Atomic spectroscopy on a chip

Guiding light through hollow optical waveguides has opened the field of photonics to the investigation of non-solid materials that have all the convenience of integrated optics. Of particular interest is the confinement of atomic vapours, such as rubidium, because of its wide range of applications, including slow and stopped light(1), single-photon nonlinear optics(2), quantum information processing(3), precision spectroscopy(4) and frequency stabilization(5). Here, we present the first monolithically integrated rubidium vapour cell using hollow-core antiresonant reflecting optical waveguides ( ARROWs) on a silicon chip. The cells have a footprint of less than 1 cm(2), fully planar fibre-optical access, and a cell volume more than 7 orders of magnitude less than conventional bulk cells. The micrometre-sized mode areas enable high beam intensities over near centimetre lengths. We demonstrate optical densities in excess of 2, and saturation absorption spectroscopy on a chip. These results allow the study of atoms and molecules on a platform that combines the advantages of photonic-crystallike structures with integrated optics.