CN114512885B - Rare earth doped optical fiber with optimized back bottom loss and preparation method thereof - Google Patents

Rare earth doped optical fiber with optimized back bottom loss and preparation method thereof Download PDF

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CN114512885B
CN114512885B CN202210188847.1A CN202210188847A CN114512885B CN 114512885 B CN114512885 B CN 114512885B CN 202210188847 A CN202210188847 A CN 202210188847A CN 114512885 B CN114512885 B CN 114512885B
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alkali metal
core layer
doped
oxide
optical fiber
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CN114512885A (en
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郑伟
汪松
雷高清
钟力
汪亨
袁飚
曹蓓蓓
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Yangtze Optical Fibre and Cable Co Ltd
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    • H—ELECTRICITY
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    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
    • H01S3/06729—Peculiar transverse fibre profile
    • H01S3/06733—Fibre having more than one cladding
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/24—Deposition of silicon only
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
    • C23C16/40—Oxides
    • C23C16/401—Oxides containing silicon
    • C23C16/402—Silicon dioxide
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
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Abstract

The invention provides a rare earth doped optical fiber with optimized back bottom loss, which comprises a core layer, a transition cladding layer and a pure silicon cladding layer which are sequentially arranged from inside to outside, wherein the core layer and the transition cladding layer are multi-element doped silicon dioxide layers; the doping material in the core layer comprises aluminum, ytterbium, phosphorus and one or more alkali metal elements; the average concentration of the alkali metal oxide doped in the core layer is 50ppm to 1000ppm when the doping concentration of the alkali metal element is calculated according to the oxide form; the doping material in the transition cladding comprises fluorine, phosphorus, and one or more alkali metal elements; the average concentration of the alkali metal element doped in the transition cladding is 500ppm to 300ppm according to the doping concentration of the alkali metal element calculated in the form of oxide; wherein the core layer and the transition cladding layer are doped with the same alkali metal element. The invention can form good viscosity matching between the core layer and the transitional cladding layer through the doping of alkali metal, reduces the defects and stress loss in the preparation of the optical fiber, and further optimizes the back-bottom loss of the rare earth doped optical fiber.

Description

Rare earth doped optical fiber with optimized back bottom loss and preparation method thereof
Technical Field
The invention relates to the technical field of optical fibers, in particular to a rare earth doped optical fiber with optimized back loss and a preparation method thereof.
Background
With the rapid development of optical fiber communication technology, the application range of optical fibers is more and more wide, and in recent years, the optical communication industry integrally presents a prosperous scene under the promotion of a series of favorable policies and plans such as 'broadband China strategy', 'optical improvement', 'speed-raising and cost-lowering', wherein the optical fibers are not only widely used in the conventional communication field, but also widely applied to industries such as consumer electronics, material processing and the like. The active rare earth doped optical fiber can be used as a key raw material in an optical fiber laser, and can also be used for manufacturing optical fiber communication devices such as optical amplifiers, wavelength conversion and the like.
At present, the mainstream preparation method of the rare earth doped preform is an improved chemical vapor deposition (MCVD), most research institutions and enterprises at home and abroad adopt a solution soaking method or chelate vapor evaporation method on the process platform to prepare the rare earth doped preform, but the two process routes are easy to generate the phenomena of rare earth ion clusters and chelate decomposition in the process of preparing the rare earth doped optical fiber, so that the intrinsic loss of the optical fiber is increased, and the light conversion efficiency of the optical fiber in a laser is affected.
Specifically, the existing rare earth doped fiber technology is basically based on product development and process research by an improved chemical vapor method, for example, patent CN104865634a mentions a double-cladding ytterbium doped fiber and a preparation method thereof, and the optimization of beam quality is mainly performed by adjusting the cladding structure of the fiber. The patent CN109031516a optimizes the refractive index distribution and doping distribution of the optical fiber core layer to improve the extraction efficiency of the fundamental mode, and obtain the laser output with high beam quality. Patent CN112764155A mentions that the application requirements of ytterbium-doped optical fibers under ultra-high power working conditions are met by designing an outer fluorine-doped cladding. Therefore, in the existing rare earth doped fiber design, the alkali chloride is very difficult to volatilize and dope on the MCVD platform process route, so that the rare earth doped fiber is rarely involved.
