Fiber-optic sensors based on Bragg gratings

Abstract

The rapid development of fiber optics initiated by the increasing demand for the information content and information transmission rate resulted in the development of new technologies in other areas, primarily next-generation lasers and sensors. These achievements are based on the unique properties of optical fibers. These are small optical losses in the propagation of radiation in the fiber ( ~0.2 dB/km in the low-loss transmission window in the region of ~1.55 µ m), the effective heat withdrawal due to the fiber geometry, and low distortions of a light beam. As a result, a high-intensity light can propagate over large distances without decline in beam quality. Furthermore, an important characteristic of fibers is photosensitivity or the ability to locally change the refractive index by the action of UV radiation. This effect makes it possible to construct a light control device directly in the fiber core. The fiber Bragg grating (FBG), a periodic refractive index structure, is an example of such a device. In this study, the properties of FBG are considered as a one-dimensional photonic crystal (PC), and prospects for FBG application as elements of laser and sensor systems are evaluated. The FBG is a piece of a light guide, in the core of which the periodic structure of the refractive index is induced [1]. The FBG possesses the property of narrow-band reflection of radiation at the Bragg wavelength: