A batch preparation method for micro fiber gratings

Abstract

The present invention discloses a batch preparation method for micro fiber gratings. It belongs to the field of micro fiber grating technology, and the steps are: preparing a fiber grating of original diameter to be corroded; preparing a NaOH solution; fixing the fiber grating in a reactor device, adding the NaOH solution, and placing it in a constant temperature box for heating; obtaining a semi-finished product with a reduced diameter, treating its rough surface, and obtaining a finished micro fiber grating. The present invention uses NaOH solution to react with the optical fiber to produce a stable chemical corrosion reaction at a specific temperature and pressure, and can prepare a large number of micro fiber grating sensors with the same diameter and consistent surface morphology at one time. The reaction device is a hydrothermal reactor, and NaOH solution is added to the lining; the entire device is placed in a constant temperature oven greater than 100°C, and by controlling the reaction time, micro fiber grating sensors with different diameters and smooth surfaces can be obtained. The preparation method proposed by the present invention has the advantages of low cost, safety, simplicity, and large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of micro fiber gratings and relates to a batch preparation method of micro fiber gratings. Background Art

[0002] With the rapid development of fiber-optic communications, demands for the performance of communication devices are constantly increasing. Device miniaturization has become a key trend in scientific and technological research and application. Micro-fiber Bragg gratings (FBGs) offer advantages such as small size, high sensitivity, and strong optical field confinement, making them widely used in fields such as sensing, lasers, biology, medicine, and chemistry.

[0003] Currently, the main methods for fabricating micro-fiber Bragg gratings (FBGs) are the melt taper method (e.g., patents CN 109856721A, CN 101445320A, CN 109580562A, and CN 110196070A) and the chemical etching method (CN 108844559A). The melt taper method utilizes the thermal melting properties of SiO2 to heat specific areas of the optical fiber and apply a uniform tension on both sides, thereby reducing its diameter. This method produces finished products with uniform diameter and smooth surfaces. However, parameters such as the fuel (hydrogen) flow rate and taper speed require precise instrumentation. Furthermore, to avoid high-temperature damage to the grating during heating, the grating must be inscribed after the micro-fiber taper is formed, making the process complex and costly. Regarding chemical etching, hydrofluoric acid etching is the most commonly used method for fabricating micro-fiber Bragg gratings. This method uses simple equipment and is easy to operate. However, during the etching process, the etching rate and depth vary among different parts of the fiber, resulting in a rough surface and significant optical loss. In addition, hydrofluoric acid solution and volatile hydrogen fluoride gas are extremely dangerous to the human body and will bring certain safety risks to mass production.

[0004] In view of this, in order to overcome the limitations of the above methods, the present invention provides a new low-cost batch preparation method for micro fiber gratings, aiming to solve the problems of high preparation cost, complex process and poor safety of the existing technology. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a device and method for preparing micro fiber Bragg gratings based on hydrothermal technology. Micro fiber Bragg gratings are prepared by chemically etching the fiber Bragg grating.

[0006] Technical solution: The batch preparation method of a micro fiber Bragg grating described in the present invention has the following specific preparation steps:

[0007] Step (1), preparing a plurality of fiber Bragg gratings of original diameter required for etching;

[0008] Step (2), preparing a NaOH solution of a certain concentration;

[0009] Step (3), using a special fixture to fix multiple fiber Bragg gratings in a reactor device, adding a certain amount of NaOH solution, sealing it and placing it in a constant temperature box, setting a certain heating temperature, and controlling the reaction time;

[0010] Step (4): After the reaction is completed, the fiber grating (micro fiber grating) with a reduced diameter is taken out and its rough surface is treated to finally obtain a finished micro fiber grating with a smooth and dry surface.

[0011] Furthermore, in step (1), the prepared fiber grating is made of high-purity quartz glass.

[0012] Furthermore, in step (2), the concentration of the NaOH solution is in the range of 1 to 10 mol / L.

