High-power laser output low-concentration erbium-ytterbium co-doped optical fiber and preparation method thereof

Abstract

The application relates to a high-power laser output low-concentration erbium-ytterbium co-doped optical fiber and a preparation method thereof, and belongs to the technical field of optical fiber manufacturing. The optical fiber comprises, from inside to outside, a core area, an inner cladding, an outer cladding and a coating layer, wherein the core area comprises a plurality of symmetrically arranged low-concentration core rods. The number of the low-concentration core rods is n, and 2<=n<=4. The diameter of any low-concentration core rod is 5-7 mu m, and the spacing between adjacent low-concentration core rods is 1-3 mu m. The diameter of the core area is 25-40 mu m. The inner cladding is made of quartz material, the outer cladding is made of high-temperature-resistant low-refractive-index material, and the coating layer is made of high-strength acrylic resin. The application avoids the problems of serious optical fiber crystallization and low product yield caused by high-concentration rare earth doping. In the preparation process of the low-concentration core rod, a hydrogen-oxygen flame generated by a metal torch is used to deposit and heat the loose body, so that the deposition quality and consistency of the loose body are ensured, and the optical fiber product yield is improved.

Description

Technical Field

[0001] This invention relates to a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output and its preparation method, belonging to the field of optical fiber manufacturing technology. Background Technology

[0002] High-power erbium-ytterbium co-doped fiber lasers are increasingly widely used in laser ranging, precision measurement, military guidance, and sensing. As a core component, the fabrication of erbium-ytterbium co-doped fibers is attracting increasing attention and interest from researchers and application engineers. Higher doping concentrations of erbium and ytterbium ions indicate higher achievable laser output power. Currently, commercially available high-concentration erbium-ytterbium co-doped fibers are largely monopolized by foreign research institutions or companies, with few domestically produced mature high-concentration erbium-ytterbium co-doped fibers capable of large-scale replacement of foreign products.

[0003] The main reason for the above situation is that there are many technical difficulties in the preparation process of high-concentration erbium-ytterbium co-doped optical fibers. For example, high concentrations of rare earth dopants can cause severe crystallization, damage to fiber consistency, and substandard fiber loss. During the rod fabrication process, excessively high concentrations can cause rod cracking. Therefore, the low yield and lack of performance consistency of high-concentration erbium-ytterbium co-doped optical fibers prepared with existing processes directly affect the development of this type of optical fiber, which is also one of the reasons why the cost of this type of optical fiber remains high.

[0004] In the traditional process of preparing high-concentration erbium-ytterbium co-doped optical fibers, a relatively complex MCVD vapor deposition process combined with liquid-phase doping or chelate vapor-phase doping is used for core rod fabrication. The consistency and uniformity of high-concentration rare earth doping are key to core rod fabrication, but this is extremely difficult. The core rod needs to be doped with a large amount of elements such as ytterbium, erbium, phosphorus, and aluminum. The technology for fabricating this type of optical fiber is not fully disclosed abroad. The main problem facing this type of optical fiber is that, on the one hand, it is necessary to achieve high-power laser output per core, and on the other hand, it is necessary to achieve high production and cost reduction per rod. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-power laser output low-concentration erbium-ytterbium co-doped optical fiber and its preparation method, which can realize high-power laser output, reduce preparation difficulty, improve yield, and reduce production cost.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: a low-concentration erbium-ytterbium co-doped optical fiber for realizing high-power laser output, comprising a core region, an inner cladding, an outer cladding and a coating layer arranged sequentially from the inside to the outside, wherein the core region comprises a plurality of symmetrically arranged low-concentration core rods.

[0007] The number of low-concentration core rods is n, where 2 ≤ n ≤ 4.

[0008] The diameter of any one of the low-concentration core rods is 5 to 7 μm, and the spacing between adjacent low-concentration core rods is 1 to 3 μm.

[0009] The diameter of the fiber core region is 25–40 μm.

[0010] The inner cladding is made of quartz material, the outer cladding is made of high-temperature resistant, low-refractive-index material, and the coating layer is made of high-strength acrylic resin.

