Inverse-design based photonic spin splitter and optical switch for miniaturized cold-atom magnetometer

With the development of cold atom physics and maturation of micro/nano processing integration technology, new opportunities for the integration and miniaturization of cold-atom magnetometer systems have arisen. In addition to reduced footprint and lower cost advantages, integrated photon-atom chips provide a unique physical platform for miniaturized cold atom systems. Especially, on-chip optical field modulation devices for the 780/795 nm band are indispensable for the cold-atom magnetometer systems. An inverse-designed photonic spin splitter and an optical switch for a miniaturized cold-atom magnetometer system have been designed using a direct binary search and concomitant method, respectively. The designed photonic spin splitter spatially resolves the spin directionality of incident photons by driving the incident photons to different waveguides according to their spins. The final device achieved a maximum contrast of 3.01% and a contrast ratio of 81.04%. The experimental results show that the angular resolution of the device can reach 0.35°. A Kerr nonlinear optical switch is designed with a footprint of 5.5 μm × 5.5 μm, corresponding to a switching ratio of more than 10 dB for both switching states with a maximum insertion loss of 0.79 dB. The flexibility provided by miniaturization enables the future development of high-resolution and sensitive magnetic detection techniques.