WO2021204006A1 - 一种光纤、光放大器及光通信系统 - Google Patents

一种光纤、光放大器及光通信系统 Download PDF

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WO2021204006A1
WO2021204006A1 PCT/CN2021/083637 CN2021083637W WO2021204006A1 WO 2021204006 A1 WO2021204006 A1 WO 2021204006A1 CN 2021083637 W CN2021083637 W CN 2021083637W WO 2021204006 A1 WO2021204006 A1 WO 2021204006A1
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optical
gain
fiber
wavelength
optical signal
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French (fr)
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吴波
张楷
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Huawei Technologies Co Ltd
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Huawei Technologies Co Ltd
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Priority to US17/962,068 priority patent/US12266899B2/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06754—Fibre amplifiers
    • 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
    • H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
    • 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
    • H01S3/06758—Tandem 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
    • H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
    • H01S3/06716—Fibre compositions or doping with active elements
    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/29—Repeaters
    • H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
    • H04B10/2912—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/29—Repeaters
    • H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
    • H04B10/293—Signal power control
    • H04B10/294—Signal power control in a multiwavelength system, e.g. gain equalisation
    • H04B10/2941—Signal power control in a multiwavelength system, e.g. gain equalisation using an equalising unit, e.g. a filter
    • 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
    • H01S2301/02—ASE (amplified spontaneous emission), noise; Reduction thereof
    • 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
    • H01S3/005—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
    • 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
    • H01S3/06762—Fibre amplifiers having a specific amplification band
    • H01S3/0677—L-band amplifiers, i.e. amplification in the range of about 1560 nm to 1610 nm
    • 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 technology, in particular to an optical fiber, an optical amplifier, and an optical communication system.
  • WDM wavelength division multiplexer
  • EDFA erbium doped fiber amplifier
  • GFF gain flattening filter
  • IL insertion loss
  • This application provides an optical fiber, an optical amplifier, and an optical communication system, which are used to flatten the gain of the optical amplifier without increasing the noise of the optical amplifier.
  • the present application provides an optical fiber, which can be applied to an optical amplifier.
  • the optical fiber includes a rare-earth-doped core and a cladding sequentially distributed from the inside to the outside.
  • the refractive index of the cladding is smaller than that of the rare-earth-doped core, and the rare-earth-doped core includes a gain equalization unit.
  • the fiber core doped with rare earth is used to amplify the optical signals of each wavelength in the received multiplex respectively; the gain equalization unit is used to equalize the gain of the optical signals of each wavelength, so that the optical signal emitted from the exit port of the optical fiber
  • the gain of the optical signal of each wavelength is within a preset range, and the gain of the optical signal of each wavelength in the optical signal of each wavelength is determined according to the ratio of the power of the optical signal after amplification to the power of the optical signal before amplification.
  • the rare earth-doped fiber core can amplify the optical signals of each wavelength separately.
  • the gain equalization unit can equalize the gain of the optical signal of each wavelength (or called flat change). In this way, the optical amplifier using the optical fiber does not need to introduce new devices to equalize the gain of the optical signal of each wavelength, so that gain equalization can be achieved without increasing noise.
  • the starting position of the gain equalization unit on the rare earth-doped fiber core is based on the absorption coefficient corresponding to the maximum absorption peak in the absorption spectrum of the core doped with rare earth and the corresponding preset absorption. The total amount is determined.
  • the gain equalization unit may be specifically configured to perform energy attenuation on the optical signal corresponding to the gain greater than the threshold in the gain of the optical signal of each wavelength according to the total attenuation function of the optical fiber.
  • the gain equalization unit is used to radiate the attenuated energy in the direction of the cladding.
  • the gain equalization unit may include M long-period fiber gratings, and M is an integer greater than or equal to 1.
  • M is an integer greater than or equal to 1.
  • M long-period fiber gratings start from the starting position and are distributed on the rare earth-doped fiber core in a dispersed manner. In this way, it is helpful to further reduce the noise of the optical amplifier; and, if the light is curved, the distributed distribution facilitates the arrangement of the gain equalization unit in the non-curved part.
  • each long-period fiber grating in the M long-period fiber gratings is the same as the function of the total attenuation function of the fiber, and the sum of the attenuation amplitudes of the M long-period fiber gratings is equal to the amplitude of the total attenuation function.
  • the total attenuation function can be equally divided into M parts, and distributed to a certain length of the fiber core doped with rare earth, so as to realize the decentralized effect of the optical amplifier using the fiber. The gain is flattened.
  • the attenuation amplitude of each long-period fiber grating is equal to the amplitude/M of the total attenuation function.
  • the long-period fiber grating may be a tilted grating.
  • the present application provides an optical amplifier.
  • the optical amplifier may include at least one-stage amplifying structure.
  • Selector, pump source and second light selector are used to receive optical signals of various wavelengths and transmit optical signals of various wavelengths to the multiplexer;
  • the pump source is used to transmit pump light to the multiplexer;
  • the multiplexer is used to pump The light and the optical signal of each wavelength are combined into one channel, and the multiplexed wave is coupled into the optical fiber;
  • the second optical selector is used to output the optical signal of each wavelength after amplification and gain equalization from the optical fiber.
  • the rare earth-doped fiber core can amplify the optical signal of each wavelength separately.
  • the gain equalization unit can equalize the gain of the optical signal of each wavelength (also known as flattened). In this way, in the optical amplifier, there is no need to introduce new devices to equalize the optical signals of each wavelength, so that gain equalization can be achieved without increasing noise.
  • the first optical selector and the second optical selector are also used to isolate the reverse propagation of the amplified optical signal.
  • the present application provides an optical communication system, which may include any optical amplifier, transmitter, and receiver of the second aspect or the second aspect; the transmitter is used to emit light of various wavelengths to the optical amplifier. Signal; The receiver is used to receive the amplified and gain-balanced optical signal of each wavelength from the output of the optical amplifier, and convert the amplified and gain-balanced optical signal of each wavelength into an electrical signal.
  • Figure 1a is a simplified schematic diagram of the energy level of an erbium ion provided by this application;
  • Figure 1b is a schematic diagram of the intrinsic gain spectrum of an EDFA provided by this application.
  • Figure 1c is a schematic structural diagram of an EDFA in the prior art
  • Figure 1d is a schematic structural diagram of another EDFA in the prior art
  • Fig. 2a is a schematic diagram of the NF curve of a working EDFA provided by this application at different gains in the L band;
  • Fig. 2b is a schematic diagram of the NF curve of another working EDFA provided by this application at different gains in the L band;
  • FIG. 3 is a schematic structural diagram of an optical fiber provided by this application.
  • FIG. 4 is a schematic diagram of an ideal gain spectrum provided by this application.
  • FIG. 5a is a schematic diagram of the position distribution of a gain equalization unit on the fiber core provided by this application;
  • 5b is a schematic diagram of the absorption spectrum of an erbium-doped core provided by this application.
  • 6a is a schematic diagram of the distribution of M long-period fiber gratings on the core provided by this application;
  • Fig. 6b is a schematic diagram of the distribution of another M long-period fiber gratings on the core provided by this application;
  • FIG. 7 is a schematic diagram of an attenuation curve of an optical fiber provided by this application.
  • FIG. 8 is a schematic diagram of the relationship between a total attenuation function and the attenuation function of a long-period fiber grating provided by this application;
  • FIG. 9 is a schematic structural diagram of an optical fiber circulator provided by this application.
  • FIG. 10a is a schematic diagram of the structure of an optical amplifier provided by this application.
  • FIG. 10b is a schematic diagram of the structure of another optical amplifier provided by this application.
  • FIG. 11a is a schematic diagram of the relationship between different wavelengths and gains provided by this application.
  • Figure 11b is a schematic diagram of the relationship between different wavelengths and noise provided by this application.
  • FIG. 12 is a schematic diagram of an optical communication system architecture provided by this application.
  • EDFA Erbium doped fiber application amplifier
  • erbium ions In an erbium-doped fiber (EDF), erbium ions have three energy levels, as shown in FIG. 1a, which exemplarily shows a simplified schematic diagram of the energy levels of an erbium ion.
  • Energy level 1 represents the ground state and has the lowest energy
  • energy level 2 is a metastable state and is at an intermediate energy level
  • energy level 3 represents the excited state and has the highest energy.
  • erbium ions absorb the pump light and transition from the ground state to the excited state.
  • the erbium ion Since the excited state is unstable, the erbium ion quickly returns to energy level 2. If the energy of the input optical signal is equal to the energy difference between energy level 2 and energy level 1, the erbium ion at energy level 2 will transition to the ground state, generating stimulated radiation, and the optical signal will be amplified. In other words, the amplification of the optical signal is due to the conversion of the energy of the pump light into the energy of the optical signal. Therefore, in order to increase the gain of the EDFA, the absorption of the pump light can be increased to make the ground state erbium ions transition to the excited state as much as possible.
  • the gain of the optical amplifier represents the amplification capability of the optical amplifier.
  • the optical amplifier since the output power of the EDFA does not always increase in proportion to the input power, it tends to be saturated.
  • the saturated output characteristic of EDFA is related to the wavelength of the optical signal.
  • the gain spectrum of EDFA is relatively wide, up to 45nm, that is, EDFA produces different gains for optical signals of different wavelengths. This change in gain will make the power of each transmission channel unbalanced. Therefore, it is necessary to perform gain equalization for the optical signals of each wavelength, or also called gain flattening.
  • the so-called gain flatness means that the gain of the optical signal of each wavelength after being amplified by the optical amplifier is the same or similar, that is, the gain spectrum is flat, so that the same gain can be provided for each channel that needs to be amplified.
  • Fig. 1b a schematic diagram of the gain spectrum of an EDFA provided in this application.
  • the gain spectrum has a gain peak near 1530nm and 1555nm respectively.
  • the gain peak at 1530nm is sharper with a spectral width of about 5nm; the gain peak near 1555nm is relatively flat with a spectral width of about 15-20nm.
  • the gain flatness of EDFA is mainly due to These two gain peaks are reduced.
  • GFF is also called a gain equalization filter, which is used to flatten or smooth different gains within a specified wavelength range.
  • GFF is used together with optical amplifiers to ensure that the amplified optical signals all have the same gain.
  • the loss characteristic curve (or attenuation function) of the corresponding GFF can be determined, and finally the GFF that meets the requirements is selected and placed in the corresponding optical amplifier.
  • Fig. 1c it is a schematic diagram of a passive filter interpolated in an EDFA.
  • the EDFA may include a two-stage or more than two-stage amplifying structure.
  • Fig. 1c takes the passive filter inserted in the EDFA as GFF, and the EDFA includes S1 level amplification structure, GFF and S2 level amplification structure as examples.