[0011] A method for fabricating a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output, the method comprising the following steps:

[0012] Step 1: Preparation of porous body: The base tube is mounted on an MCVD lathe and etched and polished; SiCl4, SF6, and POCl3 are introduced into the base tube, and hydrogen-oxygen flame is sprayed using a metal torch to deposit and form a porous body;

[0013] Step 2: Preparation of rare earth ion solution: The solvent is placed in a beaker, and the weighed ytterbium chloride and erbium chloride powders are poured into the solvent and stirred to form a rare earth ion solution; the molar mass of ytterbium chloride is controlled at 0.04-0.06 mol / L, and the molar mass of erbium chloride is controlled at 0.005-0.02 mol / L.

[0014] Step 3: Preparation of low-concentration core rod: The base tube with a loose body layer is immersed in a rare earth ion solution and left to stand. Then it is installed on an MCVD lathe for oxidation, drying and vitrification to complete one deposition layer. The loose body deposition, immersion, standing, oxidation, drying and vitrification are repeated multiple times to form a multi-layer deposition layer. Then it is collapsed into a rod to form a low-concentration core rod.

[0015] Step 4: Repeat steps 1 to 3 to prepare n low-concentration core rods;

[0016] Step 5: Extend and shape the n low-concentration core rods: Extend the prepared low-concentration core rods, and then shape one side of the low-concentration core rods so that the low-concentration core rods are semi-elliptical.

[0017] Step 6: Light rod assembly: Select a sleeve, tape the head of the sleeve, stack multiple low-concentration core rods, fix them with a quartz ring, and insert them into the sleeve to assemble the light rod.

[0018] Step 7: Optical fiber drawing: The optical fiber is placed into the drawing furnace, and a vacuum is drawn into the drawing furnace to create a negative pressure inside the furnace before drawing the fiber to form an optical fiber.

[0019] Step 8: Winding up the fiber: After the inner and outer layers of the optical fiber are coated and cured, the fiber is wound up into a roll.

[0020] In step one, the flow rate of SiCl4 is controlled at 150 sccm to 300 sccm, the flow rate of POCl3 gas is controlled at 5 to 10 sccm, the flow rate of SF6 gas is controlled at 3 to 5 sccm, and the flame temperature is controlled at 1600 to 1630 °C. ℃ The moving speed of the metal torch should be controlled between 100 and 140 mm / min.

[0021] The solution in step two is one of methanol, ethanol, or water.

[0022] The soaking time in step three is 20-30 minutes, and the standing time is 20-30 minutes.

[0023] In step six, the extension dimension is controlled to be 8-12mm; grinding or acid soaking is used for shaping, so that 2-4mm is ground off or soaked off one side of the low-concentration mandrel.

[0024] In step eight, the temperature of the drawing furnace is controlled at 1700–1800℃, the drawing speed is controlled at 20–30 m / min, and the drawing tension is controlled at 0.8–1.4 N.

[0025] Compared with the prior art, the advantages of the present invention are: a high-power laser output low-concentration erbium-ytterbium co-doped optical fiber and its preparation method;

[0026] 1. By preparing low-concentration core rods, multi-core low-concentration erbium-ytterbium co-doped optical fibers are obtained, avoiding the problems of severe crystallization and low yield caused by high-concentration rare earth doping in optical fibers. In the process of preparing low-concentration core rods, the porous body is heated by generating an oxyhydrogen flame with a metal torch, which ensures the deposition quality and consistency of the porous body and improves the yield of optical fibers.

[0027] 2. During the rod fabrication stage, the low-concentration core rods are micro-shaped. On the one hand, high-stress drawing forces the fiber cores to become round; on the other hand, micro-shaping of the core rods makes the distance between the cores in each core rod closer than before they are formed, ensuring higher overall beam quality and stronger light-gathering ability.

