High sensitivity multiscale and multitasking terahertz Janus sensor based on photonic spin Hall effect

Photonic spin Hall effect (PSHE) is an effective metrological tool to characterize the variation in weak refractive index (RI) and nanostructure parameters. In this Letter, a highly sensitive terahertz Janus sensor (JS) based on PSHE is proposed. Through the asymmetric arrangement of different dielectrics, the sensor has a Janus feature, realizing the multitasking of thickness and RI detection on multiple scales. When electromagnetic waves (EWs) are incident into the JS from the forward scale, the number of graphene layers (1–7 layers) can be exactly identified by thickness detection. Enhancing the PSHE by the property of graphene, the JS can extend the thickness change of the graphene layer at the nanometer level by 106 times to the millimeter level with a sensitivity of 3.02 × 10−3 m/nm. In the case of EWs backward scale propagation, based on the sensitivity of 6.244 × 10−3 m/RIU, the JS can identify different kinds of waterborne bacterium such as Vibrio cholerae, Escherichia coli, and Shigella flexneri, in the RI range of 1.355–1.43 with high precision. The design of the multiscale and multitasking JS with high sensitivity is of great significance for accelerating the research and exploration of graphene materials. In addition, it provides an idea for real-time, no-label, and low-cost detection in the biomedical field.