Basic Characteristic Analysis And Application Research On All-fiber Orbital Angular Momentum(oam)mode Couplers

In recent years,with the rapid development of technologies such as the Internet,5G,VR,cloud computing and big data,human demand for optical communication capacity has increased exponentially.However,fiber-optic communication systems based on singlemode fiber have gradually reached the Shannon capacity limit.To further maintain the rapid growth of fiber-optic communication capacity and address the new round capacity crunch,an effective way is to develop new dimensions of lightwaves,e.g.spatial dimension.Orbital angular momentum(OAM)mode multiplexing technology,one of the technologies fully exploiting the spatial dimension of lightwaves,in principle,can realize infinite order OAM mode multiplexing because of the orthogonality of OAM modes carrying different topological charges,showing great potential of applications and high value of research.Previously,there have been many studies and experiments on free-space OAM mode multiplexing communications.However,in order to connect with the existing fiber-optic communication systems and realize ultra-long-distance and ultra-high-capacity optical fiber transmission,various all-fiber functional devices,such as OAM mode generator,mode splitter,wavelength-division multiplexer,mode multiplexer and demultiplexer,are of great importance.The main work of this dissertation is to comprehensively study the theory,simulation and manufacturing technique of all-fiber OAM mode couplers,fabricate a series of all-fiber OAM mode couplers with different functions,and carry out experimental demonstration on their applications in fiber-optic communications.The major contents of this dissertation are summarized as follows:(1)The basic theory of all-fiber OAM mode coupler is analyzed with its feasibility verified by simulations.Two methods for fabricating OAM mode couplers,i.e.fused-taper method and D-shaped fiber coupling method,are studied in depth.A packaging technique is proposed to improve the stability and environmental tolerance of the fabricated couplers.(2)Various all-fiber OAM mode couplers with different functionalties are designed and fabricated,including high-purity different-order all-fiber OAM mode generators,90:10and 50:50 OAM mode splitters,1550/980 nm and 1550/1455 nm OAM wavelength-division multiplexers,and OAM mode(de)multiplexer.(3)The two OAM mode multiplexing communiation sytem through a 150-km ringcore fiber(RCF),each carrying a 20-Gbit/s quadrature phase-shift keying(QPSK)signal,is demonstrated in the experiment.Meanwhile,the applications of all-fiber OAM mode couplers in other communication experiments are also explored,such as heterogeneous optical networks incorporating OAM mode multiplexing communication systems based on ultra-low-loss single-mode fiber(SMF)and low-loss RCF,all-fiber full-duplex bidirectional OAM mode multiplexing data communications for data centers,and 110-km OAM mode multiplexing communications based on distributed Raman amplification.