High concentration, high uniformity rare earth doped optical fiber and method of making same

Abstract

The application relates to a preparation method of a high-concentration and high-uniformity rare earth doped optical fiber, and belongs to the field of doped optical fiber preparation. The doping mode comprises the following steps: depositing a silica loose body on the inner wall of a base pipe; introducing a phosphoric acid aqueous solution into the base pipe to ensure that the loose body on the inner wall of the base pipe is soaked in the phosphoric acid aqueous solution; after soaking, the loose body is oxidized and dried to obtain a phosphosilicate loose body; a rare earth ion solution is introduced into the inside of the base pipe to soak the surface of the loose body; an extension rotating rod is vertically deepened to the bottom of the base pipe, the outer wall of the extension rotating rod is provided with a toothed sheet, the extension rotating rod is driven to rotate to stir the rare earth ion solution, after sufficient stirring, the rare earth ion solution is recovered, and the loose body is oxidized, dried, glassified and collapsed to obtain a rare earth ion doped core rod. The application adopts the method of soaking the loose body in the phosphoric acid aqueous solution to obtain a phosphosilicate loose body medium, and uses the vertical stirring and doping solution mode of the extension rotating rod to realize uniform doping of the rare earth ion to the loose body.

Description

TECHNICAL FIELD

[0001] The present application relates to a rare earth doped optical fiber and a preparation method thereof, and belongs to the field of optical fiber manufacturing. BACKGROUND

[0002] In recent years, with the increasing demand for fiber lasers and the continuous development of fiber laser technology, the quality of gain fibers as core components of lasers has also attracted much attention. The doping uniformity and doping concentration of gain active fibers directly affect the output power of fiber lasers and the reliability of the lasers. How to achieve high concentration doping and maintain high uniformity at high concentration is a hot topic in the research of gain fibers.

[0003] Generally, gain fibers for high-power lasers are prepared by gas-phase doping and liquid-phase doping. Although the gas-phase doping method has advantages in doping uniformity, it has high equipment maintenance cost and doping raw material cost, and the fiber attenuation is large, which is not conducive to the preparation of gain fibers for high-power lasers. Compared with the gas-phase doping method, the liquid-phase doping method is conducive to the preparation of low-loss fibers, but the current liquid-phase doping generally adopts a static liquid-phase doping method, which mainly relies on the slow penetration of the static solution in the voids of the loose body, which takes a long time and has poor uniformity.

[0004] Chinese patent document CN116040932A discloses a homogenized solution doping device and a spraying method. The method sprays ion solution into a quartz reaction tube by reciprocating motion of an electric lifting platform multiple times to achieve uniform doping. However, the implementation of the method is complex and not suitable for large-scale use. Therefore, there is a need to provide an improved solution doping method to overcome the deficiencies in the related art. SUMMARY

[0005] To overcome the above technical deficiencies, the present application designs a simple and controllable preparation method for high-concentration and high-uniformity rare earth doped optical fibers. In the preparation of porous loose bodies, phosphoric acid immersion is used to form a phosphosilicate medium, and one of the dynamic solution doping methods is used. The rotation of the rare earth doping solution realizes the uniform adsorption of the doping elements by the loose body, without the need for pressure control and complex structure design. The method has simple preparation steps, high efficiency, and can realize high-concentration and high-uniformity rare earth ion doping, ensuring the consistency of the optical fiber and large-scale production.

[0006] The technical solution adopted by the present application to solve the above problems is as follows: a preparation method for high-concentration and high-uniformity rare earth doped optical fibers, the doped optical fiber comprises a core layer, an inner cladding layer, an outer cladding layer, and an outer coating layer from inside to outside, the core layer is doped with rare earth elements, and the doped optical fiber comprises the following preparation steps:

[0007] The first step is to select a base pipe, and deposit a silica loose body on the inner wall of the base pipe. The size of the loose body particles is 100-300 nm, and the porosity is 40-60%.

