CN201247073Y - Distributed optical fiber sensor based on optical fiber cavity wane sway technology - Google Patents

Abstract

The utility model relates to a distributed optical fiber sensor based on optical fiber cavity ring down technology, which is characterized in that: a laser light source is connected with an optical fiber splitter, and the optical fiber splitter is connected with several adjustable optical attenuators; the first optical fiber ring is directly connected with Connected to the adjustable optical attenuator, other optical fiber rings are connected to the corresponding adjustable optical attenuator after passing through the corresponding optical fiber delay line; the output ends of several optical fiber rings are connected to the optical fiber combiner, and the optical fiber combiner is connected to the high-speed photodetector , high-speed A/D conversion and signal processing modules are connected to each other in turn; the optical fiber ring is connected to a fiber optic coupler at the upper and lower ends of a ring-shaped optical fiber, and the left and right sides are respectively connected to a single-mode optical fiber and an optical fiber sensing element. The beneficial effect is: the measurement of the intensity or wavelength is converted into the measurement of the ring-down time of the optical fiber ring, and the time to realize a measurement is only on the order of milliseconds; the demodulation method is simple, and it is easy to realize distributed sensing; multiple physical quantities can be measured Perform simultaneous measurements.

Description

Distributed fiber optic sensor based on fiber optic cavity ring down technology

technical field

The utility model relates to a distributed optical fiber sensor based on optical fiber cavity ring down technology, belongs to the field of optical fiber sensors, and relates to a design of a distributed optical fiber sensor and a demodulation method thereof.

Background technique

Optical fiber sensing technology is a new type of sensing technology that uses light as the carrier and optical fiber as the medium to perceive and transmit external signals, which developed rapidly with the development of optical fiber and optical fiber communication technology in the 1970s. Compared with traditional mechanical and electronic sensors, fiber optic sensors have the following advantages: (1) high sensitivity and large dynamic range; (2) anti-electromagnetic interference, good electrical insulation, corrosion resistance, and can be used at high temperature and high pressure (3) The sensor head has a simple structure, small size, light weight, and is suitable for embedding in large structures; (4) The transmission loss is small, and long-distance detection can be realized; (5) Optical fiber Lightweight and soft, easy to reuse and form a sensor network, easy to realize distributed sensing and so on. Therefore, as soon as the optical fiber sensor came out, it has been widely valued by countries all over the world and extensive research has been carried out. etc. have been widely applied.

Since Morey et al first reported the use of fiber gratings as sensors in 1989, fiber grating sensing, as an important branch of fiber optic sensing, has become a hot spot in the field of fiber sensor research. In addition to the advantages of the sensor, it also has its own unique advantages, such as: the measurement information is wavelength-coded, which avoids the influence of factors such as light source intensity fluctuations, optical fiber microbending and coupling loss on the measurement results; it has high reliability and stability ; It is convenient to form various forms of optical fiber sensor networks for large-area multi-point measurement; it can realize absolute measurement, etc. At present, fiber grating sensors are mainly used to monitor parameters such as internal strain, pressure, temperature, vibration, load fatigue and structural damage, and distributed fiber grating sensors are mainly used in strain sensing.

The traditional method of measuring the wavelength shift of fiber gratings is direct observation by spectrometers, but the resolution of ordinary spectrometers is only 0.01nm, and they are large in size and high in price. Require. After years of hard work by researchers, a variety of demodulation techniques for fiber grating wavelength variation have been proposed. At present, the commonly used demodulation methods are divided into two categories: interference method and filtering method, mainly including: unbalanced Mach-Zehnder (M-Z) fiber optic interferometer demodulation method, unbalanced Michelson (Michelson) interferometer Demodulation method and Sagnac fiber interferometer demodulation method and tunable fiber Fabry-Pérot (F-P) filter demodulation method, edge filter method, matched filter method, tunable laser wavelength Matched demodulation method, grating dispersion method and chirped grating detection method, etc. These technologies have their own advantages and disadvantages, and are suitable for sensing systems under different conditions.

