Nano-Displacement Measurement System Using a Modified Orbital Angular Momentum Interferometer

In this study, a nano-displacement measurement system is proposed and demonstrated both theoretically and experimentally, which was based on a modified Mach-Zehnder (M-Z) interferometer using two conjugated orbital angular momentum (OAM) beams. In contrast to the previous M-Z-based OAM interferometer, a reflection module is inserted into the reference arm instead of a simple mirror. As a result, the effect of the transverse position-dependence phase-shift caused by the dove prism can be clearly eliminated and a stable and robust (off-axis insensitive) petal-like interference pattern can be obtained successfully. More importantly, a significant rotation angle of the petal-like pattern vs. the tiny displacement of the tested object can be clearly observed. In accordance with the modified measurement setup, a novel phase-demodulation method enabling to quickly and accurately characterize the rotation angle of the petal-like interference-patterns is proposed and demonstrated also. A tiny displacement ranging from 50 to 800 nm with resolution of similar to 50 pm has been measured successfully. The proposed approach may find applications in not only the ultra-high precision displacement sensor, but also the temperature, strain, and refractive index sensors.

Automated summary

A nano-displacement measurement system based on a modified Mach-Zehnder interferometer was proposed and demonstrated theoretically and experimentally, achieving stable and robust interference patterns. By introducing a reflection module and a novel phase-demodulation method, tiny displacements ranging from 50 to 800 nm were successfully measured with a resolution of about 50 pm. This approach may have applications in ultra-high precision displacement sensors as well as temperature, strain, and refractive index sensors.