CN115047561B - Erbium-ytterbium co-doped double-cladding double-annular few-mode gain optical fiber - Google Patents
Erbium-ytterbium co-doped double-cladding double-annular few-mode gain optical fiber Download PDFInfo
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- 238000005253 cladding Methods 0.000 title claims abstract description 101
- 239000013307 optical fiber Substances 0.000 title claims abstract description 41
- KWMNWMQPPKKDII-UHFFFAOYSA-N erbium ytterbium Chemical compound [Er].[Yb] KWMNWMQPPKKDII-UHFFFAOYSA-N 0.000 title claims abstract description 29
- 239000000835 fiber Substances 0.000 claims abstract description 81
- -1 rare earth ions Chemical class 0.000 claims abstract description 40
- 229910052691 Erbium Inorganic materials 0.000 claims abstract description 19
- 229910052761 rare earth metal Inorganic materials 0.000 claims abstract description 13
- 150000002500 ions Chemical class 0.000 claims abstract description 11
- 229910052769 Ytterbium Inorganic materials 0.000 claims abstract description 10
- 239000000463 material Substances 0.000 claims abstract description 6
- 239000010453 quartz Substances 0.000 claims abstract description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 6
- 230000007423 decrease Effects 0.000 claims abstract description 5
- 230000001788 irregular Effects 0.000 claims abstract description 4
- 238000005086 pumping Methods 0.000 claims description 18
- 230000005540 biological transmission Effects 0.000 claims description 15
- 230000003287 optical effect Effects 0.000 claims description 11
- 238000001514 detection method Methods 0.000 claims description 3
- 238000001228 spectrum Methods 0.000 claims description 3
- 238000000034 method Methods 0.000 description 6
- 230000003321 amplification Effects 0.000 description 4
- 230000008878 coupling Effects 0.000 description 4
- 238000010168 coupling process Methods 0.000 description 4
- 238000005859 coupling reaction Methods 0.000 description 4
- 238000003199 nucleic acid amplification method Methods 0.000 description 4
- 238000004891 communication Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 230000010287 polarization Effects 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 239000002019 doping agent Substances 0.000 description 2
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical compound [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000008054 signal transmission Effects 0.000 description 1
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- 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
- G02B6/03622—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 2 layers only
- G02B6/03627—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 2 layers only arranged - +
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/39—Non-linear optics for parametric generation or amplification of light, infrared or ultraviolet waves
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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
- H01S3/06716—Fibre compositions or doping with active elements
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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
- H01S3/06729—Peculiar transverse fibre profile
- H01S3/06733—Fibre having more than one cladding
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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
- H01S3/06754—Fibre amplifiers
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- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
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- General Physics & Mathematics (AREA)
- Lasers (AREA)
Abstract
The invention discloses an erbium-ytterbium co-doped double-cladding double-annular few-mode gain optical fiber, which belongs to the technical field of mode division multiplexing and is characterized by comprising the following components from inside to outside: the fiber core, the inner cladding and the outer cladding, wherein the fiber core is wrapped with an inner ring, and an outer ring is arranged in the middle of the inner cladding; wherein, the cross sections of the fiber core, the inner ring, the outer ring and the outer cladding are all round; the cross section of the inner cladding is an irregular polygon; the fiber core is made of quartz material doped with ions; the inner ring and the outer ring are doped with rare earth ions, wherein the rare earth ions comprise erbium ions and ytterbium ions; the refractive index gradually decreases from the core to the junction with the inner cladding, remains unchanged in the inner cladding, and the refractive index of the outer cladding is lower than that of the inner cladding. According to the invention, on one hand, the doping content of erbium ions is increased by introducing ytterbium ions so as to increase the gain of each mode, and on the other hand, an outer ring is added into the inner cladding layer so as to utilize the tail part of the evanescent field of the signal mode, so that the gain is further increased.
Description
Technical Field
The invention belongs to the technical field of mode division multiplexing, and particularly relates to an erbium-ytterbium co-doped double-cladding double-annular few-mode gain optical fiber.
