  Sub-wavelength diameter tapered optical fibers surrounded by rubidium vapor
can undergo a substantial decrease in transmission at high atomic densities due
to the accumulation of rubidium atoms on the surface of the fiber. Here we
demonstrate the ability to control these changes in transmission using light
guided within the taper. We observe transmission through a tapered fiber that
is a nonlinear function of the incident power. This effect can also allow a
strong control beam to change the transmission of a weak probe beam.
