Meta-device for sensing subwavelength lateral displacement

Accurate transverse displacement measurement is essential for precise mask-to-wafer positioning in lithography. While lateral displacement metrology has achieved nanometer-level precision, the limitations imposed by coherent state and grating challenge in-situ measurement speed and precision. Here, we introduce a two-photon state transverse displacement measurement method utilizing a polarization gradient metasurface by employing two-photon state interference. Compared with the classical method, our new method can experimentally reduce the number of detected photons to around 3% with equivalent precision. These attributes make the two-photon state polarization gradient metasurface approach highly suitable for integration with semiconductor lithography processes and show its promise in realizing equivalent measurement precision within notably shorter acquisition durations, providing a robust solution for next-generation transverse displacement measurement requirements.