In recent years, a new fiber grating demodulation method based on fiber cavity ring-down technology has been proposed. This method converts the demodulation of wavelength into the measurement of fiber cavity ring-down time, and improves the accuracy and speed of demodulation. In 2002, in the paper "Cavity-enhanced spectroscopy in optical fibers" (Optics Letters, 2002, 27(21): 1878-1880), Gupta M et al. used a 10m-long single-mode optical fiber cavity with a highly reflective coating on the end face to carry out Research on medium refractive index sensing; in 2004, Tarsa PB et al. used a single-mode optical fiber cavity coated with a high-reflection film on the end face and used as a The bitapered optical fiber of the sensing element has been researched on tension sensing, but the above two methods need to coat the end face of the optical fiber with a high-reflection film, and the processing technology is relatively difficult. In addition, the high-reflection area of the reflective film is generally only a dozen nm, which greatly limits range of laser wavelengths used. In 2004, Chuji Wang et al. published the papers "Fiber ringdown pressure sensors" (Optics Letters, 2004, 29(4): 352-254) and "Fiber loop ringdown for physical sensor development: pressure sensor" (Applied Optics, 2004, 43(35) : 6458-6464) proposed to use the optical fiber ring structure to study the pressure sensing of single-mode optical fiber in the range of 0-9.8×10 ⁶ Pa, and obtained the US patent authorization on July 10, 2007, the patent number is 7,241,986 , B2. In 2006, Chuji Wang et al. used the fiber ring structure to control the fiber Bragg grating ( Fiber Bragg Grating, FBG) and long-period fiber grating (Long-period fiber grating, LPFG) have carried out temperature sensing experiments, and obtained the US patent authorization on January 29, 2008, the patent number is 7,323,677, B1; 2007 Ni In the paper "Cavity ring-down long-period fiber grating strainsensor" (Measurement Science and Technology, 2007, 18: 3135-3138), N et al. used fiber rings and LPFG to conduct stress sensing experiments. However, the methods used in the above documents can only demodulate one fiber grating sensor at a time, which cannot meet the requirements of distributed sensing.

Contents of the invention

technical problem to be solved

In order to avoid the shortcomings of the existing technology, the utility model proposes a distributed optical fiber sensor based on optical fiber cavity ring down technology, which can meet the requirements of distributed sensing that the fiber grating sensor based on the optical fiber cavity ring down demodulation method is difficult to meet

Technical solutions

A distributed optical fiber sensor based on optical fiber cavity ring down technology, characterized in that it includes a pulsed laser light source 1, an optical fiber splitter 2, a number of adjustable optical attenuators 3 _1~n , a number of optical fiber delay lines 4 _{1~n- 1.} Several optical fiber rings 5 _1~n , optical fiber combiner 6, high-speed photodetector 7, high-speed analog-to-digital (A/D) conversion and signal processing module 8; laser light source 1 is connected with optical fiber splitter 2, and optical fiber splitter The router 2 is connected to several adjustable optical attenuators _31~n ; the first optical fiber ring ₅₁ is directly connected to the adjustable optical attenuator ₃₁ , and the other optical fiber rings _52~n pass through corresponding optical fiber delay lines _41~ After _n-1 , it is connected to the corresponding adjustable optical attenuator 3 _2~n ; the output ends of several fiber rings 5 _1~n are connected to the optical fiber combiner 6, and the optical fiber combiner 6 is connected with the high-speed photodetector 7, high-speed A The /D conversion and signal processing modules are connected to each other in sequence; the optical fiber ring 5 _1-n is connected in sequence with the optical fiber couplers 9 and 11 at the upper and lower ends and the single-mode optical fiber 10 and optical fiber sensing element 12 on the left and right sides, wherein the optical fiber The port with a low splitting ratio of the coupler 9 is used as an input port, and the port with a low splitting ratio of the fiber coupler 11 is used as an output port.

The optical fiber splitter 2 and the optical fiber combiner 6 are 1×n wavelength division multiplexers.

The length of the fiber delay line L _i =5(τ ₁ +τ ₂ +...+τ _i )c/n _eff , wherein: i is 0～n-1, τ _i is the pulse in the fiber ring 5 _i The ring-down time of the laser, c is the speed of light, and n _eff is the effective refractive index of the fiber.

The wavelength division multiplexer is: a grating type wavelength division multiplexer, a dielectric film filter type wavelength division multiplexer or an integrated optical waveguide type wavelength division multiplexer.

