A method for assembling panda-shaped polarization-maintaining optical fiber preforms

Abstract

This invention discloses an assembly method for a panda-shaped polarization-maintaining fiber preform. Using a quartz welding gun, acid cleaning equipment, and ultrasonic equipment, the stress bar is first inspected, its curvature adjusted, and rounded to match the aperture of the drilled single-mode fiber. The drilled single-mode fiber, connecting support tube, quartz sealing ring, and quartz end cap are prepared and then spliced ​​together using the quartz welding gun. After acid cleaning and drying of the spliced ​​single-mode fiber and stress bar, the stress bar is inserted into the drilled single-mode fiber, and a spacer and pressure block are sealed in. A vacuum tail tube is ignited and welded away from the stress bar area, followed by vacuuming and fusion sealing before fiber drawing. The assembled high-stress-doped panda-shaped polarization-maintaining fiber preform achieves a stress zone area ratio of up to 14% and a diameter ratio of up to 38%. The outer pure quartz layer thickness of the stress bar is 0.3±0.1mm. Using this method, the stress bar is kept away from the welding heat source throughout the assembly process, ensuring its integrity and preventing cracking.

Description

Technical Field

[0001] This invention relates to the field of polarization-maintaining fiber preform preparation, and specifically to a method for assembling a panda-shaped polarization-maintaining fiber preform. Background Technology

[0002] Polarization-maintaining fiber, due to its unique properties in transmitting linearly polarized light, has revolutionized the gyroscope market and is now widely used in aerospace, aviation, navigation, missile guidance, and self-propelled artillery. Since fiber optic gyroscopes and fiber optic hydrophones are used in military penetrating guidance and sonar, they are high-tech products, and polarization-maintaining fiber is their core component.

[0003] The current development trend of fiber optic gyroscopes is towards high precision and miniaturization. The core material of fiber optic gyroscopes, polarization-maintaining fiber, is also developing towards smaller and ultra-smaller diameter polarization-maintaining fibers. For the same length, when the outer diameter of the fiber decreases from 165μm to 100μm, the gyroscope's volume and weight decrease by two-thirds. Therefore, ultra-smaller diameter polarization-maintaining fiber is the mainstream product for future development.

[0004] In the design of ultra-fine diameter polarization-maintaining fibers, under mode field matching conditions, it is necessary to maintain the birefringence performance level while reducing the fiber's outer diameter area. With the increased proportion of the fiber core in ultra-fine diameter polarization-maintaining fibers, if the stress bar doping concentration, core diameter, and outer diameter remain unchanged, the birefringence performance of the ultra-fine diameter polarization-maintaining fiber will decrease, and its polarization performance will be more susceptible to external influences. To avoid this problem, the stress level of the stress bar needs to be increased during the design of ultra-fine diameter polarization-maintaining fibers, further increasing the stress bar doping concentration and core diameter to ensure stable birefringence performance.

[0005] Under the existing assembly scheme, the stress rod itself has greater stress, smaller outer diameter, and thinner quartz layer, making it difficult to restrain its own stress during the assembly heating process, and making it more prone to cracking during the polarization-maintaining fiber assembly process.

[0006] The assembly method described in patent application CN107572771A,S3 causes the stress bars to crack due to heat when processing stress bars with a pure quartz layer wall thickness of 0.2mm-0.4mm. Summary of the Invention

[0007] To address the technical problem of fiber stress bars cracking during the assembly of highly stress-doped panda-shaped polarization-maintaining fiber preforms, this invention provides an assembly method for panda-shaped polarization-maintaining fiber preforms. By employing an improved cold-working assembly method for the stress bars, the method avoids heating the stress bars during assembly, thus solving the problem of ultra-fine diameter, high doping at the preform assembly stage. This reduces the processing difficulty of the preforms, improves the stability of the high-doped polarization-maintaining fiber stress bar assembly, and increases fiber production efficiency.

[0008] The technical solution of this invention is: an assembly method for a panda-shaped polarization-maintaining optical fiber preform, comprising the following steps:

[0009] Step 1: Inspect the geometry of the stress bar, including its curvature, outer diameter, and core diameter;

[0010] Step 2: If the stress bar has excessive bending, use a quartz welding torch to first adjust the hydrogen flow rate, then adjust the oxygen flow rate until the flame is light blue and the hydrogen-oxygen ratio is 2:1. Focus the heating on the location of the abnormal bending of the stress bar. After heating to 1500-1700 degrees Celsius, use a graphite rod to adjust the bending of the stress bar.

