CN100338448C - Composite structure of fibre optical Bragg grating temperature sensor and producing method thereof - Google Patents

Abstract

The present invention discloses a composite structure of an optical fiber Bragg grating temperature sensor, which is composed of a metal sleeve pipe, a fiber coating, and an optical fiber core with a Bragg grating, wherein the optical fiber coating is connected with the sleeve pipe through epoxy resin; the cross-section of a part of optical fiber coating containing the Bragg grating is reduced to mu times, and mu is larger than 0 and is smaller than 1. The present invention also discloses a producing method for the composite structure of an optical fiber Bragg grating temperature sensor. Firstly, an optical fiber to be packed is soaked in methylene chloride, and the overlay of the optical fiber is removed; then, a part of optical fiber coating is put in hydrofluoric acid and is eroded, which causes that the cross section of the part of the optical fiber is reduced to mu times; in a third step, the optical fiber after etched is put in the metal sleeve pipe; axial tension straining is applied to the optical fiber to be packed; the part of optical fiber coating with an original cross section is stuck to the metal sleeve pipe. When the mu is about equal to 0.6, the equivalent temperature sensitivity of the present invention is 4.53 times larger than that of a normal optical fiber grating and is 0.72 times larger than that of alone metallic aluminium package.

Description

Optical fiber Bragg grating temperature sensor composite structure and manufacture method thereof

One. technical field

The present invention relates to a kind of fiber package structure and manufacture method, relate in particular to a kind of optical fiber Bragg grating temperature sensor composite structure and manufacture method thereof.

Two. background technology

The reflection kernel wavelength X of bragg grating _BIndex modulation periods lambda and optical fiber effective refractive index n with fiber grating _EffRelevant.When acting on the strain of bragg grating or temperature variation, all can make its reflection kernel wavelength X _BWill be offset.And for common λ _BThe Fiber Bragg Grating FBG of ≈ 1550nm, theoretical and experiment shows that all the temperature control of its centre wavelength is about 11pm/ ℃.

In the thermal tuning field of bragg grating sensing and bragg grating centre wavelength, always wish that its temperature control is the bigger the better, i.e. the central wavelength lambda that causes during temperature variation _BSide-play amount is big more, and the temperature control k of fiber-optic grating sensor is just high more like this, can improve temperature resolution, and the tuning efficient of fiber grating centre wavelength also can improve greatly simultaneously.The sensitivity of existing fiber bragg grating temperature sensing encapsulating structure is lower, and can not adapt to the application scenario that various high sensitivity requires.

Three. summary of the invention

1. technical matters

The invention provides a kind of high sensitivity, easy realization, wide region Bragg grating fibre optic temperature sensor encapsulating structure and manufacture method thereof.

2. technical scheme

A kind of optical fiber Bragg grating temperature sensor composite structure, by sleeve pipe 1, fibre cladding 2 and form by the fiber cores 3 of Bragg grating, there is the fiber cores 3 of Bragg grating to be arranged in fibre cladding 2, fibre cladding 2 is positioned at sleeve pipe 1, sleeve pipe 1, fibre cladding 2 and fiber cores 3 length are 10～30mm, connect with epoxy resin 4 between fibre cladding 2 and the sleeve pipe 1, the cross-sectional area that it is characterized in that comprising the part fibre cladding 5 of Bragg grating be reduced into before the not corrosion μ doubly, 0＜μ＜1, the length that comprises the part fibre cladding 5 of Bragg grating is 2～10mm, the internal diameter of sleeve pipe 1 is 1～5mm, external diameter is 1.5～10.5mm, metal sleeve 1 and do not reduce between the part fibre cladding 6 of cross-sectional area bonding with epoxy resin 4.

