We report on simple interferometric technique for the measurement of piezoelectric coefficients of thin films using GaAs:Cr adaptive photodetectors in the geometry of modified Mach-Zehnder interferometer. The technique needs no special vibroinsulation and automatically adjusts and keeps the operation point of the interferometer. Strong hysteresis effects with a slightly asymmetric form of the hysteresis loop were observed at the dependence of d(33) coefficients of the Pb(Zr, Ti)O-3 (PZT) thin film versus DC electric field. The obtained values of d33 coefficients are in agreement with known data. (C) 2003 Elsevier Ltd. All rights reserved.