CN114637068B - Gain-balanced few-mode erbium-doped optical fiber and preparation method thereof - Google Patents
Gain-balanced few-mode erbium-doped optical fiber and preparation method thereof Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 65
- 238000002360 preparation method Methods 0.000 title abstract description 17
- 239000012792 core layer Substances 0.000 claims abstract description 115
- 238000005253 cladding Methods 0.000 claims abstract description 98
- 239000010410 layer Substances 0.000 claims abstract description 89
- 239000000835 fiber Substances 0.000 claims abstract description 61
- 229910052691 Erbium Inorganic materials 0.000 claims abstract description 51
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 51
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 28
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 20
- 238000013461 design Methods 0.000 claims abstract description 7
- -1 erbium ions Chemical class 0.000 claims description 39
- 238000000034 method Methods 0.000 claims description 36
- 239000002994 raw material Substances 0.000 claims description 21
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical compound [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 claims description 20
- 239000011247 coating layer Substances 0.000 claims description 19
- 239000007789 gas Substances 0.000 claims description 17
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 17
- 150000002910 rare earth metals Chemical class 0.000 claims description 15
- 239000010453 quartz Substances 0.000 claims description 11
- VXEGSRKPIUDPQT-UHFFFAOYSA-N 4-[4-(4-methoxyphenyl)piperazin-1-yl]aniline Chemical compound C1=CC(OC)=CC=C1N1CCN(C=2C=CC(N)=CC=2)CC1 VXEGSRKPIUDPQT-UHFFFAOYSA-N 0.000 claims description 10
- 239000002019 doping agent Substances 0.000 claims description 10
- 239000005049 silicon tetrachloride Substances 0.000 claims description 10
- 239000011248 coating agent Substances 0.000 claims description 9
- 238000000576 coating method Methods 0.000 claims description 9
- HDGGAKOVUDZYES-UHFFFAOYSA-K erbium(iii) chloride Chemical compound Cl[Er](Cl)Cl HDGGAKOVUDZYES-UHFFFAOYSA-K 0.000 claims description 7
- 230000008020 evaporation Effects 0.000 claims description 7
- 238000001704 evaporation Methods 0.000 claims description 7
- 238000005491 wire drawing Methods 0.000 claims description 7
- 229910052782 aluminium Inorganic materials 0.000 claims description 6
- 229910052732 germanium Inorganic materials 0.000 claims description 6
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims description 6
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 229910052698 phosphorus Inorganic materials 0.000 claims description 6
- 239000011574 phosphorus Substances 0.000 claims description 6
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 5
- 229910052731 fluorine Inorganic materials 0.000 claims description 5
- 239000011737 fluorine Substances 0.000 claims description 5
- 239000012159 carrier gas Substances 0.000 claims description 4
- 238000005245 sintering Methods 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 4
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims 1
- 238000005498 polishing Methods 0.000 claims 1
- 230000000694 effects Effects 0.000 abstract description 9
- 230000001105 regulatory effect Effects 0.000 abstract description 9
- 238000005516 engineering process Methods 0.000 abstract description 5
- 239000000463 material Substances 0.000 description 11
- 150000002500 ions Chemical class 0.000 description 8
- 230000005540 biological transmission Effects 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 7
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 238000007740 vapor deposition Methods 0.000 description 4
- ALIHRPTZFUJDPJ-UHFFFAOYSA-N [P].[Ge].[Si] Chemical compound [P].[Ge].[Si] ALIHRPTZFUJDPJ-UHFFFAOYSA-N 0.000 description 3
- 238000004891 communication Methods 0.000 description 3
- 238000005086 pumping Methods 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- VSCWAEJMTAWNJL-UHFFFAOYSA-K aluminium trichloride Chemical compound Cl[Al](Cl)Cl VSCWAEJMTAWNJL-UHFFFAOYSA-K 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000012938 design process Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- WMIYKQLTONQJES-UHFFFAOYSA-N hexafluoroethane Chemical compound FC(F)(F)C(F)(F)F WMIYKQLTONQJES-UHFFFAOYSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- XHXFXVLFKHQFAL-UHFFFAOYSA-N phosphoryl trichloride Chemical compound ClP(Cl)(Cl)=O XHXFXVLFKHQFAL-UHFFFAOYSA-N 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000171 quenching effect Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 239000013598 vector Substances 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- IEXRMSFAVATTJX-UHFFFAOYSA-N tetrachlorogermane Chemical compound Cl[Ge](Cl)(Cl)Cl IEXRMSFAVATTJX-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01853—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
- C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
- C03B37/027—Fibres composed of different sorts of glass, e.g. glass optical fibres
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02042—Multicore optical fibres
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
- G02B6/03605—Highest refractive index not on central axis
- G02B6/03611—Highest index adjacent to central axis region, e.g. annular core, coaxial ring, centreline depression affecting waveguiding
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
- G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
