Refractive Index Detection With a Laser-Induced Graphene-Coated Tilted Fiber Bragg Grating and Spectral Profile Interrogation

In this letter, we report a tilted fiber Bragg grating (TFBG) with a laser-induced graphene coating. The device displays a cladding mode pattern with a bandwidth of 44 nm. Each spectral dip and peak senses the refractive index change, with sensitivities up to 9.62 dB/refractive index units (RIUs) and 4.00 dB/RIU, respectively. The interrogation of the whole spectral feature envelope can be performed either in the wavelength or in the amplitude domain, with sensitivities of 11.21 nm/RIU and 7.15 dB/RIU, respectively. The graphene-coated TFBG provides improved sensitivity over a standard TFBG with a simple fabrication process and does not require additional components (such as polarizers or intensity-modulating devices) or fiber manipulations (such as etching, tapering, or capillaries). The achieved precision of up to 4.17 × 10^-4 RIU is compatible with refractometry and biosensing applications.