CN113024103B

CN113024103B - Device and method for preparing rare earth doped optical fiber preform

Info

Publication number: CN113024103B
Application number: CN202110385500.1A
Authority: CN
Inventors: 黄宏琪
Original assignee: Nanjing Zhichun Hongyuan Technology Co ltd
Current assignee: Nanjing Zhichun Hongyuan Technology Co ltd
Priority date: 2021-04-10
Filing date: 2021-04-10
Publication date: 2022-08-26
Anticipated expiration: 2041-04-10
Also published as: CN113024103A

Abstract

The invention discloses a device and a method for preparing a rare earth-doped optical fiber. The preparation process utilizes the rare earth chelate to have extremely high saturated vapor pressure at about 200 ℃, can reduce the complexity of equipment and is convenient for process control; the concentration of rare earth ions is controlled by adjusting the flow of the carrier gas He through the MFC, so that accurate doping is realized; by utilizing the characteristics that the co-doping agent aluminum trichloride has extremely high vapor pressure at the high temperature of 100-200 ℃, but the aluminum trichloride is easy to absorb water vapor and deliquescent and has strong corrosivity, the pure quartz glass crucible or the pure aluminum trichloride crucible is adopted to heat and evaporate in the liner tube, and the doping amount of the aluminum trichloride is controlled by adjusting the temperature.

Description

Device and method for preparing rare earth doped optical fiber preform

Technical Field

The invention belongs to the technical field of optical fiber and optical cable preparation, and particularly relates to a device and a method for preparing a rare earth-doped optical fiber.

Background

With the rapid development of fiber lasers in the fields of industrial processing, medical treatment, aviation, military and the like, people put higher requirements on the performance of fiber lasers such as power, beam quality, photodarkening performance, conversion efficiency and the like. The rare earth doped fiber is used as a core component of the fiber laser and plays roles of a laser gain medium and an optical waveguide, so the background loss, the absorption coefficient, the light-light conversion efficiency, the numerical aperture, the beam quality, the light darkening performance and the like of the rare earth doped fiber directly determine the quality of the fiber laser.

The rare earth doped optical fiber is formed by drawing a rare earth doped optical fiber preform, and the methods for preparing the rare earth doped optical fiber preform are mainly divided into a liquid phase doping method and a gas phase doping method. The liquid phase doping method is the earliest adopted process method for preparing the rare earth doped optical fiber preform rod, and is characterized in that a deposition layer with a loose structure is deposited on the inner wall of a reaction tube through an MCVD (metal chemical vapor deposition) process, the deposition layer with the loose structure is soaked in a solution containing rare earth ions, the deposition layer adsorbs the rare earth ions in the solution, and then the rare earth ions are doped into the reaction tube through processes such as dehydration, vitrification and the like, so that the method belongs to an off-line doping process. A gas-phase doping method for rare-earth chelate is a technological process developed in recent years, which features that the rare-earth chelate containing rare-earth elements and aluminium trichloride as co-doping agent are carried in liner tube in gas mode, and under the action of external heat source, they are oxidized together with Si and P, and then transferred to the inner wall of reaction tube and deposited to directly form doped core region.

Compared with raw materials such as silicon, phosphorus and the like, the rare earth chelate can form a certain saturated vapor pressure only at a high temperature of about 200 ℃; aluminum trichloride has a certain saturated vapor pressure only at the temperature of over 100 ℃ and is very easy to absorb water vapor to deliquesce. At present, a gas phase evaporation system of raw materials such as rare earth chelate, aluminum trichloride and the like comprises a material tray, a material tank, a valve, a pipeline, a heat preservation cavity in which the material tray, the material tank, the pipeline connecting box and the gas inserting pipe are arranged, wherein the material tray is placed into the material tank from the air, and then the material tray is evaporated and conveyed into a liner pipe through the valve and the pipeline in sequence. However, aluminum trichloride is very easy to absorb water vapor, and extremely strong corrosivity is caused to a charging bucket, a pipeline, a valve and the like; in addition, the aluminum trichloride steam has extremely high temperature requirement, and is very easy to condense to block a pipeline, so that the prefabricated rod is scrapped, and great economic loss is caused.

In another rare earth chloride gas phase doping method, rare earth chlorides such as ytterbium trichloride and the like are heated and sublimated in a crucible, the chlorides of rare earth ions can have enough vapor pressure to participate in a vapor deposition process at the temperature of about 1000 ℃, and materials are easy to condense in the conveying process, so that the requirements on process equipment are high; the co-doping agent aluminum trichloride has extremely high saturated vapor pressure above 200 ℃, has extremely high concentration if being sublimated together with rare earth chloride, and has extremely complex system if being provided with an evaporation device independently, so that the co-doping of the aluminum trichloride and the rare earth chloride is extremely difficult to control.