[0011] Step 3: Connect one end of the punched single mold to the quartz head using a quartz welding gun, and then wrap the joint with a quartz sealing ring.

[0012] Step 4: Based on the length of the single-die, select two stress rods with a length that matches the single-die. At the same time, cut a connecting support tube of the same length as the stress rod and weld the connecting support tube to the other end of the single-die.

[0013] Step 5: Grind the outer diameter of the two stress bars until they match the inner diameter of the hole corresponding to the single-die drilling mold.

[0014] Step 6: Clean the drilled single mold and two stress rods with ultrasonic cleaning.

[0015] Step 7: Use a specially prepared acid solution to acid treat the punched single mold and two stress bars, followed by cleaning and drying.

[0016] Step 8: Place a stress rod in each of the two inner holes of the single-hole punch, and seal the spacer and pressure block. The gap between the spacer and the stress rod shall not exceed 5mm.

[0017] Step 9: Weld the connecting support tube and the vacuum tail tube. During welding, keep the quartz welding torch at least 300mm away from the stress bar. Then, apply a vacuum to complete the assembly process.

[0018] In step five, the gap between the outer diameter of the stress rod and the inner hole diameter corresponding to the single-drilling mold is in the range of 0.05mm-0.2mm, and the wall thickness of the pure quartz layer on the outside of the rounded stress rod is in the range of 0.2mm-0.4mm.

[0019] The method for ultrasonically cleaning the perforated single mold and two stress rods described in step six is ​​as follows: use a 1:1 mixture of alcohol and deionized water to clean the perforated single mold and two stress rods with an ultrasonic cleaner for 5 minutes, and then clean them with deionized water for 5 minutes.

[0020] The method for acid treatment and subsequent cleaning and drying of the punched single mold and two stress bars using a certain proportion of acid solution described in step seven is as follows: Prepare a mixed acid solution with a volume ratio of nitric acid: hydrofluoric acid: hydrochloric acid: high-purity water = 2:1:2:40. Soak the inner hole of the punched single mold and the stress bars in the mixed acid solution for 20 minutes. After soaking, rinse with deionized water and rinse with hot deionized water three times or more. Then place them in a drying cabinet and dry with oil-free compressed air for more than 12 hours.

[0021] The technical effect of this invention is that, due to the increase in the size of the stress rod, but the overall size of the precast rod is fixed, the wall thickness of the outer pure quartz layer of the stress rod is only 0.3±0.1mm. During the high-temperature thermal expansion process of assembly, it is difficult to restrain the stress of the entire stress rod, thus causing the stress rod to shatter and crack.

[0022] By improving the cold-working assembly method of stress rods, the stress rods are prevented from being heated during the assembly process. This solves the problem of ultra-fine diameter high doping from the preform assembly stage, reduces the processing difficulty of preforms, and solves the technical problem of high-doped stress rods being prone to cracking during the assembly of panda-type polarization-maintaining fiber preforms.

[0023] The assembled high-stress-doped panda-shaped polarization-maintaining fiber preform has a stress zone area ratio of up to 14% and a diameter ratio of up to 38%. The outer pure quartz layer of the stress rod has a thickness of 0.3±0.1mm. Using this method, the stress rod is kept away from the welding heat source throughout the assembly process, ensuring that the stress rod remains intact and does not crack during assembly. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the panda-shaped polarization-maintaining optical fiber preform of the present invention;

[0025] Figure 2 This is a schematic diagram of the punched single mold of the present invention;

[0026] Figure 3 This is a schematic diagram of the stress bar after rounding according to the present invention.

[0027] In the diagram: 1. Drilled single mold; 1-1. Inner hole; 2. Connecting support tube; 3. Quartz end cap; 4. Vacuum tail tube; 4-1. Exhaust pipe; 5. Stress rod; 6. Quartz sealing ring; 7. Pad block; 8. Pressure block. Detailed Implementation

[0028] To make the objectives and technical solutions of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0029] like Figure 1 , Figure 2, Figure 3 As shown, a method for assembling a panda-shaped polarization-maintaining fiber preform includes the following steps:

[0030] Step 1: Check the geometric dimensions of stress rod 5, including curvature, outer diameter, and core diameter. Use a preform refractive index analyzer to measure the outer diameter and core diameter of stress rod 5 every 70 mm. Stress rod 5 can be used if the difference in core diameter between two adjacent points is less than or equal to 0.2 mm and the difference in outer diameter between two adjacent points is less than or equal to 0.2 mm. If the core diameter or outer diameter is outside the range, it cannot be used.

