Bend loss oscillations in single mode optical fibre: higher order recoupling

Bend loss in buffered single mode optical fibre is an oscillatory function of wavelength. In previous work, these oscillations have been described by a two-beam interference model between a core guided mode, and a whispering gallery mode propagating in the cladding and buffer. It is shown that higher order recoupling occurs between the two modes, such that the shape of the oscillations is not given by a simple raised sinusoid. It is demonstrated theoretically and experimentally that the shape of the bend loss oscillations is given by a superposition of the harmonics of a sinusoid, and that the distribution of power amongst these harmonics depends on the bend length. © 1994.