Silicon Photonic Microdisk Sensor Based on Microwave Photonic Filtering Technique

A high-sensitivity and high-resolution silicon photonic sensor based on a microwave photonic filtering technique is proposed and demonstrated. By employing a Mach-Zehnder modulator with a fixed 90 degrees hybrid and a single DC bias control, this simple optical configuration is adopted to first tailor the amplitude of the optical field to achieve a power ratio in the sidebands which is then followed by an over-coupled integrated microdisk resonator (MDR) to provide a power equalization and pi rad phase difference in the sidebands. The proposed scheme enables a highly effective cancellation of the beating signals at RF frequencies corresponding to the MDR notch center, resulting in an ultrahigh-rejection notch in the RF domain. A change in the environmental parameters can thus be detected with high sensing resolution by monitoring the frequency shifts of the ultranarrow RF notch. The use of the MDR contributes to a high sensing sensitivity while the fabrication requirements on having an ultrahigh Q factor is removed. A temperature sensor based on the proposed scheme is demonstrated as a proof-of-concept, presenting a temperature sensitivity of 9.91 GHz/degrees C and a 25 times improvement in the sensing resolution compared to the conventional optical sensing method based on direct measurement of the optical spectrum.