WO2021143579A1 - 一种光纤滤波器以及光纤放大器 - Google Patents

一种光纤滤波器以及光纤放大器 Download PDF

Info

Publication number
WO2021143579A1
WO2021143579A1 PCT/CN2021/070312 CN2021070312W WO2021143579A1 WO 2021143579 A1 WO2021143579 A1 WO 2021143579A1 CN 2021070312 W CN2021070312 W CN 2021070312W WO 2021143579 A1 WO2021143579 A1 WO 2021143579A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical signal
optical
target
fiber
signal mode
Prior art date
Application number
PCT/CN2021/070312
Other languages
English (en)
French (fr)
Inventor
李巨浩
朱景龙
何永琪
吴圣灵
郭强
陈瑞山
周锐
Original Assignee
华为技术有限公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to EP21741756.7A priority Critical patent/EP4080256A4/en
Publication of WO2021143579A1 publication Critical patent/WO2021143579A1/zh
Priority to US17/863,100 priority patent/US11747565B2/en

Links

Images

Classifications

    • 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
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0078—Frequency filtering
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29317—Light guides of the optical fibre type
    • G02B6/29319—With a cascade of diffractive elements or of diffraction operations
    • 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
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
    • 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
    • G02B6/02295—Microstructured optical fibre
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/29391—Power equalisation of different channels, e.g. power flattening
    • 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
    • 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
    • H01S3/06783—Amplifying coupler
    • 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
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02066—Gratings having a surface relief structure, e.g. repetitive variation in diameter of core or cladding
    • 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
    • G02B6/03633—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 - -
    • 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
    • H01S2301/00—Functional characteristics
    • H01S2301/04—Gain spectral shaping, flattening
    • 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
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08018—Mode suppression
    • H01S3/0804—Transverse or lateral modes
    • 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
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1608—Solid materials characterised by an active (lasing) ion rare earth erbium