A kind of manufacture method of optical fiber Bragg grating temperature sensor composite structure, the first step, with length is that the optical fiber that will encapsulate of 10～30mm soaked in methylene chloride 5～40 minutes, remove the overlay of optical fiber, second step, it is that 10%～40% hydrofluorite corroded 20～60 minutes that the part fibre cladding 5 that will comprise Bragg grating is put into mass concentration, the feasible cross-sectional area that comprises the part fibre cladding 5 of Bragg grating reduces to μ times before the not corrosion, 0＜μ＜1, wherein, the length that comprises the part fibre cladding 5 of Bragg grating is 2～10mm, in the 3rd step, it is 1～5mm that the optical fiber after the corrosion is put into internal diameter, and external diameter is 1.5～10.5mm, length is in the metal sleeve 1 of 10～30mm, applies one 100 * 10 on the optical fiber that will encapsulate ^-6～500 * 10 ^-5The axial tension strain, the part fibre cladding 6 and the metal sleeve 1 that will not reduce cross-sectional area with epoxy resin 4 are bonding, and make epoxy resin 4 be exposed in the air 12～60 hours.

3. technique effect

(1) (sleeve pipe can be a metallic aluminium to the temperature sensitizing encapsulation technology of this fiber grating by fiber grating being sticked on sleeve pipe 1, aluminium alloy, steel, copper, and the bigger organic polymer of thermal expansivity etc.) on, the sleeve pipe bigger by thermal expansivity expands with heat and contract with cold, thereby makes the temperature control of fiber grating improve.Aluminum pipe or aluminium alloy (aluminium alloy that is suitable for tubing as duralumin, hard alumin ium alloy, rust-preventing aluminum alloy etc.) sleeve pipe, its thermal expansivity is very big, can obtain higher sensitivity with these materials.

(2) by corrosion process make the cross-sectional area of the fiber section that is carved with Bragg grating be reduced to not before the corrosion μ (0＜μ＜1) doubly, like this when being subjected to same axial force, the strain stress of fiber grating corrosion region _gIt is the strain stress that does not have the fiber section of corrosion _f(1/ μ) doubly.Then the fiber grating after excessive erosion is sticked in the metallic aluminium sleeve pipe, because the thermal expansivity of aluminium is much larger than fiber optic materials, expanding with heat and contract with cold of aluminium makes grating be subjected to axial strain when utilizing temperature variation, thereby the center wavelength shift effect that strain causes is added on the temperature effect of fiber grating centre wavelength, its equivalent temperature coefficient is improved, and since the strain that partly is subjected to of fiber grating after the corrosion greater than the part that not have corrosion, so the temperature control of the fiber grating of encapsulation has improved than only encapsulating with metallic aluminium like this

Doubly, and can control the temperature control of fiber grating, have certain dirigibility by accurate control extent of corrosion.

(3) in the process of encapsulation, need to give the certain tensile strain 100 * 10 of fiber grating by axial tension ^-6～500 * 10 ^-6,, thereby make device satisfy certain temperature-responsive scope because the tensile strain length that the shrinkage of optical fiber causes when just can offset low temperature shortens.Not loosening at certain temperature range inner fiber grating, be subjected to the influence of expanding with heat and contract with cold of aluminum casing all the time, thereby the effect of temperature sensitizing can be arranged in certain temperature range.

(4) in the various in the above parameters,, optimize some technological parameters and can obtain better effect: corrosion region length: 5～10mm in order to improve the stability of sensitivity and device; Too short etching process difficulty strengthens, and oversize package dimension increases.Metal sleeve internal diameter: 1～2mm; The too big increasing encapsulation difficulty of internal diameter, the heat conduction of sleeve pipe between optical fiber of slowing down too greatly, the response speed of the device that promptly slows down.Metal tube external diameter: 1.5～2.5mm; The heat conduction of sleeve pipe between optical fiber of slowing down greatly, the response speed of the device that promptly slows down, and increase device size.μ value size: 0.2～1; Too little optical fiber ruptures easily, strengthens encapsulation difficulty.

(5) encapsulation back epoxy resin 4 exposes a period of time and makes epoxy resin at room temperature solidify in air, thereby reaches better bond effect.

(6) comprehensive two kinds of effects can improve the temperature control of fiber grating greatly.This encapsulation technology has good dirigibility, by selecting the material of different heat expansion coefficient, in conjunction with the extent of corrosion of accurately controlling fiber grating, can be easy to realize the special package of various different temperatures sensitivity requirements.

