Realignment-free cryogenic macroscopic optical cavity coupled to an optical fiber

Area of Science:

• Quantum optics
• Cryogenic engineering
• Optomechanics

Background:

• High coupling efficiency between optical resonators and fibers is critical for quantum optomechanical experiments.
• Maintaining this efficiency at millikelvin temperatures presents significant engineering challenges due to thermal contraction and material property changes.

Purpose of the Study:

• To present a novel cryogenic setup enabling high-efficiency optical coupling at millikelvin temperatures.
• To demonstrate a method for achieving stable, high coupling efficiency without in-situ realignment during cooling.

Main Methods:

• Designing a rotation-symmetric setup to minimize alignment drift.
• Utilizing Invar (FeNi36) for core components to reduce thermal contraction.
• Prealigning the optical Fabry-Perot resonator and optical fiber at room temperature to compensate for cryogenic effects.

Main Results:

• Achieved coupling efficiency exceeding 90% at millikelvin temperatures.
• Demonstrated stability of the coupling without requiring realignment during the cooling process.
• Successfully mitigated thermal contraction and refractive index changes through material selection and prealignment.

Conclusions:

• The presented cryogenic setup provides a robust solution for high-efficiency optical coupling in quantum optomechanical systems.
• The prealignment strategy and rotation-symmetric design are effective in maintaining optical coupling stability at ultra-low temperatures.