In-plane resonant cavities with photonic crystal boundaries etched in InP-based heterostructure

The optical properties of in-plane cavities with photonic crystal boundaries fabricated into an InP/GaInAsP/InP slab waveguide structure are presented. The investigated cavities are realized as segments of different lengths bounded by V-shaped double or single mirrors in straight photonic crystal waveguides and were designed to have resonance in the 1.55 μm wavelength range. High aspect ratio etching of the photonic crystal is achieved using ${\mathrm{Ar/Cl}}_2$ -based chemically assisted ion beam etching. The optical loss inside the photonic crystal waveguide was determined by fitting the measured transmission spectra with two-dimensional finite-difference time-domain simulations. The experimental results, combined with the simulations, indicate that major sources of loss in these cavities are radiation through the cavity mirrors and out-of-plane scattering of the third-order mode inside of the cavity. The best results were obtained for a 6.2 μm long resonant cavity with double mirrors that had an appreciably high-quality factor of 460.