Few-mode erbium-doped fiber amplifier system and control method thereof

Abstract

The application belongs to the technical field of optical fiber communication, and discloses a few-mode erbium-doped optical fiber amplification system and a control method thereof. The application utilizes a signal generation module to output a multi-mode multi-wavelength signal light, utilizes a mode converter to convert and demultiplex the mode, and utilizes a pump beam combining assembly to amplify the signal light. In the process of simultaneously amplifying the multi-mode multi-wavelength, a front-end optical spectrum detector is utilized to detect and acquire first spectral information corresponding to different mode multi-wavelength signal light, a middle-end photoelectric detector is utilized to detect and acquire input power information corresponding to multi-wavelength signal light in each mode after the first mode converter, a rear-end optical spectrum detector is utilized to detect and acquire second spectral information corresponding to different mode multi-wavelength signal light after the second mode converter demultiplexes, and the front-end adjustable assembly is adjusted according to the above information to compensate the wavelength power, so as to ensure that the input power of each mode after compensation is consistent and the multi-wavelength amplification gain is flat.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber communication, and more particularly to a few-mode erbium-doped fiber amplification system and a control method thereof. BACKGROUND

[0002] With the emergence of new technologies and industrial forms such as "Internet+", "big data", "cloud computing" and "smart city", people's life has entered a new era of "Internet of Things". The rapidly growing data traffic puts higher requirements on communication networks. For optical fiber communication systems, under the support of dense wavelength division multiplexing technology and high-efficiency modulation technology, the transmission capacity of single-mode optical fiber is approaching the Shannon limit. In order to further improve the transmission capacity of future optical fiber communication systems, the use of few-mode optical fiber as a new space division multiplexing method has received widespread attention. In a mode division multiplexing (MDM) system based on few-mode optical fiber, different modes can be used as independent channels for simultaneous transmission, thereby increasing the number of transmission channels and doubling the communication capacity. In particular, a weakly coupled transmission system can realize independent detection and reception of each mode without multiple input multiple output digital signal processing (MIMO DSP), which can greatly reduce the complexity and cost of the system.

[0003] In an actual MDM system, a few-mode erbium-doped fiber amplifier (FM-EDFA) is a key component for compensating for transmission loss of an optical fiber link. However, differences in the degree of overlap between the optical field distribution of each mode signal, the pump light field distribution and the erbium distribution will result in a large differential modal gain (DMG), which will eventually lead to an increase in the bit error rate at the receiving end and an increase in the probability of communication system interruption. In addition, in an MDM system, in order to increase the communication bandwidth of each optical fiber, multiple wavelength channels need to be amplified simultaneously. This puts higher requirements on FM-EDFA to achieve gain equalization in a long-haul wavelength-division multiplexing (WDM) combined MDM transmission system. At present, most of the reported FM-EDFAs are for amplification of multiple modes at a single wavelength, and there are few studies on simultaneous amplification of multiple modes and multiple wavelengths. How to achieve simultaneous amplification of multiple modes and multiple wavelengths and achieve gain flattening for multiple wavelength amplification is a technical problem that needs to be solved in the field. SUMMARY

[0004] The present application provides a few-mode erbium-doped fiber amplification system and a control method thereof, which solves the problem of simultaneous amplification of multiple modes and multiple wavelengths and gain flattening in the prior art.

[0005] The present application provides a few-mode erbium-doped fiber amplification system, comprising a signal generation module, a front-end tunable component, a front-end spectrum detection component, a first mode converter, a middle-end power detection component, a pump amplification unit, a second mode converter and a rear-end spectrum detection component.

[0006] The front-end spectrum detection component comprises a front-end beam splitter component and a front-end spectrum detector, the middle-end power detection component comprises a middle-end beam splitter and a middle-end photoelectric detector, the pump amplification unit comprises a pump beam combination component and a few-mode erbium-doped fiber, and the rear-end spectrum detection component comprises a rear-end beam splitter component and a rear-end spectrum detector.

[0007] The signal generation module, the front-end tunable component and the front-end beam splitter component are sequentially connected, the output ends of the front-end beam splitter component are connected with the first mode converter and the front-end spectrum detector respectively, the output end of the first mode converter is connected with the input end of the middle-end beam splitter, the output ends of the middle-end beam splitter are connected with the pump amplification unit and the middle-end photoelectric detector respectively, the pump amplification unit is connected with the input end of the second mode converter, the second mode converter, the rear-end beam splitter component and the rear-end spectrum detector are sequentially connected, and the front-end tunable component is connected with the front-end spectrum detector, the middle-end photoelectric detector and the rear-end spectrum detector respectively.

[0008] The signal generation module is used for outputting multiple-mode multiple-wavelength signal light, the first mode converter has multiple single-mode input ports and is used for converting the input multiple single-mode signal light into multiple linear polarization mode signal light supported in the few-mode erbium-doped fiber, the pump beam combination component is used for amplifying the signal light, and the second mode converter is used for demultiplexing the multiple mode signal light after simultaneous amplification and outputting from multiple single-mode ports of the second mode converter.

[0009] The front-end spectrum detector is used for detecting and obtaining first spectrum information corresponding to different mode multiple-wavelength signal light, the middle-end photoelectric detector is used for detecting and obtaining input power information corresponding to multiple-wavelength signal light in each mode after the first mode converter, and the rear-end spectrum detector is used for detecting and obtaining second spectrum information corresponding to different mode multiple-wavelength signal light after demultiplexing by the second mode converter; and the front-end tunable component is used for wavelength power compensation according to the first spectrum information, the second spectrum information and the input power information, so as to ensure consistent input power of each mode after compensation and make the multiple-wavelength amplification gain flat.

[0010] Preferably, the signal generation module includes a light source laser and a wavelength coupling component; the light source laser is used to generate signal light with multiple wavelength channels; the wavelength coupling component is used to mix the signal light with multiple wavelength channels and output the mixed multi-wavelength signal light through multiple mode channels.

[0011] Preferably, the front-end tunable component includes an attenuator and a filter; the attenuator is used to adjust the attenuation of the signal optical power, and the filter is used to adjust the power at different wavelengths.

[0012] Preferably, the pump combining assembly includes a pre-positioned few-mode isolation pump combining device, a single-mode pump source, a post-positioned few-mode isolation pump combining device, and a pump adjustment assembly;

[0013] One end of the mid-range beam splitter is connected to the signal input of the pre-featured few-mode isolation pump combiner. The single-mode pump source is connected to the pump input of the pre-featured few-mode isolation pump combiner. The output of the pre-featured few-mode isolation pump combiner is connected to one side of the few-mode erbium-doped fiber. The other side of the few-mode erbium-doped fiber is connected to the input of the post-featured few-mode isolation pump combiner. The pump adjustment component is connected to the pump input of the post-featured few-mode isolation pump combiner. The amplified output of the post-featured few-mode isolation pump combiner is connected to the input of the second mode converter.