Definitions

  • This application relates to the field of optical fiber communication, and in particular to an optical fiber filter and an optical fiber amplifier.
  • the optical fiber filter is used to adjust the optical power of the optical signal to achieve gain equalization.
  • FIG. 1 shows the structure of a section of optical fiber 100.
  • the optical fiber filter is formed by cascading multiple sections of optical fibers 100.
  • the optical fiber 100 includes a core 101 and a cladding 102.
  • the optical power of the optical signal of the specific wavelength transmitted by the core 101 is coupled to the cladding 102 based on phase matching, so as to realize the adjustment of the optical power of the optical signal of the specific wavelength.
  • the optical fiber filter includes cascaded multiple sections of optical fibers 100, and different sections of optical fibers 100 are used to adjust the optical power of optical signals of different wavelengths, so as to achieve gain balance between optical signals of different wavelengths.
  • optical signals of the same wavelength of the same optical signal mode will be coupled to multiple optical signal modes supported by the cladding 102 in the optical fiber 100 based on phase matching.
  • the optical power of the optical signal is coupled to the multiple optical signal modes supported by the cladding 102, resulting in uncontrollable adjustment of the optical power of two or more optical signal modes.
  • the optical fiber filter shown in the prior art cannot achieve gain equalization of two or more optical signal modes.
  • the present application provides an optical fiber filter and an optical fiber amplifier, which can solve the problem that the existing optical fiber filter cannot achieve gain equalization for two or more optical signal modes.
  • the first aspect of the embodiments of the present application provides an optical fiber filter, including a core, an inner cladding and an outer cladding.
  • the inner cladding is wrapped around the outer peripheral surface of the core, and the outer cladding is wrapped around the outer peripheral surface of the inner cladding.
  • the refractive index of the core, the refractive index of the inner cladding and the refractive index of the outer cladding are successively decreased, the core is used to transmit at least two different first optical signal modes, and the inner cladding is used to transmit at least two For second optical signal modes that are different from each other, the core is etched to form at least one fiber grating; at least part of the optical power of the target first optical signal mode is only coupled with the target second optical signal mode at the fiber grating, wherein, The target first optical signal mode is one of at least two first optical signal modes, and the target second optical signal mode is one of at least two second optical signal modes.
  • the optical fiber filter shown in this aspect at least part of the optical power of one first optical signal mode can only be coupled to one second optical signal mode, and the optical power of the same first optical signal mode is not coupled to multiple second optical signals.
  • the condition of the signal mode effectively ensures the controllability of the optical power adjustment of the first optical signal mode, and effectively realizes the gain balance between the different first optical signal modes.
  • the optical fiber filter is based on the fiber grating to couple the optical power.
  • the fiber grating has the advantages of simple structure, small insertion loss, small size, and low cost.
  • the target first optical signal mode is coupled with the target second optical signal mode, and the following formula is satisfied:
  • the target first optical signal mode is coupled with the target second optical signal mode, and the following formula is satisfied:
  • the effective refractive index of the wavelength ⁇ and the first optical signal is created Effective refractive index of the second optical signal And the corresponding relationship of the grating period ⁇ of the fiber grating.
  • the fiber grating is enabled to couple at least part of the optical power of the first optical signal with the wavelength ⁇ to the second optical signal, so that the fiber filter can not only realize different first optical signal modes
  • the gain equalization between different first optical signals can also realize the gain equalization between different first optical signals.
  • the optical power of the first optical signal mode of the target can be accurately adjusted, and the effect of gain equalization can be improved.
  • the fiber core is etched into a plurality of fiber gratings, and the grating periods of the fiber gratings are different from each other.
  • the grating periods are different from each other, thereby effectively ensuring that different fiber gratings can reduce the optical power of different first optical signal modes. It is coupled to the inner cladding layer, thereby realizing independent adjustment of the optical power of different first optical signal modes, avoiding mutual interference, and effectively improving the accuracy of adjusting the optical power of the first optical signal mode.
  • each of the at least two first optical signal modes corresponds to a different second optical signal mode.
  • each of the at least two first optical signal modes corresponds to a second optical signal mode.
  • each of the other modes is Corresponds to one of the second optical signal modes.
  • the optical power of one first optical signal mode can only be coupled to one second optical signal mode, and the same first optical signal mode is not coupled to multiple second optical signal modes. Therefore, the controllability of the optical power adjustment of the first optical signal mode is effectively ensured, and the gain balance between different first optical signal modes is effectively realized.
  • the length of the fiber grating along the axial direction of the fiber core is positively correlated with the optical power coupled to the target second optical signal mode relation.
  • the optical power coupled to the target second optical signal mode can be adjusted by adjusting the length of the fiber grating in the axial direction of the core.
  • the optical power of the target first optical signal mode that has been coupled to the outer cladding layer is less than that of the target first optical signal mode that has been coupled to the target second light.
  • the optical power of the signal mode is less than that of the target first optical signal mode that has been coupled to the target second light.
  • the optical power of the target first optical signal mode is accurately adjusted through the outer coating.
  • the target first optical signal is controlled by controlling the optical power of the target first optical signal.
  • the optical power of the mode that has been coupled to the outer cladding layer is less than the optical power of the target first optical signal mode that has been coupled to the target second optical signal mode, and the optical power of the target first optical signal mode is only increased to the target second optical signal mode.
  • the optical signal mode coupling avoids coupling of the optical power of the target first optical signal mode to the outer cladding layer as much as possible.
  • the difference between the refractive index of the inner cladding layer and the refractive index of the outer cladding layer has a positive correlation with the number of types of the second optical signal mode.
  • the fiber grating couples at least part of the optical power of the target first optical signal mode only to the target second optical signal mode. It can be seen that the inner cladding The number of supported second optical signal modes needs to be limited. Because if the inner cladding layer supports an infinite number of second optical signal modes, it will cause the target first optical signal mode to couple to multiple second optical signal modes, resulting in the optical signal mode of the target first optical signal mode. Out of control of power regulation.
  • the difference between the refractive index of the inner cladding layer and the refractive index of the outer cladding layer can be adjusted to adjust the number of types of the second optical signal modes supported by the inner cladding layer, thereby realizing the adjustment of the first optical signal mode.
  • the radius of the inner cladding layer and the number of types of the second optical signal mode have a positive correlation.
  • the number of types of the second optical signal modes supported by the inner cladding can be adjusted by adjusting the radius of the inner cladding, so as to realize the controllable adjustment of the optical power of the first optical signal mode.
  • the second aspect of the embodiments of the present application provides a fiber amplifier.
  • the fiber amplifier includes a pump laser, a wavelength division multiplexer, a gain fiber, and a fiber filter.
  • the wavelength division multiplexer is respectively connected to the pump laser and the gain Optical fiber coupling, the gain optical fiber is coupled to the optical fiber filter; the wavelength division multiplexer is used to multiplex the pump light and the optical signal from the pump laser; the gain optical fiber is used to multiplex the optical signal from the wavelength division multiplexer
  • the optical signal of the filter is gain-amplified to output at least two first optical signal modes.
  • the optical fiber filter is as shown in the above-mentioned first aspect and will not be repeated.
  • the optical fiber amplifier shown in this aspect performs gain equalization on at least two different optical signal modes after gain amplification through the gain fiber .
  • the optical fiber amplifier effectively guarantees the gain balance between different optical signal modes, and effectively reduces the probability of interruption of optical signal transmission.
  • Fig. 1 is a schematic structural diagram of a section of optical fiber included in an optical fiber filter shown in the prior art
  • FIG. 2 is a structural example diagram of an embodiment of the optical fiber amplifier provided by this application.
  • Fig. 3 is a diagram showing an example of the first structure of the optical fiber filter provided by this application.
  • Fig. 4 is an example diagram of the first structure of the fiber core provided by this application.
  • FIG. 5 is a diagram showing an example of the second structure of the optical fiber filter provided by this application.
  • Fig. 6 is a diagram of a third structural example of the optical fiber filter provided by this application.
  • Fig. 7 is a first example diagram of the transmission spectrum provided by this application.
  • FIG. 8 is a second example diagram of the transmission spectrum provided by this application.
  • Fig. 9 is a third example diagram of the transmission spectrum provided by this application.
  • Fig. 10 is a fourth example diagram of the transmission spectrum provided by this application.
  • FIG. 11 is a first example diagram of the spectrogram provided by this application.
  • FIG. 12 is a second example diagram of the spectrogram provided by this application.
  • FIG. 13 is a diagram of a fourth structural example of the optical fiber filter provided by this application.
  • FIG. 14 is a third example diagram of the spectrogram provided by this application.
  • FIG. 15 is a fourth example diagram of the spectrogram provided by this application.
  • the optical fiber amplifier shown in this embodiment can support gain amplification of two or more optical signal modes.
  • the optical fiber amplifier is a few mode erbium-doped fiber amplifier (FM-EDFA).
  • FM-EDFA erbium-doped fiber amplifier
  • different optical signal modes have different light intensity distributions.
  • the fiber amplifier 200 includes an isolator 201, a pump laser 203, a wavelength division multiplexer 202, a gain fiber 204, and a fiber filter 205.
  • the isolator 201, the wavelength division multiplexer 202, the gain fiber 204, and the fiber filter 205 are sequentially coupled, and the wavelength division multiplexer 202 is also coupled to the pump laser 203.
  • the isolator 201 is used to inhibit the reflected light from entering the optical fiber 206 and to send the optical signal from the optical fiber 206 to the wavelength division multiplexer 202.
  • the wavelength division multiplexer 202 is used to multiplex the optical signal from the isolator 201 and the pump light from the pump laser 203.
  • the gain fiber 204 is used for gain amplifying the optical signal from the wavelength division multiplexer 202 to output at least two different optical signal modes.
  • the gain fiber 204 has different amplifying gains for different optical signal modes, which inevitably causes bit errors in the process of optical signal mode transmission.
  • the optical fiber filter 205 performs gain equalization on at least two different optical signal modes from the gain fiber 204.
  • the optical fiber filter effectively ensures the gain equalization between the different optical signal modes and effectively reduces the optical signal. Probability of transmission interruption.
  • the fiber filter 205 is a gain flattening filter (GFF) as an example for exemplification.
  • GFF gain flattening filter
  • FIG. 3 is a cross-sectional view of the optical fiber filter along the radial direction of the optical fiber filter.
  • the optical fiber filter includes a core 310, an inner cladding layer 320, and an outer cladding layer 330 sequentially arranged from the inside to the outside. Specifically, the inner cladding layer 320 is wrapped around the outer circumferential surface of the core 310, and the outer cladding layer 330 is wrapped around the outer circumferential surface of the inner cladding layer 320.
  • the fiber core 310, the inner cladding layer 320, and the outer cladding layer 330 are all circular as an example for illustration.
  • the fiber One or more of the core 310, the inner cladding layer 320, and the outer cladding layer 330 may also have a square shape, an oval shape, an irregular shape, etc., which are specifically not limited in this embodiment.
  • the refractive index of the core 310 is n core
  • the refractive index of the inner cladding 320 is n inner_clad
  • the refractive index of the outer cladding 330 is n outer_clad .
  • n core >n inner_clad >n outer_clad .
  • the refractive index of the core 310, the inner cladding layer 320, and the outer cladding layer 330 gradually decrease.
  • the refractive index n core of the core 310 specifically refers to the ratio of the propagation speed of the optical signal in vacuum to the propagation speed of the optical signal in the core 310.
  • the radius of the core 310 is r core
  • the radius of the inner cladding 320 is r inner_clad
  • the radius of the outer cladding 330 is r outer_clad .
  • r outer_clad > r inner_clad > r core It can be seen that the radii of the core 310, the inner cladding layer 320, and the outer cladding layer 330 increase sequentially.
  • the core 310 shown in this embodiment is used to transmit at least two different first optical signal modes
  • the inner cladding 320 is used to transmit at least two different second optical signal modes.
  • the signal mode and the second optical signal mode please refer to the description of the optical signal mode shown in FIG. 2 and will not be repeated.
  • FIG. 4 is a cross-sectional view of the fiber filter along the axial direction of the fiber filter.
  • a fiber grating is etched on the fiber core by laser.
  • the core is a few mode fiber (FMF) as an example for exemplification.
  • the core may also be a multimode fiber (MMF). It should be clear that this embodiment does not limit the formation of the fiber grating, as long as the fiber grating as shown in FIG. 4 can be formed on the core.
  • the core 310 includes N FBG, i.e., G 1, G 2, ... G N, for the present embodiment, the value of N is not particularly limited as long as the N is a positive integer greater than or equal to 1 .
  • the grating periods of the N fiber gratings are different from each other.
  • the length of the fiber grating G 1 in the axial direction of the core 310 is L 1
  • the length of the fiber grating G N in the axial direction of the core 310 is L N.
  • the fiber grating G 1 includes multiple sub-gratings. This embodiment does not limit the specific number of sub-gratings included in each fiber grating. Taking FIG. 4 as an example, the fiber grating G 1 specifically includes sub-gratings G 1-1 and G 1- 2 and G 1-3 .
  • the sub-grating G 1-1 has a grating period ⁇ 1_1
  • the sub-grating G 1-2 has a grating period ⁇ 1_2
  • the sub-grating G 1-3 has a grating period.
  • the period is ⁇ 1_3
  • the grating period ⁇ 1_1 , the grating period ⁇ 1-2, and the grating period ⁇ 1_3 are different from each other.
  • different sub-gratings have different grating periods as an example for illustrative description. In other examples, different sub-gratings may also have the same grating period, which is not specifically done. limited.
  • the sub-grating G 1-1 has M grating periods ⁇ 1_1 , and the sub-grating G 1-1 has M grating periods ⁇ 1_1 are all equal.
  • Each grating period ⁇ 1_1 includes a refractive index modulated part 401 and a refractive index unmodulated part 402.
  • the modulated refractive index portion 401 refers to a region where the refractive index changes on the core etched by a laser, so that the modulated portion 401 becomes a refractive index change point.
  • the non-modulated refractive index portion 402 refers to a region adjacent to the modulated refractive index portion 401 and the refractive index has not changed.
  • the specific value of M is not limited in this embodiment.
  • FIG. 5 is a cross-sectional view of the optical fiber filter along the axial direction of the optical fiber filter.
  • the inner cladding layer 320 shown in this embodiment includes at least one sub-cladding layer 51.
  • This embodiment takes the sub-cladding layer 51 as an example for exemplification.
  • the sub-cladding layers 51 that are arranged coaxially and connected in sequence constitute the inner cladding layer. 320.
  • the number of sub-cladding layers shown in this embodiment is equal to the number of fiber gratings shown above. In the case where there are multiple fiber gratings, multiple sub-cladding layers respectively wrap different fiber gratings.
  • the sub-cladding layers used to wrap different fiber gratings have different radii as an example for illustration.
  • the sub-cladding layer 511 that wraps the fiber grating G 1 and the fiber grating G 2 are wrapped.
