  We investigate an integrated optical chip immersed in atomic vapor providing
several waveguide geometries for spectroscopy applications. The narrow-band
transmission through a silicon nitride waveguide and interferometer is altered
when the guided light is coupled to a vapor of rubidium atoms via the
evanescent tail of the waveguide mode. We use grating couplers to couple
between the waveguide mode and the radiating wave, which allow for addressing
arbitrary coupling positions on the chip surface. The evanescent atom-light
interaction can be numerically simulated and shows excellent agreement with our
experimental data. This work demonstrates a next step towards miniaturization
and integration of alkali atom spectroscopy and provides a platform for further
fundamental studies of complex waveguide structures.