[0014] Multi-wavelength signal light in different modes and pump light generated by the single-mode pump source are combined by the front few-mode isolation pump combiner and sent into the few-mode erbium-doped fiber to achieve forward core pumping; pump light generated by the pump adjustment component is reverse-coupled into the few-mode erbium-doped fiber by the rear few-mode isolation pump combiner to achieve backward core pumping.

[0015] Preferably, the few-mode erbium-doped fiber amplification system further includes: a polarization controller assembly; the front-end tunable assembly, the polarization controller assembly, the front-end beam splitter assembly, and the front-end spectrometer are cascaded in each mode channel; the polarization controller assembly is used to ensure the purity of different polarization mode inputs and to control the crosstalk of the few-mode erbium-doped fiber amplification system.

[0016] Preferably, the few-mode erbium-doped fiber comprises, from the inside out, an inner core layer, a first outer core layer, a second outer core layer, and a cladding layer; the erbium ion doping concentrations of the inner core layer, the first outer core layer, and the second outer core layer are denoted as s1, s2, and s3, respectively, satisfying s3 > s1 > s2; with the inner core layer as a reference, the relative refractive index of the first outer core layer is 1.005 to 1.006, and the relative refractive index of the second outer core layer is 1.002 to 1.003.

[0017] Preferably, the absorption coefficient of the few-mode erbium-doped fiber at 1530 nm is 10 dB / m to 45 dB / m, and the length of the few-mode erbium-doped fiber is 1 to 5 m.

[0018] Preferably, the first mode converter and the second mode converter are both a plurality of cascaded all-fiber mode selection conversion devices.

[0019] Preferably, the front few-mode isolated pump combiner comprises a first ferrule, a first self-focusing lens, a first isolator, a first thin film filter, a second self-focusing lens, a second ferrule and a first transparent tube; the signal light input end of the front few-mode isolated pump combiner is arranged adjacent to the input end of the first ferrule through a few-mode fiber, the output end of the first ferrule is arranged adjacent to the input end of the first self-focusing lens, the output end of the first self-focusing lens is arranged adjacent to the second self-focusing lens through the first isolator and the first thin film filter in sequence, and the output end of the second self-focusing lens is arranged adjacent to the input end of the second ferrule; the pump input end of the front few-mode isolated pump combiner is input by a single-mode fiber, and the output end of the front few-mode isolated pump combiner is output through a few-mode fiber; the first ferrule, the first self-focusing lens, the first isolator, the first thin film filter, the second self-focusing lens and the second ferrule are all accommodated in the first transparent tube.

[0020] The rear few-mode isolated pump combiner comprises a third ferrule, a third self-focusing lens, a second thin film filter, a second isolator, a fourth self-focusing lens, a fourth ferrule and a second transparent tube; the input end of the rear few-mode isolated pump combiner is arranged adjacent to the input end of the third ferrule through a few-mode fiber, the output end of the third ferrule is arranged adjacent to the input end of the third self-focusing lens, the output end of the third self-focusing lens is arranged adjacent to the input end of the fourth self-focusing lens through the second thin film filter and the second isolator in sequence, and the output end of the fourth self-focusing lens is arranged adjacent to the input end of the fourth ferrule; the pump input end of the rear few-mode isolated pump combiner is input by a single-mode fiber, and the amplification output end of the rear few-mode isolated pump combiner is output through a few-mode fiber; the third ferrule, the third self-focusing lens, the second thin film filter, the second isolator, the fourth self-focusing lens and the fourth ferrule are all accommodated in the second transparent tube.

[0021] In another aspect, the application provides a control method of the few-mode erbium-doped fiber amplification system as described above, comprising:

[0022] The signal generation module is used to output a multi-mode multi-wavelength signal light at a set initial power; a front-end tunable component is preliminarily adjusted according to a total input power and a wavelength channel number; a first mode converter is used to convert the input multiple single-mode signal lights into multiple linear polarization mode signal lights supported in a few-mode erbium-doped fiber; a pump beam combining component is used to amplify the signal light; and a second mode converter is used to demultiplex the multiple mode signal lights after amplification.

[0023] A front-end optical spectrum detector is used to detect and acquire first spectrum information corresponding to the multi-wavelength signal light of different modes, a middle-end photoelectric detector is used to detect and acquire input power information corresponding to the multi-wavelength signal light of each mode after the first mode converter, and a rear-end optical spectrum detector is used to detect and acquire second spectrum information corresponding to the multi-wavelength signal light of different modes after the second mode converter; the front-end tunable component is feedback adjusted according to the first spectrum information, the second spectrum information and the input power information, so as to perform wavelength power compensation and ensure that the input power of each mode after compensation is consistent while the multi-wavelength amplification gain is flat.

[0024] Preferably, a front few-mode isolation pump beam combiner and a single-mode pump source in the pump beam combining component are used to realize forward core pumping, and a rear few-mode isolation pump beam combiner and a pump adjusting component in the pump beam combining component are used to realize backward core pumping; the gain characteristics are adjusted by adjusting the pump mode and / or power size of the pump adjusting component online.

[0025] One or more technical solutions provided in the application have at least the following technical effects or advantages:

[0026] (1) The application utilizes a signal generation module to output multi-mode multi-wavelength signal light, utilizes a first mode converter to convert inputted multiple single-mode signal light into signal light of multiple linear polarization modes supported in a few-mode erbium-doped fiber, utilizes a pump beam combining assembly to amplify the signal light, and utilizes a second mode converter to demultiplex the multiple mode signal light after amplification; in the process of simultaneously performing multi-mode multi-wavelength amplification (i.e. multiple modes are simultaneously amplified at different wavelengths), the application utilizes a front-end optical spectrum detector to detect and acquire first spectral information corresponding to different mode multi-wavelength signal light, utilizes a middle-end photoelectric detector to detect and acquire input power information corresponding to multi-wavelength signal light at each mode after the first mode converter, utilizes a rear-end optical spectrum detector to detect and acquire second spectral information corresponding to different mode multi-wavelength signal light after demultiplexing by the second mode converter, and according to the first spectral information, the second spectral information and the input power information, the front-end tunable assembly is feedback adjusted for wavelength power compensation, to ensure that the input power of each mode after compensation is consistent while making the multi-wavelength amplification gain flat. The application can realize gain flattening of multi-wavelength amplification by comprehensive detection of the spectrum of the amplified signal of the system, feedback adjustment of the front-end tunable assembly for wavelength power compensation using the test results, and ensuring the consistency of the input power of each mode after compensation using the middle-end photoelectric detector. That is, the few-mode erbium-doped fiber amplification system provided by the application has the characteristics of multi-mode multi-wavelength equalization and adjustment, can not only realize simultaneous amplification of multi-mode multi-wavelength, but also can perform online gain equalization adjustment, stabilize and adjust the wavelength power through negative feedback cascade adjustment, and realize gain flattening of multi-wavelength amplification. The application greatly reduces the cost while expanding the communication capacity, and has important practical application value in WDM-MDM transmission systems.