  • the radius of the sub-cladding layer 512 is different, and the radius of the sub-cladding layer 511 is smaller than the radius of the sub-cladding layer 512.
  • the radii of the sub-cladding layers used to wrap different fiber gratings may also be the same.
  • the number of types of the second optical signal modes supported by the inner cladding layer is adjusted.
  • the inner cladding layer can be reduced by reducing the radius of the inner cladding layer.
  • the number of types of second optical signal modes supported as shown in FIG. 5 as an example, the radius of the sub-cladding layer 511 is smaller than the radius of the sub-cladding layer 512, and the number of types of the second optical signal modes supported by the sub-cladding layer 511 is less than The number of types of the second optical signal mode supported by the sub-cladding layer 512.
  • the core 310 of the optical fiber filter shown in this embodiment transmits at least two different first optical signal modes.
  • at least part of the optical power of the first optical signal mode needs to be coupled to the inner cladding.
  • gain equalization of the two or more first optical signal modes transmitted by the core is an exemplary description of several optional coupling methods for achieving gain equalization:
  • Each of the at least two first optical signal modes corresponds to a different second optical signal mode, so that at least part of the optical power of each first optical signal mode is coupled to its corresponding second optical signal mode.
  • the types of the second optical signal modes coupled to different first optical signal modes are different from each other.
  • At least two first optical signal modes are LP01 and LP11
  • at least two second optical signal modes are LP03 and LP12
  • LP01 corresponds to LP03
  • LP11 corresponds to LP12
  • at least part of the optical power of LP01 is coupled to LP03
  • At least part of the optical power of LP11 is coupled to LP12 to achieve gain equalization between LP01 and LP11.
  • the at least two first optical signal modes correspond to the same second optical signal mode, so that at least part of the optical power of each first optical signal mode is coupled to its corresponding second optical signal mode, and they are different
  • the types of the second optical signal modes coupled to the first optical signal mode are all the same.
  • At least two first optical signal modes are LP01 and LP11
  • at least two second optical signal modes are LP03 and LP12
  • both LP01 and LP11 correspond to LP03
  • at least part of the optical power of LP01 and at least part of the optical power of LP11 Both are coupled to LP03 to achieve gain equalization between LP01 and LP11.
  • each of the others corresponds to the second optical signal mode.
  • At least two first optical signal modes are LP01 and LP11
  • at least two second optical signal modes are LP03 and LP12
  • the optical power of LP01 is less than that of LP11.
  • the optical power of a first optical signal mode is coupled to multiple second optical signal modes, the optical power of the first optical signal mode coupled to each second optical signal mode cannot be adjusted, resulting in the first optical signal mode.
  • the optical power adjustment of the modes is out of control, and gain equalization among the multiple first optical signal modes cannot be achieved.
  • the optical power of one first optical signal mode can only be coupled to one second optical signal mode, and the same first optical signal mode is not coupled to multiple second optical signal modes. Therefore, the controllability of the optical power adjustment of the first optical signal mode is effectively ensured, and the gain equalization between different first optical signal modes is effectively realized.
  • the specific implementation process is described below:
  • the target first optical signal mode is one of at least two first optical signal modes transmitted by the core
  • the second optical signal mode is only at least two of the second optical signals transmitted by the inner cladding layer
  • the target fiber grating is a fiber grating included in the core. It can be seen that the target fiber grating can couple at least part of the optical power of the target first optical signal mode only to the target second optical signal mode, effectively avoiding the coupling of the target first optical signal mode to multiple second optical signal modes. Circumstances, thereby avoiding the out-of-control of the optical power adjustment of the target first optical signal mode.
  • the coupling of the target first optical signal mode to the target second optical signal mode based on the phase matching condition is taken as an example for exemplification:
  • the effective refractive index Description Specifically, the target first optical signal mode includes one or more first optical signals with different wavelengths, and the Is the effective refractive index of a first optical signal included in the first optical signal mode.
  • the ⁇ 1 is a propagation constant, which is used to characterize the phase change of the first optical signal per unit distance propagated in the core, and the wavelength ⁇ is the wavelength of the first optical signal.
  • the target second optical signal mode includes one or more channels of second optical signals with different wavelengths. Is the effective refractive index of a second optical signal included in the second optical signal mode.
  • the ⁇ 2 is a propagation constant, which is used to characterize the phase change of the second optical signal per unit distance propagated in the inner cladding, and the wavelength ⁇ is the wavelength of the second optical signal.
  • the optical power of each first optical signal included in the first optical signal mode needs to be adjusted.
  • the optical power of the first optical signal can be adjusted by coupling at least part of the optical power of the first optical signal to the second optical signal.
  • the wavelength of the first optical signal and the wavelength of the second optical signal are equal, and both are equal to the wavelength ⁇ .
  • the core shown in this embodiment includes multiple fiber gratings, and different fiber gratings are used to adjust the optical power of different optical signal modes, thereby achieving Independent adjustment of the optical power of different optical signal modes.
  • a target fiber grating includes multiple sub-gratings, and different sub-gratings are used to adjust the optical power of optical signals with different wavelengths, thereby realizing independent adjustment of the optical power of different optical signals.
  • the grating period of the target fiber grating may be the grating period of the target sub-grating, where the target sub-grating is the target fiber grating A section of sub-grating included.
  • the grating period ⁇ 1_1 of the sub-grating G 1-1 included in the fiber grating G 1 satisfies the corresponding relationship shown in the above formula, then the sub-grating G 1-1 is the target sub-grating, and the target The sub-grating G 1-1 is used to adjust the optical power of the first optical signal.
  • phase matching condition 2 For the description of each parameter shown in phase matching condition 2, please refer to the description of phase matching condition 1 for details.
  • phase matching condition 1 in which it is less than 110% and greater than 90%, it has been verified that the optical power of the target first optical signal mode can be accurately adjusted, and the effect of gain equalization is improved.
  • the description of the numerical range of is an optional example and is not limited, as long as the optical signal of the target first optical signal mode can be precisely adjusted.
  • phase matching condition 1 or phase matching condition 2 the effective refractive index of the first optical signal at the wavelength ⁇ is created Effective refractive index of the second optical signal And the corresponding relationship of the grating period ⁇ of the target fiber grating.
  • the target fiber grating is enabled to couple at least part of the optical power of the first optical signal with the wavelength ⁇ to the second optical signal, so that the optical fiber filter can not only realize different first optical signals
  • the gain equalization between the modes can also realize the gain equalization between different first optical signals.
  • the target fiber grating couples at least part of the optical power of the target first optical signal mode only to the target second optical signal mode.
  • the number of types of second optical signal modes supported by the inner cladding layer needs to be limited. Because if the inner cladding layer supports an infinite number of second optical signal modes, it will cause the target first optical signal mode to couple to multiple second optical signal modes, resulting in the optical signal mode of the target first optical signal mode. Out of control of power regulation. The following describes how to control the number of types of second optical signal modes supported by the inner cladding layer:
  • the number of types of second optical signal modes supported by the inner cladding layer is controlled.
  • the difference between the refractive index of the inner cladding layer and the refractive index of the outer cladding layer has a positive correlation with the number of types of the second optical signal mode supported by the inner cladding layer.
  • the difference between the refractive index of the inner cladding layer and the refractive index of the outer cladding layer should be increased, and if the number of types of second optical signal modes needs to be reduced, the inner cladding layer should be reduced. The difference between the refractive index and the refractive index of the outer cladding.
  • the radius of the inner cladding layer By controlling the radius of the inner cladding layer, the number of types of second optical signal modes supported by the inner cladding layer is controlled. Wherein, there is a positive correlation between the radius of the inner cladding layer and the number of types of the second optical signal mode supported by the inner cladding layer.
  • the optical power of the target first optical signal mode is adjusted by adjusting the length of the target fiber grating in the axial direction of the fiber core, wherein the length of the target fiber grating in the axial direction of the fiber core is coupled to the target
  • the magnitude of the optical power in the second optical signal mode is positively correlated.
  • the process of adjusting a first optical signal of the target first optical signal mode is taken as an example to illustrate: that is, by adjusting the length of the target sub-grating along the axial direction of the fiber core to realize the first optical signal. Adjustment of the optical power of the optical signal.
  • the length of the target sub-grating has a positive correlation with the optical power in the second optical signal mode coupled to the target. As shown in Figure 4, the longer the length L 1-1 of the target sub-grating G 1-1 along the axial direction of the core is, the larger the target sub-grating G 1-1 is coupled to the target second optical signal mode.
  • the optical power of the target first optical signal mode can be precisely adjusted through the outer coating. Specifically, in order to realize the controllable adjustment of the optical power of the target first optical signal mode, the optical power of the target first optical signal mode needs to be coupled to the target second optical signal mode only, and the optical power of the target first optical signal mode needs to be avoided as much as possible.
  • the optical power is coupled to the outer cladding. The specific method is to ensure that the first coupling coefficient is smaller than the second coupling coefficient.
  • the first coupling coefficient is the ratio of the first optical power to the second optical power
  • the second coupling coefficient is the ratio of the third optical power to the second optical power
  • the first optical power is the optical power of the target first optical signal mode that has been coupled to the outer cladding
  • the second optical power is the optical power of the target first optical signal mode in an uncoupled state
  • the The third optical power is the optical power of the target first optical signal mode that has been coupled to the target second optical signal mode.
  • the second coupling coefficient is about 10 times the first coupling coefficient, it means that the first coupling coefficient is much smaller than the second coupling coefficient.
  • the optical power of the target first optical signal mode coupled to the outer cladding layer is extremely weak.
  • the coupling between the target first optical signal mode and the outer cladding layer can be neglected, which effectively ensures that the optical power of the target first optical signal mode is only coupled to the target inner cladding layer, thus realizing the optical power of the target first optical signal mode. Precise adjustment to achieve gain balance.
  • the number of types of optical signal modes transmitted by the fiber core is equal to the number of types of second optical signal modes transmitted by the inner cladding layer as an example.
  • the core transmits four first optical signal modes, namely LP01, LP11, LP21, and LP02.
  • the second optical signal modes transmitted by the inner cladding layer are LP31, LP12, LP03 and LP22.
  • the optical power adjustment of different optical signal modes based on the same structural parameters is taken as an example.
  • the structural parameters are: the radius of the core is 6.6 micrometers ( ⁇ m), the radius of the inner cladding is 12.5 ⁇ m, and the outer cladding is 12.5 ⁇ m. The radius is 62.5 ⁇ m.
  • the structural parameters are also: the refractive index of the core is 1.45952, the refractive index of the inner cladding is 1.44782, and the refractive index of the outer cladding is 1.44402.
  • the first optical signal mode LP01 transmitted by the core is coupled to the second optical signal mode LP31 based on phase matching
  • the first optical signal mode LP11 transmitted by the core is coupled to the second optical signal mode LP12 based on phase matching
  • the transmitted first optical signal mode LP21 is coupled to the second optical signal mode LP03 based on phase matching
  • the first optical signal mode LP02 transmitted by the core is coupled to the second optical signal mode LP22 based on phase matching.
  • the coupling of the first optical signal mode LP01 is realized through the target fiber grating 601.
  • the first optical signal mode LP01 includes six first optical signals, and the center wavelengths of the six first optical signals are 1530nm, 1535nm, 1540nm, 1545nm, respectively , 1555nm and 1555nm.
  • the target fiber grating 601 includes six sub-gratings, namely G 1-1 , G 1-2 , G 1-3 , G 1-4 , G 1-5 and G 1-6 .
  • the grating period ⁇ of the sub-grating G 1-1 is 0.01209 centimeters (cm)
  • the sub-grating G 1-1 includes a total of 285 grating periods ⁇
  • the sub-grating G 1-1 is along the axis of the core
  • the length in the direction is 3.45 cm.
  • the sub-grating can couple at least part of the optical power of the first optical signal with a center wavelength of 1530 nm to the second optical signal mode LP31.
  • the G 1-6 can couple at least part of the optical power of the first optical signal with a center wavelength of 1555 nm to the second optical signal mode LP31.
  • the target fiber grating 602 realizes the coupling to the first optical signal mode LP11.
  • the first optical signal mode LP11 includes three first optical signals, and the center wavelengths of the three first optical signals are 1532 nm, 1545 nm, and 1550 nm, respectively.
  • the target fiber grating 602 includes three sub-gratings, namely G 2-1 , G 2-2 and G 2-3 .
  • the grating periods of G 2-1 , G 2-2, and G 2-3 and the types and numbers of grating periods please refer to Table 2, which will not be repeated.
  • the sub-grating G 2-1 is used to couple at least part of the optical power of the first optical signal with a center wavelength of 1532 nm to the second optical signal mode LP12
  • the sub-grating G 2 -3 is used to couple at least part of the optical power of the first optical signal with a center wavelength of 1558 nm to the second optical signal mode LP12.
  • the target fiber grating 603 realizes the coupling to the first optical signal mode LP21.
  • the first optical signal mode LP21 includes three first optical signals, and the center wavelengths of the three first optical signals are 1532 nm, 1545 nm, and 1555 nm, respectively.
  • the target fiber grating 603 includes three sub-gratings, namely G 3-1 , G 3-2 and G 3-3 .
  • the grating periods of G 3-1 , G 3-2, and G 3-3 and the number of grating periods please refer to Table 3, which will not be repeated.
  • the sub-grating G 3-1 is used to couple at least part of the optical power of the first optical signal with a center wavelength of 1532 nm to the second optical signal mode LP03
  • the sub-grating G 3 -3 is used to couple at least part of the optical power of the first optical signal with a center wavelength of 1555 nm to the second optical signal mode LP03.
  • the target fiber grating 604 realizes the coupling to the first optical signal mode LP02.
  • the first optical signal mode LP02 includes three first optical signals, and the center wavelengths of the three first optical signals are 1531 nm, 1550 nm, and 1557 nm, respectively.
  • the target fiber grating 604 includes three sub-gratings, namely G 4-1 , G 4-2 and G 4-3 .
  • the grating period and the number of grating periods of G 4-1 , G 4-2, and G 4-3 please refer to Table 4, which will not be repeated.
  • the sub-grating G 4-1 is used to couple at least part of the optical power of the first optical signal with a center wavelength of 1531 nm to the second optical signal mode LP22, and so on, the sub-grating G 4 -3 is used to couple at least part of the optical power of the first optical signal mode with a center wavelength of 1557 nm to the second optical signal mode LP22.
  • This application scenario takes the optical powers of different first optical signal modes coupled to different second optical signal modes as an example for illustration. It should be clear that this is not limited here. For example, multiple first optical signal modes may also be used.
  • the optical power of the signal mode is coupled to the same second optical signal mode, as long as the optical power of any first optical signal in any first optical signal mode is coupled to only one second optical signal mode, it can be seen that one The second optical signal mode can receive the optical power of multiple first optical signal modes, and the different second optical signal mode cannot receive the optical power from the same first optical signal mode.
