Integrated optic beam combiners offer many advantages over conventional bulk optic implementations for astronomical imaging. To date, integrated optic beam combiners have only been demonstrated at operating wavelengths below 4 microns. Operation in mid-infrared wavelength region, however, is highly desirable. In this paper, a theoretical design technique based on three coupled waveguides is developed to achieve fully achromatic, broadband, polarization-insensitive, lossless beam combining. This design may make it possible to achieve the very deep broadband nulls needed for exoplanet searching.
Space-borne nulling interferometers have long been considered as the best option for searching and characterizing extra-solar planets located in the habitable zone of their parent stars. Solutions for achieving deep starlight extinction are now numerous and well demonstrated. However they essentially aim at realizing an achromatic central null in order to extinguish the star. In this communication is described a major improvement of the technique, where the achromatization process is extended to the entire fringe pattern. Therefore higher Signal-to-noise ratios (SNR) and appreciable simplifica…
A scheme to optimally design a beam combiner is discussed for any pre-determined fixed geometry nulling interferometer aimed at detection and characterization of exoplanets with multiple telescopes or a single telescope (aperture masking). We show that considerably higher order nulls can be achieved with 1-D interferometer geometries than possible with 2-D geometries with the same number of apertures. Any 1-D interferometer with N apertures can achieve a 2(N-1)-order null, while the order of the deepest null for a random 2-D aperture geometry interferometer is the order of the N-th term in the…
Integrated-optic components are being increasingly used in astrophysics, mainly where accuracy and precision are paramount. One such emerging technology is nulling interferometry that targets high contrast and high angular resolution. Two of the most critical limitations encountered by nullers are rapid phase fluctuations in the incoming light causing instability in the interference and chromaticity of the directional couplers that prevent a deep broadband interferometric null. We explore the use of a tricoupler designed by ultrafast laser inscription that solves both issues. Simulations of a …
(Abridged) Context: In the previous paper in this series, we identified that a pentagonal arrangement of five telescopes, using a kernel-nulling beam combiner, shows notable advantages for some important performance metrics for a space-based mid-infrared nulling interferometer over several other considered configurations for the detection of Earth-like exoplanets around solar-type stars. Aims: We aim to produce a physical implementation of a kernel-nulling beam combiner for such a configuration, as well as a discussion of systematic and stochastic errors associated with the instrument. Methods…
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 o…
Asgard/NOTT: L-band nulling interferometry at the VLTI -- III. The mid-infrared integrated optics beam combiner for NOTT
I. Physikalisches Institut der Universität zu Köln（科隆大学第一物理研究所）；Department of Physics & Astronomy, University of California, Los Angeles（加州大学洛杉矶分校物理与天文学系）；Institute of Astronomy, KU Leuven（鲁汶大学天体物理研究所）
Space borne nulling interferometry in the mid-infrared waveband is one of the most promising techniques for characterizing the atmospheres of extra-solar planets orbiting in the habitable zone of their parent star, and possibly discovering life markers. One of its most difficult challenges is the control of free-flying telescope spacecrafts moving around a central combiner in order to modulating the planet signal, within accuracy better than one micrometer at least. Moreover, the whole array must be reconfigured regularly in order to observe different celestial targets, thus increasing the ris…
Context: NOTT (formerly Hi-5) is a new high-contrast L' band (3.5-4.0 \textmu m) beam combiner for the VLTI with the ambitious goal to be sensitive to young giant exoplanets down to 5 mas separation around nearby stars. The performance of nulling interferometers in these wavelengths is affected both by fundamental noise from the background and by the contributions of instrumental noises. This motivates the development of end-to-end simulations to optimize these instruments. Aims: To enable the performance evaluation and inform the design of such instruments on the current and future infrastruc…