[0027] (2) Unlike the scheme of placing a gain flattening filter after fiber amplification to realize flattening in some existing technologies, which can cause high gain to drop to the same level as low gain, thereby causing the overall gain level to drop, the application can obtain high gain effect while realizing gain flattening by feedback adjusting and controlling the front-end tunable assembly for wavelength power compensation according to the wavelength flattening difference of each mode. That is, the application can not only realize gain flattening of multi-wavelength amplification, but also can obtain high gain.

[0028] (3) The application utilizes the front few-mode isolation pump combiner and the single-mode pump source in the pump combiner assembly to realize forward core pumping, utilizes the rear few-mode isolation pump combiner and the pump adjusting assembly in the pump combiner assembly to realize rear core pumping, that is, the application forms a bidirectional pumping structure, while retaining the forward pumping of the base film, rear mode selection pumping is added, different mode pumpings can be flexibly selected according to the multi-mode amplification effect, the pumping mode and the pumping power are flexibly changed online by adjusting the rear pumping adjusting assembly, the gain of each mode at different wavelengths is balanced, the adjustment of bidirectional pumping can improve the gain flatness to a certain extent, and the gain and the mode gain difference are significantly improved. In summary, the application provides bidirectional pumping, and the ratio of bidirectional pumping power can also be optimized by additionally adjusting the pumping mode and / or the power size of the pump adjusting assembly, the gain characteristics are further adjusted, the gain is accurately controlled, the inter-mode gain difference is reduced, high flatness, high gain and low mode gain difference can be realized in multi-mode multi-wavelength amplification.

[0029] (4) The few-mode erbium-doped optical fiber prepared in the application and the low-insertion-loss all-fiber device can maintain good signal mode purity and low mode crosstalk, the signal mode performance is excellent in a transmission system, and the mode matching can be guaranteed.

[0030] (5) The optimization design of the doping concentration, the relative refractive index, the absorption coefficient and the length of the few-mode erbium-doped optical fiber in the application can make the application achieve better gain balancing effect. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A structure schematic diagram of a few-mode erbium-doped optical fiber amplification system provided for an embodiment of the application is shown in the figure.

[0032] Figure 2 A structure schematic diagram of a front few-mode isolation pump combiner in a few-mode erbium-doped optical fiber amplification system provided for an embodiment of the application is shown in the figure.

[0033] Figure 3 A structure schematic diagram of a rear few-mode isolation pump combiner in a few-mode erbium-doped optical fiber amplification system provided for an embodiment of the application is shown in the figure.

[0034] Figure 4 An experimental amplification result of a few-mode erbium-doped optical fiber amplification system provided for embodiment 3 of the application is shown in the figure. Figure 1 ;

[0035] Figure 5 An experimental amplification result of a few-mode erbium-doped optical fiber amplification system provided for embodiment 3 of the application is shown in the figure. Figure 2

[0036] Figure 6An experimental amplification result of a few-mode erbium-doped fiber amplification system provided for the embodiment 3 of the present application Figure 3

[0037] Figure 7 An experimental amplification result of a few-mode erbium-doped fiber amplification system provided for the embodiment 3 of the present application Figure 4 .

[0038] Wherein, 01-light source laser, 02-single mode pump source, 03-pump adjustment assembly, 04-front few-mode isolation pump combiner, 05-rear few-mode isolation pump combiner, 06-few-mode erbium-doped fiber, 07-wavelength coupling assembly, 08-front tunable assembly, 09-polarization controller assembly, 010-front beam splitter assembly, 011-front spectrum detector, 012-first mode converter, 013-middle beam splitter, 014-middle photoelectric detector, 015-second mode converter, 016-rear beam splitter assembly, 017-rear spectrum detector;

[0039] 081-first front tunable assembly, 082-second front tunable assembly, 08n-nth front tunable assembly;

[0040] 091-first polarization controller, 092-second polarization controller, 09n-nth polarization controller;

[0041] 0101-first front beam splitter, 0102-second front beam splitter, 010n-nth front beam splitter;

[0042] 0161-first rear beam splitter, 0162-second rear beam splitter, 016n-nth rear beam splitter;

[0043] 11-first ferrule, 12-first self-focusing lens, 13-first isolator, 14-first thin film filter, 15-second self-focusing lens, 16-second ferrule, 17-first transparent tube;

[0044] 021-pump input end of the front few-mode isolation pump combiner, 041-signal input end of the front few-mode isolation pump combiner, 042-output end of the front few-mode isolation pump combiner;

[0045] 18-third ferrule, 19-third self-focusing lens, 20-second thin film filter, 21-second isolator, 22-fourth self-focusing lens, 23-fourth ferrule, 24-second transparent tube;

[0046] 031-pump input end of the rear few-mode isolation pump combiner, 051-signal input end of the rear few-mode isolation pump combiner, 052-output end of the rear few-mode isolation pump combiner. DETAILED DESCRIPTION

[0047] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings and specific embodiments of the specification.

[0048] In a first aspect, the present application provides a few-mode erbium-doped fiber amplification system, referring to Figure 1 , mainly comprising: a signal generating module, a front-end tunable component 08, a front-end beam splitter component 010, a front-end optical spectrum detector 011, a first mode converter 012, a middle-end beam splitter 013, a middle-end photodetector 014, a pump amplification unit, a second mode converter 015, a rear-end beam splitter component 016 and a rear-end optical spectrum detector 017; the pump amplification unit comprises a pump beam combining component and a few-mode erbium-doped fiber 06.

[0049] The signal generating module, the front-end tunable component 08, and the front-end beam splitter component 010 are connected in sequence, and the output ends of the front-end beam splitter component 010 are connected with the first mode converter 012 and the front-end optical spectrum detector 011 respectively; the output end of the first mode converter 012 is connected with the input end of the middle-end beam splitter 013; the output ends of the middle-end beam splitter 013 are connected with the pump amplification unit and the middle-end photodetector 014 respectively; the pump amplification unit is connected with the input end of the second mode converter 015; the second mode converter 015, the rear-end beam splitter component 016, and the rear-end optical spectrum detector 017 are connected in sequence; the front-end tunable component 08 is connected with the front-end optical spectrum detector 011, the middle-end photodetector 014, and the rear-end optical spectrum detector 017 respectively.

[0050] The signal generating module is used for outputting multi-mode multi-wavelength signal light; the first mode converter 012 has a plurality of single-mode input ports, and is used for converting the input multi-mode signal light into signal light of a plurality of linear polarization modes supported in the few-mode erbium-doped fiber 06; the pump beam combining component is used for amplifying the signal light; the second mode converter 015 is used for demultiplexing the simultaneously amplified multi-mode signal light and outputting from a plurality of single-mode ports of the second mode converter 015.

