High-Performance 2 × 2 Bent Directional Couplers Designed With an Efficient Semi-Inverse Design Method
Laiwen Yu, Jingshu Guo, Hengtai Xiang, Chaoyue Liu, Yuqi Zhao, Daoxin Dai
Abstract
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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 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.