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

TL;DR

This paper introduces a cryogenic optical cavity setup that maintains high coupling efficiency during cooling without realignment, achieved through prealignment and thermal contraction compensation, enabling advanced quantum optomechanical experiments.

Contribution

The paper demonstrates a novel cryogenic optical cavity setup with over 90% coupling efficiency that remains stable during cooling without realignment.

Findings

Achieved >90% coupling efficiency at mK temperatures

Maintained alignment during cooling without realignment

Used Invar components to minimize thermal contraction

Abstract

We present a cryogenic setup where an optical Fabry-Perot resonator is coupled to a single-mode optical fiber with coupling efficiency above 90% at mK temperatures without realignment during cooling down. The setup is prealigned at room temperature to compensate for the thermal contraction and change of the refractive index of the optical components during cooling down. The high coupling efficiency is achieved by keeping the setup rotation-symmetric around the optical axis. The majority of the setup components are made of Invar (FeNi36) which minimizes the thermal contraction. High coupling efficiency is essential in quantum optomechanical experiments.