CN100416323C - Fibre-optical and raster sensor system with multiple mould - Google Patents

Abstract

The present invention discloses a multimode optical fiber grating sensor system. The present invention is characterized in that the light emitted by a broadband light source 1 is coupled to a multimode optical fiber 2 and a multimode optical fiber coupler 4, and then the light is distributed to two multimode optical fibers 5, 6. The light emitted by the multimode optical fiber 5 is connected with a multimode optical fiber grating sensor 21 by an optical fiber connector 19, and the light penetrating through the multimode optical fiber grating sensor 21 and the light transmitted by the multimode optical fiber 6 are both lost by a wave trap at the tail ends of the multimode optical fibers. The light reflected by the multimode optical fiber grating sensor 21 passes through the multimode optical fiber coupler 4 and a multimode optical fiber 3 to enter a multimode optical fiber coupler 8 so as to be distributed to a reference grating 9 and a multimode optical fiber 13. A signal reflected by the reference grating 9 is transmitted to a photoelectric detector 11 to be converted to an electric signal passing through the multimode optical fiber coupler 8 and a multimode optical fiber 7. The light transmitted by the multimode optical fiber 13 arrives at a photoelectric detector 14 and is converted to an electric signal. The electric signal is amplified again by a voltage amplifier 16 and a proportional amplifier 17, and then an output signal Vo is detected by a spectrometer. The multimode optical fiber grating sensor system of the present invention can achieve the performance of a single-mode optical fiber grating sensor system. Due to the adoption of a multimode luminous tube light source, the cost of the system can be largely reduced as compared with the corresponding single mode optical fiber grating sensor system.

Description

Fibre-optical and raster sensor system with multiple mould

Technical field

The invention belongs to the fiber optic sensor technology field, specifically about the wavelength detection method and the device of multimode optical fiber Bragg grating sensor.

Technical background

Fibre Optical Sensor refers to the multiple sensors part made by light transmitting fiber.According to light transmitting fiber function therein, can be divided into two classes to Fibre Optical Sensor: the first kind is the Intrinsical sensor: optical fiber not only is used as information transmitting medium but also be used for constituting sensor; Second class is the extrinsic type sensor: optical fiber only is used for realizing the function of information transmission or energy acquisition, and sensor is made by other non-fiber optic materials.Compare with traditional electronic sensor, Fibre Optical Sensor has the advantage of following a series of uniquenesses, for example: be subjected to external electromagnetic field disturb little, long term drift is little, reliability is high, not charged, thereby be suitable in oil, rock gas, chemical industry and other inflammable and explosive environment, using; Volume is little, in light weight, multiplexing capacity is strong, can connect a plurality of sensors and constitute distributed sensor networks on an optical fiber.

In various fiber optic sensor technologies, based on the sensor of Fiber Bragg Grating FBG, what adopt because of it is that Wavelength-encoding and size are little, the physical strength advantages of higher comes into one's own especially.Fiber Bragg Grating FBG has been used to make various sensors, as temperature, strain, acceleration, pressure and current sensor etc.The ultimate principle that fiber grating class sensor signal is handled is to measure the wavelength of its reflected signal.Wavelength detection method commonly used has many kinds.People Yu Yiyu such as Melle reported a kind of demodulation method based on optical filter in 1992.People such as Measures delivered and have used the demodulation method of tunable laser to fiber-optic grating sensor in 1998.Kersey and its are worked together and have been delivered the employing fibre optic interferometer in 1992 and realize fiber optic high-resolution grating strain transducer measuring method.Davis and Kersey have delivered in nineteen ninety-five and have adopted the signal processing method of matched fiber grating wave filter to demodulation grating strain transducer array.In addition, wideband light source and tunable optical filter are also generally adopted.