- G02B6/03688—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 5 or more layers
Abstract
The invention provides a gain balanced few-mode erbium-doped optical fiber and a preparation method thereof, wherein the optical fiber sequentially comprises a fiber core, an inner cladding and an outer cladding from inside to outside, the fiber core is a silicon dioxide layer with different bait doping concentrations, and the fiber core comprises a circular core layer positioned in the central area of the fiber core, and a first annular core layer and a second annular core layer which are sequentially wrapped on the periphery of the circular core layer; the bait doping concentrations of the circular core layer, the first annular core layer and the second annular core layer are a1, a2 and a3 respectively, and then the relation is satisfied: a2 < a1, a2 < a3; the refractive indexes of the circular core layer, the first annular core layer and the second annular core layer are n1, n2 and n3 respectively, and then the relation is satisfied: n2 > n3 > n1. According to the invention, by matching with different refractive index profile designs, the PCVD technology is utilized to effectively regulate and control the erbium ion doping concentration in the preparation process of the fiber core, so that the accuracy control difficulty of the erbium ion doping concentration is reduced, the overlapping degree of a signal light field and erbium ion is regulated and controlled, and the effect of mode gain balance is achieved.
Description
Technical Field
The invention relates to the technical field of optical fiber communication, in particular to a gain equalization few-mode erbium-doped optical fiber and a preparation method thereof.
Background
The transmission capacity of a single common silica fiber has grown rapidly from nineties every twenty-century at a rate of about ten times every four years. The transmission capacity of the common single mode fiber (Single mode fiber, SMF) can reach 100Tbit/s, which is close to the transmission limit of shannon's theorem, but is insufficient to meet the capacity requirement of the exponential growth of data transmission in the current information society. In order to solve the problem of future communication capacity expansion, the technical bottleneck of the existing optical fiber communication is broken through, and the few-mode optical fiber can transmit a plurality of modes in one optical fiber, so that the transmission capacity of a single optical fiber is greatly improved, and the few-mode optical fiber becomes a subject front edge and a research hot spot.
In a few-mode erbium-doped fiber amplifier, the gain difference obtained in different modes determines the quality of the transmission signal and the stability of the system. Therefore, the mode gain equalization becomes a key indicator for measuring the performance of the few-mode transmission system. Currently, there are three main strategies to adjust the gain difference between different modes: adjusting the refractive index profile of the fiber, optimizing the pumping regime, and improving the rare earth ion doping profile. Research shows that the ideal effect is difficult to achieve by optimizing the pumping mode only, and the gain balance is realized by optimizing the refractive index profile and the rare earth ion doping profile of the optical fiber. Based on the method, chinese patent publication No. CN112180499A (publication No. 2021-01-05) discloses a three-layer core multi-layer erbium-doped ion 4-mode optical fiber with extremely small gain difference, and the invention provides a multi-layer core doped optical fiber structure design for realizing mode gain balance. Erbium ions with different concentrations are doped in the multilayer cores respectively, the doping concentration ratio of the erbium ions in different core layers is 1:0.9119:1.3447, the overlapping degree of a signal light field and the erbium ions is regulated and controlled, and the mode gain difference is reduced. Chinese patent publication No. CN113341499a (publication No. 2021-09-03) discloses another gain balanced few-mode erbium fiber with single-core structure and multi-layer erbium ion doping, which performs layered doping on the fiber core to obtain erbium-doped layers with different erbium-doped concentrations; the erbium-doped layer comprises a first erbium-doped layer and a second erbium-doped layer; wherein: the first erbium-doped layer is positioned in the center of the fiber core; the second erbium-doped layer surrounds the first erbium-doped layer; the body of the second erbium doped layer is located on the core and partially incorporates the cladding. The doping concentration ratio of erbium ions of different core layers is 1.05:1 to 1.25:1, the erbium ion distribution outside the core of the second erbium-doped layer can be better overlapped with a high-order mode, the overlapping integral of the optical field and the erbium ions between the modes is reduced, and then similar gain effects are generated for each mode, so that the mode gain difference is effectively reduced, and a good mode gain balancing effect is achieved. However, from the viewpoint of preparation, erbium ion doping of the two optical fibers is too complex, the doping of the rare earth optical fiber is more difficult to prepare than that of a common passive optical fiber mainly because the saturated vapor pressure of the rare earth raw material