  • the S1 level amplifying structure and the GFF can be connected through an optical fiber, and the GFF and the S2 level amplifying structure can also be connected through an optical fiber.
  • EDFA works in a wide dynamic gain range, such as 19-25dB, or 20-32dB, etc.
  • GFF is usually added to equalize the optical signal of each wavelength.
  • Gain in order to adjust the gain more finely, a variable optical attenuator (VOA) can be cascaded after the GFF, and the GFF and the VOA can also be connected through an optical fiber.
  • VOA variable optical attenuator
  • the attenuation value of the centralized GFF with a large attenuation value is usually dispersed among the multi-stage amplification structure of the EDFA, that is, the total attenuation value of GFF is divided into the attenuation value of GFF1 and GFF2 The attenuation value.
  • GFF1 and GFF2 are inserted in the EDFA, please refer to Figure 1d, where the sum of the attenuation value of GFF1 and the attenuation value of GFF2 is approximately equal to the total attenuation value of GFF.
  • Insertion loss refers to the loss of load power that occurs due to the insertion of certain devices somewhere in the transmission system. That is, the insertion loss represents the ratio of the power received on the load before the insertion of a certain device to the power received on the same load after the insertion in decibels. Combining the aforementioned Figures 1c and 1d, the loss caused by the insertion of the GFF in the EDFA is the insertion loss.
  • Wavelength division multiplexing refers to the combination of two or more optical carrier signals of different wavelengths (carrying various information) at the transmitting end through a multiplexer (also known as a multiplexer) and coupled to the optical line
  • a multiplexer also known as a multiplexer
  • This technology of simultaneously transmitting two or more optical signals of different wavelengths in the same optical fiber is called wavelength division multiplexing.
  • the performance of the optical amplifier not only needs to consider the gain of the output optical signal, but also the influence of the noise of the optical amplifier on the performance.
  • the following takes the optical amplifier as an EDFA as an example.
  • the gain flatness of EDFA usually has the following two methods.
  • Method one is to optimize the intrinsic gain spectrum of EDF. For example, doping other impurities in EDF, such as aluminum; another example, changing the EDF matrix; another example, changing the structural parameters of the EDF, such as the width of the cladding layer, the width of the core, etc.; another example, changing the optical parameters of the EDF, Such as the refractive index of the cladding, the refractive index of the core and so on.
  • the second method is to interpolate GFF and other devices used to achieve gain flatness in the EDFA.
  • the structure and the principle of gain equalization based on the second method can be referred to the introduction of FIG. 1c or FIG. 1d, which will not be repeated here.
  • EDFA corresponds to a noise figure (NF) at each gain value
  • the NF of EDFA is better in the C-band, usually 3.5-5dB, and the performance of the NF in the L-band is worse than that in the C-band, which is about 1 to 3dB worse.
  • the noise of the EDFA in the L band can be expressed by the following formula 1; for the above figure 1d, the noise of the EDFA in the L band can be expressed by the following formula 2.
  • NF Total NF 1 +[L 12 *NF 2 -1]/G 1 +[L 23 *NF 3 -1]/G 2 Formula 2
  • L 12 represents the insertion loss of the device between the S1 level amplifying structure and the S2 level amplifying structure, combined with the above figure 1c, L 12 represents the insertion loss of the GFF, VOA, ISO and WDM inserted into the EDFA; combined with the above figure 1d, L 12 represents the insertion loss of GFF 1 and ISO and WDM in the S1 level amplifying structure; L 23 represents the insertion loss of the device between the S2 level amplifying structure and the S3 level amplifying structure.
  • L 23 represents GFF 2 , VOA, and the insertion loss of ISO and WDM in the S2 level amplifying structure;
  • NF 1 represents the noise figure of the S1 level amplifying structure
  • NF 2 represents the noise figure of the S2 level amplifying structure
  • NF 3 represents the noise figure of the S3 level amplifying structure
  • G 1 represents the gain of the S1 level amplifying structure
  • G 2 represents the gain of the S2 level amplifying structure.
  • NF 1 , NF 2 , NF 3 , G 1 and G 2 generally depend on the quality of the EDF itself.
  • Fig. 2a exemplarily shows a schematic diagram of the NF curve of the EDFA under different gains in the L band.
  • Fig. 2b exemplarily shows the NF curve of the EDFA at different gains in the L band. It can be seen from Figure 2a that when the gain change interval is 19-25dB, the NF value of the EDFA with two-stage amplification structure changes 2.7dB; from Figure 2b, it can be seen that when the gain change interval is 19-25dB, three When the total loss value of GFF is divided into the loss value of GFF1 and the loss value of GFF2, the change in NF value is 1.7dB. It can be seen that the fluctuation of the NF value of the EDFA that disperses the total loss value in the entire gain interval becomes smaller.
  • this application proposes an optical fiber.
  • the gain equalization unit is arranged on the rare earth-doped fiber core.
  • the optical amplifier can use the gain equalization technology to realize the gain equalization of the optical signal of each wavelength without increasing the optical amplifier's noise.
  • the gain equalization technology refers to the use of a gain equalization unit whose characteristics are opposite to the gain of the optical amplifier to offset the unevenness of the gain.
  • a gain equalization unit whose characteristics are opposite to the gain spectrum of the EDFA flattens the gain spectrum of the EDFA.
  • the optical fiber can be applied to an optical amplifier.
  • the optical fiber includes a rare-earth-doped core and a cladding sequentially distributed from the inside to the outside.
  • the refractive index of the cladding is smaller than that of the core doped with rare-earth.
  • It includes a gain equalization unit; wherein the rare-earth-doped fiber core is used to amplify the received optical signals of each wavelength in the multiplex; the gain equalization unit is used to equalize the gain of the optical signals of each wavelength, so that the The gain of the optical signal of each wavelength emitted from the exit port of the optical fiber is in the preset range.
  • the gain of the optical signal of each wavelength in the optical signal of each wavelength is based on the power of the amplified optical signal and the optical signal before amplification. The ratio of power is determined.
  • the power of the amplified optical signal of each wavelength is the output signal power of the optical signal of that wavelength
  • the power of the optical signal before amplification of each wavelength is the input signal power of the optical signal of that wavelength.
  • the gain G of each wavelength can be determined by the following formula 3.
  • the gain of the optical signal of each wavelength emitted from the exit port of the optical fiber is the same.
  • FIG. 4 is a schematic diagram of an ideal gain spectrum provided by this application.
  • the gain of the optical signal of each wavelength emitted from the exit port of the fiber is the same, that is, the gain spectrum is a straight line.
  • passive components such as ISO and WDM
  • the preset range can be ⁇ 1dB.
  • the rare earth-doped fiber core can amplify the optical signal of each wavelength separately.
  • the gain equalization unit can equalize the gain of the optical signal of each wavelength ( Or called flattening). In this way, there is no need to introduce new devices to equalize the optical signals of each wavelength, so that gain equalization can be achieved without increasing noise.
  • arranging the gain equalization unit on the rare earth-doped fiber core can realize the equalization of the gain of the optical signal of each wavelength while amplifying the optical signal of each wavelength.
  • the gain equalization unit is arranged on the rare-earth-doped fiber core, and the gain of the optical signal of each wavelength can be synchronized and equalized by the gain equalization unit while providing gain to the fiber core.
  • the rare-earth-doped fiber core is used to respectively amplify the received optical signals of each wavelength in the multiplexed wave.
  • the gain corresponding to the optical signal of each wavelength can be obtained through design according to the intrinsic parameters of the rare-earth-doped fiber core, so as to determine the gain spectrum of each wavelength.
  • the core doped with rare earth ions is a core doped with erbium ions, and the gain spectrum of the core doped with erbium ions can be seen in Figure 1b above.
  • the rare earth doped in the core may also be thulium ions, neodymium ions, etc., which is not limited in this application.
  • Cladding refers to a layer of glass or other transparent materials covering the core.
  • the refractive index of the cladding is smaller than that of the core doped with rare earths, so that the optical signal can be restricted to be transmitted in the core.
  • the cladding layer may include an inner cladding layer and an outer cladding layer.
  • the ring structure tightly wrapped around the core is called the inner cladding layer, and the outermost ring structure is called the outer cladding layer.
  • the inner cladding layer and the outer cladding layer It may also include a gully layer (also called a sag layer).
  • the NF of the optical amplifier using the optical fiber is greatly affected by the NF1 of the first-stage amplifying structure (which can be combined with the above formula 1). Therefore, it is very important to determine the starting position of the gain equalization unit on the core of the rare earth doped fiber. important.
  • the so-called starting position refers to the position from the fiber entrance port to the beginning of the gain equalization unit.
  • the A position is the starting position of the gain equalization unit on the rare earth-doped fiber core.
  • the distance between the starting position and the entrance port of the optical fiber is represented by L 0.
  • the starting position of the gain equalization unit on the core doped with rare earth can be based on the absorption coefficient (or called the absorption capacity) corresponding to the maximum absorption peak in the absorption spectrum of the core doped with rare earth. ) And the corresponding preset total amount of absorption, where the preset total amount of absorption is the total amount of absorption at the wavelength corresponding to the maximum absorption peak. It can also be understood that when the gain equalization unit is set at the starting position of the rare-earth-doped fiber core, the optical amplifier using the fiber has a better noise clamping effect.
  • FIG. 5b is a schematic diagram of the absorption spectrum of an erbium-doped core provided in this application.
  • the maximum absorption peak in the absorption spectrum of the core is at 1530nm, the absorption coefficient corresponding to the maximum absorption peak is about 85dB/m, and the preset total absorption at the maximum absorption peak is about 40-90dB. Therefore, the gain equalization unit is doped
  • the starting position on the core of the rare earth is equal to the preset total absorption at the maximum absorption peak/absorption coefficient corresponding to the maximum absorption peak.
  • the gain equalization unit can be installed from a position about 0.47 to 1.06 m away from the inlet port of the fiber core, that is, L 0 is about 0.47 to 1.06 m.
  • the gain equalization unit may include M long period fiber gratings (LPFG), where M is an integer greater than or equal to 1.
  • M is an integer greater than or equal to 1.
  • the long-period fiber grating is a fiber grating with a period greater than 1um. It can also be understood that the combination of M long-period fiber gratings is the gain equalization unit of this application, and the specificity of the gain equalization unit is opposite to the EDFA gain.
  • M long-period fiber gratings can be written on the rare-earth-doped fiber core through the long-period fiber grating writing technology.
  • a carbon dioxide (CO 2 ) laser or a femtosecond laser can be used to write M long-period fiber gratings on the core from the determined starting position.
  • M long-period fiber gratings start from the starting position and can be distributed on the rare earth-doped fiber core in a dispersed manner. It can be uniformly distributed on the core or non-uniformly distributed on the core.
  • FIG. 6a a schematic diagram of the distribution of M long-period fiber gratings on the core provided by this application.
  • FIG. 6b is a schematic diagram of the distribution of another M long-period fiber gratings on the core provided by this application.
  • the fiber is a ring fiber, and the long-period fiber grating can be in the non-bending area.
  • M long-period fiber gratings may be arranged on any one or any multiple of the area A, the area B, the area C, and the area D.
  • the distance between two adjacent long-period fiber gratings may be relatively small; In the long-period fiber grating, the distance between two adjacent long-period fiber gratings is relatively small.
