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

The total loss of the HE/sub 11/ 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 /spl Omega/ is in the range /spl beta/-k/sub 2/</spl Omega/</spl beta/+k/sub 2/ where /spl beta/ is the modal propagation constant and k/sub 2/ 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.