Source: https://patents.google.com/patent/CN101680781B/en
Timestamp: 2020-07-15 06:29:52
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CN101680781B - Physical quantity measuring device of optical frequency range reflection measuring type, and temperature and strain simultaneous measuring method using the device - Google Patents
Physical quantity measuring device of optical frequency range reflection measuring type, and temperature and strain simultaneous measuring method using the device Download PDF
CN101680781B
CN101680781B CN2009800002856A CN200980000285A CN101680781B CN 101680781 B CN101680781 B CN 101680781B CN 2009800002856 A CN2009800002856 A CN 2009800002856A CN 200980000285 A CN200980000285 A CN 200980000285A CN 101680781 B CN101680781 B CN 101680781B
CN2009800002856A
CN101680781A (en
大道浩儿
坂元明
平船俊一郎
2008-02-29 Priority to JP2008051343 priority Critical
2008-02-29 Priority to JP051343/2008 priority
2008-09-18 Priority to JP239368/2008 priority
2008-09-18 Priority to JP2008239368 priority
2009-03-02 Application filed by 株式会社藤仓 filed Critical 株式会社藤仓
2009-03-02 Priority to PCT/JP2009/053899 priority patent/WO2009107839A1/en
2010-03-24 Publication of CN101680781A publication Critical patent/CN101680781A/en
2011-11-23 Publication of CN101680781B publication Critical patent/CN101680781B/en
239000003365 glass fiber Substances 0.000 claims description 172
240000004718 Panda Species 0.000 description 48
G01D5/35393—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infra-red, visible, or ultra-violet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques using frequency division multiplexing
Provided is a physical quantity measuring device of optical frequency range reflection measuring type, which comprises a first polarization holding fiber connected at one end with a tunable laser and at the other end with a polarization holding coupler, a second polarization holding fiber connected at one end with the polarization holding coupler and having a reference reflecting terminal at the other end, a third polarization holding fiber having a sensor formed of a fiber Bragg grating at a core and connected at one end with the polarization holding coupler, a fourth polarization holding fiber connected at one end with the polarization holding coupler, an incident unit for making a measuring light incident on both the two orthogonal polarization axes of the second polarization holding fiber and the two orthogonal polarization axes of the third polarization holding fiber, and an optical path length adjusting unit arranged in the third polarization holding fiber for making constant the optical path lengths of the Bragg reflection lights from the two orthogonal polarization axes in the sensor. The incident unit is arranged either at the first polarization holding fiber or at both the second polarization holding fiber and the third polarization holding fiber.
The physical amount measuring device of optical frequency range reflection mode and used its temperature and measuring method strain the time
The present invention relates to protect partially configuration one or more fiber gratings (Fiber Bragg Grating, FBG) sensor on (Polarization Maintaining, PM) optical fiber the physical amount measuring device of optical frequency range reflection (Optical Frequency Domain Reflectometry, the OFDR) mode that physical quantitys such as the strain of the position of this FBG sensor and FBG sensor, temperature are measured and used the temperature of this physical amount measuring device and measuring method strain the time at one.
The application with on February 29th, 2008 spy to Japanese publication be willing to 2008-51343 number and on September 18th, 2008 spy to Japanese publication be willing to serve as for 2008-239368 number that right of priority is advocated on the basis, and quote their content at this.
Use optical fiber to measure the sensor of physical quantitys such as temperature, strain, because life-span length, light weight, diameter are carefully and have flexibility, so can in narrow space, use.And this sensor is because optical fiber has insulativity, so have the characteristic of anti-electromagnetic noise.Therefore, wait in expectation and this sensor is used for the viability evaluation of aviations such as buildings such as bridge or building, passenger plane or artificial satellite, universe equipment etc.
As the performance that sensor was required of the viability evaluation that is used to carry out these structures, can enumerate the spatial resolution height, have the sensor (investigative range is wide) of multiple spot and can measure in real time etc.
Proposed various fiber optic sensor systems up to now, but, can enumerate the Fibre Optical Sensor of the analytic method that has used FBG sensor and OFDR mode as the most promising Fibre Optical Sensor that fully satisfies the above-mentioned requirements performance.
Used the fiber optic sensor system of the analytic method of FBG sensor and OFDR mode, be used to determine the position of FBG sensor from the Bragg reflection optical of FBG sensor with from cyclical variation with reference to the catoptrical interference strength of using reflection end.And this fibre system is measured strain, the temperature of detection portion according to the wavelength change amount of Bragg reflection optical.
As this fiber optic sensor system, it has been disclosed has the following high spatial resolution (for example with reference to non-patent literature 1) of 1mm, can amount to the strain measurement (for example with reference to non-patent literature 2) more than 3000 simultaneously and the real-time measured (for example with reference to patent documentation 1) etc. remarkably by 4 optical fiber at 800 FBG sensors of configuration on the optical fiber of 8m.And,, can also measure the Strain Distribution (dependent variable along long side direction that is meant the FBG sensor is inhomogeneous) of the long side direction of FBG sensor according to non-patent literature 1.For the measurement of this Strain Distribution, in patent documentation 3, also put down in writing.
On the other hand,, change, then can't independent identification measure their variable quantity if can enumerate temperature, strain etc. physical quantity is multinomial as the general issue of fiber optic sensor system.Therefore, for example using under the situation of fiber optic sensor system as strain transducer,, needing the sensor of other serviceability temperature compensation usefulness in order the temperature variation of detection portion not to be captured as the variation of strain.
As the method that addresses this problem, can enumerate the method (for example with reference to patent documentation 1) of the FBG sensor that use is made of PM optical fiber.This method is to use a kind of PANDA optical fiber as PM optical fiber, by being measured thus, the wavelength change amount of Bragg reflection optical can measure the method for temperature and strain simultaneously, two polarization axles of the quadrature in the FBG sensor that next free this PANDA optical fiber of described Bragg reflection optical constitutes.
That is, this method is not needing to realize the method for temperature compensation with the strain transducer of sensor.
If make up technology discussed above, use has utilized the fiber optic sensor system of the analytic method of the FBG sensor that is made of PM optical fiber and OFDR mode, then thinks and measures when can realize high resolving power, multimetering, measurement in real time, temperature and strain simultaneously.
Patent documentation 1: No. 3740500 communique of Japan's patent
Patent documentation 2: No. 3819119 communique of Japan's patent
Patent documentation 3: No. 4102291 communique of Japan's patent
Non-patent literature 1:H.Murayama, H.Igawa, K.Kageyama, K.Ohta, I.Ohsawa, K.Uzawa, M.Kanai, T.Kasai and I.Yamaguchi, " Distributed StrainMeasurement with High Spatial Resolution Using Fiber Bragg Gratings andOptical Frequency Domain Reflectometry " Proceedings OFS-18, ThE40 (2006)
Non-patent literature 2:B.Childers, M.E.Froggatt, S.G.Allison, T.C.Moore, D.A.Hare, C.F.Batten and D.C.Jegley, " Use of 3000 Bragg grating strainsensors distributed on four eight-meter optical fibers during static loadtest of a composite structure. " Proceedings SPIE ' s 8th InternationalSymposium on Smart Structure and Materials, Vol.4332, pp.133-142 (2001)
Yet, used the fiber optic sensor system of the analytic method of the FBG sensor that constitutes by PM optical fiber and OFDR mode, be not suggested as yet up to now.Its reason is, for analytic method by the OFDR mode, stably measure the Bragg reflection optical of two polarization axles of the quadrature in the FBG sensor that free PM optical fiber constitutes, need will measure two the polarization axle partial waves of light with good controllability, it is propagated to the FBG sensor and with reference to the reflection end of usefulness to quadrature.But, generally measure light with single polarized wave outgoing.Therefore, when being formed into the FBG sensor by PM optical fiber and with reference to the time with the light path till the reflection end, though can be from one in the Bragg reflection of two polarization axles of the quadrature in the FBG sensor to measure, the opposing party can't measure.As a result, can't measure the Bragg reflection optical that comes self-orthogonal two polarization axles like that as mentioned above.
As with the mensuration light of single polarized wave method, can enumerate by single-mode fiber and be formed into the FBG sensor and with reference to the method for at least a portion of the light path till the reflection end of usefulness to two polarization axle partial waves of quadrature.But existing in the method can't will be by the mensuration light of the single polarized wave outgoing problem to two polarization axle partial waves of quadrature with good controllability.
In addition, in the fiber optic sensor system of the analytic method that has used the FBG sensor that constitutes by PM optical fiber and OFDR mode, the effective refractive index difference of two polarization axles of quadrature.Therefore, in the parsing of OFDR mode, there are different these problems in position from the Bragg reflection optical of two polarization axles.Therefore, be difficult to determine the position of FBG sensor with high resolving power.
