  We study the optical characteristics of a photonic crystal (PhC)
heterostructure cavity consisting of two-dimensional monolayer PhC, sandwiched
between two identical passive multilayers. In the range of stopband of the
multilayer, guided resonance of the sandwiched PhC are excited by the
evanescent waves of the multilayer stack and the quality factor of these
cavity-coupled guided resonances is about 10e6. The calculated field
distribution facilitates the distinction between the cavity defect modes and
the coupled guided resonances of the proposed design. The line shapes of the
resonances are explained using a theoretical model. Significant decrease in the
lasing threshold is observed for these resonant modes in comparison to the
defect modes. These results will find use in designing compact PhC-based
ultra-low threshold lasers and narrow band filters.
