Optimization of a metalens-based fiber-to-chip coupler for efficient and broadband coupling

Broadband and efficient vertical coupling remains a major challenge in silicon photonics. Conventional grating couplers enable efficient fiber-to-chip coupling but offer a limited bandwidth of around 30 nm, which restricts their use in applications such as wavelength-division multiplexing. In this work, we propose a new fiber-to-chip coupling architecture based on a standard silicon-on-insulator (SOI) platform, composed of a 45° planar reflector and a metalens. We optimized the coupler to operate around 1550 nm. Finite-difference time-domain (FDTD) simulations demonstrate a maximum coupling efficiency of -0.73 dB and a 1 dB bandwidth of 300 nm. An alternative optimization strategy increases the bandwidth to 430 nm, at the expense of a slightly lower maximum coupling efficiency of –0.88 dB.