Chip-Based Optical Interactions with Rubidium Vapor

Chip-based optical waveguides that are evanescently coupled to strongly resonant vapors offer significant potential for realizing low-photon and single-photon nonlinear interactions in a system consistent with an integrated optics approach. We demonstrate evanescent coupling of rubidium (Rb) vapor with chip-based optically guiding silicon-nitride nanowires in a small, robust and portable set-up. We perform spectroscopy of Rb D2 resonances, with optical depths of 2 observed for the guided mode. We observe noticeable broadening and shifting of the D2 lines with respect to their free-space counterparts. This is consistent with the homogeneous broadening due to transit-time effects, and inhomogeneous broadening and shifting due to Van der Waals interactions between the atoms and the surface of the waveguide. We also demonstrate excitation of ring resonators coupled to these waveguides.