Preparation method of spiral annular core coaxial double-waveguide type rare earth-doped optical fiber

Abstract

The invention relates to the technical field of optical fibers, in particular to a preparation method of a spiral annular core coaxial double-waveguide type rare earth-doped optical fiber. According to the preparation method provided by the invention, the central rare-earth-doped core rod, the annular core rod and the quartz tube are prepared by rod assembling, so that the process of drilling and external processing on the rod body is avoided, the hole of the rod body does not need to be polished and cleaned, the process difficulty is reduced, and meanwhile, the production cost is reduced. According to the preparation method provided by the invention, the annular core rod can be spirally wound on the central rare-earth-doped core rod only by rotating the annular core rod, and the whole rod body does not need to be rotated, so that the problem that the optical performance of the fiber core is influenced by torsion stress generated by rotation of the central rare-earth-doped core rod is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fibers, and in particular to a method for preparing a spiral ring-core coaxial dual-waveguide rare-earth-doped optical fiber. Background Art

[0002] With the increasingly rapid development of special optical fibers, the requirements of fiber lasers for rare-earth-doped active optical fibers are also getting higher and higher. In recent years, rare-earth-doped active optical fibers with conventional core designs have been unable to meet the requirements of fiber lasers for high-power laser output and high beam quality. When a rare-earth-doped active optical fiber with a conventional core design is used in a fiber laser, pump light is amplified by the core to generate laser light. However, the coupling efficiency of the pump light in this structure is not high, so it has a greater impact on the output laser efficiency. The spiral ring-core coaxial dual-waveguide rare-earth-doped optical fiber has two high-refractive-index waveguide cores. Its ring core surrounds the central rare-earth-doped core. The pump light is transmitted in the ring core of the optical fiber and is transmitted into the central rare-earth-doped core through the coupling between the two cores, and is absorbed and excited by its rare-earth ions to generate laser light. This fiber structure can greatly improve the absorption efficiency of rare-earth ions for pump light, and the output power and light output efficiency of a laser using this type of optical fiber will also be improved.

[0003] To make a spiral ring core around the central core of an optical fiber, a preform rod is usually processed and placed in a core rod, and the core rod is made into a spiral ring core by the way of overall rotation drawing. However, during the processing of the preform rod, the core rod and the glass rod need to be ground separately. The preparation process is complex and cumbersome. Especially for grinding the inner wall of the glass rod, the processing difficulty is large and the precision is low. At the same time, the internal grinding also limits the length of the glass rod, and there are disadvantages such as poor adaptability. In addition, during the drawing process of the preform rod, the entire rod needs to rotate. While forming the spiral ring core, the central core will also be twisted due to rotation. At this time, rotational stress will be generated in the core, affecting the optical performance of the core. Summary of the Invention

[0004] In order to provide a spiral ring-core optical fiber with better optical performance, the present invention provides a method for preparing a spiral ring-core coaxial dual-waveguide rare-earth-doped optical fiber.

[0005] The method for preparing a spiral ring-core coaxial dual-waveguide rare-earth-doped optical fiber provided by the present invention adopts the following technical solutions:

[0006] (1) Provide a central rare-earth-doped core rod, a ring-core rod and a quartz tube. The ring-core rod includes a preform core and a second quartz support rod connected to the preform core; one end of the quartz tube has a round hole.

[0007] (2) Arrange the central rare-earth doped core rod and the annular core rod side by side inside the quartz tube, align the central axis of the central rare-earth doped core rod with the central axis of the quartz tube, and fix the two; insert the preform core into the circular hole of the quartz tube, and connect the second quartz support rod to the drawing tower;

[0008] (3) Heat the finished rod to the molten state and draw it into a wire. At the same time, rotate the annular core rod. Driven by the drawing tower, make the preform core wind spirally around the central rare-earth doped core rod in the circular hole.