Disclosure of Invention
In order to meet the above defects or improvement demands of the prior art, the invention provides a rare earth doped optical fiber and a preparation method thereof, wherein the rare earth halide evaporation system and a plasma vapor deposition (PCVD) process are utilized to effectively dope alkali metal in the preparation process of an optical fiber preform, and the same alkali metal element doping is set in a core layer and a transitional cladding layer; thereby improving the viscosity matching of the cladding layer and the core layer of the preform, reducing the stress defect generated by the viscosity difference in the preparation process and reducing the back loss of the fiber core of the optical fiber.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a rare earth doped optical fiber with optimized back loss, comprising a core layer, a transition cladding layer and a pure silicon cladding layer sequentially arranged from inside to outside, wherein the core layer and the transition cladding layer are both multiple doped silica layers;
The doping material in the core layer comprises aluminum, ytterbium, phosphorus and one or more alkali metal elements; the doping concentration of the alkali metal element is calculated according to the oxide form, and the average concentration of the alkali metal oxide doped in the core layer is 50ppm to 1000ppm;
The doping materials in the transition cladding comprise chlorine, fluorine, phosphorus, other halogens and one or more alkali metal elements; the doping concentration of the alkali metal element is calculated according to the oxide form, and the average concentration of the alkali metal oxide doped in the transition cladding is 50 ppm-300 ppm;
Wherein the core layer is the same as the alkali metal element doped in the transition cladding layer.
Further, in the core layer:
The doping concentration of the aluminum element is calculated in the form of Al 2O3, and the average concentration of the doped Al 2O3 is 6000ppm to 40000ppm;
the doping concentration of ytterbium element is calculated according to Yb 2O3, and the average concentration of doped Yb 2O3 is 1000ppm to 5000ppm;
The doping concentration of the phosphorus element is calculated in the form of P 2O5, and the average concentration of doped P 2O5 is 10000ppm to 60000ppm.
Further, in the transition cladding:
The doping concentration of the aluminum element is calculated in the form of Al 2O3, and the average concentration of the doped Al 2O3 is 1000ppm to 3000ppm;
the doping concentration of the phosphorus element is calculated in the form of P 2O5, and the average concentration of the doped P 2O5 is 1300ppm to 20000ppm.
Further, the alkali metal element is at least one of Li, na, K, rb or Cs.
Further, the relative refractive index difference delta n1 of the core layer is 0.05% -0.3%, and the radius R1 is 5-50 um; the relative refractive index difference delta n2 of the transition cladding is-0.3% -0.1%, and the radius R2 is 6 um-150 um.
Further, the radius R3 of the pure silicon cladding is 50-185 um.
Further, the fiber has a core loss of less than 5dB/km at a wavelength of 1200 nm.
Further, the optical conversion efficiency eta of the optical fiber is more than or equal to 77 percent.
According to a second aspect of the present invention, there is provided a method for preparing a rare earth doped optical fiber with optimized back loss, the rare earth doped optical fiber comprising a core layer, a transition cladding layer and a pure silicon cladding layer sequentially arranged from inside to outside, wherein the core layer and the transition cladding layer are both multiple doped silica layers; wherein the method comprises the following steps:
Adopting a rare earth halide evaporation system and combining a PCVD process to prepare the core layer; the doping material in the core layer comprises aluminum, ytterbium, phosphorus and one or more alkali metal elements; the doping concentration of the alkali metal element is calculated according to the oxide form, and the average concentration of the alkali metal oxide doped in the core layer is 100ppm to 1000ppm;
Adopting a rare earth halide evaporation system and combining a PCVD process to prepare the transition cladding; the doping material in the transition cladding comprises fluorine, phosphorus and the doping concentration of one or more alkali metal elements, wherein the doping concentration of the alkali metal elements in the transition cladding is calculated according to the oxide form, and the average doping concentration of the alkali metal elements in the transition cladding is 100 ppm-300 ppm.
Further, the alkali metal element is at least one of Li, na, K, rb or Cs.