[0051] The front-end spectrum detector 011 is used for detecting and acquiring first spectrum information corresponding to different mode multi-wavelength signal light, the middle-end photoelectric detector 014 is used for detecting and acquiring input power information corresponding to multi-wavelength signal light in each mode after the first mode converter 012, and the rear-end spectrum detector 016 is used for detecting and acquiring second spectrum information corresponding to different mode multi-wavelength signal light after being demultiplexed by the second mode converter 015; the front-end tunable component 08 is used for performing wavelength power compensation according to the first spectrum information, the second spectrum information and the input power information, and ensuring that input powers of each mode after compensation are consistent, so that multi-wavelength amplification gain is flat.

[0052] It can be understood that the front-end beam splitter component 010 and the front-end spectrum detector 011 constitute a front-end spectrum detection component, the rear-end beam splitter component 016 and the rear-end spectrum detector 017 constitute a rear-end spectrum detection component, and combination of the two spectrum detection components can detect typical spectrum signals after multi-wavelength power adjustment and compensation in different modes online. The middle-end beam splitter and the middle-end photoelectric detector constitute a middle-end power detection component, the middle-end beam splitter 013 and the middle-end photoelectric detector 014 are arranged at the rear end of the first mode converter 012, and can detect input power intensity signals in each mode channel after conversion, so as to ensure consistency of input power.

[0053] In addition, the few-mode erbium-doped fiber amplification system provided by the application can further comprise a polarization controller component 09; the front-end tunable component 08, the polarization controller component 09, the front-end beam splitter component 010 and the front-end spectrum detector 011 are cascaded in each mode channel; and the polarization controller component 09 is used for ensuring purity of different polarization mode inputs and regulating crosstalk of the few-mode erbium-doped fiber amplification system, that is, by setting the polarization controller component 09, purity of different polarization mode inputs can be ensured, and low crosstalk level of the amplification system can be accurately regulated and ensured.

[0054] For example, referring to Figure 1 The front-end tunable component 08 comprises a first front-end tunable component 081, a second front-end tunable component 082,..., and an n-th front-end tunable component 08n; the polarization controller component 09 comprises a first polarization controller 091, a second polarization controller 092,..., and an n-th polarization controller 09n; the front-end beam splitter component 010 comprises a first front-end beam splitter 0101, a second front-end beam splitter 0102,..., and an n-th front-end beam splitter 010n; and the rear-end beam splitter component 016 comprises a first rear-end beam splitter 0161, a second rear-end beam splitter 0162,..., and an n-th rear-end beam splitter 016n.

[0055] The signal generating module comprises a light source laser 01 and a wavelength coupling component 07; the light source laser 01 is used to generate signal light of multiple wavelength channels; the wavelength coupling component 07 is used to mix the signal light of multiple wavelength channels and output the mixed multi-wavelength signal light through multiple mode channels.

[0056] That is, the signal light wl1, wl2…wl of different wavelength channels generated by the light source laser 01 n-1 ,wl n is connected to different input ends of the wavelength coupling component 07, and different output ends of the wavelength coupling component 07 are respectively connected to input ends of different mode channels, and each mode channel is arranged in sequence according to the front end tunable component 08, the polarization controller component 09 and the front end beam splitter component 010.

[0057] Specifically, the light source laser 01 adopts a tunable wavelength light source, the light source laser 01 can be used to generate signal light with a wavelength of 1500-1650 nm, and taking the generation of multi-wave signals of the C wave band as an example, up to 96 wavelength channel signals can be output, and the power can be adaptively adjusted according to actual needs, and the power is stable and the adjustment range is wide. The wavelength coupling component 07 is used to mix multiple wavelength channel signals together in the same proportion, and then output the multi-wavelength signals through multiple channels, and the working wavelength is 1500-1650 nm.

[0058] Specifically, the front end tunable component 08 comprises an attenuator and a filter; the attenuator is used to attenuate and adjust the power of the signal light, and the filter is used to adjust the power of different wavelengths. The front end tunable component 08 is used to realize the adjustment and compensation of the wavelength power, and the working wavelength is 1500-1650 nm.

[0059] Specifically, referring to Figures 1 to 3The pump combining assembly comprises a front few-mode isolation pump combining device 04, a single-mode pump source 02, a rear few-mode isolation pump combining device 05 and a pump adjusting assembly 03. One end of the middle-end beam splitter 013 is connected with a signal input end 041 of the front few-mode isolation pump combining device, the single-mode pump source 02 is connected with a pump input end 021 of the front few-mode isolation pump combining device, an output end 042 of the front few-mode isolation pump combining device is connected with one side port of the few-mode erbium-doped fiber 06, the other side port of the few-mode erbium-doped fiber 06 is connected with a signal input end 051 of the rear few-mode isolation pump combining device, the pump adjusting assembly 03 is connected with a pump input end 031 of the rear few-mode isolation pump combining device, and an output end 052 of the rear few-mode isolation pump combining device is connected with an input end of the second mode converter 015. The multi-wavelength signal light in different modes and the pump light generated by the single-mode pump source 02 are combined by the front few-mode isolation pump combining device 04 and then sent into the few-mode erbium-doped fiber 06, so that forward core pumping is realized; the pump light generated by the pump adjusting assembly 03 is coupled into the few-mode erbium-doped fiber 06 by the rear few-mode isolation pump combining device 05, so that backward core pumping is realized.

[0060] Specifically, the single-mode pump source 02 outputs pump light with a wavelength of 980 or 1480 nm and an output power ranging from 0 to 1 W. The pump adjusting assembly 03 comprises a pump source, a temperature control driving module and a mode modulator. The pump source outputs pump light with a wavelength of 980 or 1480 nm and an output power ranging from 0 to 1.2 W, and the forward and backward pump wavelengths are consistent. The temperature control driving module has a driving loop monitoring module and an over-temperature protection circuit feedback module. The mode modulator is a spatial light type online mode conversion module based on a spatial light modulator and a digital micromirror device, which can be connected with a computer control end and flexibly change the pump mode. For example, if the mode gain of LP 02 is low in the mode amplified simultaneously, the phase pattern on the spatial light modulator can be adjusted online according to the actual amplification situation to realize LP 02 pumping. The front-end pump power can be fixed first, and the pump power proportion of the rear end can be increased in sequence to reach an optimal value. After adjustment, not only the gain of each mode at different wavelengths is balanced, but also the gain flatness is improved to a certain extent, and the gain and mode gain difference can be significantly changed.

