CN1216278C - Packaging structure of fibre-optical grating - Google Patents

Abstract

The present invention relates to a packing structure of an optical fiber grating, which comprises an optical fiber grating, and a packing pipe with one or two openings, wherein both ends of the packing pipe are respectively connected with bearing handles and conic caps connected with the bearing handles; the optical fiber grating is packed in the middle of the packing pipe along the axial direction of the packing pipe; filling materials are filled between the internal diameter of the packing pipe and the optical fiber grating. Light enters fiber cores; the reflecting wavelength of the light reflects the stress bore by the grating and the transmission variation; the manufacturing materials of the packing pipe and the bearing handles of both ends are the filling materials which are suitable for the application of different engineering; the filling materials enter from the opening on the packing pipe for filling and sealing the space between the optical fibers and the packing pipe; different fill-sealing materials can have different temperature sensitivity. The packing optical fiber grating of the present invention obviously increases the stability, the reliability and the safety; simultaneously, the present invention can measure the temperature and the stress.

Description

The encapsulating structure of fiber-optic grating sensor

Technical field

The present invention relates to fiber grating, particularly a kind of encapsulating structure of fiber-optic grating sensor.

Technical background

Since fiber grating came out, ultraviolet write technology, the phase mask wrting method, and the appearance in succession of optical fiber hydrogen-carrying photosensitivity-enhancing technology has made Fiber Bragg Grating technology obtain international and domestic extensive attention.Optical fiber Bragg raster is the index distribution of a kind of space periodicity of setting up in one section fiber core, and the centre wavelength of its reflectance spectrum is along with the suffered stress of grating and temperature variation and change.Based on the drift theory of fiber grating Bragg wavelength, optical fiber Bragg grating sensor can be measured many physical quantitys, as: strain, stress, temperature, vibration, pressure, voltage and some chemistry amounts.Optical fiber Bragg grating sensor is measured owing to its Wavelength-encoding, absolute value and is used wavelength-division multiplex technique and just can realize advantages such as distributed measurement on one road optical fiber, has caused extensive concern in field of sensing technologies.Fiber grating has become a kind of very important sensing means, its application very extensively, comprise the monitoring of Aero-Space, compound substance, concrete, high voltage transmission line, large scale civil engineering structure and infrastructure etc.The Sutapun of the U.S. etc. are with palladium film packaged fiber grating, utilize palladium to inhale the ability that changes grating centre wavelength behind the hydrogen and have made hydrogen sensor; The Murukeshan of Singapore etc. imbeds intelligent composite with fiber grating and monitors its solidification process; Chan etc. with the optical fiber grating measuring composite material reinforced concrete strain; The Gwandu of Britain etc. have measured the strain and the curvature of structure simultaneously with fiber grating; The Ho in Hong Kong etc. have studied the dynamic and static weighing of structure with fiber grating, and obtain resolution of 2.6 μ ε etc.At present, mainly comprise both at home and abroad aspects such as damage check after Gernral Check-up, corrosion monitoring, composite material solidification monitoring and the moulding thereof of large scale civil engineering, vibration-testing at the application of optical fiber Bragg grating sensor.Optical fiber Bragg raster mainly is subjected to the restriction of three aspect factor as strain transducer in actual application in engineering, and the one, optical fiber Bragg raster is manufactured on the single mode silica fibre that removes coat, fractures easily; The 2nd, the variation of environment temperature and strain can both cause the drift of cloth loudspeaker lattice centre wavelength, i.e. the cross sensitivity problem of temperature and strain must be taked the temperature compensation measure during strain measurement.The 3rd, the working environment of sensor is abominable relatively, and usually in humidity, under the perishable environment, the reliability of long-term work is difficult to guarantee.Therefore, must seek effective packaged type, fiber grating is protected, to guarantee that sensor can be survived and operate as normal in the industry spot environment.

Existing encapsulation technology adopts the tubulose encapsulation or the rectangular configuration sealing of organic polymer and metal-coating usually, and in practical engineering application, this polymer encapsulated stability of structure, reliability and practicality all are difficult to reach the practical project requirement, and the characteristic of polymkeric substance has determined the characteristic of fiber-optic grating sensor; Encapsulating structure in the existing strain gauge is not eliminated the influence of the centre wavelength of temperature on fiber grating simultaneously, and there is certain error in its measured value.