is different from that of a conventional silicon germanium phosphorus material, the conventional silicon germanium phosphorus material has very high saturated vapor pressure at a low temperature of 30-40 ℃, the raw material is only required to be placed in a sufficiently large material jar to be evaporated at a certain temperature, the partial pressure of the raw material is ensured to be unchanged by utilizing carrier gas or directly pumping with negative pressure, the flow is controlled by an MFC, the flow and the doping concentration are in a linear relation, and the concentration of each doping raw material can be controlled accurately by the MFC. The saturated vapor pressure of rare earth raw materials such as chelates is far smaller than that of conventional materials at 30-40 ℃ even at the temperature close to 200 ℃, so that the flow and the doping concentration are not in linear relation, and the precise control of the doping profile of complex erbium ions is difficult to realize.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the invention provides a gain-balanced few-mode erbium-doped fiber and a preparation method thereof, and aims to overcome the defects of large mode gain difference and large manufacturing process difficulty caused by complex erbium ion doping in the prior art. According to the invention, by matching different refractive index profile designs and utilizing a plasma vapor deposition (PCVD) process and a self-made rare earth raw material high-temperature feeding system, the erbium ion doping concentration can be effectively regulated and controlled in the preparation process of the fiber core of the optical fiber preform, the accuracy control difficulty of the erbium ion doping concentration is greatly reduced, and the overlapping degree of a signal light field and erbium ion is effectively regulated and controlled, so that the mode gain balancing effect is achieved.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a gain-balanced few-mode erbium-doped fiber, the fiber comprising, from inside to outside, a core, an inner cladding and an outer cladding, the core being a silica layer having different erbium-doped concentrations, the core comprising a circular core layer located in a central region of the core, and a first annular core layer and a second annular core layer sequentially surrounding the periphery of the circular core layer; wherein,
the erbium-doped concentrations of the circular core layer, the first annular core layer and the second annular core layer are a1, a2 and a3 respectively, and then the relation is satisfied: a2 < a1, a2 < a3;
the refractive indexes of the circular core layer, the first annular core layer and the second annular core layer are n1, n2 and n3 respectively, and then the relation is satisfied: n2 > n3 > n1.
Further, the erbium doped concentrations of the circular core layer, the first annular core layer and the second annular core layer further satisfy the relationship: a2 < a1=a3;
further, the doping concentration of erbium ions in the circular core layer and the second annular core layer is 4 x 10 -24 m -3 ～5*10 - 24 m -3 The doping concentration of erbium ions in the first annular core layer is 0.
Further; wherein,
the radius of the circular core layer is 2-3 mu m, the radius of the first annular core layer is 7-8 mu m, and the radius of the second annular core layer is 11-12 mu m;
the outer cladding layer is used as a reference layer, the relative refractive index of the circular core layer is 0.005-0.0055, the relative refractive index of the first annular core layer is 0.0075-0.008, and the relative refractive index of the second annular core layer is 0.006-0.0065.
Further, the dopant in the circular core layer further includes aluminum ions; the dopants in the first annular core layer and the second annular core layer further comprise at least one of aluminum, germanium, or phosphorus ions.
Further, the inner cladding includes a first inner cladding, and a second inner cladding adjacent to the outer cladding; wherein, the refractive indexes of the second inner cladding layer and the outer cladding layer are n4 and n5 respectively, and then the relation is satisfied: n4 is less than or equal to n5.
Further; wherein,
the radius of the first inner cladding is 12-16 mu m, and the radius of the second inner cladding is 20-22 mu m; the radius of the outer cladding is 61.5-63.5 mu m;
the outer cladding is used as a reference layer, the relative refractive index of the first inner cladding is-0.0005, and the relative refractive index of the second inner cladding is-0.01-0.
Further; wherein,
the first inner cladding is a pure silicon dioxide layer or a multi-doped silicon dioxide layer, and the doping agent in the first inner cladding comprises at least one of germanium, phosphorus or fluoride ions;
the second inner cladding is a pure silica layer or a fluorine doped silica layer.
Further, the cross section of the outer cladding is round or regular octagon, the optical fiber further comprises a coating layer coated on the outer surface of the outer cladding, and the coating layer comprises a first coating layer adjacent to the outer cladding and a second coating layer; when the section of the outer cladding is regular octagon, the first coating layer contains fluorine low-folding coating; and the outer cladding layer is taken as a reference layer, and the relative refractive index of the first coating layer is less than or equal to-0.073.