[0013] Furthermore, in step (3), the special fixture includes a disk body, a plurality of limiting holes are evenly distributed on the surface of the disk body, a plurality of optical fiber guide tubes are installed on the lower wall of the disk body, and at least four bottom pillars are also installed on the periphery of the lower wall of the disk body. The amount of NaOH added is 10-70% of the maximum volume of the reaction liner, the heating temperature range is 110-220°C, and the heating time range is 2-24 hours;

[0014] The material of the special fixture cannot react chemically with the NaOH solution, and the special fixture can ensure structural stability under high temperature and high pressure environments;

[0015] Wherein, an anti-corrosion plastic coating layer is applied on the outer wall of the disc body, and the disc body is used to isolate the corrosive solution, thereby ensuring the integrity of the remaining optical fiber in the decorroded section;

[0016] The limiting hole is used to change the length of the optical fiber immersed in the solution and to fix the position; the material of the limiting hole is rubber, which has a certain degree of stretchability and can fix the optical fiber through deformation without causing damage to it;

[0017] At the same time, the multiple limiting holes opened on the surface of the disk can ensure the batch preparation of micro optical fibers;

[0018] The optical fiber conduit is used to ensure that the optical fiber in the corrosion section is in a vertical downward state, so that the optical fiber is in uniform contact with the corrosion solution;

[0019] The clamping and fixing of the limiting hole and the optical fiber conduit can prevent the optical fiber from loosening and falling off during the preparation process.

[0020] Furthermore, in step (3), the reactor device includes a reactor body, a reactor cover is installed on the top of the reactor body, and a polytetrafluoroethylene lining for containing the corrosive solution is installed in the inner cavity of the reactor body.

[0021] A PTFE gland is installed on the top of the PTFE liner, and the PTFE gland is threadedly connected to the inner wall of the kettle cover;

[0022] A gasket is mounted on the underside thereof;

[0023] An explosion-proof disk is installed on the upper side of the PTFE gland;

[0024] A pressure relief hole is also provided on the kettle cover and the kettle body;

[0025] The polytetrafluoroethylene lining is used for containing the corrosive solution.

[0026] Furthermore, the diameter of the micro fiber grating can be controllably changed within a range smaller than the diameter of the original optical fiber.

[0027] Furthermore, in step (4), the specific operation steps of the surface treatment are as follows:

[0028] (4.1) Use dilute hydrochloric acid to corrode the semi-finished micro fiber Bragg grating;

[0029] The hydrochloric acid concentration range is 1 to 5 mol / L, and the reaction time is 2 to 12 hours;

[0030] (4.2) Ultrasonic cleaning is performed using deionized water for 5 to 30 minutes;

[0031] (4.3) Take out the cleaned product and place it in an oven for drying at a temperature range of 40 to 60°C for 10 to 30 minutes to obtain a finished micro fiber grating.

[0032] Beneficial effects: Compared with the prior art, the present invention is characterized in that: 1) the present invention uses NaOH solution to prepare micro fiber Bragg gratings under constant temperature and constant pressure conditions, which has a simple process and can achieve one-time batch production. At the same time, the micro fiber Bragg grating is directly prepared by etching the single-mode fiber Bragg grating, which greatly reduces the preparation cost and shortens the preparation cycle; 2) the present invention adopts a chemical etching preparation method. Under constant temperature and constant pressure conditions, the optical fiber is vertically immersed in the liquid. All parts of the optical fiber are in uniform contact with the NaOH solution, and the reaction rate is similar. Finally, a micro fiber Bragg grating with a uniform diameter and a smooth surface can be obtained. It is also convenient to accurately control the required length of the optical fiber etching section, which is convenient for subsequent packaging operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a cross-sectional view of the reaction device structure in an embodiment of the present invention;

[0034] Figure 2 Schematic diagram of the structure of the optical fiber fixing fixture provided in an embodiment of the present invention;

[0035] Figure 3 This is an electron microscope image of a micro fiber Bragg grating prepared in an embodiment of the present invention;

[0036] Figure 4 This is a graph showing the relationship between reaction time and finished product diameter change in an embodiment of the present invention;

[0037] Figure 5 This is a comparison chart of the reflection spectra of the finished product prepared in the embodiment of the present invention and ordinary FBG;

[0038] In the figure, 1 is the pressure relief hole, 2 is the kettle cover, 3 is the polytetrafluoroethylene liner, 4 is the gasket, 5 is the kettle body, 6 is the disc body, 7 is the limit hole, 8 is the bottom support, 9 is the optical fiber conduit, 10 is the polytetrafluoroethylene pressure cover, and 11 is the explosion-proof disk. DETAILED DESCRIPTION

