CN1200290C - Bandwidth-adjustable bevel fiber grating and manufacturing method thereof - Google Patents

Abstract

A bandwidth-adjustable beveled fiber grating and a manufacturing method thereof, wherein the bandwidth-adjustable beveled fiber grating is made by installing a section of optical fiber with a variable outer diameter on a tuning mechanism and manufacturing the beveled fiber grating. The manufacturing steps include: ① manufacturing the beveled fiber grating; ② etching the outer diameter of the beveled fiber grating according to the design requirements; ③ installing the tuning mechanism. The advantages of the present invention are: the beveled edge bandwidth of the fiber grating reflection spectrum is large and the linearity is good; the bandwidth can be dynamically tuned and the tuning range is large; the manufacturing process of the beveled fiber grating is relatively simple, the stability is good, and the yield rate is high.

Description

Bevel edge fiber grating with adjustable bandwidth and its manufacturing method

technical field

The invention relates to optical fiber sensing, in particular to a hypotenuse optical fiber grating with adjustable bandwidth and a manufacturing method thereof.

Background technique

Fiber Bragg Grating is a mature all-fiber device. Due to its small size, low insertion loss, and easy integration with other fiber devices, it has very important applications in the fields of fiber optic communication and fiber sensing. The hypotenuse fiber grating is a special fiber grating with a hypotenuse triangular spectral line shape. Within the hypotenuse bandwidth of the hypotenuse fiber grating, the reflectivity is linearly related to the wavelength. The hypotenuse fiber grating has its own unique role in the field of fiber optic sensing and measurement. In the field of fiber optic sensing, sensors based on fiber gratings have high sensitivity when measuring parameters such as external temperature and strain, and are not subject to electromagnetic interference. The basic principle of FBG sensor is to use the characteristics of FBG spectrum, especially its peak position, which changes with temperature and stress. The fiber grating used as the sensor head should have a narrow spectrum, so as to read the position of the center wavelength of the fiber grating accurately. In order to read out the peak wavelength position of the sensing FBG, a simple and inexpensive spectral measurement method is required to replace the expensive spectrometer usually used in the laboratory. People hope to obtain a fiber grating with large bandwidth and linear distribution of reflectivity with wavelength. When it is combined with the narrow-band fiber grating of the sensing head, the peak wavelength position of the sensing grating can be converted to the amplitude of the signal. Therefore, the fiber Bragg grating with hypotenuse reflection spectrum has important application value in the field of fiber optic sensing.

There have been some reports on the fabrication technology of fiber gratings with hypotenuses. One of the prior technologies, A.D.Kersey et al. ("Fiber grating sensors" J.Lightwave Technol.15 (8) pp: 1442-1463 1997) used the fiber bending method to make the hypotenuse fiber grating, the hypotenuse grating produced by this method The linearity of the hypotenuse is relatively poor. In the second prior art, Y Liu et al. ("Fabricating fiber edge filters with arbitrary spectral response based on tilted chirped grating structures" Meas.Sci.Technol.10 pp: L1-L3 1999) made a tilted chirped fiber grating, using tilted The loss effect of the radiation mode of the grating realizes the hypotenuse filter function. Similarly, the hypotenuse linearity of the hypotenuse grating produced by this method is not good enough, and the oblique fiber grating is sensitive to bending and external environment, and requires good packaging, which increases the production cost of the grating. The third prior art, M.A.Putnam et al. ("Fabrication of tapered, strain-gradent chirped fiber Bragg gratings" Electron. Lett. 31 (4) pp: 309-310 1995) used the method of corroding the grating to apply strain to make a bandwidth adjustable tunable chirped fiber gratings, but there is no mention of fabricating hypotenuse fiber gratings with tunable bandwidth in the literature.

In one of the prior technologies, the hypotenuse bandwidth of the hypotenuse fiber grating produced in the prior technology two is not adjustable. In order to make the hypotenuse fiber grating adapt to the application of different sensing ranges, improve the practicability and performance of the hypotenuse fiber grating Flexibility, it is necessary to continue to adjust the width of the hypotenuse fiber grating after the fabrication of the hypotenuse fiber grating. So far, there have been no reports about FBG hypotenuse filters with adjustable hypotenuse bandwidth.