Above-mentioned sensing system based on the single-mode fiber grating is compared with traditional electronic sensor, although have superior performance aspect a lot, the cost of signal processing system is higher relatively, has therefore limited the widespread usage in fields such as industry.On multimode optical fiber, also can use with the similar method of single mode grating and make fiber grating.Because the core diameter and the numerical aperture of multimode optical fiber are all big than single-mode fiber, when using the luminotron device as light source, the coupling efficiency of light can improve 30 to 100 times than single-mode fiber.Because the luminotron device cost is far below tunable laser, fibre-optical and raster sensor system with multiple mould has the cost that big potentiality can be significantly less than single mode fiber system on cost.

People such as the Wanser of the U.S. reported and use the multimode optical fiber Bragg grating to carry out application and theoretical analysis that crooked sensory detects in 1994.In its scheme, the shape of reflectance spectrum is usually relevant with the angle of bend of optical fiber before the sensing grating element.The people such as Mizunami of Japan have then delivered the multimode grating made with the 50/125um graded fiber of standard and the characteristic of few mould grating made from chromatic dispersion transfer optical fiber and at the experimental study of temperature detection and crooked sensory.Zhao and Claus also demonstrate has proved the feasibility that adopts the multimode grating to carry out strain and temperature sensing monitoring.People such as Lim have issued a kind of based on the sensor reflectance spectrum with solve the multi-peak wavelength measurement problem of multimode grating sensor with the signal processing method that sensor prerecord reference spectra is associated.Above-mentioned research about the multi-mode optica lfiber grating sensor is confined to adopt traditional Laboratory Instruments, such as spectroanalysis instrument etc.Both do not related to and used luminotron light source cheaply, do not related to the wavelength detection method that adopts the multimode matching grating yet.

In sum, although fiber grating has become a mainstream technology of Fibre Optical Sensor, comparative maturity is the single-mode fiber optical-mechanical system on signal processing technology.And the signal processing technology at the multi-mode optica lfiber grating sensor that is fit to the engineering application awaits further to solve.

Summary of the invention

The purpose of this invention is to provide a kind of signal processing method at the multi-mode optica lfiber grating sensor, this method utilization coupling multi-mode optica lfiber grating, use multimode light source cheaply to substitute the light source or the tunable laser of traditional single-mode fiber output, can reach the wavelength resolution of 1pm.

The technical solution used in the present invention be wideband light source send couple light to first multimode optical fiber and first multi-module optical fiber coupler, be assigned to second multimode optical fiber and the 3rd multimode optical fiber then; The light that sends from second multimode optical fiber links to each other with the multi-mode optica lfiber grating sensor through the joints of optical fibre; The light that sees through the light of multi-mode optica lfiber grating sensor and spread out of by the 3rd multimode optical fiber all adopts first microwave trap, second microwave trap respectively and it is all lost in fiber ends, makes it no longer to return original optical path; Light by multi-mode optica lfiber grating sensor reflected back enters second multi-module optical fiber coupler through first multi-module optical fiber coupler, the 4th multimode optical fiber, and then is assigned to reference to grating and the 5th multimode optical fiber; Pass to first photodetector by the signal of reference optical grating reflection through second multi-module optical fiber coupler and the 6th multimode optical fiber and be converted into electric signal; The light that is spread out of by the 5th multimode optical fiber arrives second photodetector and is converted into electric signal; First voltage amplifier and second voltage amplifier are respectively the light signal voltage that is used for amplifying by first photodetector and the conversion of second photodetector; First proportional amplifier is accepted from the signal of first voltage amplifier and the output of second voltage amplifier, enters second proportional amplifier from the signal of first proportional amplifier output and amplifies again, is detected with spectrometer by the signal Vo of second proportional amplifier output.

Signal processing has increased by a closed-loop control unit, but from the dynamic output signal of second proportional amplifier and the reference voltage signal of an external setting-up, produces a difference signal V _DCAnd by amplifier it is amplified, the output signal of amplifier is used for controlling photo gate driver, and the signal of photo gate driver drives grating.