Tri-coupler geometries for achromatic nulling interferometry in the near-infrared
Astrophotonics Australia；Department of Astronomy, California Institute of Technology（加州理工学院天文学系）；Physics & Astronomy Department, University of California, Los Angeles（加州大学洛杉矶分校物理与天文系）
The Nulling Interferometry Cryogenic Experiment (NICE): Architecture, requirements, and preliminary warm precursor results
ETH Zürich, Institute for Particle Physics & Astrophysics（苏黎世联邦理工学院，粒子物理与天体物理研究所）；ETH Zürich, Department of Earth and Planetary Sciences（苏黎世联邦理工学院，地球与行星科学系）
The number of terrestrial exoplanets accessible to high-contrast coronagraphic imaging with large telescopes is limited by the smallest angular offset from bright stars at which coronagraphs can observe. However, it is possible to reach inside a telescopes coronagraphic regime by employing nulling interferometry across a telescopes pupil. Indeed, cross-aperture nulling interferometry can observe significantly closer to stars than typical coronagraphs, enabling observations even within the stellar diffraction core. Identifying an optimal nulling coronagraph, i.e., one with both a very small IWA…
Herein is discussed the performance of spaceborne nulling interferometers searching for extra-solar planets, in terms of their extinction maps projected on-sky. In particular, it is shown that the designs of Spatial Filtering (SF) and Achromatic Phase Shifter (APS) subsystems, both required to achieve planet detection and characterization, can sensibly affect the nulling maps produced by a simple Bracewell interferometer. Analytical relationships involving cross correlation products are provided and numerical simulations are performed, demonstrating marked differences in the aspect of extincti…
Aims: Optical interferometry from space for the purpose of detecting and characterising exoplanets is seeing a revival, specifically from missions such as the proposed Large Interferometer For Exoplanets (LIFE). A default assumption since the design studies of Darwin and TPF-I has been that the Emma X-array configuration is the optimal architecture for this goal. Here, we examine whether new advances in the field of nulling interferometry, such as the concept of kernel nulling, challenge this assumption. Methods: We develop a tool designed to derive the photon-limited signal to noise ratio of …
Technologies and novel components for broadband splitting and coupling in pairwise and nulling interferometry
Astrophotonics Australia, Monash（蒙纳士大学天体光子学澳大利亚）；Department of Astronomy, California Institute of Technology（加州理工学院天文系）；Physics & Astronomy Department, University of California, Los Angeles（加州大学洛杉矶分校物理与天文系）；LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎天文台LIRA实验室，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎大学）；Commissariat à l’Energie Atomique, Leti（法国原子能和替代能源委员会LETI实验室）；Astralis-AITC, Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天文与天体物理研究学院）；Department of Quantum Science, Research School of Physics, Australian National University（澳大利亚国立大学量子科学系，物理研究学院）
Understanding exoplanet formation and finding potentially habitable exoplanets is vital to an enhanced understanding of the universe. The use of nulling interferometry to strongly attenuate the central starlight provides the opportunity to see objects closer to the star than ever before. Given that exoplanets are usually warm, the 4 microns Mid-Infrared region is advantageous for such observations. The key performance parameters for a nulling interferometer are the extinction ratio it can attain and how well that is maintained across the operational bandwidth. Both parameters depend on the des…
Interferometry provides one of the possible routes to ultra-high angular resolution for X-ray and gamma-ray astronomy. Sub-micro-arc-second angular resolution, necessary to achieve objectives such as imaging the regions around the event horizon of a super-massive black hole at the center of an active galaxy, can be achieved if beams from parts of the incoming wavefront separated by 100s of meters can be stably and accurately brought together at small angles. One way of achieving this is by using grazing incidence mirrors. We here investigate an alternative approach in which the beams are recom…
Hi-5 is the L'-band (3.5-4.0 $μ$m) high-contrast imager of Asgard, an instrument suite in preparation for the visitor focus of the VLTI. The system is optimized for high-contrast and high-sensitivity imaging within the diffraction limit of a single UT/AT telescope. It is designed as a double-Bracewell nulling instrument producing spectrally-dispersed (R=20, 400, or 2000) complementary nulling outputs and simultaneous photometric outputs for self-calibration purposes. In this paper, we present an update of the project with a particular focus on the overall architecture, opto-mechanical design o…