In the parsing of OFDR mode,, determine the position of FBG sensor according to from the Bragg reflection optical of FBG sensor with from cycle of the catoptrical interference signal of the reflection end of reference usefulness.Promptly, by for resulting interference signal, the effective refractive index of the optical fiber that substitution is suitable, carry out Short Time Fourier Transform (Short-time Fourier transform :) and resolve, can obtain the position (it is poor with reference to the fiber lengths of the reflection end of usefulness and FBG sensor to say so exactly) of FBG sensor thus hereinafter referred to as STFT.Here, different with the effective refractive index of two polarization axles of quadrature irrelevant in the FBG sensor that constitutes by PM optical fiber, because so a certain constant effective refractive index of substitution as a result of, causes the position difference from the Bragg reflection optical of two polarization axles.
The present invention In view of the foregoing proposes, its purpose is, a kind of physical amount measuring device of the OFDR mode that especially can measure temperature and strain simultaneously and can measure with high spatial resolution in fiber optic sensor system is provided, measuring method in the time of with the temperature of having used this physical amount measuring device and strain, described fiber optic sensor system is the one or more FBG sensors of configuration on a PM optical fiber, utilizes the analytic method of OFDR mode to measure the fiber optic sensor system of physical quantitys such as the strain of the position of this FBG sensor and FBG sensor, temperature.
The present invention has adopted following scheme in order to solve above-mentioned problem, to realize corresponding target.
(1) physical amount measuring device of optical frequency range reflection mode of the present invention possesses: penetrate the tunable laser of measuring light; First polarization maintaining optical fibre that one end is connected with this tunable laser; The polarization-maintaining coupler that is connected with the other end of this first polarization maintaining optical fibre; One end is connected with this polarization-maintaining coupler, and the other end is as second polarization maintaining optical fibre of reference with reflection end; The 3rd polarization maintaining optical fibre that one end is connected with above-mentioned polarization-maintaining coupler; Be formed on the fibre core of the 3rd polarization maintaining optical fibre and the sensor that constitutes by fiber grating; The 4th polarization maintaining optical fibre that one end is connected with above-mentioned polarization-maintaining coupler; Be connected with above-mentioned polarization-maintaining coupler by the 4th polarization maintaining optical fibre, to from the Bragg reflection optical of the sensor and from above-mentioned with reference to the photodiode that detects with reference to light with reflection end; According to by the detected above-mentioned Bragg reflection optical of this photodiode and above-mentioned with reference to light close glistening light of waves Strength Changes, to these Bragg reflection opticals and the control part surveyed with reference to the modulation of the interference strength between the light; To two polarization axles of the quadrature of above-mentioned second polarization maintaining optical fibre, and two polarization axle both sides of the quadrature of above-mentioned the 3rd polarization maintaining optical fibre, the incident section of incident said determination light; Be disposed at above-mentioned the 3rd polarization maintaining optical fibre, make the constant optical path length adjustment part of optical path length from the Bragg reflection optical of two polarization axles of the quadrature in the sensor; Above-mentioned incident section is configured in above-mentioned first polarization maintaining optical fibre or above-mentioned second polarization maintaining optical fibre and above-mentioned the 3rd polarization maintaining optical fibre both sides.
(2) for above-mentioned incident section, preferably be configured under the situation of above-mentioned first polarization maintaining optical fibre in this incident section, be to have 45 ° polarization axle deviation angle and the fusion connecting portion that forms at this first polarization maintaining optical fibre; Being configured in above-mentioned incident section under above-mentioned second polarization maintaining optical fibre and above-mentioned the 3rd polarization maintaining optical fibre both sides' the situation, is to have 45 ° polarization axle deviation angle and the fusion connecting portion that forms at above-mentioned second polarization maintaining optical fibre and above-mentioned the 3rd polarization maintaining optical fibre respectively.
(3) preferred above-mentioned optical path length adjustment part is to have 90 ° polarization axle deviation angle and the fusion connecting portion that forms at above-mentioned the 3rd polarization maintaining optical fibre that is formed with the sensor.
(4) preferred above-mentioned optical path length adjustment part is set at the centre from the position suitable with the length of above-mentioned second polarization maintaining optical fibre to the fiber lengths of the sensor.
(5) preferably in above-mentioned the 3rd polarization maintaining optical fibre, dispose a plurality of the sensors.
(6) preferred above-mentioned optical path length adjustment part is configured in the centre of the fiber lengths between the sensor of adjacency respectively.
(7) preferably from above-mentioned first polarization maintaining optical fibre to above-mentioned the 4th polarization maintaining optical fibre, the effective refractive index of two polarization axles of the quadrature in above-mentioned at least the 3rd polarization maintaining optical fibre is 4.4 * 10 -4More than.
(8) measuring method comprises temperature of the present invention and strain the time: use the physical amount measuring device of the optical frequency range reflection mode of any record in above-mentioned (1)～(7), measure the step from the wavelength of the Bragg reflection optical of two polarization axles of the quadrature in one or more the sensors; According to the wavelength of the above-mentioned Bragg reflection optical of measuring, calculate the wavelength Yin Wendu of the above-mentioned Bragg reflection optical in the sensor and the step of the variable quantity that strain causes; With the above-mentioned variable quantity that basis calculates, measure the temperature at the position that disposes the sensor and the step of strain simultaneously.
(9) preferably calculate the Temperature Distribution and the Strain Distribution along the position long side direction that disposes the sensor of above-mentioned the 3rd polarization maintaining optical fibre.
The physical amount measuring device of the optical frequency range reflection mode of being put down in writing according to above-mentioned (1), owing to have the sensor of the fibre core that is formed at polarization maintaining optical fibre and be used for measuring the incident section of light, so measure when can carry out the temperature of sensor and strain to two polarization axle incidents of the quadrature of the polarization maintaining optical fibre that disposes this sensor.And, owing to have the constant optical path length adjustment part of optical path length that is used to make from the Bragg reflection optical of two polarization axles of the quadrature of sensor, so can determine the position of sensor exactly, can carry out the measurement of physical quantity with high spatial resolution.
Measuring method in the time of temperature of being put down in writing according to above-mentioned (8) of the physical amount measuring device of the optical frequency range reflection mode of having used any record in above-mentioned (1)～(7) and strain can be measured strain and temperature simultaneously from a FBG sensor.And, can measure simultaneously along the Temperature Distribution and the Strain Distribution of the long side direction of sensor.
Fig. 1 is the concise and to the point pie graph of first embodiment of the physical amount measuring device of expression optical frequency range reflection mode of the present invention.
Fig. 2 is the concise and to the point pie graph of the variation of this embodiment of expression.
Fig. 3 is that the concise and to the point stereographic map that connects is merged in the polarization axle angular deflection (offset) of expression when having used PANDA optical fiber.
Fig. 4 is the concise and to the point pie graph of second embodiment of the physical amount measuring device of expression optical frequency range reflection mode of the present invention.
Fig. 5 is the concise and to the point pie graph of physical amount measuring device of the optical frequency range reflection mode of expression embodiments of the invention 1.
Fig. 6 is the spectrogram that the result that this embodiment measures the state of sensor is used in expression.
Fig. 7 is the physical amount measuring device that the optical frequency range reflection mode of comparative example 1 is used in expression, the result's that the state of sensor is measured spectrogram.
Fig. 8 is the physical amount measuring device that the optical frequency range reflection mode of comparative example 2 is used in expression, the result's that the state of sensor is measured spectrogram.
Fig. 9 is illustrated in this comparative example 2 carry out the curve map of result calculated from the position amount of staggering of the Bragg reflection optical of the slow axis of sensor and fast axle.
Figure 10 is the concise and to the point pie graph of physical amount measuring device of the optical frequency range reflection mode of expression embodiments of the invention 2.
Figure 11 is that this embodiment 2 is used in expression, the result's that the state of sensor (first sensor) is measured spectrogram.
Figure 12 is that this embodiment 2 is used in expression, the result's that the state of sensor (second sensor) is measured spectrogram.
Figure 13 is the physical amount measuring device that the optical frequency range reflection mode of embodiments of the invention 3 is used in expression, the result's that the state of sensor is measured spectrogram.
Figure 14 is illustrated among this embodiment 3, and the birefringence of PANDA optical fiber and bragg wavelength are with respect to the curve map of the relation of the shift characteristics difference of the temperature variation of the formed sensor of FBG that is made of PANDA optical fiber.