Wideband light source sends couples light to first multimode optical fiber and first multi-module optical fiber coupler, is assigned to second multimode optical fiber and the 3rd multimode optical fiber then; The light that sends from second multimode optical fiber links to each other with the multi-mode optica lfiber grating sensor through the joints of optical fibre; The light that sees through the light of multi-mode optica lfiber grating sensor and spread out of by the 3rd multimode optical fiber all adopts first microwave trap, second microwave trap respectively and it is all lost in fiber ends, makes it no longer to return original optical path; Light by multi-mode optica lfiber grating sensor reflected back enters second multi-module optical fiber coupler through first multi-module optical fiber coupler, the 4th multimode optical fiber, and then is assigned to reference to grating and the 5th multimode optical fiber; Pass to first photodetector by the signal of reference optical grating reflection through second multi-module optical fiber coupler and the 6th multimode optical fiber and be converted into electric signal; The transmitted light that second multi-module optical fiber coupler is assigned to reference to grating enters second photodetector and is converted into electric signal, and the end of the 5th multimode optical fiber has the 3rd microwave trap, and first voltage amplifier and second voltage amplifier are respectively the light signal voltage that is used for amplifying by first photodetector and the conversion of second photodetector; First proportional amplifier is accepted from the signal of first voltage amplifier and the output of second voltage amplifier, enters second proportional amplifier from the signal of first proportional amplifier output and amplifies again, is detected with spectrometer by the signal Vo of second proportional amplifier output.Described wideband light source is the transmitting illuminant at random or the heating filament light sources of luminotron or super luminotron or amplification.

The principle of multimode optical fiber Bragg grating be when the refractive index of multimode optical fiber fibre core along fiber axis after modulation uniformly with space periodic, just form the multimode grating.The light propagation coefficient of decision grating Bragg's condition of reflection will satisfy β ₁-β ₂=2 π/Λ, β here ₁And β ₂Be respectively that same spatial mode forward direction and back are to the Propagation of guided waves constant.For 50/125 micron multimode optical fiber of standard, can support the guided modes more than the hundreds of in wavelength 1310nm or 1550nm zone.Yet,, on grating reflection spectrum, just show as same bragg reflection wavelength because many guided modeses can have almost equal propagation constant.This guided modes with same propagation constant can equivalence be a degenerate mode when analyzing.For N degenerate mode in the multimode optical fiber, its propagation constant β _NCan be described as:

${\mathrm{\β}}_N=\frac{2\mathrm{\π}{n}_c}{\mathrm{\λ}}\sqrt{1-\frac{4\mathrm{\Δ}(N+1)}{V}}---\left(1\right)$

Here n _cRepresent the refractive index of fibre core, Δ is the difference of maximum relative refractive index, and V=2 π aNA/ λ is a normalized frequency, and a is a fiber core radius, and NA is the numerical aperture of optical fiber.

Bragg's condition of reflection can be the phase matching coupling between guided wave at the forward direction of same degenerate mode and back, also can be to be produced by the coupling of the phase matching between the two adjacent degenerate modes.Because the bragg wavelength that the forward direction of N degenerate mode and the coupling of back-propagating intermode are produced is

$\mathrm{\&lambda;}=2{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">n</figure-callout>}}_1\mathrm{\&Lambda;}\left(\sqrt{(1-4\mathrm{\&Delta;}(N+1))/V}\right)---\left(2\right)$

Wherein Λ is the cycle of grating.The bragg wavelength that is produced by the coupling between N and (N+1) individual reflection mould will depend on the mean value of these two adjacent mould propagation constants, β=β _N+ β _N+1Therefore also will be positioned on the spectrum between the Bragg reflection peak of N and (N+1) individual mould.

For a multi-mode optica lfiber grating, the quantity of the observed degenerate mode of energy depends on has obtain excitation for how many moulds in the optical fiber.If multimode optical fiber is advanced in the optically-coupled that the broadband white light source sends, nearly all communication mode can obtain excitation.In the case, a Bragg reflection crest about generally can observing.Yet ought for example have the SLD of single-mode tail fiber, and be used for being coupled to multi-mode optica lfiber grating only from single-mode fiber or narrow-band light source, not every conduction mode can both be energized, and can observe bragg wavelength like this and also just reduce, usually below 10.Similar with the single-mode fiber grating, the reflection wavelength of multi-mode optica lfiber grating also can be subjected to environment temperature and modulate along the optical fiber axial strain.To the bragg wavelength of arbitrary merger mould, can be described as by the caused wave length shift of strain:

Δλ＝(1-P _e)λε(3)

Here λ and Δ λ are respectively the relative variations of bragg wavelength and wavelength, P _eBeing effective photoelastic coefficient, is 0.22 for its numerical value of standard fiber.

