Improved Sensitivity of Microring Resonator-Loaded Mach–Zehnder Interferometer Biosensor

Abstract

We investigated the improvement in the sensitivity of a biosensor based on a silicon microring resonator-loaded Mach-Zehnder interferometer (MRR-MZI). Thermo-optic-driven variable optical attenuators (VOAs) were used to balance the optical power in one arm with that in the other to obtain a high extinction ratio of the MRR-MZI. The change in the transmittance as large as 12.9 and 7.5 dB for the detection of 200 and 20 pM avidin, respectively, was successfully obtained. These values are larger than those observed before the adjustment of the optical power balance by 4.8 and 5.3 dB, respectively. We discuss the characteristics of light power adjustment of the VOA and confirmation of biotin modification of the surface of the silicon waveguide using fluoresceinpolyethylene glycol-N-hydroxylsuccinimide (fluorescein-PEG-NHS).