Inverse Design of a 2×2 Coupler

Density-based topology-optimization can be used to design photonic components that are more compact and broadband than their traditionally designed counterparts. In this paper, a 90° 2×2 coupler is designed using MIT's Electromagnetic Equation Propagation software's adjoint variable method. The design was optimized over the wavelengths 1500–1600 nm in a 4 × 4 µm. design region. The final design meets the design rule constraints of minimum linewidth and line spacing for a standard electron beam lithography process. It also has an insertion loss of less than 0.085dB for all wavelengths and a port imbalance of less than 1%.