Spatial Division Multiplexing (SDM) for optical fiber transmission is useful for overcoming the capacity limit of wavelength division multiplexing. SDM increases the spectral efficiency per fiber by multiplexing the signals in orthogonal LP modes in few mode fibers (FMF) and multi-core fibers. In SDM systems, the mode multiplexer/demultiplexer (MUX/DEMUX) is a key component because it equalizes the mode-dependent loss, compensates for differential mode delays, and is used to construct transceivers. Different types of mode MUX/DEMUX have been proposed in recent years. RSoft BeamPROP is a great tool to model and design mode MUX/DEMUX.

This note will introduce the simulations for two proposed mode MUX/DEMUX structures for FMF. The first structure is a compact mode multiplexer using a 3D silicon-rich silica waveguide on a silicon chip, based on a paper by Hiraki et al.1 It can demultiplex three modes with an approximate 0.6mm^2 chip area. The second structure is a PLC-based asymmetric parallel waveguide to realize the mode conversion function by matching the effective indices of the LP01 and LP11 modes, based on a paper by Hanzawa et al.2

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