Picometer-Displacement Measurements With Global Phase Demodulation Method Using OAM Interferometer

Orbital angular momentum (OAM) interferometers are extensively employed in ultraprecise metrology. Conventional demodulation techniques for petal-like interference patterns typically rely on localized measurements of individual petals or radial intensity distributions. However, such localized approaches face inherent limitations imposed by interference pattern quality, ultimately constraining measurement accuracy. Hence, this study introduces a phase demodulation method that integrates an adaptive polar transform (APT) with azimuthal spectrum analysis, enabling global Fourier domain characterization of petal-like fringe patterns. Experimental validation demonstrates exceptional performance, as at a 100-nm displacement, the system achieves a maximum absolute error of 0.39 nm with 0.23-nm repeatability. The configuration maintains stability better than 0.2 nm within 10 s, and a strong anti-vibration capability. Furthermore, the proposed approach attains microdisplacement measurement precision of ±0.13 nm, demonstrating exceptional potential for monitoring in microfluidic and lab-on-a-chip environments, resolving trace biochemical concentrations and tiny thermal fluctuations, as well as demonstrating excellent potential for microdeformation measurements of mechanical components.