Variable-Ratio Mode-Insensitive 1 x 2 Power Splitter Based on MMI Couplers and Phase Shifters

Mode-division multiplexing (MDM) has been considered as a low-cost and high-density means for high-bandwidth on-chip optical communications in a high-performance computer and a data center. However, simultaneously controlling the power of multiple modes in the MDM systems is difficult due to the complex mode coupling for high-order modes (HOMs). Here we propose a novel schematic structure of variable-ratio mode-insensitive 1 x 2 power splitter, which is based on multimode interference (MMI) couplers cascaded with phase shifters. We theoretically reveal the phase shifting relations between the fundamental mode and the HOMs for the phase shifter formed by two unequal-width waveguides. Then, the operating principles for the proposed structure are presented. Numerical simulations are carried out and it is found that the structure has the ability to realize variable-ratio dual-mode mode-insensitive 1 x 2 power splitter by designing the number and lengths of the phase shifters, which shows a good agreement with our theoretical analysis. The structural parameters of the MMI couplers and the phase shifters are optimized to minimize the transmittance losses and the differences of mode power splitting ratio. The simulation results also show that the optimized power splitters have the advantages of high tolerance to fabrication errors and wide operating bandwidths, which indicates that the proposed structure can operate on multiple modes and would be suited to potential applications in on chip optical communications.