[0008] The second step is to prepare a phosphoric acid aqueous solution with a concentration of 1.0-1.4 mol / L, and to stir the solution thoroughly and then let it stand. A rare earth ion solution is also prepared, with a concentration of 0.15-0.45 mol / L, and the prepared solution is allowed to stand.

[0009] The third step is to introduce the phosphoric acid aqueous solution prepared in the second step into the base pipe prepared in the first step, so that the loose body on the inner wall of the base pipe is fully soaked in the phosphoric acid aqueous solution. The base pipe is kept in a vertical state and allowed to stand for 50-100 min, after which the phosphoric acid aqueous solution is recovered, and the loose body is oxidized and dried to obtain a phosphosilicate loose body containing phosphorus elements.

[0010] The fourth step is to vertically install the base pipe at a designated position, and to block the lower end of the base pipe. The rare earth ion solution prepared in the second step is introduced into the base pipe, so that the surface of the loose body is fully infiltrated. An extension rotating rod is vertically inserted into the bottom of the base pipe, and the outer wall of the extension rotating rod has teeth. The extension rotating rod is driven to rotate to stir the rare earth ion solution. After sufficient stirring, the rare earth ion solution is recovered, and the loose body is oxidized, dried, glassified, and collapsed, to finally obtain a core rod doped with rare earth ions.

[0011] The fifth step is to sleeve the prepared core rod, and to process the sleeve into an inner cladding structure to form an optical fiber preform. The optical fiber preform is drawn, and after the drawing is completed, an outer cladding coating and an outer coating are applied, to finally obtain an optical fiber product.

[0012] As one of the embodiments of the present application, the inner cladding is a pure quartz layer, and the cross-sectional shape is circular or polygonal. The outer cladding is a low-refractive coating, and the outer coating is a high-modulus acrylic resin coating.

[0013] As one of the embodiments of the present application, the doping element in the core layer is one of ytterbium, erbium, erbium / yttterbium, and ytterbium / cerium.

[0014] As one of the embodiments of the present application, the doping concentration of ytterbium in the core layer is 1.2-1.5 mol%, and the doping concentration of erbium ions is 0.15-0.35 mol%. The element doping uniformity is ≤3% at every 50 mm on the optical rod.

[0015] As one of the embodiments of the present application, in the fourth step, the stirring time of the extension rotating rod on the rare earth ion solution in the base pipe is 30-60 min, and the stirring speed of the extension rotating rod is 60 revolutions / min.

[0016] As one of the embodiments of the present application, in the fifth step, the drawing tension of the preform rod is controlled at 0.8N-1.1N, and the drawing speed is controlled at 30-50m / min.

[0017] Compared with the prior art, the present application has the advantages of:

[0018] 1、The present application adopts phosphoric acid aqueous solution to soak the loose body, so as to obtain the phosphosilicate loose body medium, avoid the conventional reverse deposition phosphorus doping process for preparing the phosphosilicate loose body, and simplify the preparation process.

[0019] 2、The present application uses the extending rotating rod to vertically stir the doping solution, so as to realize the uniform doping effect of the rare earth ions on the loose body, so that the base pipe can be kept stationary, the operation complexity of directly rotating the base pipe is avoided, and the high concentration uniform doping of the solution is ensured.

[0020] 3、The present application can control the rotating speed of the extending rotating rod, and theoretically can also control the depth of the extending rotating rod in the base pipe, so as to ensure the time control in the solution doping process. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a rare earth doped optical fiber preparation process flowchart in the embodiment of the present application;

[0022] Figure 2 It is an extending rotating rod working system schematic diagram;

[0023] Figure 3 It is a radial doping component schematic diagram of the optical fiber cross section in the embodiment of the present application;

[0024] Figure 4 It is an axial doping component schematic diagram of the optical fiber in the embodiment of the present application

[0025] In the figure, 101-rotating rod tooth piece, 102-extending rotating rod, 103-screw rod, 104-driving unit, 105-motor, 106-reducer. DETAILED DESCRIPTION

[0026] The present application will be further described in detail below in combination with the embodiments, which are exemplary and intended to explain the present application, and cannot be understood as a limitation of the present application.