The optical fiber sensing element 12 is: a fiber Bragg grating, a long period fiber grating, a Fabry-Perot fiber cavity, a fiber microbender or a single-mode fiber.

The fiber couplers 9 and 11 are 1×2 fiber couplers with a splitting ratio greater than 90%:10%.

之间，其中t_p为脉冲激光器的脉冲宽度。The length of the single-mode fiber 10 ranges from and

Between, where t _p is the pulse width of the pulsed laser.

Beneficial effect

The beneficial effect of the utility model is that: the optical fiber sensor based on the optical fiber cavity ring-down technology converts the measurement of the intensity or wavelength into the measurement of the ring-down time of the optical fiber ring. When the insertion loss of the optical fiber sensing element in the optical fiber ring changes due to the external physical quantity, since the pulsed laser circles continuously in the ring, the variation of the insertion loss will be amplified once every time it goes around, so its measurement accuracy is relatively high. High; the ring-down time of each pulse laser in the fiber ring is generally on the order of microseconds. Even if each ring-down signal needs to be averaged multiple times in the subsequent processing, the time to achieve a measurement is only on the order of milliseconds , so the measurement speed is very fast; the detected laser pulse sequence is the relative value of the intensity, so the fluctuation of the laser pulse intensity inherent in the light source has no effect on the measurement result; the demodulation method is simple, and it is easy to realize miniaturization, engineering and practicality; It is easy to realize distributed sensing, the optical fiber sensing elements in each optical fiber ring can be different, multiple physical quantities can be measured simultaneously, and the number of sensing heads can be easily expanded.

Description of drawings

Figure 1: Schematic diagram of the structure of the implementation of the distributed optical fiber sensor based on the optical fiber cavity ring-down technology of the present invention;

Fig. 2: the ring-down signal 1 that the pulsed laser of the utility model experiment measurement is exported from the optical fiber ring 5 ₁ ;

Fig. 3: is the schematic diagram of the ring-down signals 1, 2, ... _{, n} output from the optical fiber ring 5 ₁ , _{5 2} , ..., 5 n of the utility model;

Fig. 4: the utility model extracts the peak value of the ring down signal 1 shown in Fig. 2 and carries out the result of single exponential fitting;

Fig. 5: a typical reflection spectrum of the FBG used as the optical fiber sensing element for the experiment of the present invention;

1—laser light source; 2—fiber splitter; 3 _1~n —adjustable optical attenuator; 4 _1~n —fiber delay line; 5 _1~n —fiber ring; 6—fiber combiner; 7—high speed Photodetector; 8—High-speed A/D conversion and signal processing module; 9—Fiber optic coupler; 10—Single-mode fiber; 11—Fiber optic coupler; 12—Fiber optic sensing element.

Detailed ways

Now in conjunction with accompanying drawing, the utility model is further described:

Device embodiment 1, as shown in Figure 1, this embodiment takes n=4, the measuring device of the present invention includes: laser light source 1, optical fiber splitter 2, adjustable optical attenuator 3 ₁ , 3 ₂ , 3 ₃ , 3 ₄ , fiber delay lines 4 ₁ , 4 ₂ , 4 ₃ , fiber rings 5 ₁ , 5 ₂ , 5 ₃ , 5 ₄ , fiber combiner 6, high-speed photodetector 7, high-speed A/D conversion and signal processing Module 8. The optical fiber ring ₅₁ includes two 1×2 optical fiber couplers 9 and 11 with a splitting ratio of 99%: 1%, a single-mode optical fiber 10 and an optical fiber sensing element 12 . The two ends of the single-mode optical fiber 10 are respectively fused with 99% of the two ports of the two optical fiber couplers 9 and 11, and the optical fiber sensing element 12 is respectively connected to the two ports of the two optical fiber couplers 9 and 11 with only one pigtail. The ports are fused together, so the two fiber couplers 9 and 11 together with the single-mode fiber 10 and the fiber sensing element 12 form a fiber ring 5 ₁ , and the fiber rings 5 ₂ , 5 ₃ , 5 ₄ have the same structure as the fiber ring 5 ₁ . In addition, 1% of the ports of the fiber coupler 9 in the fiber ring ₅₁ are connected to the first port of the fiber splitter 2 through the adjustable optical attenuator _31, and the fibers in the fiber rings ₅₂ , ₅₃ , and ₅₄ 1% of the ports of the coupler 9 respectively pass through the fiber delay lines 4 ₁ , 4 ₂ , 4 ₃ and the adjustable optical attenuators 3 ₂ , 3 ₃ , 3 ₄ and the second, third, and fourth ports of the fiber splitter 2 respectively. The two ports are coupled and connected, and the fiber splitter 2 is directly coupled and connected with the laser light source 1. The optical fiber rings ₅₁ , ₅₂ , ₅₃ , ₅₄ are respectively coupled and connected to each port of the optical fiber combiner 6 through 1% of the ports of the respective optical fiber couplers 11, and finally the optical fiber combiner 6 is connected to the high-speed photodetector 7. The high-speed A/D conversion and signal processing modules 8 are connected sequentially.