Contents of the invention

The technical problem to be solved by the present invention is to provide a hypotenuse optical fiber grating with adjustable bandwidth and a manufacturing method thereof in order to overcome the above-mentioned deficiencies in the prior art. The optical fiber grating should have the characteristics of wide-range adjustable hypotenuse bandwidth, good linearity of the hypotenuse, easy manufacture and low cost.

Technical solution of the present invention is as follows:

A kind of hypotenuse fiber grating with adjustable bandwidth, its structure is that a section of optical fiber is installed on a tuning mechanism, and a hypotenuse fiber grating is made on the outer diameter changing section of the fiber.

Specifically, an optical fiber with a hypotenuse fiber grating on an outer diameter changing section is installed in a guide rail whose aperture is slightly larger than the outer diameter of the fiber coating layer, the optical fiber and the guide rail are fixed on the support with glue, and the support is fixed on On the base, the other end of the optical fiber is fixed on a one-dimensional precision translation platform through a support, and the one-dimensional precision translation platform is driven by a micro motor.

The main points of making the hypotenuse fiber grating with adjustable bandwidth of the present invention are: use the ultraviolet laser irradiation method to make a chirped fiber grating whose core refractive index distribution is apodized in the form of a hypotenuse triangular function, and obtain a fiber grating with a hypotenuse triangular spectrum ; On the outer surface of the fiber grating part, the optical fiber cross-section with a monotonously decreasing diameter is produced by corrosion; the mechanical mechanism is used to apply a precise and controllable pulling force to the fiber grating, so as to obtain the hypotenuse fiber grating with a wide range of adjustable hypotenuse bandwidth.

The specific steps of the manufacturing method of the bandwidth-tunable hypotenuse fiber grating are as follows:

① Manufacture of hypotenuse fiber gratings: write chirped fiber gratings in which the refractive index distribution of the core is apodized in the form of hypotenuse trigonometric functions on photosensitive optical fibers by irradiation with ultraviolet laser;

② Corrosion of the outer diameter of the hypotenuse fiber grating: the corrosion tank is made of corrosion-resistant polyethylene material and has a layered structure. The corrosion tank is composed of an inner tank and an outer tank. The plate can be a flat plate or an inverted funnel. In the center of the inner groove and the upper and lower partitions, there is a small hole with a diameter slightly larger than the outer diameter of the optical fiber coating; the bottom of the inner groove and the space between the inner and outer grooves are filled with For heavy oil, the corrosive solution is filled between the upper and lower partitions of the inner tank, and light oil is injected above the upper partition of the inner tank. The corrosive solution is an aqueous solution based on hydrofluoric acid. During the corrosion process, the optical fiber is first passed through Three small holes, and installed on the shaft of the stepping motor, then inject heavy oil and light oil, and finally inject corrosive liquid with a polyethylene pipe, so that it is filled between the upper and lower partitions, after injecting corrosive liquid, it will start The stepping motor makes it pull up the optical fiber at a controllable speed; after the corrosion is completed, the optical fiber is immediately taken out and cleaned with water and organic solvents;

③ Tuning mechanism installation: install the optical fiber of the hypotenuse fiber grating produced in step ② in the guide rail whose aperture is slightly larger than the outer diameter of the fiber coating, the optical fiber and the guide rail are fixed on the support with glue, and the support is fixed on the base , the other end of the optical fiber is fixed on a one-dimensional precision translation platform through a support, and the one-dimensional precision translation platform is connected with a micro motor to form a driving relationship.

The optical fiber is an optical fiber after high-pressure hydrogen loading, or a highly germanium-doped photosensitive optical fiber.

The hypotenuse fiber grating is written by using an apodized phase plate method, a scanning method or a light source optical fiber movement disturbance method.

