阅读说明：本技术 一种大芯径稀土掺杂光纤预制棒及其制备方法 (Large-core-diameter rare earth doped optical fiber preform and preparation method thereof ) 是由 李进延 刘业辉 王一礴 林贤峰 程永师 彭景刚 李海清 于 2018-06-15 设计创作，主要内容包括：本发明公开了一种大芯径稀土掺杂光纤预制棒及其制备方法,该方法包括：在首管末端的第一预设位置处烧塌第一凹槽,在第一凹槽后开孔,并将进料管与开设的孔连接；将首管与反应管进行熔接,将熔接好的反应管与尾管相连；在反应管内表面沉积疏松层,在反应管末端的第二预设位置处塌缩第二凹槽；从进料管注入稀土掺杂溶液后,密封进料管的进料口,旋转反应管让稀土掺杂溶液充分浸透疏松层；将反应管与尾管分离,并将浸透好疏松层的剩余稀土掺杂溶液排出,将反应管内的多余稀土掺杂溶液吹干,以完成掺杂；将掺杂好稀土溶液的反应管内的疏松层进行玻璃化,并重复沉积疏松层及掺杂操作,直至制备得到满足需要的光纤预制棒。本发明方法效率高、操作简单。(The invention discloses a large-core-diameter rare earth doped optical fiber preform and a preparation method thereof, wherein the method comprises the following steps: a first groove is collapsed at a first preset position at the tail end of the first pipe, a hole is formed behind the first groove, and the feeding pipe is connected with the formed hole; the first pipe is welded with the reaction pipe, and the welded reaction pipe is connected with the tail pipe; depositing a loose layer on the inner surface of the reaction tube, and collapsing a second groove at a second preset position at the tail end of the reaction tube; after the rare earth doping solution is injected from the feeding pipe, the feeding hole of the feeding pipe is sealed, and the reaction pipe is rotated to enable the rare earth doping solution to fully soak the loose layer; separating the reaction tube from the tail tube, discharging the residual rare earth doping solution soaked in the loose layer, and drying the residual rare earth doping solution in the reaction tube to complete doping; and (3) vitrifying the loose layer in the reaction tube doped with the rare earth solution, and repeating the deposition of the loose layer and the doping operation until the optical fiber preform meeting the requirement is prepared. The method has high efficiency and simple operation.)

1. A preparation method of a rare earth doped optical fiber preform is characterized by comprising the following steps:

a first groove is collapsed at a first preset position at the tail end of the first pipe, then a hole is formed in the rear of the first groove, and the feeding pipe is connected with the formed hole;

welding the first pipe with the reaction pipe, and connecting the welded reaction pipe with the tail pipe;

depositing a loose layer on the inner surface of the reaction tube, and collapsing a second groove at a second preset position at the tail end of the reaction tube so that the rare earth doping solution injected into the reaction tube stays in the reaction tube and does not overflow;

after the rare earth doping solution is injected from the feeding pipe, the feeding hole of the feeding pipe is sealed, and the reaction pipe is rotated to enable the rare earth doping solution to fully soak the loose layer;

separating the reaction tube from the tail tube, discharging the residual rare earth doping solution soaked with the loose layer, and drying the residual rare earth doping solution in the reaction tube to complete doping;

and (3) vitrifying the loose layer in the reaction tube doped with the rare earth solution, and repeating the deposition of the loose layer and the doping operation until the optical fiber preform meeting the core diameter requirement is prepared.

2. The method of claim 1, wherein the depth of the recess needs to be greater than the product of the deposition thickness per pass and the total number of passes and less thanThe width of the groove isTo r₀Wherein r is₀The radius of the reaction tube is shown.

3. The method of claim 1 wherein the welded reactor tube is attached to the tailpipe by a tetrafluoro adapter.

4. A method according to claim 3, characterized in that the deposition temperature of the loose layer is between 1600 ℃ and 1730 ℃ and the gas flow rate inside the reaction tube during deposition is between 0.012m/s and 0.022 m/s.