  • the cascaded target fiber grating 601, target fiber grating 602, target fiber grating 603, and target fiber grating 604 in the fiber core can achieve gain equalization for the entire C-band (1530-1565 nm).
  • the fiber core shown in this application scenario takes the realization of gain equalization of the entire C-band as an example for illustration. In other examples, the core can also achieve gain equalization for other bands, for example, achieve gain equalization for the L-band.
  • the first optical signal modes LP01, LP11, LP21, and LP02 all include an optical signal with a center wavelength of 1545 nm, passing through the fiber grating G 1 , fiber grating G 2 , fiber grating G 3 and fiber grating G 4 Realize the adjustment of the optical power of the optical signal with a center wavelength of 1545 nm, respectively, so as to realize the gain equalization of the optical signal with a center wavelength of 1545 nm in the first optical signal modes LP01, LP11, LP21, and LP02.
  • the target fiber grating shown in this application scenario can adjust the optical power of a first optical signal mode, and different target fiber gratings can adjust different first optical signal modes. It can be seen that different target fiber gratings will Based on different phase matching, the adjustment of the optical power of the different first optical signal modes is realized. That is, each target fiber grating can independently adjust the optical power of each first optical signal mode, effectively avoiding mutual interference. Among them, avoiding mutual interference means that the target fiber grating will not interfere with the first optical signal mode during the process of transmitting the first optical signal modes LP01, LP11, LP21, and LP02. The optical power of other first optical signal modes transmitted by the target fiber grating. In order to better illustrate that the fiber filter shown in this application scenario can effectively avoid mutual interference, please refer to the simulation example shown below for details:
  • This simulation example is shown in combination with the above-mentioned coupling mode 1, that is, the first optical signal mode LP01 transmitted by the fiber core is coupled to the second optical signal mode LP31.
  • the simulation is performed according to different values of the number N of grating periods of the target fiber grating 601.
  • the number N of grating periods please refer to the coupling method 1 for details. Go into details.
  • This simulation example does not limit the sub-gratings including the number N of grating periods.
  • the sub-gratings including the number N of grating periods can be G 1-1 , G 1-2 , G 1-3 , G 1- 4.
  • the number N of grating periods is taken as an example in the interval 40 to 400.
  • the number N of grating periods is taken within the interval in a manner of increasing the period of 40, then the number of grating periods N Values are: 40, 80, 120, 160, 200, 240, 280, 320, 360, and 400.
  • the first optical signal mode LP01 is coupled to obtain the transmission spectrum 701 as shown in FIG. 7.
  • the abscissa of the transmission spectrum 701 is the wavelength and the unit is nanometer (nm ), the ordinate is the relative power in decibels (dB), and the relative power is the magnitude of the optical power between the first optical signal mode LP01 coupled to the second optical signal mode LP31 and the first optical signal mode LP01 that has not yet been coupled
  • the size of the optical power is the size of the optical power.
  • the first optical signal mode LP01 has different attenuation curves under the coupling action of the target fiber grating.
  • the value of N has the above ten kinds
  • ten attenuation curves as shown in the transmission spectrum 701 can be obtained. It can be seen that the target fiber grating 601 with the number N of different grating periods can couple the optical power of the first optical signal mode LP01.
  • the transmission spectra of the first optical signal modes LP11, LP21, and LP02 are as shown in the transmission spectra 702, 703, and 704 as shown in FIG. 7, respectively.
  • the attenuation curves of the first optical signal modes LP11, LP21, and LP02 hardly vary with the value of the number N of each grating period of the target fiber grating 601. That is, when there are the above ten kinds of values of N, the ten obtained transmission spectra 702, 703, and 704 show almost coincident attenuation curves.
  • the maximum relative powers of the first optical signal modes LP11, LP21, and LP02 are 0.027, 0.25, and 0.35, respectively. It can be seen that when the target fiber grating 601 couples the first optical signal mode LP01, it will hardly cause interference to the optical power of the first optical signal modes LP11, LP21, and LP02.
  • This simulation example is shown in combination with the above-mentioned coupling mode 2, that is, the first optical signal mode LP11 transmitted by the fiber core is coupled to the second optical signal mode LP12. Specifically, in this simulation example, the simulation is performed according to the different values of the number N of grating periods of the target fiber grating 602. For the description of the value of the number N of grating periods, please refer to the above simulation example 1. , Do not repeat it.
  • the first optical signal mode LP11 is coupled to obtain the transmission spectrum 802 as shown in FIG. 8.
  • the coordinates of the transmission spectrum 802 please refer to the above simulation example for details As shown in 1, do not repeat them.
  • the first optical signal mode LP11 has different attenuation curves under the coupling action of the target fiber grating 602.
  • the value of N has the above ten kinds
  • ten attenuation curves as shown in the transmission spectrum 802 can be obtained. It can be seen that the target fiber grating 602 with the number N of different grating periods can couple the optical power of the first optical signal mode LP11.
  • the transmission spectra of the first optical signal modes LP01, LP21, and LP02 are as shown in the transmission spectra 801, 803, and 804 as shown in FIG. 8, respectively.
  • the attenuation curves of the first optical signal modes LP01, LP21, and LP02 hardly change with the value of the number N of each grating period of the target fiber grating 602. That is, when there are the above ten kinds of values of N, ten attenuation curves that almost coincide with each other as shown in the transmission spectra 801, 803, and 804 are obtained.
  • the maximum relative powers of the first optical signal modes LP01, LP21, and LP02 are 0.0028, 0.06, and 0.07, respectively. It can be seen that when the target fiber grating 602 couples the first optical signal mode LP11, it will not cause interference to the first optical signal modes LP01, LP21, and LP02.
  • This simulation example is shown in combination with the above-mentioned coupling mode 3, that is, the first optical signal mode LP21 transmitted by the fiber core is coupled to the second optical signal mode LP03. Specifically, in this simulation example, the simulation is performed according to the different values of the number N of grating periods of the target fiber grating 603. For the description of the value of the number N of grating periods, please refer to the above simulation example 1. , Do not repeat it.
  • the first optical signal mode LP21 is coupled to obtain the transmission spectrum 903 as shown in FIG. 9.
  • the coordinates of the transmission spectrum 903 please refer to the above simulation example for details As shown in 1, do not repeat them.
  • the first optical signal mode LP21 has a different attenuation curve under the coupling action of the target fiber grating 603.
  • the target fiber grating 603 with the number N of different grating periods can couple the optical power of the first optical signal mode LP21.
  • the transmission spectra of the first optical signal modes LP01, LP11, and LP02 are as shown in the transmission spectra 901, 902, and 904 shown in FIG. 9, respectively.
  • the attenuation curves of the first optical signal modes LP01, LP11, and LP02 hardly vary with the value of the number N of each grating period of the target fiber grating 603. That is, when there are the above ten kinds of values of N, the ten obtained transmission spectra 901, 902, and 904 show almost coincident attenuation curves.
  • the maximum relative powers of the first optical signal modes LP01, LP11, and LP02 are 0.002, 0.005, and 0.055, respectively. It can be seen that when the target fiber grating 603 couples the first optical signal mode LP21, it will not cause interference to the first optical signal modes LP01, LP11, and LP02.
  • This simulation example is shown in combination with the above-mentioned coupling mode 4, that is, the first optical signal mode LP02 transmitted by the fiber core is coupled to the second optical signal mode LP22. Specifically, in this simulation example, the simulation is performed according to different values of the number N of grating periods of the target fiber grating 604. For the description of the value of the number N of grating periods, please refer to the simulation example 1 above. , Do not repeat it.
  • the first optical signal mode LP02 is coupled to obtain the transmission spectrum 1004 as shown in FIG. 10.
  • the coordinates of the transmission spectrum 1004 please refer to the above simulation example for details As shown in 1, do not repeat them.
  • the first optical signal mode LP02 has different attenuation curves under the coupling action of the target fiber grating 604.
  • the value of N has the above ten kinds
  • ten attenuation curves as shown in the transmission spectrum 1004 can be obtained. It can be seen that the target fiber grating 604 with the number N of different grating periods can couple the optical power of the first optical signal mode LP02.
  • the transmission spectra of the first optical signal modes LP01, LP11, and LP21 are shown as the transmission spectra 1001, 1002, and 1004 as shown in FIG. 10, respectively.
  • the attenuation curves of the first optical signal modes LP01, LP11, and LP21 hardly change with the value of the number N of each grating period of the target fiber grating 604. That is, when there are the above ten kinds of values of N, ten attenuation curves that almost coincide with each other as shown in the transmission spectra 1001, 1002, and 1004 are obtained.
  • the maximum relative powers of the first optical signal modes LP01, LP11, and LP21 are 0.001, 0.023, and 0.07, respectively. It can be seen that when the target fiber grating 604 couples the first optical signal mode LP02, it will not cause interference to the first optical signal modes LP01, LP11, and LP21.
  • FIG. 11 is a spectrum diagram of the four first optical signal modes LP01, LP11, LP21, and LP02 output by the above-mentioned gain fiber.
  • the abscissa of the spectrogram represents the wavelength, and the ordinate represents the power.
  • the first optical signal modes LP01, LP11, LP21, and LP02 are not filtered by the optical fiber filter.
  • the power of each optical signal mode in the spectrogram has relatively large fluctuations, and the power difference between the optical signal modes is also It is relatively large and cannot achieve the balance between modes.
  • FIG. 12 is a spectrum diagram of the four optical signal modes output by the gain fiber after being filtered by the fiber filter.
  • the first optical signal modes LP01, LP11, LP21, and LP02 have been filtered by optical fiber filters.
  • the power of each optical signal mode in the spectrogram has quite small fluctuations.
  • the power of each optical signal mode is the largest The ratio of the power value to the minimum power value is less than 0.47, and the power difference between the optical signal modes is very small, and the balance is basically maintained.
  • the optical power of the four first optical signal modes LP01, LP11, LP21, and LP02 output by the gain fiber can be adjusted to realize the interoperability between different first optical signal modes.
  • the gain is balanced.
  • the number of types of optical signal modes transmitted by the fiber core and the number of types of second optical signal modes transmitted by the inner cladding layer are not equal as an example.
  • the core transmits two optical signal modes, namely LP01 and LP11.
  • the second optical signal modes transmitted by the inner cladding layer are LP21, LP02, LP12, and LP31.
  • the first optical signal mode LP01 transmitted by the core is coupled to the second optical signal mode LP21 based on phase matching
  • the first optical signal mode LP11 transmitted by the core is coupled to the second optical signal mode LP02 based on phase matching.
  • the power adjustment for different optical signal modes based on different structural parameters is taken as an example.
  • the first structural parameter is used to couple the first optical signal mode LP01
  • the second structural parameter is used to adjust the first optical signal mode.
  • the signal mode LP11 is coupled.
  • the first structure parameter is: the radius of the core is 6.8 ⁇ m, the radius of the inner cladding is 9.0 ⁇ m, and the radius of the outer cladding is 62.5 ⁇ m.
  • the refractive index of the core is 1.4536, the refractive index of the inner cladding is 1.4473, and the refractive index of the outer cladding is 1.44402.
  • the second structural parameters are: the radius of the core is 6.8 ⁇ m, the radius of the inner cladding is 11.0 ⁇ m, and the radius of the outer cladding is 62.5 ⁇ m.
  • the refractive index of the core is 1.4536, the refractive index of the inner cladding is 1.4473, and the refractive index of the outer cladding is 1.44402.
  • the specific coupling method is described below:
  • the coupling of the first optical signal mode LP01 transmitted by the fiber core to the second optical signal mode LP21 will be specifically described in conjunction with FIG. 13 and Table 6.
  • the coupling of the first optical signal mode LP01 is realized through the target fiber grating 1301.
  • the first optical signal mode LP01 includes three first optical signals, and the center wavelengths of the three first optical signals are 1530 nm as shown in Table 6. , 1545nm and 1555nm.
  • the target fiber grating 1301 includes three sub-gratings, namely G 1-1 , G 1-2 and G 1-3 . Among them, the grating period of each sub-grating, the number and length of grating period are shown in Table 6.
  • the sub-grating G 1-1 is capable of coupling at least part of the optical power of the first optical signal with a center wavelength of 1530 nm to the second optical signal mode LP21 based on phase matching.
  • phase matching please refer to the above Show, do not repeat it.
  • the sub-grating G 1-3 can couple at least part of the optical power of the first optical signal with a center wavelength of 1555 nm to the second optical signal mode LP21.
  • the coupling of the first optical signal mode LP11 is realized through the target fiber grating 1302.
  • the first optical signal mode LP11 includes three first optical signals, and the center wavelengths of the three first optical signals are 1530 nm as shown in Table 7. , 1545nm and 1555nm.
  • the target fiber grating 1302 includes three sub-gratings, namely G 2-1 , G 2-2 and G 2-3 . Among them, the grating period of each sub-grating, the number, length and center wavelength of the grating period are shown in Table 7.
  • the sub-grating G 2-1 can couple at least part of the optical power of the first optical signal with a center wavelength of 1530 nm to the second optical signal mode LP02 based on phase matching.
  • phase matching please refer to the above Show, do not repeat it.
  • the sub-grating G 2-3 can couple at least part of the optical power of the first optical signal with a center wavelength of 1555 nm to the second optical signal mode LP02.
  • each target fiber grating can independently adjust the optical power of each first optical signal mode, effectively avoiding mutual interference.
  • the following is a simulation method to verify the effect of the fiber filter shown in this application scenario to achieve gain equalization.
  • FIG. 14 is a spectrum diagram of the two first optical signal modes LP01 and LP11 output by the above-mentioned gain fiber.
  • the first optical signal modes LP01 and LP11 are not filtered by the optical fiber filter, and the power of each first optical signal mode in the spectrogram has relatively large fluctuations.
  • FIG. 15 is a spectrum diagram of the two first optical signal modes LP01 and LP11 output by the gain fiber.
  • the first optical signal modes LP01 and LP11 have been filtered by the optical fiber filter, and the power of each first optical signal mode in the spectrogram has relatively small fluctuations, as shown in Figure 15, the power of each first optical signal mode
  • the ratio of the maximum value to the minimum power value is less than 0.5.
  • the optical fiber filter shown in this embodiment can independently adjust the optical power of two or more first optical signal modes, thereby effectively achieving gain balance between different optical signal modes and different optical signals.
  • the gain balance between the first optical signals of different wavelengths in the mode effectively reduces the probability of interruption of optical signal transmission.
  • Adjusting the optical power of the target first optical signal mode based on the target fiber grating does not interfere with the optical power of other first optical signals, effectively avoiding interference.
  • the target fiber grating of the fiber filter can couple at least part of the optical power of the target first optical signal mode to a target second optical signal mode, and the target second optical signal mode is only one optical signal mode supported by the inner cladding It can be seen that the optical power of the first optical signal mode of the same target will not be coupled to multiple second optical signal modes, so that the controllable adjustment of the optical power of the target first optical signal mode is achieved, and the optical power of the target first optical signal mode is effectively improved. The accuracy of the optical power adjustment for the first optical signal mode of the target is improved.
  • the fiber filter is based on the fiber grating in the fiber core to couple the optical power.
  • the fiber grating has the advantages of simple structure, small insertion loss, small size, and low cost.