Background
With the development of big data, cloud services and the internet of things, capacity demands of people on existing communication networks are exponentially growing. However, the transmission capacity of existing single-mode fiber communication systems has approached shannon's limit, and therefore, it has become urgent to develop new information transmission dimensions to meet the increasing capacity demand. In other multiplexing dimensions of single mode optical fibers such as: on the basis of fully utilizing time division multiplexing, polarization multiplexing, orthogonal frequency division multiplexing, wavelength division multiplexing and the like, space division multiplexing is widely focused and rapidly developed in a large-capacity optical fiber communication system.
The space division multiplexing technology comprises core division multiplexing and mode division multiplexing, wherein the core division multiplexing refers to the transmission of signals by using each fiber core of the multi-core optical fiber as an independent transmission channel; the mode division multiplexing technology uses few-mode optical fibers to transmit a small number of space modes, loads signals of different channels onto each mode, and uses orthogonality of the modes to transmit the signals. The space division multiplexing transmission system based on the few-mode optical fiber can realize simultaneous transmission of a plurality of channels, so that the transmission capacity is multiplied. The space division multiplexing technology adopting the few-mode optical fiber as the transmission line is used for realizing long-distance transmission, and the few-mode erbium-doped optical fiber amplifier is a key device for compensating the transmission loss of the few-mode transmission system. However, during optical amplification, the overlap of each of the signal mode optical field, the pump optical field, and the erbium ion distribution over the fiber cross-section is inconsistent, resulting in different modes being amplified in the few-mode fiber to obtain different gains, and high differential mode gain can result in limited transmission, so minimizing differential mode gain in the few-mode erbium-doped fiber amplifier is critical.
The existing methods for reducing the differential modal gain of the few-mode erbium-doped fiber amplifier mainly comprise two methods: (1) regulating and controlling the pump mode proportion. The mode of pumping is changed, the power proportion is adjusted to reduce the difference of overlapping factors of the optical field of each signal mode, the optical field of pumping and erbium ion distribution, and gain equalization among modes is realized, but the mode only changes the information of the pumping light intensity, so that the gain equalization capability is limited. (2) The doping ion distribution and the refractive index profile of the few-mode gain fiber are designed. The difference of overlapping factors among modes is reduced by designing the erbium ion distribution and the erbium ion concentration of the few-mode erbium-doped fiber; by designing the refractive index profile, the mode field distribution of various modes of the optical fiber can be adjusted, the overlapping integral factor of the signal light and the pump light is increased, and gain balance among modes is realized. This approach has a better effect by designing a special structure of the fiber to equalize the gain between modes.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the invention provides an erbium-ytterbium co-doped double-cladding double-annular few-mode gain optical fiber, which aims to effectively reduce the difference of overlapping factors of all modes by designing annular doped optical fibers and solve the technical problem that the prior art cannot reduce differential modal gain while guaranteeing the gain of a few-mode erbium-doped optical fiber amplifier.
In order to achieve the above object, according to one aspect of the present invention, there is provided an erbium ytterbium co-doped double-clad double-ring-shaped few-mode gain fiber, comprising, from inside to outside: the fiber comprises a fiber core 1-2, an inner cladding layer 1-4 and an outer cladding layer 1-5, wherein the fiber core 1-2 is wrapped with an inner ring 1-1; an outer ring 1-3 is arranged in the middle of the inner cladding 1-4; wherein,,
the cross sections of the fiber core 1-2, the inner ring 1-1, the outer ring 1-3 and the outer cladding 1-5 are all round; the cross section of the inner cladding 1-4 is an irregular polygon;
the fiber core 1-2 is made of quartz material doped with ions; the inner ring 1-1 and the outer ring 1-3 are doped with rare earth ions, wherein the rare earth ions comprise erbium ions and ytterbium ions;
the refractive index decreases gradually from the core 1-2 to the interface with the inner cladding 1-4, remains unchanged in the inner cladding 1-4, and the refractive index of the outer cladding 1-5 is lower than that of the inner cladding 1-4.
