Designing a Fano-resonance-based temperature sensor by side-coupling double cavities to waveguide in photonic crystals

Optical sensors are widely used for temperature measurement in chemistry, biomedical detection, and food processing industries. In this paper, we present a highly sensitive temperature sensor based on the Fano resonance in two-dimensional photonic crystals. A carefully designed double cavity is used within the photonic crystals to symmetrically side-couple to a line-defect waveguide. Due to the direct and indirect coupling between two cavities, we found an asymmetric Fano-like line shape in the transmission spectrum. The optimized quality factor of the Fano resonance and the modulation depth are improved to a maximum of 10672 and above 90%, respectively. Furthermore, the sensitivity of the temperature sensor can reach as high as 91.9 pm/°C, which is direct evidence for its high sensing capability. Thus, our proposed temperature sensor has comparable quality factor and sensitivity with other reported sensors, indicating its high application potential in the sensing field.