(7) if only adopt the method for metal sleeve, then the temperature control of grating relies on the thermal expansivity of metal fully, realize that the grating of specified temp sensitivity will be selected corresponding metal, is difficult to realize even can't realize the grating of some temperature control; And if only adopt the technology of corrosion, can only improve the strain sensitivity of fiber grating, and the encapsulating structure that we propose can be converted into temperature control to the strain sensitivity that the corrosion back increases, and only rely on corrosion to come the scope of temperature sensitizing tuning sensitivity very little, and can remedy the shortcoming of two kinds of technology in conjunction with Metal Packaging and corrosion enhanced sensitivity two kinds of technology, can carry out the temperature control coarse adjustment by selecting shell material, and then pass through the fine tuning of corrosion realization temperature control, thereby be more prone to realize the grating of various particular sensitivity requirements.

(8) fiber grating after the metallic aluminium encapsulation is in-20 ℃～90 ℃ temperature ranges, in the time of μ ≈ 0.6, its effective temperature sensitivity is 5.53 times of ordinary optic fibre grating, be the encapsulation of independent metallic aluminium grating temperature control and also encapsulation after 1.72 times, the optical fiber grating temperature family curve linearity has reached 0.9973.

Principle of work:

To periodic distribution, this device has good wavelength selectivity to the refractive index of fiber grating along fiber axis, has only the light of the wavelength that satisfies Bragg condition to be coupled in the reverse transfer mould central wavelength lambda of bragg grating _BSatisfy following Bragg equation:

λ _B＝2·n _eff·Λ (1)

In the formula: n _EffBe the effective refractive index of fiber grating, Λ is the index modulation cycle of fiber grating.(1) formula can obtain the temperature T differentiate:

$\frac{d{\mathrm{\λ}}_B}{\mathrm{dT}}=2\·(\frac{{\mathrm{dn}}_{\mathrm{eff}}}{\mathrm{dT}}\·\mathrm{\Λ}+\frac{\mathrm{d\Λ}}{\mathrm{dT}}\·n_{\mathrm{eff}})---\left(2\right)$

(1) formula can obtain divided by (2) formula:

$\frac{d{\mathrm{\λ}}_B}{{\mathrm{\λ}}_B}=(\frac{1}{n_{\mathrm{eff}}}\·\frac{{\mathrm{dn}}_{\mathrm{eff}}}{\mathrm{dT}}+\frac{1}{\mathrm{\Λ}}\·\frac{\mathrm{d\Λ}}{\mathrm{dT}})\mathrm{dT}---\left(3\right)$

In the formula:

Be the thermo-optical coeffecient of fiber grating, represent with parameter beta; Be the thermal expansivity of fiber grating, represent with parameter alpha.So (3) formula can be expressed as again:

$\frac{d{\mathrm{\λ}}_B}{{\mathrm{\λ}}_B}=(\mathrm{\β}+\mathrm{\α})\·\mathrm{dT}=\mathrm{\η}\·\mathrm{dT}---\left(4\right)$

In the formula: if hypothesis η is the temperature control coefficient of fiber grating; For common silica fibre, β=6.8 * 10 ^-6/ ℃, α=0.55 * 10 ^-6/ ℃, temperature control coefficient η=7.35 * 10 of ordinary optic fibre grating then ^-6/ ℃, and from the temperature control that (4) formula can obtain fiber grating be:

Δλ _B＝λ _B·η·ΔT＝k·ΔT (5)

Wherein $k=\frac{{\mathrm{\Δ\λ}}_B}{\mathrm{\Δ}}={\mathrm{\λ}}_B\·\mathrm{\η}$ Be the temperature control of fiber grating, and the effective temperature sensitivity of hypothesis encapsulation back fiber grating is k '.Because the thermo-optic effect of optical fiber accounts for the leading position of temperature control, so the fiber grating thermal expansion effects almost can be ignored.If we can increase the influence of thermal expansion to temperature control, just can increase the effective temperature sensitivity k ' of fiber grating.Fiber grating is sticked in the metallic aluminium substrate, because the thermalexpansioncoefficient of aluminium _s=23 * 10 ^-6/ ℃ α greater than silica fibre, so the strain that produces on the fiber grating during temperature variation dT is:

ε _T＝(α _s-α)·dT (6)

