Radiation on Losses Due to Variations of Radius Dielectric or Optical Fibers

The total loss of the HE₁₁ mode to the radiation field of a finite dielectric rod with small amplitude surface irregularities is considered, and a simple approximate analytic expression for radiation due to sinusoidal roughness is presented. It is shown that radiation occurs only when the frequency of surface roughness Ω is in the range β-k₂<Ω<β+k₂ where β is the modal propagation constant and k₂ is the wavenumber of the surrounding medium. An analysis of isolated irregularities and a linear taper with a small change in radius are also presented.