  • the distance between two adjacent long-period fiber gratings can be larger; for example, in the long-period fiber gratings set in the area A and the area C, two adjacent long-period fiber gratings The distance between them can be relatively large. It should be noted that in area A, area B, area C and area D, the distance between two adjacent long-period fiber gratings can also be equal (Figure 6b means that the long-period fiber grating is uniform in each area). Distribution, and the distance between two adjacent long-period fiber gratings is the same in the four regions), this application does not limit this.
  • the gain equalization unit may be used to perform energy attenuation on the optical signal corresponding to the gain greater than the threshold in the gain of the optical signal of each wavelength according to the total attenuation function of the optical fiber.
  • the threshold value may be the value of the minimum gain in the intrinsic gain spectrum of the doped core, or may be any set value.
  • the gain equalization unit equalizes the gain spectrum of the optical fiber by attenuating the optical energy of the wavelength with a large gain, and the optical energy of the wavelength with a small gain is not attenuated, thereby achieving the effect of gain equalization.
  • the principle of gain equalization performed by the gain equalization unit is to separate the optical signals of each wavelength, and perform different attenuations on the optical signals of different wavelengths, so that the optical signals of the wavelengths with large gains correspond to large attenuation energy.
  • the total attenuation function of the optical fiber can be obtained through simulation or testing.
  • FIG. 7 a schematic diagram of the attenuation curve of an optical fiber provided in this application.
  • the attenuation curve of the fiber is designed based on the gain spectrum of Fig. 1b, which can represent the distribution relationship between different wavelengths and attenuation energy. It can be seen from Figure 7 that the attenuation energy of the wavelengths at 1530nm and 1555nm is relatively large. When the optical signals at the wavelengths of 1530nm and 1555nm are passed through the optical amplifier using this fiber, the attenuated energy is relatively large, so as to achieve the optical signal of each wavelength. Gain equalization.
  • the attenuation function of each long-period fiber grating in the M long-period fiber gratings is the same as the function of the total attenuation function of the fiber, and the sum of the attenuation amplitudes of the M long-period fiber gratings is equal to that of the fiber.
  • the magnitude of the total attenuation function is the same as the function of the total attenuation function of the fiber, and the sum of the attenuation amplitudes of the M long-period fiber gratings.
  • the following exemplarily shows how the sum of the attenuation amplitudes of two M long-period fiber gratings is equal to the amplitude of the total attenuation function of the optical fiber.
  • Implementation mode 1 The attenuation amplitude of each long-period fiber grating in the M long-period fiber gratings is equal to the amplitude/M of the total attenuation function of the fiber.
  • the amplitude of the total attenuation function of the fiber is divided into M parts uniformly.
  • the total attenuation function and the attenuation function of the long-period fiber grating shown in Figure 8 and the amplitude of the total attenuation function and the long-period fiber Schematic diagram of the relationship between the attenuation amplitude of the grating.
  • the attenuation function of each long-period fiber grating in the M long-period fiber gratings is Loss( ⁇ )
  • each long-period fiber The attenuation amplitude of the grating is 1/M.
  • Implementation mode 2 The attenuation amplitude of each long-period fiber grating in the M long-period fiber gratings is equal to the value of the amplitude of the total attenuation function * less than 1, that is, the amplitude of the total attenuation function is divided into M parts according to a certain ratio.
  • the amplitude of the total attenuation function can be divided into 1:2:4:1.
  • the attenuation function of the four long-period fiber gratings and the total fiber The attenuation function is the same, where the amplitude of the first long-period fiber grating is the amplitude of the total attenuation function*1/8, the amplitude of the second long-period fiber grating is the amplitude of the total attenuation function*2/8, and the third long-period
  • the amplitude of the fiber grating is the amplitude of the total attenuation function*4/8
  • the amplitude of the fourth long-period fiber grating is the amplitude of the total attenuation function*1/8.
  • the total attenuation function can be divided into M parts, and distributed to a certain length of the rare-earth-doped fiber core, constituting the gain equalization unit in the present application, thereby realizing distributed pair application
  • the gain of the optical amplifier of the fiber is flattened.
  • the gain equalization unit also has a requirement on the dissipation direction of the attenuated energy.
  • the gain equalization unit can be used to radiate (or called escape) attenuation energy in the direction of the cladding (see Figure 5a), and the remaining optical signal is along the positive direction of the fiber (that is, perpendicular to the cladding). Direction) transmission.
  • an inclined long-period fiber grating can be used to radiate attenuated energy toward the cladding direction.
  • the gain equalization unit may be M inclined long-period fiber gratings.
  • the optical amplifier may include at least one stage amplifying structure, and each stage of the at least one stage amplifying structure includes the above-mentioned optical fiber, a multiplexer, a first optical selector, a pump source, and a second optical selector.
  • the optical fiber may be an EDF-doped fiber (EDF), and the EDF is the main body of the optical amplifier; the first optical selector is used to receive optical signals of various wavelengths, and transmit optical signals of various wavelengths to the multiplexer.
  • EDF EDF-doped fiber
  • the pump source is used to emit pump light, that is, to provide energy to the EDF, mainly to provide energy to the erbium ions in the EDF, so that the erbium ions absorb energy and then transition from the ground state to the metastable state.
  • the multiplexer can also be called a wavelength division multiplexer, which is used to combine the pump light and the received optical signal of each wavelength into a multiplex, and couple the multiplex into the optical fiber; the second optical selector is used to combine the optical signal from the optical fiber The optical signal of each wavelength after the amplification and gain equalization is output.
  • the optical amplifier may also include other devices, which are not limited in this application. That is to say, the optical fiber provided in the above-mentioned embodiment can be used in all devices with optical amplification function.
  • the first optical selector and the second optical selector are also used to isolate the reverse propagation of the amplified optical signal. It can also be understood that the first optical selector can also be used to isolate the back propagation of the optical signal amplified by the optical fiber due to spontaneous radiation.
  • the second optical selector can be used to output the amplified and gain-equalized optical signals of each wavelength, and can also be used to prevent the back reflection of the optical signal in the next span. Further, optionally, the first optical selector and the second optical selector can also be used to isolate noise.
  • the first optical selector and the second optical selector may be optical isolators.
  • the optical isolator is a unidirectional optical transmission device, which can suppress the back and forth reflection of light, thereby Ensure the stable operation of the optical amplifier.
  • the first optical selector and the second optical selector may also be optical fiber circulators.
  • the optical fiber circulator is a multi-port non-reciprocal optical device, and light can only propagate in one direction. As shown in FIG. 9, it is a schematic structural diagram of an optical fiber circulator provided in this application. If light is input from port 1, it will be output from port 2; if light is input from port 2, it will be output from port 3. The output loss is very small. If the light is input from port 2, the loss is great when it is output from port 1. Similarly, when the light is input from port 3, the loss is great when it is output from port 1 or port 2.
  • FIG. 10a it is a schematic structural diagram of an optical amplifier provided in this application.
  • the optical amplifier includes a first-stage amplifying structure, the amplifying structure includes the above-mentioned optical fiber, a multiplexer, a first optical selector, a pump source and a second optical selector, wherein the first optical selector and the second optical selector are
  • the optical isolator is taken as an example, and the functions and principles of each structure can be referred to the introduction of the aforementioned related content, which will not be repeated here.
  • FIG. 10b it is a schematic structural diagram of another optical amplifier provided in this application.
  • the structure of the optical amplifier includes a two-stage amplifying structure as an example, that is, the optical amplifier includes an S1 level amplifying structure and an S2 level amplifying structure.
  • the S1 level amplifying structure and the S2 level amplifying structure can be connected by an optical waveguide.
  • the optical waveguide includes but not Limited to optical fiber.
  • the number of long-period fiber gratings included in the S1-level amplifying structure may be the same as or different from the number of long-period fiber gratings included in the S2-level amplifying structure, which is not limited in this application.
  • at least one level refers to one or more levels
  • multiple levels refers to two or more levels.
  • the rare earth-doped fiber core can amplify the optical signal of each wavelength separately.
  • the gain equalization unit can equalize the gain of the optical signal of each wavelength (also called flattened).
  • the optical amplifier there is no need to introduce new devices to equalize the optical signals of each wavelength, so that the gain of the amplified optical signals of each wavelength can be equalized without increasing the noise of the optical amplifier. That is to say, when the noise of the optical amplifier is relatively low, the optical amplifier can be cascaded with more stages of amplifying structures to achieve a greater amplification effect.
  • the gain equalization unit includes 10 long-period fiber gratings, and the preset total absorption is 50dB as an example, according to the preset total absorption and the maximum absorption peak in the absorption spectrum of the EDFA
  • the absorption coefficient and the corresponding preset total absorption can determine the starting position of the long-period fiber grating on the core doped with rare earth, that is, L 0 ⁇ 0.6m.
  • the gain distribution relationship of different wavelengths can be obtained by simulation. ( Figure 11a), and the distribution of noise at different wavelengths ( Figure 11b).
  • the EDFA of the present application can achieve gain equalization for the optical signals of each wavelength; it can be seen from the above figure 11b that when the gain of the EDFA drops from 25dB to 19dB, the NF increases by about 0.25dB. Therefore, with the optical amplifier in the present application, it is possible to achieve flat gain for optical signals of various wavelengths without increasing noise.
  • the present application may also provide an optical communication system.
  • FIG. 12 is a schematic diagram of the architecture of an optical communication system provided in this application.
  • the optical communication system may include an optical amplifier, a transmitter, and a receiver.
  • the transmitter is used to transmit the optical signal of each wavelength to the optical amplifier;
  • the receiver is used to receive the amplified and gain-balanced optical signal of each wavelength from the output of the optical amplifier, and convert the amplified and gain-balanced optical signal of each wavelength into electrical Signal;
  • the functions and possible implementations of the optical amplifier can be found in the above-mentioned related descriptions, which will not be repeated here.
  • the optical communication system may include two or more optical amplifiers between the transmitter and the receiver.
  • FIG. 12 is only an example of one optical amplifier.
  • the transmitter may include a light source, and the light source may be used to emit light signals of different wavelengths.
  • the light source may be a laser, and the laser may emit an optical signal with a wavelength range between the C-band and the L-band.
  • the optical amplifier can be used as a pre-amplifier, line-amplifier, or power-amplifier in a WDM communication system.
  • a preamplifier the noise figure is generally required to be very small, and the output power is not too large.
  • the signal input power is about -40dBm.
  • a line amplifier it can be directly inserted into the optical fiber transmission link as an optical relay amplifier, eliminating the optical/electrical/optical conversion process of the electrical repeater, and directly amplifying the optical signal to compensate for the loss of the transmission line and extend the relay distance .
  • a relatively small noise index and a relatively large output optical power are required.
  • the requirements for noise figure and gain are not very high, but the amplified optical signal is required to have a larger output power.

