  The use of sub-wavelength diameter tapered optical fibers (TOF's) in warm
rubidium vapor has recently been identified as a promising system for realizing
ultra-low-power nonlinear optical effects. However, at the relatively high
atomic densities needed for many of these experiments, rubidium atoms
accumulating on the TOF surface can cause a significant loss of overall
transmission through the fiber. Here we report direct measurements of the
time-scale associated with this transmission degradation for various rubidium
density conditions. Transmission is affected almost immediately after the
introduction of rubidium vapor into the system, and declines rapidly as the
density is increased. More significantly, we show how a heating element
designed to raise the TOF temperature can be used to reduce this transmission
loss and dramatically extend the effective TOF transmission lifetime.
