Phase stepping in fiber-based speckle shearing interferometry

An optical-fiber-based speckle shearing interferometer for an out-of-plane displacement derivative measurement is described. The technique uses a highly birefringent optical fiber to illuminate a test object with equal amounts of orthogonally polarized light, and the interferometer is readily phase stepped, without mechanical movement of components, by strain modulation of the relative phase of the polarization states in the fiber. A Wollaston prism is used to produce two sheared images with adjustable shear.