| Citation: | ZHENG Yi-chen, WU Jin-hui, LIU Ji, ZHANG Bo-yang, YUAN Tao. Micro-displacement measurement based on opposed dual-surface differential conjugate vortex beam interference[J]. Chinese Optics. doi: 10.37188/CO.2026-0097 |
To address the limitations of conventional conjugate vortex beam interference-based micro-displacement measurement methods, including limited rotation-angle variations of interference patterns and insufficient capability for sub-nanometer displacement detection, a micro-displacement measurement method based on opposed dual-surface differential conjugate vortex beam interference is proposed. The proposed method exploits the linear relationship between the rotation angle of the conjugate vortex interference pattern and the phase difference between two interferometric paths, converting micro-displacement into the angular rotation of petal-shaped interference patterns. To overcome the constraints imposed by camera pixel resolution and pattern distortion on tiny rotation-angle extraction, an opposed dual-surface differential optical path is developed, where two conjugate vortex beams interact with opposite surfaces of the same target. Compared with the conventional single-surface reflection configuration, the proposed structure doubles the relative optical path difference, thereby theoretically doubling the interference-pattern rotation angle under identical displacement conditions. Furthermore, an H-Nets model based on circular harmonic convolution is introduced to extract rotation-equivariant features from the rotating interference patterns. Continuous angular variations are encoded as phase shifts in the complex-valued feature space, enabling stable characterization of tiny rotation angles and accurate displacement inversion. Experimental results demonstrate that, within a displacement range of 0–500 nm, the maximum absolute error is below 0.61 nm, with a mean absolute error of 0.37 nm. The proposed method achieves enhanced micro-displacement measurement accuracy and stability through the synergistic integration of differential optical-path amplification and rotation-equivariant feature decoding.
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