Relation between transition loss and mode-field half-width for curved noncircular weakly-guiding single-mode waveguides

The relation between the transition loss and the near-field second-moment mode-field half-width W/sub T1/, W/sub y1/ for curved arbitrary noncircular weakly-guiding single-mode waveguides is derived. For symmetric noncircular single-mode waveguides, under an elliptical Gaussian approximation, we also derive the beam shifts. We find that the formula for the transition loss is the same as the formula of the transverse offset loss, and the formulas of beam shifts and transition loss are reduced to the formulas of Gambling et al. for circular single-mode fibers.>