Summary of the invention

Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, a kind of encapsulating structure of fiber-optic grating sensor is provided, adopt the stabilized fiber of this construction packages qualitative, reliability and security all be significantly improved; Measure when simultaneously, encapsulating structure of the present invention has been realized temperature and stress.

One of technical solution of the present invention is: the encapsulating structure of fiber-optic grating sensor, its characteristics are to comprise: fiber grating, have one or two perforate package tube, be connected to stressed handle respectively at the two ends of described package tube, fiber grating is along the centre that axially is encapsulated in this package tube of described package tube, irritating between the inwall of described package tube and fiber grating has fill material, and Embedding Material enters from the perforate of described package tube.

Embedding Material is a low melting point metal material, and decision grating temperature susceptibility, promptly different Embedding Materials has different temperature sensitivities; Embedding Material enters from the perforate of described package tube, and Embedding Material is just in time sealed the perforate of described package tube; When Embedding Material enters package tube, also be added with air extractor respectively at the two ends of package tube, so that no emptying aperture in the Embedding Material, no bubble; Package tube and stressed handle are the materials that meets the engineering applied environment; The profile of package tube and stressed handle decides at common desired paster operation, can be circular configuration or easier rectangular configuration of carrying out paster.For fiber-optic output is shielded, also be connected to tapered cap at the two ends of described stressed handle.

When package tube has two perforates, fill inert gas between two perforates, to improve the stability of fiber grating.Can be on the structure with reference to accompanying drawing 2 (another example structure synoptic diagram of one of the technology of the present invention solution).From protection and intensity aspect, the embedding hole on the package tube is thinner eyelet.This is for long grating and thin package tube, and Embedding Material is metal material particularly, and is very big to whole section grating whole fill difficulty.Take the above-mentioned method of opening diplopore can encapsulate the grating two ends, under pure vertical pulling stress application occasion, identical effect is arranged with whole fill.Middle filling with inert gas can not done special processing to exposed grating, and fiber grating can be because of the aging sex change of long-term use yet.

Two of technical solution of the present invention is: the encapsulating structure of fiber-optic grating sensor; its characteristics are to be included in the optical fiber that diverse location is carved with two different centre wavelength gratings; the package tube that has perforate; be positioned at the stressed handle of described package tube one end; be positioned at the hollow metal protection bucket of the described package tube other end; the inward flange of bucket is welded on the centre position on the package tube; annular end face plays with the same function of stressed handle; have the centre that axially be encapsulated in this package tube of the optical fiber of grating along described package tube; irritating between the inwall of described package tube and fiber grating has Embedding Material, and Embedding Material enters from the perforate of described package tube.End at described stressed handle can also connect the tapered cap that fiber-optic output is shielded.Fig. 4 (the technology of the present invention solution two embodiment synoptic diagram) has introduced this method for packing.

When this invention device is imbedded concrete or other are by side structure, temperature all exerts an influence to two gratings, but by the distortion of side structure, barrel second grating of outside protected in a pulling, and first fiber grating is subjected to less than external pull owing to package tube, and only generation responds to temperature, the difference of such two a centre wavelengths counter stress sensitivity, realize stress measurement, first grating can be measured temperature simultaneously, measures when realizing temperature stress; The metal coating bucket of a hollow shields to first grating, and external force can only act on the protection bucket, and grating and not stressing, so grating is only to responsive to temperature; The profile of the metal coating bucket of described in addition package tube, stressed handle and hollow decides at common desired paster operation, can be circular configuration or easier rectangular configuration of carrying out paster.

The advantage that the present invention compared with prior art has:

(1) the present invention adopts metal material as Embedding Material, and overall construction intensity is big, is fit to rugged surroundings.

(2) the present invention adopts metal material as Embedding Material, and temperature-responsive is fast, and the stress that the temperature difference produces is little.

(3) the present invention is adapted to carry out simultaneously the measurement of temperature and stress.

(4) the present invention encapsulates simply, reliable, compact, is fit to multiple industrial occasions and uses.

(5) plate metal earlier before the encapsulation of the fiber grating of the present invention encapsulation, safe, temperature-responsive is fast, is particularly suitable for temperature sensor.

