One of the objectives of modern astronomy is the characterization of terrestrial exoplanets orbiting Sun-like stars in the mid-infrared, where instruments face requirements that can only be overcome by nulling interferometry. Particularly, optical effects such as polarization aberrations require careful attention for they deteriorate the null depth. Using the optical design of the Exoplanet Explorer concept study, we simulate the influence of polarization aberrations over the 3–20μm band, analyze their impact on the null depth and propose multiple compensation strategies for polarization aberrations. Furthermore, we present our nulling interferometry test bench, where we will experimentally investigate polarization aberrations in the beam combiner and phase shifter to provide more insights into the required polarization errors. These results will be used to implement polarization control subsystems in our 4-beams broadband nulling interferometry test bench CAPIBARA (Combining 4 APertures for mid-Infrared Broadband Analysis of Rocky-exoplanets Atmospheres). ... Read more

The optical design layout of a single-spacecraft nulling interferometer is presented here as part of an ESA-initiated study to explore the design parameters and performance of an interferometric concept based on a single spacecraft with multiple
sub-apertures. Launch constraints drive the ray-traced model to cover the entire optical chain, from the telescope entrance to the null output after the recombination scheme. A trade-off among several telescope architectures led to the choice of a compact two-mirror solution consisting of four 2.5m diameter telescopes arranged in a linear configuration with an extended baseline. Optical performance at the null output is evaluated, confirming compatibility with starlight suppression
targets and establishing the key figures of merit for the interferometer. This work presents the first integrated optical design of the mission concept, laying the groundwork for future iterations that include mechanical, thermal, and control aspects. ... Read more

Hi-5 is a proposed L' band high-contrast nulling interferometric instrument for the visitor focus of the Very Large Telescope Interferometer (VLTI). As a part of the ERC consolidator project called SCIFY (Self-Calibrated Interferometry For exoplanet spectroscopY), the instrument aims to achieve sufficient dynamic range and angular resolution to directly image and characterize the snow line of young extra-solar planetary systems. The spectrometer is based on a dispersive grism and is located downstream of an integrated optics beam-combiner. To reach the contrast and sensitivity specifications, the outputs of the I/O chip must be sufficiently separated and properly sampled on the Hawaii-2RG detector. This has many implications for the photonic chip and spectrometer design. We present these technical requirements, trade-off studies, and phase-A of the optical design of the Hi-5 spectrometer in this paper. For both science and contract-driven reasons, the instrument design currently features three different spectroscopic modes (R=20, 400, and 2000). Designs and efficiency estimates for the grisms are also presented as well as the strategy to separate the two polarization states. ... Read more