The part fiber optical corrosive that grating will be arranged then diminishes its cross-sectional area, and the corrosion factor of establishing cross-sectional area is $\mathrm{\μ}=\frac{S^{\′}}{S}\left(\mathrm{\μ}\≤1\right),$ It is long-pending that wherein S and S ' are respectively the cross section of optic fibre that corrodes front and back, and according to Hooke's law,

The axial strain that optical fiber produces before and after the corrosion is:

${\mathrm{\ϵ}}_T=\frac{1}{E}\·\frac{F}{S}---\left(7\right)$

${{\mathrm{\ϵ}}_T}^{\′}=\frac{1}{E}\·\frac{F}{S^{\′}}---\left(8\right)$

ε wherein _TAnd ε _T' be respectively and do not corrode and corrode the suffered strain size of part, so:

$\frac{{{\mathrm{\ϵ}}_T}^{\′}}{{\mathrm{\ϵ}}_T}=\frac{S}{S^{\′}}=1/\mathrm{\μ}---\left(9\right)$

Can draw by (6) and (9), be encapsulated in the strain stress that the grating of the corrosion on the aluminium substrate is subjected to _T' be:

${{\mathrm{\ϵ}}_T}^{\′}=(1/\mathrm{\μ})\·({\mathrm{\α}}_s-\mathrm{\α})\·\mathrm{dT}---\left(10\right)$

On the basis that directly utilizes the metal enhanced sensitivity, increased 1/ μ again doubly.So the bragg wavelength that the strain that temperature variation causes causes is changed to:

$\frac{d{\mathrm{\λ}}_B}{{\mathrm{\λ}}_B}=(1-p_e)\·{{\mathrm{\ϵ}}_T}^{\′}=(1-p_e)\·(1/\mathrm{\μ})\·({\mathrm{\α}}_s-\mathrm{\α})\·\mathrm{dT}---\left(11\right)$

P in the formula _e=0.22 is effective strain optical coefficient of fiber optic materials.The effective temperature sensitivity k ' that can be drawn the fiber grating after encapsulation by (11) is

k′＝[1/μ·(1-p _e)·(α _s-α)+η]·λ _H＝[(β+α)+1/μ(1-p _e)·(α _s-α)]·λ _B (12)

Four. description of drawings

Fig. 1 is an optical fiber Bragg grating temperature sensor composite structure synoptic diagram of the present invention.

Fig. 2 is the temperature coefficient comparison diagram of packaged fiber grating, metallic aluminium packaged fiber grating and corrosion enhanced sensitivity metallic aluminium packaged fiber grating not, and wherein data point is an optical fiber Bragg grating temperature sensor composite structure of the present invention for black triangle.

Five. specific embodiments

1 one kinds of optical fiber Bragg grating temperature sensor composite structures of embodiment, by sleeve pipe 1 (can be aluminum casing), fibre cladding 2 and form by the fiber cores 3 of Bragg grating, have the fiber cores 3 of Bragg grating to be arranged in fibre cladding 2, fibre cladding 2 is positioned at sleeve pipe 1, sleeve pipe 1, fibre cladding 2 and fiber cores 3 length are 10～30mm, (market can be buied with epoxy resin 4 between fibre cladding 2 and the sleeve pipe 1, can use the DP460 type of 3M company) connect, in the present embodiment, the cross-sectional area that comprises the part fibre cladding 5 of Bragg grating is reduced into the preceding μ of not corrosion doubly, 0＜μ＜1, can be 0.1,0.2,0.3,0.5,0.6,0.8,0.9, the length that comprises the part fibre cladding 5 of Bragg grating is 2～10mm, can be 2mm, 5mm, 8mm, sleeve pipe 1 is a metal sleeve, its internal diameter is 1～5mm, can be 1mm, 1.5mm, 2mm, 3mm, 4mm, 5mm, external diameter is 1.5～10.5mm, 1.5mm, 2.0mm, 2.5mm, 3.0mm, 5mm, 7mm, 9mm, 10mm, metal sleeve 1 and do not reduce between the part fibre cladding 6 of cross-sectional area bonding with epoxy resin 4 (market can be buied).

