CMOS-compatible ultra-compact silicon multimode waveguide bend based on inverse design method

Waveguide bend is one of the indispensable fundamental devices in building various integrated optical circuits. It is commonly used so that its footprints would affect the compactness of the whole circuit. However, in mode-division multiplexing systems, the radii of multimode waveguide bends are typically large ( ∼ the order of 10 micrometers), which would limit the high-density integration of on-chip multimode devices. We designed a CMOS-compatible ultra-compact multimode waveguide bend based on the inverse design approach. The device ensures 90-degree high-performance transmission of TE 0 , TE 1 , and TE 2 modes simultaneously with the footprint of 5 . 1 μ m × 5 . 1 μ m in an equivalent bend radius of 4 . 4 μ m . Simulation results show that the insertion loss of the device is 0.045 dB, 0.062 dB, and 0.056 dB for TE 0 , TE 1 , and TE 2 modes at 1550 nm, respectively, and the inter-modes crosstalk is lower than – 21.8 dB.