Description of drawings

Fig. 1 is the example structure synoptic diagram of one of the technology of the present invention solution;

Fig. 2 is another example structure synoptic diagram of one of the technology of the present invention solution;

Fig. 3 is that the embodiment of one of the technology of the present invention solution is embedded in the synoptic diagram in the concrete;

Fig. 4 is two an embodiment synoptic diagram of the technology of the present invention solution;

Fig. 5 is attached to the measured object schematic surface for two example structure of the technology of the present invention solution;

Fig. 6 is the connection diagram in actual test system of the embodiment of the invention;

Fig. 7 is the stress characteristic curve of the centre wavelength of the grating of structure among Fig. 1.

Embodiment

As shown in Figure 1, the encapsulating structure of one of the technology of the present invention solution embodiment comprises the fiber grating 40 that a centre wavelength is 1554nm, has 8, two the stressed handles 27 of package tube (package tube 8 and stressed handle 27 all adopt circular in the present embodiment) and the tapered cap 16 of a perforate 22, the length 12cm of package tube 8 wherein, external diameter 1.5mm, internal diameter 0.8mm, the diameter 0.8mm of the perforate 22 on it, the external diameter 12mm of stressed handle 27, internal diameter 0.8mm, wide 10mm, the diameter of its groove are 8mm.Package tube 8 and stressed handle 27 are the materials that are fit to various abominable engineering-environments, can be stainless steel or titanium alloy or aluminium alloy.Package tube 8 and stressed handle 27 must be welded together, and can or stick with glue with soldering to connect.

At first peel the optical fiber coating at fiber grating two ends off 14mm, make optical fiber pass package tube 8 from the centre.Embedding Material 26 enters into the space 31 of grating 40 and package tube 8 centres from perforate 22, diffusion from the middle to both ends, packing space 31 slowly, Embedding Material 26 is just in time sealed perforate 22, when Embedding Material 26 enters package tube 8, two ends at package tube 8 can also be added with air extractor respectively, so that no emptying aperture in the Embedding Material 26, no bubble.Embedding Material 26 is low melting point metal materials, as tin etc., and its directly be bonded in fiber grating 40 around.Hermetically-sealed construction 21 in the circular groove of stressed handle 27 can be relative softer material, is in the same place by epoxy resin 37 and stressed handle 27, bonding fiber, has sealed Embedding Material 26 simultaneously.Tapered cap 16 adopts betal can, can weld or be bonded on the stressed handle 27, and middle space 17 can pour into the material of some plasticity, realizes the protective effect to fiber-optic output.

As shown in Figure 2, another embodiment of one of the technology of the present invention solution is: package tube 8 has hole 24 and 25 at two ends, Embedding Material 26 24,25 enters from the hole, play bonding and sealing function, Embedding Material 26 is filled inert gas to improve the stability and the life-span of grating in the middle of just in time sealing perforate 24,25, two holes simultaneously.In addition, when Embedding Material 26 enters package tube 8, can also be added with air extractor respectively at the two ends of package tube 8, so that no emptying aperture in the Embedding Material 26, no bubble.

The fiber grating 40 of above-mentioned two embodiment of the present invention plates layer of metal before encapsulation, as metallic copper, tin and zinc etc., to improve the response speed to temperature, can also improve the bonding force between grating and the package tube simultaneously.

As shown in Figure 3, the principle of Embedding Material decision grating temperature susceptibility and while sensitive temperature and strain is in the encapsulating structure of the present invention: the central wavelength lambda of fiber grating _B=2n Λ, n are the effective refractive index of optical fiber, and Λ is the cycle of grating.

Grating centre wavelength is with variation of temperature can differentiate draws to temperature T by the following formula both sides:

$\frac{1}{{\mathrm{\λ}}_B}\frac{{\mathrm{d\λ}}_B}{\mathrm{dT}}=\frac{1}{n}\frac{\mathrm{dn}}{\mathrm{dT}}+\frac{1}{\mathrm{\Λ}}\frac{\mathrm{d\Λ}}{\mathrm{dT}}=\mathrm{\ξ}+{\mathrm{\α}}_f$

Wherein, $\mathrm{\ξ}=\frac{1}{n}\frac{\mathrm{dn}}{\mathrm{dT}}$ Be the thermo-optical coeffecient of fiber optic materials, ${\mathrm{\α}}_f=\frac{1}{\mathrm{\Λ}}\frac{\mathrm{d\Λ}}{\mathrm{dT}}$ Thermal expansivity for optical fiber.