The laser light source 1 mentioned therein is used to generate pulsed laser, the time interval between two laser pulses should be greater than 5 times of the ring-down time of all pulsed lasers in the fiber ring, and the spectral line width can cover the fiber ring 5 ₁ , 5 ₂ The working wavelength and pulse width of the optical fiber sensing element 12 used in , 5 ₃ , 5 ₄ should be less than the maximum value of the time for each pulsed laser to go around in the fiber ring 5 ₁ , 5 ₂ , 5 ₃ , 5 ₄ respectively.

The fiber splitter 2 is a 1×4 wavelength division multiplexer, its function is to divide a pulsed laser into four pulsed lasers with different wavelengths, and the intensity of these pulsed lasers will be slightly different.

The function of the adjustable optical attenuators 3 ₁ , 3 ₂ , 3 ₃ , and 3 ₄ is to fine-tune the optical fiber splitter 2 on the basis of roughly adjusting the intensity of each pulse laser, so that the light coupled into each optical fiber ring The intensity of the pulsed laser is basically equal so as to match the detection capability of the subsequent high-speed photodetector 7 .

The optical fiber delay lines 4 ₁ , 4 ₂ , and 4 ₃ are composed of single-mode optical fibers, which have the same function but different lengths. They all delay the pulse laser, but the delay time is different. The delay time of the laser is 5 times the sum of the pulse laser ring-down time in the previous fiber rings. And because the length L ₀ of the optical fiber is determined by the formula L ₀ =tc/n _eff , wherein t is the propagation time of the pulsed laser in the optical fiber whose length is L ₀ , so the length L ₁ of the first optical fiber delay line 4 ₁ = 5τ ₁ c/n _eff , where τ ₁ is the ring-down time of the pulsed laser in the fiber ring 5 ₁ . The length L ₂ of the fiber delay line 4 ₂ =5(τ ₁ +τ ₂ )c/n _eff , where τ ₂ is the ring-down time of the pulse laser in the fiber ring 5 ₂ . Similarly, the length L ₃ =5(τ ₁ +τ ₂ +τ ₂ )c/n _eff of the fiber delay line 4 ₃ can be obtained, where τ ₃ is the ring-down time of the pulse laser in the fiber ring 5 ₃ .

The length of the single-mode optical fiber 10 should be such that the time for each pulse laser to go around in the corresponding fiber ring 5 ₁ , 5 ₂ , 5 ₃ , 5 ₄ is longer than the pulse width of the pulse laser.

The optical fiber sensing element 12 is FBG, LPFG, F-P optical fiber cavity, optical fiber microbender or single-mode optical fiber.

The optical fiber combiner 6 is a 4×1 wavelength division multiplexer, and its function is to combine the ring-down signals output from each optical fiber ring 5 ₁ , 5 ₂ , 5 ₃ , and 5 ₄ into one channel and transmit them to The high-speed photodetector 7 performs photoelectric conversion on each ring-down signal by the high-speed photodetector 7 .

Described high-speed A/D conversion and signal processing module 8 extract the peak value of each ring-down signal and carry out single-exponential fitting to the peak value, draw the ring-down time of each pulse laser in the corresponding optical fiber ring, and do further data processing.

