Anti-external interference sensor based on cascaded side-coupled photonic crystal nanobeam cavities for simultaneous sensing of the refractive index and temperature

We present a cascaded side-coupled silicon-on-insulator (SOI) photonic crystal nanobeam cavities (PCNCs) sensor for simultaneous sensing of the refractive index (RI) and temperature. Two types of PCNCs are designed for increasing the demodulation coefficient: the low-index mode cavity exposed to water directly (cav1) and the high-index mode cavity covered with SU-8 cladding (cav2). Moreover, the cascaded side-coupled system is modeled, and the transmission expression is derived based on temporal coupled-mode theory. Furthermore, the correlations between the structural parameters, the transmission, quality factor are discussed. By using three-dimensional finite-difference time-domain simulations, we further prove the ability to detect RI and temperature simultaneously, obtaining a RI sensitivity of 210 nm/RI unit (RIU) and a temperature sensitivity of 53 pm/K for cav1, whereas there is a RI sensitivity of 0 nm/RIU and a temperature sensitivity of −90pm/K for cav2. Moreover, the maximum of external interference ranges of the proposed sensor are 7.5×10−6 and 0.01 for the RI and temperature, respectively, and the deviation ratios are approximately 0.56% and 3.33% for the RI and temperature, respectively. Therefore, the proposed sensor has strong anti-interference ability and accuracy, which is a promising platform for future applications of dual-parameter sensing.