[0028] 3. This application relates to a multi-core fiber structure, and the structural design of this multi-core fiber shortens the center-to-center distance of the multiple cores, ensuring that the mode field diameter of the multiple cores as a whole is consistent with that of existing large-core passive fibers, thus reducing splicing difficulty and improving coupling efficiency. Furthermore, the multi-core structure enables high-power laser output, significantly reducing the impact of nonlinear effects. The manufacturing process of this application is simple and highly operable, allowing for continuous production. Attached Figure Description

[0029] Figure 1 This is a schematic cross-sectional view of a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the cross-section of the light rod;

[0031] Figure 3 This is a process flow diagram of a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output according to an embodiment of the present invention;

[0032] In the figure, 1 is the fiber core area, 2 is the inner cladding, 3 is the outer cladding, 4 is the coating layer, 5 is the optical rod, and 6 is the low-concentration core rod. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] like Figure 1 , 2 As shown in this embodiment, a low-concentration erbium-ytterbium co-doped fiber for high-power laser output includes a core region 1, an inner cladding layer 2, an outer cladding layer 3, and a coating layer 4 arranged sequentially from the inside out. The outer diameter of the core region 1 is 25–40 μm. The core region 1 includes n low-concentration core rods 6, where 2 ≤ n ≤ 4, and the low-concentration core rods 6 are symmetrically arranged. The diameter of any low-concentration core rod 6 is 5–7 μm, and the distance between adjacent low-concentration core rods 6 is 1–3 μm. The low-concentration core rods 6 contain doping elements such as Er, Yb, P, and F, with each low-concentration core rod containing erbium ion concentrations of 200–500 ppm and ytterbium ion concentrations of 1000–5000 ppm.

[0035] Compared with pure quartz, the refractive index height difference Δ1 in core region 1 is 0.003 to 0.005, the NA value is controlled at 0.07 to 0.09, and the numerical aperture is controlled at a low level.

[0036] The inner cladding 2 is made of pure quartz material, and the water content of this quartz layer is controlled below 0.5 ppm. The inner cladding has a circular or polygonal structure to maximize the pump light transmission energy.

[0037] The outer cladding layer 3 is made of fluorinated resin material, and the refractive index of the outer cladding layer 3 is 1.36 to 1.39, which is a low refractive index outer cladding layer.

[0038] The coating layer 4 is made of high-temperature resistant acrylic resin with a modulus controlled between 1000 and 1300 MPa.

[0039] A method for fabricating a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output, such as... Figure 3 As shown, the steps are as follows:

[0040] Step 1: Preparation of the porous body: A base tube of suitable size and wall thickness is mounted on an MCVD lathe. The base tube is etched and polished. SiCl4 and a small amount of SF6 and POCl3 are introduced into the base tube, and an oxyhydrogen flame is sprayed using a metal torch to create a porous body with good deposition quality. The flow rate of SiCl4 is controlled at 150 sccm–300 sccm, the flow rate of POCl3 is 5–10 sccm, the flow rate of SF6 is 3–5 sccm, and the temperature of the oxyhydrogen flame is 1600–1630 °C. ℃ The metal torch moves at a speed of 100–140 mm / min.

[0041] Step 2: Preparation of rare earth ion solution: Select methanol, ethanol, or water as the solvent and place them in a beaker. Pour the pre-weighed ytterbium chloride and erbium chloride powders into the solvent and stir thoroughly to form a rare earth ion solution. The molar mass of ytterbium chloride is controlled at 0.04–0.06 mol / L, and the molar mass of erbium chloride is controlled at 0.005–0.02 mol / L.

[0042] Step 3: Preparation of low-concentration core rod: The base tube with a loose body layer is immersed and placed in a rare earth ion solution for 20-30 minutes, followed by a standing time of 20-30 minutes. Then, it is mounted on an MCVD lathe for oxidation, drying, and vitrification to complete one deposition layer. The loose body deposition, immersion, standing, oxidation, drying, and vitrification process is repeated 3-5 times to control the number of deposition layers in the base tube to 3-5 layers. After completion, it is collapsed into a rod to form a low-concentration core rod.

[0043] Step 4: Repeat steps 1 to 3 to prepare n low-concentration core rods. The number of low-concentration core rods is determined according to the optical fiber design requirements.

