Fibre Bragg Gratings

Abstract

Fibre Bragg gratings (FBGs) are characterized by a periodic refractive-index variation along the z-axis; that is, along the propagation axis in an optical fibre. FBGs have very interesting wavelength-dependent characteristics and thus they find important applications as sensors, dispersion compensators and in many other diverse areas. In this chapter, we will present a detailed analysis of the working of the FBG using what is usually referred to as coupled-mode theory. Thus, this chapter is tutorial in nature primarily because of the fact that the (simple) analysis would allow us to understand from first principles the basic characteristics of an FBG. Our analysis will assume a periodic refractive-index variation in a slab waveguide; however, the final results will also be applicable to fibres. In addition to FBGs, such periodic structures are of great importance and form the fundamental building block of many interesting photonic devices.