FSR-free multimode Fabry–Perot cavity sensor enhanced by a subwavelength grating chamber

A free spectral range (FSR)-free multimode Fabry-Pérot (FP) cavity sensor that overcomes the limitations of conventional FP cavities, particularly in terms of FSR and sensitivity, has been proposed and demonstrated. The sensor utilizes a pair of misaligned multimode Bragg gratings (MBGs) to broaden the spectral bandwidth and achieve a single resonance peak. The multimode subwavelength grating (MSWG) is integrated within the cavity to enhance the light-matter interaction, achieving high refractive index sensitivity with minimal loss. The device, fabricated on SOI wafers, demonstrates a temperature sensitivity of 91.17 pm/°C and a bulk refractive index sensitivity of 305.83 nm/RIU. The proposed sensor shows significant potential for multiparameter sensing in fields such as environmental monitoring, biomedical diagnostics, and chemical analysis, offering a scalable and high-performance solution.