Overview

Expressions for electric fields, propagating modes, group delays, and coupling coefficients will be derived because of their critical importance to understanding the performance capabilities and limitations of optical fibers. Potential scalar modes and hybrid modes in an optical fiber will be discussed. The TE and TM modes are not of practical importance and are very much easier to describe than the hybrid modes. Mathematical expressions for optical power carried by the core, cladding and jacket will be derived for the most prominent hybrid mode. Power level computation supporting the hybrid modes such as HE ₁₁ or EH ₁₁ needs the complex form of the dyadic function for a rigorous formulation and analysis. In case of optical communication fibers, the magnitude of electric field, radiation loss, and power levels in various modes are strictly dependent on surface irregularities, frequency or wavelength of surface roughness, variations in optical fiber radius, and dielectric differences between the core and cladding. High computation accuracy for the electric field and modal power levels is only possible when the optical fibers have a very small dielectric difference between the core and cladding. Radiation loss due to random variation in the core radius along the fiber length is critical, particularly in long-haul communication fibers. Power loss due to trapped-surface modes will be briefly investigated.

Expression for the electric field and modal power will be developed at cutoff for the TE and TM modes. Modal power produced by the core surface irregularities generates forward and backward...