FIRST is a post Extreme Adaptive-Optics (ExAO) spectro-interferometer operating in the Visible (600-800 nm, R∼400). Its exquisite angular resolution (a sensitivity analysis of on-sky data shows that bright companions can be detected down to 0.25λ/D) combined with its sensitivity to pupil phase discontinuities (from a few nm up to dozens of microns) makes FIRST an ideal self-calibrated solution for enabling exoplanet detection and characterization in the future. We present the latest on-sky results along with recent upgrades, including the integration and on-sky test of a new spectrograph (R∼3,600) optimized for the detection of Hα emission from young exoplanets accreting matter.
Integrated optics are used to achieve astronomical interferometry inside robust and compact materials, improving the instrument’s stability and sensitivity. To perform differential phase measurements at the Hα line (656.3 nm) with the 600- to 800-nm spectro-interferometer fibered imager for a single telescope (FIRST), a photonic integrated circuit (PIC) is being developed in collaboration with TEEM Photonics. This PIC performs the interferometric combination of the beams coming from subapertures selected in the telescope pupil, thus implementing the pupil remapping technique to restore the diffraction limit of the telescope. In this work, we report on the latest developments carried out within the FIRST project to produce a high-performance visible PIC. The PICs are manufactured by TEEM Photonics, using their technology based on K + : Na + ion exchange in glass. The first part of the study consists in the experimental characterization of the fundamental properties of the waveguides, to build an accurate model, which is the basis for the design of more complex functions. In the second part, theoretical designs and their optimization for three types of combiner architectures are presented: symmetric directional coupler, asymmetric directional couplers, and ABCD cells, including achromatic phase shifters.
Integrated optics are used to achieve astronomical interferometry inside robust and compact materials, improving the instruments stability and sensitivity. In order to perform differential phase measurements at the Hα line (656.3nm) with the 600-800nm spectro-interferometer FIRST, a photonic integrated circuit (PIC) is being developed. This PIC performs the visible combination of the beams coming from the telescope pupil sub-apertures. In this work, TEEM Photonics waveguides fabricated by K+ : Na+ ion exchange in glass are characterized in terms of single-mode range and mode field diameter. The waveguide diffused index profile is modeled on Beamprop software. FIRST beam combiner building blocks are simulated, especially achromatic directional couplers and passive π/2 phase shifters for a potential ABCD interferometric combination.
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