Packaging device and method for compensating temperature unevenness of ultra-long fiber bragg grating through thermal expansion

Abstract

The invention provides a packaging device and method for compensating temperature unevenness of a super-long fiber bragg grating through thermal expansion, the packaging device comprises a packaging structural member composed of a duralumin lower sleeve and an invar upper sleeve, the fiber bragg grating is installed in U-shaped grooves formed in the duralumin lower sleeve and the invar upper sleeve, and the packaging structural member is installed in a metal shell. And the TEC is adhered to the bottom of the packaging structural member through a solidifiable curing adhesive. Based on the characteristic that the thermal expansion coefficients of duralumin and invar are greatly different, when the temperature is changed, the length of the invar part is basically not changed, and the duralumin part is changed in length, and different length changes can generate stress on the fiber bragg grating, so that the influence of uneven temperature on the wavelength of the fiber bragg grating is compensated; the stability performance of the central wavelength of the ultra-long fiber grating is improved, and the requirements of scientific research fields and related engineering applications are better met.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber grating packaging, and in particular relates to a packaging device and method for compensating for uneven temperature of an ultra-long fiber grating by thermal expansion. The technology can be applied to the packaging of a single-frequency fiber laser resonant cavity in the fields of coherent optical communication, gravitational wave detection, etc. Background Art

[0002] As a common fiber passive device, fiber Bragg grating has the advantages of small size, high stability, low cost, easy connection with optical fiber, and low insertion loss. With the increasing demand for fiber Bragg gratings, ultra-long fiber Bragg gratings with grating areas greater than 10 cm have appeared, such as ultra-narrowband fiber Bragg gratings and chirped fiber Bragg gratings, which can be used in fiber laser technology, fiber sensing, and fiber communication. One application of ultra-long fiber Bragg gratings is the temperature control packaging of fiber Bragg gratings. Generally, TEC is used to control the temperature of the substrate, thereby affecting the fiber Bragg grating fixed on the substrate. For the temperature control of ultra-long fiber Bragg gratings with a grating area length greater than 10 cm, due to the size limitations of the common TEC on the market, the substrate will be heated unevenly, causing the central wavelength of the ultra-long fiber Bragg grating to drift and the spectrum to be distorted.

[0003] In order to achieve the effect of grating temperature compensation from the packaging material and structure, the prior art (CN200610169809.2) proposes a method for fiber Bragg grating temperature compensation packaging, the basic principle of which is to use a material that does not have a negative temperature coefficient, and after special processing, to make a packaging sleeve with a weak negative thermal expansion coefficient, which can just compensate for the wavelength drift caused by the temperature change of the fiber Bragg grating; the fiber Bragg grating is quickly packaged at high temperature using the prepared packaging sleeve to produce a fiber Bragg grating that is insensitive to temperature and has high thermal stability, and is subjected to multiple high and low temperature cycle aging. However, when this packaging technology is applied to the fiber Bragg grating used to package fiber lasers, it can only offset part of the impact of the ambient temperature, and cannot eliminate the wavelength drift caused by the heating of the fiber Bragg grating itself, and cannot meet the increasingly high wavelength stability requirements for fiber lasers in practical applications.

[0004] Therefore, in order to solve the above technical problems, the present invention designs a packaging device and method for compensating the temperature unevenness of ultra-long fiber gratings by thermal expansion. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a packaging device and method for compensating for the uneven temperature of an ultra-long fiber Bragg grating by thermal expansion. Based on the temperature control packaging technology of the fiber Bragg grating, the different thermal expansion coefficients of metals are utilized to solve the central wavelength drift caused by the uneven temperature distribution of the ultra-long fiber Bragg grating by changing the stress on the fiber Bragg grating. While fixing the fiber laser in the metal shell structure to ensure its reliability, the packaging stress introduced by the temperature in the traditional thermal curing process is eliminated by selecting a room temperature curing packaging glue, thereby realizing compensation for the disturbance of the grating area's own temperature and the ambient temperature, further improving the central wavelength stability performance of the ultra-long fiber Bragg grating, and better meeting the needs of scientific research and related engineering applications.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A packaging device for compensating the uneven temperature of an ultra-long optical fiber Bragg grating by thermal expansion comprises a packaging structure composed of a duralumin lower sleeve and an invar upper sleeve, wherein the optical fiber is placed in the packaging structure, and the packaging structure is fixed in a metal shell with an upper shell cover. A TEC is attached between the bottom of the packaging structure and the bottom wall of the metal shell by a solidifiable curable adhesive for controlling the temperature, and a thermistor is also installed on the top of the packaging structure for monitoring the temperature of each area.