The main working process of the implementation of the distributed optical fiber sensor based on the optical fiber cavity ring down technology of the utility model is as follows: firstly, the laser light source 1 emits a pulsed laser, and the pulsed laser is transmitted to the optical fiber splitter 2 through the optical fiber and then divided into four beams with different wavelengths pulse laser, wherein the first pulse laser is coupled into the fiber ring 5 ₁ by the 1% port of the fiber coupler 9 through the adjustable optical attenuator 3 ₁ , and the second, third, and fourth pulse lasers respectively pass through the corresponding Adjustable optical attenuators 3 ₂ , 3 ₃ , 3 ₄ and fiber delay lines 4 ₁ , 4 ₂ , 4 ₃ are coupled into corresponding fiber rings 5 ₂ , 5 ₃ , 5 ₄ through 1% ports of fiber coupler 9 , where due to the delay effect of the fiber delay lines 4 ₁ , 4 ₂ , 4 ₃ , the delayed pulsed laser must enter the corresponding fiber ring after 5 times the ring-down time of the pulsed laser in the last fiber ring. Wherein the pulsed laser light coupled into the fiber ring ₅₁ by the fiber coupler 9 will continue to go around in the fiber ring ₅₁ , because there are various losses in the fiber ring ₅₁ , these losses include: the coupling of the fiber coupler 9,11 Loss and insertion loss, transmission loss of single-mode optical fiber 10 and pigtails of fiber couplers 9 and 11, insertion loss of optical fiber sensing element 12 and insertion loss of four fusion points fused with each other. Therefore, the intensity of the pulsed laser in the fiber ring ₅₁ will be constantly attenuated, and what is output from 1% of the ports of the fiber coupler 11 is a laser pulse sequence whose peak value is mono-exponentially attenuated, which is called the ring-down signal 1, and Fig. 2 shows The ring-down signal output by the optical fiber ring 5 ₁ measured experimentally. After 5 times the ring-down time of the first beam of pulsed laser in the fiber ring ₅₁ , the second beam of pulse laser that is time-delayed by the delay line ₄₁ is coupled into the fiber ring 5 by the 1% port of the fiber coupler 9 ₂ , the output from the 1% port of the fiber coupler 11 is also a laser pulse sequence whose peak value is mono-exponentially attenuated, which is called the ring-down signal 2. Based on the same reason, the third and fourth beams of pulsed lasers pass through the corresponding delay line After ₄₂ and ₄₃ , 1% of the ports of the fiber coupler 9 in the fiber rings ₅₃ and ₅₄ are respectively coupled into the fiber rings ₅₃ and ₅₄ , and the ring-down signals ₃ and ₅₄ are respectively output from the fiber rings 53 and 54. 4. Please refer to the schematic diagram 4. The ring-down signals corresponding to each optical fiber ring are staggered by a certain time due to the action of the optical fiber delay lines 4 ₁ , 4 ₂ , 4 ₃ , and are all coupled into the optical fiber combiner 6 . The ring-down signals are combined by the optical fiber combiner 6 and detected by the high-speed photodetector 7, and the optical signal is converted into an electrical signal by the high-speed photodetector 7, and then the high-speed A/D conversion and signal processing module 8 pair each The ringdown signal is used for further data processing.