[0009] In the present invention, the annular core rod formed by fusing the preform core and the second quartz support rod is used as the satellite core. During the drawing process, by rotating the annular core rod, it winds spirally around the central rare-earth doped core rod to obtain a spiral annular core coaxial double-waveguide type rare-earth doped optical fiber. The annular core rod prepared by assembling rods in the present invention avoids the external processing of drilling holes on the rod body, and thus there is no need to polish and clean the holes inside the rod body, reducing the process difficulty. At the same time, in the preparation method provided by the present invention, only by rotating the annular core rod can the annular core rod wind spirally around the central rare-earth doped core rod, without rotating the entire rod body, avoiding the rotation of the central rare-earth doped core rod and generating torsional stress that affects the optical performance of the core.

[0010] Optionally, the central rare-earth doped core rod is formed by fusing a first quartz support rod and a rare-earth doped core rod.

[0011] Optionally, the quartz tube is formed by fusing a quartz support tail tube and a thick-walled quartz tube.

[0012] The central rare-earth doped core rod and the quartz tube prepared by assembling rods in the present invention avoid the external processing of drilling holes on the rod body, and thus there is no need to polish and clean the holes inside the rod body, reducing the process difficulty. Optionally, in step (3), the drawing speed of the wire drawing is 7 m / min - 9 m / min, and the rotation speed is 20 r / min - 30 r / min.

[0013] By limiting the drawing speed and rotation speed of the wire drawing, the present invention can ensure that the annular core rod is tightly wound around the central rare-earth doped core rod and has a reasonable annular core pitch.

[0014] Optionally, in step (3), the heating temperature is 2050 °C - 2100 °C.

[0015] By limiting the heating temperature, the present invention can avoid the inability to perform the drawing process due to insufficient heating temperature, and at the same time can also avoid the too fast melting of the finished rod due to too high heating temperature, resulting in the inability to form a spiral annular core structure.

[0016] Optionally, in step (2), the central rare-earth doped core rod is clamped by a quartz support rod on the stepping motor chuck of the drawing tower, the quartz tube is clamped by a quartz support tail tube on another stepping motor chuck of the drawing tower, and the annular core rod is partially fixed on the rotating motor chuck on the drawing tower by a quartz support rod.

[0017] By defining the clamping methods of the central rare-earth doped core rod, the quartz tube and the annular core rod, the present invention ensures that the annular core rod can be spirally wound around the central rare-earth doped core rod under the action of the motor, and ensures that the central rare-earth doped core rod does not rotate during the drawing process, thereby avoiding the generation of torsional stress and affecting the optical properties of the fiber core.

[0018] Optionally, the preparation method of the quartz tube includes the following steps: grinding and polishing a thick-walled pure quartz tube to a regular octagon and performing pickling and cleaning, then welding a quartz support tail tube at one end of the thick-walled pure quartz tube, and melting and burning the other end of the thick-walled pure quartz tube into a conical shape and performing flame polishing treatment to obtain the quartz tube.

[0019] By pickling and cleaning, the present invention makes the surface of the quartz tube smooth and reduces the impurity content of the prepared optical fiber. Moreover, by welding the thick-walled pure quartz tube and the quartz support tail tube to form the quartz tube, the present invention avoids the external processing of drilling holes on the rod body, and thus there is no need to polish and clean the inside of the holes of the rod body, reducing the process difficulty.

[0020] Optionally, the diameter of the thick-walled pure quartz tube is 40 mm - 45 mm, and the wall thickness of the tube is 5 mm - 10 mm. By defining the diameter and wall thickness of the quartz tube, the present invention can ensure that the prepared optical fiber has an outer wall with sufficient thickness and good stability.

[0021] Optionally, the preparation method of the annular core rod includes the following steps: taking a preform, drilling and coring to take out the core rod part in the middle of the preform, and then welding a second quartz support rod at one end to obtain the annular core rod.

[0022] The present invention defines that the annular core rod is obtained by welding the core rod and the second quartz support rod, avoiding the external processing of drilling holes on the rod body, and thus there is no need to polish and clean the inside of the holes of the rod body, reducing the process difficulty.

[0023] Optionally, the diameter of the preform is 15 mm - 17 mm, and the core diameter of the preform is 3 mm - 5 mm.

[0024] By defining the diameter and core diameter of the preform, the present invention can ensure that the annular core rod is stably wound around the central rare-earth doped core rod.