Multi-mode optica lfiber grating can be described by following formula the response coefficient of temperature:

$\frac{\mathrm{d\&lambda;}}{\mathrm{dT}}=\frac{{\mathrm{\&lambda;}}^2}{\mathrm{<figure-callout\; id="1"\; label="d\; n"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">d</figure-callout>}{n}_{}{}_1{\mathrm{\&Lambda;}}^2}\frac{\mathrm{d\&Lambda;}}{\mathrm{dT}}+[\frac{{\mathrm{\&lambda;}}^2}{2{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">n</figure-callout>}}_1^2\mathrm{\&Lambda;}}-\frac{{\mathrm{\&lambda;}}^2(N+1)(3n_2-2n_1)}{2\mathrm{\&pi;a}{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">n</figure-callout>}}_1^2\sqrt{2n_1(n_1-n_2)}}]\frac{\mathrm{<figure-callout\; id="1"\; label="d\; n"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">d</figure-callout>}{n}_{}{}_1}{\mathrm{dT}}+\frac{{\mathrm{\&lambda;}}^2(N+1)}{2\mathrm{\&pi;a}{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">n</figure-callout>}}_1\sqrt{2n_1\left(n_1{n}_2\right)}}\frac{\mathrm{<figure-callout\; id="2"\; label="d\; n"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">d</figure-callout>}{n}_{}{}_2}{\mathrm{dT}}---\left(4\right)$

Wherein, dn ₁/ dT and dn ₂/ dT is respectively the refractive index of fiber core and covering to the variation of temperature coefficient, is about 0.55 * 10 ^-5/ ℃; D Λ/dT is the thermal expansivity of optical fiber, and its numerical value is about 0.55 * 10 ^-6/ ℃.Utilization is to the response characteristic of temperature and strain, and multi-mode optica lfiber grating can be packaged into temperature or strain transducer.Can realize detection by measurement to temperature and strain to grating wavelength.The wavelength detection method that the present invention adopts is based on coupling multimode optical fiber Bragg grating.

Similar based on the principle that the wavelength detection scheme multimode optical fiber coupling grating wavelength that mates the multimode optical fiber Bragg grating detects to single-mode fiber.The light that wideband light source sends is transferred to the multi-mode optica lfiber grating sensor through coupling mechanism.Part energy will transfer back to above-mentioned coupling mechanism by this multimode grating device reflection.The luminous energy that reflects is distributed into two-way by another coupling mechanism: the one tunnel directly to first photodetector, and other one the tunnel through a reference grating same with the sensor grating, promptly mates grating, arrives second photodetector then.When the environment temperature of sensing grating with identical with reference to grating, and when not strained, two grating reflection spectrum are identical, and the luminous energy major part that is transferred to reference to grating is reflected back, therefore by the luminous energy minimum with reference to arrival second photodetector behind the grating.And when the wavelength departure of sensing grating during with reference to grating, the luminous energy that second photodetector receives will increase.The light intensity that first photodetector receives does not change with the wavelength of sensing grating, therefore can be used for compensating the intensity owing to light source, the flatness of spectrum, the influences that variation caused such as fiber transmission attenuation.

Except that above-mentioned acquisition of signal mode, utilization is with reference to the relative variation of energy with the signal of the reflected energy of representing sensing grating of optical grating reflection, or utilize with reference to the signal of optical grating reflection with also can reach the purpose that saves described grating wavelength detection and intensity compensation by the relative variation between the signal of its transmission.

The advantage of above-mentioned coupling grating wavelength detection method is highly sensitive, and detection speed is fast, and is with low cost.When the reference grating did not adopt closed-loop control, the wavelength sensing range of this scheme was narrower.Can be for wavelength detection in a big way by the closed-loop control of reference grating is carried out.At this moment, the bandwidth of this wide range wavelength detection will depend on the response speed of following the tracks of with reference to grating wavelength.