[0039] In order to more clearly illustrate the technical solution of the present invention, the technical solution of the present invention is further described in detail below with reference to the accompanying drawings:

[0040] The batch preparation method of a micro fiber Bragg grating according to the present invention has the following specific preparation steps:

[0041] Step (1), preparing a plurality of fiber Bragg gratings of original diameter required for etching;

[0042] Step (2), preparing a NaOH solution of a certain concentration;

[0043] Step (3), using a special fixture to fix multiple fiber Bragg gratings in a reactor device, adding a certain amount of NaOH solution, sealing it and placing it in a constant temperature box, setting a certain heating temperature, and controlling the reaction time;

[0044] Step (4): After the reaction is completed, the fiber grating (micro fiber grating) with a reduced diameter is taken out and its rough surface is treated to finally obtain a finished micro fiber grating with a smooth and dry surface.

[0045] Furthermore, in step (1), the prepared fiber grating is made of high-purity quartz glass.

[0046] Furthermore, in step (2), the concentration of the NaOH solution is in the range of 1 to 10 mol / L.

[0047] Furthermore, in step (3), the special fixture includes a disk body 6, a plurality of limiting holes 7 are evenly distributed on the surface of the disk body 6, a plurality of optical fiber guide tubes 9 are installed on the lower wall of the disk body 6, and at least four bottom supports 8 are also installed on the periphery of the lower wall of the disk body 6. The amount of NaOH added is 10-70% of the maximum volume of the reaction liner, the heating temperature range is 110-220°C, and the heating time range is 2-24 hours;

[0048] The material of the special fixture cannot react chemically with the NaOH solution, and the special fixture can ensure structural stability under high temperature and high pressure environments;

[0049] The outer wall of the tray 6 is coated with an anti-corrosion plastic coating layer, and the tray 6 is used to isolate the corrosive solution, thereby ensuring the integrity of the remaining optical fiber in the decorroded section.

[0050] The limiting hole 7 is used to change the length of the optical fiber immersed in the solution and to fix the position; the material of the limiting hole 7 is rubber, which has a certain degree of stretchability and can fix the optical fiber by deformation without causing damage to it;

[0051] At the same time, the multiple limiting holes opened on the surface of the disk 6 can ensure the batch preparation of micro optical fibers;

[0052] The optical fiber conduit 9 is used to ensure that the optical fiber in the corrosion section is in a vertical downward state so that the optical fiber is in uniform contact with the corrosion solution;

[0053] The clamping and fixing of the limiting hole 7 and the optical fiber conduit 9 can prevent the optical fiber from loosening or falling off during the preparation process.

[0054] Furthermore, in step (3), the reactor device includes a reactor body 5, a reactor cover 2 is installed on the top of the reactor body 5, and a polytetrafluoroethylene lining 3 for containing the corrosive solution is installed in the inner cavity of the reactor body 5.

[0055] A PTFE gland 10 is installed on the top of the PTFE liner 3, and a gasket 4 is installed on the lower side thereof;

[0056] An explosion-proof disk 11 is installed on the upper side of the PTFE gland 10;

[0057] A pressure relief hole 1 is also provided on the kettle cover 2 and the kettle body 5;

[0058] The polytetrafluoroethylene liner 3 is used to contain the corrosive solution.

[0059] Furthermore, the diameter of the micro fiber grating can be controllably changed within a range smaller than the diameter of the original optical fiber.

[0060] Furthermore, in step (4), the specific operation steps of the surface treatment are as follows:

[0061] (4.1) Use dilute hydrochloric acid to corrode the semi-finished micro fiber grating;

[0062] The hydrochloric acid concentration range is 1 to 5 mol / L, and the reaction time is 2 to 12 hours;

[0063] (4.2) Ultrasonic cleaning is performed using deionized water for 5 to 30 minutes;

[0064] (4.3) Take out the cleaned product and place it in an oven for drying at a temperature range of 40 to 60°C for 10 to 30 minutes to obtain a finished micro fiber grating.

[0065] Since the reaction rate between NaOH solution and optical fiber is slow under normal temperature and pressure conditions, the reaction rate can be accelerated by a hydrothermal method. The reactor device used mainly includes: a hydrothermal reactor and a constant temperature oven. Multiple optical fibers are fixed to the reactor lining (polytetrafluoroethylene lining 3) by a clamp and immersed in the NaOH solution.