[0027] MCVD: Modified Chemical Vapour Deposition, improved chemical vapor deposition.

[0028] Phosphoric acid aqueous solution: a certain amount of phosphoric acid liquid is poured into deionized water to mix a uniform solution;

[0029] The extension rotating rod system is composed of an extension rotating rod 102, a screw rod 103, a driving unit 104, a motor 105, a speed reducer 106, and the like. The speed reducer 106 is used to control the output of the motor to control the rotating speed of the extension rotating rod. The length of the extension rotating rod is 200-800 mm. The extension rotating rod and the screw rod are cooperated to be a spiral telescopic type. The outer diameter of the screw rod is 10-40 mm. The embedded tooth piece is triangular or semicircular. The maximum length of the tooth piece is 15 mm. The extension rotating rod is driven by the driving unit and the motor. The material of the extension rod can be tetrafluoroethylene plastic or hollow stainless steel pipe. The extension rod is composed of an outer threaded rod and an inner threaded straight rod. Rotating the outer threaded rod pipe can realize the length growth of the extension rotating rod, which is convenient for matching the length of the base pipe.

[0030] Example 1

[0031] The preparation method of the high-concentration and high-uniformity rare earth-doped optical fiber in the embodiment is shown in the flowchart as shown in the figure. In order to facilitate understanding, the embodiment introduces one of the high-uniformity doping methods of the rare earth-doped optical fiber, which is used to illustrate. Figure 1

[0032] The first step is to prepare the base pipe. A base pipe with a certain size and length is selected. The size of the base pipe is Heraeus 25*2*500 (outer diameter 25 mm, wall thickness 2 mm, length 500 mm). The base pipe is respectively welded to a head pipe and a tail pipe and installed on an MCVD lathe. A loose body with a certain porosity is deposited on the inner wall of the base pipe. The requirements are that the porosity reaches 50%, and the particle size of the loose body is 120 nm.

[0033] The second step is to configure a phosphoric acid aqueous solution. 200 mL of deionized water and 40 g of phosphoric acid liquid are taken respectively. The phosphoric acid is added to the 200 mL of deionized water. After being fully stirred and uniformly mixed for 60 min, the solution is made up to 250 mL.

[0034] The third step is to configure a rare earth ion solution. Taking the erbium / ytterbium co-doped rare earth-doped solution as an example, the weighed ErCl3 solid powder and YbCl3 solid powder are loaded into a weighing bottle. One of methanol or ethanol is selected as the solvent. The concentration of the ErCl3 solution is controlled at 0.1-0.2 mol / L. The concentration of the YbCl3 solution is controlled at 1.2-1.5 mol / L. Finally, the rare earth ion solution is made up to 250 mL in a volumetric flask.

[0035] The fourth step is to introduce the prepared phosphoric acid aqueous solution into the loose body base pipe. The base pipe is in a vertical state. It is required that the phosphoric acid aqueous solution fully infiltrates the loose body. After being placed for 90 min, the phosphoric acid aqueous solution is discharged. The loose body soaked in the phosphoric acid is dried and oxidized and then placed. After weighing the weight of the loose body base pipe before and after soaking in the phosphoric acid aqueous solution, the salt absorption rate of the loose body per unit length is 12.34 g / m. ​

[0036] Fifth step: the fourth step of drying loose body vertical fixed in the specified position, the lower end of the base pipe outlet plug plug, the third step of the rare earth ion solution is poured into the base pipe inside, all infiltration loose body surface, the extension of the vertical rod inserted into the base pipe bottom, manual opening extension pipe on the rotating rod teeth, in order to facilitate the mixing of the doping solution.

[0037] Sixth step: open the motor, set the extension of the rotating speed of the rotating rod 60 / min, stirring time control in 30min, after sufficient stirring, stop rotating, stand for 10min, the extension of the rotating rod out, and the rare earth ion solution is exported to the pear-shaped bottle.

