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

Abstract

The invention 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. According to the invention, the signal generation module is used for outputting multi-mode multi-wavelength signal light, the mode converter is used for mode conversion and demultiplexing, and the pumping beam combining assembly is used for amplifying the signal light; in the process of simultaneously carrying out multi-mode multi-wavelength amplification, a front-end spectrum detector is used for detecting and acquiring first spectrum information corresponding to multi-wavelength signal light in different modes, and a middle-end photoelectric detector is used for detecting and acquiring input power information corresponding to the multi-wavelength signal light in each mode after passing through a first mode converter; a rear-end spectrum detector is used for detecting and acquiring second spectrum information corresponding to different-mode multi-wavelength signal light demultiplexed by a second mode converter, and feedback adjustment is carried out on a front-end tunable component according to the information, so that wavelength power compensation is carried out; and the multi-wavelength amplification gain is flattened while the input power of each mode after compensation is ensured to be consistent.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and more specifically, relates to a few-mode erbium-doped optical fiber amplification system and a control method thereof. Background Art

[0002] With the emergence of new technologies and industrial forms such as "Internet+", "big data", "cloud computing" and "smart cities", people's lives have entered a new era of "Internet of Everything". The rapidly growing data traffic has put forward higher requirements for communication networks. For optical fiber communication systems, with 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 the mode-division multiplexing (MDM) system based on few-mode optical fiber, different modes can be transmitted simultaneously as independent channels, thereby increasing the number of transmission channels and doubling the communication capacity. In particular, the weakly coupled transmission system can realize independent detection and reception of each mode without the need for multiple input multiple output digital signal processing (MIMO DSP), which can greatly reduce the complexity and cost of the system.

[0003] In actual MDM systems, the few-mode erbium-doped fiber amplifier (FM-EDFA) is a key component for compensating for the transmission loss of optical fiber links. However, the difference in the degree of overlap between the optical field distribution of each mode signal, the pump optical field distribution and the erbium doping distribution will lead to 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 the MDM system, in order to increase the communication bandwidth of each optical fiber, multiple wavelength channels need to be amplified at the same time. This puts higher requirements on the FM-EDFA to achieve gain equalization in long-distance wavelength division multiplexing (WDM) combined with MDM transmission systems. At present, most of the reported FM-EDFAs are aimed at the amplification of multiple modes at a single wavelength, but there are few studies on the simultaneous amplification of multiple modes and multiple wavelengths. How to achieve simultaneous amplification of multiple modes and multiple wavelengths and achieve gain flatness of multi-wavelength amplification is a technical problem that is of concern and needs to be solved in this field. Summary of the invention

[0004] The present invention provides a few-mode erbium-doped optical fiber amplification system and a control method thereof, thereby solving the problem in the prior art that it is difficult to realize simultaneous amplification of multiple modes and multiple wavelengths and achieve gain flatness.

[0005] The present invention 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 mid-end power detection component, a pump amplifier unit, a second mode converter and a back-end spectrum detection component;

[0006] The front-end spectrum detection component includes a front-end beam splitter component and a front-end spectrum detector, the mid-end power detection component includes a mid-end beam splitter and a mid-end photoelectric detector, the pump amplification unit includes a pump beam combining component and a few-mode erbium-doped optical fiber, and the back-end spectrum detection component includes a back-end beam splitter component and a back-end spectrum detector;

[0007] The signal generating module, the front-end tunable component, and the front-end beam splitter component are connected in sequence, and the output end of the front-end beam splitter component is respectively connected to the first mode converter and the front-end spectrum detector; the output end of the first mode converter is connected to the input end of the middle-end beam splitter; the output end of the middle-end beam splitter is respectively connected to the pump amplifier unit and the middle-end photodetector; the pump amplifier unit is connected to 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 connected in sequence; the front-end tunable component is respectively connected to the front-end spectrum detector, the middle-end photodetector, and the rear-end spectrum detector;

[0008] The signal generating module is used to output multi-mode multi-wavelength signal light; the first mode converter has a plurality of single-mode input ports, and the first mode converter is used to convert the input multiple single-mode signal lights into multiple linear polarization mode signal lights supported by the few-mode erbium-doped optical fiber; the pump beam combining component 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 the multiple single-mode ports of the second mode converter;

[0009] The front-end spectrum detector is used to detect and obtain first spectrum information corresponding to multi-wavelength signal lights of different modes, the mid-end photoelectric detector is used to detect and obtain input power information corresponding to the multi-wavelength signal lights in each mode after passing through the first mode converter, and the back-end spectrum detector is used to detect and obtain second spectrum information corresponding to the multi-wavelength signal lights of different modes after demultiplexing through the second mode converter; the front-end tunable component is used to perform wavelength power compensation according to the first spectrum information, the second spectrum information and the input power information, so as to make the multi-wavelength amplification gain flat while ensuring that the input powers of each mode after compensation are consistent.

[0010] Preferably, the signal generating module comprises a light source laser and a wavelength coupling component; the light source laser is used to generate signal light of multiple wavelength channels; the wavelength coupling component is used to mix the signal light of 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 light power, and the filter is used to adjust the power of different wavelengths.