[0061] The few-mode erbium-doped fiber 06 is a weakly coupled fiber, and has a three-layer core structure with multi-layer erbium ion doping. Specifically, the few-mode erbium-doped fiber 06 comprises, from inside to outside, an inner core layer, a first outer core layer, a second outer core layer, and a cladding, and has a trench auxiliary structure. The trench auxiliary structure can reduce the bending loss and effectively suppress the signal mode in the core region. By increasing the erbium ion concentration at the edge of the core, the gain of the high-order mode can be improved to achieve gain equalization. The erbium ion doping concentrations of the inner core layer, the first outer core layer, and the second outer core layer are denoted as s1, s2, and s3, respectively, and satisfy s3>s1>s2. With the inner core layer as a reference, the relative refractive index of the first outer core layer is 1.005 to 1.006, and the relative refractive index of the second outer core layer is 1.002 to 1.003. The absorption coefficient of the few-mode erbium-doped fiber 06 at 1530 nm is 10 dB / m to 45 dB / m, and the length of the few-mode erbium-doped fiber 06 is 1 to 5 m.

[0062] The first mode converter 012 and the second mode converter 015 are both a plurality of cascaded all-fiber mode selection conversion devices. The first mode converter 012 has a plurality of single-mode input ports, and can be used to convert the input multiple single-mode signal light into light of two or more linear polarization modes supported by the few-mode erbium-doped fiber 06; the second mode converter 015 can complete the demultiplexing of the multiple mode signal light after amplification, and output from multiple single-mode ports.

[0063] Referring to Figure 2 , the front few-mode isolated pump combiner 04 comprises a first clamping sleeve 11, a first self-focusing lens 12, a first isolator 13, a first thin film filter 14, a second self-focusing lens 15, a second clamping sleeve 16, and a first transparent tube 17. The signal input end 041 of the front few-mode isolated pump combiner is arranged adjacent to the input end of the first clamping sleeve 11 by a few-mode fiber, the output end of the first clamping sleeve 11 is arranged adjacent to the input end of the first self-focusing lens 12, the output end of the first self-focusing lens 12 is arranged adjacent to the second self-focusing lens 15 in sequence after the first isolator 13 and the first thin film filter 14, and the output end of the second self-focusing lens 15 is arranged adjacent to the input end of the second clamping sleeve 16. The pump input end 021 of the front few-mode isolated pump combiner is input by a single-mode fiber, and the output end 042 of the front few-mode isolated pump combiner is output via a few-mode fiber matched with the refractive index profile of the few-mode erbium-doped fiber 06. The first clamping sleeve 11, the first self-focusing lens 12, the first isolator 13, the first thin film filter 14, the second self-focusing lens 15, and the second clamping sleeve 16 are all accommodated in the first transparent tube 17.

[0064] The front-positioned few-mode isolation pump combiner 04 integrates an isolator in the device, can reduce the insertion loss caused by excessive devices, and the obtained entire combiner has high integration, the tail fiber of the device is matched with the self-made few-mode erbium-doped optical fiber 06, and then has good mode purity and low insertion loss, and can realize the beam combination of pump light and signal light and prevent the light interference of amplified spontaneous emission from affecting the front-end device.

[0065] Referring to Figure 3 The rear-positioned few-mode isolation pump combiner 05 includes a third clamping sleeve 18, a third self-focusing lens 19, a second thin film filter 20, a second isolator 21, a fourth self-focusing lens 22, a fourth clamping sleeve 23 and a second transparent tube 24; the signal input end 051 of the rear-positioned few-mode isolation pump combiner is arranged adjacent to the input end of the third clamping sleeve 18, the output end of the third clamping sleeve 18 is arranged adjacent to the input end of the third self-focusing lens 19, the output end of the third self-focusing lens 19 is sequentially arranged adjacent to the input end of the fourth self-focusing lens 22 through the second thin film filter 20 and the second isolator 21, and the output end of the fourth self-focusing lens 22 is arranged adjacent to the input end of the fourth clamping sleeve 23; the pump input end 031 of the rear-positioned few-mode isolation pump combiner is input by a single-mode optical fiber, and the output end 052 of the rear-positioned few-mode isolation pump combiner is output through a few-mode optical fiber; the third clamping sleeve 18, the third self-focusing lens 19, the second thin film filter 20, the second isolator 21, the fourth self-focusing lens 22 and the fourth clamping sleeve 23 are all accommodated in the second transparent tube 24.

[0066] The rear-positioned few-mode isolation pump combiner 05 is used in reverse, can perform beam combination of rear-end pump light, and prevent the influence of residual pump light, and also has high integration.

[0067] It should be noted that the few-mode erbium-doped optical fiber amplification system provided by the application can simultaneously use the front-positioned few-mode isolation pump combiner and the rear-positioned few-mode isolation pump combiner with the above structure, or can only use the front-positioned few-mode isolation pump combiner with the above structure at the front end and use a combiner with a common structure at the rear end, and similarly, can only use the rear-positioned few-mode isolation pump combiner with the above structure at the rear end and use a combiner with a common structure at the front end.

[0068] In another aspect, the present application provides a control method of the few-mode erbium-doped fiber amplification system as described above, mainly comprising: using a signal generation module to output a multi-mode multi-wavelength signal light at a set initial power; preliminarily adjusting a front-end tunable component according to the total input power and the number of wavelength channels; using a first mode converter to convert the input multiple single-mode signal lights into multiple linearly polarized mode signal lights supported in the few-mode erbium-doped fiber; using a pump beam combining component to amplify the signal light; using a second mode converter to demultiplex the multiple mode signal lights after amplification; using a front-end optical spectrum detector to detect and obtain first spectral information corresponding to the different mode multi-wavelength signal light, using a middle-end photoelectric detector to detect and obtain input power information corresponding to the multi-wavelength signal light in each mode after the first mode converter, and using a rear-end optical spectrum detector to detect and obtain second spectral information corresponding to the different mode multi-wavelength signal light after demultiplexing by the second mode converter; and feeding back and adjusting the front-end tunable component according to the first spectral information, the second spectral information and the input power information, so as to perform wavelength power compensation and ensure that the input power of each mode after compensation is consistent while the multi-wavelength amplification gain is flat.

[0069] Specifically, the present application can realize forward core pumping by using the front few-mode isolation pump beam combiner and the single-mode pump source in the pump beam combining component, and realize backward core pumping by using the rear few-mode isolation pump beam combiner and the pump adjusting component in the pump beam combining component; and the gain characteristics can be adjusted by adjusting the pump mode and / or the power size of the pump adjusting component online.

[0070] The second aspect of the present application will be further illustrated below in combination with specific devices and wavelength bands.

[0071] Referring to Figure 1 The present application provides a control method of a few-mode erbium-doped fiber amplification system, comprising the following steps:

[0072] Step 1: the light source laser 01 generates multi-wavelength signals in the C band, and sets a specific initial power.

[0073] Step 2: the signal light of each wavelength channel is coupled through the wavelength coupling component 07, and then output through the multi-channel, so as to perform multi-wavelength amplification.