In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:
Firstly, the invention utilizes a plasma vapor deposition (PCVD) process and a matched high-temperature rare earth feeding system to dope alkali metal, aluminum, phosphorus and rare earth elements in a core layer and a cladding layer of the optical fiber preform, so that the core layer and the cladding layer form good viscosity matching. Secondly, the invention improves the stress defect in the rare earth doped optical fiber through the doping of alkali metal, thereby optimizing the core back loss of the optical fiber and improving the light conversion efficiency of the optical fiber in a laser. Thirdly, the same alkali metal element doping is set in the core layer and the transitional cladding layer, so that concentration difference diffusion caused by doping of different elements between the core layer and the transitional cladding layer can be effectively reduced, movement of alkali metal ions is reduced, attenuation of the optical fiber is lower, performance of the optical fiber is stable, and the optical fiber has longer service life.
Drawings
FIG. 1 is a line sweep of elements for core doping in accordance with the present invention to achieve example 1;
fig. 2 is a schematic view of a refractive index profile of an optical fiber according to embodiment 1 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
It should be noted that, in the function equations related to the present invention, the symbol "×" is the operation symbol representing the multiplication of the two constants or vectors before and after, and "/" is the operation symbol representing the division of the two constants or vectors before and after, and all the function equations in the present invention follow the mathematical addition, subtraction, multiplication and division algorithm.
The following are definitions and illustrations of some of the attributes involved in the present invention:
The central part of the cross section of the optical fiber is defined as a fiber core layer according to the change of the refractive index, the annular area of the optical fiber, which is close to the core layer, is a transitional cladding layer, and the annular area of the pure silicon dioxide, which is close to the transitional cladding layer, is a pure silicon cladding layer.
Ppm: parts per million by weight.
Relative refractive index difference:
Numerical aperture:
Where n i is the refractive index corresponding to the different deposited layers and n 0 is the refractive index of pure SiO 2.
The invention provides a rare earth doped optical fiber, which comprises a core layer, a transition cladding layer and a pure silicon cladding layer which are sequentially arranged from inside to outside, wherein the core layer and the transition cladding layer are multi-element doped silicon dioxide layers; specifically, the doping material in the core layer includes aluminum, ytterbium, phosphorus, and one or more alkali metal elements; the doping material in the transition cladding comprises fluorine, phosphorus, and one or more alkali metal elements; the invention can effectively improve the stress defect in the rare earth doped optical fiber through the doping of alkali metal, thereby optimizing the core back loss of the optical fiber and improving the light conversion efficiency of the optical fiber in a laser.
Specifically, the doping concentration of the alkali metal element is calculated according to the oxide form, and the average concentration of the alkali metal oxide doped in the core layer is 50ppm to 1000ppm; preferably 100ppm, because an appropriate amount of alkali metal doping can effectively reduce structural defects generated in the core rod deposition, and if the doping concentration is too high, the refractive index is adversely affected.
Specifically, the average concentration of the alkali metal element doped in the transition cladding is 50ppm to 300ppm, calculated according to the oxide form of the alkali metal element; preferably 150-300ppm, in order to reduce the concentration difference between the core and the cladding and to reduce concentration diffusion between the core/cladding. Specifically, the core layer is the same as the alkali metal element doped in the transition cladding layer. The invention can effectively reduce concentration difference diffusion caused by doping different elements between the core layer and the transitional cladding layer by setting the same alkali metal element doping in the core layer and the transitional cladding layer, reduce the movement of alkali metal ions, lower the attenuation of the optical fiber, stabilize the optical fiber performance and prolong the service life.
More specifically, the alkali metal element is at least one of Li, na, K, rb or Cs, preferably K. The doping of alkali metal in the core layer and the transitional cladding layer is mainly carried out by transmitting the raw material gas of the alkali metal source compound into a quartz liner tube of a PCVD lathe for deposition, and the concentration of the alkali metal doping is controlled by adjusting the flow rate of carrier gas entering the material by using a mass flowmeter. The alkali metal source compound is alkali metal halide or other alkali metal salt compound, and halogen comprises F, cl, br, I, at.
The invention provides a rare earth doped optical fiber with optimized back bottom loss, which comprises the following core layers:
The doping concentration of the aluminum element is calculated in the form of Al 2O3, and the average concentration of the doped Al 2O3 is 6000ppm to 40000ppm; preferably 13000-20000 ppm.
