Manipulation of Structured Light in an Atom-Clad Optical Nanofiber (conference Presentation)

Optical nanofibers (ONF) have been proved useful tools to probe cold atomic systems. Due to the intense evanescent field at their waist, ONFs have been used to probe or even trap atoms. However, very little experimental work has been done on exploiting the higher order modes (HOM) of such devices. The HOMs feature inhomogeneous polarization distributions around the ONF’s waist and can lead to the guiding of light carrying orbital angular momentum (OAM), via selective excitation of modes. In this work, we have experimentally studied the interaction between an ensemble of cold rubidium atoms and the HOMs of an ONF. The ONF, tailored to allow propagation of the first 6 guided modes at 780 nm, is embedded in a cold atomic ensemble and its modes are selectively excited by coupling vector beams from free-space. Using modal decomposition at the output of the ONF, we can calculate the transfer matrix of the system. This information, when combined with the amplitude extinction resulting from the scattering of the guided light by atoms surrounding the waist, allows us to non-destructively infer the modal excitation at the waist of the ONF. We further investigate the effect of temperature-induced strain on the modal decomposition at the waist and fiber output pigtail. Our results allow us to encode more than one quantum of information on the total angular momentum of a single guided photon. The inhomogeneous polarization distributions featured by the HOMs also offer a new tool to study chiral quantum systems.