Mode Coupling Effects in Ring Core Fibers for Space Division Multiplexing Systems
An optical fiber with weak mode coupling is desirable for future ultrahigh capacity space division multiplexing (SDM) systems because mode coupling in an optical fiber results in extrinsic loss of the fiber and crosstalk between guided optical modes. To study the feasibility of a ring core fiber (RCF) for SDM systems, in this paper, we investigate the mode coupling in the RCF supporting five or seven guided mode groups (MGs) at a wavelength of 1550 nm. For this purpose, the coupled mode/power theory with identified spatial power spectrum of random perturbations of fiber axis is used to estimate the bend loss/crosstalk of the RCF due to microbending. It is shown that based on the identified parameters for the spatial power spectrum in the 5/7 MG RCF, the estimated bend loss/crosstalk of the RCF agrees well with experimental results. In addition, the impact of the gradient parameter a and refractive index contrast D of the fiber refractive index profile on bend loss and crosstalk of the RCF is explored. Simulation results indicate that the D instead of the a significantly affects bend loss and crosstalk of the RCF. The magnitude improvement in bend loss by increasing the D is dependent on the spatial power spectrum.
Journal of Lightwave Technology