5. The method as claimed in claim 4, wherein the flame combustion is moved at a speed of 100mm/min to 150mm/min and the hot zone length is 16cm to 25cm while depositing the porous layer.

6. The method according to any one of claims 1 to 5, wherein the rotation speed of the reaction tube is between 20r/min and 35 r/min.

7. The method of claim 6, wherein before rotating the reaction tube to substantially saturate the bulk layer with the rare earth doping solution, the method further comprises:

sealing the tail end of the reaction tube, and introducing gas into the reaction tube, wherein the flow rate of the gas is between 0.003m/s and 0.005 m/s.

8. The method of claim 7, wherein the vitrification temperature is between 1850 ℃ and 1950 ℃.

9. The method of claim 1, wherein the core diameter of the preform for the optical fiber when depositing the m-pass loose layer is:wherein h is_mFor preparing the core diameter, r, of an m-pass optical fiber preform₁The radius of the fiber core of the optical fiber preform is deposited once.

10. A rare earth-doped optical fiber preform prepared by the method for preparing a rare earth-doped optical fiber preform according to any one of claims 1 to 9.

Technical Field

The invention belongs to the field of special optical fiber preparation, and particularly relates to a rare earth doped optical fiber preform with large core diameter, high doping efficiency and high doping uniformity and a preparation method thereof.

Background

The fiber laser has the advantages of good heat dissipation performance, high efficiency, good beam quality, small volume, light weight and the like, and shows wide application prospect and great application value in the fields of material processing, intelligent manufacturing, medical treatment, national defense and the like. The core of various amplifiers or lasers is a gain medium rare earth doped fiber, so the efficient fabrication of various rare earth doped fibers is a key technology for promoting the development of fiber lasers.

The Modified Chemical Vapor Deposition (MCVD) method for preparing the doped rare earth optical fiber preform is a widely used method at present. The main doping methods for preparing the active optical fiber preform by the MCVD process include a gas phase doping method, a sol-gel dip coating method, a liquid phase dipping method and the like.

The gas phase doping method belongs to an online doping mode, a quartz tube for deposition is not required to be dismounted from an MCVD lathe midway, the rare earth ions are doped directly through gas phase deposition, the high cleanness in the whole method process can be ensured, and an optical fiber preform with a large core diameter can be prepared. However, since the saturation vapor pressure of the rare earth ions is too high, the control and the equipment of the gasified rare earth ions are complex, the equipment cost is expensive, and the longitudinal doping uniformity of the optical fiber preform is difficult to ensure, so that the high-efficiency mass production is difficult to realize. The sol-gel dip coating method is that the rare earth oxide and the silicon dioxide nano particles are mixed uniformly in advance and then are coated on the inner surface of the silicon dioxide glass tube uniformly, and finally the optical fiber prefabricated rod is manufactured by adopting MCVD technology. The method omits the step of introducing rare earth ions into a loose powder layer by a solution doping technology or other methods, avoids the formation of rare earth ion microcrystals and clusters, and can also prepare the optical fiber preform with a large core diameter, but the method needs a precise control technology and the purity of the core of the prepared preform is difficult to reach the optical fiber level standard, so that the optical fiber has large additional loss. Liquid phase doping is a commonly used doping method, and doping is realized by soaking loose pores deposited in the reaction tube by MCVD in a mixed solution of rare earth ions and co-doped ions. The method has two selection modes, one mode is liquid phase on-line doping, the reaction tube deposited with the loose layer is not taken down from a lathe and is directly doped on line, and the mode can avoid the process that the reaction tube is pulled down from the lathe and is welded, so that the cleanliness in the reaction tube is improved. However, the operation of injecting rare earth ions into the reaction tube is complicated, and waste materials in the tail tubes connected with the tail end of the reaction tube (in MCVD deposition, the two ends of the quartz tube are connected with a common high-purity quartz tube, the gas inlet end is called a head tube, and the gas outlet end is called a tail tube) are easily introduced into the reaction tube to cause pollution, and the method is not easy to suck out residual rare earth solution after the rare earth ions are injected into the reaction tube and are well soaked, so that the phenomenon of crystallization is easily caused. Another way is to take the reaction tube off the lathe and mount it on the lathe again after soaking the rare earth solution, this method requires the whole loose layer to be soaked in the rare earth solution, which requires a large amount of rare earth solution and cannot be reused due to solution contamination after one soaking. Meanwhile, when the rare earth doping ions are soaked in the vertical reaction tube, different pressures are generated due to different depths, so that longitudinal non-uniformity of doping of the prefabricated rod can be caused during soaking. And the quality requirement on the porous layer of the porous layer is very strict, the porous layer of the porous layer is too thin and has small doping concentration, and the porous layer of the porous layer is too thick and is easy to fall off and has nonuniform doping. When the reaction tube is formed into a rod, because rare earth ions and co-doped ions are concentrated in the center of the fiber core, clusters or microcrystals of doped ions easily appear during high-temperature collapse, so that the doping is not uniform.