[0012] Preferably, the pump beam combiner assembly includes a front minority-mode isolation pump beam combiner, a single-mode pump source, a rear minority-mode isolation pump beam combiner and a pump adjustment assembly;

[0013] One end output of the mid-end beam splitter is connected to the signal input end of the front few-mode isolation pump combiner, the single-mode pump source is connected to the pump input end of the front few-mode isolation pump combiner, the output end of the front few-mode isolation pump combiner is connected to one side port of the few-mode erbium-doped fiber, the other side port of the few-mode erbium-doped fiber is connected to the input end of the rear few-mode isolation pump combiner, the pump adjustment component is connected to the pump input end of the rear few-mode isolation pump combiner, and the amplified output end of the rear few-mode isolation pump combiner is connected to the input end of the second mode converter;

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

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

[0016] Preferably, the few-mode erbium-doped optical fiber comprises, from the inside to the outside, an inner core layer, a first outer core layer, a second outer core layer and a cladding; the erbium ion doping concentrations corresponding to 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; taking 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 optical fiber at 1530 nm is 10 dB / m to 45 dB / m, and the length of the few-mode erbium-doped optical fiber is 1 to 5 m.

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

[0019] Preferably, the front few-mode isolation pump combiner includes 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 isolation pump combiner is arranged adjacent to the input end of the first ferrule via a few-mode optical 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 after passing 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 isolation pump combiner is input by a single-mode optical fiber, and the output end of the front few-mode isolation pump combiner is output via a few-mode optical fiber, and the refractive index profile of the few-mode optical fiber matches that of the few-mode erbium-doped optical 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 post-positioned few-mode isolation pump combiner includes 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 post-positioned few-mode isolation pump combiner is arranged adjacent to the input end of the third ferrule via the few-mode optical 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 after sequentially passing through the second thin film filter and the second isolator, 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 post-positioned few-mode isolation pump combiner is input by a single-mode optical fiber, and the amplified output end of the post-positioned few-mode isolation pump combiner is output via the few-mode optical 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] On the other hand, the present invention provides a control method for the few-mode erbium-doped fiber amplifier system as described above, comprising:

[0022] The signal generation module is used to output multi-mode multi-wavelength signal light at a set initial power; the front-end tunable component is preliminarily adjusted according to the total input power and the number of wavelength channels; the first mode converter is used to convert the input multiple single-mode signal lights into multiple linear polarization mode signal lights supported by the few-mode erbium-doped optical fiber; the pump beam combining component is used to amplify the signal light; and the second mode converter is used to demultiplex the multiple mode signal lights that have been amplified simultaneously;

[0023] A front-end spectrum detector is used to detect and obtain first spectrum information corresponding to multi-wavelength signal lights of different modes, a mid-end photoelectric detector is used to detect and obtain input power information corresponding to the multi-wavelength signal lights in each mode after passing through the first mode converter, and a back-end spectrum detector is used to detect and obtain second spectrum information corresponding to the multi-wavelength signal lights of different modes after demultiplexing by the second mode converter; feedback adjustment is performed on the front-end tunable component according to the first spectrum information, the second spectrum information and the input power information to perform wavelength power compensation, thereby ensuring that the input powers of each mode after compensation are consistent while making the multi-wavelength amplification gain flat.

[0024] Preferably, the forward core pumping is realized by using the front few-mode isolation pump combiner and the single-mode pump source in the pump combining assembly, and the backward core pumping is realized by using the rear few-mode isolation pump combiner and the pump adjustment assembly in the pump combining assembly; and the gain characteristic is adjusted by online adjusting the pump mode and / or power of the pump adjustment assembly.

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

[0026] (1) The present invention uses a signal generation module to output multi-mode multi-wavelength signal light, uses a first mode converter to convert multiple input single-mode signal lights into multiple linear polarization mode signal lights supported in a few-mode erbium-doped optical fiber, uses a pump beam combiner to amplify the signal light, and uses a second mode converter to demultiplex the multiple mode signal lights that have been amplified simultaneously. In the process of simultaneously performing multi-mode multi-wavelength amplification (i.e., multiple modes are amplified simultaneously at different wavelengths), the present invention uses a front-end spectrum detector to detect and obtain first spectrum information corresponding to multi-wavelength signal lights of different modes, uses a mid-end photoelectric detector to detect and obtain input power information corresponding to multi-wavelength signal lights of each mode after passing through the first mode converter, uses a back-end spectrum detector to detect and obtain second spectrum information corresponding to multi-wavelength signal lights of different modes after demultiplexing through the second mode converter, and performs feedback adjustment on the front-end tunable component according to the first spectrum information, the second spectrum information and the input power information to perform wavelength power compensation, thereby ensuring that the input powers of each mode after compensation are consistent and making the multi-wavelength amplification gain flat. The present invention performs comprehensive spectrum detection on the system amplified signal, uses the test result feedback to adjust the front-end tunable component to perform wavelength power compensation, and uses the mid-end photoelectric detector to ensure that the input power of each mode after compensation is consistent, so as to achieve the gain flatness of multi-wavelength amplification. That is, the few-mode erbium-doped fiber amplifier system provided by the present invention has the characteristics of multi-mode multi-wavelength balanced and adjustable, which can not only achieve multi-mode multi-wavelength simultaneous amplification, but also perform online gain balance adjustment, and achieve the gain flatness of multi-wavelength amplification by stably adjusting the wavelength power through negative feedback cascade regulation. The present invention greatly reduces the cost while expanding the communication capacity, and has important practical application value in WDM-MDM transmission systems.

