Inverse Design of Functionalized Photonic Patches for On-Chip Imaging and Spectroscopy

In this talk, we present our work on the inverse design and experimental characterization of compact functionalized photonic structures, called “photonic patches”, using adjoint optimization coupled with the rigorous two-dimensional generalized Mie theory (2D-GMT) and validated by three-dimensional finite elements simulations. In particular, we demonstrate compact (10µm×10µm) silicon and silicon nitride structures that steer four different wavelengths into four predefined far-field directions with efficiencies close to 60%. Moreover, we inverse design structures for the compact spectrometers with nanometer-level spectral resolution. In addition, we demonstrate novel photonic patch geometries for near-field focusing at multiple focal lengths, achieving focusing efficiencies that exceed 70%. We also present our results on achromatic focusing devices with optimal aperiodic geometries and enhanced local density of states (LDOS) at predefined spatial and spectral locations. We show that our devices support localized optical modes with two-orders of magnitude enhancement of the Purcell factor for both TE and TM polarizations, enabling the fabrication of active photonic devices with ultracompact footprints. The performances of the fabricated devices are characterized experimentally using light emission spectroscopy and spectroscopic ellipsometry from the visible to the infrared spectral range. Leveraging on the rigorous mesh-free solution of the multiple scattering problem of dielectric cylinders, our approach provides an efficient and accurate inverse design methodology for the realization of novel aperiodic structures with optimal functionalities for nonlinear photonics, miniaturized light sources, and on-chip imaging and spectroscopic devices.