Novel laser machining of optical fibers for long cavities with low birefringence

TL;DR

This paper introduces a new laser machining technique for optical fibers that produces highly symmetric, low-birefringence mirrors, enabling long, high-finesse Fabry-Perot cavities suitable for advanced quantum optics applications.

Contribution

The authors developed a laser machining process with fiber rotation to create symmetric, low-birefringence fiber mirrors for long cavities, improving upon previous methods.

Findings

Achieved high finesse in long cavity lengths (>200 μm)

Produced fiber mirrors with remarkably low birefringence

Validated mirror quality through cavity finesse and polarization measurements

Abstract

We present a novel method of machining optical fiber surfaces with a CO${}_2$ laser for use in Fiber-based Fabry-Perot Cavities (FFPCs). Previously FFPCs were prone to large birefringence and limited to relatively short cavity lengths ($\le$ 200 $\mu$m). These characteristics hinder their use in some applications such as cavity quantum electrodynamics with trapped ions. We optimized the laser machining process to produce large, uniform surface structures. This enables the cavities to achieve high finesse even for long cavity lengths. By rotating the fibers around their axis during the laser machining process the asymmetry resulting from the laser's transverse mode profile is eliminated. Consequently we are able to fabricate fiber mirrors with a high degree of rotational symmetry, leading to remarkably low birefringence. Through measurements of the cavity finesse over a range of cavity lengths and the polarization dependence of the cavity linewidth, we confirmed the quality of the produced fiber mirrors for use in low-birefringence FFPCs.