Figure 15 is the physical amount measuring device that the optical frequency range reflection mode of embodiments of the invention 4 is used in expression, the result's that the state of sensor is measured spectrogram.
Figure 16 is the figure that schematically is illustrated in the experimental system that is used to measure the Temperature Distribution that produces at sensor and strain among this embodiment 4.
Figure 17 is illustrated among this embodiment 4 temperature variation of the position of the position of peak A and peak value B and the result's that strain is measured spectrogram.
Figure 18 is illustrated among this embodiment 4 temperature variation of the position of the position of peak A and peak value B and the result's that strain is measured curve map.
Among the figure: 10A, 10B, 10C, 10D, 10E, the physical amount measuring device of 10F (10)-optical frequency range reflection mode, 11,31, the 32-polarization-maintaining coupler, the 12-tunable laser, 13, the 35-photodiode, 14,37,38-is with reference to using reflection end, 15,15a, the 15b-sensor, 16,17,18, the 19-polarization maintaining optical fibre, the 20-incident section, 21,21a, 21b-optical path length adjustment part, the 22-control part, 41,42,43,44,47,48-PANDA optical fiber, the 53-system controller, the 54-A/D converter, 60 (60A, 60B)-and PANDA optical fiber, 61 (61A, 61B)-and fibre core (core), 62 (62A, 62a, 62B, 62b)-the stress assigning unit.
Below with reference to accompanying drawing, the embodiment of fiber optic sensor system of the present invention is described.
Fig. 1 is the concise and to the point pie graph of first embodiment of the physical amount measuring device of expression optical frequency range reflection of the present invention (being designated hereinafter simply as " OFDR ") mode.
The physical amount measuring device 10A (10) of the OFDR mode of present embodiment roughly possesses: penetrate the tunable laser 12 of measuring light, first polarization maintaining optical fibre 16 that one end is connected with this tunable laser 12, the polarization-maintaining coupler 11 that is connected with the other end of this first polarization maintaining optical fibre 16, one end is connected with this polarization-maintaining coupler 11 and the other end is second polarization maintaining optical fibre 18 of reference with reflection end 14, the 3rd polarization maintaining optical fibre 19 that one end is connected with polarization-maintaining coupler 11, be formed on the fibre core of the 3rd polarization maintaining optical fibre 19 and the sensor 15 that constitutes by fiber grating, the 4th polarization maintaining optical fibre 17 that one end is connected with polarization-maintaining coupler 11, be connected with polarization-maintaining coupler 11 and to from the Bragg reflection optical of sensor 15 with from reference to the photodiode 13 that detects with reference to light by the 4th polarization maintaining optical fibre 17 with reflection end 14, according to by these photodiode 13 detected above-mentioned Bragg reflection opticals and above-mentioned with reference to light close that glistening light of waves Strength Changes detects these Bragg reflection opticals and with reference to the modulated control portion 22 of the interference strength between the light, incident section 20 to two polarization axle both sides incident said determination light of the quadrature of two polarization axles of the quadrature of second polarization maintaining optical fibre 18 and the 3rd polarization maintaining optical fibre 19, with be disposed at the 3rd polarization maintaining optical fibre 19 and make the constant optical path length adjustment part 21 of optical path length from the Bragg reflection optical of two polarization axles of the quadrature in the sensor 15.In the present embodiment, polarization-maintaining coupler 11 by with first～the 4th protect partially (below be abbreviated as " PM ") congener PM optical fiber of optical fiber and constitute.
As tunable laser 12, preferably use coherent length to be reflected by sensor 15 and incide the long tunable laser of optical path length till the photodiode 13 than the mensuration light that penetrates from tunable laser 12.
As photodiode 13, the preferred use when the mensuration light wavelength that penetrates from tunable laser 12 is changed has the photodiode of the cutoff frequency that can detect the intensity modulated of the interference of light that obtains with reflection end 14 and sensor 15 from two reflection spots, i.e. reference.
Control part 22 possesses: for example to A/D converter 54 of taking a sample from the signal of photodiode 13 and the system controller 53 that this sampled data is resolved.As A/D converter 54, the preferred converter that uses with the sampling frequency that can detect to the intensity modulated of the interference of light that detects by photodiode 13.54 pairs of optical interference signals by the simulation of photodiode 13 measurements of A/D converter are taken a sample with digital form.This digitalized intervention signal is transmitted to system controller 53.In system controller 53, use this digitalized intervention signal to carry out STFT (Short timeFourier Transform:STFT) and resolve.About analytic method, will narrate in the back.As this system controller 53, resolve as long as can carry out STFT the digitalized intervention signal that obtains by A/D converter 54, be not particularly limited.System controller 53 links to each other with tunable laser 12 by general purpose interface bus (GPIB), carries out the control of tunable laser 12.
Incident section 20 is set at a PM optical fiber 16, and the mensuration light that will penetrate with single polarized wave from tunable laser 12 is to two polarization axle partial waves of the quadrature of a PM optical fiber 16.As incident section 20,, as shown in Figure 2, can be disposed at the 2nd PM optical fiber 18 and the 3rd PM optical fiber 19 both sides as long as can measure light to two polarization axle both sides incidents of the quadrature of two polarization axles of the quadrature of the 2nd PM optical fiber 18 and the 3rd PM optical fiber 19.From incident section 20 being arranged at a viewpoint that gets final product, preferred incident section 20 is set at the 3rd PM optical fiber 19 and the leading portion (i.e. a PM optical fiber 16) that has with reference to the branching portion of the 2nd PM optical fiber 18 of using reflection end 14 that is formed with sensor 15.
As incident section 20, so long as insert the method for λ/2 plates; The polarization axle angular deflection is set merges the method that connects; Perhaps dispose PM optical fiber with respect to the mode that the mensuration light from the single polarized wave of tunable laser 12 has angular deflection according to the polarization axle of PM optical fiber, make from the emergent light of tunable laser 12 and the method for PM optical fiber coupling etc., the mensuration light of single polarized wave can be got final product to the scheme of two polarization axle partial waves of the quadrature of PM optical fiber, can use any means.
Wherein, from easy viewpoint, can with measure light equably partial wave become the viewpoint of two polarized waves, as this incident section 20, preferably in a PM optical fiber 16, has 45 ° polarization axle deviation angle and the fusion that forms connects (hereinafter referred to as " 45 ° of skews are merged ").
Here, the fusion with polarization axle angular deflection connects and to be meant, has mode as the deviation angle of merging point according to a polarization axle of PM optical fiber, and two PM optical fiber are merged connection.The deviation angle that a polarization axle of PM optical fiber has as merging point is meant that another polarization axle of quadrature also has identical deviation angle and two PM optical fiber are merged connection.
Fig. 3 is the figure of the form that merges of 45 ° of skews when schematically having represented to use PANDA (Polarization-maintaining andAbsorption reducing) optical fiber as PM optical fiber.
Here, PANDA optical fiber 60 is meant that in order to make optical fiber the have birefringence covering (clad) at fibre core 61 two ends is provided with the optical fiber of circular stress assigning unit 62.By this stress assigning unit 62, between two polarization modes of quadrature, produce propagation constant poor (effective refractive index is poor).Therefore, can suppress from of the coupling of each polarization mode to another polarization mode.Two polarization axles that polarization mode is propagated of this quadrature are called as slow axis, fast axle, and the difference of the effective refractive index of slow axis and fast axle is called as birefringence.
(that is, two stress assigning unit 62A, the 62a of PANDA optical fiber 60A and the straight line 63A of fibre core 61A have been connected for the straight line that has connected these two stress assigning unit 62 and fibre core 61; Two stress assigning unit 62B, the 62b of PAND optical fiber 60B and the straight line 63B of fibre core 61B have been connected), according to the mode that between two PANDA optical fiber 60A, 60B, becomes desirable polarization axle deviation angle θ this straight line is connected, can realize that thus desirable skew fusion connects.
As optical path length adjustment part 21, constant as long as the optical path length of the Bragg reflection optical of two polarization axles of the quadrature in the future in the autobiography sensor 15 is adjusted into, can use any member.For example, can enumerate the method that connects to the fusion that PM optical fiber inserts the method for birefringence crystallization, setting has the polarization axle angular deflection to PM optical fiber etc.
As optical path length adjustment part 21, from easy viewpoint, adjust the viewpoint of optical path length easily, preferably among above-mentioned adopt 90 ° of skews to merge.