[0025] Optionally, the core diameter of the rare-earth doped core rod is 2 mm - 4 mm.

[0026] By defining the core diameter of the rare-earth-doped core rod, the present invention can ensure that the prepared spiral annular core coaxial dual-waveguide rare-earth-doped optical fiber has good optical performance.

[0027] In summary, the present invention includes at least one of the following beneficial technical effects:

[0028] 1. The present invention uses a central rare-earth-doped core rod as the core and a quartz tube as the outer wall. During the wire drawing process, the annular core rod is wound around the central rare-earth-doped core rod in a spiral shape to obtain a spiral annular core coaxial dual-waveguide rare-earth-doped optical fiber. The preparation method provided by the present invention can wind the annular core rod around the central rare-earth-doped core rod without rotating the entire rod, avoiding the rotation of the central rare-earth-doped core rod and the generation of torsional stress that affects the optical performance of the core.

[0029] 2. The central rare-earth-doped core rod, the annular core rod, and the quartz tube in the present invention are prepared by the rod assembly method. Using the rod assembly method to prepare the central rare-earth-doped core rod, the annular core rod, and the quartz tube avoids the external processing of drilling holes on the rod body, and thus there is no need to polish and clean the inside of the holes of the rod body, greatly reducing the process difficulty. Description of the Drawings

[0030] Figure 1 is a schematic structural diagram of the spiral annular core coaxial dual-waveguide rare-earth-doped optical fiber in Embodiment 1 of the present invention;

[0031] Description of the reference numerals: 1. Rare-earth-doped core rod; 2. First quartz support rod; 3. Thick-walled quartz tube; 4. Quartz support tail tube; 5. Preform core; 6. Second quartz support rod. Detailed Embodiments

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Embodiment 1:

[0034] A method for preparing a spiral annular core coaxial dual-waveguide rare-earth-doped optical fiber includes the following steps:

[0035] (1) Prepare a rare-earth doped core rod with a core diameter of 3 mm by using the MCVD deposition process, and fuse a quartz support rod 2 of the same diameter at one end of the core rod to obtain a central rare-earth doped core rod. Grind and polish a circular thick-walled pure quartz tube 3 with a diameter of 42 mm and a wall thickness of 8 mm into a regular octagon, and perform pickling and cleaning on its surface. Then, fuse a quartz support tail tube 4 of the same diameter at one end of the thick-walled pure quartz tube, melt the other end of the thick-walled pure quartz tube into a conical shape, and perform flame polishing treatment on its surface to obtain a quartz tube. Prepare a large-core preform with a rod diameter of 16 mm and a core diameter of 4 mm by using the MCVD deposition process. Drill and core to remove the core rod part in the middle of the large-core preform, and fuse a quartz support rod 6 of the same diameter at one end to obtain an annular core rod;

[0036] (2) Insert the central rare-earth doped core rod and the annular core rod side by side into the quartz tube, so that the preform core of the central rare-earth doped core rod is at the center of the quartz tube and remains collinear to obtain a finished rod. The preform core of the annular core rod, the rare-earth doped core rod of the central rare-earth doped core rod, and the thick-walled quartz tube of the quartz tube are located at the same end. The central rare-earth doped core rod is clamped by the quartz support rod on the stepping motor chuck of the drawing tower, the quartz tube is clamped by the quartz support tail on another stepping motor chuck of the drawing tower, and the annular core rod is partially fixed on the rotating motor chuck on the drawing tower by the quartz support rod;

[0037] (3) Place the finished rod in a graphite furnace, heat the graphite furnace to 2075 °C, lower the conical part of the finished rod to the center position of the graphite furnace, heat the finished rod to the molten state and perform fiber drawing at a speed of 8 mm / min, lower the finished rod at a speed of 2 mm / min, and at the same time start the rotating motor chuck to make the annular core rod 5 rotate uniformly at a rotation speed of 25 r / min, so that the annular core rod is spirally wound around the central rare-earth doped core rod to obtain a spiral annular core coaxial double waveguide type rare-earth doped fiber with a central rare-earth doped core diameter of 35 um, a spiral annular core diameter of 48 um, a pitch of 0.5 m, and a cladding diameter of 400 um.

