Slow light structure implementation to improve Fano response of optical waveguide as a refractive index sensing

Optical sensor based on the coupled cavity is an interesting topic because these types of sensors have higher Figure of merit (FOM) and sensitivity in comparison to other types of sensors. In this paper, a novel refractive sensor based on the coupled cavity by using T-stub and grating transmission line is suggested. The T-stub interaction with the cavity and coupled line make two capacitances and the Fano-shape of the transmission appeared. The grating as a slow light structure enhanced the transmission and Q-factor of the proposed coupled waveguide sensor by controlling the phase in the transmission line. The proposed sensor is modified to have dual-band characteristics as a Fano form at 1286 and 1629 nm (233 and 184 THz respectively) and for this aim, the T-Stub and the grating structure play the main role. This sensor is used to check the materials with refractive index in the range of 1–1.5 and the maximum sensitivity and FOM are obtained at 1730 nm/RIU and 728 RIU−1, respectively. The full wave method of FIT (Finite Integrated Technique) as a time domain method is utilized for analyzing this sensor. © 2023 Elsevier GmbH