In addition, optical path length adjustment part 21 is constant for the optical path length of the Bragg reflection optical of two polarization axles of the quadrature in the future autobiography sensor 15 is made as, be set at from have with reference to the fiber lengths (L shown in Figure 1 that plays with the suitable position of the length of the PM optical fiber 18 of reflection end 14 till the sensor 15 1) the centre.By optical path length adjustment part 21 is arranged on this position, can make from the optical path length of the Bragg reflection optical of two polarization axles of the quadrature in the sensor 15 constant, when the Bragg reflection optical that comes self-orthogonal two polarization axles is resolved, can carry out in the same measured position.
In the physical amount measuring device 10A of the OFDR of this embodiment mode, be provided with incident section 20 between tunable laser 12 and PM coupling mechanism 11, this incident section 20 is used to make the mensuration light that penetrates from tunable laser 12 with the form of single polarized wave two polarization axle branches to the quadrature of the 2nd PM optical fiber 18 and the 3rd PM optical fiber 19.Thus, can obtain Bragg reflection optical from two polarization axles of the quadrature in the sensor 15.By the wavelength variations from the Bragg reflection optical of two polarization axles of this quadrature, temperature and the strain that can measure the position that disposes sensor 15 simultaneously.As a result, can realize need not to be provided with in addition the strain transducer of temperature compensation with sensor.
And, in the physical amount measuring device 10A of this OFDR mode, from have the centre of playing the fiber lengths of sensor 15 with reference to the suitable position of the length of the 2nd PM optical fiber 18 of reflection end 14, be provided with optical path length adjustment part 21.Thus, can make from the optical path length of the Bragg reflection optical of two polarization axles of the quadrature in the sensor 15 constant.That is, when to from the Bragg reflection optical of sensor 15 with from carrying out STFT with reference to the catoptrical interference signal with reflection end 14 when resolving, the Bragg reflection optical of self-orthogonal two polarization axles becomes same position.
And, by using the physical amount measuring device 10A of this OFDR mode, to measuring, can measure the temperature and the strain of detection portion thus simultaneously from the Yin Wendu of the wavelength of the Bragg reflection optical of two polarization axles of the quadrature in the sensor 15 and the variable quantity that strain causes.
The location determining method of＜sensor 〉
Then, the location determining method to the sensor 15 of the physical amount measuring device 10A of the OFDR mode of having used present embodiment describes.Illustration used the situation of PANDA optical fiber as first～the 4th PM optical fiber.
In the physical amount measuring device 10A of the OFDR of present embodiment mode, to photodiode 13 incidents from the Bragg reflection optical of sensor 15 with from reference to catoptrical interference light with reflection end 14.Incide this optical interference signals D of photodiode 13 1Become the signal sum of two polarization axles of quadrature, represent with following formula (1).
D 1＝R slowcos{k(n slow+n fast)L 1}+R fastcos{k(n slow+n fast)L 1} (1)
In above-mentioned formula (1), R SlowAnd R FastExpression is from the interference light intensity of two polarization axles of the quadrature of PANDA optical fiber, promptly from the interference light intensity of slow axis (X-axis) and fast axle (Y-axis).K is a wave number, n SlowAnd n FastThe effective refractive index of expression slow axis (X-axis) and fast axle (Y-axis).L 1Represent in the 2nd PANDA optical fiber (PM optical fiber) 18 from PM coupling mechanism 11 to reference to the length of reflection end 14, with the 3rd PANDA optical fiber (PM optical fiber) 19 poor (fiber lengths is poor) of 15 length from PM coupling mechanism 11 to sensor.That is, as shown in Figure 1, L 1Be illustrated in the fiber lengths from the position suitable to sensor 15 in the 3rd PANDA optical fiber 19 with the length of the 2nd PANDA optical fiber 18 with reference usefulness reflection end 14.
Use the physical amount measuring device 10A of the OFDR mode of present embodiment, obtain above-mentioned D 1, the optical interference signals D that utilizes 53 pairs of system controllers to obtain 1Carrying out STFT resolves.Here, (the n in first and second on the right of formula (1) Slow+ n Fast) L 1, expression moves back and forth fiber lengths difference L from the mensuration light that tunable laser 12 penetrates 1Optical path length.That is, with the L of the 3rd PANDA optical fiber 1Suitable optical path length becomes and (n Slow+ n Fast) L 1Half suitable { (n Slow+ n Fast)/2}L 1
In addition, in physical amount measuring device of the present invention, the A/D converter 54 that utilizes control part 22 to be possessed, with digital form the simulated light interference signal of measuring in photodiode 13 that is equivalent to above-mentioned formula (1) is taken a sample, 53 pairs of these digitalized intervention signals of system controller that utilize control part 22 to be possessed carry out STFT and resolve, but in this article, when brief note carries out STFT when resolving for utilize 53 pairs of optical interference signals of measuring of system controller that control part 22 possessed in photodiode 13, also mean and carried out same processing.As previously mentioned, because A/D converter 54 has the sampling frequency that can detect the intensity modulated of the interference of light surveyed by photodiode 13, so the digitalized intervention signal after the optical interference signals of simulation and the sampling is same signal on principle.In addition, by using the mathematical expression of expression simulated light interference signal,, use optical interference signals to describe for position that can more effective explanation feature of the present invention.
Then, in the physical amount measuring device 10A of the OFDR of present embodiment mode, for the optical path length { (n that obtains Slow+ n Fast)/2}L 1, the n that substitution is known SlowAnd n Fast, try to achieve L 1
As this n SlowAnd n Fast, can use and measure the value of trying to achieve etc. according to the value of obtaining from the wavelength of the Bragg reflection optical of sensor 15 with according to the grating cycle that the interval calculation of the diffraction grating of the even phase mask that uses goes out or according to near-field pattern in the making of sensor 15.Here, constant being meant of optical path length that first on the right of formula (1) and the right are second, the Bragg reflection optical of slow axis and fast axle is with respect to fiber lengths difference L 1Has identical optical path length.
In the present embodiment, so two polarization axles of the quadrature from sensor 15 obtain Bragg reflection optical.Therefore, can measure temperature and strain simultaneously.Thus, the physical amount measuring device 10A in the OFDR mode of using present embodiment carries out under the situation of strain measurement the sensor that does not need temperature compensation to use.In addition, since the Bragg reflection optical in slow axis and the fast axle with respect to fiber lengths difference L 1Have identical optical path length,, can carry out strain measurement with high spatial resolution so can determine the position of sensor 15 exactly.
The measuring method of＜temperature and strain 〉
Then, the temperature of the physical amount measuring device 10A of the OFDR mode of having used present embodiment and the measuring method of strain are described.This measuring method is the shift amount of basis from the wavelength of the Bragg reflection optical of two polarization axles of the quadrature of sensor 15, obtains the method for temperature and strain by calculating.
Measure the wavelength under a certain reference temperature (for example 20 ℃), the benchmark strain (for example 0 μ ε) at first, in advance from the Bragg reflection optical of two polarization axles of the quadrature of sensor 15.
Then, sensor 15 is configured in wants the place (hereinafter referred to as " detection portion ") surveyed,, measure wavelength from the Bragg reflection optical of two polarization axles of the quadrature of sensor 15 at this detection portion place.
Then, calculate the Bragg reflection optical of detection portion wavelength, with reference temperature, benchmark strain under the wavelength difference (variable quantity) of Bragg reflection optical.
Then, the wavelength difference that obtains is updated to following formula (2), obtain the poor of the strain of poor, detection portion of the temperature of detection portion and reference temperature and benchmark strain, calculate the actual temperature and the actual strain of detection portion at last according to known reference temperature, benchmark strainometer.
&Delta;T &Delta;&epsiv; = 1 D &PartialD; &lambda; fast &PartialD; &epsiv; , - &PartialD; &lambda; slow &PartialD; &epsiv; - &PartialD; &lambda; fast &PartialD; T , &PartialD; &lambda; slow &PartialD; T &Delta;&lambda; slow &Delta;&lambda; fast - - - ( 2 )
Wherein, D = &PartialD; &lambda; fast &PartialD; &epsiv; &CenterDot; &PartialD; &lambda; slow &PartialD; T - &PartialD; &lambda; fast &PartialD; T &CenterDot; &PartialD; &lambda; slow &PartialD; &epsiv;
In above-mentioned formula (2), Δ T represents the poor of the temperature of detection portion and reference temperature, and Δ ε represents the poor of the strain of detection portion and benchmark strain.T represents the temperature of detection portion, and ε represents the strain of detection portion, λ SlowAnd λ FastExpression is from the wavelength of the Bragg reflection optical of two polarization axles of the quadrature of the sensor 15 at detection portion place.Δ λ SlowWith Δ λ FastExpression from the wavelength of the Bragg reflection optical of two polarization axles of the quadrature of the sensor 15 at detection portion place, with reference temperature, benchmark strain under poor from the wavelength of the Bragg reflection optical of two polarization axles of the quadrature of sensor 15. With The bragg wavelength shift amount of the slow axis of representation unit strain and fast axle. With The bragg wavelength shift amount of the slow axis of representation unit temperature and fast axle.