According to a second aspect of the present invention, there is provided a method of preparing a gain-balanced few-mode erbium-doped optical fiber as described above, the method comprising:
introducing silicon tetrachloride gas and corresponding doping raw material gas into a quartz liner tube by adopting a PCVD process so as to deposit the silicon tetrachloride gas and the corresponding doping raw material gas on the inner wall of the tube to form a first inner cladding;
the PCVD technology is adopted, the rare earth feeding system is utilized to heat erbium chloride and other doping raw materials to the evaporation temperature and transmit the erbium chloride and other doping raw materials into the quartz liner tube, and the doping concentration is controlled by adjusting the flow rate of carrier gas and the evaporation temperature which are introduced into the rare earth feeding system, so that silicon dioxide layers with different erbium doping concentrations are prepared to be used as fiber cores;
carrying out a shrinking sintering process on the deposited quartz liner tube to form a solid erbium-doped optical fiber preform;
sleeving the erbium-doped optical fiber preform into a sleeve with a proper size, and preparing the small-mode erbium-doped optical fiber with a target size through a high-speed wire drawing process; or alternatively
The erbium-doped optical fiber preform is sleeved into a sleeve with proper size, the sleeve is polished into an octagon, the surface of the octagon is coated with low refractive index coating, and then the low-mode erbium-doped optical fiber with target size is manufactured through a high-speed wire drawing process.
In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:
first, an erbium-doped few-mode fiber with balanced gain is provided, wherein the fiber core is a silica layer with different erbium-doped concentrations, and comprises a round core layer positioned in the central area of the fiber core,And a first annular core layer and a second annular core layer which are sequentially wrapped around the periphery of the circular core layer; the concentration of the erbium-doped layers of the circular core layer and the second annular core layer can be regulated and controlled to be larger than that of the erbium-doped layer of the first annular core layer; the design process not only greatly reduces the difficulty of erbium ion doping precisionSimultaneously adjustingThe overlapping degree of the signal light field and the erbium-doped ions is controlled, and the effect of good mode gain balance is achieved.
Secondly, the invention provides a preparation method of erbium-doped few-mode optical fiber with balanced gain, which utilizes a plasma vapor deposition (PCVD) process and a self-made high-temperature feeding system to deposit base materials and doped materials by matching with different refractive index profile designs, no particles are generated in the deposition process, and the deposition components are ion and atomic levels, so that the preparation method has natural advantages for realizing the rare earth-doped optical fiber with high uniformity and dispersibility. Meanwhile, the advantages of accurate refractive index control of a large-size deep fluorine-doped cladding layer and a core layer by PCVD are utilized, and the method is more suitable for preparing the small-mode erbium fiber with a complex section.
Thirdly, the invention provides a preparation method of the erbium-doped few-mode optical fiber with balanced gain, which uses a plasma vapor deposition (PCVD) process. However, the conventional optical fiber doping technology mainly comprises two processes of gas phase and liquid phase based on an improved chemical vapor deposition (MCVD), but the doping materials of the conventional optical fiber doping technology mostly exist in the form of submicron particles, so that the uniformity is poor, the erbium-doped optical fiber is easy to aggregate to form clusters when the doping concentration is high, concentration quenching and the like are caused, and the optical amplification performance of the erbium-doped optical fiber is restricted. Meanwhile, the MCVD process has the risks of poor refractive index precise control, difficult preparation of a complex section structure and easy occurrence of liner tube variability and tube blockage when the deposited layer is doped too thick. When the erbium-doped few-mode optical fiber is prepared by using a plasma vapor deposition (PCVD) method, the deposition components are atoms, ions or active groups, so that the doped ions have the characteristics of high uniformity, dispersibility and high doping concentration, and the requirement of a large-size deep fluorine-doped cladding is met.
Drawings
FIG. 1 is a schematic diagram of a gain-balanced few-mode erbium-doped fiber according to embodiment 1 of the present invention;
FIG. 2 is a schematic structural diagram of a gain-balanced few-mode erbium-doped fiber according to embodiment 2 of the present invention;
fig. 3 is a gain spectrum of a gain-balanced few-mode erbium-doped fiber implemented 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:
optical fiber or optical fiber preform structure: starting from the centremost axis of the fiber, the central part of the fiber cross section is defined as the core 1, the annular region of the fiber cross section immediately adjacent to the core layer is the inner cladding 2, and the annular region of pure silica immediately adjacent to the inner cladding 2 is the outer cladding 3.
m -3 : number of dopant ions per cubic meter.