[0038] Example 2:

[0039] (1) Prepare a rare-earth doped core rod with a core diameter of 1 mm by using the MCVD deposition process, and fuse a quartz support rod 2 with the same diameter at one end of the core rod to obtain a central rare-earth doped core rod. Grind and polish a circular thick-walled pure quartz tube 3 with a diameter of 40 mm and a wall thickness of 5 mm into a regular octagon, and perform pickling and cleaning on its surface. Then, fuse a quartz support tail tube 4 with the same diameter at one end of the thick-walled pure quartz tube, melt the other end of the thick-walled pure quartz tube into a conical shape, and perform flame polishing treatment on its surface to obtain a quartz tube. Prepare a large-core preform with a rod diameter of 15 mm and a core diameter of 3 mm by using the MCVD deposition process. Drill and extract the core rod part in the middle of the large-core preform, and fuse a quartz support rod 6 with the same diameter at one end to obtain an annular core rod;

[0040] (2) Insert the central rare-earth doped core rod and the annular core rod side by side into the inner tube of the quartz tube, so that the preform core of the central rare-earth doped core rod is located at the center of the inner tube of the quartz tube and remains collimated to obtain a finished rod. The preform core of the annular core rod, the rare-earth doped core rod of the central rare-earth doped core rod, and the thick-walled quartz tube of the quartz tube are located at the same end. The central rare-earth doped core rod is clamped by the quartz support rod on the stepping motor chuck of the drawing tower, the quartz tube is clamped by the quartz support tail on another stepping motor chuck of the drawing tower, and the annular core rod is partially fixed on the rotating motor chuck on the drawing tower by the quartz support rod;

[0041] (3) Place the finished rod in a graphite furnace, heat the graphite furnace to 2050 °C, lower the conical part of the finished rod to the center position of the graphite furnace, heat the finished rod to the molten state and perform optical fiber drawing at a speed of 7 m / min, lower the finished rod at a speed of 1 mm / min, and at the same time start the rotating motor chuck to make the annular core rod 5 rotate uniformly at a rotational speed of 20 r / min, so that the annular core rod is spirally wound around the central rare-earth doped core rod to obtain a spiral annular core coaxial double waveguide type rare-earth doped optical fiber with a central rare-earth doped core diameter of 20 μm, a spiral annular core diameter of 64 μm, a pitch of 0.1 m, and a cladding diameter of 600 μm.

[0042] Example 3:

[0043] (1) Prepare a rare-earth doped core rod with a core diameter of 4 mm using the MCVD deposition process and fuse a quartz support rod 2 of the same diameter at one end to obtain a central rare-earth doped core rod; grind and polish a circular thick-walled pure quartz tube 3 with a diameter of 45 mm and a wall thickness of 10 mm into a regular octagon, clean its surface by pickling, then fuse a quartz support tail tube 4 of the same diameter at one end of the thick-walled pure quartz tube, melt the other end of the thick-walled pure quartz tube into a conical shape, and at the same time perform flame polishing on its surface to obtain a quartz tube; prepare a large-core preform with a rod diameter of 17 mm and a core diameter of 5 mm using the MCVD deposition process, drill to remove the core rod part in the middle of the large-core preform, and fuse a quartz support rod 6 of the same diameter at one end to obtain an annular core rod;

[0044] (2) Insert the central rare-earth doped core rod and the annular core rod side by side into the tube of the quartz tube, so that the preform core of the central rare-earth doped core rod is at the center of the tube of the quartz tube and remains collimated to obtain a finished rod. The preform core of the annular core rod, the rare-earth doped core rod of the central rare-earth doped core rod, and the thick-walled quartz tube of the quartz tube are located at the same end. The central rare-earth doped core rod is clamped by the quartz support rod on the stepping motor chuck of the drawing tower, the quartz tube is clamped by the quartz support tail on another stepping motor chuck of the drawing tower, and the annular core rod is partially fixed on the rotating motor chuck on the drawing tower by the quartz support rod;

