Photonic Fractional-Order Differentiator Using an SOI Microring Resonator With an MMI Coupler

An optically tunable fractional order temporal differentiator implemented using a silicon-on-isolator microring resonator with a multimode interference (MMI) coupler is proposed and experimentally demonstrated. Through changing the input polarization state, the self coupling coefficient and the loss factor of the designed ring resonator with the MM! coupler are changed. Correspondingly, the coupling regime is changed. Through changing the coupling regime from over-coupled to under-coupled regime, the phase shift in the resonance wavelength is changed from <;π to >π. This tunable phase shift is used to implement a tunable fractional order photonic differentiator with an order tunable from <;1 to 1. The proposed fractional order differentiator is demonstrated experimentally. A Gaussian pulse with a bandwidth of 45 GHz is temporally differentiated with a tunable order of 0.37, 0.67, 1, 1.2, and 1.3.