Disclosure of Invention

In response to the above-identified deficiencies in the art or needs for improvement, the present invention provides a method and apparatus for making a rare-earth doped optical fiber. The preparation process method is based on the following process principle:

1、SiCl ₄ 、POCl ₃ when the process gas has extremely high saturated vapor pressure at 30-50 ℃, the gas is supplied by adopting a conventional gas holder, and the flow of the gas is accurately controlled by an MFC (micro-fuel cell);

2. the rare earth ions are doped by adopting high-purity rare earth chelate as a raw material, and the high-purity rare earth chelate has extremely high saturated vapor pressure at about 200 ℃, so that the complexity of equipment can be reduced, and the process control is facilitated. The method is characterized in that a high-temperature evaporation system with high cleanness and high temperature precision is adopted to realize accurate control of rare earth steam, the concentration of rare earth ions is controlled by adjusting the flow rate of carrier gas He through an MFC, and high-temperature steam is conveyed into a liner tube through a high-temperature steam conveying pipeline to realize accurate doping;

3. the co-doping agent aluminum trichloride has extremely high vapor pressure at the high temperature of 100-200 ℃, but the aluminum trichloride is extremely easy to absorb water vapor and deliquesce, and the generated acidic substances have extremely strong corrosivity on valves and pipelines. Therefore, the pure quartz glass crucible or the pure aluminum trichloride crucible is adopted to heat and evaporate in the liner tube, and the doping amount of the aluminum trichloride is controlled by adjusting the temperature.

Based on the process principle, the invention provides a doping device of a rare earth-doped optical fiber preform, which comprises an MCVD gas holder, a rare earth chelate high-temperature evaporation system, an aluminum trichloride evaporation device and the like, and the device has the advantages of super cleanliness, compact structure, good heat preservation effect, convenience in operation, good air tightness, low energy consumption, low cost and long service life. Can ensure that the rare earth and the co-doping agent raw materials are in an ultra-clean state in the processes of filling and using, and high-temperature steam reaches a reaction area at accurate flow and temperature, thereby realizing the high-quality doping of the rare earth.

The MCVD gas holder is a gas control system with the functions of caching, heat preservation, flow control, valve opening and the like for process gases such as SiCl 4/POCl 3/O2/He/SF 6 and the like;

the rare earth chelate high-temperature evaporation system increases the temperature by 150 ℃ and 250 ℃ to ensure that the rare earth chelate has certain saturated vapor pressure, and then the helium is conveyed to the interior of the liner tube through a high-temperature steam conveying pipeline;

the aluminum trichloride evaporation device is a crucible extending into the liner tube, the crucible is fixed on the high-temperature steam conveying pipeline, and the crucible can be made of high-purity quartz glass or high-purity aluminum oxide; a heating wire for heating is embedded in the crucible for heating the raw material in the crucible; the evaporation capacity of the aluminum trichloride can be controlled by adjusting the temperature in the crucible;

the high-temperature steam conveying pipeline is a rigid pipeline with heating and heat-preserving functions, a quartz glass tube or a stainless steel tube is arranged outside the high-temperature steam conveying pipeline, a high-temperature steam pipeline is arranged inside the high-temperature steam conveying pipeline, and a rotary sealing joint between the high-temperature steam conveying pipeline and the MCVD gas end is sealed by adopting O-ring in the deposition process.

Compared with the prior art, the invention has the following beneficial effects:

1. by adopting a rare earth chelate high-temperature evaporation system, higher rare earth saturated vapor pressure can be obtained at lower temperature, the complexity of evaporation equipment is reduced, and meanwhile, the doping concentration of rare earth can be accurately controlled;

2. by evaporating the aluminum trichloride in the extension tube, the deliquescence of the aluminum trichloride due to the absorption of water vapor can be reduced, the corrosion of the aluminum trichloride to equipment after the deliquescence can be avoided, and through accurate temperature control, the accurate doping of the aluminum trichloride is ensured, and the loss of the preform is reduced;

in conclusion, the gas phase doping method and the gas phase doping device of the invention carry out doping control by utilizing different physicochemical characteristics of different raw materials, can ensure that the rare earth and the co-doping agent raw materials are in an ultra-clean state during deposition, and high-temperature steam reaches a reaction region at accurate flow and temperature, thereby realizing high-quality doping of the rare earth.

Drawings

FIG. 1 is a schematic structural view of an apparatus for producing a rare-earth doped optical fiber according to an embodiment of the present invention;

fig. 2 is a graph showing the doping concentrations of NA and ytterbium ions of the prepared ytterbium-doped preform;

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

1-MCVD gas holder process gas 2-rare earth chelate high-temperature evaporation system 3-high-temperature steam delivery pipe 4-conventional gas input port 5-crucible fixing support 6-crucible with heating function 7-deposition liner tube 8-oxyhydrogen flame main lamp 9-tail gas discharge.

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 do not limit the invention.

