Microresonator devices lithographically introduced at the optical fiber surface

We present a simple lithographic method for fabrication of microresonator devices at the optical fiber surface. First, we undress the predetermined surface areas of a fiber segment from the polymer coating with a focused CO₂ laser beam. Next, using the remaining coating as a mask, we etch the fiber in a hydrofluoric acid solution. Finally, we completely undress the fiber segment from coating to create a chain of silica bottle microresonators with nanoscale radius variation [surface nanoscale axial photonics (SNAP) microresonators]. We demonstrate the developed method by fabrication of a chain of five 1 mm long and 30 nm high microresonators at the surface of a 125 µm diameter optical fiber and a single 0.5 mm long and 291 nm high microresonator at the surface of a 38 µm diameter fiber. As another application, we fabricate a rectangular 5 mm long SNAP microresonator at the surface of a 38 µm diameter fiber and investigate its performance as a miniature delay line. The propagation of a 100 ps pulse with 1 ns delay, 0.035c velocity, and negligible dispersion is demonstrated. In contrast to previously developed approaches in SNAP technology, the developed method allows the introduction of much larger fiber radius variation ranging from nanoscale to microscale.