The shift amount of the bragg wavelength of above-mentioned unit strain or unit temperature, by using the physical amount measuring device 10A of OFDR mode, under reference temperature (20 ℃), give strain to sensor 15, the strain-dependent that the bragg wavelength of slow axis in the survey sensor 15 and fast axle changes, under benchmark strain (0 μ ε), give temperature variation to sensor 15, the temperature dependency that the bragg wavelength of slow axis in the survey sensor 15 and fast axle changes is obtained thus.
Then, according to these Value, obtain the D value of record in the above-mentioned formula (2).Then, with this D value and the Δ λ that obtains according to measurement result SlowAnd Δ λ FastBe updated in the above-mentioned formula (2) and carry out computing, obtain Δ T and Δ ε thus.Then, if from these values, deduct reference temperature, benchmark strain, then can obtain the temperature and the strain of detection portion.
These computings can use the system controller 53 of the physical amount measuring device 10A of OFDR mode to carry out simply.
Fig. 4 is the concise and to the point pie graph of second embodiment of the physical amount measuring device of expression OFDR mode of the present invention.The physical amount measuring device 10C (10) of the OFDR mode of present embodiment is with the difference of above-mentioned first embodiment, disposes a plurality of sensors 15 (being two sensor 15a, 15b in illustrated example) on the 3rd PM optical fiber 19.
And in the physical amount measuring device 10C of the OFDR of this embodiment mode, the centre of the fiber lengths between adjacent sensor (first sensor 15a, the second sensor 15b) further disposes the second optical path length adjustment part 21b (21).Therefore, can make respectively from the optical path length of the Bragg reflection optical of two polarization axles of the quadrature among the first sensor 15a and the second sensor 15b constant.Promptly, when to from the Bragg reflection optical of the first sensor 15a and the second sensor 15b with when carrying out the STFT parsing with reference to catoptrical interference signal with reflection end, these come the Bragg reflection optical of self-orthogonal two polarization axles, in first sensor 15a and the intrinsic position of the second sensor 15b, be detected as identical position respectively.As a result, can determine the position of each sensor 15a, 15b exactly.
Used the situation of physical amount measuring device 10C of the OFDR mode of present embodiment, same during with above-mentioned first embodiment, can carry out the measurement of the determining of position, temperature and the strain of sensor 15.In the present embodiment, illustration be provided with the situation of two sensors 15 (the first sensor 15a and the second sensor 15b) at the 3rd PM optical fiber 19, but the physical amount measuring device of the OFDR mode of present embodiment is not limited to this.For the physical amount measuring device of the OFDR mode of present embodiment, can sensor 15 more than three be set at the 3rd PM optical fiber 19.Under this situation, also the same with the present embodiment that is provided with two sensors 15, can be by each sensor 15, will detect as same position from the Bragg reflection optical of two polarization axles of its quadrature.That is,, also can determine the position of each sensor 15 exactly, carry out strain measurement with high spatial resolution even if be provided with sensor 15 more than three at the 3rd PM optical fiber 19.
The physical amount measuring device 10 of the OFDR mode that relates to about above-mentioned first embodiment～second embodiment, preferred disposition have the 3rd PM optical fiber 19 of sensor 15 to be made of the big PM optical fiber of the effective refractive index of two polarization axles of quadrature poor (birefringence).
Thus, the poor sensitivity with respect to temperature and strain of two polarization axles of quadrature increases, and measures when can realize more high-precision temperature and distortion.More specifically, the effective refractive index difference of two polarization axles of preferred quadrature is 4.4 * 10 -4More than.By satisfying this value, as can obtaining, make shift characteristics difference with respect to the bragg wavelength of the temperature variation of sensor greater than-5.0 * 10 from embodiment described later -4Nm/ ℃.As a result, can obtain temperature accuracy is that 2 ℃, strain precision are the temperature of 30 these very high degree of precision of μ ε and the measuring accuracy of strain.
Below, further specify the present invention by embodiment, but the present invention is not limited to following embodiment.
Fig. 5 is the concise and to the point pie graph of physical amount measuring device 10D of the OFDR mode of expression embodiment 1.Present embodiment serves as that the basis constitutes with the physical amount measuring device 10A of the OFDR mode of above-mentioned first embodiment.In Fig. 5, to the inscape additional phase identical with the inscape of the physical amount measuring device 10A of the OFDR mode of first embodiment shown in Figure 1 with symbol, and omit its explanation.
The physical amount measuring device 10D of the OFDR mode of embodiment 1 forms with reflection end 37,38 by further possess two PM coupling mechanisms 31,32, photodiode 35 and two references in the physical amount measuring device 10A of OFDR mode shown in Figure 1.These parts connect setting by a kind of PANDA optical fiber 41,42,43,44,47,48 as PM optical fiber.And first～the 4th PM optical fiber and PM coupling mechanism 11 have also used PANDA optical fiber.
Tunable laser 12 is connected with system controller 53 by general purpose interface bus (GPIB), controls thus.
Signal from two photodiodes 13,35 is taken a sample by A/D converter 54, and this sampled data is carried out STFT by system controller 53 and resolved.About this analytic method, as record in the first above-mentioned embodiment.
As PM coupling mechanism 11,31,32, the PTAP-0150-2-B (model) that has used rattan storehouse company to make.
As tunable laser 12, used the 8164A (model) of Agilent corporate system.
As photodiode 13,35, the 2117FC (model) that has used New Focus company to make.
As PANDA optical fiber 17,18,19,20,41,42,43,44,47,48, the SM-15-PS-U25A (model) that has used rattan storehouse company to make.
As system controller 53, used the PXI-8106 (model) of American National instrument (National Instruments) corporate system.
As A/D converter 54, used the PXI-6115 (model) of American National instrument (National Instruments) corporate system.
Tunable laser 12 penetrates the mensuration light with the single polarized wave of a certain constant speed, a certain constant wavelength coverage scanning (dull increasing or dull the minimizing).
In this embodiment 1, output is with the mensuration light of speed 10nm/s in wavelength coverage 1545～1555nm scanning.
The mensuration light of the single polarized wave that penetrates from tunable laser 12 is propagated in the slow axis of PANDA optical fiber 41 and is incided PM coupling mechanism 31.Then, carried out luminous power branch, incide in two optical interferometers by this PM coupling mechanism 31.
One in above-mentioned two optical interferometers by PM coupling mechanism 32, with reference to briefly constituting with reflection end 37,38 and 35 photodiodes.In this optical interferometer, generated and had with reference to the PANDA optical fiber 47 of reflection end 37 with have the corresponding trigger pip of fiber lengths poor (optical path difference) with reference to the PANDA optical fiber 48 of usefulness reflection end 38.In this embodiment 1, the fiber lengths difference of establishing PANDA optical fiber 47 and PANDA optical fiber 48 is 50m.
This trigger pip generates by following method.
When making the mensuration light that scans with a certain constant speed, a certain constant wavelength coverage incide this optical interferometer from tunable laser 12, to measure light and be referenced with reflection end 37,38 reflections, this interference light is measured by photodiode 35.The signal of being obtained by photodiode 35 is taken a sample by A/D converter 54 and is converted voltage signal to.This voltage signal is taken in by system controller 53.From the mensuration light that tunable laser 12 penetrates, its wavelength changes with constant speed.Therefore, the signal of being measured by photodiode becomes the sine function that changes at interval with constant light wave number.Thereby, by with a certain constant magnitude of voltage as threshold value, utilize system controller 53 the moment that surpasses this threshold value (from the value below the threshold value above moment of threshold value or be lower than moment of threshold value from the value more than the threshold value) generate trigger pip, the trigger pip that is generated becomes a certain constant light wave number at interval thus.
The generation method of this trigger pip is even if under the inconstant situation of the sweep velocity of tunable laser 12, also very effective on the always constant this point in light wave number interval that trigger pip produced.
In above-mentioned two optical interferometers another briefly is made of first embodiment shown in Figure 1.
Sensor 15 is made by the common exposure method that has used KrF excimer laser and even phase mask.In this embodiment 1, establishing grating length (sensor length) is 5mm.And, establish from have with reference to the distance L of the suitable position of the PANDA optical fiber 14 of reflection end 14 till the sensor 15 1Be about 20m.And, from L 1The centre position, promptly with have the position of playing about 10m with reference to the suitable position of the length of the PANDA optical fiber 18 of reflection end 14, be provided with 90 ° and be offset fusion as optical path length adjustment part 21.As incident section 20, in PANDA optical fiber 16, be provided with 45 ° of skews and merge.
