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

摘要

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 FFPCswere prone to large birefringence and limited to relatively short cavitylengths ($\le$ 200 $\mu$m). These characteristics hinder their use in someapplications such as cavity quantum electrodynamics with trapped ions. Weoptimized the laser machining process to produce large, uniform surfacestructures. This enables the cavities to achieve high finesse even for longcavity lengths. By rotating the fibers around their axis during the lasermachining process the asymmetry resulting from the laser's transverse modeprofile is eliminated. Consequently we are able to fabricate fiber mirrors witha high degree of rotational symmetry, leading to remarkably low birefringence.Through measurements of the cavity finesse over a range of cavity lengths andthe polarization dependence of the cavity linewidth, we confirmed the qualityof the produced fiber mirrors for use in low-birefringence FFPCs.