Landscapes

  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Manufacturing & Machinery (AREA)
  • Lasers (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

一种光纤滤波器（205）以及光纤放大器（200），其能够实现对少模光信号的平坦放大，使光纤滤波器（205）的纤芯（310）所传输的多个光信号模式中的每个光信号模式的光功率实现可控调节。光纤滤波器（205）包括纤芯（310）、内包层（320）以及外包层（330），纤芯（310）的折射率、内包层（320）的折射率和外包层（330）的折射率依次递减，纤芯（310）用于传输至少两种互不相同的第一光信号模式，内包层（320）用于传输至少两种互不相同的第二光信号模式，纤芯（310）被刻蚀出至少一个光纤光栅；目标第一光信号模式的至少部分光功率在光纤光栅处仅与目标第二光信号模式耦合，其中，目标第一光信号模式为至少两种第一光信号模式中的一种，目标第二光信号模式为至少两种第二光信号模式中的一种。

Description

一种光纤滤波器以及光纤放大器
本申请要求于2020年1月14日提交中国国家知识产权局、申请号为202010039133.5、发明名称为“一种光纤滤波器以及光纤放大器”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及光纤通信领域，尤其涉及一种光纤滤波器以及光纤放大器。
背景技术
光纤滤波器用于对光信号的光功率的调节，以实现增益均衡。如图1所示，图1所示为一段光纤100的结构。该光纤滤波器由多段光纤100级联而成。
光纤100包括纤芯101和包层102。该纤芯101所传输的特定波长的光信号的光功率，基于相位匹配耦合至包层102，以实现对该特定波长的光信号的光功率的调节。该光纤滤波器包括级联的多段光纤100，不同段的光纤100用于对不同波长的光信号的光功率进行调节，以实现不同波长的光信号之间的增益均衡。
但是，若该纤芯101传输两个或两个以上的光信号模式，同一光信号模式的同一波长光信号会在光纤100中基于相位匹配向包层102所支持的多个光信号模式耦合，从而使得该光信号的光功率耦合至包层102所支持的多个光信号模式，导致对两个或两个以上光信号模式的光功率调节的不可控。可见，现有技术所示的光纤滤波器无法实现两个或两个以上的光信号模式的增益均衡。
发明内容
本申请提供了一种光纤滤波器以及光纤放大器，可以解决现有光纤滤波器无法实现对两个或两个以上的光信号模式的增益均衡的问题。
本申请实施例第一方面提供了一种光纤滤波器，包括纤芯、内包层以及外包层，该内包层包裹于该纤芯的外周面，该外包层包裹于该内包层的外周面，该纤芯的折射率、该内包层的折射率和该外包层的折射率依次递减，该纤芯用于传输至少两种互不相同的第一光信号模式，该内包层用于传输至少两种互不相同的第二光信号模式，该纤芯被刻蚀出至少一个光纤光栅；目标第一光信号模式的至少部分光功率在该光纤光栅处仅与目标第二光信号模式耦合，其中，该目标第一光信号模式为至少两种第一光信号模式中的一种，该目标第二光信号模式为至少两种第二光信号模式中的一种。
采用本方面所示的光纤滤波器，一个第一光信号模式的至少部分光功率仅能够耦合至一个第二光信号模式，不会出现同一第一光信号模式的光功率耦合至多个第二光信号模式的情况，从而有效的保证了对该第一光信号模式的光功率调节的可控，有效的实现了不同的第一光信号模式之间的增益均衡。而且该光纤滤波器是基于光纤光栅对光功率进行耦合的，光纤光栅具有结构简单，插损小、体积小、成本低等优点。
基于本申请实施例第一方面，一种可选地实现方式中，该目标第一光信号模式与该目标 第二光信号模式耦合，满足如下公式：
Figure PCTCN2021070312-appb-000001
其中，所述
Figure PCTCN2021070312-appb-000002
为所述目标第一光信号模式所包括的一路第一光信号的有效折射率；所述
Figure PCTCN2021070312-appb-000003
为所述目标第二光信号模式所包括的一路第二光信号的有效折射率；所述λ为所述第一光信号和所述第二光信号所具有的波长，所述Λ为所述光纤光栅的光栅周期。
基于本申请实施例第一方面，一种可选地实现方式中，该目标第一光信号模式与该目标第二光信号模式耦合，满足如下公式：
Figure PCTCN2021070312-appb-000004
其中，所述
Figure PCTCN2021070312-appb-000005
为所述目标第一光信号模式所包括的一路第一光信号的有效折射率；所述
Figure PCTCN2021070312-appb-000006
为所述目标第二光信号模式所包括的一路第二光信号的有效折射率；所述λ为所述第一光信号和所述第二光信号所具有的波长，所述Λ为所述光纤光栅的光栅周期。
可见，基于上述所示的公式，创建了该波长λ、第一光信号的有效折射率
Figure PCTCN2021070312-appb-000007
第二光信号的有效折射率
Figure PCTCN2021070312-appb-000008
以及该光纤光栅的光栅周期Λ的对应关系。基于该对应关系，使能该光纤光栅能够将具有该波长λ的第一光信号的至少部分光功率耦合至该第二光信号，从而使得该光纤滤波器不仅能够实现不同的第一光信号模式之间的增益均衡，还能够实现不同的第一光信号之间的增益均衡。能够实现对该目标第一光信号模式的光功率的精确调节，提高了增益均衡的效果。
基于本申请实施例第一方面，一种可选地实现方式中，该纤芯被刻蚀出多个光纤光栅，该光纤光栅的光栅周期彼此不同。
采用本方面所示的光纤滤波器，在纤芯被刻蚀出多个光纤光栅中，光栅周期互不相同，从而有效的保证了不同的光纤光栅能够将不同的第一光信号模式的光功率耦合至内包层，从而实现了对不同的第一光信号模式的光功率的独立调节，避免了互相干扰，有效提高了第一光信号模式的光功率的调节的精确性。
基于本申请实施例第一方面，一种可选地实现方式中，该至少两种第一光信号模式中的每一种均对应不同的一种第二光信号模式。
基于本申请实施例第一方面，一种可选地实现方式中，该至少两种第一光信号模式中的每一种均对应一种第二光信号模式。也就是说，也可能有多种不同的第一光信号模式对应同一种第二光信号模式；甚至，所有的第一光信号模式均对应同一种第二光信号模式，也是有可能的。
基于本申请实施例第一方面，一种可选地实现方式中，在该至少两种第一光信号模式中，除对应的光功率最低的那种第一光信号模式，其余每一种均对应一种该第二光信号模式。
采用本方面所示的光纤滤波器，一个第一光信号模式的光功率仅能够耦合至一个第二光信号模式，不会出现同一第一光信号模式耦合至多个第二光信号模式的情况，从而有效的保证了对该第一光信号模式的光功率调节的可控，有效的实现了不同的第一光信号模式之间的增益均衡。
基于本申请实施例第一方面，一种可选地实现方式中，该光纤光栅沿该纤芯的轴向方向的长度与耦合至该目标第二光信号模式中的光功率大小之间呈正相关关系。
采用本方面所示的光纤滤波器，为实现对目标第一光信号模式的光功率的精确调节，以 实现增益均衡，则需要调节耦合至目标第二光信号模式的光功率的大小，本方面所示可通过调节该光纤光栅沿该纤芯的轴向方向的长度的方式以调节耦合至该目标第二光信号模式中的光功率的大小。
基于本申请实施例第一方面，一种可选地实现方式中，该目标第一光信号模式已耦合至该外包层的光功率小于该目标第一光信号模式已耦合至该目标第二光信号模式的光功率。
为实现对目标第一光信号模式的光功率的精确调节，则通过外包层实现对目标第一光信号模式的光功率的精确调节，具体地，本方面所示通过控制该目标第一光信号模式已耦合至该外包层的光功率小于该目标第一光信号模式已耦合至该目标第二光信号模式的光功率的方式，实现该目标第一光信号模式的光功率仅向目标第二光信号模式耦合，尽量避免了目标第一光信号模式的光功率耦合至外包层。
基于本申请实施例第一方面，一种可选地实现方式中，该内包层的折射率和该外包层的折射率之间的差值与该第二光信号模式的种类数呈正相关关系。
为保证对目标第一光信号模式的光功率的可控调节，则该光纤光栅将该目标第一光信号模式的至少部分光功率仅向目标第二光信号模式进行耦合，可见，该内包层所支持的第二光信号模式的种类数需要是有限的。因为若该内包层所支持的第二光信号模式为无限多个，会导致该目标第一光信号模式会向多个第二光信号模式进行耦合，导致对该目标第一光信号模式的光功率调节的失控。本方面所示可通过调节该内包层的折射率和该外包层的折射率之间的差值的方式以实现对内包层所支持的第二光信号模式的种类数的调节，从而实现对第一光信号模式的光功率的可控调节。
基于本申请实施例第一方面，一种可选地实现方式中，该内包层的半径大小与该第二光信号模式的种类数之间呈正相关关系。
本方面所示可通过调节该内包层的半径大小的方式以实现对内包层所支持的第二光信号模式的种类数的调节，从而实现对第一光信号模式的光功率的可控调节。
本申请实施例第二方面提供了一种光纤放大器，该光纤放大器包括泵浦激光器、波分复用器、增益光纤以及光纤滤波器，该波分复用器分别与该泵浦激光器以及该增益光纤耦接，该增益光纤与该光纤滤波器耦接；该波分复用器用于对来自该泵浦激光器的泵浦光和光信号进行复用；该增益光纤用于对来自该波分复用器的该光信号进行增益放大以输出至少两种第一光信号模式，该光纤滤波器如上述第一方面所示，不做赘述。
在面向例如中长距离传输、超大容量模分传输、超大容量波分传输等场景，本方面所示的光纤放大器对经由该增益光纤进行增益放大后的至少两种不同的光信号模式进行增益均衡，该光纤放大器有效的保证了不同光信号模式之间的增益均衡，有效的降低光信号传输中断的概率。
附图说明
图1为现有技术所示的光纤滤波器所包括的一段光纤的结构示意图；
图2为本申请所提供的光纤放大器的一种实施例结构示例图；
图3为本申请所提供的光纤滤波器的第一种结构示例图；
图4为本申请所提供的纤芯的第一种结构示例图；
图5为本申请所提供的光纤滤波器的第二种结构示例图；
图6为本申请所提供的光纤滤波器的第三种结构示例图；
图7为本申请所提供的透射谱的第一种示例图；
图8为本申请所提供的透射谱的第二种示例图；
图9为本申请所提供的透射谱的第三种示例图；
图10为本申请所提供的透射谱的第四种示例图；
图11为本申请所提供的光谱图的第一种示例图；
图12为本申请所提供的光谱图的第二种示例图；
图13为本申请所提供的光纤滤波器的第四种结构示例图；
图14为本申请所提供的光谱图的第三种示例图；
图15为本申请所提供的光谱图的第四种示例图。
具体实施方式
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
以下首先结合图2所示对本申请所提供的光纤放大器的具体结构进行说明：
本实施例所示的光纤放大器能够支持两个或两个以上光信号模式的增益放大。例如，该光纤放大器为少模掺铒光纤放大器(few mode erbium-doped fiber amplifier，FM-EDFA)。其中，不同的光信号模式具有不同的光强分布。
该光纤放大器200包括隔离器201、泵浦激光器203、波分复用器202、增益光纤204以及光纤滤波器205。该隔离器201、波分复用器202、增益光纤204以及光纤滤波器205依次耦接，且该波分复用器202还与泵浦激光器203耦接。
该隔离器201用于抑制回波反射光进入光纤206，并用于将来自光纤206的光信号发送给波分复用器202。该波分复用器202用于对来自该隔离器201的光信号和来自泵浦激光器203的泵浦光进行复用。该增益光纤204用于对来自波分复用器202的光信号进行增益放大以输出至少两种不同的光信号模式。
在面向例如中长距离传输、超大容量模分传输、超大容量波分传输等场景，增益光纤204对不同光信号模式的放大增益不同，不可避免地在光信号模式传输的过程中产生误码。本实施例通过光纤滤波器205对来自该增益光纤204的至少两种不同的光信号模式进行增益均衡，该光纤滤波器有效的保证了不同光信号模式之间的增益均衡，有效的降低光信号传输中断的概率。本实施例以光纤滤波器205为增益平坦滤波器(gain flattening filter，GFF)为例进行示例性说明。
以下结合图3所示对光纤滤波器的具体结构进行说明，其中，图3为沿该光纤滤波器的径向，该光纤滤波器的切面图。
该光纤滤波器包括由内而外依次设置的纤芯310、内包层320和外包层330。具体地，该内包层320包裹于该纤芯310的外周面，该外包层330包裹于该内包层320的外周面。沿该光纤滤波器的径向，本实施例以纤芯310、内包层320和外包层330均为圆形为例进行示例性说明，在其他示例中，沿该光纤滤波器的径向，纤芯310、内包层320和外包层330中的一个或多个还可为方形、椭圆形、不规则形状等，具体在本实施例中不做限定。
具体地，该纤芯310的折射率为n core，该内包层320的折射率为n inner_clad，该外包层330 的折射率为n outer_clad。其中，n core>n inner_clad>n outer_clad。可见，该纤芯310、内包层320和外包层330的折射率依次递减。以纤芯310为例，纤芯310的折射率n core具体是指，光信号在真空中的传播速度与光信号在该纤芯310的传播速度之比。
该纤芯310的半径为r core，该内包层320的半径为r inner_clad，该外包层330的半径为r outer_clad。其中，r outer_clad>r inner_clad>r core。可见，该纤芯310、内包层320和外包层330的半径依次递增。
本实施例所示的该纤芯310用于传输至少两种互不相同的第一光信号模式，该内包层320用于传输至少两种互不相同的第二光信号模式，对第一光信号模式以及第二光信号模式的具体说明，请参见图2所示对光信号模式的说明，不做赘述。
以下结合图4所示，对纤芯310的具体结构进行说明，其中，图4为沿该光纤滤波器的轴向方向，该光纤滤波器的切面图。
沿该光纤滤波器的轴向方向，在纤芯上利用激光刻蚀出光纤光栅。其中，本实施例以该纤芯为少模光纤(few mode fiber,FMF)为例进行示例性说明。在其他示例中，该纤芯还可为多模光纤(multi mode fiber,MMF)。需明确的是，本实施例对光纤光栅的形成方式不做限定，只要能够在纤芯上形成如图4所示的光纤光栅即可。
具体地，该纤芯310包括N个光纤光栅，即G 1、G 2、…G N，本实施例对N的具体取值不做限定，只要该N为大于或等于1的正整数即可。该N各光纤光栅的光栅周期彼此不同。光纤光栅G 1沿该纤芯310的轴向方向的长度为L 1，依次类推，光纤光栅G N沿该纤芯310的轴向方向的长度为L N。
以下以光纤光栅G 1为例，对光纤光栅的具体结构进行说明：
光纤光栅G 1包括多段子光栅，本实施例对各光纤光栅所包括的子光栅的具体数量不做限定，以图4为例，光纤光栅G 1具体包括子光栅G 1-1、G 1-2以及G 1-3。
不同的子光栅可具有不同的光栅周期，例如，子光栅G 1-1具有的光栅周期为Λ 1_1，子光栅G 1-2具有的光栅周期为Λ 1_2，子光栅G 1-3具有的光栅周期为Λ 1_3，且光栅周期Λ 1_1、光栅周期Λ 1-2以及光栅周期Λ 1_3互不相同。
需明确的是，本实施例以一个光纤光栅中，不同的子光栅具有不同的光栅周期为例进行示例性说明，在其他示例中，不同的子光栅也可具有相同的光栅周期，具体不做限定。
以下以子光栅G 1-1为例，对子光栅所具有的光栅周期进行说明：
具体地，子光栅G 1-1具有M个光栅周期Λ 1_1，且子光栅G 1-1所具有M个光栅周期Λ 1_1均相等。每个光栅周期Λ 1_1包括折射率已调制部分401和折射率未调制部分402。其中，该折射率已调制部分401是指通过激光在纤芯上刻蚀出的折射率发生变化的区域，以使该已调制部分401成为一个折射率改变点。该折射率未调制部分402是指与该折射率已调制部分401相邻，且折射率未发生变化的区域，本实施例对M的具体取值不做限定。
以下结合图5所示对内包层的具体结构进行说明，图5为沿该光纤滤波器的轴向方向，该光纤滤波器的切面图。
本实施例所示的内包层320包括至少一段子包层51，本实施例以子包层51为多段为例进行示例性说明，多段同轴设置且依次连接的子包层51组成该内包层320。本实施例所示的子包层的数量与上述所示的光纤光栅的数量相等，在光纤光栅的数量为多个的情况下，则多个子包层分别包裹不同光纤光栅。