The doping concentration of ytterbium element is calculated according to Yb 2O3, and the average concentration of doped Yb 2O3 is 1000ppm to 5000ppm; preferably 24000 to 35000ppm.
The doping concentration of the phosphorus element is calculated in the form of P 2O5, and the average concentration of doped P 2O5 is 10000ppm to 60000ppm; preferably 20000 to 38000ppm.
The invention provides a rare earth doped optical fiber, which is characterized in that:
The doping concentration of the aluminum element is calculated in the form of Al 2O3, and the average concentration of the doped Al 2O3 is 1000ppm to 3000ppm; preferably 1500 to 3000ppm.
The doping concentration of the phosphorus element is calculated in the form of P 2O5, and the average concentration of doped P 2O5 is 1300ppm to 20000ppm; preferably 1300 to 4200ppm.
The invention provides a rare earth doped optical fiber with optimized back bottom loss, wherein the relative refractive index difference delta n1 of a core layer is 0.05% -0.3%, and the radius R1 is 5 um-50 um; the relative refractive index difference delta n2 of the transition cladding is-0.3% -0.1%, and the radius R2 is 6 um-150 um; the radius R3 of the pure silicon cladding is 50 um-185 um.
The invention provides a rare earth doped optical fiber with optimized back bottom loss, the core loss of the optical fiber at 1200nm wavelength is less than 5dB/km, and the optical conversion efficiency eta of the optical fiber is more than or equal to 77%. The invention improves the stress defect in the rare earth doped optical fiber through the doping of alkali metal, thereby optimizing the core back bottom loss of the optical fiber and improving the light conversion efficiency of the optical fiber in a laser.
The invention provides a preparation method of a rare-earth doped optical fiber with optimized back-to-back loss, which comprises a core layer, a transition cladding layer and a pure silicon cladding layer which are sequentially arranged from inside to outside, wherein the core layer and the transition cladding layer are multi-element doped silicon dioxide layers; the method comprises the following steps:
adopting a rare earth halide evaporation system and combining a PCVD process to prepare a core layer; the doping material in the core layer comprises aluminum, ytterbium, phosphorus and one or more alkali metal elements; the average concentration of the alkali metal oxide doped in the core layer is 100ppm to 1000ppm when the doping concentration of the alkali metal element is calculated according to the oxide form;
Adopting a rare earth halide evaporation system and combining a PCVD process to prepare a transitional cladding; the doping material in the transition cladding comprises fluorine, phosphorus, and the doping concentration of one or more alkali metal elements, calculated as oxides thereof, the average concentration of the alkali metal elements doped in the transition cladding is 100ppm to 300ppm.
Specifically, the rare earth halide evaporation system adopted by the invention comprises a heating device, a storage device for loading raw materials and a conveying device for conveying raw material compounds, wherein the conveying device is connected with a PCVD lathe. The heating device is used for heating the raw material chemical compound in the storage device to the evaporation temperature, and transmitting the raw material chemical compound steam into a quartz liner tube of the PCVD lathe through the material conveying device, and controlling the rare earth doping concentration by adjusting the carrier gas flow entering the storage device through the mass flowmeter. Wherein silicon tetrachloride is used as a raw material compound of the matrix material silicon dioxide, and the flow rate of the silicon tetrachloride is 500ml/min. The phosphorus doping material uses phosphorus oxychloride as a raw material compound, and the flow rate of the phosphorus oxychloride is 50-100ml/min; aluminum chloride is used as a raw material compound, and the flow rate of the aluminum chloride is 20ml/min; ytterbium chloride is used as a raw material compound, and the flow rate of aluminum chloride is 10m/min. The O2 flow rate was 1500ml/min.
More specifically, the alkali metal element is at least one of Li, na, K, rb or Cs, preferably K. The doping of alkali metal in the core layer and the transitional cladding layer is mainly carried out by transmitting the raw material gas of the alkali metal source compound into a quartz liner tube of a PCVD lathe for deposition, and the concentration of the alkali metal doping is controlled by adjusting the flow rate of carrier gas entering the material by using a mass flowmeter. The alkali metal source compound is alkali metal halide or other alkali metal salt compound, and halogen comprises F, cl, br, I, at. The flow rate of the alkali metal source compound was 10m/min.
The invention is described in further detail below with reference to the drawings and examples.
