Vibration analysis by modulated time-averaged speckle shearing interferometry

An optical fibre based, speckle shearing interferometer for out-of-plane time-averaged vibration analysis is described. The technique uses a highly birefringent optical fibre to illuminate a test object with equal intensities of light guided by the orthogonal polarization eigenstates of the fibre. Phase modulation between the sheared images is readily achieved, without mechanical movement of components, by sinusoidally strain modulating the relative phase of the polarization states in the fibre. A Wollaston prism is used to obtain two sheared images with adjustable shear.