Independently Tunable Multichannel Fractional-Order Temporal Differentiator Based on a Silicon-Photonic Symmetric Mach–Zehnder Interferometer Incorporating Cascaded Microring Resonators

A multichannel fractional-order temporal differentiator with independently tunable differentiation order based on an integrated silicon-photonic symmetric Mach-Zehnder interferometer consisting of cascaded microring resonators (MRRs) is designed, fabricated, and experimentally demonstrated. By controlling the radii of the MRRs, a multichannel spectral response with uniform channel spacing is obtained, which is used to function as a multichannel temporal differentiator with multiple subdifferentiators. The differentiation order of each subdifferentiator is independently tunable by optically pumping the corresponding MRR, which leads to the phase change in the spectral response due to the two-photon absorption induced nonlinear effect. A five-channel temporal differentiator with a channel spacing of 0.49 nm is fabricated on a silicon-on-insulator chip using a CMOS-compatible process with 193-nm-deep ultraviolet lithography. Independent tuning of the differentiation orders of the subdifferentiators is experimentally demonstrated.