[0008] Furthermore, the duralumin lower sleeve and one end of the invar upper sleeve are mounted in a stepped manner; the duralumin lower sleeve includes a duralumin U-shaped groove, a stress release groove, a fixing screw hole A, and a fixing through hole A; the invar upper sleeve includes an invar U-shaped groove, a fixing screw hole B, and a fixing through hole B;

[0009] The duralumin U-shaped groove and the Invar U-shaped groove 201 are respectively arranged along the length direction of the duralumin lower sleeve and the Invar upper sleeve for fixing the optical fiber; a plurality of stress release grooves are arranged along the width direction of the duralumin lower sleeve for releasing the stress generated when thermal expansion occurs; the duralumin lower sleeve and the Invar upper sleeve are spliced ​​up and down and fixed by fixing screw holes A, fixing screw holes B and screws to form a packaging structure; the packaging structure is fixed to the fixing studs in the metal shell by fixing through holes A, fixing through holes B and screws.

[0010] A packaging method for the packaging device using thermal expansion to compensate for uneven temperature of an ultra-long fiber grating comprises the following steps:

[0011] Step 1: Design a temperature-compensated fiber Bragg grating packaging structure, which is divided into two parts: aluminum and invar;

[0012] Step 2: Clean the packaging structure and place the hard aluminum lower sleeve on the displacement platform;

[0013] Step 3: Wipe the optical fiber with alcohol, and place the optical fiber in the hard aluminum U-shaped groove on the hard aluminum lower sleeve, with the optical fiber close to the bottom of the hard aluminum U-shaped groove;

[0014] Step 4: Use a two-point glue sealing process to fix one end of the hard aluminum lower sleeve without applying stress;

[0015] Step 5: The optical fiber with one end not fixed passes through the Invar U-shaped groove on the Invar upper sleeve, the screw micrometer is turned to apply a pre-tightening force to the optical fiber, and the optical fiber is fixed to the Invar upper sleeve by applying glue;

[0016] Step 6: After the glue between the optical fiber and the packaging structure is completely cured, apply thermal conductive silicone grease in each U-shaped groove;

[0017] Step 7: Use curable adhesive to stick the TEC to the bottom of the hard aluminum lower sleeve;

[0018] Step 8: Install the thermistor on the packaging structure;

[0019] Step 9: After the glue is completely cured, place the entire packaging structure in a metal shell to complete the ultra-long fiber grating temperature control packaging.

[0020] Furthermore, after the temperature control packaging is completed, the specific method for compensating for the center wavelength drift caused by the fiber grating temperature is as follows:

[0021] Both temperature and strain will cause the wavelength of the fiber Bragg grating to change. When the wavelength shift change caused by strain and the wavelength change caused by temperature unevenness are equal in magnitude but opposite in direction, they can offset each other, thereby eliminating the change in wavelength caused by temperature unevenness. Therefore, to achieve wavelength compensation for ultra-long fiber Bragg gratings, it is required that the wavelength change caused by the thermal contraction of the negative expansion material just offset the wavelength change caused by temperature change.

