A Compact Mode Controller (Switch) Using an Inverse-Designed 2-Mode Y-Junction

As photonic circuits become more densely packed, designing smaller devices without sacrificing their performance is essential. This work demonstrates an optical mode controller architecture using a 2-mode y-junction. The junction is inverse designed to generate a compact and efficient device with only 3 μm in length. The device splits the incoming light transverse electric fundamental (TE0) and first order (TE1) modes into TE0 modes with symmetric or anti-symmetric phases at its output waveguides, respectively. The y-junction is then used as the input and output couplers in a Mach-Zehnder Interferometer (MZI) with a multimode output waveguide. Using a thermo-electric phase shifter, efficient mixing and conversion between the TE0 and TE1 modes are achieved at the output of the MZI to any arbitrary level. When the MZI is operated as a switch, the system's high performance is shown in terms of insertion loss as low 0.64 dB and TE0 mode fraction of-0.03 dB at 1550 nm, or loss of 0.84 dB and mode fraction of-0.17 dB measured across the C-Band, which corresponds to crosstalk <16.9 dB. The proposed mode conversion process offers the possibility for the system to work in high-speed applications.