Silicon ring resonator-coupled Mach-Zehnder interferometers for the Fano resonance in the mid-IR.

We present ring resonator (RR)-coupled Mach -Zehnder interferometers (MZIs) based on silicon-on-insulator rib waveguides, operating around the mid-IR wavelength of 3.8 mu m. A number of different photonic integrated devices have been designed and fabricated experimentally to obtain the asymmetric Fano resonances in the mid-IR. We have investigated the influence of the coupling efficiency between the RR and the MZI as well as the phase shift between the two arms of the MZI on the Fano-type resonance spectral features, in agreement with theoretical predictions. Finally, wavelength-dependent Fano transmittances have been successfully measured with insertion losses up to similar to 1 dB and extinction ratios of similar to 20 dB. A slope of sharp Fano resonances as high as -574.6/mu m has been achieved and estimated to be 35.5% higher than the slope of single RR Lorentzian-type resonances. (C) 2017 Optical Society of America.