2 one kinds of optical fiber Bragg grating temperature sensor composite structures of embodiment, (can be aluminium or aluminium alloy sleeve pipe by metal sleeve 1, aluminium alloy can be duralumin, hard alumin ium alloy or rustproof aluminum alloy), fibre cladding 2 and form by the fiber cores 3 of Bragg grating, have the fiber cores 3 of Bragg grating to be arranged in fibre cladding 2, fibre cladding 2 is positioned at sleeve pipe 1, sleeve pipe 1, fibre cladding 2 and fiber cores 3 length are 10～30mm, (market can be buied with epoxy resin 4 between fibre cladding 2 and the sleeve pipe 1, the DP460 type of 3M company) connect, the cross-sectional area that comprises the part fibre cladding 5 of Bragg grating is reduced into the preceding μ of not corrosion doubly, 0＜μ＜1, can be 0.1,0.2,0.3,0.5,0.6,0.8,0.9, the length that comprises the part fibre cladding 5 of Bragg grating is 2～10mm, can be 2mm, 5mm, 8mm, the internal diameter of metal sleeve 1 are 1～5mm, can be 1mm, 1.5mm, 2mm, 3mm, 4mm, 5mm, external diameter are 1.5～10.5mm, 1.5mm, 2.0mm, 2.5mm, 3.0mm, 5mm, 7mm, 9mm, 10mm, metal sleeve 1 and do not reduce between the part fibre cladding 6 of cross-sectional area bonding with epoxy resin 4 (market can be buied).

The manufacture method of 3 one kinds of optical fiber Bragg grating temperature sensor composite structures of embodiment, the first step is that the optical fiber that will encapsulate of 10～30mm soaked in methylene chloride 5～40 minutes with length, can be 10 minutes, 20 minutes, remove the overlay of optical fiber, in second step, it is that 10%～40% hydrofluorite corroded 20～60 minutes that the part fibre cladding 5 that will comprise Bragg grating is put into mass concentration, make the cross-sectional area of the part fibre cladding 5 that comprises Bragg grating reduce to before the not corrosion μ doubly, 0＜μ＜1, μ can be 0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9, wherein, the length that comprises the part fibre cladding 5 of Bragg grating is 2～10mm, can be 3mm, 5mm, 7mm, 9mm, the concentration of hydrofluorite can be 10%, 20%, 25%, 30%, etching time can be 60 minutes, 50 minutes, 30 minutes, 10 minutes, the 3rd step, it is 1～5mm that optical fiber after the corrosion is put into internal diameter, for example can be 1mm, 2mm, 3mm, 4mm, external diameter is 1.5～10.5mm, can be chosen for 1.5mm, 2.5mm, 3.5mm, 4.5m length is in the metal sleeve 1 of 10～30mm, applies one 100 * 10 on the optical fiber that will encapsulate ^-6～500 * 10 ^-6Axial tension strain (adopt fiber clamp apply axial strain), strain can be 100 * 10 ^-6, 200 * 10 ^-6, 300 * 10 ^-6, 400 * 10 ^-6, the part fibre cladding 6 and the metal sleeve 1 that will not reduce cross-sectional area with epoxy resin 4 (market can be buied) are bonding, and make epoxy resin 4 (market can be buied) be exposed in the air 12～60 hours, can be 24 hours.

The manufacture method of 4 one kinds of optical fiber Bragg grating temperature sensor composite structures of embodiment, the first step is that the optical fiber that will encapsulate of 10～30mm soaked in methylene chloride 5～40 minutes with length, can be 10 minutes, 20 minutes, remove the overlay of optical fiber, in second step, it is that 10%～30% hydrofluorite corroded 20～50 minutes that the part fibre cladding 5 that will comprise Bragg grating is put into mass concentration, make the cross-sectional area of the part fibre cladding 5 that comprises Bragg grating reduce to before the not corrosion μ doubly, 0＜μ＜1, μ can be 0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9, wherein, the length that comprises the part fibre cladding 5 of Bragg grating is 2～10mm, can be 3mm, 5mm, 7mm, 9mm, the concentration of hydrofluorite can be 10%, 20%, 30%, etching time can be 50 minutes, 30 minutes, 10 minutes, in the 3rd step, it is 1～5mm that the optical fiber after the corrosion is put into internal diameter, for example can be 1mm, 2mm, 3mm, 4mm, external diameter are 1.5～10.5mm, can be chosen for 1.5mm, 2.5mm, 3.5mm, 4.5m, length is in the metal sleeve 1 of 10～30mm, applies one 200 * 10 on the optical fiber that will encapsulate ^-6～300 * 10 ^-6Axial tension strain (adopt fiber clamp apply axial strain), strain can be 200 * 10 ^-6, 300 * 10 ^-6The part fibre cladding 6 and the metal sleeve 1 that to not reduce cross-sectional area with epoxy resin 4 (market can be buied, the DP460 type of 3M company) are bonding, and (market can be buied to make epoxy resin 4, the DP460 type of 3M company) is exposed in the air 12～60 hours, can be 24 hours.