[0022] The relationship between fiber strain and fiber Bragg grating center wavelength is:

[0023] The thermal expansion coefficient of the Invar upper sleeve is negligible according to its properties, and the temperature change of the duralumin lower sleeve corresponds to its length change:

[0024] ΔL=ξLΔT(2);

[0025] In strain sensing, the strain magnitude of the fiber Bragg grating is expressed as:

[0026] The relationship between temperature change and fiber Bragg grating center wavelength is:

[0027] When ultra-long fiber Bragg grating is packaged for temperature control, the fiber Bragg grating will be heated unevenly due to the size limitation of TEC. The temperature distribution coefficient can be obtained through experimental simulation: ΔT = T + βL′ (5);

[0028] To achieve temperature compensation for optical fiber, the change in grating wavelength Δλ caused by thermal expansion of the packaging material is required. ε , which just offsets the wavelength drift Δλ caused by uneven temperature changes T , that is, Δλ ε =Δλ T (6);

[0029] From the formula for the effect of strain and temperature on wavelength drift, we can know:

[0030] When (ξ+α f )ΔT=(1-ρ e )Δε, the above formula is:

[0031] (ξ+α f )(T+βL′)=(1-ρ e )ξΔTε (7)

[0032] Δλ ε =Δλ T

[0033] Among them, ΔT is the temperature change of the hard aluminum lower sleeve, Δε is the strain change of the optical fiber, and λ f is the thermal expansion coefficient of the optical fiber, ξ is the thermal expansion coefficient of the hard aluminum sleeve, ρ e is the effective elastic-optic coefficient, Δλε represents the change in grating wavelength caused by thermal expansion of the package material; Δλ represents the total change in grating wavelength; ε z Indicates the axial force on the optical fiber, ε = ε z ; K ε represents the strain sensitivity coefficient; ε represents the total stress on the optical fiber; ΔL represents the change in the length of the hard aluminum sleeve; L represents the length of the hard aluminum sleeve at 0°; Δλ T Indicates the change in grating wavelength caused by temperature; K T represents the temperature sensitivity coefficient of the fiber Bragg grating; T represents the controlled temperature of the TEC; β represents the temperature distribution coefficient; L′ represents the distance from a certain position of the packaging structure to the middle of the packaging structure;

[0034] When encapsulated with duralumin and invar, the grating is integrated with the two materials, making the thermal expansion coefficient of the optical fiber α f = 0, ignoring the thermal expansion coefficient of Invar steel, when the thermal expansion coefficient of duralumin ξ = Δε / ΔT satisfies the condition of formula (7), the compensation for the uneven temperature of the fiber Bragg grating can be achieved. The different thermal expansion coefficients of the two materials are used to compensate for the center wavelength drift caused by the temperature of the fiber Bragg grating.

[0035] The present invention has the following beneficial effects:

[0036] 1. The present invention utilizes the thermal expansion characteristics to achieve compensation for the temperature uneven wavelength of the ultra-long fiber Bragg grating, designs a double substrate structure (i.e., packaging structural parts), and reduces environmental impact; this packaging substrate has low cost and simple process, effectively improves the working life of the laser, solves the problem of fiber Bragg grating temperature-strain cross-sensitivity, has the advantages of light weight, good thermal shock resistance, and high precision, and is suitable for strain measurement in high and low temperature extreme environments.

[0037] 2. The present invention compensates for the uneven temperature of the ultra-long fiber Bragg grating under the temperature control package based on the thermal expansion characteristics. By using two different thermal expansion characteristics, the temperature response of the fiber Bragg grating is significantly improved while compensating the central wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is an overall schematic diagram of the packaging structure of the present invention;

[0039] Figure 2 Schematic diagram of fiber Bragg grating temperature control packaging.

[0040] In the figure: 1-duralumin lower sleeve; 101-duralumin U-shaped groove; 102-stress release groove; 103-fixing screw hole A; 104-fixing through hole A; 2-Invar upper sleeve; 201-Invar U-shaped groove; 202-fixing screw hole B; 203-fixing through hole B; 301-packaging structure; 302-metal shell; 303-TEC; 304-curable curing glue. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0042] like Figure 1 , 2 As shown, the packaging device for compensating the uneven temperature of ultra-long fiber Bragg gratings by thermal expansion according to the present invention includes a packaging structure 301 composed of a hard aluminum lower sleeve 1 and an Invar upper sleeve 2, and also includes a metal shell 302, TEC303, a solidifiable curable glue 304, a shell cover, and fixing studs.

