The talk highlights our recent efforts in modelling the nonlinear optical processes integrated with nanophotonic devices with a particular emphasis on lasing with feedback from topologically exotic metasurfaces. We have developed a computational multiphysics framework that provides a comprehensive understanding of the nonlinear light-matter interaction dynamics in nanophotonic devices. Our technique relies on a semi-classical approach that utilises carrier kinetics to model the nonlinear media in the time domain, where the rate equations are coupled to the Maxwell equations to provide a full-wave multiphysics framework for modelling nonlinear nanophotonic structures. The framework has been applied to a large number of nonlinear processes, including the enhancement of optical limiting in a plasmonic metasurface, spacing from a nanohole array, two-photon absorption, random lasing, and many others.
The talk presents a computational effort in modeling nanophotonics devices coupled to two-photon absorbing media. A six-level system is used to model the kinetics of two-photon absorption with organic dyes. This model is successfully used to match the spectral response of the organic 4,4’-bis(diphenylamino) stilbene (BDPAS) at low and high excitation energies and can be employed for accurate full-wave analysis of structured nanophotonic devices with multi-photon absorption media.
Then, the numerical analysis of a dielectric metasurface-based nanolaser and the experimental validation of the numerical results is chosen as the central theme, considering nanolasers with feedback from exotic all-dielectric metasurfaces with bound states in the continuum (BICs).
Metasurfaces find a wide variety of applications due to their versatile functionalities and more straightforward fabrication vs bulk metamaterials. However, their spectral response is generally broad, hindering their applicability to devices requiring sharp spectral features. We utilise the exotic phenomenon of BICs to realise high Q-factor resonances in all-dielectric metasurfaces. The designed BIC-based metasurfaces exhibit operation independent of polarisation with resonances in the visible.