Mapping whispering-gallery modes in microspheres with a near-field probe

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Whispering-gallery modes (WGMs) in dielectric microspheres are sensitive to surface perturbations.
• Mapping the angular dependence of these modes is crucial for understanding light-matter interactions in micro-resonators.

Purpose of the Study:

• To demonstrate a novel near-field probe technique for mapping WGMs in fused-silica microspheres.
• To investigate the lifting of spherical degeneracy using this mapping method.

Main Methods:

• Utilizing a monomode fiber with a micrometer-sized tip to interact with the evanescent field of microsphere WGMs.
• Coupling light from microsphere resonances into the fiber guided mode.
• Measuring fiber output while scanning the probe tip across the microsphere surface.

Main Results:

• Successfully mapped the angular dependence of high-Q whispering-gallery modes.
• Provided experimental evidence for the lifting of spherical degeneracy in the microsphere system.
• Demonstrated the efficacy of the near-field probe technique for mode analysis.

Conclusions:

• The near-field probe method offers a powerful tool for characterizing optical modes in microspheres.
• This technique facilitates the investigation of subtle optical phenomena like degeneracy lifting.
• The findings contribute to the understanding and application of micro-resonator devices.