需明确的是，图5所示以用于包裹不同的光纤光栅的子包层具有不同的半径为例进行示例性说明，例如，包裹光纤光栅G 1的子包层511和包裹光纤光栅G 2的子包层512的半径不同， 且子包层511的半径小于子包层512的半径。在其他示例中，用于包裹不同光纤光栅的子包层的半径也可相同。
本实施例通过调节该内包层的半径的方式，以实现对该内包层所支持的第二光信号模式的种类数的调节，例如，可通过缩减该内包层半径的方式缩减该段内包层所支持的第二光信号模式的种类数，以图5所示为例，子包层511的半径小于子包层512的半径，则子包层511所支持的第二光信号模式的种类数小于子包层512所支持的第二光信号模式的种类数。
本实施例所示的光纤滤波器的纤芯310传输至少两种互不相同的第一光信号模式，为实现增益均衡，则需要将第一光信号模式的至少部分光功率耦合至内包层，以实现对纤芯所传输的两个或两个以上的第一光信号模式的增益均衡。以下对实现增益均衡的几种可选的耦合方式进行示例性说明：
耦合方式1
该至少两种第一光信号模式中的每一种均对应不同的一种第二光信号模式，从而使得每一种第一光信号模式的至少部分光功率耦合至其对应的一种第二光信号模式中，且不同的第一光信号模式所耦合的第二光信号模式的种类互不相同。
例如，至少两种第一光信号模式为LP01以及LP11，至少两种第二光信号模式为LP03以及LP12，且LP01与LP03对应，LP11与LP12对应，则LP01的至少部分光功率耦合至LP03，LP11的至少部分光功率耦合至LP12，以实现LP01与LP11之间的增益均衡。
耦合方式2
该至少两种第一光信号模式对应同一种第二光信号模式，从而使得每一种第一光信号模式的至少部分光功率耦合至其对应的一种第二光信号模式中，且不同的第一光信号模式所耦合的第二光信号模式的种类均相同。
例如，至少两种第一光信号模式为LP01以及LP11，至少两种第二光信号模式为LP03以及LP12，且LP01以及LP11均对应LP03，则LP01的至少部分光功率以及LP11的至少部分光功率均耦合至LP03，以实现LP01与LP11之间的增益均衡。
耦合方式3
在该至少两种第一光信号模式中，除对应的光功率最低的那种第一光信号模式，其余每一种均对应一种该第二光信号模式。
例如，至少两种第一光信号模式为LP01以及LP11，至少两种第二光信号模式为LP03以及LP12，且LP01的光功率小于LP11的光功率，为实现增益均衡，在可仅调节LP11的光功率，在LP11对应LP12的情况下，可仅将LP11的至少部分光功率耦合至LP12，以实现LP01与LP11之间的增益均衡。
以下对第一光信号模式的至少部分光功率向内包层耦合的过程进行说明：
若一个第一光信号模式的光功率耦合至多个第二光信号模式，则无法调节该第一光信号模式耦合至各第二光信号模式的光功率的大小，从而导致对该第一光信号模式的光功率调节的失控，无法实现多个第一光信号模式之间的增益均衡。
而本实施例所示的光纤滤波器，一个第一光信号模式的光功率仅能够耦合至一个第二光信号模式，不会出现同一第一光信号模式耦合至多个第二光信号模式的情况，从而有效的保证了对该第一光信号模式的光功率调节的可控，有效的实现了不同的第一光信号模式之间的增益均衡，以下对具体实现过程进行说明：
本实施例中，目标第一光信号模式的至少部分光功率在目标光纤光栅处仅与目标第二光 信号模式耦合。其中，该目标第一光信号模式为纤芯所传输的至少两种第一光信号模式中的一种，该第二光信号模式仅为该内包层所传输的至少两种该第二光信号模式中的一种，该目标光纤光栅为纤芯所包括的一个光纤光栅。可见，该目标光纤光栅能够将该目标第一光信号模式的至少部分光功率仅向目标第二光信号模式耦合，有效的避免了该目标第一光信号模式耦合至多个第二光信号模式的情况，进而避免了对该目标第一光信号模式的光功率调节的失控。
具体地，本实施例以目标第一光信号模式基于相位匹配条件向目标第二光信号模式耦合为例进行示例性说明：
相位匹配条件1
基于该相位匹配条件所创建的对应关系如下述公式所示：
Figure PCTCN2021070312-appb-000009
以下对该公式中的各参数进行说明：
首先，对有效折射率
Figure PCTCN2021070312-appb-000010
进行说明：具体地，该目标第一光信号模式包括一路或多路具有不同波长的第一光信号，该
Figure PCTCN2021070312-appb-000011
为该第一光信号模式所包括的一路第一光信号的有效折射率。
其中，
Figure PCTCN2021070312-appb-000012
该β1为传播常数，用于表征该第一光信号在纤芯中传播的单位距离上的相位变化，该波长λ为该第一光信号的波长。
其次，对
Figure PCTCN2021070312-appb-000013
进行说明：具体地，该目标第二光信号模式包括一路或多路具有不同波长的第二光信号，该
Figure PCTCN2021070312-appb-000014
为该第二光信号模式所包括的一路第二光信号的有效折射率。
其中，
Figure PCTCN2021070312-appb-000015
该β2为传播常数，用于表征该第二光信号在内包层中传播的单位距离上的相位变化，该波长λ为该第二光信号的波长。
本实施例所示的为实现对第一光信号模式的光功率的调节，则需要对该第一光信号模式所包括的各第一光信号的光功率的调节。具体地，可通过将该第一光信号的至少部分光功率耦合至该第二光信号，以实现对该第一光信号的光功率的调节。而为实现该第一光信号向该第二光信号耦合，则该第一光信号的波长和该第二光信号的波长相等，且均等于该波长λ。
再次，对光栅周期Λ进行说明：由图4所示可知，本实施例所示的纤芯包括多个光纤光栅，不同的光纤光栅用于对不同的光信号模式进行光功率调节，从而实现了对不同的光信号模式的光功率的独立调节。一个目标光纤光栅包括多个子光栅，不同的子光栅用于对具有不同波长的光信号进行光功率的调节，从而实现了对不同的光信号的光功率的独立调节。
在目标光纤光栅用于对具有波长λ的第一光信号进行光功率调节的情况下，该目标光纤光栅的光栅周期可为目标子光栅的光栅周期，其中，该目标子光栅为该目标光纤光栅所包括的一段子光栅。继续如图4所示，该光纤光栅G 1所包括的子光栅G 1-1的光栅周期Λ 1_1满足上述公式所示的对应关系，则该子光栅G 1-1为目标子光栅，该目标子光栅G 1-1用于对该第一光信号的光功率大小进行调节。
相位匹配条件2
Figure PCTCN2021070312-appb-000016
相位匹配条件2所示的各参数的说明，请详见相位匹配条件1所示，不做赘述。本示例 中，在
Figure PCTCN2021070312-appb-000017
小于110％且大于90％的情况下，经过验证，能够实现对该目标第一光信号模式的光功率的精确调节，提高了增益均衡的效果。本实施例对该
Figure PCTCN2021070312-appb-000018
的数值范围的说明为可选地的示例，不做限定，只要能够实现对该目标第一光信号模式的光信号的精确调节即可。
可见，基于相位匹配条件1或相位匹配条件2所示的公式，创建了该波长λ、第一光信号的有效折射率
Figure PCTCN2021070312-appb-000019
第二光信号的有效折射率
Figure PCTCN2021070312-appb-000020
以及该目标光纤光栅的光栅周期Λ的对应关系。基于该对应关系，使能该目标光纤光栅能够将具有该波长λ的第一光信号的至少部分光功率耦合至该第二光信号，从而使得该光纤滤波器不仅能够实现不同的第一光信号模式之间的增益均衡，还能够实现不同的第一光信号之间的增益均衡。
由上述可知，为保证对目标第一光信号模式的光功率的可控调节，则目标光纤光栅将该目标第一光信号模式的至少部分光功率仅向目标第二光信号模式进行耦合，可见，该内包层所支持的第二光信号模式的种类数需要是有限的。因为若该内包层所支持的第二光信号模式为无限多个，会导致该目标第一光信号模式会向多个第二光信号模式进行耦合，导致对该目标第一光信号模式的光功率调节的失控。以下对如何控制该内包层所支持的第二光信号模式的种类数的方式进行说明：
需明确的是，以下提供了控制内包层所支持的第二光信号模式的种类数的几种方式，在实际应用中，可通过如下所示的一项或多项方式，以实现对内包层所支持的第二光信号模式的种类数的控制。
方式1
通过控制内包层的折射率和该外包层的折射率的方式，实现对内包层所支持的第二光信号模式的种类数的控制。其中，该内包层的折射率和该外包层的折射率的差值与该内包层所支持的该第二光信号模式的种类数之间呈正相关关系。
可见，若需要提高第二光信号模式的种类数，则提高内包层的折射率和外包层的折射率之间的差值，若需要降低第二光信号模式的种类数，则降低内包层的折射率和外包层的折射率之间的差值。
方式2
通过控制内包层的半径大小的方式，实现对内包层所支持的第二光信号模式的种类数的控制。其中，该内包层的半径大小与该内包层所支持的该第二光信号模式的种类数之间呈正相关关系。
可见，若需要提高第二光信号模式的种类数，则提高内包层的半径大小，若需要降低第二光信号模式的种类数，则降低内包层的半径大小。
本实施例所示的光纤滤波器为实现对目标第一光信号模式的光功率的精确调节，以实现增益均衡，则需要调节耦合至目标第二光信号模式的光功率的大小，具体调节方式参见如下所示：
需明确的是，以下提供了对光功率调节的几种方式，在实际应用中，可通过如下所示的一项或多项方式，以实现对光功率的调节。
调节方式1
通过调节目标光纤光栅沿纤芯轴向方向的长度大小，以实现对该目标第一光信号模式的光功率的调节，其中，该目标光纤光栅沿纤芯轴向方向的长度与耦合至该目标第二光信号模式中的光功率大小呈正相关关系。
具体地，以对该目标第一光信号模式的一路第一光信号的调节过程为例进行示例性说明：即通过调节目标子光栅沿纤芯轴向方向的长度大小，以实现对该第一光信号的光功率的调节。对该目标子光栅的说明，请详见图4所示，不做赘述。该目标子光栅的长度与耦合至该目标第二光信号模式中的光功率大小呈正相关关系。继续如图4所示，目标子光栅G 1-1沿该纤芯的轴向方向的长度L 1-1越大，则该目标子光栅G 1-1向目标第二光信号模式耦合的光功率越大，该长度L 1-1越小，则该目标子光栅G 1-1向目标第二光信号模式耦合的光功率越小。可见，可根据需要对目标第一光信号模式的光功率调节的大小，确定该目标子光栅G 1-1的长度L 1-1。
调节方式2
通过外包层实现对目标第一光信号模式的光功率的精确调节。具体地，为实现对目标第一光信号模式的光功率的可控调节，需要目标第一光信号模式的光功率仅向目标第二光信号模式耦合，需要尽量避免目标第一光信号模式的光功率耦合至外包层。具体方式为，保证第一耦合系数小于第二耦合系数。
其中，该第一耦合系数为第一光功率与第二光功率的比值，该第二耦合系数为第三光功率与该第二光功率的比值。
该第一光功率为该目标第一光信号模式已耦合至该外包层的光功率，该第二光功率为该目标第一光信号模式处于未被耦合的状态下所具有的光功率，该第三光功率为该目标第一光信号模式已耦合至该目标第二光信号模式的光功率。
该第一耦合系数小于该第二耦合系数的程度越大，目标第一光信号模式能够耦合至外包层的光功率越小，从而有效地保证了对该目标第一光信号模式的光功率调节的精确性。例如，若该第二耦合系数为第一耦合系数的10倍左右，则说明第一耦合系数远小于第二耦合系数，此时目标第一光信号模式耦合至外包层的光功率极为微弱，此时可以忽略目标第一光信号模式与外包层之间的耦合，有效的保证了目标第一光信号模式的光功率仅向目标内包层耦合，实现了对目标第一光信号模式的光功率的精确调节，实现增益均衡。
为更好的理解本申请所提供的光纤滤波器，以下结合具体应用场景对光纤滤波器进行具体说明：
应用场景一
本应用场景结合图6所示进行说明，本应用场景以纤芯所传输的光信号模式的种类数和该内包层所传输的第二光信号模式的种类数相等为例。具体地，该纤芯传输有四个第一光信号模式，即LP01、LP11、LP21和LP02。内包层所传输的第二光信号模式为LP31、LP12、LP03和LP22。
本实施例以基于相同的结构参数实现对不同的光信号模式的光功率调节为例，其中，该结构参数为：纤芯的半径为6.6微米(μm)、内包层半径为12.5μm，外包层半径为62.5μm。该结构参数还为：纤芯的折射率为1.45952，内包层的折射率为1.44782，外包层的折射率为1.44402。
其中，纤芯所传输的第一光信号模式LP01基于相位匹配向第二光信号模式LP31耦合，纤芯所传输的第一光信号模式LP11基于相位匹配向第二光信号模式LP12耦合，纤芯所传输的第一光信号模式LP21基于相位匹配向第二光信号模式LP03耦合，纤芯所传输的第一光信号模式LP02基于相位匹配向第二光信号模式LP22耦合。以下对具体地耦合方式进行说明：
耦合方式1
结合图6和表1所示对纤芯所传输的第一光信号模式LP01向第二光信号模式LP31耦合 进行具体说明：
表1
Figure PCTCN2021070312-appb-000021
通过目标光纤光栅601实现对第一光信号模式LP01的耦合，该第一光信号模式LP01包括有六路第一光信号，且该六路第一光信号的中心波长分别为1530nm、1535nm、1540nm、1545nm、1555nm以及1555nm。
该目标光纤光栅601包括六段子光栅，即G 1-1、G 1-2、G 1-3、G 1-4、G 1-5以及G 1-6。其中，该子光栅G 1-1的光栅周期Λ为0.01209厘米(cm)，且该子光栅G 1-1共包括有285个光栅周期Λ，该子光栅G 1-1沿该纤芯的轴向方向的长度为3.45cm。该子光栅基于相位匹配能够将具有中心波长为1530nm的第一光信号的至少部分光功率耦合至第二光信号模式LP31，对相位匹配的具体说明，请详见上述所示，不做赘述。基于表1所示可知，依次类推，该G 1-6能够将中心波长为1555nm的第一光信号的至少部分光功率耦合至第二光信号模式LP31。
耦合方式2
结合图6和表2所示对纤芯所传输的第一光信号模式LP11向第二光信号模式LP12耦合进行具体说明：
表2
Figure PCTCN2021070312-appb-000022
通过目标光纤光栅602实现对第一光信号模式LP11的耦合，该第一光信号模式LP11包括有三路第一光信号，且该三路第一光信号的中心波长分别为1532nm、1545nm以及1550nm。
该目标光纤光栅602包括三段子光栅，即G 2-1、G 2-2以及G 2-3。对G 2-1、G 2-2以及G 2-3的光栅周期以及光栅周期的种类数的说明，请参见表2所示，不做赘述。以子光栅G 2-1为例，该子光栅G 2-1用于将具有中心波长1532nm的第一光信号的至少部分光功率耦合至第二光信号模式LP12，依次类推，子光栅G 2-3用于将具有中心波长1558nm的第一光信号的至少部分光功率耦合至第二光信号模式LP12。
耦合方式3
结合图6和表3所示对纤芯所传输的第一光信号模式LP21向第二光信号模式LP03耦合进行具体说明：
表3
Figure PCTCN2021070312-appb-000023
通过目标光纤光栅603实现对第一光信号模式LP21的耦合，该第一光信号模式LP21包括有三路第一光信号，且该三路第一光信号的中心波长分别为1532nm、1545nm以及1555nm。
该目标光纤光栅603包括三段子光栅，即G 3-1、G 3-2以及G 3-3。对G 3-1、G 3-2以及G 3-3的光栅周期以及光栅周期的种类数的说明，请参见表3所示，不做赘述。以子光栅G 3-1为例，该子光栅G 3-1用于将具有中心波长1532nm的第一光信号的至少部分光功率耦合至第二光信号模式LP03，依次类推，子光栅G 3-3用于将具有中心波长1555nm的第一光信号的至少部分光功率耦合至第二光信号模式LP03。
耦合方式4
结合图6和表4所示对纤芯所传输的第一光信号模式LP02向第二光信号模式LP22耦合进行具体说明：
表4
Figure PCTCN2021070312-appb-000024
通过目标光纤光栅604实现对第一光信号模式LP02的耦合，该第一光信号模式LP02包括有三路第一光信号，且该三路第一光信号的中心波长分别为1531nm、1550nm以及1557nm。
该目标光纤光栅604包括三段子光栅，即G 4-1、G 4-2以及G 4-3。对G 4-1、G 4-2以及G 4-3的光栅周期以及光栅周期的数量的说明，请参见表4所示，不做赘述。以子光栅G 4-1为例，该子光栅G 4-1用于将具有中心波长1531nm的第一光信号的至少部分光功率耦合至第二光信号模式LP22，依次类推，子光栅G 4-3用于将具有中心波长1557nm的第一光信号模式的至少部分光功率耦合至第二光信号模式LP22。
