Temperature-controlled photonic nanojet via VO₂ coating

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Photonic nanojets (PNJs) are highly localized optical fields generated by sub-wavelength dielectric microspheres.
• Tuning PNJ characteristics like Full Width at Half Maximum (FWHM) and Working Distance (WD) is crucial for advanced applications.
• Phase change materials offer dynamic control over optical properties.

Purpose of the Study:

• To numerically investigate the temperature-dependent tunability of PNJ FWHM and WD.
• To explore the use of vanadium oxide (VO2) as a phase change material for PNJ tuning.
• To identify optimal parameters for a VO2-coated microsphere for maximum PNJ tunability.

Main Methods:

• Numerical simulation of light interaction with a glass microsphere coated with VO2.
• Modeling the phase transition of VO2 from semiconducting to metallic state with temperature changes.
• Analysis of PNJ FWHM and WD variations across a temperature range (20°C to 90°C).

Main Results:

• A 75 nm VO2 coating on a 5.0 μm diameter microsphere (n=1.50) was found to be optimal.
• Temperature variation from 20°C to 90°C resulted in a 14.0% change in FWHM (0.43 to 0.37 μm).
• Working Distance (WD) showed a significant 31.0% change (0.29 to 0.20 μm) within the same temperature range.

Conclusions:

• Temperature-induced phase transition in VO2 effectively tunes PNJ characteristics.
• The optimized VO2-coated microsphere demonstrates significant tunability in FWHM and WD.
• Tunable PNJs hold promise for applications in nanolithography and high-resolution imaging.