Technique effect

The technical feature of coupling multimode optical fiber Bragg grating wavelength detection system depends on energy, grating reflection coefficient and the Optical Fiber Transmission distance etc. of light source.For short-range transmission (in 1 kilometer), if use low-power (50 microwatt), have the 1310nm LED of multimode optical fiber tail optical fiber, with the high reflectance fiber grating of on the 50/125m of standard multimode graded-index optical fiber, processing (the maximum reflection peak can reach 80%), and measure bandwidth in 10kHz, sensitivity can reach and be better than 0.1pm so, and measurement range is 0.3nm.When the reference grating was adopted closed-loop control, the wavelength measurement scope can reach 5nm.If adopt more powerful light source, during as super luminotron (SLD), under the situation of same sensitivity (0.1pm) and measurement range (0.3nm), signal transmission distance can reach several kilometers, measures bandwidth and can reach 100kHz.

The signal processing method of fibre-optical and raster sensor system with multiple mould of the present invention, can reach the performance of single-mode fiber grating sensor system, what adopt is optics or fiber optic passive device, do not have mechanical moving element, steady in a long-term, system cost is lower than the cost of corresponding single-mode fiber grating sensor system.

Description of drawings

One of Fig. 1 matched fiber grating detection scheme block diagram.

Two of Fig. 2 matched fiber grating detection scheme block diagram.

Three of Fig. 3 matched fiber grating detection scheme block diagram.

Four of Fig. 4 matched fiber grating detection scheme block diagram.

Fig. 5 is used for the reflectance spectrum of two 1310nm multi-mode optica lfiber gratings of matched fiber grating test experience.The light source that uses is the luminotron that has the multimode optical fiber tail optical fiber, and its centre wavelength is near 1310nm.The fundamental frequency wavelength of two fiber gratings is all near 1310.2nm.

Fig. 6 is used for the reflectance spectrum of two 1550nm multi-mode optica lfiber gratings of matched fiber grating test experience.The light source that uses is the luminotron that has the single-mode fiber tail optical fiber, and its centre wavelength is near 1550nm.The fundamental frequency wavelength of two fiber gratings is all near 1549nm.

Fig. 7 is for using the measurement result of matched-filter approach for 1310nm multimode grating sensor.The X-axle is the wavelength of sensor grating; The Y-axle is according to the resulting testing result of the scheme of Fig. 1.The sensor signal spectrum is the dotted line among Fig. 5, and the reference light gate signal is the solid line among Fig. 5.The wavelength of grating is corresponding to reflection peak the highest among Fig. 5, i.e. several second reflection peak from the right side.Fig. 7 shows that the result of matching detection scheme is linear basically.

Fig. 8 is for using the test result of matched-filter approach for 1550nm multimode grating.The X-axle is the wavelength of sensor grating; The Y-axle is according to the resulting testing result of the scheme of Fig. 1.The result of Fig. 8 shows that the matching detection scheme is for the multimode grating of 1550nm, and its result is linear basically.

Embodiment

Describe fibre-optical and raster sensor system with multiple mould of the present invention in detail below in conjunction with accompanying drawing: as shown in Figure 1, wideband light source 1 sends couples light to first multimode optical fiber 2 and first multi-module optical fiber coupler 4, is assigned to second multimode optical fiber 5 and the 3rd multimode optical fiber 6 then; The light that sends from second multimode optical fiber 5 links to each other with multi-mode optica lfiber grating sensor 21 through the joints of optical fibre 19; The light that sees through the light of multi-mode optica lfiber grating sensor 21 and spread out of by the 3rd multimode optical fiber 6 all adopts first microwave trap 22 and second microwave trap 10 that it is all lost in fiber ends, makes it no longer to return original optical path; Light by multi-mode optica lfiber grating sensor 21 reflected backs enters second multi-module optical fiber coupler 8 through first multi-module optical fiber coupler 4, the 4th multimode optical fiber 3, and then is assigned to reference to grating 9 and the 5th multimode optical fiber 13; Pass to first photodetector 11 by the signal of reference grating 9 reflection through second multi-module optical fiber coupler 8 and the 6th multimode optical fiber 7 and be converted into electric signal; The light that is spread out of by the 5th multimode optical fiber 13 arrives second photodetector 14 and is converted into electric signal; First voltage amplifier 12 and second voltage amplifier 15 are respectively the light signal that is used for amplifying by first photodetector 11 and 14 conversions of second photodetector; First proportional amplifier, 16 its output signals enter second proportional amplifier 17 amplifies again, and the signal Vo that is exported by second proportional amplifier 17 detects with spectrometer.

