Bottle microresonator with actively stabilized evanescent coupling.

Area of Science:

• Optics and Photonics
• Quantum Optics
• Microcavity Physics

Background:

• Whispering-gallery-mode (WGM) microresonators offer high optical confinement.
• Efficiently coupling light into and maintaining stable operation of these resonators is challenging.
• Evanescent coupling via subwavelength fibers is a common but sensitive method.

Purpose of the Study:

• To actively stabilize the evanescent coupling between a WGM bottle microresonator and a subwavelength fiber.
• To achieve long-term, critically coupled operation with minimal light loss.
• To demonstrate simultaneous stabilization of resonator mode frequency.

Main Methods:

• Utilized the Pound-Drever-Hall (PDH) technique for active feedback control.
• Employed a subwavelength-diameter fiber for evanescently coupling light to the microresonator.
• Implemented a feedback loop to actively adjust coupling parameters.

Main Results:

• Achieved active stabilization of the critically coupled resonator.
• Demonstrated a low residual transmission of (9±3)×10⁻³.
• Maintained stable coupling for over one hour.
• Simultaneously stabilized the resonator mode frequency.

Conclusions:

• Active stabilization using PDH technique enables robust evanescent coupling in WGM microresonators.
• The demonstrated method significantly reduces light loss and ensures long-term operational stability.
• This technique is crucial for applications requiring precise control of light-matter interactions in micro-optical systems.