  We demonstrate chip-scale sub-Doppler spectroscopy in an integrated and
fiber-coupled photonic-metasurface device. The device is a stack of three
planar components: a photonic mode expanding grating emitter circuit with a
monolithically integrated tilt compensating dielectric metasurface, a
microfabricated atomic vapor cell and a mirror. The metasurface photonic
circuit efficiently emits a 130 micrometer-wide $1/e^2$ diameter) collimated
surface-normal beam with only -6.3 dB loss and couples the reflected beam back
into the connecting fiber, requiring no alignment between the stacked
components. We develop a simple model based on light propagation through the
photonic device to interpret the atomic spectroscopy signals and explain
spectral features covering the full Rb hyperfine state manifold.