[0066] The hydrothermal method is a wet chemical method performed in a sealed container. By heating and pressurizing the reaction system (or autogenous steam pressure), a relatively high-temperature, high-pressure reaction environment is created, allowing substances that are difficult to dissolve or insoluble at room temperature and pressure to dissolve. The hydrothermal method generally uses a temperature of 110 to 220°C, and the corresponding steam pressure is 0.3 to 4.0 MPa.

[0067] The hydrothermal reactor device is a sealed container that can decompose insoluble substances; it uses the strong acid or strong alkali, high temperature, high pressure and sealed environment in the tank to quickly decompose insoluble substances.

[0068] Furthermore, the components of the reactor device include: a reactor body 5, a polytetrafluoroethylene liner 3, a reactor cover 2, an explosion-proof disk 11, a gasket 4, a pressure relief hole 1, a polytetrafluoroethylene pressure cover 10, and a threaded connection between the polytetrafluoroethylene pressure cover 10 and the inner wall of the reactor body 5.

[0069] The constant temperature oven increases the temperature in the reactor by heating and maintains the temperature constant during the reaction process.

[0070] The fiber Bragg Grating is used to prepare a micro fiber Bragg Grating, but is not limited to a fiber Bragg Grating (FBG).

[0071] The reactor lining (polytetrafluoroethylene lining 3) is used to hold the corrosion reaction solution; the polytetrafluoroethylene lining 3 must meet the requirements of acid and alkali corrosion resistance, high temperature resistance, smooth surface, non-stickiness and non-toxicity, but is not limited to polytetrafluoroethylene material.

[0072] Wipe the optical fiber clean with anhydrous ethanol and dry it in an oven. Determine the appropriate etching section length and simultaneously secure multiple optical fibers to the reactor lining. Add a pre-prepared NaOH solution of a certain concentration to the lining, adjusting the length of the optical fiber immersed in the NaOH solution.

[0073] Furthermore, the concentration of the NaOH solution is not a fixed value and can be adjusted according to the lining volume, the number of optical fibers, and the heating temperature.

[0074] Place the polytetrafluoroethylene 3 liner in the kettle body 5 and tighten the seal. Place the entire device in the oven, set the reaction temperature and time, and after the test is completed, wait for the device to cool naturally to room temperature before opening it.

[0075] After the micro-fiber Bragg grating is taken out of the NaOH solution, it is immersed in dilute hydrochloric acid to remove the sodium silicate reaction product on the surface, making the surface of the micro-fiber Bragg grating smooth; it is then ultrasonically cleaned with deionized water to remove the acidic solution adhering to the surface, and cleaned again with anhydrous ethanol, followed by drying.

[0076] Example:

[0077] The invention uses NaOH solution and a hydrothermal method to achieve batch preparation of micro fiber gratings with different diameters by controlling solution concentration, reaction time and temperature.

[0078] Figure 1 The cross-sectional view of the micro fiber Bragg grating preparation device provided by an embodiment of the present invention is shown, which includes a pressure relief hole 1, a kettle cover 2, a polytetrafluoroethylene liner 3, a gasket 4, a kettle body 5, a polytetrafluoroethylene pressure cover 10 and an explosion-proof disk 11.

[0079] Determine the length of the required corroded optical fiber segment in advance, remove its coating, use a clamp to fix multiple optical fibers, place them in the polytetrafluoroethylene liner 3, and leave a certain length of original diameter optical fiber at the tail end for subsequent fusion splicing.

[0080] The fixture is as Figure 2 As shown, the main components include a disk body 6, a limiting hole 7, a bottom support 8 and an optical fiber guide tube 9;

[0081] The limiting hole 7 is made of a rubber-like material (which does not react with NaOH) and has a certain degree of stretchability; the optical fiber with the original diameter is passed through the limiting hole 7 and fixed.

[0082] Place the fixture in polytetrafluoroethylene 3 and add 5 mol / L NaOH solution into the interior, ensuring that the liquid level is lower than the fixture support 8.

[0083] Place the polytetrafluoroethylene liner 3 in the kettle body 5 and tighten the kettle cover 2. After the reactor is sealed, place it in a constant temperature oven with the temperature set at 120°C.

