Three-Dimensional Simulation of Particle-Induced Mode Splitting in Large Toroidal Microresonators

Area of Science:

• Optics and Photonics
• Nanotechnology
• Biomedical Engineering

Background:

• Whispering gallery mode (WGM) resonators, like silica microtoroids, are utilized as sensitive biochemical sensors.
• Mode-splitting, a sensing mechanism, occurs when target binding breaks resonance degeneracy, offering a theoretically position-insensitive signal.
• Existing analytical theories face limitations with larger biomolecules and computational challenges in simulating large microtoroids.

Discussion:

• This study introduces an efficient 3D electromagnetic simulation using a beam envelope method for large microtoroids (~90 µm).
• The simulation accurately models mode-splitting, addressing discrepancies between theory and previous experimental/numerical results.
• It validates particle sizing accuracy and simplifies polarizability calculations, requiring only background media properties.

Key Insights:

• The developed numerical approach accurately simulates mode-splitting in large microtoroid resonators.
• The simulation method overcomes previous computational intractability for large microtoroid electromagnetic analysis.
• It demonstrates the capability to model mode-splitting induced by larger particles, such as bacteria and viruses, beyond the dipole approximation's validity.

Outlook:

• This validated simulation technique can be extended to analyze other microresonator sizes and shapes.
• It paves the way for more accurate biochemical sensing applications using WGM resonators.
• Future work may involve optimizing resonator designs and sensing strategies based on these simulation insights.