[0044] Step 5: Extend each of the n low-concentration mandrels, controlling the extension dimension to 8-12mm. Then, grind and shape one side of each low-concentration mandrel or immerse it in HF acid to remove 2-4mm from one side, ultimately shaping the low-concentration mandrel into a near-elliptical shape. The near-elliptical shape consists of a semicircle and a semi-ellipse, and the dimensions of the near-elliptical shape are defined by the major axis and the minor axis.

[0045] Step Six: Optical Rod Assembly: Select a quartz sleeve with an outer diameter of 35-40 mm and an inner diameter of 15-20 mm. After tapering the head of the quartz sleeve, stack n low-concentration core rods and fix them with quartz rings before inserting them into the quartz sleeve to assemble optical rod 5. The quartz sleeve forms the inner cladding.

[0046] Step 7: Optical Preform Drawing: The optical preform is placed in a drawing furnace. The furnace temperature is controlled at 1700–1800℃, the drawing speed at 20–30 m / min, and the drawing tension at 0.8–1.4 N. Vacuum negative pressure drawing is applied to form an optical fiber. After inner and outer layer coating and curing, the fiber is wound into a roll. The inner layer coating and curing form the outer cladding, and the outer layer coating and curing form the outer coating layer.

[0047] Example 1

[0048] To facilitate understanding, this implementation case uses the fabrication process of a four-core erbium-ytterbium co-doped optical fiber as an example.

[0049] Step 1: Preparation of the porous body: A 25*3*600 (outer diameter 25mm, wall thickness 3mm, length 600mm) base tube was mounted on an MCVD lathe and etched and polished. SiCl4 and a small amount of SF6 and POCl3 were introduced into the base tube, and an oxyhydrogen flame was used to spray the tube, resulting in a porous body with good deposition quality. The SiCl4 flow rate was 200 sccm, the POCl3 gas flow rate was 7 sccm, the SF6 gas flow rate was 4 sccm, and the oxyhydrogen flame temperature was 1620 °C. ℃ The metal torch moves at a speed of 120 mm / min.

[0050] Step 2: Preparation of rare earth ion solution: Methanol is selected as the solvent and placed in a beaker. The pre-weighed ytterbium chloride and erbium chloride powders are poured into the solvent. After stirring thoroughly for 180 minutes, the solution is completely dissolved and forms a light pink solution, thus forming a rare earth ion solution. The molar mass of ytterbium chloride is controlled at 0.05 mol / L, and the molar mass of erbium chloride is controlled at 0.01 mol / L.

[0051] Step 3: Preparation of low-concentration core rod: The base tube with a loose body layer is immersed and placed in the prepared rare earth ion solution for 25 minutes and 40 minutes respectively. Afterwards, it is mounted on an MCVD lathe for oxidation, drying, and vitrification to complete one deposition layer. The loose body deposition, immersion, standing, oxidation, drying, and vitrification steps are repeated four times to achieve a total of four deposition layers. After completion, the core rod is collapsed into a rod, thus forming a low-concentration core rod.

[0052] Step 4: Repeat steps 1 to 3 to complete the preparation of four low-concentration core rods.

[0053] Step 5: Extend each of the four low-concentration mandrels by 10mm. Then, grind and shape one side of each low-concentration mandrel, removing 3mm from one side, ultimately shaping the mandrel into a near-elliptical shape. This near-elliptical shape consists of a semi-circle and a semi-ellipse, with the dimensions defined by the major and minor axes. In Example 1, the major axis is 10mm and the minor axis is 7mm.

[0054] Step Six: Optical Rod Assembly: Select a quartz sleeve with an outer diameter of 38mm and an inner diameter of 18mm. After tapering the head of the quartz sleeve, stack four low-concentration core rods and fix them with quartz rings before inserting them into the quartz sleeve to assemble the optical rod. The quartz sleeve forms the inner cladding. Quartz rings are installed at both ends of the assembled core rod, and the inner diameter of the quartz rings is 0.1–0.2mm larger than the assembled size of the four core rods.

[0055] Step 7: Optical Preform Drawing: The optical preform is placed in a drawing furnace, and vacuum drawing is performed to form optical fibers. The pressure is 50 mbar, the furnace temperature is 1750℃, the drawing speed is 25 m / min, and the drawing tension is controlled at 1 N. After inner and outer layer coating and curing, the optical fiber is wound into a roll. The inner layer coating and curing form the outer cladding, and the outer layer coating and curing form the coating layer.