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Abstract

一种光纤、光放大器及光通信系统，用于解决现有技术中因对光放大器进行增益平坦时噪声增加的问题。本申请中，光纤可应用于光放大器，该光纤包括掺杂稀土的纤芯和包层，纤芯上包括增益均衡单元; 纤芯用于对接收到的合波中的各波长的光信号分别进行放大; 增益均衡单元用于对各波长的光信号的增益进行均衡，使得从光纤的出端口射出的各波长的光信号的增益均在预设范围，各波长的光信号中的每个波长的光信号的增益是根据放大后的光信号的功率与放大前的光信号的功率的比值确定的。即，经掺杂稀土的纤芯放大的光信号传输至增益均衡单元时，增益均衡单元可对各波长的光信号的增益进行均衡(即平坦化)，可在不增加噪声的情况下，实现光信号的增益均衡。

Description

一种光纤、光放大器及光通信系统
本申请要求于2020年4月8日提交中国国家知识产权局、申请号为202010277671.8、发明名称为“一种光纤、光放大器及光通信系统”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
本申请涉及光纤技术领域，尤其涉及一种光纤、光放大器及光通信系统。
背景技术
随着通信技术的发展，通信系统中的流量呈爆炸式增长，因此，对通信系统的频谱宽度和噪声提出了更高的要求。以波分复用(wavelength division multiplexer，WDM)光通信系统为例，在该WDM光通信系统中，C波段的单波频谱效率的提升遇到了瓶颈，开始向C波段之外的波段进行扩展。由于L波段在光纤中的衰减系数较低，成为扩展的首选波段。
在WDM光通信系统中，掺珥光纤放大器(erbium doped fiber amplifier，EDFA)是较重要的器件，由于EDFA对不同波长的光信号有不同的饱和特性，因此，EDFA对WDM光通信系统中的各波长的光信号会产生不同增益，从而导致一些信道产生严重的误码率，使得整个WDM光通信系统性能下降。
为了保证EDFA输出的放大后的光信号的增益是平坦的，通常会在EDFA中加入增益平坦器滤波器(gain flattening filter，GFF)等器件。但是由于GFF等器件自身有插入损耗(insertion loss，IL)，IL会导致EDFA的噪声较大。特别是，需要级联较多的GFF时，EDFA的噪声显著增大。
发明内容
本申请提供一种光纤、光放大器及光通信系统，用于在不增加光放大器的噪声的情况下，对光放大器的增益进行平坦。
第一方面，本申请提供一种光纤，该光纤可应用于光放大器。该光纤包括从内向外依次分布的掺杂稀土的纤芯和包层，包层的折射率小于掺杂稀土的纤芯的折射率，掺杂稀土的纤芯上包括增益均衡单元。其中，掺杂稀土的纤芯用于对接收到的合波中的各波长的光信号分别进行放大；增益均衡单元用于对各波长光信号的增益进行均衡，使得从光纤的出端口射出的各波长的光信号的增益均在预设范围，各波长的光信号中的每个波长的光信号的增益是根据放大后的光信号的功率与放大前的光信号的功率的比值确定的。
基于该方案，掺杂稀土的纤芯可以对各波长的光信号分别进行放大，放大的光信号经过增益均衡单元时，增益均衡单元可以对各波长的光信号的增益进行均衡(或称为平坦化)。如此，应用该光纤的光放大器不需要引入新的器件来均衡各波长的光信号的增益，从而可以在不增加噪声的情况下，实现增益均衡。
为了进一步降低应用该光纤的光放大器的噪声，需要控制增益均衡单元在掺杂稀土的 纤芯上起始位置。在一种可能的实现方式中，增益均衡单元在掺杂稀土的纤芯上的起始位置是根据掺杂稀土的纤芯的吸收谱中的最大吸收峰对应的吸收系数和对应的预设吸收总量确定的。
在一种可能的实现方式中，增益均衡单元具体可用于根据光纤的总衰减函数，对各波长的光信号的增益中大于阈值的增益所对应的光信号进行能量衰减。
为了防止光反射至起始位置之前的纤芯的区域，增益均衡单元用于向包层的方向辐射衰减的能量。
在一种可能的实现方式中，增益均衡单元可包括M个长周期光纤光栅，M为大于或等于1的整数。当M大于1时，M个长周期光纤光栅从起始位置开始，分散式分布在掺杂稀土的纤芯上。如此，有助于进一步降低光放大器的噪声；而且，如果光线是弯曲的，分散式分布便于将增益均衡单元设置在非弯曲的部分。
进一步，M个长周期光纤光栅中每个长周期光纤光栅的衰减函数与光纤的总衰减函数的函数相同，且M个长周期光纤光栅的衰减幅度之和等于总衰减函数的幅度。通过M个长周期光纤光栅，可将总衰减函数等效的均分为M份，并分散式分布到掺杂稀土的纤芯的一定长度内，从而实现分散式对应用该光纤的光放大器的增益进行平坦化。
在一种可能的实现方式中，每个长周期光纤光栅的衰减幅度等于总衰减函数的幅度/M。
在一种可能的实现方式中，长周期光纤光栅可以是倾斜光栅。
第二方面，本申请提供一种光放大器，该光放大器可包括至少一级放大结构，至少一级放大结构可包括上述第一方面或第一方面任一种光纤、合波器、第一光选择器、泵浦源和第二光选择器。其中，第一光选择器用于接收各波长的光信号，并向所述合波器传输各波长的光信号；泵浦源用于向合波器发射泵浦光；合波器用于将泵浦光和各波长的光信号合成一路合波，并将合波耦合进光纤；第二光选择器用于将来自光纤的放大且增益均衡后的各波长的光信号输出。
基于该光放大器，掺杂稀土的纤芯可以对各波长的光信号分别进行放大，放大的光信号经过增益均衡单元时，增益均衡单元可以对各波长的光信号的增益进行均衡(亦称为平坦化)。如此，在该光放大器中，不需要引入新的器件来均衡各波长的光信号，从而可在不增加噪声的情况下，实现增益均衡。
在一种可能的实现方式中，第一光选择器和第二光选择器还用于隔离放大后的光信号的反向传播。
第三方面，本申请提供一种光通信系统，该光通信系统可包括上述第二方面或第二方面任一种光放大器、发射器和接收器；发射器用于向光放大器发射各波长的光信号；接收器用于接收来自光放大器输出的放大且增益均衡后的各波长的光信号，并将放大且增益均衡后的各波长的光信号转为电信号。
第三方面可以达到的技术效果可以参照上述第二方面中的有益效果的描述，此处不再重复赘述。
附图说明
图1a为本申请提供的一种铒离子的能级简化示意图；
图1b为本申请提供的一种EDFA的本征增益谱的示意图；
图1c为现有技术中的一种EDFA的结构示意图；
图1d为现有技术中的另一种EDFA的结构示意图；
图2a为本申请提供的一种工作EDFA在L波段在不同增益下的NF曲线示意图；
图2b为本申请提供的另一种工作EDFA在L波段在不同增益下的NF曲线示意图；
图3为本申请提供的一种光纤的结构示意图；
图4为本申请提供的一种理想增益谱的示意图；
图5a为本申请提供的一种增益均衡单元在纤芯上的位置分布示意图；
图5b为本申请提供的一种掺杂铒的纤芯的吸收谱的示意图；
图6a为本申请提供的一种M个长周期光纤光栅在纤芯上的分布示意图；
图6b为本申请提供的另一种M个长周期光纤光栅在纤芯上的分布示意图；
图7为本申请提供的一种光纤的衰减曲线示意图；
图8为本申请提供的一种总衰减函数和长周期光纤光栅的衰减函数之间关系示意图；
图9为本申请提供的一种光纤环形器的结构示意图；
图10a为本申请提供的一种光放大器的结构的示意图；
图10b为本申请提供的另一种光放大器的结构的示意图；
图11a为本申请提供的一种不同波长与增益之间的关系示意图；
图11b为本申请提供的一种不同波长与噪声之间的关系示意图；
图12为本申请提供的一种光通信系统架构示意图。
具体实施方式
以下，对本申请中的部分用语进行解释说明，以便于本领域技术人员理解。
一、掺铒光纤放大器(erbium doped fiber application amplifier，EDFA)