The base and the support are made of a material with a low expansion coefficient, such as a ceramic material, a glass-ceramic material, or an alloy material with a low expansion coefficient.

The glue is ultraviolet curing glue or epoxy resin with good stability.

The advantage of the hypotenuse fiber grating with adjustable bandwidth of the present invention is:

1. The hypotenuse bandwidth of the fiber grating reflection spectrum is large and the linearity is good;

2. The bandwidth can be dynamically tuned, and the tuning range is large;

3. The manufacturing process of the hypotenuse fiber grating is relatively simple, with good stability and high yield.

Description of drawings

Figure 1. Schematic diagram of the structure of a hypotenuse fiber grating with adjustable bandwidth;

Fig. 2. Simulation calculation results of the spectrum of the hypotenuse fiber optic shed and its tuning characteristics;

Figure 3. Schematic diagram of an etching device for fabricating a fiber grating with a variable outer diameter;

Figure 4. Schematic diagram of the bandwidth tuning mechanism of the hypotenuse fiber grating;

Figure 5. Fiber Bragg grating with triangular reflection spectrum;

Fig. 6. The curves of the reflected and transmitted light signals of the triangular fiber grating with strain.

Detailed ways

The structure of the fiber grating of the present invention is shown in FIG. 1 . A fiber grating 1a with a triangular spectrum is fabricated on the optical fiber 2; a fiber segment 1b with a change in the outer diameter of the fiber is fabricated at the position of the grating.

The working principle of the bandwidth adjustable hypotenuse fiber grating of the present invention is as follows:

The spectral shape of a fiber grating is determined by its refractive index modulation distribution, and a fiber grating with a hypotenuse triangle spectrum can be obtained by modulating the fiber grating with a hypotenuse triangle. The mathematical expression of the triangular modulation function is:

Here L is the length of the grating and z represents the position of the grating. The p-value is a control parameter. The period of the refractive index in the fiber grating can be distributed with different amounts of chirp or no chirp, so as to obtain a hypotenuse fiber grating with a wide range of adjustable bandwidth. The theoretically simulated grating reflection spectrum is shown in Fig. 2 . The principle of adjusting the bandwidth of the present invention is to apply stress to the optical fiber grating with changing outer diameter, so that different parts of the optical fiber grating are subjected to different strains. The strain relationship of the FBG peak wavelength is

λ _B (ε)≈λ _B (0)(1+0.78ε) (2)

Under the action of tension F, the strain ε generated by the grating is:

ε=F/ES=F/[πER ² (z)] (3)

Here, E is the Young's modulus of the fiber and S is the cross-sectional area of the grating. It can be seen that ε is inversely proportional to S. When S gradually changes along the grating axis, ε will also gradually change along the grating axis under a certain F, so that a strain gradient is established in the grating axis, that is, a chirp is introduced to the grating. Chirp. F is not the same, the size of the amount of chirp introduced to the grating is also different. From (2) and (3), it can be seen that to introduce linear chirp to the fiber grating, the distribution of the fiber radius along the length of the grating should satisfy:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>\frac{\mathrm{<span\; class="notranslate">\; z</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Here, R ₀ , _RL are the radii of the cross section of the grating at z=0, z=L. Therefore, by applying different tensions to this fiber grating, a hypotenuse fiber grating with adjustable bandwidth can be obtained. Figure 2 shows the simulated calculation results of the reflection spectrum of the fiber grating under different tensions.

The specific manufacturing method of the bandwidth adjustable hypotenuse fiber grating of the present invention is as follows:

1. Preparation of hypotenuse fiber grating 1a: Various optical fibers 2 with photosensitivity can be used, such as ordinary single-mode fiber after high-voltage hydrogen-carrying fiber, or high-germanium-doped photosensitive fiber, etc.; craft manufacturing. In the production process, the apodization phase plate method, scanning method, light source fiber movement disturbance method, etc. can be used to write the optical fiber grating with the triangular distribution of refractive index modulation and chirp amount designed and controlled in advance, including the uniform fiber grating with zero chirp amount. fiber grating.