[0027] (2) Unlike some prior art solutions that achieve gain flattening by placing a gain flattening filter after optical fiber amplification, which results in a high gain decreasing to the same level as a low gain, thereby reducing the overall gain level, the present invention controls the front-end tunable component to perform wavelength power compensation based on the wavelength flattening difference of each mode through feedback adjustment, and can achieve gain flattening while obtaining a high gain effect. That is, the present invention can not only achieve gain flattening of multi-wavelength amplification, but also obtain high gain.

[0028] (3) The present invention utilizes the front few-mode isolation pump combiner and the single-mode pump source in the pump combining assembly to realize forward core pumping, and utilizes the rear few-mode isolation pump combiner and the pump adjustment assembly in the pump combining assembly to realize backward core pumping, that is, the present invention constitutes a bidirectional pumping structure, while retaining the forward pumping of the base film, a backward mode selection pump is added, and different mode pumps can be flexibly selected for the amplification effect of multiple modes. By adjusting the backward pump adjustment assembly, the pump mode and pump power can be flexibly changed online, so that the gain of each mode at different wavelengths can be balanced. The adjustment of the bidirectional pumping can improve the gain flatness to a certain extent, and significantly improve the gain and mode gain difference. In summary, the present invention provides bidirectional pumping, and by additionally adjusting the pump mode and / or power size of the pump adjustment assembly, the ratio of the bidirectional pump power can be optimized, and the gain characteristics can be further adjusted to achieve precise gain control while reducing the inter-mode gain difference, and can achieve high flatness, high gain and low mode gain difference in multi-mode multi-wavelength amplification.

[0029] (4) The present invention uses the prepared few-mode erbium-doped optical fiber and the low insertion loss all-fiber device, which can maintain good signal mode purity and low modal crosstalk, maintain excellent signal mode performance in the transmission system, and ensure high mode matching.

[0030] (5) The optimized design of doping concentration, relative refractive index, absorption coefficient and length in the few-mode erbium-doped optical fiber of the present invention enables the present invention to achieve better gain equalization effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of a few-mode erbium-doped fiber amplification system provided by an embodiment of the present invention;

[0032] Figure 2 A schematic structural diagram of a front few-mode isolation pump combiner in a few-mode erbium-doped fiber amplification system provided by an embodiment of the present invention;

[0033] Figure 3 A schematic structural diagram of a post-placed few-mode isolation pump combiner in a few-mode erbium-doped fiber amplification system provided by an embodiment of the present invention;

[0034] Figure 4 Experimental amplification results of a few-mode erbium-doped fiber amplifier system provided in Example 3 of the present invention Figure 1 ;

[0035] Figure 5 Experimental amplification results of a few-mode erbium-doped fiber amplifier system provided in Example 3 of the present invention Figure 2

[0036] Figure 6Experimental amplification results of a few-mode erbium-doped fiber amplifier system provided in Example 3 of the present invention Figure 3

[0037] Figure 7 Experimental amplification results of a few-mode erbium-doped fiber amplifier system provided in Example 3 of the present invention Figure 4 .

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

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

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

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

[0042] 0161-first rear end beam splitter, 0162-second rear end beam splitter, 016n-nth rear end 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-the pump input end of the post-positioned few-mode isolation pump combiner, 051-the signal input end of the post-positioned few-mode isolation pump combiner, 052-the output end of the post-positioned few-mode isolation pump combiner. DETAILED DESCRIPTION

[0047] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0048] In a first aspect, the present invention provides a few-mode erbium-doped fiber amplifier system, see Figure 1 , mainly including: a signal generating module, a front-end tunable component 08, a front-end beam splitter component 010, a front-end spectrum detector 011, a first mode converter 012, a mid-end beam splitter 013, a mid-end photodetector 014, a pump amplifier unit, a second mode converter 015, a rear-end beam splitter component 016 and a rear-end spectrum detector 017; the pump amplifier unit includes a pump beam combining component and a few-mode erbium-doped optical 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 end of the front-end beam splitter component 010 is respectively connected to the first mode converter 012 and the front-end spectrum detector 011; the output end of the first mode converter 012 is connected to the input end of the middle-end beam splitter 013; the output end of the middle-end beam splitter 013 is respectively connected to the pump amplifier unit and the middle-end photodetector 014; the pump amplifier unit is connected to 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 spectrum detector 017 are connected in sequence; the front-end tunable component 08 is respectively connected to the front-end spectrum detector 011, the middle-end photodetector 014 and the rear-end spectrum detector 017.

[0050] The signal generating module is used to output multi-mode multi-wavelength signal light; the first mode converter 012 has multiple single-mode input ports, and the first mode converter 012 is used to convert the input multiple single-mode signal lights into signal lights of multiple linear polarization modes supported in the few-mode erbium-doped optical fiber 06; the pump beam combining component is used to amplify the signal light; the second mode converter 015 is used to demultiplex the multiple mode signal lights that have been amplified simultaneously, and output them from the multiple single-mode ports of the second mode converter 015.

