Integrated fibre resonator for atom detection using deep UV-lithography

We present a novel method to mount and align an optical fibre based resonator on the flat surface of an “atom chip” with ultra high precision. To this end, we have realised an alignment structure for a fibre resonator with a finesse of 101. The structures for mounting a pair of fibres, which constitute the fibre resonator, are produced by UV-lithography using SU-8 photoresist. From the measured finesse we calculated the coupling loss of the alignment structures to be smaller than 0.011dB, which corresponds to a pure lateral/angular misalignment of 120nm/0.3°. By special process optimisation we obtain an undercut profile, which assists in clamping the fibre.