LED source interferometer for microscopic fringe projection profilometry using a Gates' interferometer configuration

The fringe projection technique is considered one of the most reliable solutions for structured light technology, developed for non-contact three-dimensional (3D) data acquisition. When working with this technique, applying it on a microscopic scale, one often encounters some problems such as the limited depth of field of the projected fringe pattern, typical of the imaging lenses, or the formation of speckle-noise when laser interferometric fringes are projected, which are problems that can cause significant errors on test surfaces whose height exceeds the depth of field, and on which, the other hand, speckle noise affects the resolution of the technique. This paper presents a Gates' interferometer configuration with a LED source to project a fringe pattern without speckle noise and a very long field depth. We explain how a non-located sinusoidal fringe pattern can be obtained using two-beamsplitter cubes and a LED light source. Moreover, we compare measurements made using the LED and laser concerning a commercial contact profilometer.