Performance Analysis of a Broadband Second-Order Mode Converter Based on Multimode Interference Coupler and Phase Shifter

A novel mode converter with broad bandwidth, high mode conversion efficiency, and large fabrication tolerance is proposed and fabricated on a silicon-on-insulator (SOI) platform. By using a modified 3 × 3 multimode interference coupler and an enlarged butterfly-shaped phase shifter, mode conversion from the fundamental mode (TE₀) to second-order mode (TE₂) is achieved numerically and experimentally. Performance analysis of the mode converter is carried out numerically, and the results show high performance of the mode converter with mode conversion efficiency larger than 91% (i.e., insertion loss less than 0.40 dB) in the whole C-band. In addition, the mode converter has large fabrication tolerance. For example, the width and the length deviations of the multimode interference coupler can be as large as 50 and 250 nm, respectively, whereas the width and the length deviations of the phase shifter can be up to 25 and 400 nm, respectively.