Silicon Non-Blocking Four-Mode Exchanger Assisted by Mode-Selective Phase Shifter for 2-μm Waveband

Silicon photonics in the 2-μm waveband is gaining much attention due to the emergence of GeSn lasers [1]. In particular, high-bandwidth communications using mode-division multiplexing (MDM) is one of the likely candidates for the next-generation on-chip interconnects. As for MDM devices, multimode optical switch is the hot research topic regardless of the target waveband. Non-blocking mode exchanger (NME), which is a type of multimode switch, can arbitrarily reorder the guided modes [2]. As an example of configuration, an NME with mode multiplexers and single-mode (SM) 2 × 2 switches is proposed in [2]. However, the mode multiplexers and 2 × 2 3-dB couplers are cascaded in multiple stages, and the degradation accumulates at each stage. This results in the mode crosstalk as the number of mode increases. In this report, we propose a novel configuration of four-mode NME (4M-NME) that excludes mode multiplexers and reduces the number of 2 × 2 3-dB couplers.