Novel integrated metalens – grating coupler input/output workflow for photonic integrated circuits

Designing a fiber-to-waveguide coupler can be difficult due to this system’s high sensitivity to misalignment as well as mode mismatch. It has been shown that the integration of a microlens into a fiber-to-grating coupler (GC) system design can result in a significant improvement in the alignment tolerancing between the fiber and the grating. In this article, we introduce an alternative solution where the microlens element is replaced by a metalens. Metalenses are advantageous for their potential to manipulate the phase, amplitude and polarization of light incident upon them to perform various optical functions within a single flat element. They are very thin, compact and lightweight, which can be more advantageous compared to the conventional curved-surface microlens in fiber-waveguide coupling and makes metalenses versatile for many applications. In this workflow, a database of meta-atom responses is generated using Rigorous Coupled-Wave Analysis (RCWA) and is combined with a target phase optimized in the overall system to generate the metalens layout. Our multiscale workflow provides an effective integration of the metalens element into the optical system using an efficient combination of ray tracing and wave optics propagation methods. The validity of the simulation is confirmed by comparing the results with a full-lens simulation performed with the Finite-Difference-Time-Domain (FDTD) method. The coupling efficiency and losses of this design are computed, in both directions (fiber to grating, and grating to fiber), and directly compared to those of the microlens-integrated GC design. The tolerance of the system to shifts in fiber position is also assessed. Overall, this work paves the way to exploiting the powerful functionalities of metalenses in photonic systems, reaching beyond the capabilities of a conventional microlens.