The very recent years have seen a promising start in scientific publications making use of images produced by near-infrared long-baseline interferometry. The technique has reached, at last, a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arcsecond model-independent imaging. The Very Large Telescope Interferometer (VLTI) is on the path to be equipped with instruments capable to combine between four to six telescopes. In the framework of the VLTI second generation instruments Gravity and VSI, we propose a new beam combining concept using Integr…
Seidr update: photonic 'black magic' for high-contrast interferometry using kernel-nulling and photonic lanterns
University of Sydney（悉尼大学）；Observatoire de la Cote d’Azur, Université Côte d’Azur（蔚蓝海岸天文台，蔚蓝海岸大学）；Australian National University（澳大利亚国立大学）；University of Exeter（埃克塞特大学）；Leiden University（莱顿大学）
In the last few years, integrated optics (IO) beam combiners have facilitated the emergence of 4-telescope interferometers such as PIONIER or GRAVITY, boosting the imaging capabilities of the VLTI. However, the spectral range beyond 2.2microns is not ideally covered by the conventional silica based IO. Here, we propose to consider new laser-written IO prototypes made of GLS glasses, a material that permits access to the mid-infrared spectral regime. Our goal is to conduct a full characterization of our mid-IR IO 2-telescope coupler in order to measure the performance levels directly relevant f…
Status and performance of the Asgard/NOTT cold nulling camera
KU Leuven（荷语鲁汶大学）；Fornax（福纳克斯研究所）；University of Liège（列日大学）；Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences（孔科利天文台，匈牙利研究与教育网络天文学与地球科学研究中心）；Australian National University（澳大利亚国立大学）；Delft University of Technology（代尔夫特理工大学）；University of Arizona（亚利桑那大学）；University of Exeter（埃克塞特大学）；Université Côte d’Azur（蔚蓝海岸大学）；European Organisation for Astronomical Research in the Southern Hemisphere（欧洲南方天文台）；Large Binocular Telescope Observatory（大型双筒望远镜天文台）
In this communication is described a new type of Achromatic phase shifter (APS) suitable for both nulling interferometry and coronagraphy, based on a couple of crossed beamsplitter cubes, well-suited for equipping future spaceborne instruments searching for extra-solar planets located in a habitable zone. We present the general principle of this APS and discuss possible implementations into a nulling coronagraph telescope or into a sparse-aperture interferometer, either of the Fizeau or Michelson type. Expected performance in terms of transmission maps and a preliminary tolerance analysis are …
Tricouplers for nulling interferometry with photonic integrated circuits
California Institute of Technology（加州理工学院）；Astrophotonics Australia（天文光子学澳大利亚）；University of California, Los Angeles（加利福尼亚大学洛杉矶分校）；NASA Jet Propulsion Laboratory（美国国家航空航天局喷气推进实验室）；University of Maryland（马里兰大学）
The use of interferometric nulling for the direct detection of extrasolar planets is in part limited by the extreme sensitivity of the instrumental response to tiny optical path differences between apertures. The recently proposed kernel-nuller architecture attempts to alleviate this effect with an all-in-one combiner design that enables the production of observables inherently robust to residual optical path differences (<< lambda). Until now, a unique kernel nuller design has been proposed ad hoc for a four-beam combiner. We examine the properties of this original design and generalize them …
Achieving efficient broadband spatial filtering for LIFE: status and plan
ETH Zürich（苏黎世联邦理工学院）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院天体物理研究所）；Research School of Astronomy & Astrophysics, Australian National University（澳大利亚国立大学天文与天体物理研究学院）
Asgard/NOTT: Cryogenic characterization of the mid-infrared chip
ETH Zürich（苏黎世联邦理工学院）；KU Leuven（荷语鲁汶大学）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学、蔚蓝海岸天文台、法国国家科学研究中心、拉格朗日实验室）；The University of Arizona（亚利桑那大学）；Large Binocular Telescope Observatory（大型双筒望远镜天文台）；Macquarie University（麦考瑞大学）；European Southern Observatory（欧洲南方天文台）；Australian National University（澳大利亚国立大学）；Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences（孔科利天文台，匈牙利研究与教育网络天文学与地球科学研究中心）；University of Exeter（埃克塞特大学）；Universität zu Köln（科隆大学）；STAR Institute, University of Liège（列日大学STAR研究所）
