Annular Bragg defect mode resonators

Abstract

We propose and analyze a new type of resonator in an annular geometry which is based on a single defect surrounded by radial Bragg reflectors on both sides. Unlike conventional, total internal reflection based ring resonators, this structure supports modal fields with very low azimuthal number (large radial k-vector component). We show that the conditions for efficient mode confinement are different from those of conventional Bragg waveguiding in a rectangular geometry. To realize tight confinement of the light in the defect, chirped gratings are required. Compared to a conventional resonator, the new resonator exhibits larger FSR and lower losses making it suitable for both telecom and sensing applications. In addition, the resonance wavelength and Q factor of the device are very sensitive to environmental changes, and thus provide ideal observables for sensing applications. Annular Bragg resonators with several unique geometries have been fabricated in an InGaAsP multi-quantum-well membrane. The spectral properties of the resonators have been investigated through analysis of photoluminescence induced by pulsed optical excitation.