Chiral long-period fiber grating based conjugate vortex beam interference for nano-displacement measurement

Abstract

A novel nano-displacement measurement system is proposed, which distinctively exploits the interference of conjugated vortex beams generated by a chiral long-period fiber grating (CLPG). The orbital angular momentum vortex beam generator in this system features a simple structure, enabling both flexible design and high-precision guarantee. Additionally, a modified Mach Zehnder interferometer is used for nano-displacement measurement, accompanied by the development of an optimized centroid rotation demodulation method. By combining image preprocessing with a Gaussian weighting approach, the proposed method effectively mitigates errors arising from petal-shaped interference pattern modulation, significantly improving demodulation accuracy and stability. As a result, the optimized centroid rotation demodulation method effectively reduces the errors caused by petal-shaped interference pattern modulation. Both theoretical analysis and experimental results demonstrate extremely high accuracy and good agreement. The displacement measurement sensitivity in the experiment is above 0.23358°/nm when the displacement ranges from 1 nm to 100 nm with a perfect linearity of 0.99997. Given its simple structure, strong robustness and excellent measurement accuracy, this displacement measurement system, which capitalizes on the vortex beam generated by CLPG, is poised to play a crucial role and exert profound impacts in a variety of high-precision fields, such as micro/nano manufacturing, micro vibration monitoring, and biomedical measurement, etc.