Then, the optical interference signals D that utilizes 53 pairs of system controllers to obtain 1Carrying out STFT resolves.The optical interference signals D of this moment 1, usefulness formula (1) expression same with first embodiment.In this embodiment 1, with about 40ms (if make tunable laser 12 be the speed of 10nm/s, is converted into wavelength, then is about the 400pm interval) suitable window width optical interference signals D at interval to obtaining 1Resolve.Under the inconstant situation of the sweep velocity of tunable laser 12, can not be a certain constant time interval, but be equivalent to a certain constant light wave number at interval the window width of (that is a certain constant wavelength interval) resolve.
Use the physical amount measuring device 10D of the OFDR mode of present embodiment, measured the state of sensor 15.The results are shown in Fig. 6.
In the physical amount measuring device 10D of OFDR mode, represent Bragg reflection optical from sensor 15 with spectrogram.For this spectrogram, transverse axis is represented wavelength, the longitudinal axis represent fiber position (from have with reference to fiber lengths with the suitable position of the PANDA optical fiber 18 of reflection end 14), tone is represented Bragg reflection intensity.
In spectrogram shown in Figure 6, think the Bragg reflection optical of 1550.6nm from the slow axis of sensor 15, the Bragg reflection optical of 1550.2nm has obtained position separately and has been about the approximate consistent result of 19.672nm from the fast axle of sensor 15.
In this embodiment 1, owing to obtained Bragg reflection optical from two polarization axles of the quadrature of sensor 15, so confirmed to measure temperature and strain simultaneously.Confirmed thus, carried out under the situation of strain measurement the sensor that does not need temperature compensation to use at the physical amount measuring device 10D of the OFDR mode of using present embodiment.And, owing to can determine the position of sensor 15 exactly, so can carry out strain measurement with high spatial resolution.
Then, use the physical amount measuring device 10D of the OFDR mode of present embodiment, under reference temperature (20 ℃), give strain, measured the strain-dependent that the bragg wavelength of slow axis in the sensor 15 and fast axle changes sensor 15.And, by adopting present embodiment, under benchmark strain (0 μ ε), give temperature variation to sensor 15, the temperature variation dependence that the bragg wavelength of slow axis in the determination sensor 15 and fast axle changes, obtain the every of above-mentioned formula (2) in the sensor 15 thus, the result has obtained following formula (3).When using this formula (3) when calculating, the D value in the above-mentioned formula (2) becomes D=-9.1515 * 10 -7(nm 2/ μ ε ℃).
By the Δ λ that will obtain by measurement result SlowWith Δ λ FastReach above-mentioned D and be updated in the above-mentioned formula (2), carry out computing, obtain Δ T and Δ ε thus.Then, if deduct reference temperature, benchmark strain, then obtain the temperature and the strain of detection portion from these values.
Then, the comparative example 1,2 that carries out in order to verify effect of the present invention is described.This comparative example 1,2 is not a prior art, is the new technology of implementing in order to verify effect of the present invention.
Except the polarization axle deviation angle with the fusion connecting portion of incident section and optical path length adjustment part is made as 0 °, made the physical amount measuring device of OFDR mode similarly to Example 1, with its as a comparative example 1.Use the physical amount measuring device of the OFDR mode of this comparative example 1, measured the state of sensor.The results are shown in Fig. 7.
According to the result of Fig. 7 as can be known, in this comparative example 1, can only obtain Bragg reflection optical from the slow axis of sensor 15.Only be used to Bragg reflection optical, simultaneously the temperature and the strain of survey sensor 15 from a polarization axle.Therefore, the physical amount measuring device in the OFDR mode of using comparative example 1 carries out under the situation of strain measurement the sensor that needs temperature compensation to use.
Except the polarization axle deviation angle with the fusion connecting portion of optical path length adjustment part is made as 0 °, made the physical amount measuring device of OFDR mode similarly to Example 1, with its as a comparative example 2.Use the physical amount measuring device of the OFDR mode of this comparative example 2, measured the state of sensor.The results are shown in Fig. 8.
According to the result of Fig. 8 as can be known, in this comparative example 2, can obtain from the slow axis of sensor 15 and the Bragg reflection optical of fast axle.Therefore, carry out under the situation of strain measurement at the physical amount measuring device of the OFDR mode of using comparative example 2, similarly to Example 1, the sensor that does not need temperature compensation to use.But, because the position difference of each Bragg reflection optical so can't determine the position of sensor 15 exactly, as a result of, can't be carried out strain measurement with high spatial resolution.
In this comparative example 2, the optical interference signals D that obtains by photodiode 13 2Represent with following formula (4).
D 2＝R slowcos(k2n slowL 1)+R fostcos(k2n fastL 1) (4)
With the optical interference signals D that in first embodiment and embodiment 1, obtains 1Difference be that the mensuration light that penetrates from tunable laser 12 in first and second on the right moves back and forth fiber lengths difference L 1The optical path length difference.This be because, for n SlowAnd n Fast, always satisfy n Slow＞n FastRelation.Different being meant of optical path length on first on the right in the formula (4) and second on the right, the Bragg reflection optical of slow axis and fast axle is with respect to fiber lengths difference L 1Has different optical path lengths.That is, shown in the result of Fig. 8, the position difference of Bragg reflection optical separately.
This be because, carrying out STFT when resolving, and must use the effective refractive index (n that has nothing in common with each other respectively to the signal of two polarization axles of quadrature SlowAnd n Fast) irrelevant because these signals are closed ripple, by photodiode 13 as optical interference signals D 2Measure, so must (in comparative example 2, use n with a certain constant effective refractive index Slow) calculate.
In spectrogram shown in Figure 8, be about 19.629m from the position of the Bragg reflection optical of the slow axis of sensor 15, be about 19.624m from the position of the Bragg reflection optical of the fast axle of sensor 15.Therefore, its difference is about 5mm.
Owing to used the fiber optic sensor system of the analytic method of sensor and OFDR mode to have the following spatial resolution of 1mm, this is poor so can detect.In other words, owing in the fiber optic sensor system of other modes, do not have the spatial resolution (perhaps, not determining the means of position) of this level, offset so can't detect this position.That is in the fiber optic sensor system of the analytic method that has used FBG sensor and OFDR mode, be effective means only.
Then, to calculating from the slow axis of sensor 15 and the position offsetting amount Δ 1 of the Bragg reflection optical of fast axle.The results are shown in Fig. 9.This Fig. 9 obtains according to following formula (5).
n slow &Delta;l = n slow L 1 - n fast L 1 &CenterDot; &CenterDot; &CenterDot; &Delta;l = ( n slow - n fast ) L 1 n slow - - - ( 5 )
Wherein, this moment sensor 15 the relative L of length 1Enough short, can ignore.
In above-mentioned formula (5), n SlowAnd n FastAdopted based on measure the value obtained etc. by the wavelength of the Bragg reflection optical of sensor 15 and the value of obtaining according to the grating cycle that the interval calculation of the diffraction grating of the even phase mask that uses goes out, from near-field pattern in the making of sensor 15.
In this comparative example 2, used by following formula (6), based on the wavelength of the Bragg reflection optical of sensor 15 and the value, the n that obtain according to the grating cycle that the interval calculation of the diffraction grating of the even phase mask that uses in the making of sensor 15 goes out Slow=1.44756, n Fast=1.44720.
n slow = &lambda; slow 2 &Lambda; n fast = &lambda; fast 2 &Lambda; - - - ( 6 )
In above-mentioned formula (6), λ SlowAnd λ FastExpression is from the wavelength of the Bragg reflection optical of two polarization axles of the quadrature in the sensor 15.A represents the grating cycle that the interval calculation of the diffraction grating of the even phase mask of basis goes out.
According to the result of Fig. 9 as can be known, at fiber lengths difference L 1, promptly from the position that becomes benchmark when the distance of sensor 15 is 20m, the position offsetting amount of calculating the Bragg reflection optical of the slow axis of autobiography sensor 15 and fast axle is about 5mm.Therefore, confirmed well consistent with the experimental result of comparative example 2.
According to this result of calculation, spatial resolution at the fiber optic sensor system of the analytic method that will use FBG sensor and OFDR mode is made as under the situation of 1mm, when being 4m when above to the distance of sensor 15, thinking and to confirm clearly that the position from the Bragg reflection optical of the slow axis of sensor 15 and fast axle offsets from the position that becomes benchmark.
