DISPERSION IN AN ELECTRONICALLY-SCANNED DUAL-WAVELENGTH LOW-COHERENCEINTERFEROMETER

An experimental evaluation, coupled with an appropriate theoretical an alysis, of a dual-wavelength low coherence (often termed white-light) interferometer (WLI) experiencing dispersion effects, is reported. The dual wavelength arrangement, typical of practical optical sensing sys tems that were employed, utilized an electronically-scanned WLI config uration with a Fabry-Perot interferometer as the sensing interferomete r, and a modified Mach-Zehnder configuration as the processing interfe rometer. The results analyze the situation that may be experienced whe re either the sensing or processing interferometer is dispersive, show ing that the central fringe in the visibility profile due to each wave length will no longer result at the same position as would otherwise o ccur in the absence of dispersion. In view of the importance of the we ll-known dispersion effects for practical remote sensors using low coh erence techniques, the extreme case is highlighted where the fringe pa tterns of each wavelength do not overlap at all with each other, refle cting real problems in the use of such apparatus in sensor application s, and offering a means to solutions for actual measurements.