3D optical profilometry using a fiber optic Lloyd's mirror

Abstract

This study defines measurements of three-dimensional rigid-body shapes by using a fiber optic Lloyd’s mirror. A fiber optic Lloyd's mirror assembly is basically a technique to create an optical interference pattern using real light point sources and their images. The generated fringe pattern thanks to this technique is deformed when projected on an object's surface. The deformed fringe pattern containing information of the object's surface profile is captured by a digital CCD camera. The two-dimensional Fourier transformation is applied to the image, which is digitized with a frame grabber card. After applying a band-pass filter to this transformed data in its spatial frequency domain, the twodimensional inverse Fourier transform is applied. Using the complex data obtained by the inverse Fourier transform, the phase information is determined. A phase unwrapping algorithm is applied to eliminate discontinuities in the phase information and to make the phase data continuous. Finally, the continuous data determines the depth information and the surface topography of the object. It is illustrated for the first time that the use of such a fiber optic Lloyd's system increases the compactness and the stability of the fringe projection system. Such a fiber optic Lloyd’s system which provides an accurate non-contact measurement without contaminating and harming the object surface has a wide range of applications from laser interference lithography (LIL) in nano-scale to macro-scale interferometers.