Quadrature wavelength scanning interferometry

Abstract

A novel method to double the measurement range of wavelength scanning interferometery (WSI) is described. In WSI the measured optical path difference (OPD) is affected by a sign ambiguity, i.e. from an interference signal it is not possible to distinguish whether the OPD is positive or negative. The sign ambiguity can be resolved by measuring an interference signal in quadrature. A method to obtain a quadrature interference signal for WSI is described and a theoretical analysis of the advantages is reported. Simulations of the advatanges of the technique and of signal errors due to non-ideal quadrature are discussed. The analysis and simulation are supported by experimental measurements to show the improved performances.

Smart optical coordinate and surface metrology

“…• Non-scanning technologies: While CSI, FVM and CM represent the cutting edge in areal surface topography measurement, these technologies are inherently limited in terms of their measurement speed by the fact that they require a scanning operation in at least one axis [17]. For real-time applications, non-scanning areal surface texture measurement technologies, such as wavelength-scanning interferometry [70,71], dispersed reference interferometry [72], chromatic CM [68] and micro-scale fringe projection are required [73]. These technologies are commonly capable of significant decreases in measurement time, generally at the cost of decreased precision and/or accuracy.…”