Circular resonators are key elements, essential for research involving highly confined fields and strong photon-atom interactions such as cavity QED, as well as for practical applications in optical communication systems, biochemical sensing and more. The main characteristics of such resonators are the Q-factor, the free spectral range (FSR) and the modal volume, where the last two are primarily determined by the resonator radius. The Total-Internal-Reflection (TIR) mechanism employed in"conventional" resonators couples between these characteristics and limits the ability to realize compact devices exhibiting large FSR, small modal volume and high Q. Recently, a new class of annular resonator, based on a single defect surrounded by radial Bragg reflectors, has been proposed and analyzed. The radial Bragg confinement decouples the modal volume and the Q and paves a new way for the realization of compact and low loss resonators. Such properties as well as the unique mode profile of the annular Bragg resonators (ABRs) make this class of devices an excellent tool for ultra-sensitive biochemical detection as well as for studies in nonlinear optics.