Differential phase measurements in low-coherence interferometry without 2 pi ambiguity

Quantitative phase measurements by low-coherence interferometry and optical coherence tomography are restricted by the well-known 2 pi ambiguity to pa th-length differences smaller than lambda /2. We present a method that over comes this ambiguity. Introducing a slight dispersion imbalance between ref erence and sample arms of the interferometer causes the short and long wave lengths of the source spectrum to separate within the interferometric signa l. This causes the phase slope to vary within the signal. The phase-differe nce function between two adjacent sample beam components is calculated by s ubtraction of their phase functions obtained from phase-sensitive interfero metric signal recording. Because of the dispersive effect, the phase differ ence varies across the interferometric signal. The slope of that phase diff erence is proportional to the optical path difference, without 2 pi ambigui ty. (C) 2001 Optical Society of America.