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 (TE ₀ ) and first order (TE ₁ ) modes into TE ₀ 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 TE ₀ and TE ₁ 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 TE ₀ 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.