[0051] The front-end spectrum detector 011 is used to detect and obtain the first spectrum information corresponding to the multi-wavelength signal light of different modes, the mid-end photoelectric detector 014 is used to detect and obtain the input power information corresponding to the multi-wavelength signal light in each mode after passing through the first mode converter 012, and the back-end spectrum detector 016 is used to detect and obtain the second spectrum information corresponding to the multi-wavelength signal light of different modes after demultiplexing by the second mode converter 015; the front-end tunable component 08 is used to perform wavelength power compensation according to the first spectrum information, the second spectrum information and the input power information, and ensure that the input powers of each mode after compensation are consistent, so that the 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, and the rear-end beam splitter component 016 and the rear-end spectrum detector 017 constitute a rear-end spectrum detection component. The combination of the two spectrum detection components can detect online the typical spectrum signals after multi-wavelength power adjustment and compensation in different modes. The mid-end beam splitter and the mid-end photoelectric detector constitute a mid-end power detection component, and the mid-end beam splitter 013 and the mid-end photoelectric detector 014 are placed at the rear end of the first mode converter 012, and can detect the input power light intensity signal under each mode channel after conversion to ensure the consistency of the input power.

[0053] In addition, the few-mode erbium-doped fiber amplifier system provided by the present invention may also include: 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 under each mode channel; the polarization controller component 09 is used to ensure the purity of different polarization mode inputs and to regulate the crosstalk of the few-mode erbium-doped fiber amplifier system, that is, by setting the polarization controller component 09, the purity of different polarization mode inputs can be ensured, and the low crosstalk level of the amplifier system can also be accurately regulated and guaranteed.

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

[0055] The signal generating module includes 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 lights wl1, wl2…wl of different wavelength channels generated by the light source laser 01 n-1 ,wl n Connected to different input ends of the wavelength coupling component 07, 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, and the light source laser 01 can be used to generate signal light with a wavelength of 1500-1650nm. Taking the generation of multi-wave signals in the C band as an example, it can output signals of up to 96 wavelength channels, and the power can be adaptively adjusted according to actual needs, with stable power and a wide adjustment range. The wavelength coupling component 07 is used to mix multiple wavelength channel signals in the same proportion, and then output the multi-wavelength signal through multiple channels, and the working wavelength is 1500-1650nm.

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

[0059] For details, see Figures 1 to 3The pump combining component includes a front minority mode isolation pump combiner 04, a single mode pump source 02, a rear minority mode isolation pump combiner 05 and a pump adjustment component 03. One end output of the mid-end beam splitter 013 is connected to the signal input end 041 of the front minority mode isolation pump combiner, the single mode pump source 02 is connected to the pump input end 021 of the front minority mode isolation pump combiner, the output end 042 of the front minority mode isolation pump combiner is connected to a side port of the minority mode erbium-doped fiber 06, the other side port of the minority mode erbium-doped fiber 06 is connected to the signal input end 051 of the rear minority mode isolation pump combiner, the pump adjustment component 03 is connected to the pump input end 031 of the rear minority mode isolation pump combiner, and the output end 052 of the rear minority mode isolation pump combiner is connected to the 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 combiner 04 and then sent into the few-mode erbium-doped optical fiber 06 to realize forward core pumping; the pump light generated by the pump adjustment component 03 is reversely coupled into the few-mode erbium-doped optical fiber 06 through the rear few-mode isolation pump combiner 05 to realize backward core pumping.

[0060] Specifically, the single-mode pump source 02 outputs pump light at a wavelength of 980 or 1480 nm, and an output power range of 0 to 1 W. The pump adjustment component 03 includes a pump source, a temperature-controlled drive module, and a mode modulator. The pump source outputs pump light at a wavelength of 980 or 1480 nm, and an output power range of 0 to 1.2 W. The forward and backward pump wavelengths remain consistent. The temperature-controlled drive module has a drive circuit monitoring module and an over-temperature protection circuit feedback module. The mode modulator is an online mode conversion module for spatial light types based on spatial light modulators and digital micromirror devices, which can be connected to a computer control terminal to flexibly change the pump mode. For example, if in the simultaneously amplified mode, LP 02 If the mode gain is low, the LP can be achieved by adjusting the phase diagram on the spatial light modulator online according to the actual amplification situation. 02 For pumping, you can first fix the front-end pump power and then increase the rear-end pump power ratio in sequence to reach an optimal value. After adjustment, not only will the gain of each mode at different wavelengths be balanced, the gain flatness will be improved to a certain extent, but the gain and mode gain difference can also be significantly changed.

[0061] The few-mode erbium-doped fiber 06 is a weakly coupled fiber having a three-layer core structure doped with multiple layers of erbium ions. Specifically, the few-mode erbium-doped fiber 06 includes an inner core layer, a first outer core layer, a second outer core layer and a cladding layer from the inside to the outside, and has a groove auxiliary structure. The groove auxiliary structure can reduce bending loss and effectively suppress the signal mode in the core area. By increasing the erbium ion concentration at the edge of the core, the gain of the high-order mode can be increased to achieve gain balance. The erbium ion doping concentrations corresponding to the inner core layer, the first outer core layer, and the second outer core layer are recorded as s1, s2, and s3, respectively, satisfying s3>s1>s2; taking 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 optical fiber 06 at 1530nm is 10dB / m to 45dB / m, and the length of the few-mode erbium-doped optical fiber 06 is 1 to 5m.

