Proceedings Article | 28 August 2024
KEYWORDS: Nulling interferometry, Electrodes, Electrooptics, Waveguides, Optical path differences, Directional couplers, Mid infrared, Lithium niobate
This work aims to present a complex mid-infrared (L-band : 3.4μm - 4.1μm) astrophotonic chip made in Lithium Niobate (LiNbO3), an electro-optic crystal, using Titanium diffused waveguides. The L-band presents several key characteristics interesting in astrophysics, notably for imaging and characterise young exo-planetary systems, as well as exo-zodiacal disks. With the increasing interest in exo-planetary science, new instruments and projects are focusing in the mid infrared, such as METIS (ground-based), NOTT (ground based), or LIFE (space-based). Combining such projects with photonics and on-chip beam combination will allow for more compact instruments, easing their integration on ground or, even more so, space based projects, hence the interest for improving the performances of photonic building blocks used for astrophysics.
Here, we are presenting building blocks such as Y-splitters, directional couplers, unbalanced beam splitters... that have been optimised for the L-band in Lithium Niobate. Although such blocks have already been developed in the mid-IR in this material, we are here using a different crystal orientation and newer design that are producing lower losses and birefringence. In particular, a 4-telescope mid-infrared combiner (linked to the NOTT project) was made in order to achieve nulling interferometry in the L-band. We show that we have relatively low loss waveguides, controlled photometric splitters (20/80 flux ratio), as well as functional couplers and beam splitting techniques. Furthermore, we will implement the electro-optic effect in this chip, in order to have internal modulation, and to be able to finely tune the fringes and improve the contrast, allowing for a step further into compact nulling interferometry.
