Operational Principles of Fibre Bragg Grating and No-Core Fibre
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Fibre optics is an overlap of applied science and engineering concerned with the design and application of optical fibre. Normal optical fibre s possess a uniform refractive index along their lengths. Such fibre is referred to as fibre Bragg grating (FBG). FBG is defined as a periodic perturbation of a refractive index formed by exposing its naked core to an intense optical interference pattern. FBG is a passive optical component which selectively reflects and transmits lights at certain wavelengths. The portion of light where the wavelength is equal to the Bragg wavelength will be reflected and the rest will be transmitted through the FBG. The refractive index variation scatters light that passes through the fibre. It provides modulation of core refractive index for single-mode fibre. In FBG, the gratings are uniformly spaced regions in fibre where the refractive index has been raised from the rest of the core. These radiations scatter light and they are called the Bragg effect. Every time the light hits the region of the scattered higher refractive index, a few light beams will be scattered from each higher index zone, interfering constructively and producing strong refraction as shown in Fig. 2.1. High-index regions scatter light at other wavelengths, but the scattered wave differs in phase by canceling each other out in destructive interference.