Photo-induced SNAP: fabrication, trimming, and tuning of microresonator chains.

We introduce multiple series of uncoupled and coupled surface nanoscale axial photonics (SNAP) microresonators along the 30 micron diameter germanium-doped photosensitive silica optical fiber and demonstrate their permanent trimming and temporary tuning with a CO2 laser and a wire heater. Hydrogen loading allows us to increase the introduced variation of the effective fiber radius by an order of magnitude compared to the unloaded case, i.e., to around 5 nm. It is demonstrated that the CO2 laser annealing of the fabricated microresonator chain can be used to modify the fiber radius variation. Depending on the CO2 laser beam power, the microresonator effective radius variation can be increased in depth up to the factor of two or completely erased. In addition, we demonstrate temporary tuning of a microresonator chain with a wire heater.