SEMIAUTOMATIC PHASE-SHIFT CALIBRATION USING DIGITAL SPECKLE PATTERN INTERFEROMETRY

A semi-automatic method for calibrating phase shifting devices using a simple speckle pattern interferometric arrangement has been demonstrated, The method applies a simple two-beam digital speckle pattern interferometer (DSPI) and a personal computer with a frame grabber to achieve this purpose. The principle of the technique, together with the optical arrangement, is described and the system is then used for the calibration of a phase shifting device based on a piezoelectric transducer (PZT). The calibration results are presented, and advantages and limitations of the technique are discussed. Calibrating a PZT of 3.5 mu m full expansion in one-direction takes no more than 17 s and the RMS error of the calibration is 0.6% in terms of the derived sensitivity of the phase-shifting device. The error in phase measurement by a four-step phase stepping algorithm using the calibrated phase shifting device is of the order of 0.20 degrees (RMS) or 1/1800 of a wave.