[0074] Step 3: each mode channel is arranged in sequence according to the front-end tunable component 08, the polarization controller component 09, the front-end beam splitter component 010 and the front-end optical spectrum detector 011, and the front-end tunable component 08 is preliminarily adjusted according to the total input power and the number of different wavelength channels.

[0075] Step 4: The multi-wavelength signal light in C-band in different modes and the pump light generated by the single-mode pump source 02 are combined by the front few-mode isolation pump combiner 04, and then are sent into the few-mode erbium-doped fiber 06 to realize forward core pumping.

[0076] Step 5: The pump light generated by the pump adjustment assembly 03 is coupled into the few-mode erbium-doped fiber 06 in the reverse direction by the rear few-mode isolation pump combiner 05 to realize backward core pumping. The selection of the pump mode and the change of the power size are realized by adjusting the mode modulator in the pump adjustment assembly 03, and the ratio of the bidirectional pump power is optimized to realize the accurate control of the gain and reduce the inter-mode gain difference.

[0077] Step 6: The spectrum information is obtained according to the front-end spectrum detector 011 and the rear-end spectrum detector 017, and then the wavelength power compensation is realized by adjusting and controlling the front-end tunable assembly 08 according to the wavelength flatness difference of each mode through feedback adjustment, and the consistency of the compensated input power is ensured by using the middle-end photoelectric detector 014, so that the equalization and adjustment of the multi-mode and multi-wavelength amplification are realized.

[0078] In step 4, the multi-wavelength signal light in different modes is input from the input end, and sequentially passes through the first sleeve 11, the first self-focusing lens 12, the first isolator 13, the first thin film filter 14, the second self-focusing lens 15 and the second sleeve 16 to reach the multiplexing end; the pump light generated by the single-mode pump source 02 is input from the input end, is collimated by the second self-focusing lens 15 and the first thin film filter 14 and is output to the multiplexing port; the first self-focusing lens 12 and the second self-focusing lens 15 are used to collimate the light emitted from the input few-mode fiber and refocus the collimated light into the output few-mode fiber; the first thin film filter 14 is used to reflect the pump light and transmit the signal light at the same time; the first isolator 13 is placed in the forward direction and can suppress the reflection of the signal light and the pump light; the combined light is transmitted through the output few-mode fiber and the few-mode erbium-doped fiber 06 to match the refractive index profile, so that the signal mode has excellent performance and good mode purity.

[0079] In step 5, the pump light generated by the pump adjustment assembly 03 is input from the input end, is collimated in the reverse direction by the third self-focusing lens 19 and the second thin film filter 20 and is output into the few-mode erbium-doped fiber 06; the amplified signal sequentially passes through the third sleeve 18, the third self-focusing lens 19, the second thin film filter 20, the second isolator 21, the fourth self-focusing lens 22 and the fourth sleeve 23 to reach the output end, is demultiplexed by the second mode converter 015 and is output from the corresponding port.

[0080] In order to make the embodiments and technical solutions of the present application more clear, the present application will be further described in detail in combination with specific embodiments.

[0081] Embodiment 1:

[0082]

[0082] The first mode converter 012 and the second mode converter 015 in the few-mode erbium-doped fiber amplification system provided in Embodiment 1 are both photonic lantern type all-fiber devices, which can support the conversion and demultiplexing of LP 01 , LP 11a and LP 11b modes.

[0083] In Embodiment 1, the light source laser 01 generates a multi-wavelength signal in the C band and sets an initial power. The signal light of each wavelength channel is coupled via the wavelength coupling assembly 07 and then output through a multi-channel to perform multi-wavelength amplification. Each mode channel is arranged in sequence according to the front adjustable assembly 08, the polarization controller assembly 09, the front beam splitter assembly 010 and the front optical spectrum detector 011, respectively. The first mode converter 012 converts the input multi-single-mode signal light into signal light of LP 01 , LP 11a and LP 11b modes. The multi-wavelength signal light in the C band in the three modes and the pump light generated by the single-mode pump source 02 are combined by the front few-mode isolated pump combiner 04 and then sent into the few-mode erbium-doped fiber 06 to realize forward core pumping. The pump light generated by the pump adjustment assembly 03 is coupled into the few-mode erbium-doped fiber 06 in the reverse direction by the rear few-mode isolated pump combiner 05 to realize backward core pumping. The amplified signal is demultiplexed by the rear few-mode isolated pump combiner 05 and the second mode converter 015 and then output from the corresponding ports. The rear end beam splitter assembly 016 and the rear end optical spectrum detector 017 are connected in sequence to perform detection.

[0084] Specifically, the pump wavelength of the single-mode pump source 02 is 1480 nm, the pump source wavelength in the pump adjustment assembly 03 is 1480 nm, the mode modulator is an online mode conversion module based on a spatial light modulator, and the selection of LP 11a or LP 11b mode and the change of power size are performed.

[0085] When the few-mode erbium-doped fiber amplification system provided in Embodiment 1 is controlled, the length of the few-mode erbium-doped fiber 06 is first optimized, and then the mode modulator in the pump adjustment assembly 03 is adjusted to perform LP 11a or LP 11bThe selection of the pumping mode and the change of the power size, and the optimization of the power ratio of the bidirectional pumping, can realize the precise control of the gain and the reduction of the inter-mode gain difference. Since the front-end tunable component 08 is connected with the front-end spectrum detector 011, the middle-end photoelectric detector 014 and the rear-end spectrum detector 017, the wavelength flatness difference of each mode can be obtained according to the detection results of the above-mentioned detectors (the front-end spectrum detector 011 and the rear-end spectrum detector 017), and then the wavelength power compensation can be realized by adjusting and controlling the front-end tunable component 08 according to the wavelength flatness difference of each mode, and the consistency of the compensated input power can be ensured by using the middle-end photoelectric detector 014, so as to realize the balanced adjustment of the three-mode multi-wavelength amplification.

[0086] Embodiment 2:

[0087] The few-mode erbium-doped fiber amplification system provided in Embodiment 2 has the same specific structure as Embodiment 1, and the difference lies in that the first mode converter 012 and the second mode converter 015 in Embodiment 2 are side-polished full-fiber devices, which can support the conversion and demultiplexing of LP 01 , LP 11a , LP 11b , LP 21a and LP 21b modes.

[0088] In Embodiment 2, the first mode converter 012 converts the input multiple single-mode signal light into signal light of LP 01 , LP 11a , LP 11b , LP 21a modes, and then performs amplification and demultiplexing. The pump wavelength of the single-mode pump source 02 in Embodiment 2 is 980 nm, the pump source wavelength in the pump adjustment component 03 is 980 nm, the mode modulator is an online mode conversion module based on a digital micromirror device, and the selection of the LP 11a or LP 21a mode and the change of the power size are performed.

