ABSTRACT
The goal of this chapter is to introduce to the readers basic physics and theories of optical bers relevant to ber lasers. Basic physics of light guidance in optical bers is introduced rst through ray optics and then modes in waveguides. Important properties of optical bers are introduced. Mode-coupling theory is described in order for readers to appreciate the key physics of mode coupling, which is important for understanding behaviors and operations of multimode bers and ber devices used in ber lasers. These topics are also critical for understanding fundamental issues in ongoing research and development in ber lasers.
