Integrated optics are used to achieve astronomical interferometry inside robust and compact materials, improving the instrument's stability and sensitivity. In order to perform differential phase measurements at the H$α$ line (656.3 nm) with the 600-800 nm spectro-interferometer 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 sub-apertures 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, in order 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 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.
Low wind and petaling effects, caused by the discontinuous apertures of telescopes, are poorly corrected -- if at all -- by commonly used workhorse wavefront sensors (WFSs). Wavefront petaling breaks the coherence of the point spread function core, splitting it into several side lobes, dramatically shutting off scientific throughput. We demonstrate the re-purposing of non-redundant sparse aperture masking (SAM) interferometers into low-order WFSs complementing the high-order pyramid WFS, on the SCExAO experimental platform at Subaru Telescope. The SAM far-field interferograms formed from a 7-h…
We present a compact setup based on a three-dimensional integrated optical component, allowing the mea- surement of spectrally resolved complex-visibilities for three channels of polychromatic light. We have tested a prototype of the component in R band and showed that accurate complex visibilities could be retrieved over a bandwidth of 50 nm centered at 650 nm (resolution: R=130). Closure phase stability in the order of $λ$/60 was achieved implying that the device could be used for spectro-interferometry imaging.
Integrated-optic, astronomical, two-beam and three-beam, interferometric combiners have been designed and fabricated for operation in the L band (3 - 4 microns) for the first time. The devices have been realized in titanium-indiffused, x-cut lithium niobate substrates, and on-chip electro-optic fringe scanning has been demonstrated. White light fringes were produced in the laboratory using the two-beam combiner integrated with an on-chip Y-splitter.
The Sydney University Stellar Interferometer (SUSI) now incorporates a new beam combiner, called the Microarcsecond University of Sydney Companion Astrometry instrument (MUSCA), for the purpose of high precision differential astrometry of bright binary stars. Operating in the visible wavelength regime where photon-counting and post-processing fringe tracking is possible, MUSCA will be used in tandem with SUSI's primary beam combiner, Precision Astronomical Visible Observations (PAVO), to record high spatial resolution fringes and thereby measure the separation of fringe packets of binary stars…
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…
The astronomical J-band (1.25 micrometres) is a relatively untapped wave-band in long-baseline infrared interferometry. It allows access to the photosphere in giant and super-giant stars relatively free from opacities of molecular bands. The J-band can potentially be used for imaging spots in the 1350 nm ionised iron line on slowly rotating magnetically-active stars through spectro-interferometry. In addition, the access to the 1080 nanometres He I line may probe outflows and funnel-flows in T-Tauri stars and allow the study of the star-disk interaction. We present the progress in the developm…
Observations at mas-resolution scales and high dynamic range hold a central place in achieving, for instance, the spectroscopic characterization of exo-Earths or the detailed mapping of their protoplanetary disc birthplace. Ground or space-based multi-aperture infrared interferometry is a promising technique to tackle these goals. But significant efforts still need to be undertaken to achieve a simplification of these instruments if we want to combine the light from a large number of telescopes. Integrated-optics appears as an alternative to the current conventional designs, especially if its …
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…
Regular two-dimensional lattices of evanescently coupled waveguides may provide in the near future photonic components capable of combining interferometrically and simultaneously a large number of telescopes, thus easing the imaging capabilities of optical interferometers. In this paper, the theoretical modeling of the so-called Discrete Beam Combiners (DBC) is described and compared to the conventional model used for photonic beam combiners for astronomical interferometry. The performance of DBCs as compared to an ideal ABCD beam combiner is discussed and applications to astronomical instrume…
Stellar interferometry with a K-band integrated optics beam combiner instrument at the CHARA Array - I. First on-sky fringes for CHARIOT
Corning Optical Communications GmbH & Co. KG（康宁光学通讯有限公司）；Leibniz-Institut für Astrophysik Potsdam（波茨坦阿斯特罗物理学会莱布尼茨研究所）；I. Physikalisches Institut, Universität zu Köln（科隆大学第一物理研究所）；The CHARA Array of Georgia State University（佐治亚州立大学CHARA阵列）；Institute of Photonics and Quantum Sciences, Heriot-Watt University（赫瑞-瓦特大学光子与量子科学研究所）；Humboldt-Universität zu Berlin（柏林洪堡大学）
In this contribution, we review the results of the ALSI project (Advanced Laser-writing for Stellar Interferometry), aimed at assessing the potential of ultrafast laser writing to fabricate mid-infared integrated optics (IO) devices with performance compatible with an implementation in real interferometric instruments like Hi5 or PFI. Waveguides for the L, L' and M bands with moderate propagation losses were manufactured in Gallium Lanthanum Sulfide and ZBLAN glasses and used to develop photonic building blocks as well as a full mid-IR 4-telescope beam combiner. We discuss the advantages and d…