In one embodiment, the cross-section of the inner cladding 1-4 is "D" shaped, eccentric circular or "quincuncial" shaped.
In one embodiment, the inner diameter of the outer ring 1-3 is greater than or equal to the outer diameter of the inner ring 1-1; the outer diameter of the outer ring 1-3 is smaller than or equal to the radius of the corresponding inscribed circle of the inner cladding 1-4.
In one embodiment, the diameter of the core 1-2 is less than 20 microns.
In one embodiment, the inner diameter of the inner ring 1-1 is 0.48 times the radius of the core 1-2 and the diameter of the inner cladding 1-4 is around 125 microns.
In one embodiment, when a few-mode gain fiber is used as the gain medium, it is cladding pumped with a multimode pump light source.
In one embodiment, the pumping mode adopts forward pumping or backward pumping.
According to another aspect of the present invention there is provided a few-mode erbium doped fibre amplifier comprising:
signal light providing means for providing signal light;
a multimode pump light source emitting pump light;
the beam combiner is used for combining the signal light and the pump light to obtain coupled light;
the few-mode gain optical fiber is arranged on an emergent light path of the coupling light and is used for amplifying the coupling light to obtain amplified light;
the spectrum detection device is arranged on the transmission light path of the amplified light and is used for collecting the light spot of the amplified light and measuring the power of the light spot.
In general, the above technical solutions conceived by the present invention, compared with the prior art, enable the following beneficial effects to be obtained:
(1) The method can solve the defect that gain equalization is difficult to realize under the condition that the existing few-mode optical fiber realizes simultaneous amplification of a plurality of modes: in the optical amplification process of the few-mode erbium-doped fiber amplifier, the overlapping of each signal mode optical field, the pumping optical field and erbium ion distribution on the cross section of the fiber is inconsistent, so that gains obtained by amplifying different modes in the few-mode fiber are different, and the transmission is limited due to high differential mode gain. The existing methods for reducing the differential modal gain of the few-mode erbium-doped fiber amplifier mainly comprise two methods: firstly, the pump mode proportion is regulated and controlled, and secondly, the doping ion distribution and the refractive index profile of the few-mode gain optical fiber are designed. The invention can effectively reduce the problem of large difference of overlapping factors of all modes by designing the annular doped optical fiber, and can balance gain to a certain extent.
(2) The annular doped optical fiber can reduce the differential modal gain to a certain extent, but the rare earth ion content of the gain optical fiber is greatly reduced due to the doping in the annular region, so that the gain of the few-mode erbium-doped optical fiber amplifier is reduced due to the certain erbium ion concentration in the annular region, and the phenomenon of 'clustering' can be generated by uniformly increasing the erbium ion concentration in the erbium-doped optical fiber. According to the invention, the erbium-ytterbium double-cladding double-annular gain fiber is designed, on one hand, the doping content of erbium ions is improved by introducing ytterbium ions so as to improve the gain of each mode, and on the other hand, an outer ring is added into the inner cladding so as to utilize the tail part of an evanescent field of a signal mode, so that the gain is further improved.
Drawings
FIG. 1 is a cross-sectional view of an erbium-ytterbium co-doped double-clad double-annular few-mode fiber according to an embodiment of the present invention;
FIG. 2 is a graph of the refractive index profile and dopant concentration of an erbium-ytterbium co-doped double-clad double-ring few-mode fiber according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an erbium-ytterbium co-doped double-clad double-ring-shaped few-mode fiber for a few-mode erbium-doped fiber amplifier according to an embodiment 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.