Relative refractive index:
numerical aperture:
wherein n is i For refractive index of different deposited layers, n 0 For the outer cladding 3 of pure SiO 2 Is a refractive index of (c).
The invention provides a gain balanced few-mode erbium-doped optical fiber, which sequentially comprises a fiber core 1, an inner cladding 2 and an outer cladding 3 from inside to outside, wherein the fiber core 1 is a silicon dioxide layer with different erbium-doped concentrations, and comprises a circular core layer 1-1 positioned in the central area of the fiber core 1, and a first annular core layer 1-2 and a second annular core layer 1-3 which are sequentially wrapped on the periphery of the circular core layer 1-1; wherein,
the erbium-doped concentrations of the circular core layer 1-1, the first annular core layer 1-2 and the second annular core layer 1-3 are a1, a2 and a3 respectively, and then the relation is satisfied: a2 < a1, a2 < a3;
the refractive indexes of the circular core layer 1-1, the first annular core layer 1-2 and the second annular core layer 1-3 are n1, n2 and n3 respectively, and then the relation is satisfied: n2 > n3 > n1.
According to the invention, the overlapping degree of the signal light field and the erbium-doped ions can be effectively regulated and controlled by controlling the concentration of the erbium ions of the first annular core layer 1-2 to be smaller than that of the circular core layer 1-1 and the second annular core layer 1-3, so that the mode gain difference is reduced. In addition, the concentration regulation and control process is easy to realize, and the actual operation difficulty is greatly reduced; it is well known that the main reason why doping of rare earth fibers, especially erbium ions, is more difficult to produce than ordinary passive fibers is that the saturated vapor pressure of rare earth materials is different from that of conventional silicon germanium phosphorus materials, which can control the concentration of each doping material relatively precisely by MFC. The saturated vapor pressure of rare earth raw materials such as chelates is far smaller than that of conventional materials at 30-40 ℃ even when the rare earth raw materials are close to 200 ℃, so that the flow and the doping concentration are not in linear relation, and the precise control of the doping profile of complex erbium ions is difficult to realize; therefore, the conventional process for precisely controlling the concentrations of different erbium-doped ions is quite complicated to operate. The erbium ion concentration of the first annular core layer 1-2 is smaller than that of the circular core layer 1-1 and the second annular core layer 1-3, so that on one hand, the mode gain difference can be reduced, and on the other hand, the process difficulty can be reduced.
Specifically, the erbium doped concentrations of the circular core layer 1-1, the first annular core layer 1-2, and the second annular core layer 1-3 further satisfy the relationship: a2 < a1=a3.
The invention can further design the erbium-doped concentration of the circular core layer 1-1 and the second annular core layer 1-3 to be the same, so that the operation is simpler from the perspective of the preparation process, the same preparation process and process conditions can be used when the circular core layer 1-1 and the second annular core layer 1-3 are prepared, the process equipment parameters are not required to be frequently adjusted, and the corresponding technical effect can be achieved.
Specifically, the doping concentration of erbium ions in the circular core layer 1-1 and the second annular core layer 1-3 is 4×10 -24 m -3 ～5*10 -24 m -3 The doping concentration of erbium ions of the first annular core layer 1-2 is 0.
The invention can further set the erbium doping concentration of the circular core layer 1-1 and the second annular core layer 1-3 in a certain range, and set the erbium doping concentration of the first annular core layer 1-2 to 0, so that the operation steps can be further simplified while simultaneously satisfying the inequality relation. The invention controls the doping concentration range of erbium ions in the round core layer 1-1 and the second annular core layer 1-3 to be 4 x 10 -24 m -3 ～5*10 -24 m -3 Because when the concentration is higher than 5 x 10 -24 m -3 Concentration quenching occurs and fiber loss increases; when the concentration is lower than 4 x 10 -24 m -3 The gain factor of the fiber is affected.
Specifically, the present invention relates to a method for manufacturing a semiconductor device; wherein the radius of the circular core layer 1-1 is 2-3 mu m, the radius of the first annular core layer 1-2 is 7-8 mu m, and the radius of the second annular core layer 1-3 is 11-12 mu m; with the outer cladding layer 3 as a reference layer, the relative refractive index of the circular core layer 1-1 is 0.005-0.0055, the relative refractive index of the first annular core layer 1-2 is 0.0075-0.008, and the relative refractive index of the second annular core layer 1-3 is 0.006-0.0065.
In the invention, other elements are doped simultaneously for ensuring the numerical aperture NA of the optical fiber. Specifically, the dopant in the circular core layer 1-1 further includes aluminum ions; the dopants in the first annular core layer 1-2 and the second annular core layer 1-3 further comprise at least one of aluminum, germanium or phosphorus ions.