[0038] Seventh step: after the immersion of the rare earth ion solution of loose body oxidation, drying, vitrification, collapse and other steps, the preparation of the core rod, then the core rod is cannulated (cannula as the inner cladding) after the formation of the final preform, the preform in the drawing furnace drawing, drawing tension control in 1.1N, drawing speed control in 25m / min, after the drawing of the outer coating, the outer coating, the outer coating is high temperature resistant low fold coating, the outer coating is high modulus acrylic resin, the preparation of the final rare earth doped active optical fiber, the optical fiber refractive index and EPMA component test, verify the uniformity and effect of doping.

[0039] The concentration of the prepared fiber rare earth ion doping is shown in Figure 3 , 4 .

[0040] In addition to the above examples, the present application also includes other implementation ways, any technical solutions formed by equivalent transformation or equivalent replacement should fall within the protection scope of the claims of the present application.

Claims

1. A method for preparing a high-concentration, highly uniform rare-earth-doped optical fiber, characterized in that: The doped optical fiber comprises, from the inside out, a core layer, an inner cladding layer, an outer cladding layer, and an outer coating layer. The core layer is doped with rare earth elements. The doped optical fiber comprises the following fabrication steps: Step 1: Select a base tube and deposit silica porous body on the inner wall of the base tube. The porous body particles are 100nm to 300nm in size and have a porosity of 40% to 60%. Step 2: Prepare a phosphoric acid aqueous solution with a concentration of 1.0–1.4 mol / L. Stir the phosphoric acid aqueous solution thoroughly and let it stand. Prepare a rare earth ion solution with a concentration of 0.15–0.45 mol / L. Let the prepared rare earth ion solution stand. Step 3: Pour the phosphoric acid aqueous solution prepared in Step 2 into the base tube prepared in Step 1, ensuring that the loose material on the inner wall of the base tube is completely immersed in the phosphoric acid aqueous solution. After the base tube is kept vertical and left to stand for 50 min to 100 min, the phosphoric acid aqueous solution is recovered, and the loose material is oxidized and dried to obtain phosphorus silicate loose material containing phosphorus. Step 4: Vertically install the base tube in the designated position, block the lower end of the base tube, and introduce the rare earth ion solution prepared in Step 2 into the base tube to completely wet the surface of the porous body. Vertically insert the extension rod into the bottom of the base tube. The outer wall of the extension rod has toothed plates. Drive the extension rod to rotate and stir the rare earth ion solution. After thorough stirring, recover the rare earth ion solution, oxidize, dry, vitrify, and collapse the porous body to finally obtain a rare earth ion doped core rod. Step 5: The prepared core rod is sheathed, and the sheath is processed into an inner cladding structure to form an optical fiber preform. The optical fiber preform is drawn into fibers, and after the fiber drawing is completed, an outer cladding coating and an outer coating are applied to finally obtain the finished optical fiber.

2. The method according to claim 1, characterized in that: The inner cladding is a pure quartz layer with a circular or polygonal cross-sectional shape; the outer cladding is a low-refractive-index coating, and the outer coating is a high-modulus acrylic resin coating.

3. The method according to claim 1, characterized in that: The doping element in the fiber core layer is one of ytterbium, erbium, erbium / ytterbium, or ytterbium / cerium.

4. The method according to claim 3, characterized in that: The doping concentration of ytterbium in the fiber core layer is 1.2–1.5 mol%, and the doping concentration of erbium ions is 0.15–0.35 mol%. The element doping uniformity is such that the ion concentration difference is ≤3% every 50 mm along the optical rod.

5. The method according to claim 1, characterized in that: In the fourth step, the stirring time of the extended rotor in the rare earth ion solution in the base tube is 30 min to 60 min, and the stirring speed of the extended rotor is 60 rpm.

6. The method according to claim 1, characterized in that: In the fifth step, the drawing tension of the preform is controlled at 0.8N to 1.1N, and the drawing speed is controlled at 30 to 50m / min.

Images