Wideband light source 1, it can be a luminotron, can be super luminotron also, amplifies transmitting illuminant (ASE) or white flag filament light sources at random.For the short transmission distance with such as common temperature, low frequency measurement situations such as pressure, can adopt lower cost, be generally used for luminotron that low bit rate, short distance optical fiber communication use as light source.When the measurement situation of long distance of needs or higher speed, can select other high-power light source for use, as super luminotron (SLD), or amplify transmitting illuminant (ASE) at random.Optical source wavelength commonly used can be near 850nm, 1310nm or 1550nm.2,3,5,6,7,13,20 are respectively first to the 7th multimode optical fiber.In Fig. 1, square frame 18 representation signal processing sections; The 7th multimode optical fiber 20 representative sensor signal transmssion lines.Operable multimode optical fiber comprises that the 50/125m of standard and 62.5/125m rank get over type or multimode graded-index optical fiber, also can be 105/125m large-numerical aperture or other special multimode optical fiber.First multi-module optical fiber coupler 4 and second multi-module optical fiber coupler 8 are 50: 50 multi-module optical fiber couplers.Fiber ends adopts first microwave trap 22 and second microwave trap 10 can adopt the combination of following a kind of method or two kinds of methods: (I) optic fibre end cutting or polishing are had a certain degree; (II) optic fibre end is immersed in the refractive index match glue; (III) the procephalic fibre-optical bending of optical fiber end is fixed or method of other machinery decay.The function of second proportional amplifier 17 is the signal V of first voltage amplifier 12 and 15 outputs of second voltage amplifier ₁₂And V ₁₅Amplify according to the certain calculation relation.Consequently eliminate because the measurement of common-mode noise sensor light wavelength such as the reflection coefficient of the intensity of light source, spectral shape, sensor, optical fiber transmission line loss exerts an influence.The general type of this operational method is:

$V_o=k_0\frac{k_1{V}_{12}-k_2{V}_{15}}{k_3{\mathrm{<figure-callout\; id="12"\; label="V"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">V</figure-callout>}}_{12}+k_4{\mathrm{<figure-callout\; id="15"\; label="V"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">V</figure-callout>}}_{15}}+V_{\mathrm{offset}}---\left(5\right)$

Wherein, k _iBe scale factor, i=0 to 4; V _OffsetBe working point zeroing voltage.Below two kinds of situations be two special cases in the practical application:

$V_o=k_0\frac{V_{12}-V_{15}}{{\mathrm{<figure-callout\; id="12"\; label="V"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">V</figure-callout>}}_{12}+{\mathrm{<figure-callout\; id="15"\; label="V"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">V</figure-callout>}}_{15}}+V_{\mathrm{offset}}---\left(6\right)$

$V_o=k_0\frac{V_{12}}{{\mathrm{<figure-callout\; id="15"\; label="V"\; filenames="C20041007582000111.png,C20041007582000112.png"\; state="\{\{state\}\}">V</figure-callout>}}_{15}}+V_{\mathrm{offset}}---\left(7\right)$

Can convert the variation of sensor wavelength to the voltage strength signal according to the resulting detection signal of algorithm in equation (5)-(7), and can effectively suppress the common-mode noise of system.