Specifically, the inner cladding 2 includes a first inner cladding 2-1, and a second inner cladding 2-2 adjacent to the outer cladding 3; wherein, the refractive indexes of the second inner cladding layer 2-2 and the outer cladding layer 3 are n4 and n5 respectively, and then the relation is satisfied: n4 is less than or equal to n5. In order to further improve the bending loss of the optical fiber, the refractive index of the second inner cladding layer 2-2 is designed to be smaller than that of the outer cladding layer 3.
Specifically, the present invention relates to a method for manufacturing a semiconductor device; wherein the radius of the first inner cladding layer 2-1 is 12-16 mu m, and the radius of the second inner cladding layer 2-2 is 20-25 mu m; the radius of the outer cladding layer 3 is 61.5-63.5 mu m; with the outer cladding layer 3 as a reference layer, the relative refractive index of the first inner cladding layer 2-1 is-0.0005 to 0.0005, and the relative refractive index of the second inner cladding layer 2-2 is-0.01 to 0.
In the invention, other elements are doped simultaneously for ensuring the numerical aperture NA of the optical fiber. Specifically, the present invention relates to a method for manufacturing a semiconductor device; wherein the first inner cladding layer 2-1 is a pure silicon dioxide layer or a multi-doped silicon dioxide layer, and the doping agent in the first inner cladding layer 2-1 comprises at least one of germanium, phosphorus or fluoride ions; the second inner cladding layer 2-2 is a pure silica layer or a fluorine doped silica layer.
Specifically, the section of the outer cladding 3 is circular or regular octagon, the optical fiber further comprises a coating layer coated on the outer surface of the outer cladding 3, and the coating layer comprises a first coating layer adjacent to the outer cladding 3 and a second coating layer; when the section of the outer cladding layer 3 is regular octagon, the first coating layer contains fluorine low-folding coating; and the outer cladding layer 3 is taken as a reference layer, and the relative refractive index of the first coating layer is less than or equal to-0.073. As is well known, the general optical fiber is a single-clad optical fiber, light is only transmitted in the fiber core, and the glass part at the periphery of the fiber core is commonly called as a glass cladding, namely an outer cladding 3 in the invention; the preparation process of the invention can prepare the single-clad optical fiber and double-clad optical fiber, wherein the outer surface of the outer cladding 3 is coated with a layer of low refractive index coating, so that light can be transmitted in the cladding and the fiber core at the same time. In the double-cladding optical fiber process, the section of the outer cladding 3 is regular octagon, the outer cladding 3 is taken as a reference layer, the relative refractive index of the first coating layer is less than or equal to-0.07, and the refractive index range is beneficial to the bending loss of the optical fiber.
The invention provides a preparation method of the gain equalization few-mode erbium-doped fiber, which comprises the following steps:
step 1: introducing silicon tetrachloride gas and corresponding doping raw material gas into a quartz liner tube by adopting a PCVD process so as to deposit the silicon tetrachloride gas and the corresponding doping raw material gas on the inner wall of the tube to form a first inner cladding layer 2;
step 2: the PCVD technology is adopted, the rare earth feeding system is utilized to heat erbium chloride and other doping raw materials to the evaporation temperature and transmit the erbium chloride and other doping raw materials into the quartz liner tube, and the doping concentration is controlled by adjusting the flow rate of carrier gas and the evaporation temperature which are introduced into the rare earth feeding system, so that silicon dioxide layers with different erbium doping concentrations are prepared to be used as fiber cores 1;
step 3: carrying out a shrinking sintering process on the deposited quartz liner tube to form a solid erbium-doped optical fiber preform;
step 4: if a single clad optical fiber is prepared:
sleeving the erbium-doped optical fiber preform into a sleeve with a proper size, and preparing the small-mode erbium-doped optical fiber with a target size through a high-speed wire drawing process;
step 5: if a double clad optical fiber is prepared:
the erbium-doped optical fiber preform is sleeved into a sleeve with proper size, the sleeve is polished into an octagon, the surface of the octagon is coated with low refractive index coating, and then the low-mode erbium-doped optical fiber with target size is manufactured through a high-speed wire drawing process.
The invention is described in further detail below with reference to the drawings and examples.
