Adsorption on straight and bent optical fibers considered as a perturbation problem

The effect of a thin adsorbed layer of a foreign material on the modal propagation constant in an optical fiber is calculated by the use of a time-independent perturbation theory. The effect is measured on a straight fiber but is enhanced on a bent fiber because of tunneling, which is analogous to the Zener effect in quantum mechanics. Experimental results obtained with a fiber interferometer are presented.