[0056] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A method for fabricating a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output, characterized in that: The low-concentration erbium-ytterbium co-doped optical fiber includes a core region, an inner cladding, an outer cladding, and a coating layer arranged sequentially from the inside out. The core region includes a plurality of symmetrically arranged low-concentration core rods. The diameter of any one of the low-concentration core rods is 5~7μm, and the spacing between adjacent low-concentration core rods is 1~3μm. The preparation method includes the following steps: Step 1: Preparation of porous body: The base tube is mounted on an MCVD lathe and etched and polished; SiCl4, SF6, and POCl3 are introduced into the base tube, and hydrogen-oxygen flame is sprayed using a metal torch to deposit and form a porous body; Step 2: Preparation of rare earth ion solution: The solvent is placed in a beaker, and the weighed ytterbium chloride and erbium chloride powders are poured into the solvent and stirred to form a rare earth ion solution; the molar mass of ytterbium chloride is controlled at 0.04~0.06 mol / L, and the molar mass of erbium chloride is controlled at 0.005~0.02 mol / L. Step 3: Preparation of low-concentration core rod: The base tube with a loose body layer is immersed in a rare earth ion solution and left to stand. Then it is installed on an MCVD lathe for oxidation, drying and vitrification to complete one deposition layer. The loose body deposition, immersion, standing, oxidation, drying and vitrification are repeated multiple times to form a multi-layer deposition layer. Then it is collapsed into a rod to form a low-concentration core rod. Step 4: Repeat steps 1 to 3 to prepare n low-concentration core rods; Step 5: Extend and shape n low-concentration core rods: Extend the prepared low-concentration core rods, and then shape one side of the low-concentration core rods to make them semi-elliptical; the extension dimension in step 5 is controlled at 8~12mm; shaping is performed by grinding or acid soaking, so that 2~4mm is ground or soaked off one side of the low-concentration core rods. Step 6: Light rod assembly: Select a sleeve, tape the head of the sleeve, stack multiple low-concentration core rods, fix them with a quartz ring, and insert them into the sleeve to assemble the light rod. Step 7: Optical fiber drawing: The optical fiber is placed into the drawing furnace, and a vacuum is drawn into the drawing furnace to create a negative pressure inside the furnace before drawing the fiber to form an optical fiber. Step 8: Winding up the fiber: After the inner and outer layers of the optical fiber are coated and cured, the fiber is wound up into a roll.

2. The method for preparing a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output according to claim 1, characterized in that: The number of low-concentration core rods is n, where 2≦≤n≦4.

3. The method for preparing a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output according to claim 1, characterized in that: The diameter of the fiber core region is 25~40μm.

4. The method for preparing a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output according to claim 1, characterized in that: The inner cladding is made of quartz material, the outer cladding is made of high-temperature resistant, low-refractive-index material, and the coating layer is made of high-strength acrylic resin.

5. The method for preparing a low-concentration erbium-ytterbium co-doped optical fiber with high-power laser output according to claim 1, characterized in that: In step one, the flow rate of SiCl4 is controlled between 150 sccm and 300 sccm, and the flow rate of POCl4 is... 3 The gas flow rate is controlled at 5~10 sccm, the SF6 gas flow rate is controlled at 3~5 sccm, the flame temperature is controlled at 1600~1630℃, and the metal torch moving speed is controlled at 100~140mm / min.

6. The method for preparing a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output according to claim 1, characterized in that: The solution in step two is one of methanol, ethanol, or water.

7. The method for preparing a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output according to claim 1, characterized in that: The soaking time in step three is 20-30 minutes, and the standing time is 20-30 minutes.

8. The method for preparing a low-concentration erbium-ytterbium co-doped optical fiber for high-power laser output according to claim 1, characterized in that: In step eight, the temperature of the drawing furnace is controlled at 1700~1800℃, the drawing speed is controlled at 20~30m / min, and the drawing tension is controlled at 0.8~1.4N.

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