On-Chip Sensor for Simultaneous Temperature and Refractive Index Measurements Based on a Dual-Passband Microwave Photonic Filter

We propose and experimentally demonstrate an on-chip optical sensor based on a dual-passband microwave photonic filter (MPF) incorporating a silicon photonic integrated microdisk resonator (MDR). Two whispering gallery modes supported by the MDR that are experiencing different wavelength shifts are employed for simultaneous temperature and refractive index (RI) measurements. To increase the interrogation speed and resolution, the MDR is incorporated in an MPF to produce two microwave passbands. By applying a broadband linearly chirped microwave waveform to the MPF, two filtered microwave waveforms with their temporal locations or equivalently central frequencies corresponding to the wavelength shifts of the notches are generated. The measurement of the temporal locations or equivalently the central frequencies is performed at high speed and high resolution using a digital signal processor. To increase the signal-to-noise ratio of the filtered microwave waveforms, a noise reduction algorithm based on phase-only filtering is proposed and employed. The on-chip optical sensing system is experimentally demonstrated. The sensing system can provide high temperature and RI interrogation resolutions of 2.4 × 10^-5 °C and 9.1 × 10^-8 RIU at a high interrogation speed of 1 MHz.