  Light-atom interaction can be engineered by interfacing atoms with various
specially designed media and optical fibers are convenient platforms for
realization of compact interfaces. Here, we show that an optical fiber sensor
bearing a plasmonic metasurface at its tip can be used to detect modifications
of the Doppler-free hyperfine atomic spectra induced by coupling between atomic
and plasmonic excitations. We observed the inversion of the phase modulation
reflectivity spectra of Cesium vapor in presence of the metamaterial. This work
paves the way for future compact hybrid atomic devices with a cleaved tip as
substrate platform to host various two-dimensional materials.
