Scalable Silicon Nitride OPA‐Based Free‐Space Photonic Interface for Chip‐Scale Atomic Magnetometry

Optically pumped atomic magnetometers (AMs) have become powerful tools for biomagnetic sensing owing to their ultrahigh sensitivity. However, their broader deployment increasingly requires compact, scalable, and low‐cost free‐space photonic interfaces capable of delivering high quality beams for light‐atom interaction. Here, we present a photonic chip based on a silicon nitride (SiN) optical phased array (OPA) that serves as a free‐space optical interface for AMs, combining high radiation efficiency, low divergence, and compatibility with batch fabrication. The device generates a stable linearly polarized beam with long propagation capability, a polarization extinction ratio of 26.1 dB, and a degree of linear polarization of 99.5%, with a maximum overall radiation efficiency of 26.5%. In a dual beam atomic magnetometer, the chip emitted beam serves as the probe beam and enables differential detection with a sensitivity of 8 fT/Hz 1/2 . To assess fabrication reliability and reproducibility, we performed a statistical analysis of 168 devices fabricated by deep‐ultraviolet (DUV) lithography, with more than 50% exhibiting radiation efficiencies above 15%. These results demonstrate a low‐cost, scalable photonic interface for chip integrated AMs and highlight its potential for large scale implementation.