Application of a low-loss criterion to optical waveguides and devices

Optical waveguides and devices suffer loss due to a variety of nonuniformities. The calculation of the actual loss is usually involved and requires a fair degree of mathematical sophistication. However, if the goal of the waveguide designer is to minimise loss, a well known universal criterion can determine qualitatively whether loss increases or decreases with the variation in each of the waveguide or device parameters. To demonstrate the simplicity and generality of this criterion, it is applied to examples covering: microbending, pure bending, tapering, sinusoidal deformations (fibre gratings), helical fibres and Y-junctions.