[0045] (3) Place the finished rod in a graphite furnace, heat the graphite furnace to 2100 °C, lower the conical part of the finished rod to the center position of the graphite furnace, heat the finished rod to the molten state and perform optical fiber drawing at a speed of 9 mm / min, lower the finished rod at a speed of 3 mm / min, and at the same time start the rotating motor chuck to make the annular core rod 5 rotate uniformly at a rotational speed of 30 r / min, so that the annular core rod is wound around the central rare-earth doped core rod in a spiral shape, obtaining a spiral annular core coaxial double waveguide type rare-earth doped optical fiber with a central rare-earth doped core diameter of 20 μm, a spiral annular core diameter of 33 μm, a pitch of 2 m, and a cladding diameter of 250 μm.

[0046] The present invention uses a group rod assembly process method to replace the traditional sleeve rod process and preform splicing process to draw a spiral annular core coaxial double waveguide type rare-earth doped optical fiber, without performing special-shaped processing on the finished rod, reducing the difficulty of optical fiber preparation. At the same time, the present invention uses the method of group rod assembly drawing, which can be unrestricted by the diameter size of the preform in the sleeve rod process, improving the flexibility of optical fiber preparation. In addition, the present invention uses a rotating drawing method for the annular core rod, replacing the traditional overall rotation of the preform for drawing, avoiding the generation of rotational stress due to the rotation of the central rare-earth doped core rod during the drawing process.

[0047] The above are all preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present invention shall be covered within the protection scope of the present invention.

Claims

1. A method for preparing a spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber, characterized in that: The following steps are involved: (1) providing a central rare earth doped core rod, an annular core rod and a quartz tube, wherein the annular core rod comprises a preformed rod core and a second quartz support rod connected to the preformed rod core; one end of the quartz tube has a circular hole; (2) arranging the central rare earth doped core rod and the annular core rod side by side in a quartz tube, so that the central axis of the central rare earth doped core rod and the central axis of the quartz tube are collinear, and fixing the two; extending the preform rod core into the circular hole of the quartz tube, and connecting the second quartz support rod to the drawing tower; (3) The finished rod is heated to a molten state and drawn into a wire, and the annular core rod is rotated at the same time. Driven by a wire drawing tower, the prefabricated core rod is spirally wound around the central rare earth-doped core rod in the circular hole.

2. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 1, characterized in that: The central rare earth-doped core rod is formed by welding a first quartz support rod and a rare earth-doped core rod.

3. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 1, characterized in that: The quartz tube is formed by welding a quartz support tail tube and a thick-walled quartz tube.

4. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 1, characterized in that: In step (3), the drawing speed of the filament is 7m / min-9m / min, and the rotation speed is 20r / min-30r / min.

5. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 1, characterized in that: In step (3), the heating temperature is 2050°C-2100°C.

6. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 1, characterized in that: In step (2), the central rare earth-doped core rod is supported on the stepper motor chuck of the drawing tower through a quartz support rod, the quartz tube is supported on another stepper motor chuck of the drawing tower through a quartz support tail, and the annular core rod is partially fixed on the rotating motor chuck on the drawing tower through the quartz support rod.

7. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 1, characterized in that: The preparation method of the quartz tube comprises the following steps: The thick-walled pure quartz tube is ground and polished into a regular octagon and pickled and cleaned, and then a quartz support tail tube is fused to one end of the thick-walled pure quartz tube, and the other end of the thick-walled pure quartz tube is sintered into a cone and flame polished to obtain a quartz tube.

8. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 7, characterized in that: The diameter of the thick-walled pure quartz tube is 40mm-45mm, and the tube wall thickness is 5mm-10mm.

9. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 1, characterized in that: The method for preparing the annular core rod comprises the following steps: Take the preform rod, drill and core out the core rod part in the middle of the preform rod, and then weld a second quartz support rod at one end to obtain a ring-shaped core rod.

10. The method for preparing the spiral annular core coaxial dual-waveguide type rare earth-doped optical fiber according to claim 9, characterized in that: The diameter of the preform rod is 15 mm-17 mm, and the core diameter of the preform rod is 3 mm-5 mm.

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