[0031] Step 2: If stress rod 5 has excessive bending, wear rubber gloves and use a quartz welding torch. Turn on the exhaust fan during welding to avoid burns. Ignite the quartz welding torch with an igniter. When using an oxyhydrogen flame, first open the hydrogen valve slightly, then slowly open it as needed after ignition. Then slowly open the oxygen valve as needed and adjust the oxygen flow until the flame is light blue. The hydrogen-oxygen ratio should be 2:1. Then use the quartz welding torch to concentrate the heating on the area of ​​abnormal bending of stress rod 5. After heating to 1600 degrees Celsius, use a graphite rod to adjust the bending of stress rod 5.

[0032] Step 3: Based on the selected Φ40mm punched single mold 1 outer diameter, select a matching Φ36.5mm×Φ15mm quartz head 3 and Φ41mm×2mm quartz sealing ring 6. Splice one end of the punched single mold 1 to the quartz head 3 using a quartz welding gun. After splicing, wrap the splicing gap with the quartz sealing ring 6. During the splicing process, ensure uniform heating and avoid uneven stress.

[0033] Step 4: Select two stress rods 5 with a length of 350mm that are compatible with the 300mm length of the single-die 1. Use a quartz welding gun to melt the two stress rods 5 to a length of 300mm that is the same as the single-die 1. At the same time, cut a Φ42mm×3mm connecting support tube 2 with a length of 300mm and weld it to the other end of the single-die 1.

[0034] Step 5: Grind the two stress rods 5 until the outer diameter of the stress rod 5 matches the inner hole diameter 1-1 of the drilling single mold 1 (Φ13mm). The gap between the outer diameter of the stress rod 5 and the inner hole diameter 1-1 of the drilling single mold 1 is 0.05mm-0.2mm. The outer pure quartz layer wall thickness of the stress rod 5 after grinding is 0.2mm-0.4mm.

[0035] Step 6: Place the drilled single mold 1 and two stress rods 5, which are spliced ​​with the quartz head 3, into the plastic box of the ultrasonic cleaner. Clean them with a 1:1 mixture of alcohol and deionized water for 5 minutes, and then clean them with deionized water for 5 minutes. During cleaning, make sure that the anhydrous ethanol completely submerges the drilled single mold 1 and stress rods 5.

[0036] Step 7: Based on the inner diameter of the connecting support tube 2 (Φ36mm), grind out a pad 7 that is 0.2mm smaller than the inner diameter of the connecting support tube 2 and 8mm higher, and a pressure block 8 that is 40mm higher. Grind the side of the pad 7 facing the stress rod 5 flat, wash with hydrofluoric acid, and rinse with deionized water.

[0037] Step 8: Prepare a mixed acid by mixing nitric acid, hydrofluoric acid, hydrochloric acid, and high-purity water in a volume ratio of 2:1:2:40. Soak the inner hole of the single-drilled mold 1 and stress bar 5 in the mixed acid for 20 minutes. Rinse with deionized water and then rinse with hot deionized water three times or more. After that, put them in a drying cabinet and dry them with oil-free compressed air for more than 12 hours.

[0038] Step 9: Take out two stress rods 5 and insert them into the two inner holes 1-1 of the punched single mold 1 from the tail end of the connecting support tube 2. Place the pad 7 and the pressure block 8 into the connecting support tube 2 respectively. Use a quartz welding gun to heat the pad 7 and the pressure block 8 at the corresponding positions on the surface of the connecting support tube 2, so that the connecting support tube 2 is fused and fixed with the pad 7 and the pressure block 8 respectively. The gap between the pad 7 and the stress rod 5 shall not exceed 5mm.

