ABSTRACT
Optical micro-ring resonators have attracted increasing attention in the photonics community. Their applications range from quantum electro-dynamics to sensors and filtering devices for optical telecommunication systems, where they are likely to become an essential building block. An often-used component in micro-ring-based optical circuitry is the directional coupler, which is a twin waveguide structure used to couple a fraction of light from one waveguide to another. Directional couplers were used to transfer light into and out of micro-ring resonators, and these can be designed with a high degree of accuracy. Optical ring waveguide resonators are useful components for wavelength filtering, multiplexing, switching and modulation. The main performance characteristics of these resonators are the Free-Spectral Range, the finesse, the transmission at resonance, and the extinction ratio. The major physical characteristics underlying these performance criteria are the size of the ring, the propagation loss, and the input and output coupling ratios.