In examples 1 to 8 and comparative examples 1 and 2, the rare earth doped optical fiber of the present invention comprises a core layer and a cladding layer, wherein the radius of the core layer is R1, the relative refractive index difference of the core layer is Deltan 1, the core layer is a transition cladding layer and a pure silicon cladding layer in sequence from inside to outside, the radius of the transition cladding layer is R2, the relative refractive index difference is Deltan 2, and the radius of the pure silicon cladding layer is R3.
In examples 1 to 8 and comparative examples 1 and 2, the rare earth doped optical fiber of the present invention was produced with a flow rate of 500ml/min for silicon tetrachloride, 50 to 100ml/min for phosphorus oxychloride, 1500ml/min for O 2, 20ml/min for aluminum chloride, and 10m/min for carrier gases for rare earth compounds and alkali metals.
Example 1
The optical fiber comprises aluminum oxide, ytterbium oxide, phosphorus oxide and alkali metal oxide in the core layer, wherein the aluminum oxide (Al 2O3) in the core layer has the doping concentration of 13000ppm, the ytterbium oxide (Yb 2O3) has the doping concentration of 2400ppm, the phosphorus oxide (P 2O5) has the doping concentration of 20000ppm, the alkali metal oxide (K 2 O) has the content of 100ppm, the radius R1 of the optical fiber core layer is 15um, the relative refractive index difference of the core layer is 0.095%, the transition cladding layer comprises aluminum oxide, phosphorus oxide and alkali metal oxide and has the similar uniform distribution, the aluminum oxide (Al 2O3) in the cladding layer has the doping concentration of 1500ppm, the phosphorus oxide (P 2O5) has the doping concentration of 1600ppm, the alkali metal oxide (K 2 O) has the content of 50ppm, the radius R2 of the cladding layer has the radius of 60um, the cladding layer has the relative refractive index difference of delta n2 of-0.02%, the pure silicon cladding layer has the radius of 50um, and the fiber core loss at 1200nm is 2.4/dB.
Example 2
The optical fiber comprises aluminum oxide, ytterbium oxide, phosphorus oxide, fluorine oxide and alkali metal oxide which are approximately uniformly distributed, wherein the doping concentration of aluminum oxide (Al 2O3) in the core layer is 15000ppm, the doping concentration of ytterbium oxide (Yb 2O3) is 2500ppm, the doping concentration of phosphorus oxide (P 2O5) is 30000ppm, the content of alkali metal oxide (K 2 O) is 50ppm, the radius R1 of the optical fiber core layer is 10um, the relative refractive index difference of the core layer is 0.08 percent, the transition cladding layer comprises aluminum oxide, phosphorus oxide and alkali metal oxide and is approximately uniformly distributed, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 1000ppm, the doping concentration of phosphorus oxide (P 2O5) is 1300ppm, the content of alkali metal oxide (K 2 O) is 100ppm, the radius R2 of the cladding layer is 40um, the relative refractive index difference of the cladding layer is-0.1 percent, the radius of the pure silicon cladding layer is 150um, and the core loss of the optical fiber at 1200nm is 3.3dB/km.
Example 3
The optical fiber comprises aluminum oxide, ytterbium oxide, phosphorus oxide, fluorine oxide and alkali metal oxide which are approximately uniformly distributed, wherein the doping concentration of aluminum oxide (Al 2O3) in the core layer is 20000ppm, the doping concentration of ytterbium oxide (Yb 2O3) is 3500ppm, the doping concentration of phosphorus oxide (P 2O5) is 38000ppm, the content of alkali metal oxide (K 2 O) is 200ppm, the radius R1 of the optical fiber core layer is 18um, the relative refractive index difference of the core layer is 0.138 percent, the transition cladding layer comprises aluminum oxide, phosphorus oxide and alkali metal oxide and is approximately uniformly distributed, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 3000ppm, the doping concentration of phosphorus oxide (P 2O5) is 4200ppm, the content of alkali metal oxide (K 2 O) is 150ppm, the radius R2 of the cladding layer is 62um, the relative refractive index difference of the cladding layer is-0.1 percent, the radius of the pure silicon cladding layer is 185um, and the core loss of the optical fiber at 1200nm is 4.7 dB/dB.