With the development of the current double-clad active optical fiber technology, especially the development of optical fiber lasers, the demand for active optical fibers is increasing, the industrialized optical fiber lasers need stable active optical fiber guarantee, and the diameter of the doped fiber core of the optical fiber preform needs to be further improved on the basis of good doping concentration, doping uniformity and background loss.

Disclosure of Invention

Aiming at the defects or improvement requirements in the prior art, the invention provides a large-core-diameter rare earth doped optical fiber preform and a preparation method thereof, so that the technical problem that the doping concentration, the doping uniformity and the background loss cannot be effectively ensured in the conventional preparation of an active optical fiber preform by an MCVD (metal-chemical vapor deposition) process is solved.

To achieve the above object, according to an aspect of the present invention, there is provided a method for preparing a large-core rare-earth-doped optical fiber preform, including:

a first groove is collapsed at a first preset position at the tail end of the first pipe, then a hole is formed in the rear of the first groove, and the feeding pipe is connected with the formed hole;

welding the first pipe with the reaction pipe, and connecting the welded reaction pipe with the tail pipe;

depositing a loose layer on the inner surface of the reaction tube, and collapsing a second groove at a second preset position at the tail end of the reaction tube so that the rare earth doping solution injected into the reaction tube stays in the reaction tube and does not overflow;

after the rare earth doping solution is injected from the feeding pipe, the feeding hole of the feeding pipe is sealed, and the reaction pipe is rotated to enable the rare earth doping solution to fully soak the loose layer;

separating the reaction tube from the tail tube, discharging the residual rare earth doping solution soaked with the loose layer, and drying the residual rare earth doping solution in the reaction tube to complete doping;

and (3) vitrifying the loose layer in the reaction tube doped with the rare earth solution, and repeating the deposition of the loose layer and the doping operation until the optical fiber preform meeting the core diameter requirement is prepared.

Preferably, the depth of the recess needs to be greater than the product of the deposition thickness per pass and the total number of passes and less thanThe width of the groove isTo r₀Wherein r is₀The radius of the reaction tube is shown.

Preferably, the welded reaction tube is connected to the tail tube by a tetrafluoro adapter.

Preferably, the deposition temperature of the loose layer is 1600-1730 ℃, and the gas flow rate in the reaction tube during deposition is 0.012-0.022 m/s.

Preferably, the moving speed of the flame combustion is between 100mm/min and 150mm/min and the hot zone length is between 16cm and 25cm when the loose layer is deposited.

Preferably, the rotation speed of the reaction tube is between 20r/min and 35 r/min.

Preferably, before the rotating the reaction tube to allow the rare earth doping solution to sufficiently saturate the loose layer, the method further includes:

sealing the tail end of the reaction tube, and introducing gas into the reaction tube, wherein the flow rate of the gas is between 0.003m/s and 0.005 m/s.

