Enhanced coupled-resonator-induced transparency and optical Fano resonance via intracavity backscattering

We look into the use of the intracavity backscattering in twin-coupled traveling wave microresonators (TWMRs) to generate enhanced coupled-resonator-induced transparency (CRIT) and optical Fano resonance (OFR). Intracavity backscattering makes it possible to either generate a single CRIT peak or a pair of CRIT peaks within one free spectral range in the transmission spectrum. The distance between the twin-CRIT peaks can be tuned by controlling the intracavity backscattering strength. Also, the use of intracavity backscattering allows the simultaneous production of both fast and slow light effects. In addition, it is found that the symmetric CRIT peaks can be reshaped into asymmetric OFR line shapes either by using TWMRs with different intracavity backscattering strengths when one input is launched into the circuit or by modulating the phase/amplitude difference between the dual contrapropagating inputs, which are launched into the circuit in the presence of intracavity backscattering. These allow switching between CRIT and OFR to be realized in the absence of gain or phase tuning elements in the cavities, unlike conventional twin-coupled TWMR systems. (C) 2012 Optical Society of America