EDFA的工作原理是把泵浦光的能量转换为光信号的能量。具体过程为：在掺铒光纤(EDF)中，铒离子有三个能级，如图1a所示，示例性地的示出了一种铒离子的能级简化示意图。能级1代表基态，能量最低；能级2是亚稳态，处于中间能级；能级3代表激发态，能量最高。当泵浦光的光子能量等于能级3和能级1的能量差时，铒离子吸收泵浦光从基态跃迁到激发态。由于激发态是不稳定的，铒离子很快返回到能级2。如果输入的光信号的能量等于能级2和能级1的能量差，则处于能级2的铒离子将跃迁到基态，产生受激辐射光，因而光信号得到放大。也就是说，光信号的放大是由于泵浦光的能量转换为光信号能量，因此，为了提高EDFA的增益，可提高对泵浦光的吸收，使基态铒离子尽可能跃迁到激发态。
二、增益平坦
光放大器的增益(Gain)表示光放大器的放大能力。以光放大器为EDFA为例，由于EDFA的输出功率并不总是与输入功率成正比例增加，而是呈饱和趋势。EDFA的饱和输出特性与光信号的波长相关。作为光放大器，希望在宽的频带内获得高的增益，EDFA的增益谱是比较宽的，可达45nm，即EDFA对不同波长的光信号产生的增益不同。这种增益的变化会使各传输通道的功率不平衡。因此，需要对各波长的光信号的进行增益均衡，或者也称为增益平坦。
所谓增益平坦是指经光放大器放大后的各个波长的光信号的增益是相同的或相近的， 即增益谱是平坦的，如此，可对需要放大的各个信道提供相同的增益。如图1b所示，为本申请提供的一种EDFA的增益谱的示意图。该增益谱在1530nm和1555nm附近分别有一个增益峰，1530nm附件的增益峰较尖，谱宽约5nm；在1555nm附近的增益峰相对平坦，谱宽约15～20nm，EDFA的增益平坦主要是将这两个增益峰降低。
三、增益平坦滤波器(gain flattening filter，GFF)
GFF也称为增益均衡滤波片，用于在指定波长范围内平坦或平滑不同的增益。通常GFF与光放大器一起使用，以确保放大的光信号都具有相同的增益。可根据光放大器的增益谱及光纤的损耗谱，确定对应的GFF的损耗特性曲线(或称为衰减函数)，最后选择合乎要求的GFF并将其置于相应的光放大器中。
如图1c所示，为一种在EDFA内插无源滤波器的结构示意图。该EDFA可包括两级或两级以上的放大结构。图1c以EDFA内插入的无源滤波器为GFF，EDFA包括S1级放大结构、GFF和S2级放大结构为例。其中，S1级放大结构和GFF之间可通过光纤连接，GFF与S2级放大结构之间也可通过光纤连接。由于EDFA工作在一个较宽的动态增益区间，如19～25dB、或20～32dB等，为了保证EDFA输出的放大后的光信号的增益是平坦的，通常会加入GFF来均衡各个波长光信号的增益。进一步，为了更精细的调整增益，可在GFF后级联可调光功率衰减器(variable optical attenuator，VOA)，GFF与VOA之间也可通过光纤连接。
进一步，由于光放大器的饱和输出光功率受限，光信号经两级放大结构后输出的光功率接近饱和后，仍不能满足需求，则需要级联多级放大结构来满足光功率放大需求。此时，为了兼顾光放大器的噪声，通常将衰减值较大的集中式的GFF的衰减值分散到EDFA的多级放大结构之间，即将GFF的总衰减值拆分成为GFF1的衰减值和GFF2的衰减值。也就是说，EDFA中插入GFF1和GFF2，请参阅图1d，其中，GFF1的衰减值与GFF2的衰减值之和约等于GFF的总衰减值。
四、插入损耗
插入损耗是指在传输系统的某处由于某些器件的插入而发生的负载功率的损耗。即插入损耗表示某些器件插入前负载上所接收到的功率与插入后同一负载上所接收到的功率以分贝为单位的比值。结合上述图1c和图1d，EDFA中因GFF插入后所引起的损耗即为插入损耗。
五、波分复用(wavelength division multiplexing，WDM)
波分复用是指将两种或多种不同波长的光载波信号(携带各种信息)在发送端经复用器(亦称合波器(multiplexer))汇合在一起，并耦合到光线路的同一根光纤中进行传输的技术；在接收端，经解复用器(亦称分波器或称去复用器，demultiplexer)将各种波长的光载波分离，然后由光接收机作进一步处理以恢复原信号。这种在同一根光纤中同时传输两个或两个以上的不同波长光信号的技术，称为波分复用。
前文介绍了本申请所涉及到的一些用语的解释，下面介绍本申请涉及的技术特征。
光放大器的性能不仅需要考虑输出的光信号的增益，还需要考虑光放大器的噪声对性能的影响。为了便于方案的说明，如下以光放大器为EDFA为例说明。
目前，EDFA的增益平坦通常有如下两种方式。方式一，优化EDF的本征增益谱。例 如在EDF中掺杂其它杂质，如铝；再比如，改变EDF的基质；再比如，改变EDF的结构参数，如包层的宽度、纤芯的宽度等；再比如，改变EDF的光学参数，如包层的折射率、纤芯的折射率等。方式二，在EDFA内插GFF等用于实现增益平坦的器件，基于该方式二的结构和增益均衡的原理可参见上述图1c或图1d的介绍，此处不再重复赘述。
EDFA在每个增益值下都对应一个噪声系数(noise figure，NF)，
Figure PCTCN2021083637-appb-000001
EDFA的NF在C波段较好，通常为3.5～5dB，在L波段的NF比在C波段的NF性能差，约劣化1～3dB。为了保证C波段和L波段的光信号能无差异的传输至目标，需要降低EDFA在L波段的噪声。
针对上述图1c，EDFA在L波段的噪声可用如下公式1表示；针对上述图1d，EDFA在L波段的噪声可用如下公式2表示。
NF Total＝NF 1+[L 12*NF 2-1]/G 1           公式1
NF Total＝NF 1+[L 12*NF 2-1]/G 1+[L 23*NF 3-1]/G 2    公式2
其中，L 12表示S1级放大结构和S2级放大结构之间的器件的插入损耗，结合上述图1c，L 12表示插入EDFA的GFF、VOA、ISO和WDM的插入损耗；结合上述图1d，L 12表示GFF 1、以及S1级放大结构中的ISO和WDM的插入损耗；L 23表示S2级放大结构和S3级放大结构之间的器件的插入损耗，结合上述图1d，L 23表示GFF 2、VOA、以及S2级放大结构中的ISO和WDM的插入损耗；NF 1表示S1级放大结构的噪声系数，NF 2表示S2级放大结构的噪声系数，NF 3表示S3级放大结构的噪声系数，G 1表示S1级放大结构的增益，G 2表示S2级放大结构的增益。应理解，NF 1、NF 2、NF 3、G 1和G 2通常是取决于EDF本身的质量优劣。
基于上述图1c，图2a示例性示出了EDFA在L波段的不同增益下的NF曲线示意图。基于上述图1d，图2b示例性地示出了EDFA在L波段的不同增益下的NF曲线。由图2a可以看出，增益变化区间为19～25dB时，采用两级放大结构的EDFA的NF值的变化为2.7dB；由图2b可以看出，增益变化区间为19～25dB时，采用三级放大结构、且将GFF总的损耗值分散成GFF1的损耗值和GFF2的损耗值时，NF值的变化为1.7dB。由此可见，将总的损耗值分散的EDFA在整个增益区间的NF值波动变小。
由上述内容可以看出，通过上述方式一和方式二实现了EDFA的增益平坦，但是由于方式一是改变EDF的材料，需要重新制作新的EDF，实现较为复杂。对于方式二，由于每增加一个GFF都需要引入WDM和ISO，但是GFF、WDM和ISO都有自身的插入损耗。随着放大级数的增加，需要引用更多的ISO和WDM；例如，一个ISO和一个WDM的插入损耗是1.5dB，将GFF的总损耗值分散在5级放大结构，就会引入7.5dB的插入损耗，这些插入损耗对于GFF的衰减函数中的损耗值为0的波长的光信号来说，是额外引入了的损耗，会导致EDFA的总噪声会增加。为了使EDFA的噪声比较低，则不能级联较多的放大结构。也就是说，方式二的增益均衡的方式不能级联较多级的放大结构；若级联较多的放大结构，光放大器的噪声会比较大。
鉴于上述问题，本申请提出一种光纤。该光纤中，增益均衡单元设置于掺稀土的纤芯上，当该光纤应用于光放大器时，光放大器可利用增益均衡技术，实现对各波长的光信号进行增益均衡，且可不增加光放大器的噪声。其中，增益均衡技术是指利用特性与光放大 器的增益相反的增益均衡单元来抵消增益的不均匀性。例如，特性与EDFA增益谱相反的增益均衡单元将EDFA的增益谱平坦化。
