ABSTRACT
This chapter describes the conditions under which a circular optical waveguide can operate as a few-mode fiber. It discusses the fundamental concepts of waveguiding in the circular optical waveguide or optical fibers, including approaches from the Maxwell equations and the wave equations leading to guided conditions for the modes subject to boundary conditions. For a single mode there are two polarized modes whose polarizations can be vertical or horizontal. The main issues are on the optical amplification gain for the transmission of modulated signals in such few-mode fibers. Besides optical fibers for transmission of signals, there are a number of special types of fibers that are essential for optical systems, for applications in either telecommunication systems or sensing devices. The manufacturing techniques and cabling process affect the transmission and physical properties of the fibers. The chapter focuses on the aspects for a general understanding of optical transmission systems.