The invention provides an erbium-ytterbium co-doped double-cladding double-annular few-mode gain optical fiber, as shown in fig. 1, wherein a schematic diagram of a section of the few-mode gain optical fiber is shown in fig. 1, and the few-mode gain optical fiber comprises, from inside to outside: the fiber comprises a fiber core 1-2, an inner cladding layer 1-4 and an outer cladding layer 1-5, wherein the fiber core 1-2 is wrapped with an inner ring 1-1; an outer ring 1-3 is arranged in the middle of the inner cladding 1-4; wherein, the cross sections of the fiber core 1-2, the inner ring 1-1, the outer ring 1-3 and the outer cladding 1-5 are all round; the cross section of the inner cladding 1-4 is an irregular polygon; the fiber core 1-2 is made of quartz material doped with ions; the inner ring 1-1 and the outer ring 1-3 are doped with rare earth ions, wherein the rare earth ions comprise erbium ions and ytterbium ions; the refractive index decreases gradually from the core 1-2 to the interface with the inner cladding 1-4, remains unchanged in the inner cladding 1-4, and the refractive index of the outer cladding 1-5 is lower than that of the inner cladding 1-4.
The invention provides an erbium-ytterbium co-doped double-cladding double-annular few-mode gain optical fiber which comprises an inner ring 1-1, a fiber core 1-2, an outer ring 1-3, an inner cladding 1-4 and an outer cladding 1-5, wherein the fiber core 1-2 wraps the inner ring 1-1, the outer ring 1-3 is positioned outside the fiber core 1-2 and inside the inner cladding 1-4, and the outer cladding 1-5 wraps the inner cladding 1-4, so that the double-cladding double-annular few-mode gain optical fiber is integrally formed. Wherein, the cross section of the fiber core 1-2, the inner ring 1-1, the outer ring 1-3 and the outer cladding 1-5 is round, the cross section of the inner cladding 1-4 is 'D' -shaped, eccentric round or polygonal, and the 'D' -shaped is taken as an example in the patent. The outer diameter of the inner ring 1-1 is inscribed in the fiber core 1-2, the inner diameter of the outer ring 1-3 is larger than the radius of the fiber core 1-2, and the outer diameter of the outer ring 1-3 is not larger than the inscribed circle radius of the inner cladding 1-4. The refractive index distribution of the few-mode gain fiber is graded refractive index distribution, and the rare earth ions doped in the double rings are erbium ions and ytterbium ions.
In the optical fiber design according to practical application, the diameter of the fiber core 1-2 is not more than 20 micrometers, the inner diameter of the inner ring 1-1 is 0.48 times of the radius of the fiber core 1-2, the inner diameter of the outer ring 1-3 is larger than the radius of the fiber core 1-2, the outer diameter of the outer ring 1-3 is not larger than the inscribed circle radius of the inner cladding 1-4, and the width of the outer ring 1-3 can be properly optimized and adjusted; the diameter of the inner cladding 1-4 is about 125 microns, and the diameter of the outer cladding 1-5 is greater than the diameter of the inner cladding 1-4. The gain fiber is made of quartz material doped with ions, rare earth ions are doped only in the double rings, the doped rare earth ions are erbium ions and ytterbium ions, and the concentration of the doped ions can be properly optimized and adjusted. FIG. 2 is a graph of refractive index profile and dopant ion concentration for an erbium ytterbium co-doped double-clad double-annular few-mode fiber according to the present invention.
In one embodiment, the cross-section of the inner cladding 1-4 is "D" shaped, eccentric circular or "quincuncial" shaped.
In one embodiment, the inner diameter of the outer ring 1-3 is greater than or equal to the outer diameter of the inner ring 1-1; the outer diameter of the outer ring 1-3 is smaller than or equal to the radius of the corresponding inscribed circle of the inner cladding 1-4; the width of the outer rings 1-3 can be adjusted.
In one embodiment, the diameter of the core 1-2 is less than 20 microns.
In one embodiment, the inner diameter of the inner ring 1-1 is 0.48 times the radius of the core 1-2 and the diameter of the inner cladding 1-4 is around 125 microns.
In one embodiment, when a few-mode gain fiber is used as the gain medium, it is cladding pumped with a multimode pump light source. In one embodiment, the pumping mode adopts forward pumping or backward pumping.
Specifically, when the erbium-ytterbium co-doped double-cladding double-annular few-mode fiber is used as a gain medium, a multimode pumping light source is required to be used for cladding pumping, and the pumping mode can be forward pumping or backward pumping.
