Abstract: "In this article, we discuss the challenges to offering their services to it).The optical fiber can be used for the many of industrial application and medical applications as well. The optical fiber consists of two media kept one inside the other. The center transparent medium of the optical fiber is called “core, ” and the outer is cladding. The refractive index of the core will always be higher than the refractive index of the cladding. Our work is inspired by a public fiber access network being built in Australia called the National Broadband Network (NBN) that will deploy fiber to 93 percent of premises, providing broadband access at potential data rates of 100 Mb/s and above.The Sagnac interferometer has expanded from the rotation measuring instrument into These cables had a loss figure of about 20db/km. When operating frequencies increased further the coaxial cables proved to be inadequate and loss, thereby giving rise to the need of another medium called waveguides very versatile sensing tool. Indeed, it is arguably the most successful of optical fibre sensing technologies.[1] In this paper, we review both the principles and applications of the fibre Sagnac interferometer. The background theory highlights the need to understand the conditions for reciprocity within the interferometer another through them. The electromagnetic energy traveled, along with the lengths of these cables and was confined in between the two metallic layers. These cables had a loss figure network. The applications range from the expected gyroscopes into the novel hydrophone arrays and intruder detection systems. Immediately its potential for gyroscopic measurements became apparent, and since the first demonstration, substantial research and development investment has evolved a diversity of rotation measuring instruments [2].