Example 4
The optical fiber comprises aluminum oxide, ytterbium oxide, phosphorus oxide, fluorine oxide and alkali metal oxide in the core layer, wherein the aluminum oxide (Al 2O3) in the core layer has a doping concentration of 6000ppm, the ytterbium oxide (Yb 2O3) in the core layer has a doping concentration of 2400ppm, the phosphorus oxide (P 2O5) in the core layer has a doping concentration of 60000ppm, the alkali metal oxide (Li 2 O) in the core layer has a content of 100ppm, the radius R1 of the optical fiber core layer is 10um, the relative refractive index difference of the core layer is deltan 1 of 0.078%, the transition cladding layer comprises aluminum oxide, phosphorus oxide and alkali metal oxide in the transition cladding layer and has an approximate uniform distribution, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 1000ppm, the phosphorus oxide (P 2O5) in the core layer has a doping concentration of 1600ppm, the alkali metal oxide (Li 2 O) in the core layer has a doping concentration of 100ppm, the radius R2 of the cladding layer has a refractive index difference of deltan 2 of-0.1%, the pure silicon cladding layer has a radius of 150um, and the core loss of 4.2/dB at 1200 nm.
Example 5
The optical fiber core layer comprises aluminum oxide, ytterbium oxide, phosphorus oxide, fluorine oxide and alkali metal oxide, and the oxides are approximately uniformly distributed, wherein the doping concentration of aluminum oxide (Al 2O3) in the core layer is 40000ppm, the doping concentration of ytterbium oxide (Yb 2O3) is 2400ppm, the doping concentration of phosphorus oxide (P 2O5) is 10000ppm, the content of alkali metal oxide (Na 2 O) is 100ppm, the radius R1 of the optical fiber core layer is 10um, the relative refractive index difference of the core layer is 0.08 percent, the transition cladding layer comprises aluminum oxide, phosphorus oxide and alkali metal oxide and is approximately uniformly distributed, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 1000ppm, the doping concentration of phosphorus oxide (P 2O5) is 10000ppm, the content of alkali metal oxide (Na 2 O) is 100ppm, the radius R2 of the cladding layer is 41um, the relative refractive index difference of the cladding layer is-0.1 percent, the radius of the pure silicon cladding layer is 185um, and the core loss of the optical fiber at 1200nm is 5.2 dB/dB.
Example 6
The optical fiber comprises aluminum oxide, ytterbium oxide, phosphorus oxide, fluorine oxide and alkali metal oxide which are approximately uniformly distributed, wherein the doping concentration of aluminum oxide (Al 2O3) in the core layer is 13000ppm, the doping concentration of ytterbium oxide (Yb 2O3) is 2400ppm, the doping concentration of phosphorus oxide (P 2O5) is 20000ppm, the content of alkali metal oxide (Rb 2 O) is 100ppm, the radius R1 of the optical fiber core layer is 15um, the relative refractive index difference of the core layer is 0.093%, the transition cladding layer comprises aluminum oxide, phosphorus oxide and alkali metal oxide and is approximately uniformly distributed, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 3000ppm, the doping concentration of phosphorus oxide (P 2O5) is 4200ppm, the content of alkali metal oxide (Rb 2 O) is 50ppm, the radius R2 of the cladding layer is 60um, the relative refractive index difference of the cladding layer is-0.02%, the radius of the pure silicon cladding layer is 50um, and the core loss of the optical fiber at 1200nm is 3.9 dB/dB.
Example 7
The optical fiber core layer comprises aluminum oxide, ytterbium oxide, phosphorus oxide, fluorine oxide and alkali metal oxide, and the oxides are approximately uniformly distributed, wherein the doping concentration of aluminum oxide (Al 2O3) in the core layer is 15000ppm, the doping concentration of ytterbium oxide (Yb 2O3) is 2400ppm, the doping concentration of phosphorus oxide (P 2O5) is 30000ppm, the content of alkali metal oxide (Cs 2 O) is 100ppm, the radius R1 of the optical fiber core layer is 14.8um, the relative refractive index difference of the core layer is deltan 1 and is 0.097%, the transition cladding layer comprises aluminum oxide, phosphorus oxide and alkali metal oxide and is approximately uniformly distributed, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 1500ppm, the doping concentration of phosphorus oxide (P 2O5) is 1600ppm, the content of alkali metal oxide (Cs 2 O) is 50ppm, the radius R2 of the cladding layer is 60um, the relative refractive index difference of deltan 2 is-0.02%, the radius of pure silicon cladding layer is 50um, and the core loss of the optical fiber at 1200nm is 5.8 dB/dB.
