Fiber Bragg grating sensors can be used to measure the refractive index of fluids by etching the surface of a D- shaped fiber to expose the evanescent field to the superstrate layer. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a. Bragg gratings are crucial components in passive photonic signal processing, with wide-ranging applications including biosensing, pulse compression, photonic computing, and addressing. The cladding is modified and the modal propagation constants are changed thereby shifting the Bragg wavelength of a.