COMPUTER-AIDED INTERFEROMETRIC MEASUREMENTS OF DRIFT AND PHASE-SHIFTER CALIBRATION FOR DIGITAL SPECKLE PATTERN INTERFEROMETRY

A phase-shifting digital speckle pattern interferometer (DSPI) has bee n calibrated using a Michelson interferometer. Calibration consists in measuring phase shifts generated by piezoelectric transducers (PZTs) and also to determine drift of the phase with time in the interferomet er arms. The calibration fringes are displayed live on the TV monitor and then processed slice by slice after recombination following their recording sequence (PZT voltage or time). Dark fringes are detected to compute the wavelength with good accuracy (lambda/170 theoretical) an d the optical path difference is stored in a datasheet for every slice . This leads to the measurements of the drift and the calibration of t he phase shifters with an accuracy about lambda/20. Out-of-plane and i n-plane optical fiber DSPIs have been successfully characterized using the same algorithm. The method presented also enables inexpensive dat a processing. Moreover the real-time measurement of the interferometer drift enables feedback loop active control during DSPI measurements.