Two-dimensional Close-packed Arrays of Polystyrene Microspheres Bragg Grating for Refractive Index Sensing

For fiber Bragg grating (FBG) with a one-dimensional (1D) photonic crystal structure based on silica materials, its photonic bandgap can only respond to temperature and strain. We combined close-packed arrays of polystyrene (PS) microspheres with a side-polished multimode fiber to fabricate a two-dimensional (2D) PS microspheres Bragg grating with refractive index (RI) sensing capability. The close-packed arrays of PS microspheres with large surface area and porosity in the periodic structure could be filled in liquids, which enable its RI sensing ability. With the 450 nm PS microspheres to form 2D close-packed PS arrays, the photonic bandgap of the optical structure is 1078.8 nm, and its RI sensitivity can be up to 229.4 nm/RIU for NaCl solution in the range of 1.334-1.398.