NOISY FRINGE PATTERN DEMODULATION BY AN ITERATIVE PHASE-LOCKED LOOP

The phase locked loop (PLL) technique applied to demodulate two-dimens ional carrier-frequency fringe patterns has been developed recently. H ere we present an extension to the basic PLL scheme to demodulate nois y fringe patterns. This modified technique estimates the phase in the fringe pattern iteratively; that is, the first wavefront estimation is done using a flat reference phase and the second iteration takes the demodulated phase found in the first iteration as the new reference. T he third demodulating iteration uses the second phase estimation as th e reference and so on, until further changes in the detected wavefront fall below a predefined threshold. During the iterative process the b andwidth of the iterative PLL system is gradually decreased to improve the signal-to-noise ratio of the detected phase as well as to resolve noise-generated phase inconsistencies.