Impact of indirect mode coupling on planar lightwave circuit based mode converters/multiplexers

To improve fiber transmission capacity, space division multiplexing has been proposed and demonstrated, in which mode division multiplexing (MDM) is one option. To implement MDM transmission, mode converters/multiplexers are essential, which can be designed using planar lightwave circuits (PLC). In this work, we propose indirect mode coupling for design of mode converters/multiplexers to improve the performance. It is found that the performance of conversion efficiency, extinction ratio, and crosstalk can be significantly improved by using indirect mode coupling.