Orbital angular momentum beam-based interferometry for an in-plane displacement measurement.

In this Letter, a novel, to the best of our knowledge, robust interferometry based on orbital angular momentum (OAM) is proposed for an in-plane displacement measurement. A vortex beam (VB) is incident onto a diffraction grating, and the ±1st order diffraction beams with conjugate OAM interfere with each other. By demodulating the petal-like interferogram, the in-plane displacement of the grating can be determined. Theoretically, a 1° rotation of the interferogram corresponds to a displacement of 2.31 nm. Experimental results revealed that the maximum measurement error was less than 3.35%. The proposed measurement system combines the advantages of both OAM interferometry and grating interferometry. It adopts the grating pitch instead of the wavelength as the measurement reference, providing robust immunity to environmental disturbances while maintaining high resolution simultaneously.