[0089] When the few-mode erbium-doped fiber amplification system provided in Embodiment 2 is controlled, the difference from Embodiment 1 lies in that the selection of the LP 11a or LP 21a pumping mode and the change of the power size are performed by adjusting the mode modulator in the pump adjustment component 03, and the power ratio of the bidirectional pumping is optimized, so as to finally realize the balanced adjustment of the five-mode multi-wavelength amplification.

[0090] Embodiment 3:

[0091] The few-mode erbium-doped fiber amplifier system provided in Embodiment 3 has the same specific structure as Embodiment 1, but the difference is that the first mode converter 012 and the second mode converter 015 in Embodiment 3 are fused biconical taper type all-fiber devices, which can support the conversion and demultiplexing of LP 01 , LP 11 and LP 21 modes.

[0092] In Embodiment 3, the first mode converter 012 converts the input multiple single-mode signal light into signal light of LP 01 , LP 11 and LP 21 modes, and then amplifies and demultiplexes the signal light. The pump wavelength of the single-mode pump source 02 in Embodiment 3 is 980 nm, the pump source wavelength in the pump adjustment assembly 03 is 980 nm, and the mode modulator is an online mode conversion module based on a spatial light modulator, which performs the selection of LP 21 mode and the change of power size.

[0093] When the few-mode erbium-doped fiber amplifier system provided in Embodiment 3 is controlled, the difference from Embodiment 1 is that the selection of LP 21 pump mode and the change of power size are performed by adjusting the mode modulator in the pump adjustment assembly 03, so as to optimize the ratio of bidirectional pump power, and finally realize the balanced adjustment of three-mode multi-wavelength amplification.

[0094] The experimental amplification results of the few-mode erbium-doped fiber amplifier system provided in Embodiment 3 are shown in Figures 4 to 7 , wherein Figure 4 shows the gain characteristics of three modes (LP 01 , LP 11 and LP 21 ) amplifying 8-wavelength channels under the condition of total input power of -15dBm, total pump power of 650mW and 2.5m fiber length. Figure 5 shows the gain characteristics of three modes amplifying 8-wavelength channels under the condition of total input power of -15dBm, total pump power of 650mW and 2m fiber length. Figure 6 shows the gain characteristics of three modes amplifying 8-wavelength channels under the condition of total input power of -12dBm, total pump power of 650mW and 2m fiber length. Figure 7 shows the gain characteristics of three modes amplifying 8-wavelength channels under the condition of total input power of -15dBm, total pump power of 570mW and 2m fiber length. Among them, Figure 4 and Figure 5 are variables of fiber length, and it can be known by comparison that the mode gain difference and gain flatness of the system can be further reduced by optimizing the appropriate fiber length. Figure 5 andFigure 6 The variable is total input power, and through comparison, it can be known that the gain of each mode is improved with the decrease of input power. Figure 5 and Figure 7 The variable is total pump power, and through comparison, it can be known that the multi-wavelength amplification in multi-mode can be further made to realize ideal gain balance by optimizing pump power.

[0095] Next, on the basis of example 3, the multi-mode and multi-wavelength balance adjustable performance of the system is verified in combination with parameters.

[0096] The light source laser 01 generates multi-wavelength signals between 1530-1565nm in C band, the wavelength channel is set to 8, 16 or 32, and the initial power is set. For example, the total signal input power of all wavelength channels in each mode is set to-15dBm, the length of the used few-mode erbium-doped fiber 06 is 2m, the wavelength channel number is 8, the forward pump power is adjusted to 400mW, and the high-order mode LP 21 is excited by loading the phase pattern corresponding to the mode on the spatial light modulation module in the pump adjustment assembly 03. The pump source and the loaded phase pattern are adjusted, when the backward pump power is increased to 90mW, the average gain can reach more than 24dB, but the maximum modal gain difference and the maximum gain flatness need to be improved. With the increase of the proportion of the backward pump mode power, the average gain of the three-mode signal used for 8-wavelength channel amplification is improved to 25.24dB, the maximum modal gain difference and the maximum gain flatness reach an ideal level, and the gain balance in multi-mode and multi-wavelength amplification can be realized. The amplification results when the total pump power is 490mW, 570mW and 650mW are given in table 1.

[0097] Table 1 amplification result data

[0098]

[0099] It can be known that the present application can realize the gain balance in multi-mode and multi-wavelength amplification, and has promoting significance for simultaneously realizing multi-wavelength transmission of long-distance MDM system.

[0100] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present application but not limit the present application, although the present application is described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application, and all should be covered in the scope of claims of the present application.

Claims

1. A few-mode erbium-doped fiber amplifier system, characterized by, include: The signal generation module, front-end tunable component, front-end spectral detection component, first mode converter, mid-range power detection component, pump amplification unit, second mode converter and back-end spectral detection component; The front-end spectral detection component includes a front-end beam splitter component and a front-end spectral detector; the mid-end power detection component includes a mid-end beam splitter and a mid-end photodetector; the pump amplification unit includes a pump beam combiner component and a few-mode erbium-doped fiber; and the back-end spectral detection component includes a back-end beam splitter component and a back-end spectral detector. The signal generation module, the front-end tunable component, and the front-end beam splitter component are connected in sequence. The output terminal of the front-end beam splitter component is connected to the first mode converter and the front-end spectroscopic detector, respectively. The output terminal of the first mode converter is connected to the input terminal of the mid-range beam splitter. The output terminal of the mid-range beam splitter is connected to the pump amplification unit and the mid-range photodetector, respectively. The pump amplification unit is connected to the input terminal of the second mode converter. The second mode converter, the back-end beam splitter component, and the back-end spectroscopic detector are connected in sequence. The front-end tunable component is connected to the front-end spectroscopic detector, the mid-range photodetector, and the back-end spectroscopic detector, respectively. The signal generation module is used to output multi-mode, multi-wavelength signal light; the first mode converter has multiple single-mode input ports, and the first mode converter is used to convert the multiple input single-mode signal lights into signal lights with multiple linear polarization modes supported in the few-mode erbium-doped fiber; the pump bundler is used to amplify the signal light; The second mode converter is used to demultiplex the simultaneously amplified multiple mode signal lights and output them from multiple single-mode ports of the second mode converter; The front-end spectral detector is used to detect and acquire the first spectral information corresponding to multi-wavelength signal light in different modes. The mid-end photodetector is used to detect and acquire the input power information corresponding to multi-wavelength signal light in each mode after passing through the first mode converter. The back-end spectral detector is used to detect and acquire the second spectral information corresponding to multi-wavelength signal light in different modes after being demultiplexed by the second mode converter. The front-end tunable component is used to perform wavelength power compensation based on the first spectral information, the second spectral information, and the input power information, so as to ensure that the input power of each mode is consistent after compensation while making the multi-wavelength amplification gain flat.