According to another aspect of the present invention there is provided a few-mode erbium doped fibre amplifier comprising:
signal light providing means for providing signal light;
a multimode pump light source emitting pump light;
the beam combiner is used for combining the signal light and the pump light to obtain coupled light;
the few-mode gain optical fiber is arranged on an emergent light path of the coupling light and is used for amplifying the coupling light to obtain amplified light;
the spectrum detection device is arranged on the transmission light path of the amplified light and is used for collecting the light spot of the amplified light and measuring the power of the light spot.
Specifically, the invention also provides a schematic structure diagram of the erbium-ytterbium co-doped double-cladding double-annular few-mode optical fiber for the few-mode erbium-doped optical fiber amplifier, the structure of which is shown in fig. 3, and the erbium-ytterbium co-doped double-cladding double-annular few-mode optical fiber amplifier comprises an erbium-ytterbium co-doped double-cladding double-annular few-mode optical fiber 1, a signal light source 2, a tunable attenuator 3, a polarization controller 4, an optical isolator 5, a mode selection photon lantern 6, a beam combiner 7, a multimode pump light source 8, a charge coupler camera 9, a spectrometer 10 and a multimode jumper 11 of an FC/APC port. The mode selection photon lantern 6 comprises six signal mode input arms and one signal output arm; one end of the beam combiner 7 comprises a pump input arm, a signal input arm, and the other end is a signal output arm.
The seed light is provided by the signal light source 2; the tunable attenuator 3 adjusts the signal light power and controls the input power of each signal mode; the polarization controller 4 is used for ensuring the purity of the converted signal mode; after the optical isolator, the signal fundamental mode LP01 is coupled to one input branch (LP 01, LP11a, LP11b, LP21a, LP21b, or LP 02) of the mode-selective photonic lantern, which converts the signal into the mode it supports; the pump light is provided by a multimode pump light source; and then, the beam combiner 7 couples the signal light and the pump light, and inputs the signal light and the pump light into the erbium-ytterbium co-doped double-cladding double-annular few-mode optical fiber for amplification, and the tail end of the few-mode optical fiber is welded with a multimode jumper of an FC/APC port, so that the output power can be conveniently measured by an access spectrometer. The spot is collected using a charge-coupled camera.
The erbium-ytterbium co-doped double-clad double-annular few-mode fiber 1 in example 1 is used as the erbium-ytterbium co-doped double-clad double-annular few-mode fiber, namely: the erbium-ytterbium co-doped double-cladding double-annular few-mode optical fiber comprises an inner ring 1-1, a fiber core 1-2, an outer ring 1-3, an inner cladding 1-4 and an outer cladding 1-5, wherein the fiber core 1-2 wraps the inner ring 1-1, the outer ring 1-3 is positioned outside the fiber core 1-2 and inside the inner cladding 1-4, and the outer cladding 1-5 wraps the inner cladding 1-4, so that the double-cladding double-annular few-mode gain optical fiber is integrally formed. Further, the cross sections of the fiber core 1-2, the inner ring 1-1, the outer ring 1-3 and the outer cladding 1-5 are circular, and the cross section of the inner cladding 1-4 is D-shaped, eccentric circular or polygonal. The outer diameter of the inner ring 1-1 is inscribed in the fiber core 1-2, the inner diameter of the outer ring 1-3 is larger than the radius of the fiber core 1-2, and the outer diameter of the outer ring 1-3 is not larger than the inscribed circle radius of the inner cladding 1-4. The inner diameter of the inner ring 1-1 is 0.48 times the radius of the fiber core 1-2, and the diameter of the fiber core 1-2 is not more than 20 micrometers. The inner diameter of the outer ring 1-3 is larger than the radius of the fiber core 1-2, the outer diameter of the outer ring 1-3 is not larger than the inscribed circle radius of the inner cladding 1-4, and the width of the outer ring 1-3 can be properly optimized and adjusted; the diameter of the inner cladding 1-4 is about 125 micrometers; the outer cladding 1-5 has a diameter greater than the diameter of the inner cladding 1-4. The refractive index distribution of the gain fiber is graded-index distribution, that is, the refractive index in the fiber core 1-2 gradually decreases from the center of the fiber core 1-2 to the junction of the fiber core 1-2 and the inner cladding 1-4, and is constant in the inner cladding 1-4, and the refractive index of the outer cladding 1-5 is lower than that of the inner cladding 1-4. The gain fiber is made of quartz material doped with ions, rare earth ions are doped only in the double rings, the doped rare earth ions are erbium ions and ytterbium ions, and the concentration of the doped ions can be properly optimized and adjusted.