This paper presents how photonics associated with new arising detection technologies is able to provide fully integrated instrument for coherent beam combination applied to astrophysical interferometry. The feasibility and operation of on-chip coherent beam combiners has been already demonstrated using various interferometric combination schemes. More recently we proposed a new detection principle aimed at directly sampling and extracting the spectral information of an input signal together with its flux level measurement. The so-called SWIFTS demonstrated concept that stands for Stationary-Wa…
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…
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…
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…
Visible-light long baseline interferometry holds the promise of advancing a number of important applications in fundamental astronomy, including the direct measurement of the angular diameters and oblateness of stars, and the direct measurement of the orbits of binary and multiple star systems. To advance, the field of visible-light interferometry requires development of instruments capable of combining light from 15 baselines (6 telescopes) simultaneously. The Visible Imaging System for Interferometric Observations at NPOI (VISION) is a new visible light beam combiner for the Navy Precision O…
On-sky demonstration of dual-field interferometry at the CHARA Array
The CHARA Array of Georgia State University Mount Wilson Observatory Mount Wilson California USA（佐治亚州立大学查拉阵列威尔逊山天文台）；Department of Astronomy University of Michigan Ann Arbor Michigan USA（密歇根大学天文学系）；School of Physics and Astronomy University of Exeter Exeter United Kingdom（埃克塞特大学物理与天文学院）；Université Côte d’Azur Observatoire de la Côte d’Azur CNRS Laboratoire Lagrange Nice France（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）
Optical interferometry is a powerful technique to achieve high angular resolution. However, its main issue is its lack of sensitivity, compared to other observation techniques. Efforts have been made in the previous decade to improve the sensitivity of optical interferometry, with instruments such as PIONIER and GRAVITY at VLTI, or MIRC-X and MYSTIC at CHARA. While those instruments pushed on sensitivity, their design focus was not the sensitivity but relative astrometric accuracy, imaging capability, or spectral resolution. Our goal is to build an instrument specifically designed to optimize …
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…
Single-aperture spectro-interferometry in the visible at the Subaru telescope with FIRST: First on-sky demonstration on Keho'oea (α Lyrae) and Hokulei (α Aurigae)
(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…
FIRST (Fibered Imager foR a Single Telescope instrument) is a post-AO instrument that enables high contrast imaging and spectroscopy at spatial scales below the diffraction limit. FIRST achieves sensitivity and accuracy by a unique combination of sparse aperture masking, spatial filtering by single-mode fibers and cross-dispersion in the visible. The telescope pupil is divided into sub-pupils by an array of microlenses, coupling the light into single-mode fibers. The output of the fibers are rearranged in a non redundant configuration, allowing the measurement of the complex visibility for eve…
We characterize a near-infrared C-RED ONE camera from First Light Imaging (FLI). This camera uses a SAPHIRA electron avalanche photo-diode array (e-APD) from Leonardo (previously Selex). To do so, we developed a model of the signal distribution. This model allows a measurement of the gain and the Excess Noise Factor (ENF) independently of preexisting calibration such as the system gain. The results of this study show a gain which is 0.53 +/- 0.04 times the gain reported by the manufacturer. The measured ENF is 1.47 +/- 0.03 when we expected 1.25. For an avalanche gain of 60 and a frame rate la…
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…
FIRSTv2 (Fibered Imager foR a Single Telescope version 2) is the upgrade of a post-AO spectro-interferometer (FIRST) that enables high contrast imaging and spectroscopy at spatial scales below the diffraction limit of a single telescope. FIRST is currently installed, and routinely used, on the Subaru telescope as a module of the Subaru Extreme AO (SCExAO) platform. It achieves sensitivity and accuracy by a unique combination of sparse aperture masking, spatial filtering by single-mode fibers and cross-dispersion in the visible (600-900nm). The ongoing upgrade aims at using a photonic chip beam…
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）
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…
During the last two decades, the first generation of beam combiners at the Very Large Telescope Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWS…
We present the first high angular resolution observation of the B[e] star/X-ray transient object CI Cam, performed with the two-telescope Infrared Optical Telescope Array (IOTA), its upgraded three-telescope version (IOTA3T) and the Palomar Testbed Interferometer (PTI). Visibilities and closure phases were obtained using the IONIC-3 integrated optics beam combiner. CI Cam was observed in the near-infrared H and K spectral bands, wavelengths well suited to measure the size and study the geometry of the hot dust surrounding CI Cam. The analysis of the visibility data over an 8 year period from s…
NAIR-APREXIS: Enabling photonics-based instruments for long-baseline interferometry and integral-field spectroscopy
I. Physikalisches Institut, Universität zu Köln（科隆大学第一物理研究所）；Centre for Advanced Instrumentation, Department of Physics, Durham University（杜伦大学物理系先进仪器中心）；Leibniz-Institut für Astrophysik Potsdam（波茨坦莱布尼茨天体物理研究所）；Institute of Photonics and Quantum Sciences, Heriot-Watt Univ.（赫瑞-瓦特大学光子与量子科学研究所）；The CHARA Array of Georgia State University, Mount Wilson Observatory（佐治亚州立大学CHARA阵列威尔逊山天文台）；Corning Optical Communications GmbH & Co. KG（康宁光学通信有限公司）