2. The few-mode erbium-doped fiber amplifier system of claim 1, wherein, The signal generation module includes a light source laser and a wavelength coupling component; the light source laser is used to generate signal light with multiple wavelength channels; the wavelength coupling component is used to mix the signal light with multiple wavelength channels and output the mixed multi-wavelength signal light through multiple mode channels.

3. The few-mode erbium-doped fiber amplifier system of claim 1, wherein, The front-end tunable component includes an attenuator and a filter; the attenuator is used to adjust the attenuation of the signal optical power, and the filter is used to adjust the power at different wavelengths.

4. The few-mode erbium-doped fiber amplifier system of claim 1, wherein, The pump combining assembly includes a front-mounted few-mode isolation pump combining unit, a single-mode pump source, a rear-mounted few-mode isolation pump combining unit, and a pump adjustment assembly. One end of the middle-end beam splitter is connected with a signal input end of the front-end few-mode isolation pump combiner, the single-mode pump source is connected with a pump input end of the front-end few-mode isolation pump combiner, an output end of the front-end few-mode isolation pump combiner is connected with one side port of the few-mode erbium-doped fiber, the other side port of the few-mode erbium-doped fiber is connected with an input end of the rear-end few-mode isolation pump combiner, the pump adjustment assembly is connected with a pump input end of the rear-end few-mode isolation pump combiner, and an amplified output end of the rear-end few-mode isolation pump combiner is connected with an input end of the second mode converter; The multi-wavelength signal light in different modes and the pump light generated by the single-mode pump source are combined by the front-end few-mode isolation pump combiner and then sent into the few-mode erbium-doped fiber to realize forward core pumping, and the pump light generated by the pump adjustment assembly is coupled into the few-mode erbium-doped fiber by the rear-end few-mode isolation pump combiner to realize backward core pumping.

5. The few-mode erbium-doped fiber amplifier system of claim 1, wherein, Further comprising: a polarization controller assembly; the front-end tunable assembly, the polarization controller assembly, the front-end beam splitter assembly and the front-end spectrum detector are cascaded under each mode channel; the polarization controller assembly is used for ensuring the purity of different polarization mode inputs and regulating the crosstalk of the few-mode erbium-doped fiber amplification system.

6. The few-mode erbium-doped fiber amplifier system of claim 1, wherein, The few-mode erbium-doped fiber comprises, from inside to outside, an inner core layer, a first outer core layer, a second outer core layer and a cladding layer; the corresponding erbium ion doping concentrations of the inner core layer, the first outer core layer and the second outer core layer are respectively denoted as s1, s2 and s3, and satisfy s3>s1>s2; with the inner core layer as a reference, the relative refractive index of the first outer core layer is 1.005 to 1.006, and the relative refractive index of the second outer core layer is 1.002 to 1.

003.

7. The few-mode erbium-doped fiber amplifier system of claim 6, wherein, The absorption coefficient of the few-mode erbium-doped fiber at 1530 nm is 10 dB / m to 45 dB / m, and the length of the few-mode erbium-doped fiber is 1 to 5 m.

8. The few-mode erbium-doped fiber amplifier system of claim 1, wherein, The first mode converter and the second mode converter are both multiple cascaded all-fiber mode selection conversion devices.

9. The few-mode erbium-doped fiber amplifier system of claim 4, wherein, The front few-mode isolation pumping combiner comprises a first sleeve, a first self-focusing lens, a first isolator, a first film filter, a second self-focusing lens, a second sleeve and a first transparent tube; the signal light input end of the front few-mode isolation pumping combiner is arranged adjacent to the input end of the first sleeve through a few-mode optical fiber, the output end of the first sleeve is arranged adjacent to the input end of the first self-focusing lens, the output end of the first self-focusing lens is arranged adjacent to the second self-focusing lens through the first isolator and the first film filter in sequence, and the output end of the second self-focusing lens is arranged adjacent to the input end of the second sleeve; the pump input end of the front few-mode isolation pumping combiner is input by a single-mode optical fiber, and the output end of the front few-mode isolation pumping combiner is output through a few-mode optical fiber, which matches the refractive index profile of the few-mode erbium-doped optical fiber; the first sleeve, the first self-focusing lens, the first isolator, the first film filter, the second self-focusing lens and the second sleeve are all accommodated in the first transparent tube; The rear few-mode isolation pumping combiner comprises a third sleeve, a third self-focusing lens, a second film filter, a second isolator, a fourth self-focusing lens, a fourth sleeve and a second transparent tube; the input end of the rear few-mode isolation pumping combiner is arranged adjacent to the input end of the third sleeve through a few-mode optical fiber, the output end of the third sleeve is arranged adjacent to the input end of the third self-focusing lens, the output end of the third self-focusing lens is arranged adjacent to the input end of the fourth self-focusing lens through the second film filter and the second isolator in sequence, and the output end of the fourth self-focusing lens is arranged adjacent to the input end of the fourth sleeve; the pump input end of the rear few-mode isolation pumping combiner is input by a single-mode optical fiber, and the amplification output end of the rear few-mode isolation pumping combiner is output through a few-mode optical fiber; the third sleeve, the third self-focusing lens, the second film filter, the second isolator, the fourth self-focusing lens and the fourth sleeve are all accommodated in the second transparent tube.

10. A method of controlling a few-mode erbium-doped fiber amplifier system as claimed in any one of claims 1-9, characterized by, Comprise: A signal generation module is used to output a multi-mode multi-wavelength signal light at a set initial power; According to the total input power and the number of wavelength channels, the front-end tunable component is preliminarily adjusted; a first mode converter is used to convert the input multiple single-mode signal lights into multiple linear polarization mode signal lights supported in the few-mode erbium-doped optical fiber; a pumping combiner component is used to amplify the signal light; A second mode converter is used to demultiplex the multiple mode signal lights amplified at the same time; The first spectrum information corresponding to different mode multi-wavelength signal light is detected by a front-end spectrum detector, the input power information corresponding to multi-wavelength signal light in each mode after the first mode converter is detected by a middle-end photoelectric detector, and the second spectrum information corresponding to different mode multi-wavelength signal light after the second mode converter is detected by a rear-end spectrum detector; the front-end tunable component is feedback adjusted according to the first spectrum information, the second spectrum information and the input power information, so as to compensate the wavelength power and ensure that the compensated input power of each mode is consistent and the multi-wavelength amplification gain is flat.

11. The method of claim 10, wherein the step of controlling the few-mode erbium-doped fiber amplifier system further comprises the step of: Forward core pumping is realized by using a front few-mode isolation pump combiner and a single-mode pump source in the pump combining component, and backward core pumping is realized by using a rear few-mode isolation pump combiner and a pump adjusting component in the pump combining component; the gain characteristics are adjusted by adjusting the pump mode and / or power size of the pump adjusting component online. ​

Images