Observation of secondary bend loss oscillations arising from propagation of cladding modes in buffered monomode optical fibres

Experimental results for the oscillation of bend loss with wavelength and temperature in buffered monomode optical fibre are reported. The oscillations have a compound structure characterised by two distinct periods. The observations are explained on the basis of interference between the core guided mode and two “whispering gallery” modes, one of which propagates by reflections at the buffer-air interface, the other by reflections at the cladding-buffer interface.