[0039] Step 10: Weld the connecting support tube 2 and the vacuum tail tube 4. When welding with the quartz welding gun, the quartz welding gun should be at least 300mm away from the stress rod 5. During this process, the stress rod 5 will not be heated, and the stress rod 5 and the inner hole 1-1 of the punched single mold 1 will not be squeezed against each other due to thermal expansion, thus avoiding the risk of the stress rod 5 cracking due to heat during the assembly process.

[0040] Step 11: Use a vacuum pump to evacuate the inside of the assembled polarization-maintaining fiber preform through the vacuum tail tube 4. Use a vacuum spark leak detector to check the vacuum inside the preform. If the electric spark is dispersed inside the quartz tube, the vacuuming is normal. Use a quartz welding torch to heat the vent tube 4-1 on the vacuum tail tube 4 to close the vent tube 4-1. Then remove the panda-shaped polarization-maintaining fiber preform to complete the cold processing assembly process of the stress rod, ready to enter the wire drawing process.

[0041] Step 12: Rinse the acid in the pickling tank thoroughly, turn off the water valve, turn off the power to the electric furnace, turn off the hydrogen and oxygen supply, and turn off the exhaust.

Claims

1. A method for assembling a panda-shaped polarization-maintaining optical fiber preform, characterized in that, Includes the following steps: Step 1: Check the geometric dimensions of the stress bar (5), including curvature, outer diameter, and core diameter; Step 2: If the stress bar (5) has excessive bending, use a quartz welding torch to first adjust the hydrogen flow rate, then adjust the oxygen flow rate until the flame is light blue and the hydrogen-oxygen ratio is 2:

1. Focus on heating the position of the stress bar (5) with abnormal bending. After heating to 1500-1700 degrees Celsius, use a graphite rod to adjust the bending of the stress bar (5). Step 3: Connect one end of the punched single mold (1) to the quartz head (3) using a quartz welding gun, and then wrap the joint with a quartz sealing ring (6). Step 4: Based on the length of the single-die (1), select two stress rods (5) with the same length as the single-die (1), and cut a connecting support tube (2) of the same length as the stress rod (5). Weld the connecting support tube (2) to the other end of the single-die (1). Step 5: Grind the outer diameter of the two stress rods (5) until the outer diameter of the stress rod (5) matches the inner hole (1-1) of the punching single mold (1); Step 6: Clean the perforated single mold (1) and two stress rods (5) with ultrasonic cleaning. Step 7: Use an acid solution to acid treat the punched single mold (1) and the two stress bars (5), and then perform subsequent cleaning and drying. Step 8: Place a stress rod (5) into each of the two inner holes (1-1) of the punched single mold (1), and seal the pad (7) and pressure block (8). The gap between the pad (7) and the stress rod (5) shall not exceed 5 mm. Step 9: Weld the connecting support tube (2) and the vacuum tail tube (4). During welding, the quartz welding gun should be at least 300mm away from the stress bar (5). Then, vacuum the tube to complete the assembly process.

2. The assembly method of a panda-type polarization-maintaining optical fiber preform according to claim 1, characterized in that, In step five, the gap between the outer diameter of the stress rod (5) and the inner hole (1-1) corresponding to the hole diameter of the single-drilled mold (1) is 0.05mm-0.2mm, and the wall thickness of the pure quartz layer on the outside of the stress rod (5) after rounding is 0.2mm-0.4mm.

3. The assembly method of a panda-type polarization-maintaining optical fiber preform according to claim 1, characterized in that, The method for ultrasonically cleaning the perforated single mold (1) and the two stress rods (5) in step six is ​​as follows: use a 1:1 mixture of alcohol and deionized water to clean the perforated single mold (1) and the two stress rods (5) with an ultrasonic cleaner for 5 minutes, and then clean them with deionized water for 5 minutes.

4. The assembly method of a panda-type polarization-maintaining optical fiber preform according to claim 1, characterized in that, The method for acid treatment and subsequent cleaning and drying of the perforated single mold (1) and two stress rods (5) using acid solution described in step seven is as follows: Prepare a mixed acid according to the volume ratio of nitric acid: hydrofluoric acid: hydrochloric acid: high-purity water = 2:1:2:40, soak the inner hole (1-1) of the perforated single mold (1) and the stress rod (5) with the mixed acid respectively, rinse with deionized water after soaking for 20 minutes, rinse with hot deionized water three times or more, and then put them in a drying cabinet and dry with oil-free compressed air for more than 12 hours.

Images