Triple Coupled Ring‐Core Fiber with Dual Highly Dispersive Windows for Orbital Angular Momentum Mode

Abstract

With the exponential growth of the carrying information in optical communication systems, tremendous efforts have been made to further boost the channel capacity and spectral efficiency. Multiplexing is one of the most efficient methods, which contains optical time-division multiplexing (OTDM), [1][2][3] wavelength division multiplexing (WDM), [4][5][6] and space-division multiplexing (SDM) techniques. [7][8][9] SDM simultaneously transmits multiple independent data channels in multicore or multimode fiber. Particularly, if the channels are orthogonal to each other, the different beams can be efficiently (de-)multiplexed and propagate with little inherent crosstalk, which could tremendously improve the information transmission capacity. [10] L. Allen et al. reported that helically phased beams featured by an azimuthal phase term exp(ilφ) carry an orbital angular momentum (OAM) of lℏ per photon, where l is the topological charge, φ represents the azimuthal angle, and ℏ denotes the Plank's constant h divided by 2п. [11] OAM theoretically has an infinite quantity of intrinsic orthogonality modes with varied topological charges, thus having the potential to provide a great amount of independent channels for the SDM system. [12][13][14][15][16] The phase front of beams carrying OAM modes twists along the transmission path, which leads to an annular intensity distribution. It has attracted extensive attention for various applications in optical tweezers, [17,18] sensing, [19,20] and communications in the classical [21,22] and quantum regimes. [23] Research into OAM multiplexing for communication originated from free-space communication systems. [24,25] However, the interferences from ambient microparticles