Known α _f=0.55 * 10 ^-6/ ℃, get ξ=6.1 * 10 ^-6/ ℃, when 100 ℃ of temperature variation, according to following formula, the centre wavelength 1.03nm (temperature coefficient 0.0103nm/ ℃) that will drift about, this is a sizable variation, so in the practical application, grating must carry out temperature compensation.

Center Bragg grating Bragg wavelength with stress variation can differentiate obtains to strain stress by the following formula both sides:

$\frac{1}{{\mathrm{\λ}}_B}\frac{d{\mathrm{\λ}}_B}{\mathrm{d\ϵ}}=\frac{1}{\mathrm{\Λ}}\frac{\mathrm{d\Λ}}{\mathrm{d\ϵ}}+\frac{1}{n}\frac{\mathrm{dn}}{\mathrm{d\ϵ}}=1-P_e$

Wherein, $P_e=-\frac{1}{n}\frac{\mathrm{dn}}{\mathrm{d\ϵ}}$ Elasto-optical coefficient for fiber optic materials.

When temperature and stress all change, can obtain:

$\frac{\mathrm{\Δ}{\mathrm{\λ}}_B}{{\mathrm{\λ}}_B}=({\mathrm{\α}}_f+\mathrm{\ξ})\mathrm{\ΔT}+(1-P_e)\mathrm{\Δ\ϵ}$

To structure shown in Figure 3, the total expansion coefficient after the encapsulation is

α=α _f+ α _c, wherein ${\mathrm{\α}}_c=\frac{\mathrm{d\ϵ}}{\mathrm{dT}}$

So, $\frac{\mathrm{d\λ}}{\mathrm{dT}}=\frac{\∂\mathrm{\λ}}{\∂T}+\frac{\∂\mathrm{\λ}}{\∂\mathrm{\ϵ}}{\mathrm{\α}}_c$

$\frac{1}{\mathrm{\λ}}\frac{\mathrm{d\λ}}{\mathrm{dT}}=\mathrm{\ξ}+(1-P_e)\mathrm{\α}+P_e{\mathrm{\α}}_f,$

When $\mathrm{\α}=\frac{-1}{1-P_e}(\mathrm{\ξ}+P_e{\mathrm{\α}}_f)$ The time, can realize temperature-insensitive.

By mechanics principle, the thermal expansivity that can draw encapsulating structure shown in Figure 3 is,

$\mathrm{\α}=\frac{E_f{S}_f{\mathrm{\α}}_f+E_1{S}_1{\mathrm{\α}}_1+E_s{S}_s{\mathrm{\α}}_s}{E_f{S}_f+E_1{S}_1+E_s{S}_s}$

Wherein E is a Young modulus, and S is a cross-sectional area, and f, 1, s represent the encapsulating structure of two gratings basic identical respectively, can obtain required temperature coefficient by rational selection material and design size.

Shown in Figure 4; the enclosed construction of two embodiment of the technology of the present invention solution is: comprise that an optical fiber is carved with different centre wavelength fiber gratings 41 and 42 at diverse location, have 8, one stressed handles 27 of package tube of a perforate 22; 28, one tapered cap 16 of the metal coating bucket of a hollow.Wherein apart from 8cm, centre wavelength is respectively 1556nm and 1542nm to two gratings 41 and 42 at a distance of certain, and the temperature coefficient of two gratings is the same.The length of package tube 8 is 16cm, external diameter 1.8mm, internal diameter 0.8mm, the diameter 0.8mm of perforate 22.The external diameter of stressed handle 27 is 14mm, internal diameter 0.8mm.The external diameter of metal coating bucket 28 is 14mm, and internal diameter is 3mm, length 10cm.Package tube 8, stressed handle 27 and metal coating bucket 28 are the materials that are fit to various abominable engineering-environments, can be stainless steel or aluminium alloy or titanium alloy etc.Peel the optical fiber coating between grating two ends and two fiber gratings off, pass from the centre of package tube 8, Embedding Material 26 enters into space 31 in the middle of grating 41,42 and the package tube 8, diffusion from the middle to both ends, packing space 31 slowly from perforate 22, Embedding Material 26 is just in time sealed perforate 22, two ends are sealed with glue, when Embedding Material 26 enters package tube 8, can also be added with air extractor respectively at the two ends of package tube 8, so that no emptying aperture in the Embedding Material 26, no bubble.The metal coating bucket 28 of hollow, welds together to crossing perforate 22 places and package tube 8 to grating 42 from the right cover, so just can make grating 42 avoid stress influence, obtains the precise dose value.

