This Book is divided into two main parts. The first part deals with the applications of interferometric methods on characterization of bent optical fibres. Also, image processing method is applied to extract the contour lines of the produced patterns. Then, a new mathematical model is proposed and used to calculate the optical parameters of the bent optical fibres. The second part deals with the application of digital holographic phase shifting interferometric microscopy to determine the refractive index and some optical parameters of graded index optical fibres, as well as the refractive index profile of bent optical fibres.