Enhanced measurement of tiny rotational angles using conjugate orbital angular momentum modes.

We report the enhanced experimental measurement of tiny rotational angles using two conjugate OAM modes upon rotation of a Dove prism. The two conjugate OAM modes interfere in a petal-like pattern and the orientation of the pattern depends on the phase difference between the two modes. We propose an accurate method of digital image processing to measure the tiny rotational angles of the Dove prism. In the presence of an imperfect pattern and light path, the measurement precision was enhanced by a factor of l. This scheme has potential applications in high-precision sensing and monitoring of tiny rotation angles.