基于上述内容，下面结合附图3至附图12，对本申请提出的光纤进行具体阐述。
如图3所示，为本申请提供的一种光纤的结构示意图。该光纤可应用于光放大器，该光纤包括从内向外依次分布的掺杂稀土的纤芯和包层，包层的折射率小于掺杂稀土的纤芯的折射率，掺杂稀土的纤芯上包括增益均衡单元；其中，掺杂稀土的纤芯用于对接收到的合波中的各波长的光信号分别进行放大；增益均衡单元用于对各波长的光信号的增益进行均衡，使得从光纤的出端口射出的各波长的光信号的增益均在预设范围，各波长的光信号中的每个波长的光信号的增益是根据放大后的光信号的功率与放大前的光信号的功率的比值确定的。
其中，每个波长的放大后的光信号的功率即为该波长的光信号的输出信号功率，每个波长的放大前的光信号的功率即为该波长的光信号的输入信号功率。示例性地，每个波长的增益G可通过如下公式3确定。
Figure PCTCN2021083637-appb-000002
需要说明的是，理想情况下，从该光纤的出端口射出的各波长的光信号的增益是相同的。参阅图4，为本申请提供的一种理想增益谱的示意图。该图4中，各波长的光信号经该光纤的增益均衡单元进行增益均衡后，从光纤的出端口射出的各波长的光信号的增益是相同的，即增益谱是一条直线。在实际中，由于无源器件(例如ISO和WDM)的制造工艺偏差等影响，增益谱中各波长的光信号的增益可能会存在一些差异，但是各波长的光信号的增益均在预设范围，该预设范围可以是±1dB。
基于上述光纤，掺杂稀土的纤芯可以对各波长的光信号分别进行放大，放大的光信号经过纤芯上的增益均衡单元时，增益均衡单元可以对各波长的光信号的增益进行均衡(或称为平坦化)。如此，不需要引入新的器件来均衡各波长的光信号，从而可以在不增加噪声的情况下，实现增益均衡。进一步，将增益均衡单元设置在掺稀土的纤芯上，可以实现在对各波长的光信号进行放大的同时，并对各波长的光信号的增益进行均衡。也就是说，将增益均衡单元设置在掺稀土的纤芯上，可实现对纤芯提供增益的同时，并通过增益均衡单元对各波长的光信号的增益进行同步均衡。
下面对图3所示的各个结构分别进行介绍说明，以给出示例性的具体实现方案。
一、掺杂稀土的纤芯
本申请中，掺杂稀土的纤芯用于对接收到的合波中的各波长的光信号分别进行放大。进一步，可选地，可根据掺杂稀土的纤芯的本征参数，经过设计得到各波长的光信号对应的增益，从而确定出各波长的增益谱。例如，掺杂稀土的纤芯为掺杂铒离子的纤芯，该掺杂铒离子的纤芯的增益谱可参见上述图1b。
需要说明的是，纤芯中掺杂的稀土还可以是铥离子、或钕离子等，本申请对此不做限定。
二、包层
包层是指在纤芯外面覆盖的一层玻璃或其它透明材料，包层的折射率小于掺杂稀土的纤芯的折射率，从而可以将光信号限制在纤芯内传输。
在一种可能的实现方式中，包层可包括内包层和外包层，紧包裹于纤芯的环形结构称为内包层，最外层的环形结构称为外包层，内包层和外包层之间还可以包括沟壑层(亦称为下陷层)。
三、增益均衡单元
本申请中，应用光纤的光放大器的NF受第一级放大结构的NF1(可结合上述公式1)的影响比较大，因此，确定增益均衡单元在掺杂稀土的纤芯上的起始位置很重要。所谓起始位置是指从光纤的入端口到开始设置增益均衡单元的位置，如图5a所示，A位置即为增益均衡单元在掺杂稀土的纤芯上的起始位置，增益均衡单元的起始位置与光纤的入端口之间的距离用L 0表示。
在一种可能的实现方式中，增益均衡单元在掺杂稀土的纤芯上的起始位置可根据掺杂稀土的纤芯的吸收谱中的最大吸收峰对应的吸收系数(或称为吸收能力)和对应的预设吸收总量确定，其中，预设的吸收总量为最大吸收峰对应波长处的吸收总量。也可以理解为，增益均衡单元设置在掺杂稀土的纤芯起始位置时，应用该光纤的光放大器对噪声的钳制效果较好。
如下，以掺杂铒离子的纤芯为例说明。参阅图5b，为本申请提供的一种掺杂铒的纤芯的吸收谱的示意图。该纤芯的吸收谱中最大吸收峰在1530nm，最大吸收峰对应的吸收系数约为85dB/m，最大吸收峰处预设的吸收总量约为40～90dB，因此，增益均衡单元在掺杂稀土的纤芯上的起始位置等于最大吸收峰处预设的吸收总量/最大吸收峰对应的吸收系数。也就是说，增益均衡单元可从距离纤芯的入端口约0.47～1.06m的位置开始设置，即L 0约为0.47～1.06m。
在一种可能的实现方式中，增益均衡单元可以包括M个长周期光纤光栅(long period fiber grating，LPFG)，M为大于或等于1的整数。其中，长周期光纤光栅为周期大于1um的光纤光栅。也可以理解为，M个长周期光纤光栅组合即为本申请的增益均衡单元，增益均衡单元的特定与EDFA增益相反。
在一种可能的实现方式中，可通过长周期光纤光栅的刻写技术，在掺杂稀土的纤芯上刻写M个长周期光纤光栅。例如可通过二氧化碳(CO 2)激光器或飞秒激光器从确定出的起始位置开始，在纤芯上刻写M个长周期光纤光栅。
当M大于1时，M个长周期光纤光栅从起始位置开始，可以分散式分布在掺杂稀土的纤芯上。可以是均匀的分布在纤芯上，也可以是非均匀的分布在纤芯上。如图6a所示，为本申请提供的一种M个长周期光纤光栅在纤芯上的分布示意图。图6a以M＝4为例，从起始位置开始，4个长周期光纤光栅均匀的分布在掺杂的稀土的纤芯上。
请参阅图6b，为本申请提供的另一种M个长周期光纤光栅在纤芯上的分布示意图。该光纤为环形光纤，长周期光纤光栅可处于非弯折区域。例如，M个长周期光纤光栅可以设置在区域A、区域B、区域C和区域D中的任一个区域或任多个区域上。进一步，可选地，当非弯折区域比较小时，相邻两个长周期光纤光栅之间的距离可以比较小；例如，区域B和区域D比较小，则在区域B和区域D中设置的长周期光纤光栅中，相邻两个长周期光纤光栅之间的距离比较小。当非弯折区域比较长时，相邻两个长周期光纤光栅之间的 距离可以较大；例如，在区域A和区域C中设置的长周期光纤光栅中，相邻两个长周期光纤光栅之间的距离可以比较大。需要说明的是，在区域A、区域B、区域C和区域D中，相邻两个长周期光纤光栅之间的距离也可以均是相等(图6b即是以长周期光纤光栅在各个区域均匀分布，且相邻两个长周期光纤光栅之间的距离在4个区域中都是相同的示例)，本申请对此不做限定。
本申请中，增益均衡单元可用于根据光纤的总衰减函数，对各个波长的光信号的增益中大于阈值的增益对应的光信号进行能量衰减。其中，阈值可以是掺杂的纤芯的本征增益谱中最小增益的值，或者也可以是设置的任意一个值。本申请中，增益均衡单元对光纤的增益谱进行均衡是通过把增益大的波长的光能量进行衰减，增益小的波长的光能量不进行衰减，进而达到增益均衡的效果。或者也可以理解为，增益均衡单元进行增益均衡的原理为：把各波长的光信号分开，分别对不同波长的光信号进行不同的衰减，使增益大的波长的光信号对应大的衰减能量。
光纤的总衰减函数可通过仿真或测试得到，如图7所示，为本申请提供的一种光纤的衰减曲线示意图。该光纤的衰减曲线是基于图1b的增益谱设计得到的，可表示不同波长与衰减能量之间的分布关系。从图7可以看出，波长在1530nm和1555nm的衰减能量较大，当1530nm和1555nm波长的光信号经过应用该光纤的光放大器后，被衰减的能量较大，从而实现各波长的光信号的增益均衡。
在一种可能的实现方式中，M个长周期光纤光栅中每个长周期光纤光栅的衰减函数与光纤的总衰减函数的函数相同，且M个长周期光纤光栅的衰减幅度之和等于光纤的总衰减函数的幅度。
如下示例性地的示出两种M个长周期光纤光栅的衰减幅度之和等于光纤的总衰减函数的幅度的实现方式。
实现方式一，M个长周期光纤光栅中每个长周期光纤光栅的衰减幅度等于光纤的总衰减函数的幅度/M。
也可以理解为，将光纤的总衰减函数的幅度均匀的分为M份，可参阅图8所示出的总衰减函数与长周期光纤光栅的衰减函数、以及总衰减函数的幅度与长周期光纤光栅的衰减幅度之间的关系示意图。进一步，可结合上述图5a，若光纤的总衰减函数为Loss(λ)，则M个长周期光纤光栅中每个长周期光纤光栅的衰减函数也均为Loss(λ)，每个长周期光纤光栅的衰减幅度为1/M。
实现方式二，M个长周期光纤光栅中每个长周期光纤光栅的衰减幅度等于总衰减函数的幅度*小于1的值，即将总衰减函数的幅度按一定的比例分为M份。
