Rotational Motion Encoder Based on Optical Vortex Interferometry

We present a prove of rotational encoder concept based on a coherent optical vortex interferometry to determine small angular rotations. Employing a computer processing of resulting images of interferograms with a characteristic circular motion of the zero intensity allows exact measurements of angular movement of rotational stage over a range of about ±21° with the smallest measurable displacement around 0.75 arcsec.