Temperature-dependent coupling characteristics in a silicon photonic crystal waveguide coupler

This paper presents a systematic analysis of temperature-dependent coupling characteristics in a photonic crystal waveguide (PCW) coupler. Unlike previous works that primarily rely on either numerical simulations or experimental studies, our approach integrates an analytical framework based on Coupled Mode Theory (CMT) with computational validation using COMSOL Multiphysics. The proposed PCW coupler, composed of silicon rods in air, exhibits a significant reduction in coupling length, enhancing its suitability for photonic integrated circuits (PICs). Through a combination of Plane Wave Expansion (PWE) simulations and wavelength-domain modelling, we demonstrate that the coupling length decreases with increasing temperature, indicating enhanced efficiency for thermally sensitive applications. The study not only provides theoretical insights into thermo-optic coupling in PCWs but also offers a practical design strategy for compact photonic devices operating at variable temperatures.