Preferably, the vitrification temperature is between 1850 ℃ and 1950 ℃.

Preferably, the core diameter of the optical fiber preform when depositing the m loose layers is:wherein h is_mFor preparing the core diameter, r, of an m-pass optical fiber preform₁The radius of the fiber core of the optical fiber preform is deposited once.

Preferably, after the feeding pipe is connected with the opened hole, the method further comprises the following steps: and sealing the feed inlet of the feed pipe.

According to another aspect of the present invention, there is provided a rare earth-doped optical fiber preform prepared by the method for preparing a rare earth-doped optical fiber preform according to any one of the above aspects.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

1. the operation is simple and convenient, the first pipe can be recycled after being prepared, and the joint can be recycled after being cleaned each time. After the loose layer is deposited each time, the doping can be finished only by injecting the same amount of rare earth solution into the reaction tube through the thin glass tube and rotating and soaking, and then the detachable joint is convenient for the treatment of the residual solution in the reaction tube to avoid crystallization or cluster effect and also avoid the introduction of waste silicon dioxide dust in the tail tube into the reaction tube;

2. can effectively save fuel cost and rare earth ion solution. The diameter of the fiber core of the prefabricated rod is increased only by a plurality of processes of deposition of multiple loose layers, solution soaking and vitrification of the loose layers, and finally, the reaction tube is collapsed into the solid prefabricated rod. However, for the conventional preparation of the preform with the same number of times, a plurality of reaction tubes need to be collapsed into the solid preform, and the collapsed preform needs to consume a large amount of fuel in the preparation process of the preform, so that the method can save a large amount of fuel cost; when the loose layer is soaked in the solution, only a small amount of rare earth solution is needed to be injected each time, the whole reaction tube is not needed to be soaked in the rare earth solution, so that the use of the rare earth solution can be greatly reduced, and the high-purity rare earth ion raw material is very expensive, so that the manufacturing cost of the doped optical fiber can be greatly saved;

3. the optical fiber preform prepared by the method has larger fiber core diameter, the fiber core diameter can be accurately controlled to meet the requirement of large-scale production, and the large-core optical fiber preform can be accurately prepared by accurately controlling the deposition temperature of the loose layer, the gas flow in the reaction tube, the solution soaking and the vitrification of the loose layer. And finally, more special optical fibers can be drawn by sleeving a proper sleeve, so that the fiber output quantity of a single prefabricated rod is greatly increased.

4. The longitudinal and axial doping uniformity is good. Because the reaction tube is horizontally arranged, the rare earth solution can uniformly cover the loose layer, and the longitudinal uniformity of the doping of the prefabricated rod can be ensured. And the rare earth solution soaked in each time can be controlled to be equal (or the gradient optical fiber prefabricated rod with different refractive index changes can be prepared), so that the uniformity of doping in each time in the axial direction can be completely ensured.

Drawings

Fig. 1 is a schematic view of a head pipe according to an embodiment of the present invention;

FIG. 2 is a schematic view of a reaction tube according to an embodiment of the present invention;

FIG. 3 is a schematic view of a coupling for coupling a reactor tube and a liner according to an embodiment of the present invention;

FIG. 4 is a schematic view of a tailpipe provided in accordance with an embodiment of the present invention;

FIG. 5 is a schematic view of an immersion porosity layer provided in an embodiment of the present invention;

FIG. 6 is a cross-sectional view of refractive index of a large-core diameter highly-doped highly-uniform rare-earth-doped optical fiber preform fabricated by the present invention;

FIG. 7 is a cross-sectional view showing the refractive index of a single-pass optical fiber preform fabricated by a conventional process according to an embodiment of the present invention;

the same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:

1-first pipe, 2-feeding pipe, 3-first groove, 4-reaction pipe, 5-loose layer, 6-second groove, 7-tetrafluoro joint, 8-high temperature resistant rubber ring, 9-tail pipe and 10-heating device.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.