Space-borne nulling interferometers have long been considered as the bestoption for searching and characterizing extra-solar planets located in thehabitable zone of their parent stars. Solutions for achieving deep starlightextinction are now numerous and well demonstrated. However they essentially aimat realizing an achromatic central null in order to extinguish the star. Inthis communication is described a major improvement of the technique, where theachromatization process is extended to the entire fringe pattern. Thereforehigher Signal-to-noise ratios (SNR) and appreciable simplification of thedetection system should result. The basic principle of this Fully achromaticnulling interferometer (FANI) consists in inserting dispersive elements alongthe arms of the interferometer. Herein this principle is explained andillustrated by a preliminary optical system design. The typical achievableperformance and limitations are discussed and some initial tolerancerequirements are also provided
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