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

[0063] See also Figure 2 The front few-mode isolation pump combiner 04 includes a first ferrule 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 ferrule 16 and a first transparent tube 17; the signal input end 041 of the front few-mode isolation pump combiner is arranged adjacent to the input end of the first ferrule 11 through a few-mode optical fiber, the output end of the first ferrule 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 after passing through the first isolator 13 and the first thin film filter 14 in sequence, and the output end of the second self-focusing lens 15 is arranged adjacent to the input end of the second ferrule 16; the pump input end 021 of the front few-mode isolation pump combiner is input by a single-mode optical fiber, and the output end 042 of the front few-mode isolation pump combiner is output via a few-mode optical fiber, and the refractive index profile of the few-mode optical fiber matches that of the few-mode erbium-doped optical fiber 06. The first ferrule 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 ferrule 16 are all accommodated in the first transparent tube 17 .

[0064] The front few-mode isolation pump combiner 04 integrates the isolator in the device, which can reduce the insertion loss caused by too many devices. The entire combiner obtained has a high degree of integration. The tail fiber of the device is matched with the homemade few-mode erbium-doped optical fiber 06, thereby having good mode purity and low insertion loss. It can simultaneously realize the combination of pump light and signal light and prevent the light generated by amplified spontaneous radiation from interfering with the front-end device.

[0065] See also Figure 3 The post-positioned few-mode isolation pump combiner 05 comprises a third ferrule 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 ferrule 23 and a second transparent tube 24; the signal input end 051 of the post-positioned few-mode isolation pump combiner is arranged adjacent to the input end of the third ferrule 18 via a few-mode optical fiber, the output end of the third ferrule 18 is arranged adjacent to the input end of the third self-focusing lens 19, and the output end of the third self-focusing lens 19 is arranged adjacent to the input end of the third self-focusing lens 19 via the second thin film filter 20, the second isolator 2 1 is arranged adjacent to the input end of the fourth self-focusing lens 22, and the output end of the fourth self-focusing lens 22 is arranged adjacent to the input end of the fourth ferrule 23; the pump input end 031 of the rear few-mode isolation pump combiner is input by a single-mode optical fiber, and the output end 052 of the rear few-mode isolation pump combiner is output via the few-mode optical fiber; the third ferrule 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 ferrule 23 are all accommodated in the second transparent tube 24.

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

[0067] It should be noted that the few-mode erbium-doped fiber amplifier system provided by the present invention can simultaneously adopt the front few-mode isolation pump combiner and the rear few-mode isolation pump combiner with the above structure, or only use the front 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. Similarly, only use the rear 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] On the other hand, the present invention provides a control method for the above-mentioned few-mode erbium-doped fiber amplifier system, which mainly includes: using a signal generating module to output a multi-mode multi-wavelength signal light with a set initial power; preliminarily adjusting the front-end tunable component according to the total input power and the number of wavelength channels; using a first mode converter to convert multiple input single-mode signal lights into signal lights of multiple linear polarization modes 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 that have been amplified simultaneously; using a front-end spectrum detector to detect and obtain first spectrum information corresponding to multi-wavelength signal lights of different modes, using a mid-end photoelectric detector to detect and obtain input power information corresponding to the multi-wavelength signal light in each mode after passing through the first mode converter, and using a back-end spectrum detector to detect and obtain second spectrum information corresponding to the multi-wavelength signal light of different modes after demultiplexing through the second mode converter; feedback-adjusting the front-end tunable component according to the first spectrum information, the second spectrum information and the input power information to perform wavelength power compensation, so as to ensure that the input powers of each mode after compensation are consistent while making the multi-wavelength amplification gain flat.

[0069] Specifically, the present invention can utilize the front few-mode isolation pump combiner and the single-mode pump source in the pump combining assembly to realize forward core pumping, and utilize the rear few-mode isolation pump combiner and the pump adjustment assembly in the pump combining assembly to realize backward core pumping; and adjust the gain characteristics by online adjusting the pump mode and / or power of the pump adjustment assembly.

[0070] The second aspect of the present invention is further illustrated below with reference to specific devices and band selection.

[0071] See also Figure 1 The present invention provides a control method for a few-mode erbium-doped fiber amplifier system, comprising the following steps:

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

[0073] Step 2: The signal light of each wavelength channel is coupled via the wavelength coupling component 07 and then output through multiple channels for 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 spectrum detector 011, and the front-end tunable component 08 is preliminarily adjusted according to the total input power and the number of channels at different wavelengths.

[0075] Step 4: The multi-wavelength signal light in the C band under 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 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 component 03 is reversely coupled into the few-mode erbium-doped fiber 06 through the rear few-mode isolation pump combiner 05 to achieve backward core pumping. The pump mode is selected and the power is changed by adjusting the mode modulator in the pump adjustment component 03 to optimize the ratio of bidirectional pump power, so as to achieve precise gain control while reducing the inter-mode gain difference.