[0043] The duralumin lower sleeve 1 and the Invar upper sleeve 2 are installed at one end by step-like fitting; Figure 1 As shown, the duralumin lower sleeve 1 includes a duralumin U-shaped groove 101, a stress release groove 102, a fixing screw hole A103, and a fixing through hole A104; the Invar upper sleeve 2 includes an Invar U-shaped groove 201, a fixing screw hole B202, and a fixing through hole B203.

[0044] like Figure 1As shown, the duralumin U-shaped groove 101 and the Invar U-shaped groove 201 are respectively arranged along the length direction of the duralumin lower sleeve 1 and the Invar upper sleeve 2 for fixing the optical fiber Bragg grating; a plurality of stress release grooves 102 are arranged along the width direction on the duralumin lower sleeve 1 for releasing the stress generated when thermal expansion occurs; the duralumin lower sleeve 1 and the Invar upper sleeve 2 are spliced ​​up and down and fixed by fixing screw holes A103, fixing screw holes B202 and screws, and together form a packaging structure 301.

[0045] like Figure 2 As shown, the packaging structure 301 is fixed to the fixing studs in the metal shell 302 through the fixing through hole A104, the fixing through hole B203 and screws, the bottom of the hard aluminum lower sleeve 1 is adhered with TEC303 through the solidifiable curing glue 304, and the solidifiable curing glue 304 is also adhered between TEC303 and the inner wall of the metal shell 302, and the top of the metal shell 302 is also installed with a shell cover; the top of the packaging structure 301 is also installed with a thermistor for monitoring the temperature of each area.

[0046] The stepped packaging structure design of the present invention can transmit more effectively under stress, thereby enhancing the fiber grating's ability to perceive tiny physical changes. At the same time, metal has good thermal conductivity and can respond quickly to temperature changes.

[0047] The present invention selects duralumin and invar as packaging materials mainly because their thermal expansion characteristics are quite different. Invar thermal expansion coefficient is very small and basically does not change, while duralumin thermal expansion coefficient is relatively large. There is a significant difference between the two. According to the thermal expansion coefficients of the two, when the temperature changes, the design structure of the present invention will exert stress on the fiber grating and change the central wavelength. By utilizing the large difference in thermal expansion coefficients between duralumin and invar, the present invention can effectively compensate for the central wavelength drift caused by uneven temperature of the ultra-long fiber grating. When the temperature changes, the length of the invar part basically does not change, while the length of the duralumin part changes. Different length changes will generate stress on the fiber grating, thereby compensating for the influence of uneven temperature on the wavelength of the fiber grating, and ensuring the stability and accuracy of the measurement results.

[0048] The specific principle of achieving effective compensation for temperature effects is: both temperature and strain can cause the wavelength of the fiber Bragg grating to change. If the wavelength shift change caused by strain and the wavelength change caused by temperature unevenness are strictly equal in amplitude and opposite in direction, they can offset each other, thereby eliminating the change in wavelength caused by temperature unevenness. To achieve wavelength compensation for ultra-long fiber Bragg gratings, it is necessary to require that the wavelength change caused by the thermal contraction of the negative expansion material just offset the wavelength change caused by temperature change.