Promptly as can be known, when being 4m when above from the position that becomes benchmark to the distance of FBG sensor, the present invention is very effective.
Figure 10 is the concise and to the point pie graph of physical amount measuring device 10E of the OFDR mode of expression embodiment 2.Present embodiment 2 is with the difference of embodiment 1, is that the physical amount measuring device 10C in the OFDR mode of above-mentioned second embodiment serves as that the basis makes.Promptly, the difference of present embodiment and embodiment 1 is, on the 3rd PM optical fiber (PANDA optical fiber) 19, dispose the first sensor 15a and the second sensor 15b, the second optical path length adjustment part 21b (90 ° of skews are merged) is arranged in the intermediate configurations of this first sensor 15a and the second sensor 15b.It is the position of 5m that the second sensor 15b is arranged on apart from first sensor 15a.The second optical path length adjustment part 21b is arranged on the position that is about 2.5m apart from first sensor 15a and the second sensor 15b.
Figure 11 has represented to use the physical amount measuring device 10E of the OFDR mode of present embodiment, measures the result of first sensor 15a, and Figure 12 represents to measure the result of the second sensor 15b.
From the result of Figure 11 as can be known, roughly consistent from the position of the Bragg reflection optical of the slow axis of first sensor 15a with position from the Bragg reflection optical of the fast axle of first sensor 15a, all be about 19.672m.
From the result of Figure 12 as can be known, roughly consistent from the position of the Bragg reflection optical of the slow axis of the second sensor 15b with position from the Bragg reflection optical of the fast axle of the second sensor 15b, all be about 24.757m.
According to The above results as can be known, even if under the situation that has disposed a plurality of sensors, by centre optical path length adjustment part (90 ° of skews are merged) is set respectively at these adjacent sensors, can be by each FBG sensor, make Bragg reflection optical from two polarization axles of its quadrature in identical position.
Except the 3rd PM optical fiber 19 that disposes sensor 15 is made of the big PANDA optical fiber of the effective refractive index poor (birefringence) of slow axis and fast axle, make similarly to Example 1, with it as embodiment 3.
When using Fig. 3 to describe, the PANDA optical fiber that this birefringence is big can be realized near fibre core 61 by the configuration that makes stress assigning unit 62.That is,, can adjust the birefringence of PANDA optical fiber arbitrarily by the configuration of stress assigning unit 62.
Use the physical amount measuring device of the OFDR mode of present embodiment, measured the state of sensor 15.The results are shown in Figure 13.
In spectrogram shown in Figure 13, the Bragg reflection optical of 1551.1nm is from the slow axis of sensor 15, and the Bragg reflection optical of 1550.4nm is from the fast axle of sensor 15.
When the spectrogram to the sensor 15 that obtains in embodiment 3 carried out more detailed parsing, slow axis was 0.670nm with the bragg wavelength difference of fast axle.And the birefringence that calculates according to this bragg wavelength difference is 6.22 * 10 -4The spectrogram of the sensor 15 that obtains in embodiment 1 is carried out more detailed parsing and the bragg wavelength difference that obtains is 0.391nm, and the birefringence that calculates according to this bragg wavelength difference is 3.65 * 10 -4That is, constitute the PANDA optical fiber of the sensor 15 of embodiment 3, compare, have big birefringence near 2 times with the PANDA optical fiber of the sensor 15 that constitutes embodiment 1.
Then, adopt present embodiment, under reference temperature (20 ℃), give strain, measured the strain-dependent that the bragg wavelength of slow axis in the sensor 15 and fast axle changes sensor 15.And, adopt present embodiment, under benchmark strain (0 μ ε), give temperature variation, measured the temperature variation dependence that the bragg wavelength of slow axis in the sensor 15 and fast axle changes sensor 15, obtain the every of above-mentioned formula (2) in the sensor 15 thus, the result obtains following formula (7).When this formula of use was calculated, the D value in the above-mentioned formula (2) became D=-10.908 * 10 -7(nm 2/ μ ε ℃).
When stating formula (2) accounting temperature and strain in the use, With Poor (bragg wavelength is poor with respect to the shift characteristics of the strain of slow axis and fast axle), and With Poor (bragg wavelength is poor with respect to the shift characteristics of the temperature variation of slow axis and fast axle) big more, the computational accuracy of temperature and strain is high more.For for the above-mentioned formula (7) that obtains among the embodiment 3, it should be noted and compare that bragg wavelength is bigger with respect to the shift characteristics difference of the temperature variation of slow axis and fast axle with the above-mentioned formula (3) that in embodiment 1, obtains.
Particularly, in the above-mentioned formula (3) that embodiment 1 obtains, be-3.7 * 10 -4Nm/ ℃, relative therewith, in the above-mentioned formula (7) that embodiment 3 obtains, be-7.2 * 10 -4Nm/ ℃.That is, the sensor 15 of embodiment 3 have with the sensor 15 of embodiment 1 compare near 2 times bragg wavelength poor with respect to the shift characteristics of temperature variation.
Can think that this is that difference by the birefringence of the PANDA optical fiber that constitutes each sensor causes.For PANDA optical fiber, be known in the birefringence of producing in the fibre core and the rising of temperature and reduce pro rata, as about 800～900 ℃ of the fusing point of stress assigning unit, birefringence is roughly 0.That is, the birefringence under the reference temperature is big more, and the birefringent reduction of rising unit temperature increases more.Therefore, the sensor 15 of embodiment 3 have with the sensor 15 of embodiment 1 compare near 2 times bragg wavelength poor with respect to the shift characteristics of temperature variation.
Then, give temperature variation and strain arbitrarily, utilize the physical amount measuring device of the OFDR mode of embodiment 3 to measure temperature variation and strain, its result is shown in table 1 sensor 15 of embodiment 3.
To be made as 20 ℃, 40 ℃, 100 ℃ (being that design temperature is 40 ℃, 60 ℃, 120 ℃) from the temperature variation of reference temperature (20 ℃), to be made as 257 μ ε, 535 μ ε, 1056 μ ε from the strain variation of benchmark strain (0 μ ε), amount to the measurement of having carried out temperature and strain under 9 kinds of conditions.Measurement result when as a result, obtaining temperature accuracy is below 2 ℃, the strain precision is following this very high degree of precision of 30 μ ε temperature and strain.
Such as described above, according to embodiment 3, the sensor that is formed by FBG that uses in the physical amount measuring device of OFDR mode of the present invention preferably is made of the big PANDA optical fiber of birefringence.Measuring accuracy studies in great detail in the time of to the temperature variation of the sensor that formed by FBG and strain, the result as can be known, preferably have bragg wavelength with respect to the shift characteristics difference of the temperature variation of this sensor greater than-5.0 * 10 -4Nm/ ℃ shift characteristics.
The result's that the bragg wavelength of Figure 14 formed sensor of FBG that to be expression constitute to the birefringence of PANDA optical fiber with by this optical fiber is estimated with respect to the shift characteristics difference of temperature variation curve map.
According to the result of Figure 14, be 4.4 * 10 in the birefringence of PANDA optical fiber -4When above, has shift characteristics difference that the bragg wavelength relative temperature of this sensor changes greater than-5.0 * 10 -4Nm/ ℃ shift characteristics.That is, the birefringence of preferred PANDA optical fiber is 4.4 * 10 -4More than.But,, then have this problem of fabrication yield variation of PANDA optical fiber if make the stress assigning unit excessively near fibre core in order to increase birefringence.Therefore, the birefringence of preferred PANDA optical fiber be can with good yield rate make 2.0 * 10 -3Below.
Wherein, in the present embodiment, for the bragg wavelength that makes the sensor that forms by FBG with respect to the shift characteristics difference of temperature variation greater than-5.0 * 10 -4Nm/ ℃, used the stress assigning unit near fibre core and the big PANDA optical fiber of birefringence.As realizing other PANDA optical fiber of the present invention, can enumerate the PANDA optical fiber that possesses low-melting stress assigning unit.More specifically, be below 600 ℃ the time at the fusing point of stress assigning unit, the shift characteristics difference that can make bragg wavelength is greater than-5.0 * 10 -4Nm/ ℃.
Except establishing sensor length is the 100mm, make similarly to Example 3, with it as embodiment 4.Use the physical amount measuring device 10F of the OFDR mode of present embodiment, measured the state of sensor 15, the result is shown in Figure 15.
In spectrogram shown in Figure 15, the Bragg reflection optical of 1549.4nm is from the slow axis of sensor 15, and the Bragg reflection optical of 1548.7nm is from the fast axle of sensor 15.