Because the amplifier of the embodiment uses the erbium-ytterbium co-doped double-cladding double-annular few-mode optical fiber, the annular structure in the fiber core 1-2 is doped, and the gain can be balanced to a certain extent; the doped outer ring 1-3 in the inner cladding 1-4 can utilize the tail part of the evanescent field of the signal mode, thereby being beneficial to improving the gain of the annular optical fiber; and ytterbium ions are introduced into the double-ring-shaped doped region, so that the doping concentration of erbium ions is improved, and the gain of the amplifier can be further improved.
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 erbium-ytterbium co-doped double-cladding double-annular few-mode gain optical fiber is characterized by comprising the following components from inside to outside: a fiber core (1-2), an inner cladding (1-4) and an outer cladding (1-5), wherein the fiber core (1-2) is wrapped with an inner ring (1-1); an outer ring (1-3) is arranged in the middle of the inner cladding (1-4); wherein,,
the cross sections of the fiber core (1-2), the inner ring (1-1), the outer ring (1-3) and the outer cladding (1-5) are all round; the cross section of the inner cladding (1-4) is an irregular polygon;
the fiber core (1-2) is made of quartz material doped with ions; the inner ring (1-1) and the outer ring (1-3) are doped with rare earth ions, including erbium ions and ytterbium ions;
the refractive index decreases gradually from the core (1-2) to the junction with the inner cladding (1-4), remains unchanged in the inner cladding (1-4), and the refractive index of the outer cladding (1-5) is lower than that of the inner cladding (1-4).
2. Erbium ytterbium co-doped double-cladding double-annular few-mode gain fiber according to claim 1, characterized in that the cross section of the inner cladding (1-4) is "D" -shaped, eccentric circular or "quincuncial" -shaped.
3. Erbium ytterbium co-doped double-cladding double-annular few-mode gain fiber according to claim 1 or 2, characterized in that the inner diameter of the outer ring (1-3) is larger than or equal to the outer diameter of the inner ring (1-1); the outer diameter of the outer ring (1-3) is smaller than or equal to the radius of the corresponding inscribed circle of the inner cladding (1-4).
4. Erbium ytterbium co-doped double cladding double annular few-mode gain fiber according to claim 1, characterized in that the diameter of the core (1-2) is below 20 μm.
5. The erbium ytterbium codoped double-clad double-annular few-mode gain fiber of claim 4, wherein the inner diameter of the inner ring (1-1) is 0.48 times the radius of the fiber core (1-2), and the diameter of the inner cladding (1-4) is about 125 microns.
6. The erbium ytterbium co-doped double-clad double-annular few-mode gain fiber of claim 1, wherein when the few-mode gain fiber is used as a gain medium, it is clad pumped with a multimode pump light source.
7. The erbium ytterbium co-doped double-cladding double-annular few-mode gain fiber of claim 6, wherein the pumping mode adopts forward pumping or backward pumping.
8. A few-mode erbium-doped fiber amplifier, comprising:
signal light providing means for providing signal light;
a multimode pump light source emitting pump light;
the beam combiner is used for combining the signal light and the pump light to obtain coupled light;
the few-mode gain fiber of any one of claims 1-7, disposed on an outgoing optical path of the coupled light, for amplifying the coupled light to obtain amplified light;
the spectrum detection device is arranged on the transmission light path of the amplified light and is used for collecting the light spot of the amplified light and measuring the power of the light spot.
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