A modified OAM Mach-Zehnder interferometer for displacement measurement

In this study, a modified OAM Mach-Zehnder (M-Z) interferometer for displacement measurement has been proposed and experimentally proved, where two conjugate OAM beams propagate on two arms respectively. The traditional M-Z OAM interferometer was modified by introducing a reflection module in the reference arm. As a result, the optical path shift mismatched reflections on two arms is eliminated, which improves the quality of the petal-like pattern produced by the interference between two conjugate OAM beams. And a significant rotation angle of the petal-like pattern vs. the tiny displacement of the tested object can be clearly observed. By accurately measuring the rotation angle of the petal-like pattern, a tiny displacement ranging from 50 to 800 nm with resolution of similar to 50 pm has been measured successfully.