On-Chip High Extinction Ratio Single-Stage Mach-Zehnder Interferometer Based on Multimode Interferometer

On-chip high extinction ratio Mach-Zehnder interferometers (MZI) have always attracted interest from researchers as it can be used in many applications including astrophotonics, optical switching, programmable photonic circuit, and quantum information. However, previous research studies, ultra-high on-chip MZIs only been achieved by using a multi-stage MZI approach. In this paper, we investigate single-stage based on two cascaded multimode (MMI). We determine that TM noise is an important factor prevent us achieving MZI. By introducing bend-based filter without additional loss, experimentally demonstrate such improve the maximum of MMI-MZI more than 10 dB. With filter, report record 61.2 dB single stage, thermally tunable with 1.5 insertion loss 60 nm bandwidth. These results pave way for interesting applications.