Chip-scale sub-Doppler atomic spectroscopy enabled by a metasurface integrated photonic emitter.

This article focuses on the demonstration of chip-scale sub-Doppler spectroscopy using an integrated and fiber-coupled photonic-metasurface device. The device combines a photonic mode-expanding grating emitter with a monolithically integrated tilt-compensating dielectric metasurface, a microfabricated rubidium (Rb) vapor cell, and a mirror to generate a surface-normal, collimated beam for precision atomic spectroscopy without requiring alignment between components. A two-cavity optical model is developed to interpret the atomic spectra, showing good agreement with experimental results across varying atomic densities. This integration approach enables compact, alignment-free atomic spectroscopy and suggests pathways toward manufacturable quantum sensors based on warm atomic vapors with potential for further on-chip integration of lasers and detectors.