# All-Optical Nanopositioning of High-Q Silica Microspheres

## TL;DR

This paper introduces an all-optical nanopositioning technique for high-Q silica microspheres, enabling precise control of coupling with waveguides through thermal expansion induced by laser heating.

## Contribution

A novel optical nanopositioning method based on thermal expansion of microsphere stems for tunable coupling in microresonator systems is demonstrated.

## Key findings

- Achieved microcavity displacements up to 1.5 μm
- Nanometer-scale sensitivity of 2.81-7.39 nm/mW
- Linear relationship between laser heating and coupling distance

## Abstract

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.