Signal Processing scheme shown in Figure 2 is the distortion of Fig. 1, be characterized in that the transmitted light that second multi-module optical fiber coupler 8 is assigned to reference to grating 9 enters second photodetector 14, and be converted into electric signal, and the end of the 5th multimode optical fiber 13 has the 3rd microwave trap 23.The mode of signal Processing is identical with the described scheme of Fig. 1.The advantage of this scheme is, when the signal that is received when first photodetector 11 reduced, the signal intensity that arrives second photodetector 14 can increase, and vice versa.Therefore, the sensitivity meeting of signal increases than scheme shown in Figure 1.

Signal Processing scheme shown in Figure 3 is another distortion of Fig. 1 and Fig. 2, be characterized in that the light that second multi-module optical fiber coupler 8 is assigned to reference to grating 9 enters second photodetector 14 and is converted into electric signal, the light of the 5th multimode optical fiber 13 enters first photodetector 11, and the end of the 6th multimode optical fiber 7 has the 4th microwave trap 25.The basic mode of signal Processing is identical with the described scheme of Fig. 1, and the position of second photodetector 14 is identical with Fig. 2; But the position of first photodetector 11 is different with Fig. 1.The variation of second photodetector, 14 detected signals will be depended on the grating of multi-mode optica lfiber grating sensor 21 and with reference to the relative different of spectrum between the grating 9.Compare with the scheme of Fig. 1, this signal is not owing to must return second multi-module optical fiber coupler 8 thereby avoid the loss that is brought thus.

Scheme shown in Figure 4, be based on the basis of Fig. 1 and increased the closed loop modulation function, be characterized in that signal processing has increased by a closed-loop control unit, but, produce a difference signal V from the dynamic output signal of second proportional amplifier 17 and the reference voltage signal 29 of an external setting-up _DCAnd by amplifier 30 it is amplified, the output signal of amplifier 30 is used for controlling photo gate driver 31, and the signal of photo gate driver 31 drives grating 9.This scheme makes with reference to the state of grating relative constant with the state maintenance of sensor.Consequently can improve the low frequency sensing range of system greatly.V _DCBy amplifier 30 it is amplified, this difference signal is as the low frequency output of signal Processing, and it indicates that the absolute wavelength of sensor grating changes, and can be used for measuring low frequency sensing amounts such as temperature, strain, pressure.VO is the detection of suitable high speed Dynamic Signal then, such as, vibration, ultrasonic, seismic event detection etc.The output signal of amplifier 30 is used for controlling photo gate driver 31.31 can be heating arrangement, also can be a mechanical-stretching device, and its function is to adjust state with reference to grating by temperature or strain, makes the state of its tracking transducer grating.The closed loop control method of describing in Fig. 4 that comprises 28-31 is suitable for adopting in an identical manner in the input scheme of Fig. 2 and Fig. 3 too.

List of references:

S.M.Melle，K.Liu?and?R.M.Measures?“A?passive?wavelength?demodulation?system?for?guided-wave?Bragggrating?sensors”IEEE?Photonics?Technology?Letters，4，516-18，1992.

R.M.Measures，M.M.Ohn，S.Y.Huang，J.Bigue?and?N.Y.Fan，“Tunable?laser?demodulation?of?various?fiberBragg?grating?sensing?modalities”，Smart?Materials?and?Structures，7，237-247，1998.

A.D.Kersey，T.A.Berkoff，and?W.W.Morey，“High-resolution?fiber-grating?based?strain?sensor?withinterferometric?wavelength-shift?detection”，Electronics?Letters，28，236-238，1992.

M.A.Davis?and?A.D.Kersey，“Matched-filter?interrogation?techniques?for?fiber?Bragg?grating?arrays”，ElectronicsLetters，31，822-824，1995.

K.H.Wanser，K.F.Voss，and?A.D.Kersey，“Novel?fiber?devices?and?sensors?based?on?multimode?fiber?Bragggratings”，Proc.SPIE?2360，265-268，1994.

