Coupling Efficiency in Multimodal Photonic Crystal Cavities

Photonic crystal (PhC) cavities based on III-V materials emerge as key components in integrated photonic circuits thanks to their capability of confining light within small modal volumes and owning high quality factors up to 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> [1]. In particular, InGaP PhC cavities are used to enable applications in the generation of classical and quantum states of light through nonlinear interactions [2], [3]. Such applications require careful design of the PhC cavity to support equally spaced frequency modes. Techniques relying on the nearly-harmonic shaping of the effective photonic potential [1], [4] are used to design PhC cavities with equally space modes and Hermite-Gauss spatial distribution. Integrating these III-V nonlinear sources on silicon waveguides proves necessary to further envisage their usage in complex photonic circuitry. Experimental realizations of multimodal InGaP PhC cavities coupled to an underneath silicon waveguide have been previously reported [3], [5]. However, a study of the coupling between the PhC cavity higher-order modes and the Si waveguide is still missing.