Whispering gallery mode excitation using exposed-core fiber

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Nanotechnology

Background:

• Whispering gallery modes (WGMs) in micro-resonators offer high Q-factors but practical light coupling remains a challenge.
• Existing methods using ultra-thin fiber tapers lack stability and are difficult for out-of-lab applications.

Purpose of the Study:

• To propose and demonstrate a new, stable, and practical WGM coupling scheme using exposed-core silica fiber (ECF).
• To overcome the limitations of fragile fiber tapers for micro-resonator coupling.

Main Methods:

• Developed a novel coupling scheme utilizing an ECF with microspheres deposited on its exposed channel.
• Excited WGMs via the evanescent field of the fiber's guided modes, with the ECF jacket protecting the microspheres.
• Utilized Fano resonance and controlled ECF mode launching conditions for spectral tunability and multi-particle WGM excitation.

Main Results:

• Demonstrated a high degree of tunability in the reflection spectrum by varying ECF mode launching conditions and employing Fano resonance.
• Achieved controlled multi-particle WGM excitation, allowing for simultaneous or separate activation.
• Showcased a robust WGM coupling scheme that protects microspheres from external disturbances.

Conclusions:

• The proposed ECF-based WGM coupling scheme offers a stable and practical alternative to traditional fiber tapers.
• This method facilitates tunable WGM excitation and multi-particle control, paving the way for integrated optical devices.
• Potential applications include optical switches, modulators, multiplexed/distributed biosensing, and multi-point lasing.