Phase-measuring fiber optic electronic speckle pattern interferometer: phase step calibration and phase drift minimization

Abstract. A phase-measuring fiber optic electronic speckle pattern in- terferometer (ESPI) was recently constructed and demonstrated. In thisarrangement, phase stepping is introduced by stretching the fiber wrappedaround a piezoelectric transducer. Calibration of the phase step is criticalin phase measurement techniques for obtaining good phase plots. Meth-ods used for calibrating the stretcher are outlined and the drifts in thephase caused by fluctuations in temperature and mechanical stressesare discussed. Ways to minimize this drift are also presented. Subject terms: speckle interferometry; electronic speckle pattern interferometry.Optical Engineering 31(2), 315-321 (February 1992).phase step calibration is important in order to obtain error- free phase maps. Different methods for calibrating the piezoelectric transducer (PZT) in an interferometric arrangement13 as well as in a fiber optic interferometric sensor arrangement14 have been developed. Methods suchas phase-lock, sinusoidal extrema sensing, and employingsoftware routines to evaluate the phase from equations andintensity values are successful with specular interferometricfringes. On the other hand, the ESPI fringes are speckled.Even though good calibration can be obtained with phase-lock and sensing methods ,