Claims (5)

1. optical fiber Bragg grating temperature sensor composite structure, by sleeve pipe (1), fibre cladding (2) and have the fiber cores (3) of Bragg grating to form, there is the fiber cores (3) of Bragg grating to be arranged in fibre cladding (2), fibre cladding (2) is positioned at sleeve pipe (1), sleeve pipe (1), fibre cladding (2) and fiber cores (3) length are 10～30mm, connect with epoxy resin (4) between fibre cladding (2) and the sleeve pipe (1), it is characterized in that the cross-sectional area that will comprise the part fibre cladding (5) of Bragg grating by corrosion is reduced into the preceding μ of not corrosion doubly, 0＜μ＜1, the length that comprises the part fibre cladding (5) of Bragg grating is 2～10mm, sleeve pipe (1) is a metal sleeve, its internal diameter is 1～5mm, external diameter is 1.5～10.5mm, metal sleeve (1) and do not reduce between the part fibre cladding (6) of cross-sectional area bonding with epoxy resin (4).

2. optical fiber Bragg grating temperature sensor composite structure according to claim 1, the internal diameter that it is characterized in that sleeve pipe (1) is 1～2mm, external diameter is 1.5～2.5mm.

3. optical fiber Bragg grating temperature sensor composite structure according to claim 1 is characterized in that metal sleeve (1) adopts the aluminum or aluminum alloy sleeve pipe.

4. the manufacture method of an optical fiber Bragg grating temperature sensor composite structure according to claim 1, it is characterized in that: the first step, with length is that the optical fiber that will encapsulate of 10～30mm soaked in methylene chloride 5～40 minutes, remove the overlay of optical fiber, second step, it is that 10%～40% hydrofluorite corroded 20～60 minutes that the part fibre cladding (5) that will comprise Bragg grating is put into mass concentration, the feasible cross-sectional area that comprises the part fibre cladding (5) of Bragg grating reduces to μ times before the not corrosion, 0＜μ＜1, wherein, the length that comprises the part fibre cladding (5) of Bragg grating is 2～10mm, in the 3rd step, it is 1～5mm that the optical fiber after the corrosion is put into internal diameter, and external diameter is 1.5～10.5mm, length is in the metal sleeve (1) of 10～30mm, applies one 100 * 10 on the optical fiber that will encapsulate ^-6～500 * 10 ^-6The axial tension strain, the part fibre cladding (6) and the metal sleeve (1) that will not reduce cross-sectional area with epoxy resin (4) are bonding, and make epoxy resin (4) be exposed in the air 12～60 hours.

5. the manufacture method of optical fiber Bragg grating temperature sensor composite structure according to claim 4, it is characterized in that: it is that 10%～30% hydrofluorite corroded 20～50 minutes that the part fibre cladding (5) that will comprise Bragg grating is put into mass concentration, the feasible cross-sectional area that comprises the part fibre cladding (5) of Bragg grating reduces to μ times before the not corrosion, 0.2＜μ＜1.0.

The manufacture method of optical fiber Bragg grating temperature sensor composite structure according to claim 4, the length that it is characterized in that comprising the part fibre cladding (5) of Bragg grating is 5～10mm.

The manufacture method of optical fiber Bragg grating temperature sensor composite structure according to claim 4 is characterized in that: the axial tension strain that applies on the optical fiber that will encapsulate is 200 * 10 ^-6～300 * 10 ^-6

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