本应用场景以不同的第一光信号模式的光功率耦合至不同的第二光信号模式为例进行示例性说明，需明确的是，此处不做限定，例如，也可多个第一光信号模式的光功率耦合至同一第二光信号模式中，只要任一第一光信号模式中的任一路第一光信号的光功率，仅向一个第二光信号模式耦合即可，可见，一个第二光信号模式可接收多个第一光信号模式的光功率，而不同的第二光信号模式不能接收来自同一第一光信号模式的光功率。
可见，在纤芯包括级联的目标光纤光栅601、目标光纤光栅602、目标光纤光栅603以及目标光纤光栅604，即可能够实现对整个C波段(1530-1565nm)的增益均衡。本应用场景所示的纤芯以实现整个C波段的增益均衡为例进行示例性说明，在其他示例中，该纤芯还可实现对其他波段的增益均衡，例如对L波段实现增益均衡。
采用本应用场景还能够实现相同的波长在不同的光信号模式下的增益均衡。具体地请见 如下表5所示：
表5
Figure PCTCN2021070312-appb-000025
以表5所示为例，第一光信号模式LP01、LP11、LP21和LP02均包括一路中心波长为1545nm的光信号，通过光纤光栅G 1、光纤光栅G 2、光纤光栅G 3以及光纤光栅G 4分别实现对具有中心波长为1545nm的光信号的光功率的调节，以实现具有中心波长为1545nm的光信号在第一光信号模式LP01、LP11、LP21和LP02下的增益均衡。
本应用场景所示的目标光纤光栅能够对一个第一光信号模式的光功率进行调节，且不同的目标光纤光栅能够对不同的第一光信号模式进行调节，可见，因不同的目标光纤光栅会基于不同的相位匹配，以实现对不同的第一光信号模式的光功率的调节。即各目标光纤光栅能够对各第一光信号模式的光功率的进行独立调节，有效的避免相互干扰。其中，避免相互干扰是指，目标光纤光栅在传输第一光信号模式LP01、LP11、LP21和LP02的过程中，该目标光纤光栅对一个第一光信号模式进行耦合的过程中，不会干扰该目标光纤光栅所传输的其他第一光信号模式的光功率。为更好的说明本应用场景所示的光纤滤波器能够有效地避免相互干扰的说明，请详见如下所示的仿真示例：
仿真示例1
本仿真示例结合上述所示的耦合方式1所示，即纤芯所传输的第一光信号模式LP01向第二光信号模式LP31耦合。具体地，在本仿真示例中，根据该目标光纤光栅601所具有的光栅周期的数量N的不同取值进行仿真，对光栅周期的数量N的说明，请详见耦合方式1所示，不做赘述。本仿真示例对包括该光栅周期的数量N的子光栅不做限定，例如，包括该光栅周期的数量N的子光栅可为G 1-1、G 1-2、G 1-3、G 1-4、G 1-5以及G 1-6中的一个或多个。
可选地，本仿真示例以光栅周期的数量N在区间40至400中取值为例，例如，光栅周期的数量N以周期40递增的方式在该区间内取值，则光栅周期的数量N分别取值：40、80、120、160、200、240、280、320、360以及400。
针对具有上述各光栅周期的数量N的目标光纤光栅601对第一光信号模式LP01进行耦合以获取如图7所示的透射谱701，该透射谱701的横坐标为波长，单位为纳米(nm)，纵坐标为相对功率，单位为分贝(dB)，该相对功率为第一光信号模式LP01耦合至第二光信号模式LP31中的光功率的大小与尚未耦合的第一光信号模式LP01的光功率大小。
根据该透射谱701可知，当光栅周期的数量N的取值不同时，该第一光信号模式LP01在目标光纤光栅的耦合作用下，具有不同的衰减曲线。例如，当N的取值有上述10种时，即可获取如该透射谱701所示的十条衰减曲线。可见，具有不同光栅周期的数量N的目标光纤光栅601能够对第一光信号模式LP01的光功率进行耦合。
在目标光纤光栅601传输第一光信号模式LP11、LP21以及LP02的情况下，该第一光信号模式LP11、LP21以及LP02的透射谱分别如图7所示的透射谱702、703以及704所示。可见，该第一光信号模式LP11、LP21以及LP02的衰减曲线几乎不随目标光纤光栅601的各光栅周期的数量N的取值的不同有所变化。即当N的取值有上述10种时，所获取如该透射谱 702、703以及704所示的十条几乎重合衰减曲线。
该第一光信号模式LP11、LP21以及LP02的最大相对功率分别为0.027、0.25和0.35。可见，在目标光纤光栅601对第一光信号模式LP01进行耦合时，几乎不会对第一光信号模式LP11、LP21以及LP02的光功率造成干扰。
仿真示例2
本仿真示例结合上述所示的耦合方式2所示，即纤芯所传输的第一光信号模式LP11向第二光信号模式LP12耦合。具体地，在本仿真示例中，根据该目标光纤光栅602所具有的光栅周期的数量N的不同取值进行仿真，对光栅周期的数量N的取值的说明，请参见上述仿真示例1所示，不做赘述。
针对具有上述各光栅周期的数量N的目标光纤光栅602对第一光信号模式LP11进行耦合以获取如图8所示的透射谱802，该透射谱802的坐标的说明，请详见上述仿真示例1所示，不做赘述。
根据该透射谱802可知，当光栅周期的数量N的取值不同时，该第一光信号模式LP11在目标光纤光栅602的耦合作用下，具有不同的衰减曲线。例如，当N的取值有上述10种时，即可获取如该透射谱802所示的十条衰减曲线。可见，具有不同光栅周期的数量N的目标光纤光栅602能够对第一光信号模式LP11的光功率进行耦合。
在目标光纤光栅602传输第一光信号模式LP01、LP21以及LP02的情况下，该第一光信号模式LP01、LP21以及LP02的透射谱分别如图8所示的透射谱801、803以及804所示。可见，该第一光信号模式LP01、LP21以及LP02的衰减曲线几乎不随目标光纤光栅602的各光栅周期的数量N的取值的不同有所变化。即当N的取值有上述10种时，所获取如该透射谱801、803以及804所示的十条几乎重合衰减曲线。该第一光信号模式LP01、LP21以及LP02的最大相对功率分别为0.0028、0.06和0.07。可见，在目标光纤光栅602对第一光信号模式LP11进行耦合时，不会对第一光信号模式LP01、LP21以及LP02造成干扰。
仿真示例3
本仿真示例结合上述所示的耦合方式3所示，即纤芯所传输的第一光信号模式LP21向第二光信号模式LP03耦合。具体地，在本仿真示例中，根据该目标光纤光栅603所具有的光栅周期的数量N的不同取值进行仿真，对光栅周期的数量N的取值的说明，请参见上述仿真示例1所示，不做赘述。
针对具有上述各光栅周期的数量N的目标光纤光栅603对第一光信号模式LP21进行耦合以获取如图9所示的透射谱903，该透射谱903的坐标的说明，请详见上述仿真示例1所示，不做赘述。
根据该透射谱903可知，当光栅周期的数量N的取值不同时，该第一光信号模式LP21在目标光纤光栅603的耦合作用下，具有不同的衰减曲线。例如，当N的取值有上述10种时，即可获取如该透射谱903所示的十条衰减曲线。可见，具有不同光栅周期的数量N的目标光纤光栅603能够对第一光信号模式LP21的光功率进行耦合。
在目标光纤光栅603传输第一光信号模式LP01、LP11以及LP02的情况下，该第一光信号模式LP01、LP11以及LP02的透射谱分别如图9所示的透射谱901、902以及904所示。可见，该第一光信号模式LP01、LP11以及LP02的衰减曲线几乎不随目标光纤光栅603的各光栅周期的数量N的取值的不同有所变化。即当N的取值有上述10种时，所获取如该透射谱901、902以及904所示的十条几乎重合衰减曲线。该第一光信号模式LP01、LP11以及LP02 的最大相对功率分别为0.002、0.005和0.055。可见，在目标光纤光栅603对第一光信号模式LP21进行耦合时，不会对第一光信号模式LP01、LP11以及LP02造成干扰。
仿真示例4
本仿真示例结合上述所示的耦合方式4所示，即纤芯所传输的第一光信号模式LP02向第二光信号模式LP22耦合。具体地，在本仿真示例中，根据该目标光纤光栅604所具有的光栅周期的数量N的不同取值进行仿真，对光栅周期的数量N的取值的说明，请参见上述仿真示例1所示，不做赘述。
针对具有上述各光栅周期的数量N的目标光纤光栅604对第一光信号模式LP02进行耦合以获取如图10所示的透射谱1004，该透射谱1004的坐标的说明，请详见上述仿真示例1所示，不做赘述。
根据该透射谱1004可知，当光栅周期的数量N的取值不同时，该第一光信号模式LP02在目标光纤光栅604的耦合作用下，具有不同的衰减曲线。例如，当N的取值有上述10种时，即可获取如该透射谱1004所示的十条衰减曲线。可见，具有不同光栅周期的数量N的目标光纤光栅604能够对第一光信号模式LP02的光功率进行耦合。
在目标光纤光栅604传输第一光信号模式LP01、LP11以及LP21的情况下，该第一光信号模式LP01、LP11以及LP21的透射谱分别如图10所示的透射谱1001、1002以及1004所示。可见，该第一光信号模式LP01、LP11以及LP21的衰减曲线几乎不随目标光纤光栅604的各光栅周期的数量N的取值的不同有所变化。即当N的取值有上述10种时，所获取如该透射谱1001、1002以及1004所示的十条几乎重合衰减曲线。该第一光信号模式LP01、LP11以及LP21的最大相对功率分别为0.001、0.023和0.07。可见，在目标光纤光栅604对第一光信号模式LP02进行耦合时，不会对第一光信号模式LP01、LP11以及LP21造成干扰。
以下通过仿真方式验证本应用场景所示的光纤滤波器实现增益均衡的效果：
首先参见图11所示，其中，图11为上述所示的增益光纤所输出的四种第一光信号模式LP01、LP11、LP21以及LP02的光谱图。该光谱图的横坐标表示波长，纵坐标表示功率。第一光信号模式LP01、LP11、LP21以及LP02未经光纤滤波器的滤波，每个光信号模式在光谱图中的功率均有比较大的起伏，且光信号模式彼此之间的功率差值也比较大，无法实现模式间的均衡。
结合图12所示，其中，图12为增益光纤所输出的四种光信号模式经过光纤滤波器滤波后的光谱图。第一光信号模式LP01、LP11、LP21以及LP02已经光纤滤波器的滤波，每个光信号模式在光谱图中的功率均有相当小的起伏，如图12所示，各光信号模式的功率最大值和功率最小值的比值均小于0.47，且光信号模式彼此之间的功率差值很小，基本保持均衡。
可见，基于本应用场景所示的光纤滤波器，能够对增益光纤所输出的四种第一光信号模式LP01、LP11、LP21以及LP02的光功率进行调节，以实现不同第一光信号模式之间的增益均衡。
应用场景二
本应用场景结合图13所示进行说明，本应用场景以纤芯所传输的光信号模式的种类数和该内包层所传输的第二光信号模式的种类数不相等为例。具体地，该纤芯传输有两个光信号模式，即LP01以及LP11。内包层所传输的第二光信号模式为LP21、LP02、LP12以及LP31。其中，纤芯所传输的第一光信号模式LP01基于相位匹配向第二光信号模式LP21耦合，纤芯所传输的第一光信号模式LP11基于相位匹配向第二光信号模式LP02耦合。
本实施例以基于不同的结构参数实现对不同的光信号模式的功率调节为例，其中，第一结构参数用于对第一光信号模式LP01进行耦合，第二结构参数用于对第一光信号模式LP11进行耦合。其中，第一结构参数为：纤芯的半径为6.8μm，内包层的半径为9.0μm，外包层半径为62.5μm。纤芯的折射率为1.4536，内包层的折射率为1.4473，外包层的折射率为1.44402。第二结构参数为：纤芯的半径为6.8μm，内包层的半径为11.0μm，外包层的半径为62.5μm。纤芯的折射率为1.4536，内包层的折射率为1.4473，外包层的折射率为1.44402，以下对具体地耦合方式进行说明：
耦合方式1
结合图13和表6所示对纤芯所传输的第一光信号模式LP01向第二光信号模式LP21耦合进行具体说明：
表6
Figure PCTCN2021070312-appb-000026
通过目标光纤光栅1301实现对第一光信号模式LP01的耦合，该第一光信号模式LP01包括有三路第一光信号，且该三路第一光信号的中心波长分别为表6所示的1530nm、1545nm以及1555nm。
该目标光纤光栅1301包括三段子光栅，即G 1-1、G 1-2以及G 1-3。其中，各子光栅的光栅周期、光栅周期的数量以及长度请详见表6所示。
具体地，该子光栅G 1-1基于相位匹配能够将中心波长为1530nm的第一光信号的至少部分光功率耦合至第二光信号模式LP21，对相位匹配的具体说明，请详见上述所示，不做赘述。，依次类推，该子光栅G 1-3能够将中心波长为1555nm的第一光信号的至少部分光功率耦合至第二光信号模式LP21。
耦合方式2
结合图13和表7所示对纤芯所传输的第一光信号模式LP11向第二光信号模式LP02耦合进行具体说明：
表7
Figure PCTCN2021070312-appb-000027
通过目标光纤光栅1302实现对第一光信号模式LP11的耦合，该第一光信号模式LP11包括有三路第一光信号，且该三路第一光信号的中心波长分别为表7所示的1530nm、1545nm以及1555nm。
该目标光纤光栅1302包括三段子光栅，即G 2-1、G 2-2以及G 2-3。其中，各子光栅的光栅周期、光栅周期的数量、长度以及中心波长请详见表7所示。
具体地，该子光栅G 2-1基于相位匹配能够将中心波长为1530nm的第一光信号的至少部分 光功率耦合至第二光信号模式LP02，对相位匹配的具体说明，请详见上述所示，不做赘述。依次类推，该子光栅G 2-3能够将中心波长为1555nm的第一光信号的至少部分光功率耦合至第二光信号模式LP02。
可见，在纤芯包括级联的目标光纤光栅1301以及1302能够实现对整个C波段(1530-1565nm)的增益均衡。而且各目标光纤光栅能够对各第一光信号模式的光功率的进行独立调节，有效的避免相互干扰，对相关干扰的具体说明，请详见上述应用场景一所示，不做赘述。以下通过仿真方式验证本应用场景所示的光纤滤波器实现增益均衡的效果。
首先参见图14所示，其中，图14为上述所示的增益光纤所输出的两种第一光信号模式LP01以及LP11的光谱图。该光谱图的坐标的说明，请详见图11所示，不做赘述。第一光信号模式LP01以及LP11未经光纤滤波器的滤波，每个第一光信号模式在光谱图中的功率均有比较大的起伏。
结合图15所示，其中，图15为增益光纤所输出的两种第一光信号模式LP01以及LP11的光谱图。第一光信号模式LP01以及LP11已经被光纤滤波器的滤波，每个第一光信号模式在光谱图中的功率均有相当小的起伏，如图15所示，各第一光信号模式的功率最大值和功率最小值的比值均小于0.5。
基于上述所示，以下对本申请所示的光纤滤波器的有效效果进行说明：
采用本实施例所示的光纤滤波器能够对两路或两路以上的第一光信号模式的光功率进行独立的调节，从而有效的实现了不同光信号模式之间的增益均衡以及不同光信号模式中不同波长的第一光信号之间的增益均衡，有效的降低光信号传输中断的概率。
基于目标光纤光栅对目标第一光信号模式的光功率进行调节，不会干扰其他第一光信号的光功率，有效的避免了干扰。
该光纤滤波器的目标光纤光栅，能够将目标第一光信号模式的至少部分光功率耦合至一个目标第二光信号模式中，该目标第二光信号模式仅为内包层所支持一个光信号模式，可见，不会出现同一目标第一光信号模式的光功率耦合至多个第二光信号模式中的情况，从而实现了对目标第一光信号模式的光功率的可控调节，而且有效地提高了对目标第一光信号模式的光功率调节的精确性。
该光纤滤波器是基于纤芯中的光纤光栅对光功率进行耦合的，光纤光栅具有结构简单，插损小、体积小、成本低等优点。
本申请的说明书和权利要求书及上述附图中的术语“第一”、“第二”等是用于区别类似的对象，而不必用于描述特定的顺序或先后次序。应该理解这样使用的数据在适当情况下可以互换，以便这里描述的实施例能够以除了在这里图示或描述的内容以外的顺序实施。此外，术语“包括”和“具有”以及他们的任何变形，意图在于覆盖不排他的包含，例如，包含了一系列步骤或模块的过程、方法、系统、产品或设备不必限于清楚地列出的那些步骤或模块，而是可包括没有清楚地列出的或对于这些过程、方法、产品或设备固有的其它步骤或模块。
以上所述，以上实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的精神和范围。