As shown in Figure 4, in this embodiment, for each ring-down signal detected, the peak value is extracted by software, and a single exponential decay function y=Aexp(-t/τ)+ _y0 is used to fit the peak value to obtain the The ring down time τ ₀ of the ring down signal. For each fiber ring, when the optical fiber sensing element 12 does not sense the effect of external physical quantities, the ring-down time of the pulsed laser in the fiber ring is ${\mathrm{\&tau;}}_0=\frac{{\mathrm{<figure-callout\; id="2"\; label="t\; R"\; filenames="Y200820029283E00152.png"\; state="\{\{state\}\}">t</figure-callout>}}_R}{2{\mathrm{\&alpha;}}_c+{\mathrm{\&alpha;}}_t+4{\mathrm{\&alpha;}}_f+{\mathrm{\&alpha;}}_{\mathrm{the\; s}}},$ Among them, t _R =n _eff L/c is the time for the pulsed laser to go around in the fiber ring, n _eff is the effective refractive index of the fiber, L is the length of the fiber ring, c is the speed of light in vacuum, and 2α _c is two The coupling loss and insertion loss of each fiber coupler 9 and 11, α _t is the transmission loss of single-mode fiber 10 and the pigtail of fiber coupler 9 and 11, 4α _f is the insertion loss of four fusion splicing points, α _s is the optical fiber The insertion loss of the sensing element 12. When the optical fiber sensing element 12 perceives the effect of the external physical quantity, the insertion loss of the optical fiber sensing element 12 will change, so that the total loss in the fiber ring will change. At this time, the ring-down time of the pulsed laser in the fiber ring becomes $\mathrm{\&tau;}\&prime;=\frac{{\mathrm{<figure-callout\; id="2"\; label="t\; R"\; filenames="Y200820029283E00152.png"\; state="\{\{state\}\}">t</figure-callout>}}_R}{2{\mathrm{\&alpha;}}_c+{\mathrm{\&alpha;}}_t+4{\mathrm{\&alpha;}}_f+{\mathrm{\&alpha;}}_{\mathrm{the\; s}}+\mathrm{\&Delta;}{\mathrm{\&alpha;}}_{\mathrm{the\; s}}},$ Wherein Δα _s is the variation of the insertion loss after the optical fiber sensing element 12 senses the action of the external physical quantity. From the above two formulas, the variation of the insertion loss of the optical fiber sensing element 12 can be obtained as $\mathrm{\&Delta;}{\mathrm{\&alpha;}}_{\mathrm{the\; s}}=t_R(\frac{1}{\mathrm{\&tau;}\&prime;}-\frac{1}{{\mathrm{\&tau;}}_0}),$ Since the variation of the insertion loss of the optical fiber sensing element 12 is in one-to-one correspondence with the action of the external physical quantity, the action of the external physical quantity can be obtained from Δα _s to achieve the purpose of sensing. Based on the same principle, the optical fiber sensing element 12 in each optical fiber ring can perceive the effect of the external physical quantity at its location.

The distributed optical fiber sensor based on the optical fiber cavity ring down technology of the utility model is aimed at the optical fiber _sensing element 12 in each optical fiber ring 5 ₁ , 5 ₂ , 5 ₃ , 5 _{4 2} , 5 ₃ , and 5 ₄ demodulate the external physical quantity sensed by the optical fiber sensing element 12 in the optical fiber ring, and because the optical fiber rings are independent of each other, the distributed optical fiber Sensing function.

The optical fiber sensing element 12 in each optical fiber ring of the utility model can be an FBG, LPFG or FP optical fiber cavity, or an optical fiber microbend or a single-mode optical fiber. The former has high measurement accuracy, while the latter has a large measurement range. The detailed demodulation method of the distributed optical fiber sensor based on optical fiber cavity ring down technology will be further introduced below taking the optical fiber sensing element 12 as an FBG as an example. Fig. 5 shows the reflectance spectrum of a FBG used as the optical fiber sensing element 12 in the experiment, and the wavelength of the pulse laser used is in the middle part of the main reflection peak both sides of the reflectance spectrum of FBG, such as a point or b point among the figure, when When the FBG in the fiber ring ₅₁ perceives the effect of external physical quantities, its reflection spectrum will drift. For the pulse laser with a certain wavelength incident into the ring, the reflectivity of the FBG will change, so that the total loss in the fiber ring ₅₁ Corresponding changes occur, and finally the ring-down time of the ring-down signal output from the optical fiber ring ₅₁ also changes accordingly. By measuring the two ringdown times of the pulse laser in each fiber ring before and after the action of external physical quantities, the change of the total loss in each fiber ring can be known, thereby obtaining the drift of the FBG center wavelength in the fiber ring, and further obtaining the external The action of the physical quantity achieves the purpose of using FBG to realize distributed optical fiber sensing. Based on the same principle, using LPFG, FP optical fiber cavity, optical fiber microbend, and single-mode optical fiber can achieve the purpose of distributed optical fiber sensing with different measurement accuracy and measurement range.

The optical fiber sensing elements 12 in each optical fiber ring of the utility model can be the same or different, and can measure the same physical quantity or different physical quantities at the same time, as long as the physical quantity to be measured can cause the insertion loss of the optical fiber sensing element 12 to occur Certain changes are fine. Therefore, the distributed optical fiber sensor of the utility model can not only realize the distributed measurement of the same physical quantity, but also realize the distributed measurement of different physical quantities at the same time, so it has strong functions, is convenient and practical, and has great practical application value.

