  A tunable, all-optical, coupling method has been realized for a
high-\textit{Q} silica microsphere and an optical waveguide. By means of a
novel optical nanopositioning method, induced thermal expansion of an
asymmetric microsphere stem for laser powers up to 171~mW has been observed and
used to fine tune the microsphere-waveguide coupling. Microcavity displacements
ranging from (0.612~$\pm$~0.13) -- (1.5 $\pm$ 0.13) $\mu$m and nanometer scale
sensitivities varying from (2.81 $\pm$ 0.08) -- (7.39 $\pm$ 0.17) nm/mW, with
an apparent linear dependency of coupling distance on stem laser heating, were
obtained. Using this method, the coupling was altered such that different
coupling regimes could be explored for particular samples. This tunable
coupling method, in principle, could be incorporated into lab-on-a-chip
microresonator systems, photonic molecule systems, and other nanopositioning
frameworks.
