Integrating-bucket phase stabilization method for fiber-optic fringe projector

Abstract

Ac phase tracking technique (PTAC) is an established and effective method for phase stabilization of fiber-optic fringe projectors (FoFP), but it may reduce the fringe visibility owing to the introduction of an extra sinusoidal phase modulation. In this paper we propose an integrating-bucket method to stabilize the phase of FoFPs which is applicable to both linear phase shifting (LPS) profilometry and sinusoidal phase shifting (SiPS) profilometry. The method requires no extra modulation of the interference phase; instead, it divides the interference signal period into N (N > 2) episodes with equal time intervals and directly integrates these episodes to obtain N discrete data. By manipulating these data the interference phase can be calculated and accordingly phase disturbance can be eliminated by the feedback loop. The proposed method is as effective as the PTAC technique but at the same time more computationally efficient because the operations involved are merely add, subtraction and arctangent solution. We built a digital phase controller with the proposed method, and managed to restrict the maximum phase drift of an FoFP to within 15 mrad in 5 min for both LPS and SiPS, which is similar to the result obtained with the PTAC technique. What’s more, we measured the mean value variation of the recovered phase map of a stabilized FoFP profilometer, and results are 30 mrad for LPS and 50 mrad for SiPS in 5 min.