Surface nanoscale axial photonics at a capillary fiber

Area of Science:

• Photonics
• Microfluidics
• Optical Sensing

Background:

• Whispering gallery modes (WGMs) are optical modes confined within dielectric resonators.
• Capillary fibers offer unique geometries for integrated optical sensing.
• Sensing based on WGMs requires high sensitivity to environmental changes.

Purpose of the Study:

• To present the theory and experimental demonstration of a novel sensing platform based on surface nanoscale axial photonics (SNAP).
• To utilize SNAP on capillary fibers for detecting variations in the refractive index of internal media.
• To establish a method for determining internal capillary radius variations from optical mode spectra.

Main Methods:

• Theoretical modeling of optical whispering gallery modes in capillary fibers.
• Fabrication of a SNAP resonator via localized CO2 laser annealing and hydrofluoric acid etching.
• Experimental measurement and analysis of mode spectra for empty and water-filled resonators.

Main Results:

• Successful demonstration of a SNAP sensing platform on a capillary fiber.
• Determination of internal surface nonuniformity introduced by the etching process.
• Validation of the theory relating mode spectra to internal effective radius variations.

Conclusions:

• The developed SNAP platform offers a novel approach for sensing media adjacent to internal capillary surfaces.
• This technology holds significant potential for advanced microfluidic sensing applications.
• The method allows for precise characterization of capillary geometry and internal surface properties.