| With the rapid development of Internet and its “bandwidth consumption” type business(such as large data centers, the Internet of things, the high-definition video, multi-media real-time business, etc.), the demand of the network bandwidth is increasing with nearly 60% year by year, and the capacity is increasing from 100Mb/s to 100Tb/s rapidly. In the future, with the development of the intelligent society, which is led by the “big data”, the demand of the optical network bandwidth will be much more than ever before. In response to the rapid growth of network bandwidth, researchers are committed to the research of optical network technology. At present, the technologies to increase the capacity include electric field time-division multiplexing(ETDM), wavelength division multiplexing(WDM), code division multiplexing(CDM), polarization division multiplexing(PDM), orthogonal frequency division multiplexing(OFDM), and high-dimension higher-order modulation technology, etc. However, the technologies mentioned above are all based on single mode fiber(SMF) transmission medium to realize the increase of optical network capacity. And the nonlinear effects in single mode fiber and the amplified spontaneous emission(ASE) noise, the transmission capacity is reaching its limits. In this context, mode division multiplexing(MDM) technology has aroused people’s wide concern. The MDM technology is applying the several robust finite orthogonal modes in few-mode fiber(FMF) as transmission channels, so that the transmission capacity can be improved manyfold. In this paper, we have researched the MDM technology deeply. And we have illustrated the key technologies in MDM system. Also we put forward the novel MDM technology, which is the MDM technology based on few-mode fiber Bragg grating(FBG) and optical circulator. We have established the two-input two-output MDM system, and achieved the back-to-back and 10 km transmission of different bite rate pseudo random bit sequence(PRBS) signals. The main work is as follows:Firstly, based on the theory of Maxwell, the mode in few-mode fiber is discussed in detail. Then the electric field distribution of the mode in two-mode fiber is simulated. Then the key technologies of the mode division multiplexing transmission are illustrated in detail. The technologies to realize the mode division multiplexing / de-multiplexing are analyzed emphatically.Secondly, the coupled-mode theory of few-mode FBG is analyzed, and the phase-matching condition(Bragg condition) is analyzed in detail. Then the principle of mode division multiplexing/de-multiplexing based on few-mode FBG has been illustrated. Then, the optical field distribution at the output end of the few-mode fiber is analyzed under different core-offset splicing distance to determine the core-offset splicing distance of the LP11 mode effective excitation.In addition, through the phase-mask technology, the few-mode FBG is fabricated, and the optical circulator is fabricated specially. Then the MUX/DEMUX based on few-mode FBG is prepared. And the performance of our MUX/DEMUX is tested experimentally, and the insertion loss is given.Finally, the transmission experiment of the mode division multiplexing/demultiplexing system based on the few-mode FBG is carried out. The 1.25Gb/s and 622Mb/s, 1.25Gb/s and 10 Gb/s, 4.25Gb/s and 10 Gb/s, and two channels of 10Gb/s PRBS signals in back-to-back transmission and 10 km transmission have achieved, respectively. And then the BER performance of 10Gb/s transmission system has been analyzed.At the end of the paper, we have summarized the main work of the paper. The MDM technology based on few-mode FBG has been evaluated, and then analyzed the existing problems. At last, we look forward to the development of MDM technology based on few-mode fiber. |
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