Achromatic design of a photonic tricoupler and phase shifter for broadband nulling interferometry

Abstract

Nulling interferometry is one of the most promising technologies for imaging exoplanets within stellar habitable zones. The use of photonics for carrying out nulling interferometry enables the contrast and separation required for exoplanet detection. So far, two key issues limiting current-generation photonic nullers have been identified: phase variations and chromaticity within the beam combiner. The use of tricouplers addresses both limitations, delivering a broadband, achromatic null together with phase measurements for fringe tracking. Here, we present a derivation of the transfer matrix of the tricoupler, including its chromatic behaviour, and our 3D design of a fully symmetric tricoupler, built upon a previous design proposed for the GLINT instrument. It enables a broadband null with symmetric, baseline-phase-dependent splitting into a pair of bright channels when inputs are in anti-phase. Within some design trade space, either the science signal or the fringe tracking ability can be prioritised. We also present a tapered-waveguide $180^{\circ }$-phase shifter with a phase variation of $0.6^{\circ }$ in the $1.4-1.7\mu$m band, producing a near-achromatic differential phase between beams{ for optimal operation of the tricoupler nulling stage}. Both devices can be integrated to deliver a deep, broadband null together with a real-time fringe phase metrology signal.

arXiv comment20 pages, 17 figures, submitted to Journal of Astronomical Telescopes, Instruments, and Systems

References in corpus (5)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• First Light for GRAVITY: Phase Referencing Optical Interferometry for the Very Large Telescope Interferometer
• Low bend loss waveguides enable compact, efficient 3D photonic chips
• First on-sky demonstration of an integrated-photonic nulling-interferometer: The GLINT instrument
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Cited by in corpus (3)

• 2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments
• Astrophotonics -- current capabilities and the road ahead
• Tri-coupler geometries for achromatic nulling interferometry in the near-infrared