Ultimate Q of optical microsphere resonators

Area of Science:

• Optical physics
• Materials science
• Nanotechnology

Background:

• Whispering-gallery modes (WGMs) in dielectric microspheres exhibit extremely high quality factors (Q).
• Material properties and surface conditions critically influence Q, limiting performance in applications.
• Fused silica is a promising material for high-Q resonators due to low optical loss.

Purpose of the Study:

• To demonstrate ultra-high Q factors in fused-silica microspheres near fundamental material limits.
• To investigate the impact of atmospheric water adsorption on WGM Q factors and frequencies.
• To explore the potential for supermaterial Q factors by suppressing scattering losses.

Main Methods:

• Fabrication of fused-silica microspheres.
• Excitation and measurement of whispering-gallery modes at 633 nm.
• Monitoring of Q factor and frequency shifts over time to track adsorption kinetics.
• Analysis of scattering loss mechanisms in microspheres.

Main Results:

• Achieved a quality factor (Q) of (0.8 +/- 0.1) x 10^10, approaching the material's intrinsic limit.
• Demonstrated submonolayer sensitivity in monitoring atmospheric water adsorption kinetics via Q factor and frequency changes.
• Identified atmospheric water adsorption as the primary limitation for ultimate Q in these microspheres.

Conclusions:

• Fused-silica microspheres can achieve Q factors close to fundamental material attenuation limits.
• Whispering-gallery mode parameters are sensitive probes for surface adsorption phenomena.
• Suppression of scattering losses offers a pathway towards achieving supermaterial Q factors.