[0049] The relationship between fiber strain and fiber Bragg grating center wavelength is:

[0050] This formula shows that Δλ ε There is an obvious linear relationship with Δε;

[0051] Regarding the thermal expansion coefficients of the duralumin lower sleeve 1 and the Invar upper sleeve 2, the thermal expansion coefficient of the Invar upper sleeve 2 is negligible according to its properties, and the temperature change of the duralumin lower sleeve 1 corresponds to its length change: ΔL = ξLΔT (2);

[0052] In strain sensing, the strain magnitude of the fiber Bragg grating can be expressed as:

[0053] The relationship between temperature change and fiber Bragg grating center wavelength:

[0054] According to the experimental simulation, the temperature distribution coefficient of the 15 mm package structure 301 is centered by a 3 mm long TEC 303: ΔT = T + βL′ (5);

[0055] The fiber Bragg grating is packaged with temperature control. Both temperature and strain can cause the center wavelength of the fiber Bragg grating to drift. If the wavelength drift caused by strain and the wavelength drift caused by temperature unevenness are strictly equal in amplitude but opposite in direction, they can offset each other, thereby eliminating the change of wavelength with temperature. To achieve temperature compensation for the fiber Bragg grating, it is necessary to require the change of the grating wavelength Δλ caused by the thermal expansion of the packaging material ε , just offset the wavelength drift Δλ caused by uneven temperature changes T , that is, Δλ ε =Δλ T (6);

[0056] From the formula for the effect of strain and temperature on wavelength drift, we can know:

[0057] When (ξ+α f )ΔT=(1-ρ e )Δε, the above formula is:

[0058] (ξ+α f )(T+βL′)=(1-ρ e )ξΔTε (7)

[0059] Δλ ε =Δλ T

[0060] Among them, ΔT is the temperature change of the hard aluminum lower sleeve 1, Δε is the strain change of the optical fiber, and α f is the thermal expansion coefficient of the optical fiber, ξ is the thermal expansion coefficient of the hard aluminum lower sleeve 1, ρ e is the effective elastic-optic coefficient, Δλε represents the change in grating wavelength caused by thermal expansion of the package material; Δλ represents the total change in grating wavelength; εz Indicates the axial force on the optical fiber, ε = ε z ; K ε represents the strain sensitivity coefficient; ε represents the total stress on the optical fiber; ΔL represents the length change of the hard aluminum lower sleeve 1; L represents the length of the hard aluminum lower sleeve 1 at 0°; Δλ T Indicates the change in grating wavelength caused by temperature; K T represents the temperature sensitivity coefficient of the fiber Bragg grating; T represents the controlled temperature of TEC303; β represents the temperature distribution coefficient; L′ represents the distance between a certain position of the packaging structure 301 and the middle of the packaging structure 301;

[0061] When ultra-long fiber Bragg grating is packaged for temperature control, the fiber Bragg grating will be heated unevenly due to the size limitation of TEC303. The temperature distribution coefficient can be obtained through experimental simulation. When the grating is packaged with duralumin and invar materials, the thermal expansion coefficient of the optical fiber is α f =0 (small, ignored), ignoring the thermal expansion coefficient of Invar steel, when the thermal expansion coefficient of duralumin ξ=Δε / ΔT satisfies the condition of formula (7), the compensation for the uneven temperature of the fiber Bragg grating can be achieved. The different thermal expansion coefficients of the two materials are used to compensate for the center wavelength drift caused by the temperature of the fiber Bragg grating.

[0062] The packaging of the packaging structure 301 and the fiber Bragg grating is intended to ensure that the grating does not decay in a high temperature environment and does not produce chirp in a low temperature environment, so as to overcome the strain measurement limitations of the fiber Bragg grating in extreme environments. By adopting the packaging method of ultraviolet curing glue, the combination of the packaging structure 301 and the fiber Bragg grating of the present invention provides a solution for the fiber Bragg grating strain sensor to maintain high performance in extreme temperature environments, significantly improving its application value and reliability in industrial monitoring and scientific research.

