Achromatic broadband nulling using a phase grating

Abstract

In nulling interferometry, an on-axis source such as a star is interferometrically attenuated (“nulled”) so that the surrounding area can be investigated for fainter objects. One challenge in nulling interferometry is to achieve a deep achromatic null with a simple optical system. One such system is a “fiber nuller,” a nulling interferometer in which light from two incoming beams is combined at the tip of a single-mode optical fiber. This Letter describes the use of a diffraction grating to adjust the phase of the light so that achromatic destructive interference is achieved at the fiber tip. A deep (4×10−5) achromatic null was achieved in the astronomical K-band, thus showing a performance with the potential for observing brown dwarfs and bright (young or hot) extrasolar giant planets.