High precision phase-shifter modulator in a shearing interferometric system

Abstract

Shearing interferometers measure small angular variations such as the angle between a star and a planet measured from the Earth. The detected intensity pattern usually presents few fringes or less, often just a fraction of a fringe that may be interpreted as a misalignment error. Exact alignment is a challenge in the calibration of an interferometer. The optical components frequently introduce tilt making it very difficult to retrieve the phase. Spatial light modulators (SLM) are traditionally used to shift the phase to compensate small amounts of tilt, improving the accuracy of the phase measurement. We implement a phase retrieving algorithm to evaluate the accuracy of the phase shifter based on a SLM in a vectorial shearing interferometer (VSI). Our VSI is based on a Mach-Zehnder configuration. With the SLM we are able to compensate the phase error due to the alignment and the fabrication errors. Our results also demonstrate that we may correct error in the OPD and the magnitude of the tilt in the observation plane.