TY - THES A1 - Diab, Momen T1 - Enabling astrophotonics: adaptive optics and photonic lanterns for coupling starlight into the single-mode regime T1 - Astrophotonik ermöglichen: Adaptive Optik und photonische Laternen zur Einkopplung von Sternenlicht in den Single-Mode-Bereich N2 - Ground-based astronomy is set to employ next-generation telescopes with apertures larger than 25 m in diameter before this decade is out. Such giant telescopes observe their targets through a larger patch of turbulent atmosphere, demanding that most of the instruments behind them must also grow larger to make full use of the collected stellar flux. This linear scaling in size greatly complicates the design of astronomical instrumentation, inflating their cost quadratically. Adaptive optics (AO) is one approach to circumvent this scaling law, but it can only be done to an extent before the cost of the corrective system itself overwhelms that of the instrument or even that of the telescope. One promising technique for miniaturizing the instruments and thus driving down their cost is to replace some, or all, of the free space bulk optics in the optical train with integrated photonic components. Photonic devices, however, do their work primarily in single-mode waveguides, and the atmospherically-distorted starlight must first be efficiently coupled into them if they are to outperform their bulk optic counterparts. This is doable by two means: AO systems can again help control the angular size and motion of seeing disks to the point where they will couple efficiently into astrophotonic components, but this is only feasible for the brightest of objects and over limited fields of view. Alternatively, tapered fiber devices known as photonic lanterns — with their ability to convert multimode into single-mode optical fields — can be used to feed speckle patterns into single-mode integrated optics. They, nonetheless, must conserve the degrees of freedom, and the number of output waveguides will quickly grow out of control for uncorrected large telescopes. An AO-assisted photonic lantern fed by a partially corrected wavefront presents a compromise that can have a manageable size if the trade-off between the two methods is chosen carefully. This requires end-to-end simulations that take into account all the subsystems upstream of the astrophotonic instrument, i.e., the atmospheric layers, the telescope, the AO system, and the photonic lantern, before a decision can be made on sizing the multiplexed integrated instrument. The numerical models that simulate atmospheric turbulence and AO correction are presented in this work. The physics and models for optical fibers, arrays of waveguides, and photonic lanterns are also provided. The models are on their own useful in understanding the behavior of the individual subsystems involved and are also used together to compute the optimum sizing of photonic lanterns for feeding astrophotonic instruments. Additionally, since photonic lanterns are a relatively new concept, two novel applications are discussed for them later in this thesis: the use of mode-selective photonic lanterns (MSPLs) to reduce the multiplicity of multiplexed integrated instruments and the combination of photonic lanterns with discrete beam combiners (DBCs) to retrieve the modal content in an optical waveguide. N2 - In der erdbasierten Astronomie sollen noch in diesem Jahrzehnt Teleskope der nächsten Generation mit Öffnungen von mehr als 25 Metern in Betrieb genommen werden. Mit derart riesigen Aperturen werden die Zielobjekte durch einen größeren Ausschnitt turbulenter Atmosphäre beobachtet, weswegen die meisten die dahinterliegenden Instrumente entsprechend größer werden müssen, um die aufgefangene Strahlungsleistung vollständig nutzen zu können. Die lineare Skalierung der Größe erschwert das Design astronomischer Instrumente erheblich und führt zu einem quadratischen Anstieg der Kosten. Die adaptive Optik (AO) ist ein Ansatz, diese Skalierung zu umgehen. Allerdings ist dies nur bis zu einem gewissen Grad möglich, bevor die Kosten des Korrektursystems die des Instruments oder sogar des Teleskopes übersteigen. Eine vielversprechende Methode, das Instrument zu miniaturisieren und damit die Kosten zu reduzieren besteht darin, einige oder sogar alle der voluminösen Freistrahloptiken im