Design And Application Of Ring Photonic Crystal Fiber Based On Orbital Angular Momentum

Orbital angular momentum?OAM?is carried by a beam with a spiral phase.OAM has an infinite number of orthogonal base theoretically,which can be fully used for modulation or multiplexing to enhance the capacity of optical communication greatly.OAM can be regarded as a new degree of freedom for multiplexing,similar to amplitude,phase,wavelength and polarization.At present,the OAM multiplexing technology has been applied in the fields of free-space optical communication,radio communication and optical fiber communication.In the field of optical fiber communication,the OAM modes will lead to near-degeneracy in traditional optical fiber,so the study of optical fiber which can support as many as OAM modes is of great importance.To improve the transmission capacity of optical fiber,we propose a new circular photonic crystal fiber?C-PCF?by using the finite element simulation software COMOSL,based on previous related researches.The structure possesses a ring material inlaid in the inner ring and one more air hole rings cladding,with the purpose of reducing mode couple and increasing the number of OAM modes.The achievements of this thesis are as follows:Firstly,the stability of OAM modes in optical fiber is analyzed theoretically,and the results show that the effective index differences between eigenmodes should maintain above 10^-4 to ensure good separation between eigenmodes.The propagation characteristics of OAM modes in the optical fiber,such as intensity distributions,effective refractive index difference,waveguide dispersion,nonlinear coefficient and confinement loss are studied by finite element method,and the results show that:the fiber can well support OAM modes up to 110 in C and L communication band,and the topological charge is from 1 to 28.Also,most of the effective index differences are at the order of 10^-3,which proved that these 110 OAM modes can be transmitted stably in C-PCF.Besides,for most modes the dispersions variation are within 32/?9?8)?6)8)),the nonlinear coefficients are within 2.88)^2-1,and the confinement losses are between the order of 10^-11 and 10^-7 over a 100 nm bandwidth from 1.52 to 1.62?m.Finally,the performances of the fiber are compared with the photonic crystal fiber in the references.The C-PCF can support as many as 110 OAM modes,and the stability of OAM modes is better.Besides,the fiber is applied to the forward pumped erbium-doped fiber amplifier?EDFA?,and the amplification characteristics of optical signal are studied.Using the fiber amplifier Giles model and MATLAB programming,the numerical analysis has been done and shows that the EDFA can achieve 110 OAM mode gains,which is higher than 19.5dB,and the noise coefficients are lower than 6.5dB.In this paper,the OAM modes photonic crystal fiber is proposed,which can support110 OAM modes,and can improve the transmission capacity of OAM modes division multiplexing optical fiber communication system to some extent.The fiber can provide reference for the future study of OAM modes fiber.