Examples 1 to 5 and comparative example 1
Step 1: the method comprises the steps of installing a quartz liner tube on a PCVD lathe, introducing silicon tetrachloride gas or silicon tetrachloride and hexafluoroethane gas with corresponding flow rates into the quartz liner tube to deposit corresponding thicknesses to prepare a second inner cladding layer 2-2, and then introducing silicon tetrachloride gas or silicon tetrachloride and at least one of germanium tetrachloride, phosphorus oxychloride and hexafluoroethane gas with corresponding flow rates to deposit corresponding thicknesses to prepare a first inner cladding layer 2-1;
step 2: the erbium chloride and the aluminum chloride are respectively heated to corresponding temperatures through a rare earth feeding system, the doping concentration is regulated by regulating the flow and the evaporation temperature of each raw material according to the doping concentration of each element required by the optical fiber design requirement, and the target core layers with different erbium ion doping concentrations are prepared.
Step 3: taking down the deposited liner tube from the PCVD lathe, and installing the liner tube on the HEC for a shrinking and sintering process to form a solid erbium-doped optical fiber preform;
step 4: and sheathing the multi-layer erbium-doped prefabricated rod into a sleeve with proper size, and drawing the sleeve into the small-mode erbium fiber with target size by high-speed wire drawing.
Step 5: if a double-clad optical fiber is to be prepared, the ferrule is polished to an octagon and then matched with the low refractive index coating to be drawn into a few-mode erbium fiber of a target size.
The following table 1 is a table of parameters of five different structure gain balanced few-mode erbium fibers, in which the second inner cladding 2-2 is not deep doped with F in the example 1, and the outer cladding 3 is circular; in the embodiment 2, the second inner cladding 2-2 is mainly doped with F, and the outer cladding 3 is octagonal; example 3 the parameters of other examples and comparative examples are shown in table 1, provided that the second inner cladding 2-2 is deeply doped with F and the outer cladding is circular. Examples 1-5 and comparative example 1 above were all prepared using PCVD plus a self-made high temperature delivery system. Fig. 1 and 2 show cross-sectional structural views of embodiment 1 and embodiment 2, respectively. Fig. 3 is a graph of gain after optimizing the gain test bench and the fiber parameters in example 1, and table 2 is the gain results after optimizing the gain test bench and the fiber parameters in examples 1 to 5 and comparative example 1.
Table 1 preparation parameters of examples 1 to 5 and comparative example 1 few-mode erbium-doped fiber
Table 2 gain results after parameters of few-mode erbium-doped fibers of examples 1 to 5 and comparative example 1
| Example 1 | Example 2 | Example 3 | Example 4 | Example 5 | Comparative example 1 | |
| Gain range for 6 LP modes | ＞20dB | ＞20dB | ＞20dB | ＞20dB | ＞20dB | ＞20dB |
| Gain difference for 6 LP modes | 1.3dB | 1.8dB | 1.5dB | 1.4dB | 1.3dB | 4dB |
As can be seen from fig. 3, the gain of each signal mode of embodiment 1 gradually increases in the process of increasing the pump power from 100 to 600mW, and the gain of each mode is greater than 20dB and the gain difference of 6 LP modes is 1.3dB at the pump power of 600mW, which indicates that the optical fiber prepared by the method of the present invention has a high gain amplitude, and the optical fiber of embodiment 1 of the present invention has a good gain equalization effect. By integrating tables 1-2 and figure 3, the concentration of the erbium-doped layer of the circular core layer and the concentration of the erbium-doped layer of the second annular core layer are regulated and controlled to be larger than those of the erbium-doped layer of the first annular core layer, so that the fiber cores of the erbium-doped fiber are silicon dioxide layers with different erbium-doped concentrations; the design process not only greatly reduces the difficulty of the erbium ion doping precision, but also effectively regulates and controls the overlapping degree of the signal light field and the erbium ion doped, so that the few-mode erbium-doped optical fiber has a good mode gain balancing effect.
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 (8)
1. The gain balanced few-mode erbium-doped optical fiber comprises a fiber core (1), an inner cladding (2) and an outer cladding (3) from inside to outside, and is characterized in that the fiber core (1) is a silica layer with different erbium-doped concentrations, and comprises a circular core layer (1-1) positioned in the central area of the fiber core (1), and a first annular core layer (1-2) and a second annular core layer (1-3) which are sequentially wrapped on the periphery of the circular core layer (1-1); wherein,
the erbium-doped concentrations of the circular core layer (1-1), the first annular core layer (1-2) and the second annular core layer (1-3) are a1, a2 and a3 respectively, and then the relationship is satisfied: a2 < a1, a2 < a3;
the refractive indexes of the circular core layer (1-1), the first annular core layer (1-2) and the second annular core layer (1-3) are respectively n1, n2 and n3, and then the relation formula is satisfied: n2 is more than n3 is more than n1, and the accuracy control difficulty of the erbium-doped concentration is reduced by matching the profile designs with different refractive indexes;
the inner cladding (2) comprises a first inner cladding (2-1), and a second inner cladding (2-2) adjacent to the outer cladding (3); wherein, the refractive indexes of the second inner cladding layer (2-2) and the outer cladding layer (3) are n4 and n5 respectively, and then the relation is satisfied: n4 is less than or equal to n5;
the radius of the first inner cladding (2-1) is 12-16 mu m, and the radius of the second inner cladding (2-2) is 20-25 mu m; the radius of the outer cladding layer (3) is 61.5-63.5 mu m; the relative refractive index of the first inner cladding layer (2-1) is-0.0005 to 0.0005, and the relative refractive index of the second inner cladding layer (2-2) is-0.01 to 0 by taking the outer cladding layer (3) as a reference layer.
