Integrated in-fiber coupler for a whispering-gallery mode microsphere resonator

Area of Science:

• Photonics and Optical Engineering
• Nanotechnology
• Materials Science

Background:

• Whispering-gallery modes (WGMs) are crucial for optical resonators.
• Efficiently coupling light into microsphere resonators is challenging.
• Existing methods often lack compactness or durability.

Purpose of the Study:

• To propose and demonstrate an integrated in-fiber coupler for exciting WGMs in microsphere resonators.
• To achieve simultaneous excitation of WGMs with high-Q factor.
• To present a compact, durable, and easily operable WGM resonator.

Main Methods:

• Fabrication using femtosecond laser micromachining and fusing splicing.
• Creation of an inner air cavity with a suspended fiber core.
• Drilling a micro-channel for microsphere placement and evanescent coupling.

Main Results:

• Simultaneous observation of asymmetric Fano resonance lines (41.12 dB/nm and -18.46 dB/nm).
• Obtained a symmetrical Lorentz line with a high quality factor (9.32 × 10³).
• Demonstrated successful WGM excitation via evanescent field coupling.

Conclusions:

• The proposed in-fiber coupler enables efficient WGM excitation in microsphere resonators.
• The device exhibits a compact structure, convenient operation, and high durability.
• This integrated approach offers a promising platform for various photonic applications.