Cavity-Coupled Guided Resonances With High Quality Factors in Photonic Crystal Heterostructures

We study the characteristics of a photonic crystal (PhC) heterostructure (HS) cavity consisting of a 2-D PhC sandwiched between two identical passive multilayer stacks. Guided resonances of the sandwiched PhC are excited by the evanescent waves of the multilayer stack in the range of its stopband, along with conventional defect modes. Some of these cavity-coupled guided resonances have symmetrical line shapes with very high quality factors. It is found that these resonant modes concentrate their field energy inside the dielectric spheres of the monolayer and thus possess relatively smaller mode volumes than that of the conventional defect modes. When the monolayer contains a gain medium, a significant decrease in the lasing threshold is observed for these resonant modes. The proposed HS cavity design holds immense potential in designing PhC-based ultra-low threshold lasers, narrow band filters, and to enhance non-linear effects.