[0084] Control the reaction time according to the needs. After the hydrothermal reaction is completed, do not open it immediately to ensure that the temperature in the kettle is lower than the boiling point of the solvent of the reactant system; wait for it to cool naturally to room temperature, first loosen the kettle cover 2, and then take out the polytetrafluoroethylene liner 3 and the clamp; after the reaction is completed, clean the polytetrafluoroethylene liner 3, kettle body 5, and clamp in time and keep them dry.

[0085] After all the optical fibers are taken out, they are immersed in 2% dilute hydrochloric acid (dilute hydrochloric acid does not react with optical fibers) for 6 to 8 hours. The immersion time can be adjusted appropriately according to the concentration of dilute hydrochloric acid and the number of optical fibers. On the one hand, the residual NaOH solution on the surface of the micro-fiber can be neutralized. On the other hand, the by-product sodium silicate on the surface of the micro-fiber can be removed, further improving the smoothness of the optical fiber surface.

[0086] After the optical fiber is taken out, it is ultrasonically cleaned with deionized water and dried; finally, a micro fiber grating that meets the requirements can be obtained.

[0087] According to the embodiment of the present invention, micro fiber gratings with different diameters can be obtained, and their electron microscope photos are as follows: Figure 3 As shown; Under the conditions determined by factors such as hydrothermal reaction temperature, lining space, and NaOH concentration, Figure 4 The relationship between the hydrothermal reaction time and the diameter of the micro-fiber Bragg grating is shown; as the reaction time increases, the diameter of the micro-fiber Bragg grating decreases; the method provided by the present invention achieves precise and controllable changes in the diameter of the micro-fiber, with a diameter change range of less than 125μm; and through repeated testing, it is found that the method has good stability.

[0088] Figure 5 Figure 2 shows a comparison of the reflection spectra of a micro-FBG with that of an uncorroded fiber. Compared to the uncorroded fiber, the reduced diameter of the micro-FBG leads to energy leakage and a slight "blue shift" in the central wavelength. Corrosion also reduces the cladding thickness, increasing cladding mode loss and causing a slight decrease in overall optical power in the reflected spectrum. The reflectivity of the fiber Bragg grating decreases from 0.82 to 0.70, which is within an acceptable range.

[0089] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A batch preparation method of micro fiber Bragg gratings, the specific preparation steps are as follows: Step (1), preparing a plurality of fiber Bragg gratings of original diameter whose material to be etched is high-purity quartz glass; Step (2), preparing a NaOH solution with a concentration range of 1 to 10 mol / L; Step (3), using a special fixture to fix multiple fiber Bragg gratings in a reactor device, adding a certain amount of NaOH solution, sealing it and placing it in a constant temperature box, setting a certain heating temperature, and controlling the reaction time; The specially made fixture includes a disk body, a plurality of limiting holes are evenly distributed on the surface of the disk body, a plurality of optical fiber guide tubes are installed on the lower wall of the disk body, and at least four bottom supports are also installed on the periphery of the lower wall of the disk body. The amount of NaOH added is 10-70% of the maximum volume of the reaction liner, the heating temperature range is 110-220°C, and the heating time range is 2-24 hours; The reactor device comprises a reactor body, a reactor cover is arranged on the top of the reactor body, and a polytetrafluoroethylene lining for containing a corrosive solution is arranged in the inner cavity of the reactor body. A PTFE gland is installed on the top of the PTFE liner, and a gasket is installed on the lower side thereof; an explosion-proof disk is installed on the upper side of the PTFE gland; and a pressure relief hole is opened through the kettle cover and the kettle body; Step (4): After the reaction is completed, the fiber Bragg grating with a reduced diameter is taken out and its rough surface is treated to finally obtain a finished micro fiber Bragg grating with a smooth and dry surface; The steps are as follows: (4.1) Use dilute hydrochloric acid to corrode the semi-finished micro fiber grating; in, The hydrochloric acid concentration range is 1 to 5 mol / L, and the reaction time is 2 to 12 hours; (4.2) Ultrasonic cleaning is performed using deionized water for 5 to 30 minutes; (4.3) Take out the cleaned product and place it in an oven for drying at a temperature range of 40 to 60°C for 10 to 30 minutes to obtain a finished micro fiber grating.

Images