示例性地，以M＝4为例，可将总衰减函数的幅度分为1:2:4:1，在四个长周期光纤光栅中，四个长周期光纤光栅的衰减函数与光纤的总衰减函数相同，其中，第一个长周期光纤光栅的幅度为总衰减函数的幅度*1/8，第二长周期光纤光栅的幅度为总衰减函数的幅度*2/8，第三个长周期光纤光栅的幅度为总衰减函数的幅度*4/8，第四个长周期光纤光栅的幅度为总衰减函数的幅度*1/8。
通过上述M个长周期光纤光栅，可将总衰减函数分为M份，并分散分布到掺杂稀土的纤芯的一定长度内，构成了本申请中的增益均衡单元，从而实现分散式对应用该光纤的光放大器的增益进行平坦化。
进一步，可选地，为了防止放大后的光信号反射至起始位置之前的纤芯的区域上，增益均衡单元对衰减能量的耗散方向也有要求。在一种可能的实现方式中，增益均衡单元可用于向包层方向(可参见图5a)辐射(或称为逸散)衰减能量，剩余的光信号沿光纤的正方向(即垂直于包层的方向)传输。示例性地，可通过倾斜的长周期光纤光栅实现向包层方向辐射衰减能量。也就是说，增益均衡单元可以是M个倾斜的长周期光纤光栅。
基于上述描述的光纤的结构和功能原理，本申请还可以提供一种光放大器。该光放大器可以包括至少一级放大结构，至少一级放大结构中的每级放大结构包括上述光纤、合波器、第一光选择器、泵浦源和第二光选择器。其中，光纤可以是掺饵光纤(EDF)，EDF是光放大器的主体；第一光选择器用于接收各波长的光信号，并向述合波器传输各波长的光信号。泵浦源用于发射泵浦光，即用于向EDF提供能量，主要是向EDF中的铒离子提供能量，使铒离子吸收能量后从基态跃迁到亚稳态。合波器也可称为波分复用器，用于将泵浦光和接收到的各波长的光信号合成一路合波，并将合波耦合进光纤；第二光选择器用于将来自光纤的放大且增益均衡后的各波长的光信号输出。当然，光放大器还可以包括其他器件，本申请对此不做限定。也就是说，具有光放大功能的装置中均可以采用上述实施例中提供的光纤。
本申请中，第一光选择器和第二光选择器还用于隔离放大后的光信号的反向传播。也可以理解为，第一光选择器还可用于隔离光纤因自发辐射放大的光信号的反向传播。第二光选择器可用于将放大且增益均衡后的各波长的光信号输出，还可用于防止下一跨段的光信号的反向反射。进一步，可选地，第一光选择器和第二光选择器还可用于隔离噪声。
在一种可能的实现方式中，第一光选择器和第二光选择器可以是光隔离器(Isolator)，光隔离器是一种单向光传输器件，可以抑制光的来回反射，从而可保证光放大器稳定工作。
在另一种可能的实现方式中，第一光选择器和第二光选择器也可以光纤环形器，光纤环形器是一种多端口非互易光学器件，光只能沿一个方向传播。如图9所示，为本申请提供的一种光纤环形器的结构示意图。若光从端口1输入，则从端口2输出；若光从端口2输入，则将从端口3输出，其输出损耗都很小。若光从端口2输入时，从端口1输出时损耗很大，同样光从端口3输入时，从端口1或端口2中输出时损耗很大。
如图10a所示，为本申请提供的一种光放大器的结构示意图。该光放大器包括一级放大结构，该放大结构包括上述光纤，合波器、第一光选择器、泵浦源和第二光选择器，其中，第一光选择器和第二光选择器以光隔离器为例，各结构的功能和原理可参见前述相关内容介绍，此处不再重复赘述。
如图10b所示，为本申请提供的另一种光放大器的结构示意图。该光放大器的结构以包括两级放大结构为例，即光放大器包括S1级放大结构和S2级放大结构，S1级放大结构和S2级放大结构之间可通过光波导连接，光波导包括但不限于光纤。S1级放大结构与S2级放大结构中各结构的功能和原理的介绍可参见前述内容的介绍。
需要说明的是，S1级放大结构中包括的长周期光纤光栅的数量可以与S2级放大结构中包括的长周期光纤光栅的数量相同，也可以不相同，本申请对此不做限定。另外，“至少一级”是指一级或者多级，“多级”是指两级或两级以上。
基于上述光放大器，掺杂稀土的纤芯可以对各波长的光信号分别进行放大，放大的光 信号经过增益均衡单元时，增益均衡单元可以对各波长的光信号的增益进行均衡(亦称为平坦化)。如此，在该光放大器中，不需要引入新的器件来均衡各波长的光信号，从而可在不增加光放大器的噪声的情况下，实现对各波长的放大后的光信号的增益进行均衡。也就是说，在光放大器噪声比较低的情况下，该光放大器可以级联较多级的放大结构，实现较大的放大作用。
采用上述图10a或图10b所示的光放大器，可以得到增益平坦的增益谱且光放大器的噪声较低。以图10a所示的光放大器为EDFA、增益均衡单元包括10个长周期光纤光栅、预设的吸收总量为50dB为例，根据预设的吸收总量和EDFA的吸收谱中最大吸收峰对应的吸收系数和对应的预设的吸收总量可确定出长周期光纤光栅在掺杂稀土的纤芯上的起始位置，即L 0≈0.6m，通过模拟可分别得到不同波长的增益分布关系(如图11a)，以及不同波长的噪声的分布关系(如图11b)。
由上述图11a可以看出，通过本申请的EDFA可以实现对各波长的光信号进行增益均衡；由上述图11b可以看出，当EDFA的增益从25dB下降到19dB，NF增大约0.25dB。因此，采用本申请中的光放大器，可以实现在不增加噪声的情况下，实现对各波长的光信号的增益平坦。
基于上述描述的光放大器的结构和功能原理，本申请还可以提供一种光通信系统。如图12所示，为本申请提供的一种光通信系统的架构示意图。该光通信系统可以包括光放大器、发射器和接收器。发射器用于向光放大器发射各波长的光信号；接收器用于接收来自光放大器输出的放大且增益均衡后的各波长的光信号，并将放大且增益均衡后的各波长的光信号转为电信号；光放大器的功能和可能的实现方式可参见上述相关描述，此处不再重复赘述。
需要说明的是，光通信系统中在发射器和接收器之间可以包括两个或两个以上的光放大器，图12仅是以一个光放大器示例性地的说明。
在一种可能的实现方式中，发射器可包括光源，光源可用于发射不同波长的光信号。示例性地，光源可以是激光器，该激光器可以发射波长范围在C波段和L波段之间的光信号。
本申请中，光放大器在WDM通信系统中可以作为前置放大器(pre-amplifier)、线路放大器(line-amplifier)或功率放大器(power-amplifier)。作为前置放大器，一般要求噪声系数很小，对输出功率没有太大的要求，信号输入功率约为-40dBm。作为线路放大器，可以直接插入到光纤传输链路中作为光中继放大器，省去了电中继器的光/电/光转换过程，直接放大光信号，以补偿传输线路损耗，延长中继距离。一般要求比较小的噪声指数，较大的输出光功率。作为功率放大器，对噪声系数、增益要求并不是很高，但要求放大后的光信号，有较大的输出功率。
在本申请的各个实施例中，如果没有特殊说明以及逻辑冲突，不同的实施例之间的术语和/或描述具有一致性、且可以相互引用，不同的实施例中的技术特征根据其内在的逻辑关系可以组合形成新的实施例。
可以理解的是，在本申请中涉及的各种数字编号仅为描述方便进行的区分，并不用来 限制本申请的实施例的范围。上述各过程的序号的大小并不意味着执行顺序的先后，各过程的执行顺序应以其功能和内在逻辑确定。术语“第一”、“第二”等是用于分区别类似的对象，而不必用于描述特定的顺序或先后次序。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单元。方法、系统、产品或设备不必限于清楚地列出的那些步骤或单元，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单元。
尽管结合具体特征及其实施例对本申请进行了描述，显而易见的，在不脱离本申请的精神和范围的情况下，可对其进行各种修改和组合。相应地，本说明书和附图仅仅是所附权利要求所界定的方案进行示例性说明，且视为已覆盖本申请范围内的任意和所有修改、变化、组合或等同物。
显然，本领域的技术人员可以对本申请进行各种改动和变型而不脱离本发明的精神和范围。这样，倘若本申请实施例的这些修改和变型属于本申请权利要求及其等同技术的范围之内，则本申请也意图包含这些改动和变型在内。