[0063] The packaging method of the packaging device using thermal expansion to compensate for the uneven temperature of the ultra-long fiber grating of the present invention comprises the following steps:

[0064] Step 1: Design a temperature-compensated fiber Bragg grating packaging structure 301, wherein the packaging structure 301 is composed of two parts, namely, aluminum and invar;

[0065] Step 2: Clean the packaging structure 301 and place the aluminum part of the negative expansion packaging on the displacement platform;

[0066] Step 3: Wipe the optical fiber with alcohol, and place the optical fiber in the U-shaped groove of the aluminum part (i.e., the hard aluminum U-shaped groove 101), with the fiber grating close to the bottom of the U-shaped groove (i.e., the hard aluminum U-shaped groove 101);

[0067] Step 4: Use a two-point glue sealing process to fix one end of the aluminum part without applying stress;

[0068] Step 5: The fiber Bragg grating with one end not fixed passes through the U-shaped groove of the upper part of the invar steel (i.e., the invar steel U-shaped groove 201), the screw micrometer is turned to apply a pre-tightening force to the fiber, and the fiber is fixed to the invar steel part by applying glue;

[0069] Step 6: After the glue between the optical fiber and the packaging structure 301 is completely cured, apply thermal conductive silicone grease in the U-shaped groove;

[0070] Step 7: Use the curable adhesive 304 to stick the TEC 303 to the bottom of the hard aluminum lower sleeve 1;

[0071] Step 8: Install the thermistor on the packaging structure 301;

[0072] Step 9: After the glue is completely cured, the entire device is placed in the metal housing 302 to complete the ultra-long fiber Bragg grating temperature control packaging.

[0073] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A packaging device for compensating the uneven temperature of an ultra-long fiber Bragg grating by thermal expansion, characterized in that: The invention comprises a packaging structure (301) composed of a hard aluminum lower sleeve (1) and an Invar upper sleeve (2), wherein an optical fiber is placed in the packaging structure (301), and the packaging structure (301) is fixed in a metal shell (302) with a shell upper cover, and a TEC (303) is attached between the bottom of the packaging structure (301) and the bottom wall of the metal shell (302) via a solidifiable curable adhesive (304) for controlling the temperature, and a thermistor is also installed on the top of the packaging structure (301) for monitoring the temperature of each area.

2. The packaging device for compensating the temperature unevenness of ultra-long fiber Bragg gratings by thermal expansion according to claim 1, characterized in that: The hard aluminum lower sleeve (1) and one end of the Invar upper sleeve (2) are mounted in a stepped manner; the hard aluminum lower sleeve (1) comprises a hard aluminum U-shaped groove (101), a stress release groove (102), a fixing screw hole A (103), and a fixing through hole A (104); the Invar upper sleeve (2) comprises an Invar U-shaped groove (201), a fixing screw hole B (202), and a fixing through hole B (203); The hard aluminum U-shaped groove (101) and the Invar U-shaped groove 201 are respectively arranged along the length direction of the hard aluminum lower sleeve (1) and the Invar upper sleeve (2) for fixing the optical fiber; a plurality of stress release grooves (102) are arranged along the width direction of the hard aluminum lower sleeve (1) for releasing the stress generated when thermal expansion occurs; the hard aluminum lower sleeve (1) and the Invar upper sleeve (2) are spliced ​​up and down and fixed by fixing screw holes A (103), fixing screw holes B (202) and screws to form a packaging structure (301); the packaging structure (301) is fixed to the fixing studs in the metal shell (302) by fixing through holes A (104), fixing through holes B (203) and screws.

3. A packaging method for the packaging device using thermal expansion to compensate for uneven temperature of ultra-long fiber Bragg gratings as claimed in claim 2, characterized in that: The process includes the following: Step 1: designing a temperature-compensated fiber Bragg grating packaging structure (301), wherein the packaging structure (301) is divided into two parts, namely, aluminum and invar; Step 2: Clean the packaging structure (301) and place the hard aluminum lower sleeve (1) on the displacement platform; Step 3: Wipe the optical fiber with alcohol, and place the optical fiber in the hard aluminum U-shaped groove (101) on the hard aluminum lower sleeve (1), with the optical fiber close to the bottom of the hard aluminum U-shaped groove (101); Step 4: Using a two-point glue sealing process, fix one end of the hard aluminum lower sleeve (1) without applying stress; Step 5: The optical fiber with one end not fixed passes through the Invar U-shaped groove (201) on the Invar upper sleeve (2), the screw micrometer is turned to apply a pre-tightening force to the optical fiber, and the optical fiber is fixed to the Invar upper sleeve (2) by applying glue; Step 6: After the glue between the optical fiber and the packaging structure (301) is completely cured, each U-shaped groove is filled with thermal conductive silicone grease; Step 7: Using a curable adhesive (304), the TEC (303) is glued to the bottom of the hard aluminum lower sleeve (1); Step 8: Install the thermistor on the packaging structure (301); Step nine: After the glue is completely cured, the entire packaging structure (301) is placed in the metal shell (302) to complete the ultra-long fiber Bragg grating temperature control packaging.