[0077] Step 6: Obtain spectral information based on the front-end spectral detector 011 and the back-end spectral detector 017, and then perform wavelength power compensation by controlling the front-end tunable component 08 through feedback adjustment according to the wavelength flatness difference of each mode, and use the mid-end photodetector 014 to ensure that the input power after compensation is consistent, thereby achieving balanced and adjustable multi-mode and multi-wavelength amplification.

[0078] Among them, in step 4, multi-wavelength signal light in different modes is input from the input end, and reaches the multiplexing end through the first ferrule 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 ferrule 16 in sequence; the pump light generated by the single-mode pump source 02 is input from the input end, and is reflected and collimated by the second self-focusing lens 15 and the first thin film filter 14 and output to the multiplexing port; the first self-focusing lens 12 and the second self-focusing lens 15 are used to collimate the output light from the input few-mode optical fiber, and refocus the collimated light into the output few-mode optical fiber; the first thin film filter 14 is used to simultaneously reflect the pump light and the transmission signal light; the first isolator 13 is placed forward to suppress the reflection of the signal light and the pump light; the combined light is transmitted through the output few-mode optical fiber and the refractive index profile matching of the few-mode erbium-doped optical fiber 06, thereby maintaining the excellent performance of the signal mode and having good mode purity.

[0079] In step 5, the pump light generated by the pump adjustment component 03 is input from the input end, reversely collimated by the third self-focusing lens 19 and the second thin-film filter 20 and output to the few-mode erbium-doped fiber 06; the amplified signal passes through the third ferrule 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 ferrule 23 in sequence 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 invention clearer, the present invention is further described in detail below in conjunction with specific embodiments.

[0081] Embodiment 1:

[0082] In the few-mode erbium-doped fiber amplifier system provided in Example 1, the first mode converter 012 and the second mode converter 015 are both photon lantern-type all-fiber devices, which can support LP 01 LP 11a and LP 11b Mode conversion and demultiplexing.

[0083] In Example 1, the light source laser 01 generates a multi-wavelength signal in the C band and sets the initial power. The signal light of each wavelength channel is coupled via the wavelength coupling component 07 and then output through multiple channels for multi-wavelength amplification. 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 spectrum detector 011. The first mode converter 012 converts the input multiple single-mode signal lights into LP 01 LP 11a and LP 11b The signal light of the three modes, the multi-wavelength signal light in the C band of the three 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 sent to the few-mode erbium-doped fiber 06 to achieve forward core pumping; the pump light generated by the pump adjustment component 03 is reversely coupled into the few-mode erbium-doped fiber 06 through the rear few-mode isolation pump combiner 05 to achieve backward core pumping. The amplified signal is demultiplexed by the rear few-mode isolation pump combiner 05 and the second mode converter 015 and output from the corresponding port, and then connected to the rear beam splitter component 016 and the rear spectrum detector 017 in sequence for detection.

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

[0085] When controlling the few-mode erbium-doped fiber amplifier system provided in Example 1, firstly, the length of the few-mode erbium-doped fiber 06 is optimized, and then the LP is performed by adjusting the mode modulator in the pump adjustment component 03. 11a or LP 11bThe selection of pump mode and the change of power size optimize the ratio of bidirectional pump power, which can achieve precise gain control while reducing the gain difference between modes. Since the front-end tunable component 08 is connected to the front-end spectrum detector 011, the middle-end photodetector 014 and the back-end spectrum detector 017, the wavelength flatness difference of each mode can be obtained according to the detection results of the above detectors (the front-end spectrum detector 011 and the back-end spectrum detector 017), and then the front-end tunable component 08 can be controlled by feedback adjustment to perform wavelength power compensation according to the wavelength flatness difference of each mode, and the middle-end photodetector 014 is used to ensure that the input power after compensation is consistent, thereby achieving balanced and adjustable multi-wavelength amplification of three modes.

[0086] Embodiment 2:

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

[0088] In embodiment 2, the first mode converter 012 converts the input multiple single-mode signal lights into LP 01 LP 11a LP 11b LP 21a The signal light of the mode is then amplified and demultiplexed. The pump wavelength of the single-mode pump source 02 in Example 2 is 980nm, the pump source wavelength in the pump adjustment component 03 is 980nm, and the mode modulator is an online mode conversion module based on a digital micromirror device to perform LP 11a or LP 21a Mode selection and power level change.

[0089] When controlling the few-mode erbium-doped fiber amplifier system provided in Example 2, the difference from Example 1 is that the LP is performed by adjusting the mode modulator in the pump adjustment component 03. 11a or LP 21a By selecting the pump mode and changing the power, the ratio of bidirectional pump power is optimized, and finally balanced and adjustable multi-wavelength amplification of five modes is achieved.

[0090] Embodiment 3:

[0091] The few-mode erbium-doped fiber amplification system provided in Example 3 has the same specific structure as that in Example 1, except that the first mode converter 012 and the second mode converter 015 in Example 3 are fused-tapered all-fiber devices, which can support LP 01 LP 11 and LP 21 Mode conversion and demultiplexing.