This spectrogram is carried out more detailed parsing and the wavelength difference of the Bragg reflection optical that obtains is 0.670nm.This wavelength difference and sensor length are that the sensor of the embodiment 3 of 5mm is equal to.Therefore, sensor length is the PANDA optical fiber that uses in the sensor 15 of present embodiment of 100mm, and its birefringence is the equal birefringence of using in the sensor 15 with embodiment 3 of PANDA optical fiber.
Figure 16 is the physical amount measuring device 10F that schematically represents to be used for by the OFDR mode of present embodiment, measures the figure of the experimental system of the Temperature Distribution that produces in sensor and strain.
In this experimental system, utilize counterweight W to give uniform strain along the long side direction of sensor 15.And, in this experimental system, can give uneven temperature variation along the long side direction of sensor 15 by the well heater A and the well heater B that can independently control temperature.
Use the physical amount measuring device 10F of the OFDR mode of present embodiment, utilize experimental system shown in Figure 16 to measure the state of sensor 15.The results are shown in Figure 17.At this moment, the strain that is imposed on sensor 15 by counterweight W is 1000 μ ε, and the temperature variation that is imposed on sensor 15 by well heater A is 100 ℃, and the temperature variation that is imposed on sensor 15 by well heater B is 60 ℃.
As shown in figure 17, the zone of the sensor that is heated by well heater A has taken place and the strain of 1000 μ ε and 100 ℃ the suitable bragg wavelength displacement of temperature variation.On the other hand, in the zone of the sensor that is heated by well heater B, taken place and the strain of 1000 μ ε and 60 ℃ the suitable bragg wavelength displacement of temperature variation.And the bragg wavelength displacement of working as with the strain facies of 1000 μ ε has only taken place in the not heating region between well heater A and the well heater B.That is, in the present embodiment,, can measure simultaneously along the Temperature Distribution and the strain of the long side direction of this sensor 15 by variable quantity along the bragg wavelength of the slow axis of the long side direction survey sensor 15 of sensor 15 and fast axle.
Then, in experimental system shown in Figure 16, make that to impose on the strain of sensor 15 constant by counterweight W be 1000 μ ε, make that to impose on the temperature variation of sensor 15 constant by well heater A be 100 ℃, and the temperature variation that imposes on sensor 15 by well heater B is changed in 0～100 ℃ scope.Then, the temperature variation and the strain of the position of the position of well heater A and well heater B have been measured.Its result is shown in Figure 18.
As shown in figure 18, in the position of well heater A, the strain that measures is constant to be 1000 μ ε.In addition, about temperature variation, also constant is 1 00 ℃.On the other hand, in the position of well heater B, the strain that measures is constant to be 1000 μ ε, and the design temperature of temperature variation that measures and well heater B changes relatively.That is, can measure temperature variation and the strain that takes place in the position of the position of well heater A and well heater B accurately simultaneously.
As described above such, by present embodiment, the present invention can simultaneously and measure along the Temperature Distribution and the strain of the long side direction of the sensor that is made of FBG accurately.And the application of the invention even if produce under the situation of Temperature Distribution and Strain Distribution at the long side direction along the sensor that is made of FBG, also can simultaneously and be measured them accurately.
By the physical amount measuring device of OFDR mode of the present invention, measure when can carry out the temperature of sensor and strain.And, can determine exactly the position of sensor can carry out the measurement of physical quantity with high spatial resolution.And, can measure simultaneously along the Temperature Distribution and the Strain Distribution of the long side direction of sensor.
1. the physical amount measuring device of an optical frequency range reflection mode is characterized in that possessing:
Penetrate the tunable laser of measuring light;
First polarization maintaining optical fibre that one end is connected with this tunable laser;
The polarization-maintaining coupler that is connected with the other end of this first polarization maintaining optical fibre;
One end is connected with this polarization-maintaining coupler, and the other end is as second polarization maintaining optical fibre of reference with reflection end;
The 3rd polarization maintaining optical fibre that one end is connected with described polarization-maintaining coupler;
Be formed at the fibre core of the 3rd polarization maintaining optical fibre and the sensor that constitutes by fiber grating;
The 4th polarization maintaining optical fibre that one end is connected with described polarization-maintaining coupler;
Be connected with described polarization-maintaining coupler by the 4th polarization maintaining optical fibre, to from the Bragg reflection optical of two polarization axles of the quadrature in the described sensor and from described with reference to the photodiode that detects with reference to light with reflection end;
According to by the detected described Bragg reflection optical of this photodiode and described with reference to light close glistening light of waves Strength Changes, detect above-mentioned Bragg reflection optical and with reference to the modulated control portion of the interference strength between the light;
To two polarization axle both sides of the quadrature of two polarization axles of the quadrature of described second polarization maintaining optical fibre and described the 3rd polarization maintaining optical fibre, the incident section of the described mensuration light of incident; With
Be disposed at described the 3rd polarization maintaining optical fibre, make the constant optical path length adjustment part of optical path length from the Bragg reflection optical of two polarization axles of the quadrature in the described sensor,
Described incident section is configured in described first polarization maintaining optical fibre or described second polarization maintaining optical fibre and described the 3rd polarization maintaining optical fibre both sides.
2. the physical amount measuring device of optical frequency range reflection mode according to claim 1 is characterized in that,
Be configured in this incident section under the situation of described first polarization maintaining optical fibre, described incident section is to have 45 ° polarization axle deviation angle and the fusion connecting portion that forms at this first polarization maintaining optical fibre;
Be configured in described incident section under described second polarization maintaining optical fibre and described the 3rd polarization maintaining optical fibre both sides' the situation, described incident section is to have 45 ° polarization axle deviation angle and the fusion connecting portion that forms at above-mentioned second polarization maintaining optical fibre and described the 3rd polarization maintaining optical fibre respectively.
3. the physical amount measuring device of optical frequency range reflection mode according to claim 1 and 2 is characterized in that,
Described optical path length adjustment part is to have 90 ° polarization axle deviation angle and the fusion connecting portion that forms at described the 3rd polarization maintaining optical fibre that is formed with described sensor.
4. the physical amount measuring device of optical frequency range reflection mode according to claim 1 and 2 is characterized in that,
Described optical path length adjustment part is set at the centre from the position suitable with the length of described second polarization maintaining optical fibre to the fiber lengths of described sensor.
5. the physical amount measuring device of optical frequency range reflection mode according to claim 1 and 2 is characterized in that,
Dispose a plurality of described sensors in described the 3rd polarization maintaining optical fibre.
6. the physical amount measuring device of optical frequency range reflection mode according to claim 5 is characterized in that,
Described optical path length adjustment part is configured in the centre of the fiber lengths between the described sensor of adjacency respectively.
7. the physical amount measuring device of optical frequency range reflection mode according to claim 1 and 2 is characterized in that,
The effective refractive index of two polarization axles of the quadrature in described the 3rd polarization maintaining optical fibre is 4.4 * 10 -4More than.
8. the measuring method temperature of a physical amount measuring device that has used optical frequency range reflection mode and strain the time is characterized in that, comprising:
Use the physical amount measuring device of any described optical frequency range reflection mode in the claim 1～7, measurement is from the step of the wavelength of the Bragg reflection optical of two polarization axles of the quadrature in one or more described sensors;
According to the wavelength of the described Bragg reflection optical of measuring, calculate the step of the wavelength Yin Wendu and the variable quantity that strain causes of the described Bragg reflection optical in the described sensor; With
According to the described variable quantity that calculates, measure the temperature at the position that disposes described sensor and the step of strain simultaneously.
9. measuring method in the time of the temperature of the physical amount measuring device that has used optical frequency range reflection mode according to claim 8 and strain is characterized in that,
Calculate the Temperature Distribution and the Strain Distribution along the position long side direction that disposes described sensor of described the 3rd polarization maintaining optical fibre.
CN2009800002856A 2008-02-29 2009-03-02 Physical quantity measuring device of optical frequency range reflection measuring type, and temperature and strain simultaneous measuring method using the device CN101680781B (en)
JP2008051343 2008-02-29
JP051343/2008 2008-02-29
JP239368/2008 2008-09-18
JP2008239368 2008-09-18
PCT/JP2009/053899 WO2009107839A1 (en) 2008-02-29 2009-03-02 Physical quantity measuring device of optical frequency range reflection measuring type, and temperature and strain simultaneous measuring method using the device
CN101680781A CN101680781A (en) 2010-03-24
CN101680781B true CN101680781B (en) 2011-11-23
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CN2009800002856A CN101680781B (en) 2008-02-29 2009-03-02 Physical quantity measuring device of optical frequency range reflection measuring type, and temperature and strain simultaneous measuring method using the device
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