Investigation of channel spacing for Hermite-Gaussian mode division multiplexing in multimode fiber

Mode division multiplexing (MDM) may be used to increase the capacity of multimode fiber interconnects for data centers. This paper demonstrates the importance of controlling the channel spacing of a MDM system capitalizing on Hermite-Gaussian (HG) modes in order to mitigate modal dispersion and minimize the average system bit-error rate. The effect of channel spacing of a 25-channel hybrid MDM-wavelength division multiplexing (WDM) system was examined through the x-index and y-index separations of Hermite polynomials of HG modes for different MMF lengths. Simulations prove that by controlling the index separations of the Hermite polynomials, acceptable BER was achieved for 25Gb/s data transmission for a distance of 800 meters for a 25-channel HG-based MDM-WDM system at a center wavelength of 1550.12nm. The optimal x-index and y-index Hermite polynomial separations for the HG modes are 2, 3 and 4.