Back-reflexion from fused biconic couplers

Several theories are investigated to account for the origin of back-reflexions from fused biconic couplers. Amongst the effects causing such variation are those considered in this paper, namely, tapering, surface roughness on the cladding-air interface, fiber bends and twists and, finally, stress arising from bending and packaging. The basic investigative tool is the coupled local mode equations solution for the coupling between the forward- and backward-propagating modes arising in response to these effects. Theoretical analysis shows the stress optic effect to be the most likely reflexion origin and experimental results support this assertion, as well as ruling out tapering and surface roughness as likely causes.