2. Preparation of optical fiber with variable outer diameter: It is produced by chemical corrosion technology based on hydrofluoric acid. In order to obtain the outer diameter distribution required by the design, the corrosion tank is made of corrosion-resistant polyethylene material and designed as a layered structure; different specific gravity is used. The oily liquid protects the part of the optical fiber that does not need to be corroded; the stepping motor controlled by a microcomputer is used to pull the optical fiber to obtain the required outer diameter change. The corrosion setup is shown in Figure 3. The corrosion tank is composed of an inner tank 3 and an outer tank 4 . Two partitions 5 are arranged in the inner tank: wherein the upper partition can be a flat plate, as shown in Figure 3 (a), or an inverted funnel shape, as shown in Figure 3 (b). The purpose of the inverted funnel-shaped partition is to create different corrosion rates in the longitudinal direction. A small hole with a diameter slightly larger than the outer diameter of the optical fiber coating is opened in the center of the inner groove and the two partitions.

Fill the heavy oil 6 between the bottom of the inner tank and the inner and outer tanks. Fill the corrosion solution 7 between the upper and lower partitions of the inner tank. Inject light oil 8 on the upper partition of the inner tank. The etchant is an aqueous solution based on hydrofluoric acid. Its specific gravity is close to that of water. The specific gravity distribution of the heavy oil and light oil used is larger and smaller than that of the corrosive liquid. During the etching process, first pass the optical fiber 2 through three small holes and install it on the rotating shaft 10 of the stepping motor. Then inject heavy oil 6 and light oil 8. Finally, the corrosion solution 7 is injected into the polyethylene pipe 9 so that it is filled between the two partitions. In the process of injecting these liquids, attention should be paid to adjusting and controlling the height of the liquid level. After injecting the corrosive solution, the stepper motor 10 is started to pull the optical fiber upwards at a controllable speed. After the corrosion is completed, take out the optical fiber immediately and clean it with water and organic solvents.

3. The tuning mechanism of the present invention is shown in FIG. 4 . The optical fiber 2 on which the hypotenuse fiber grating 1 has been fabricated is installed in a guide rail 11 whose hole diameter is slightly larger than the coated outer diameter of the optical fiber. This guide rail 11 adopts the technology that Chinese utility model patent [Patent No. ZL 01 2 55004.3] provides to make. The optical fiber 2 and the guide rail 11 are fixed on the supports 151 , 152 , 153 , 154 with glue 14 . The supports 151 , 152 , 153 are fixed on the base 16 . The other end of the optical fiber is fixed on the one-dimensional precision translation stage 18 through the support 154 . The one-dimensional precision translation stage 18 is driven by a micro motor 17 .

In this tuning mechanism, the base 16 and the support 15 are made of a material with a low expansion coefficient, which can be a ceramic material, or a glass-ceramic material, or an alloy material with a low expansion coefficient; the glue 14 can be cured by ultraviolet light Glue, epoxy resin with good stability can also be used to ensure the stability during stress tuning.

In this tuning mechanism, the micro motor can be driven by a driver controlled by a microcomputer to obtain a precisely controllable and stable reflection spectrum of the hypotenuse fiber grating.

Using the phase mask and aperture scanning method, on the commercial Corning SMF28 single-mode fiber that has been sensitized by high-pressure hydrogen loading, a fiber grating with a triangular refractive index modulation distribution is written, and the reflection spectrum shown in Figure 5 is obtained. . With further optimization of the control program, it will be possible to obtain spectra with large hypotenuses. The sample was fixed on a strain-controllable cantilever beam, and the variation of the transmission and reflection signals of the triangular fiber grating with strain was measured, and the relationship shown in Figure 6 was obtained. After the optical signal is amplified and processed by the circuit, the strain of the cantilever beam can be sensitively reflected through the ratio of the transmitted and reflected signals, with a resolution of 1.5 microstrain.