Example 8
The optical fiber comprises aluminum oxide, ytterbium oxide, phosphorus oxide, fluorine oxide and alkali metal oxide which are approximately uniformly distributed, wherein the doping concentration of aluminum oxide (Al 2O3) in the core layer is 20000ppm, the doping concentration of ytterbium oxide (Yb 2O3) is 5000ppm, the doping concentration of phosphorus oxide (P 2 O5) is 38000ppm, the content of alkali metal oxide (K 2 O) is 1000ppm, the radius R1 of the optical fiber core layer is 18um, the relative refractive index difference of the core layer is 0.182 percent, the transition cladding layer comprises aluminum oxide, phosphorus oxide and alkali metal oxide and is approximately uniformly distributed, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 1000ppm, the doping concentration of phosphorus oxide (P 2O5) is 20000ppm, the content of alkali metal oxide (K 2 O) is 300ppm, the radius R2 of the cladding layer is 62um, the relative refractive index difference of the cladding layer is-0.1 percent, the pure silicon radius of the cladding layer is 185um, and the core loss of the optical fiber at 1200nm is 9 dB/dB.
Comparative example 1
The optical fiber core layer comprises aluminum oxide, ytterbium oxide and phosphorus oxide, wherein the doping concentration of aluminum oxide (Al 2O3) is 13000ppm, the doping concentration of ytterbium oxide (Yb 2O3) is 2400ppm, the doping concentration of phosphorus oxide (P 2O5) is 20000ppm, the radius R1 of the optical fiber core layer is 15um, the relative refractive index difference of the core layer is delta n 1 and is 0.093%, the transition cladding layer comprises aluminum oxide and phosphorus oxide doping, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 1440ppm, the doping concentration of phosphorus oxide (P 2O5) is 1600ppm, the radius R2 of the cladding layer is 60um, the relative refractive index difference of the cladding layer is delta n 2 to be-0.02%, the radius of the pure silicon cladding layer is 50um, and the core loss of the optical fiber at 1200nm is 16dB/km.
Comparative example 2
The optical fiber core layer comprises aluminum oxide, ytterbium oxide and phosphorus oxide, wherein the doping concentration of aluminum oxide (Al 2O3) is 15000ppm, the doping concentration of ytterbium oxide (Yb 2O3) is 2500ppm, the doping concentration of phosphorus oxide (P 2O5) is 30000ppm, the radius R1 of the optical fiber core layer is 10um, the relative refractive index difference of the core layer is deltan 1 and is 0.082 percent, the transition cladding layer comprises aluminum and phosphorus oxide doping, the doping concentration of aluminum oxide (Al 2O3) in the cladding layer is 1000ppm, the doping concentration of phosphorus oxide (P 2O5) is 1300ppm, the radius R2 of the cladding layer is 40um, the relative refractive index difference of the cladding layer is deltan 2 to be-0.1 percent, the radius of the pure silicon cladding layer is 150um, and the fiber core loss of the optical fiber at 1200nm is 13dB/km.
Tables 1 and 2 show doping elements, doping concentration ranges, physical parameters and performance of the rare earth doped optical fibers prepared in examples 1 to 8 and comparative examples 1 and 2. Wherein the doping concentration of the aluminum element is calculated according to the Al 2O3 form, the doping concentration of the ytterbium element is calculated according to the Yb 2O3 form, the doping concentration of the phosphorus element is calculated according to the P 2O5 form, and the doping concentration of the alkali metal element is calculated according to the oxide form.