As shown in fig. 1, an apparatus for preparing an ytterbium-doped preform comprises an MCVD gas holder, a rare earth chelate high-temperature evaporation system, an aluminum trichloride evaporation apparatus, etc.;

the MCVD gas holder temperature is set to be 40 +/-0.5 ℃, the flow rate of SiCl4 during core layer deposition is 300sccm, the POCl3 is 100sccm, the O2 is 2500sccm, and the He is 1500 sccm;

15g of Yb (thd) 3 is filled in the high-temperature evaporation system charging bucket, the temperature is set to be 200 ℃, and the flow rate of carrier gas helium in the core layer deposition process is set to be 500 sccm;

the aluminum trichloride evaporation device is an internal heating aluminum oxide crucible with the temperature set between 150-200 ℃, 10g of ultra-dry aluminum trichloride powder is placed in the crucible, and the temperature of the crucible is gradually increased from 150 ℃ to 200 ℃ along with the deposition of a core layer;

the preparation process comprises the following steps:

1. the raw materials and the temperature of the MCVD gas holder 1 and the rare earth chelate high-temperature evaporation system 2 meet the process requirements;

2. the MCVD equipment is initialized and cleaned, and the deposition lining pipe 7 is installed at the proper position of the air pump end and locked;

3. the conventional process gas is connected into a gas end through a gas inlet 4, a high-temperature steam conveying pipeline is inserted into a proper position of the gas end for rotary sealing and sealing, an aluminum trichloride evaporation crucible 6 is fixed on the conveying pipeline through a support 5, and aluminum trichloride powder is uniformly placed in the crucible;

4. and after the three steps are finished, introducing O2 with the flow rate of 3000sccm, He with the flow rate of 1000sccm and SF6 with the flow rate of 300sccm into the MCVD gas holder, controlling the pressure in the tube to be 100 +/-2 pa and the temperature to be 2000 ℃, carrying out core layer deposition, and fusing and shrinking the deposited tube into a solid preform.

The doping concentration of the prepared ytterbium-doped preform NA and ytterbium ions is shown in figure 2, wherein the fluctuation of the NA is less than 3%, the fluctuation of the concentration of the ytterbium ions along the axial direction is less than 3.5%, and the loss is less than 60dB/km @1383nm and less than 10 dB/km @1200nm through drawing into 10/130 optical fibers. Meanwhile, the yield of the prefabricated rod is improved by 10 percent compared with that of the prefabricated rod only adopting a high-temperature evaporation system.

It will be understood by those skilled in the art that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A doping device of a rare earth-doped optical fiber preform is characterized by comprising an MCVD gas holder, a rare earth chelate high-temperature evaporation system and an aluminum trichloride evaporation device; the MCVD gas holder is used for holding SiCl ₄ 、POCl ₃ 、 O ₂ 、 He 、SF ₆ Or the buffer storage, the heat preservation and the flow control of any combination of the gases are carried out, and the gases are input into the deposition liner;

the rare earth chelate high-temperature evaporation system can raise the temperature to 150-250 ℃ so that the rare earth chelate has certain saturated vapor pressure, and then helium is conveyed to the interior of the deposition liner tube through a high-temperature vapor conveying pipeline;

aluminium trichloride evaporation plant includes crucible fixed bolster, crucible and control crucible heating temperature's controller, and the inside heater strip that inlays of crucible, the heater strip is used for right the aluminium trichloride that the crucible is inside to be placed heats, the controller is through control the heating temperature of heater strip realizes right crucible heating temperature's control, the crucible is fixed the one end of crucible fixed bolster, this end stretches into in the deposit liner.

2. The doping apparatus for a rare-earth doped optical fiber preform according to claim 1, wherein the crucible is made of high purity quartz glass or high purity alumina.

3. The doping apparatus for a rare-earth doped optical fiber preform according to claim 1, wherein the high temperature vapor transmission tube is a rigid tube with heating and thermal insulation functions, the outer portion of the rigid tube is a quartz glass tube or a stainless steel tube, the inner portion of the rigid tube is a high temperature vapor transmission tube, and the high temperature vapor transmission tube and the gas transmission end of the MCVD device are sealed by O-ring.

4. A doping method of a rare earth-doped optical fiber preform using the apparatus of any one of claims 1 to 3, characterized by comprising the steps of:

s1, enabling the raw materials in the MCVD gas holder and the rare earth chelate high-temperature evaporation system to reach the required temperature;

s2, initializing and cleaning the MCVD equipment, and installing the deposition lining pipe at a proper position of the air pump end and locking;

s3, connecting the gas generated by the MCVD gas holder into the MCVD gas end through the gas input port, inserting the high-temperature steam delivery pipe into the proper position of the gas end rotary seal and sealing, and extending the aluminum trichloride evaporation crucible into the deposition liner pipe through the fixed support;

s4, introducing O with the flow rate of 3000sccm into the MCVD gas holder ₂ He at a flow rate of 1000sccm, SF at a flow rate of 300sccm ₆ The pressure in the deposition tube is controlled at 100 +/-2 pa, the temperature is 2000 ℃, the core layer deposition is carried out, and the core layer deposition is fused into a solid prefabricated rod after the deposition is finished.