Phase-shifter calibration and error detection in phase-shifting applications: a new method.

The phase-shifting technique is used in optical metrology to evaluate the local phase of a fringe pattern. Accurate calibration of the shifting device is often essential but sometimes hardly possible because of deviations of the fringe pattern from the ideal sinusoidal shape and because of a nonconstant phase shift between consecutive frames. We introduce a new technique for calculating the phase shift between frames even in the presence of high noise and nonsinusoidal fringe patterns. In addition, this technique permits the identification of different error sources such as low signal-to-noise ratio, higher harmonics contained in the fringe pattern, and nonconstant phase shift.