The distributed optical fiber sensor based on optical fiber cavity ring down technology of the present invention is not limited to the above-mentioned embodiment, and can be further improved, such as: the number of optical fiber rings in the distributed optical fiber sensor of the present invention is not limited to four, according to actual needs and cost considerations , the number can be adjusted. The optical fiber sensing element 12 is not limited to FBG, LPFG, F-P optical fiber cavity, optical fiber microbend, single-mode optical fiber, as long as it can cause a certain change in the total loss in the optical fiber ring, and the appropriate implementation mode can be selected according to actual needs. Fiber optic sensing element 12.

In summary, the distributed optical fiber sensor based on optical fiber cavity ring down technology of the present invention can not only realize the distributed measurement of the same physical quantity, but also realize the measurement of different physical quantities at the same time through the design of multiple relatively independent optical fiber rings. High, fast, wide application range, easy to expand the sensing head, and simple operation, can realize practical and engineering, and has great practical application value.

Claims (7)

1. the distributed fiberoptic sensor based on the optical fiber cavity attenuation and vibration technique is characterized in that: comprise pulsed laser light source

(1), optical fiber splitter (2), some adjustable optical attenuators (3 _1～n), some fibre delay lines (4 _1～n-1), some fiber optic loop (5 _1～n), optical fiber combiner (6), high-speed photodetector (7), high speed analog-digital conversion (A/D) conversion and signal processing module (8); LASER Light Source (1) links to each other with optical fiber splitter (2), and optical fiber splitter (2) connects some adjustable optical attenuators (3 _1～n); First fiber optic loop (5 ₁) direct and adjustable optical attenuator (3 ₁) connect other fiber optic loop (5 _2～n) all pass through corresponding fibre delay line (4 _1～n-1) back and corresponding adjustable optical attenuator (3 _2～nConnect; Some fiber optic loop (5 _1～n) output terminal connect optical fiber combiner (6), optical fiber combiner (6) interconnects successively with high-speed photodetector (7), high-speed a/d conversion and signal processing module again; Described fiber optic loop (5 _1～n) be that the fiber coupler (9) at two ends up and down and the single-mode fiber (10) and the fiber sensing element (12) of (11) and the left and right sides are linked in sequence, wherein the port of the low splitting ratio of fiber coupler (9) is as input end, and the port of the low splitting ratio of fiber coupler (11) is as output terminal; Described optical fiber splitter (2) is 1 * n wavelength division multiplexer.

2. the distributed fiberoptic sensor based on the optical fiber cavity attenuation and vibration technique according to claim 1 is characterized in that:

Described optical fiber combiner (6) is 1 * n wavelength division multiplexer.

3. the distributed fiberoptic sensor based on the optical fiber cavity attenuation and vibration technique according to claim 1 is characterized in that:

Described fibre delay line (4 _1～n-1) length L _i=5 (τ ₁+ τ ₂+ ... + τ _i) c/n _Eff, wherein: i is 0～n-1, τ _iBe fiber optic loop (5 _i) in the ring-down time of pulse laser, c is the light velocity, n _EffEffective refractive index for optical fiber.

4. the distributed fiberoptic sensor based on the optical fiber cavity attenuation and vibration technique according to claim 2 is characterized in that: described wavelength division multiplexer is: grating type wavelength division multiplexer, dielectric film filtering type wavelength division multiplexer or integrated type optical waveguide wavelength division multiplexer.

5. the distributed fiberoptic sensor based on the optical fiber cavity attenuation and vibration technique according to claim 1 is characterized in that: described fiber sensing element (12) is: Fiber Bragg Grating FBG, long period fiber grating, Fabry-Perot optical fiber cavity, optical fiber micro-bending device or single-mode fiber.

6. the distributed fiberoptic sensor based on the optical fiber cavity attenuation and vibration technique according to claim 1 is characterized in that: described fiber coupler (9) and (11) are 1 * 2 fiber coupler, and its splitting ratio is greater than 90%:10%.

7. the distributed fiberoptic sensor based on the optical fiber cavity attenuation and vibration technique according to claim 1 is characterized in that: the length span of described single-mode fiber (10) exists

With

Between, t wherein _pPulse width for pulsed laser.

Images