2. A few-mode erbium doped fiber according to claim 1, characterized in that the erbium doped concentrations of the circular core layer (1-1), the first annular core layer (1-2) and the second annular core layer (1-3) further satisfy the relation: a2 < a1=a3.
3. A few-mode erbium doped fiber according to claim 1 or 2, characterized in that the doping concentration of erbium ions in both the circular core layer (1-1) and the second annular core layer (1-3) is 4 x 10 -24 m -3 ～5*10 -24 m -3 The doping concentration of erbium ions of the first annular core layer (1-2) is 0.
4. The few-mode erbium doped fiber of claim 1, wherein; wherein,
the radius of the circular core layer (1-1) is 2-3 mu m, the radius of the first annular core layer (1-2) is 7-8 mu m, and the radius of the second annular core layer (1-3) is 11-12 mu m;
with the outer cladding layer (3) as a reference layer, the relative refractive index of the circular core layer (1-1) is 0.005-0.0055, the relative refractive index of the first annular core layer (1-2) is 0.0075-0.008, and the relative refractive index of the second annular core layer (1-3) is 0.006-0.0065.
5. A few-mode erbium doped fiber according to claim 1, characterized in that the dopants in the circular core layer (1-1) further comprise aluminum ions; the dopants in the first annular core layer (1-2) and the second annular core layer (1-3) further comprise at least one of aluminum, germanium or phosphorus ions.
6. The few-mode erbium doped fiber of claim 1, wherein; wherein,
the first inner cladding layer (2-1) is a pure silicon dioxide layer or a multi-doped silicon dioxide layer, and the doping agent in the first inner cladding layer (2-1) comprises at least one of germanium, phosphorus or fluoride ions;
the second inner cladding layer (2-2) is a pure silicon dioxide layer or a fluorine-doped silicon dioxide layer.
7. The few-mode erbium-doped fiber according to claim 1, wherein the outer cladding (3) has a circular or regular octagon-shaped cross section, characterized in that the fiber further comprises a coating layer applied to the outer surface of the outer cladding (3), the coating layer comprising a first coating layer adjacent to the outer cladding (3) and a second coating layer; wherein,
when the section of the outer cladding layer (3) is regular octagon, the first coating layer contains fluorine low-folding coating; and the outer cladding layer (3) is taken as a reference layer, and the relative refractive index of the first coating layer is less than or equal to minus 0.073.
8. A method of making a gain-balanced few-mode erbium doped fiber according to any of claims 1 to 7, comprising:
introducing silicon tetrachloride gas and corresponding doping raw material gas into a quartz liner tube by adopting a PCVD process so as to deposit the silicon tetrachloride gas and the corresponding doping raw material gas on the inner wall of the tube to form a first inner cladding (2);
adopting a PCVD process, heating erbium chloride and other doping raw materials to an evaporation temperature by utilizing a rare earth feeding system, transmitting the erbium chloride and other doping raw materials into a quartz liner tube, and controlling doping concentration by adjusting the flow rate of carrier gas and the evaporation temperature of the rare earth feeding system, thereby preparing silicon dioxide layers with different erbium doping concentrations as fiber cores (1);
carrying out a shrinking sintering process on the deposited quartz liner tube to form a solid erbium-doped optical fiber preform;
sleeving the erbium-doped optical fiber preform into a sleeve with a proper size, and manufacturing the small-mode erbium-doped optical fiber with a target size through a high-speed wire drawing process; or alternatively
And sleeving the erbium-doped optical fiber preform into a sleeve with a proper size, polishing the sleeve into an octagon, coating low-refractive-index coating on the surface of the octagon, and preparing the small-mode erbium-doped optical fiber with a target size through a high-speed wire drawing process.
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