[0092] In embodiment 3, the first mode converter 012 converts the input multiple single-mode signal lights into LP 01 LP 11 and LP 21 The signal light of the mode is then amplified and demultiplexed. The pump wavelength of the single-mode pump source 02 in Example 3 is 980nm, the pump source wavelength in the pump adjustment component 03 is 980nm, and the mode modulator is an online mode conversion module based on a spatial light modulator to perform LP 21 Mode selection and power level change.

[0093] When controlling the few-mode erbium-doped fiber amplifier system provided in Example 3, the difference from Example 1 is that the LP is performed by adjusting the mode modulator in the pump adjustment component 03. 21 The selection of pump modes and the change of power size optimize the ratio of bidirectional pump powers, and ultimately achieve balanced and adjustable multi-wavelength amplification of three modes.

[0094] The experimental amplification results of the few-mode erbium-doped fiber amplifier system provided in Example 3 are as follows: Figures 4 to 7 As shown, Figure 4 The total input power is -15dBm, the total pump power is 650mW, and the three modes (LP 01 LP 11 and LP 21 ) amplifies the gain characteristics of the 8-wavelength channel. Figure 5 The figure shows the gain characteristics of 8 wavelength channels amplified by three modes with a total input power of -15dBm and a total pump power of 650mW at a fiber length of 2m. Figure 6 The figure shows the gain characteristics of three modes amplifying 8 wavelength channels with a total input power of -12dBm, a total pump power of 650mW and a fiber length of 2m. Figure 7 The figure shows the gain characteristics of three modes amplifying 8 wavelength channels with a total input power of -15dBm and a total pump power of 570mW at a fiber length of 2m. Figure 4 and Figure 5 The variable is the fiber length. By comparison, we can know that the mode gain difference and gain flatness of the system can be further reduced by optimizing the appropriate fiber length. Figure 5 and Figure 6 The variable is the total input power. By comparison, we can see that as the input power decreases, the gain of each mode will increase. Figure 5 and Figure 7 The variable is the total pump power. By comparison, it can be seen that by optimizing the pump power, multi-wavelength amplification in multi-mode can further achieve more ideal gain balance.

[0095] Based on Example 3, the following is a verification of the multi-mode multi-wavelength balanced tunable performance of the system in combination with parameters.

[0096] The light source laser 01 generates a multi-wavelength signal between 1530 and 1565 nm in the C band, sets the wavelength channel to 8, 16 or 32, and sets the initial power. For example, the total signal input power of all wavelength channels in each mode is set to -15 dBm, the length of the few-mode erbium-doped fiber 06 used is 2 m, the number of wavelength channels is 8, the forward pump power is adjusted to 400 mW, and the phase diagram of the corresponding mode is loaded on the spatial light modulator module in the pump adjustment component 03 to excite the high-order mode LP 21 , adjusting the phase diagram of the pump source and the loading, 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 power ratio of the backward pump mode, the average gain obtained by the three-mode signal for 8-wavelength channel amplification is increased to 25.24dB, the maximum modal gain difference and the maximum gain flatness reach the ideal level, and the gain balance in multi-mode multi-wavelength amplification can be achieved. Table 1 shows the amplification results when the total pump power is 490mW, 570mW and 650mW.

[0097] Table 1 Amplification results data

[0098]

[0099] It can be seen that the present invention can achieve gain balance in multi-mode multi-wavelength amplification, which is of great significance for promoting the simultaneous multi-wavelength transmission of long-distance MDM systems.

[0100] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A few-mode erbium-doped fiber amplifier system, characterized in that: include: A signal generating module, a front-end tunable component, a front-end spectrum detection component, a first mode converter, a mid-end power detection component, a pump amplifier unit, a second mode converter and a back-end spectrum detection component; The front-end spectrum detection component includes a front-end beam splitter component and a front-end spectrum detector, the mid-end power detection component includes a mid-end beam splitter and a mid-end photoelectric detector, the pump amplification unit includes a pump beam combining component and a few-mode erbium-doped optical fiber, and the back-end spectrum detection component includes a back-end beam splitter component and a back-end spectrum detector; The signal generating module, the front-end tunable component, and the front-end beam splitter component are connected in sequence, and the output end of the front-end beam splitter component is respectively connected to the first mode converter and the front-end spectrum detector; the output end of the first mode converter is connected to the input end of the middle-end beam splitter; the output end of the middle-end beam splitter is respectively connected to the pump amplifier unit and the middle-end photodetector; the pump amplifier unit is connected to 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 connected in sequence; the front-end tunable component is respectively connected to the front-end spectrum detector, the middle-end photodetector, and the rear-end spectrum detector; The signal generating module is used to output multi-mode multi-wavelength signal light; the first mode converter has a plurality of single-mode input ports, and the first mode converter is used to convert the input multiple single-mode signal lights into signal lights of multiple linear polarization modes supported by the few-mode erbium-doped optical fiber; the pump beam combining component is used to amplify the signal light; The second mode converter is used to demultiplex the multiple mode signal lights that are amplified simultaneously, and output them from multiple single-mode ports of the second mode converter; The front-end spectrum detector is used to detect and obtain first spectrum information corresponding to multi-wavelength signal lights of different modes, the mid-end photoelectric detector is used to detect and obtain input power information corresponding to the multi-wavelength signal lights in each mode after passing through the first mode converter, and the back-end spectrum detector is used to detect and obtain second spectrum information corresponding to the multi-wavelength signal lights of different modes after demultiplexing through the second mode converter; the front-end tunable component is used to perform wavelength power compensation according to the first spectrum information, the second spectrum information and the input power information, so as to make the multi-wavelength amplification gain flat while ensuring that the input powers of each mode after compensation are consistent.

2. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: The signal generating module comprises a light source laser and a wavelength coupling component; the light source laser is used to generate signal light of multiple wavelength channels; the wavelength coupling component is used to mix the signal light of multiple wavelength channels and output the mixed multi-wavelength signal light through multiple mode channels.

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

4. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: The pump beam combining component comprises a front few-mode isolation pump beam combiner, a single-mode pump source, a rear few-mode isolation pump beam combiner and a pump adjustment component; One end output of the mid-end beam splitter is connected to the signal input end of the front few-mode isolation pump combiner, the single-mode pump source is connected to the pump input end of the front few-mode isolation pump combiner, the output end of the front few-mode isolation pump combiner is connected to one side port of the few-mode erbium-doped fiber, the other side port of the few-mode erbium-doped fiber is connected to the input end of the rear few-mode isolation pump combiner, the pump adjustment component is connected to the pump input end of the rear few-mode isolation pump combiner, and the amplified output end of the rear few-mode isolation pump combiner is connected to the 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 few-mode isolation pump combiner and then sent into the few-mode erbium-doped optical fiber to realize forward core pumping; the pump light generated by the pump adjustment component is reversely coupled into the few-mode erbium-doped optical fiber through the rear few-mode isolation pump combiner to realize backward core pumping.

5. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: Also includes: Polarization controller assembly; The front-end tunable component, the polarization controller component, the front-end beam splitter component and the front-end spectral detector are cascaded in each mode channel; The polarization controller component is used to ensure the purity of different polarization mode inputs and to regulate the crosstalk of the few-mode erbium-doped fiber amplifier system.

6. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: The few-mode erbium-doped optical fiber includes, from the inside to the outside, an inner core layer, a first outer core layer, a second outer core layer and a cladding; the erbium ion doping concentrations corresponding to 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; taking 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 according to claim 6, characterized in that: The absorption coefficient of the few-mode erbium-doped optical fiber at 1530 nm is 10 dB / m to 45 dB / m, and the length of the few-mode erbium-doped optical fiber is 1 to 5 m.

8. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: The first mode converter and the second mode converter are both a plurality of cascaded all-fiber mode selective conversion devices.

9. The few-mode erbium-doped fiber amplifier system according to claim 4, characterized in that: The front few-mode isolation pump combiner includes 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 isolation pump combiner is arranged adjacent to the input end of the first ferrule through the few-mode optical 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 after passing 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 isolation pump combiner is input by a single-mode optical fiber, and the output end of the front few-mode isolation pump combiner is output via the few-mode optical fiber, and the refractive index profile of the few-mode optical fiber matches the refractive index profile of the few-mode erbium-doped optical 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; The post-positioned few-mode isolation pump combiner includes 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 post-positioned few-mode isolation pump combiner is arranged adjacent to the input end of the third ferrule via the few-mode optical 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 after sequentially passing through the second thin film filter and the second isolator, 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 post-positioned few-mode isolation pump combiner is input by a single-mode optical fiber, and the amplified output end of the post-positioned few-mode isolation pump combiner is output via the few-mode optical 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.

10. A control method for a few-mode erbium-doped fiber amplifier system according to any one of claims 1 to 9, characterized in that: include: Outputting multi-mode multi-wavelength signal light with a set initial power using a signal generation module; According to the total input power and the number of wavelength channels, the front-end tunable component is preliminarily adjusted; the input multiple single-mode signal lights are converted into multiple linear polarization mode signal lights supported in the few-mode erbium-doped optical fiber by using the first mode converter; the signal light is amplified by using the pump beam combining component; Demultiplexing the multiple mode signal lights that have been amplified simultaneously using a second mode converter; A front-end spectrum detector is used to detect and obtain first spectrum information corresponding to multi-wavelength signal lights of different modes, a mid-end photoelectric detector is used to detect and obtain input power information corresponding to the multi-wavelength signal lights in each mode after passing through the first mode converter, and a back-end spectrum detector is used to detect and obtain second spectrum information corresponding to the multi-wavelength signal lights of different modes after demultiplexing by the second mode converter; feedback adjustment is performed on the front-end tunable component according to the first spectrum information, the second spectrum information and the input power information to perform wavelength power compensation, thereby ensuring that the input powers of each mode after compensation are consistent while making the multi-wavelength amplification gain flat.

11. The control method of the few-mode erbium-doped fiber amplifier system according to claim 10, characterized in that: The forward core pumping is realized by using the front few-mode isolation pump combiner and the single-mode pump source in the pump combining assembly, and the backward core pumping is realized by using the rear few-mode isolation pump combiner and the pump adjustment assembly in the pump combining assembly; the gain characteristic is adjusted by online adjusting the pump mode and / or power of the pump adjustment assembly.

Images