Abstract
We present the theory and first experimental demonstration, to the best of our knowledge, of a sensing platform based on surface nanoscale axial photonics (SNAP) at a capillary fiber. The platform explores optical whispering gallery modes, which circulate inside the wall of a capillary and slowly propagate along its axis. Due to the small thickness of the capillary wall, these modes are sensitive to spatial and temporal variations of the refractive index of the media adjacent to the internal capillary surface. In particular, the developed theory allows us to determine the internal effective radius variation of the capillary from the measured mode spectra. Experimentally, a SNAP resonator is created by local annealing of the capillary with a focused CO2 laser followed by internal etching with hydrofluoric acid. The comparison of the spectra of this resonator in the cases when it is empty and filled with water allows us to determine the internal surface nonuniformity introduced by etching. The results obtained pave the way for a novel advanced approach in sensing of media adjacent to the internal capillary surface and, in particular, in microfluidic sensing.
Highlights
We present the theory and first experimental demonstration, to the best of our knowledge, of a sensing platform based on surface nanoscale axial photonics (SNAP) at a capillary fiber
A SNAP resonator is created by local annealing of the capillary with a focused CO2 laser followed by internal etching with hydrofluoric acid
In the case of a capillary fiber, it is of great interest to investigate how the spatial and temporal variations of the media adjacent to the internal capillary surface affect the spectrum of the SNAP resonator created at the capillary wall
Summary
The developed theory allows us to determine the internal effective radius variation of the capillary from the measured mode spectra. The results obtained pave the way for a novel advanced approach in sensing of media adjacent to the internal capillary surface and, in particular, in microfluidic sensing. In the case of a capillary fiber, it is of great interest to investigate how the spatial and temporal variations of the media adjacent to the internal capillary surface affect the spectrum of the SNAP resonator created at the capillary wall. It is important to find out if it is possible to determine the internal effective radius variation of the capillary from the measured spectra, as was done for the outer radius in SNAP [1,2,3]
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