Internally-loaded ring resonator configuration for optical filter applications

We study on-chip Wavelength Division Multiplexing (WDM) application of ring resonators on Silicon-on-Insulator (SOI) platform. Though WDM devices have been demonstrated earlier, there are certain challenges which are yet to be tackled. Large FSR and narrow line width requirement for a WDM device cannot be fulfilled in a conventional WDM device as the requirement for both the metrics demand opposing structural requirements from a ring resonator. A larger FSR demands for a smaller resonator length whereas smaller line width requires a large resonator length device. We overcome this using an embedded type ring resonator configuration. The structure is made of a racetrack type ring resonator with another ring embedded inside it (loading the external ring). Such structures are capable of showing coupled resonator induced transparency (CRIT) which can result in a very narrow line-width. We present initial experimental demonstration of CRIT in an internally loaded micro ring resonator fabricated on SOI material platform. The structures were optimized using 3D-FDTD analysis and coupling-matrix method.