TABLE 1 doping element and doping concentration ranges for rare earth doped fibers
TABLE 2 physical parameters and Properties of rare-earth doped fiber
Fig. 1 is a line scan of the core doped element in embodiment 1 of the present invention, and fig. 2 is a schematic view of the refractive index profile of the optical fiber in embodiment 1 of the present invention. From tables 1 to 2 and figures 1 to 2, it is apparent that the rare earth doped optical fiber prepared by the present invention has a uniform distribution of doping elements, and has a low core loss of 1200nm due to doping of alkali metal, and a high light conversion efficiency. Therefore, the invention improves the stress defect in the rare earth doped optical fiber through the doping of alkali metal, thereby optimizing the core back loss of the optical fiber and improving the light conversion efficiency of the optical fiber in the laser.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (4)

1. The rare earth doped optical fiber with optimized back bottom loss is characterized by comprising a core layer, a transition cladding layer and a pure silicon cladding layer which are sequentially arranged from inside to outside, wherein the core layer and the transition cladding layer are both multi-element doped silicon dioxide layers; the fiber core loss of the optical fiber at the wavelength of 1200nm is less than 5dB/km;
the doping material in the core layer comprises aluminum, ytterbium, phosphorus and one or more alkali metal elements; the doping concentration of the alkali metal element is calculated according to the oxide form, and the average concentration of the alkali metal oxide doped in the core layer is 50ppm to 1000ppm; the relative refractive index difference delta n1 of the core layer is 0.05% -0.3%, and the radius R1 is 5-50 um;
the doping material in the transition cladding comprises aluminum, phosphorus and one or more alkali metal elements; the doping concentration of the alkali metal element is calculated according to the oxide form, and the average concentration of the alkali metal oxide doped in the transition cladding is 50 ppm-300 ppm; the relative refractive index difference delta n2 of the transition cladding is-0.3% -0.1%, and the radius R2 is 6 um-150 um;
Wherein the core layer is the same as the alkali metal element doped in the transition cladding layer, and the alkali metal element is at least one of Li, na, K, rb or Cs;
In the core layer:
The doping concentration of the aluminum element is calculated in the form of Al 2O3, and the average concentration of the doped Al 2O3 is 6000ppm to 40000ppm;
the doping concentration of ytterbium element is calculated according to Yb 2O3, and the average concentration of doped Yb 2O3 is 1000ppm to 5000ppm;
the doping concentration of the phosphorus element is calculated in the form of P 2O5, and the average concentration of doped P 2O5 is 10000ppm to 60000ppm;
In the transition cladding:
The doping concentration of the aluminum element is calculated in the form of Al 2O3, and the average concentration of the doped Al 2O3 is 1000ppm to 3000ppm;
the doping concentration of the phosphorus element is calculated in the form of P 2O5, and the average concentration of the doped P 2O5 is 1300ppm to 20000ppm.
2. The back-loss optimized rare-earth doped fiber of claim 1, wherein said pure silicon cladding radius R3 is 50um to 185um.
3. The back-loss optimized rare-earth doped fiber according to claim 1, wherein the optical conversion efficiency η of the fiber is equal to or greater than 77%.
4. A method for preparing a rare earth doped optical fiber with optimized back loss according to any one of claims 1-3, wherein the rare earth doped optical fiber comprises a core layer, a transition cladding layer and a pure silicon cladding layer which are sequentially arranged from inside to outside, and the core layer and the transition cladding layer are both multi-doped silicon dioxide layers; wherein the method comprises the following steps:
Adopting a rare earth halide evaporation system and combining a PCVD process to prepare the core layer; the doping material in the core layer comprises aluminum, ytterbium, phosphorus and one or more alkali metal elements; the doping concentration of the alkali metal element is calculated according to the oxide form, and the average concentration of the alkali metal oxide doped in the core layer is 100ppm to 1000ppm; the relative refractive index difference delta n1 of the core layer is 0.05% -0.3%, and the radius R1 is 5-50 um;
Adopting a rare earth halide evaporation system and combining a PCVD process to prepare the transition cladding; the doping material in the transition cladding comprises aluminum, phosphorus and one or more alkali metal elements, wherein the doping concentration of the alkali metal elements is calculated according to the oxide form of the doping material, and the average doping concentration of the alkali metal elements in the transition cladding is 100 ppm-300 ppm; the relative refractive index difference delta n2 of the transition cladding is-0.3% -0.1%, and the radius R2 is 6 um-150 um;
wherein the core layer is the same as the alkali metal element doped in the transition cladding layer; the alkali metal element is at least one of Li, na, K, rb or Cs.
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