Abstract
We propose a new family of achromatic phase shifters for infrared nulling interferometry. These key optical components can be seen as optimized Fresnel rhombs, using the total internal reflection phenomenon, modulated or not. The total internal reflection indeed comes with a phase shift between the polarization components of the incident light. We propose a solution to implement this vectorial phase shift between interferometer arms to provide the destructive interference process needed to disentangle highly contrasted objects from one another. We also show that, modulating the index transition at the total internal reflection interface allows compensating for the intrinsic material dispersion in order to make the subsequent phase shift achromatic over especially broad bands. The modulation can be induced by a thin film of a well-chosen material or a subwavelength grating whose structural parameters are thoroughly optimized. We present results from theoretical simulations together with preliminary fabrication outcomes and measurements for a prototype in Zinc Selenide.
Highlights
Despite the tremendous progress in the indirect detection techniques and the increasing number of detected extrasolar planetary objects, exoplanet hunters are still struggling with the technical challenges hampering the conception of an observatory that will allow the direct imaging and characterization of Earth-like planets
The nulling interferometry consists in adjusting the phases of the beams coming from various telescopes to produce a fully destructive interference on the optical axis, nulling the starlight while letting the planetary signal pass through
We recently proposed the idea of using subwavelength gratings in total internal reflection (TIR) incidence as achromatic phase shifters [10]
Summary
Despite the tremendous progress in the indirect detection techniques and the increasing number of detected extrasolar planetary objects, exoplanet hunters are still struggling with the technical challenges hampering the conception of an observatory that will allow the direct imaging and characterization of Earth-like planets. Even best telescopes can’t see them directly because of the large flux ratio between the planet and its parent star. An Earth-like exoplanet is typically ∼ 109 times fainter than its host star in the visible spectrum, ∼ 106 in the thermal infrared. Among all raised ideas to reach the needed very high dynamic range, such as visible coronagraphy, infrared nulling interferometry proposed by R. The nulling interferometry consists in adjusting the phases (with a π phase shift in the two-telescope case) of the beams coming from various telescopes (two or more) to produce a fully destructive interference on the optical axis, nulling the starlight while letting the planetary signal pass through
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