Claims (12)

  1. 一种光纤滤波器，其特征在于，包括纤芯、内包层以及外包层，所述内包层包裹于所述纤芯的外周面，所述外包层包裹于所述内包层的外周面，所述纤芯的折射率、所述内包层的折射率和所述外包层的折射率依次递减，所述纤芯用于传输至少两种互不相同的第一光信号模式，所述内包层用于传输至少两种互不相同的第二光信号模式，所述纤芯被刻蚀出至少一个光纤光栅；
    目标第一光信号模式的至少部分光功率在所述光纤光栅处仅与目标第二光信号模式耦合，其中，所述目标第一光信号模式为至少两种第一光信号模式中的一种，所述目标第二光信号模式为至少两种第二光信号模式中的一种。
  2. 根据权利要求1所述的光纤滤波器，其特征在于，所述目标第一光信号模式与所述目标第二光信号模式耦合，满足如下公式：
    Figure PCTCN2021070312-appb-100001
    其中，所述
    Figure PCTCN2021070312-appb-100002
    为所述目标第一光信号模式所包括的一路第一光信号的有效折射率；所述
    Figure PCTCN2021070312-appb-100003
    为所述目标第二光信号模式所包括的一路第二光信号的有效折射率；所述λ为所述第一光信号和所述第二光信号所具有的波长，所述Λ为所述光纤光栅的光栅周期。
  3. 根据权利要求1所述的光纤滤波器，其特征在于，所述目标第一光信号模式与所述目标第二光信号模式耦合，满足如下公式：
    Figure PCTCN2021070312-appb-100004
    其中，所述
    Figure PCTCN2021070312-appb-100005
    为所述目标第一光信号模式所包括的一路第一光信号的有效折射率；所述
    Figure PCTCN2021070312-appb-100006
    为所述目标第二光信号模式所包括的一路第二光信号的有效折射率；所述λ为所述第一光信号和所述第二光信号所具有的波长，所述Λ为所述光纤光栅的光栅周期。
  4. 根据权利要求1至3任一项所述的光纤滤波器，其特征在于，所述纤芯被刻蚀出多个光纤光栅，所述光纤光栅的光栅周期彼此不同。
  5. 根据权利要求1至4任一项所述的光纤滤波器，其特征在于，所述至少两种第一光信号模式中的每一种均对应不同的一种第二光信号模式。
  6. 根据权利要求1至4任一项所述的光纤滤波器，其特征在于，所述至少两种第一光信号模式中的每一种均对应一种第二光信号模式。
  7. 根据权利要求5或6所述的光纤滤波器，其特征在于，在所述至少两种第一光信号模式中，除对应的光功率最低的那种第一光信号模式，其余每一种均对应一种所述第二光信号模式。
  8. 根据权利要求1至7任一项所述的光纤滤波器，其特征在于，所述光纤光栅沿所述纤芯的轴向方向的长度与耦合至所述目标第二光信号模式中的光功率大小之间呈正相关关系。
  9. 根据权利要求1至8任一项所述的光纤滤波器，其特征在于，所述目标第一光信号模式已耦合至所述外包层的光功率小于所述目标第一光信号模式已耦合至所述目标第二光信号模式的光功率。
  10. 根据权利要求1至9任一项所述的光纤滤波器，其特征在于，所述内包层的折射率和所述外包层的折射率之间的差值与所述第二光信号模式的种类数呈正相关关系。
  11. 根据权利要求1至10任一项所述的光纤滤波器，其特征在于，所述内包层的半径大小与所述第二光信号模式的种类数之间呈正相关关系。
  12. 一种光纤放大器，其特征在于，所述光纤放大器包括泵浦激光器、波分复用器、增益光纤以及光纤滤波器，所述波分复用器分别与所述泵浦激光器以及所述增益光纤耦接，所述增益光纤与所述光纤滤波器耦接；
    所述波分复用器用于对来自所述泵浦激光器的泵浦光和光信号进行复用；所述增益光纤用于对来自所述波分复用器的所述光信号进行增益放大以输出至少两种第一光信号模式，所述光纤滤波器如权利要求1至11任一项所示。
PCT/CN2021/070312 2020-01-14 2021-01-05 一种光纤滤波器以及光纤放大器 WO2021143579A1 (zh)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP21741756.7A EP4080256A4 (en) 2020-01-14 2021-01-05 FIBER OPTIC FILTER AND FIBER OPTIC AMPLIFIER
US17/863,100 US11747565B2 (en) 2020-01-14 2022-07-12 Optical fiber filter and optical fiber amplifier

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CN202010039133.5A CN113189696A (zh) 2020-01-14 2020-01-14 一种光纤滤波器以及光纤放大器
CN202010039133.5 2020-01-14

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US17/863,100 Continuation US11747565B2 (en) 2020-01-14 2022-07-12 Optical fiber filter and optical fiber amplifier

Publications (1)

Publication Number Publication Date
WO2021143579A1 true WO2021143579A1 (zh) 2021-07-22

Family

ID=76863285

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2021/070312 WO2021143579A1 (zh) 2020-01-14 2021-01-05 一种光纤滤波器以及光纤放大器

Country Status (4)

Country Link
US (1) US11747565B2 (zh)
EP (1) EP4080256A4 (zh)
CN (1) CN113189696A (zh)
WO (1) WO2021143579A1 (zh)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113189696A (zh) * 2020-01-14 2021-07-30 华为技术有限公司 一种光纤滤波器以及光纤放大器

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1292884A (zh) * 1998-03-30 2001-04-25 康宁股份有限公司 可调光纤布喇格和长周期光栅
US6337937B1 (en) * 1998-05-18 2002-01-08 Sumitomo Electric Industries, Ltd. Optical filter and method of making the same
US20020181105A1 (en) * 2001-02-26 2002-12-05 Michiko Takushima Long period grating and making method of the same
US6950576B1 (en) * 2001-03-29 2005-09-27 Sabeus Photonics, Inc. Mode coupling devices with complex spectral profile
US20150003772A1 (en) * 2011-07-12 2015-01-01 scott michlas dante lionello Stabilizing apparatus for tremolo system for string instrumen
US20150015939A1 (en) * 2013-07-15 2015-01-15 Electronics And Telecommunications Research Institute Optical pumping apparatus for few-mode fiber amplification
CN110311731A (zh) * 2019-06-27 2019-10-08 中国电子科技集团公司第十三研究所 扫描光源输出增益平坦度提升装置及扫描光源

Family Cites Families (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6005999A (en) 1997-11-21 1999-12-21 3M Innovative Properties Company Waveguide narrowband rejection filter
US6400865B1 (en) * 2000-05-31 2002-06-04 Fitel Usa Corp. Article comprising a Bragg grating in a few-moded optical waveguide
JP2003029063A (ja) * 2001-07-19 2003-01-29 Fujikura Ltd 光ファイバグレーティング
US6882776B2 (en) * 2001-11-06 2005-04-19 Intel Corporation Method and apparatus of a semiconductor-based gain equalization device for optical amplifiers
US8520299B2 (en) * 2007-02-05 2013-08-27 OFS Fitec, LLC Selectively pumping a gain-doped region of an optical fiber
WO2010057288A1 (en) 2008-11-21 2010-05-27 Coractive High-Tech Inc. Pump combiner including a multi-clad waveguide
JP2011249531A (ja) * 2010-05-26 2011-12-08 Fujitsu Ltd 光増幅装置及び光増幅媒体
US8493555B2 (en) 2011-04-29 2013-07-23 Corning Incorporated Distributed Brillouin sensing systems and methods using few-mode sensing optical fiber
WO2013023193A1 (en) * 2011-08-10 2013-02-14 Ofs Fitel, Llc Few moded fiber device employing mode conversion
US8947768B2 (en) * 2012-05-14 2015-02-03 Jds Uniphase Corporation Master oscillator—power amplifier systems
US9197030B2 (en) * 2012-07-31 2015-11-24 Corning Incorporated Few mode rare earth doped optical fibers for optical amplifiers, and amplifiers using such fibers
US20140063592A1 (en) * 2012-09-05 2014-03-06 Nec Laboratories America, Inc. 6x28-Gbaud Few-Mode Fiber Recirculating Loop Transmission with Gain-Equalized Inline Few-Mode Fiber Amplifier
US9673591B2 (en) * 2013-05-17 2017-06-06 Nlight, Inc. Wavelength locking multimode diode lasers with fiber Bragg grating in large mode area core
JP2015096938A (ja) * 2013-10-11 2015-05-21 古河電気工業株式会社 光ファイバおよび光伝送システム
CN105022114B (zh) * 2015-07-27 2018-06-26 江苏大学 一种级联型长周期光纤光栅的滤模器
JP6939728B2 (ja) * 2018-07-19 2021-09-22 日本電信電話株式会社 マルチモード光増幅器
CN109994920A (zh) 2019-05-09 2019-07-09 中国人民解放军国防科技大学 基于纤芯包层尺寸连续渐变纺锤形增益光纤的激光振荡器
CN113189696A (zh) * 2020-01-14 2021-07-30 华为技术有限公司 一种光纤滤波器以及光纤放大器
CN113497403B (zh) * 2020-04-08 2022-08-26 华为技术有限公司 一种光纤、光放大器及光通信系统
KR20230008449A (ko) * 2021-07-07 2023-01-16 한국과학기술연구원 그래핀이 포함된 광소자 구조물 및 그 제조방법

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1292884A (zh) * 1998-03-30 2001-04-25 康宁股份有限公司 可调光纤布喇格和长周期光栅
US6337937B1 (en) * 1998-05-18 2002-01-08 Sumitomo Electric Industries, Ltd. Optical filter and method of making the same
US20020181105A1 (en) * 2001-02-26 2002-12-05 Michiko Takushima Long period grating and making method of the same
US6950576B1 (en) * 2001-03-29 2005-09-27 Sabeus Photonics, Inc. Mode coupling devices with complex spectral profile
US20150003772A1 (en) * 2011-07-12 2015-01-01 scott michlas dante lionello Stabilizing apparatus for tremolo system for string instrumen
US20150015939A1 (en) * 2013-07-15 2015-01-15 Electronics And Telecommunications Research Institute Optical pumping apparatus for few-mode fiber amplification
CN110311731A (zh) * 2019-06-27 2019-10-08 中国电子科技集团公司第十三研究所 扫描光源输出增益平坦度提升装置及扫描光源

Also Published As

Publication number Publication date
US11747565B2 (en) 2023-09-05
US20220357515A1 (en) 2022-11-10
CN113189696A (zh) 2021-07-30
EP4080256A4 (en) 2023-05-31
EP4080256A1 (en) 2022-10-26

Similar Documents

Publication Publication Date Title
WO2020181586A1 (zh) 一种低差模增益少模掺铒光纤放大器
CA2355312C (en) Optical system and method having low loss and non-linear effects
KR20010043201A (ko) 배분 증폭이 구비된 분산 관리형 광도파관 및 그 시스템
CA2137082C (en) Filter with preselected attenuation/wavelength characteristic
US7773845B2 (en) Optical fiber and optical-fiber transmission line
US10782478B2 (en) Inter-mode loss difference compensator and optical amplifier
WO2020032016A1 (ja) モード間損失差補償用ファイバ、光増幅器、および伝送路設計方法
US6327403B1 (en) Reducing mode interference in transmission of LP02 Mode in optical fibers
CN109313307B (zh) 光纤和光传输系统
WO2021143579A1 (zh) 一种光纤滤波器以及光纤放大器
WO2021204006A1 (zh) 一种光纤、光放大器及光通信系统
EP2533435B1 (en) Spatial mode gain equalization
KR20040066643A (ko) 광대역 분산 제어 광섬유
JP6654064B2 (ja) モード変換器、光増幅器及び光伝送システム
KR100433297B1 (ko) 파장분할다중통신용광섬유
JP2002250833A (ja) 光ファイバおよび該光ファイバを用いた分散補償器ならびに光伝送システム
JP6939728B2 (ja) マルチモード光増幅器
CN113156574A (zh) 一种多参数优化的轨道角动量掺铒光纤
KR100284489B1 (ko) 에르븀 첨가 광증폭기의 이득평탄화 방법 및 이를 이용한 이득평탄화한 에르븀 첨가 광증폭기
US7495825B2 (en) Integration of a gain equalization filter in a gain medium
CN115986537B (zh) 一种基于高斯掺杂环芯少模光纤的纤芯泵浦光纤放大器
WO2023148863A1 (ja) 希土類添加ファイバ、光増幅器及び光増幅器を制御する方法
CN115933048A (zh) 一种分层掺杂的少模态增益均衡光纤
WO2022068711A1 (zh) 一种光放大装置以及多端口波分复用耦合器
KR100384900B1 (ko) 분산 기울기 보상용 광섬유

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 21741756

Country of ref document: EP

Kind code of ref document: A1

ENP Entry into the national phase

Ref document number: 2021741756

Country of ref document: EP

Effective date: 20220720

NENP Non-entry into the national phase

Ref country code: DE