Claims (5)

1. fibre-optical and raster sensor system with multiple mould is characterized in that: wideband light source (1) sends couples light to first multimode optical fiber (2) and first multi-module optical fiber coupler (4), is assigned to second multimode optical fiber (5) and the 3rd multimode optical fiber (6) then; The light that sends from second multimode optical fiber (5) links to each other with multi-mode optica lfiber grating sensor (21) through the joints of optical fibre (19); See through the light of multi-mode optica lfiber grating sensor (21) and all adopt first microwave trap (22) and second microwave trap (10) that it is all lost respectively, make it no longer to return original optical path in fiber ends by the light that the 3rd multimode optical fiber (6) spreads out of; Light by multi-mode optica lfiber grating sensor (21) reflected back enters second multi-module optical fiber coupler (8) through first multi-module optical fiber coupler (4), the 4th multimode optical fiber (3), and then is assigned to reference to grating (9) and the 5th multimode optical fiber (13); Pass to first photodetector (11) by the signal of reference grating (9) reflection through second multi-module optical fiber coupler (8) and the 6th multimode optical fiber (7) and be converted into electric signal; The light that is spread out of by the 5th multimode optical fiber (13) arrives second photodetector (14) and is converted into electric signal; First voltage amplifier (12) and second voltage amplifier (15) are used for respectively amplifying by first photodetector (11) and second photodetector (14) electrical signal converted; First proportional amplifier (16) is accepted from the signal of first voltage amplifier (12) and second voltage amplifier (15) output, enter second proportional amplifier (17) from the signal of first proportional amplifier (16) output and amplifies again, the signal Vo that is exported by second proportional amplifier (17) detects with spectrometer.

2. fibre-optical and raster sensor system with multiple mould according to claim 1 is characterized in that: described wideband light source (1) is the transmitting illuminant at random or the heating filament light sources of luminotron or super luminotron or amplification.

3. fibre-optical and raster sensor system with multiple mould according to claim 1, it is characterized in that: increased by a closed-loop control unit, from second proportional amplifier (17) but dynamic output signal and the reference voltage signal (29) of an external setting-up, produce a difference signal V _DCAnd by amplifier (30) it is amplified, the output signal of amplifier (30) is used for controlling photo gate driver (31), and the signal of photo gate driver (31) drives with reference to grating (9).

4. fibre-optical and raster sensor system with multiple mould is characterized in that: wideband light source (1) sends couples light to first multimode optical fiber (2) and first multi-module optical fiber coupler (4), is assigned to second multimode optical fiber (5) and the 3rd multimode optical fiber (6) then; The light that sends from second multimode optical fiber (5) links to each other with multi-mode optica lfiber grating sensor (21) through the joints of optical fibre (19); The light that sees through the light of multi-mode optica lfiber grating sensor (21) and spread out of by the 3rd multimode optical fiber (6) all adopts first microwave trap (22) second microwave trap (10) respectively and it is all lost in fiber ends, makes it no longer to return original optical path; Light by multi-mode optica lfiber grating sensor (21) reflected back enters second multi-module optical fiber coupler (8) through first multi-module optical fiber coupler (4), the 4th multimode optical fiber (3), and then is assigned to reference to grating (9) and the 5th multimode optical fiber (13); Pass to first photodetector (11) by the signal of reference grating (9) reflection through second multi-module optical fiber coupler (8) and the 6th multimode optical fiber (7) and be converted into electric signal; The transmitted light that second multi-module optical fiber coupler (8) is assigned to reference to grating (9) enters second photodetector (14) and is converted into electric signal, and the end of the 5th multimode optical fiber (13) has the 3rd microwave trap (23), and first voltage amplifier (12) and second voltage amplifier (15) are used for respectively amplifying by first photodetector (11) and second photodetector (14) electrical signal converted; First proportional amplifier (16) is accepted from the signal of first voltage amplifier (12) and second voltage amplifier (15) output, enter second proportional amplifier (17) from the signal of first proportional amplifier (16) output and amplifies again, the signal Vo that is exported by second proportional amplifier (17) detects with spectrometer.

5. fibre-optical and raster sensor system with multiple mould according to claim 4 is characterized in that: described wideband light source (1) is the transmitting illuminant at random or the heating filament light sources of luminotron or super luminotron or amplification.

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