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Quantum technologies

Dieter Meschede's research group
Home Fibre cavity QED Fibre mirror fabrication

Fiber end face mirror fabrication

In our fiber cavity QED project we use optical fibers as cavity mirrors. We fabricate the cavity mirrors directly onto the plane end facets of cleaved single-mode fibers based on a procedure developed by J. Reichel [1]: A pulse of a focused CO2 laser beam a few milliseconds long ablates a few micrometer of glass from the center of the fiber end facet, leaving a shallow depression of approximately Gaussian shape. In this way, small radii of curvature (~100 µm) can be achieved, yielding small mode waists and mode volumes. Furthermore, a slight reflow of the molten glass under the influence of its surface tension produces a very smooth surface which can be coated with a reflective coating of low scatter loss. Our fiber endfacet machine also incorporates a Mirau interferometric microscope, which allows high-resolution surface characterization by phase-shift interferometry. Mode-matching of cavity and fiber modes together with a low-loss optical coating can achieve the desired high optical in- and outcoupling efficiency. The influence of the non-spherical mirror shape on the finesse and ways to reduce polarization mode splitting (birefringence) may need further investigation.

Fig.  1: Left: Cross-sectional image of a cleaved fiber endfacet after being processed with a CO2 laser beam in our interference microscope. Middle: True phase information obtained independently for each pixel using the phase shift interferometry technique. Right: Reconstructed surface tpopgraphy (false colour) obtained via a phase-unwrapping algorithm. Radius of curvature and ellipticity can now be determined precisely.



Fig. 2: Schematics for the setup for fiber end facet mirror fabrication

1. D Hunger et al, New J. Phys. 12, 065038 (2010) http://iopscience.iop.org/1367-2630/12/6/065038