High-Performance 2 × 2 Bent Directional Couplers Designed With an Efficient Semi-Inverse Design Method

Directional couplers (DCs) are the basic elements for constructing various silicon photonic devices, including Mach–Zehnder switches (MZSs). Here, we propose a novel 2 × 2 bent directional couplers based on Bézier curves designed with an efficient semi-inverse design method. Two DCs were designed to operate at center wavelengths of 1.55 μm and 2 μm, with splitting ratios maintained between 45 to 55% over broad bandwidths of 130 nm and 160 nm respectively, and excess losses <0.05 dB. The present 1.55/2 μm DCs also have ultra-compact footprints of 16 × 1.8/24 × 2.5 μm ² , which are much smaller than conventional DCs. The fabricated DCs show good fabrication tolerance of ±10 nm waveguide width deviation. The present bent DCs are then used for realizing thermo-optic MZSs for the 1.55/2 μm wavelength-bands, which show a bandwidth of >90 nm for achieving low excess losses of <0.3 dB and high extinction ratios of ∼18/20 dB.