Compact, low-loss, and broadband 2 × 2 Si optical coupler designed by covariance matrix adaptation evolution strategy

Abstract We experimentally demonstrate compact, low-loss, and broadband 2 × 2 Si optical couplers on a Si photonic platform designed using the covariance matrix adaptation evolution strategy (CMA-ES). The measured minimum insertion losses (ILs) in the C-band were 0.071 dB, 0.016 dB, 0.016 dB, and 45%–55% optical bandwidth were 140 nm, 136 nm, and 139 nm for device lengths of 7.56 μ m, 9.64 μ m, and 12.32 μ m, respectively. The ILs are smaller than ever reported in 2 × 2 optical couplers shorter than 10 μ m, and the optical bandwidths are much larger than a conventional directional coupler. The results validate the effectiveness of the proposed CMA-ES-based design method, extending the scope of application of our design method to the design of passive devices on Si photonics platform.