Microfluidic refractive index sensor based on concave reflection grating

In this work, we introduce a novel microfluidic refractive index (RI) sensor based on concave reflection grating. COMSOL Multiphysics is employed to perform simulation calculations. We analyzed the reflection spectra withdifferent grating structural parameters and incidence angles, to evaluate its sensing performance. Additionally, sensitivity, full-width half maximum (FWHM) and figure of merit (FOM) were considered as performance parametersto evaluate the proposed optical sensor. The results demonstrate that the microfluidic channels increase the spatial overlap between the strong electric field and the analyte, ensuring the high sensitivity for refractive index sensing; thegroove structure of the periodic concave reflection gratings enhances the grating's ability to confine the optical field, improving the FOM of the sensing. With the optimum structural parameters, the sensor demonstrates a high sensitivityof 1015 nm/RIU and a high FOM of 780.88. The sensor shows the advantages of high FOM while maintaining a highsensitivity, promising excellent prospects for practical applications.