As shown in Figure 5; when the profile of package tube 8, stressed handle 27 and metal coating bucket 28 is rectangle; be attached to the synoptic diagram on measured object surface; rectangle wherein can make encapsulating structure better contact with the measured object surface; the parameter that reflects measured object more accurately; specifically adopt circle or rectangle, operate at common desired paster according to the profile of package tube 8, stressed handle 27 and metal coating bucket 8 and decide.

Two fiber gratings 41 and 42 of the above embodiment of the present invention plate layer of metal before encapsulation, as metallic copper, tin and zinc etc., to improve the response speed to temperature, can also improve the bonding force between grating and the package tube simultaneously.

As shown in Figure 6, test macro synoptic diagram for the embodiment of the invention, comprise that one has encapsulated grating 10 as measuring sensor, a resistance strain gage sensor 20 is as witness mark, fiber Bragg grating sensor inquiring instrument FBG-Interrogation system 31, the computing machine 43 of control and processing, FBG-IS31 has built-in light source and circulator, and computing machine 43 links together by data card and FBG-IS 31 and strain-ga(u)ge transducer 20.At first resistance strain gage sensor 20 and encapsulation grating 10 are bonded on the measured object, give stress of measured object, the signal that resistance strain gage sensor 20 and FBG-IS31 draw all is sent to computing machine 43, handles, compares.

Shown in Figure 7, for with the centre wavelength of the optical grating reflection of the grating measuring of fiber grating of the present invention encapsulation and the curve of suffered STRESS VARIATION, as can be seen, the stress of fiber grating impression and wavelength variations have good linear relationship in very big measurement range from the curve.

Claims (11)

1, the encapsulating structure of fiber-optic grating sensor, it is characterized in that comprising: fiber grating, have one or two perforate package tube, be connected to stressed handle respectively at the two ends of described package tube, fiber grating is along the centre that axially is encapsulated in this pipe of described package tube, irritating between the inwall of described package tube and fiber grating has Embedding Material, and described Embedding Material enters from the perforate of described package tube.

2, according to the encapsulating structure of the described fiber-optic grating sensor of claim 1, it is characterized in that: described Embedding Material is a low melting point metal material.

3, according to the encapsulating structure of the described fiber-optic grating sensor of claim 1, it is characterized in that: described Embedding Material is just in time sealed the perforate of described package tube.

4, according to the encapsulating structure of the described fiber-optic grating sensor of claim 1, it is characterized in that: the manufacturing materials of described package tube and stressed handle is stainless steel or aluminium alloy or the titanium alloy that meets different engineering applied environments.

5, according to the encapsulating structure of the described fiber-optic grating sensor of claim 1, it is characterized in that: the profile of described package tube and stressed handle decides at common desired paster operation, is circular configuration or rectangular configuration.

6, according to the encapsulating structure of the described fiber-optic grating sensor of claim 1, it is characterized in that: when described package tube has two perforates, fill inert gas between two perforates, to improve fiber grating-stabilized property.

7, the encapsulating structure of fiber-optic grating sensor according to claim 1 is characterized in that: described fiber grating plates layer of metal before encapsulation, to improve the response speed and the be connected power of optical fiber with package tube to temperature.

8, the encapsulating structure of fiber-optic grating sensor; it is characterized in that: be included in diverse location be carved with two different centre wavelength gratings optical fiber, have perforate package tube, be positioned at described package tube one end stressed handle, be positioned at the hollow metal protection bucket of the described package tube other end; have the centre that axially be encapsulated in this package tube of the optical fiber of grating along described package tube; irritating between the inwall of described package tube and fiber grating has Embedding Material, and described Embedding Material enters from the perforate of described package tube.

9, the encapsulating structure of described fiber-optic grating sensor according to Claim 8, it is characterized in that: the material of the metal coating bucket of described package tube, stressed handle and hollow is stainless steel or aluminium alloy or the titanium alloy that meets different engineering applied environments.

10, the encapsulating structure of described fiber-optic grating sensor according to Claim 8 is characterized in that: the profile of the metal coating bucket of described package tube, stressed handle and hollow decides at common desired paster operation, is circular configuration or rectangular configuration.

11, the encapsulating structure of fiber-optic grating sensor according to claim 8 is characterized in that: described fiber grating plates layer of metal before encapsulation, to improve the response speed and the be connected power of optical fiber with package tube to temperature.

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