Claims (10)

  1. 一种光纤，其特征在于，应用于光放大器，所述光纤包括从内向外依次分布的掺杂稀土的纤芯和包层，所述包层的折射率小于所述掺杂稀土的纤芯的折射率，所述掺杂稀土的纤芯上包括增益均衡单元；
    所述掺杂稀土的纤芯，用于对接收到的合波中的各波长的光信号分别进行放大；
    所述增益均衡单元，用于对所述各波长的光信号的增益进行均衡，使得从所述光纤的出端口射出的各波长的光信号的增益均在预设范围，所述各波长的光信号中的每个波长的光信号的增益是根据放大后的光信号的功率与放大前的光信号的功率的比值确定的。
  2. 如权利要求1所述的光纤，其特征在于，所述增益均衡单元在所述掺杂稀土的纤芯上的起始位置是根据所述掺杂稀土的纤芯的吸收谱中最大吸收峰对应的吸收系数和对应的预设的吸收总量确定的。
  3. 如权利要求1或2所述的光纤，其特征在于，所述增益均衡单元，具体用于：
    根据所述光纤的总衰减函数，对所述各波长的光信号的增益中大于阈值的增益所对应的光信号进行能量衰减。
  4. 如权利要求3所述的光纤，其特征在于，所述增益均衡单元还用于：
    向所述包层的方向辐射衰减的能量。
  5. 如权利要求1至4任一项所述的光纤，其特征在于，所述增益均衡单元包括M个长周期光纤光栅，所述M为大于或等于1的整数。
  6. 如权利要求5所述的光纤，其特征在于，所述M大于1时，所述M个长周期光纤光栅从起始位置开始，分散式分布在所述掺杂稀土的纤芯上。
  7. 如权利要求5或6所述的光纤，其特征在于，所述M个长周期光纤光栅中每个长周期光纤光栅的衰减函数与所述光纤的总衰减函数的函数相同，且所述M个长周期光纤光栅的衰减幅度之和等于所述总衰减函数的幅度。
  8. 一种光放大器，其特征在于，包括至少一级放大结构，所述放大结构包括如权利要求1～7任一项所述的光纤、合波器、第一光选择器、泵浦源和第二光选择器；
    所述第一光选择器，用于接收各波长的光信号，并向所述合波器传输所述各波长的光信号；
    所述泵浦源，用于向所述合波器发射泵浦光；
    所述合波器，用于将所述泵浦光和所述各波长的光信号合成一路合波，并将所述合波耦合进所述光纤；
    所述第二光选择器，用于将来自所述光纤的放大且增益均衡后的各波长的光信号输出。
  9. 如权利要求8所述的光放大器，其特征在于，所述第一光选择器和所述第二光选择器还用于隔离放大后的光信号的反向传播。
  10. 一种光通信系统，其特征在于，包括如权利要求8所述的光放大器、发射器和接收器；
    所述发射器，用于向所述光放大器发射各波长的光信号；
    所述接收器，用于接收来自所述光放大器输出的放大且增益均衡后的各波长的光信号，并将所述放大且增益均衡后的各波长的光信号转为电信号。
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114492948A (zh) * 2021-12-31 2022-05-13 杭州拓深科技有限公司 基于dfa去趋势融合多维特征的电力线损预测方法

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113189696B (zh) * 2020-01-14 2025-12-12 华为技术有限公司 一种光纤滤波器以及光纤放大器
CN114205047B (zh) * 2021-12-10 2024-07-02 中国电信股份有限公司 光复用段的自动配置方法及装置
JP7732651B2 (ja) * 2021-12-14 2025-09-02 株式会社アイシン 光を利用したヒートサイクルシステム
CN117096728A (zh) * 2022-05-10 2023-11-21 华为技术有限公司 多模激光装置、光放大器和光发送模块
CN118555009A (zh) * 2023-02-27 2024-08-27 华为技术有限公司 光放大装置、光通信设备和光放大方法
US11824588B1 (en) * 2023-04-20 2023-11-21 Attochron, Llc Reducing scintillation noise in free-space optical communications
CN118156975B (zh) * 2024-01-30 2026-01-20 华为技术有限公司 一种光放大器和相关设备
CN121056044B (zh) * 2025-11-03 2026-03-31 杭州硫通光子科技有限公司 基于信号功率自适应分级的并联光纤放大器信道均衡系统

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5703978A (en) * 1995-10-04 1997-12-30 Lucent Technologies Inc. Temperature insensitive long-period fiber grating devices
CN1266995A (zh) * 1999-03-11 2000-09-20 三星电子株式会社 具有形成在其中的光栅的铒掺杂光纤及其制造方法
JP2016167489A (ja) * 2015-03-09 2016-09-15 Kddi株式会社 光伝送システム、光増幅器及びその励起光制御方法

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5271024A (en) * 1992-07-27 1993-12-14 General Instrument Corporation Optical fiber amplifier and laser with flattened gain slope
KR100251557B1 (ko) * 1997-10-02 2000-05-01 윤종용 광섬유 증폭기
JP2000180640A (ja) * 1998-12-16 2000-06-30 Mitsubishi Cable Ind Ltd ゲインイコライザ、光増幅装置および光ファイバ通信システム
KR100318903B1 (ko) * 2000-01-14 2001-12-29 윤종용 장주기 광섬유 격자
JP2001210901A (ja) * 2000-01-25 2001-08-03 Furukawa Electric Co Ltd:The 光部品
JP2001267665A (ja) * 2000-03-16 2001-09-28 Sumitomo Electric Ind Ltd 光増幅用光ファイバ、光ファイバ増幅器および光ファイバレーザ発振器
JP5226164B2 (ja) * 2001-06-14 2013-07-03 富士通株式会社 光増幅器
KR100440763B1 (ko) * 2002-04-19 2004-07-21 전자부품연구원 광도파로형 이득평탄화 필터소자 및 그의 제조방법

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5703978A (en) * 1995-10-04 1997-12-30 Lucent Technologies Inc. Temperature insensitive long-period fiber grating devices
CN1266995A (zh) * 1999-03-11 2000-09-20 三星电子株式会社 具有形成在其中的光栅的铒掺杂光纤及其制造方法
JP2016167489A (ja) * 2015-03-09 2016-09-15 Kddi株式会社 光伝送システム、光増幅器及びその励起光制御方法

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP4116748A4

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114492948A (zh) * 2021-12-31 2022-05-13 杭州拓深科技有限公司 基于dfa去趋势融合多维特征的电力线损预测方法

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