A quarter-wave phase-stepping algorithm for fiber-optic electronic speckle pattern interferometry using zero-crossing triggers

An efficient phase-stepping method for the use in fiber-optic electronic speckle pattern interferometry is proposed. A fiber-optic Michelson interferometer is phase-modulated, and the zero-crossing points of a back-reflected interference signal, that have consecutive pi phase difference, are used to trigger the charged-coupled device camera to capture specklegrams with pi/2 phase difference. A phase error of less than 3 mrad with 100-Hz image capture speed has been obtained in an open-loop configuration. Also, it has-been experimentally shown that the phase-stepping accuracy of the proposing method does not depend on the nonlinear actions of the phase modulator.