comprise transmitting and receiving optical signal puocessing module (100), light delay parts (101), two-way fiber section (102) constitutes a two optical fiber Sagnac interferometer; Transmit and receive optical signal puocessing module (100) and comprise computer (1), light source drive (2), light source (3) removes inclined to one side device 4, the processing of circuit plate (11) of prober (10) and band prober; Light delay parts (101) comprise 3 * 3 Fiber Optic Coupler (5), short fiber (6), long optic fiber (7) and 2 * 1 Couplers (8); Two-way fiber section (102) relates to the sensor fibre (9) of two kinds of situations: vibration, percussion in the loop on optical fiber or in the loop on two optical fiber.

3, by the described system of claim 2, it is characterized in that: the frequency of light source (3) emission light pulse is smaller or equal to c/ (n _EffL), c is a light speed in a vacuum, n _EffBe the optical fiber effective refractive index, L is long optic fiber (7) and short fiber (6) length difference, and the A/D sampling retention time, the A/D sample frequency was greater than the light source repetition frequency greater than pulsewidth.

4, by the described system of claim 2, it is characterized in that: light source (7) is preferably optical fibre laser.

5, by the described system of claim 2, it is characterized in that: the Coupler that uses in the system is preferably fused-tapered fiber coupler, and the merit proportion by subtraction is preferably divided equally.

6, system according to claim 2 is characterized in that: used optical fiber or fibre delay line are Single Mode Fiber in the system, or multi-mould optical fibre.

7, system according to claim 2 is characterized in that: single detection system installs optical switch additional, carries out the multichannel cycle and patrols and examines measurement, monitor large-area vibration, impact phenomenon.

8, system according to claim 2 is characterized in that: a plurality of monitoring system networkings, realize the long-distance intelligent monitoring.

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