4. The packaging method according to claim 3, characterized in that: After the temperature control package is completed, the specific method for compensating the center wavelength drift caused by the fiber grating temperature is as follows: Both temperature and strain will cause the wavelength of the fiber Bragg grating to change. When the wavelength shift change caused by strain and the wavelength change caused by temperature unevenness are equal in magnitude but opposite in direction, they can offset each other, thereby eliminating the change in wavelength caused by temperature unevenness. Therefore, to achieve wavelength compensation for ultra-long fiber Bragg gratings, it is required that the wavelength change caused by the thermal contraction of the negative expansion material just offset the wavelength change caused by temperature change. The relationship between fiber strain and fiber Bragg grating center wavelength is: The thermal expansion coefficient of the Invar upper sleeve (2) is negligible according to its properties, and the temperature change of the duralumin lower sleeve (1) corresponds to the change in its length: ΔL = ξLΔT (2); In strain sensing, the strain magnitude of the fiber Bragg grating is expressed as: The relationship between temperature change and the central wavelength of the fiber Bragg grating is: When the ultra-long fiber Bragg grating is packaged for temperature control, the fiber Bragg grating will be heated unevenly due to the size limitation of TEC (303). The temperature distribution coefficient can be obtained through experimental simulation: ΔT = T + βL′ (5); To achieve temperature compensation for optical fiber, the change in grating wavelength Δλ caused by thermal expansion of the packaging material is required. ε , which just offsets the wavelength drift Δλ caused by uneven temperature changes T , that is, Δλ ε =Δλ T (6); From the formula for the effect of strain and temperature on wavelength drift, we can know: When (ξ+α f )ΔT=(1-ρ e )Δε, the above formula is: (x+D) f )(T+βL′)=(1-ρ e )ξΔTε (7) Dl ε =Dl T Where ΔT is the temperature change of the hard aluminum lower sleeve (1), Δε is the strain change of the optical fiber, and α f is the thermal expansion coefficient of the optical fiber, ξ is the thermal expansion coefficient of the hard aluminum lower sleeve (1), ρ e is the effective elastic-optic coefficient, Δλ ε represents the change in grating wavelength caused by thermal expansion of the package material; Δλ represents the total change in grating wavelength; ε z Indicates the axial force on the optical fiber, ε=ε z ; K ε represents the strain sensitivity coefficient; ε represents the total stress on the optical fiber; ΔL represents the length change of the hard aluminum lower sleeve (1); L represents the length of the hard aluminum lower sleeve (1) at 0°; Δλ T Indicates the change in grating wavelength caused by temperature; K T represents the temperature sensitivity coefficient of the fiber Bragg grating; T represents the controlled temperature of the TEC (303); β represents the temperature distribution coefficient; L′ represents the distance between a certain position of the packaging structure (301) and the middle of the packaging structure (301); When encapsulated with duralumin and invar, the grating is integrated with the two materials, making the thermal expansion coefficient of the optical fiber α f = 0, ignoring the thermal expansion coefficient of Invar steel, when the thermal expansion coefficient of duralumin ξ = Δε / ΔT satisfies the condition of formula (7), the compensation for the uneven temperature of the fiber Bragg grating can be achieved. The different thermal expansion coefficients of the two materials are used to compensate for the center wavelength drift caused by the temperature of the fiber Bragg grating.

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