Claims (7)

1, the adjustable hypotenuse fiber grating of a kind of bandwidth is characterized in that the adjustable hypotenuse fiber grating of this bandwidth is that an optical fiber (2) is installed on a mechanical tuning device, change section (1b) at the external diameter of this optical fiber (2) and go up and make a hypotenuse fiber grating (1a) and constitute.

2, the hypotenuse fiber grating that bandwidth according to claim 1 is adjustable, it is characterized in that will be described external diameter change the optical fiber (2) that is manufactured with hypotenuse fiber grating (1a) on the section (1b) and be installed in the guide rail (11) that the aperture is slightly larger than this optical fiber coating external diameter, this optical fiber (2) and guide rail (11) are fixed on bearing (151 with glue (14), 152,153,154) on, bearing (151,152,153) be fixed on the base (16), an other end of optical fiber (2) is fixed on the accurate translation stage of one dimension (18) by bearing (154), and the accurate translation stage of this one dimension (18) drives with micromachine (17).

3, the method for making of the adjustable hypotenuse fiber grating of bandwidth according to claim 1 and 2 is characterized in that comprising the steps:

1. the hypotenuse fiber grating is made: go up and adopt the Ultra-Violet Laser width of cloth according to writing the fine grating (1) of warbling that fiber core refractive index functional form triangular in shape becomes mark having the optical fiber of photosensitivity (2);

2. the external diameter to hypotenuse fiber grating (1a) corrodes: etching tank adopts corrosion resistant polythene material to make hierarchy, etching tank is made of inside groove (3) and water jacket (4), two dividing plates (5) have been settled in the inside groove (3), wherein upper spacer is dull and stereotyped, or fall infundibulate, reach the center of two dividing plates (5) up and down at inside groove (3), have the aperture of slightly larger in diameter in the optical fiber coating external diameter; Between the bottom of inside groove (3) and interior water jacket, fill with heavy oil (6), between the last lower clapboard (5) of inside groove (3), fill with corrosive liquid (7), on the upper spacer (5) of inside groove (3), inject light oil (8), corrosive liquid is the aqueous solution based on hydrofluorite, in corrosion process, earlier optical fiber (2) is passed three apertures, and be installed in the rotating shaft (10) of stepper motor, inject heavy oil (6) and light oil (8) then, use polyethylene pipe (9) to inject corrosive liquid (7) at last, it is filled in up and down between two dividing plates (5), behind the injection corrosive liquid, just begin to start stepper motor (10), make it upwards lift optical fiber by controlled speed; After finishing corrosion, take out optical fiber immediately, water and organic solvent clean;

3. mechanical tuning device is installed: will finish the 2. the step optical fiber (2) that is manufactured with hypotenuse fiber grating (1a) be installed in the guide rail (11) that the aperture is slightly larger than the optical fiber coating external diameter, this optical fiber (2) and guide rail (11) are fixed on the bearing (151,152,153,154) with glue (14), bearing (151,152,153) is fixed on the base (16), an other end of optical fiber (2) is fixed on the accurate translation stage of one dimension (18) by bearing (154), the accurate translation stage of this one dimension (18) links to each other with micromachine (17), forms driving relationship.

4, the method for making of the adjustable hypotenuse fiber grating of bandwidth according to claim 3 it is characterized in that the optical fiber after described optical fiber is for the high ballast hydrogen of process, or height is mixed the germanium light-sensitive optical fibre.

5, the method for making of the adjustable hypotenuse fiber grating of bandwidth according to claim 3 is characterized in that described hypotenuse fiber grating (1a) adopts change mark phase-plate method, scanning method or luminous source optical fiber to move method of perturbation and writes.

6, the method for making of the adjustable hypotenuse fiber grating of bandwidth according to claim 3, it is characterized in that described base (16) and bearing (151,152,153,154) by a kind of low-expansion material, this material is stupalith or microcrystal glass material or low-expansion alloy material.

7, the method for making of the adjustable hypotenuse fiber grating of bandwidth according to claim 3 is characterized in that described glue (14) is ultra-violet curing glue or the epoxy resin that has good stability.

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