Strahlengang durch photonische Komponenten zu ersetzen. Photonische Bauteile arbeiten jedoch in erster Linie mit Einzelmoden-Wellenleitern. Damit sie eine bessere Leistung erbringen als die entsprechenden Freistrahloptiken muss das durch die atmosphärischen Störungen verformte Sternenlicht zunächst effizient in die Wellenleiter eingekoppelt werden. Dies kann auf zwei Wegen erreicht werden: AO Systeme können Winkelausdehnung und Bewegung der Bildunschärfe der Sternscheibchen stark genug korrigieren, um diese effizient in astrophotonische Komponenten einzukoppeln. Dies ist aber nur für die hellsten Objekte und über ein begrenztes Sichtfeld möglich. Alternativ können photonische Laternen genutzt werden, um Multimoden des optischen Feldes in Einzelmoden umzuwandeln und somit die Specklemustern in die Einzelmoden-Wellenleiter der integrierten Optiken zu injizieren. Da hierbei die Anzahl der Freiheitsgrade trotzdem erhalten bleiben muss, wird die Zahl der Ausgangswellenleiter für nicht-korrigierte große Teleskope schnell unkontrollierbar anwachsen. Durch sorgfältiges Abwägen kann ein Kompromiss zwischen diesen beiden Methoden gewählt werden, bei dem man eine AO-assistierte photonische Laterne mit überschaubarer Größe erhält, in die eine partiell korrigierte Wellenfront gespeist wird. Dieser Prozess erfordert durchgehende Simulationen unter Einbeziehung aller Subsysteme vor dem astrophotonischen Instrument -Atmosphäre, Teleskop, AO System und photonische Laterne- bevor eine Entscheidung über die Dimensionierung des integrierten Multiplex-Instruments getroffen vii werden kann. Die numerischen Modelle, die die atmosphärischen Störungen und AO Korrekturen simulieren, werden in dieser Arbeit präsentiert. Die Physik und Modelle für optische Fasern, Wellenleiter-Arrays und photonische Laternen werden ebenfalls dargestellt. Jedes Modell für sich ist nützlich, um die Auswirkung des jeweiligen Subsystems nachzuvollziehen. In Kombination werden die Modelle verwendet, um die optimale Konfiguration und Größe der photonischen Laterne für die Einspeisung astrophotonischer Instrumente zu berechnen. Da photonische Laternen ein relativ neues Konzept sind, werden im weiteren Verlauf der Arbeit zusätzlich zwei neuartige Anwendungen erörtert: der Einsatz modenselektiver photonischer Laternen (MSPLs) zur Verringerung der Anzahl von Multiplex-Instrumenten sowie die Kombination photonischer Laternen mit diskreten Strahlkombinierern („Discrete Beam Combiners“: DBCs), um die Moden in einem Lichtwellenleiter zu erfassen. KW - adaptive optics KW - photonic lanterns KW - astrophotonics KW - integrated optics KW - astronomical instrumentation KW - spectrographs KW - interferometers KW - atmospheric effects KW - single-mode fiber KW - fiber coupling KW - optical fibers KW - adaptive Optik KW - astronomische Instrumente KW - Astrophotonik KW - atmosphärische Effekte KW - Faserkopplung KW - integrierten Optik KW - Interferometer KW - optische Fasern KW - photonische Laternen KW - Single-mode-Faser KW - Spektrographen Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-539012 ER - TY - JOUR A1 - Ellis, S. C. A1 - Bland-Hawthorn, Joss A1 - Lawrence, J. A1 - Horton, A. J. A1 - Trinh, C. A1 - Leon-Saval, S. G. A1 - Shortridge, K. A1 - Bryant, J. A1 - Case, S. A1 - Colless, M. A1 - Couch, W. A1 - Freeman, K. A1 - Gers, L. A1 - Glazebrook, K. A1 - Haynes, R. A1 - Lee, S. A1 - Löhmannsröben, Hans-Gerd A1 - O'Byrne, J. A1 - Miziarski, S. A1 - Roth, M. A1 - Schmidt, B. A1 - Tinney, C. G. A1 - Zheng, J. T1 - Suppression of the near-infrared OH night-sky lines with fibre Bragg gratings - first results JF - Monthly notices of the Royal Astronomical Society N2 - The background noise between 1 and 1.8 ?mu m in ground-based instruments is dominated by atmospheric emission from hydroxyl molecules. We have built and commissioned a new instrument, the Gemini Near-infrared OH Suppression Integral Field Unit (IFU) System (GNOSIS), which suppresses 103 OH doublets between 1.47 and 1.7?mu m by a factor of 1000 with a resolving power of 10?000. We present the first results from the commissioning of GNOSIS using the IRIS2 spectrograph at the Anglo-Australian Telescope. We present measurements of sensitivity, background and throughput. The combined throughput of the GNOSIS fore-optics, grating unit and relay optics is 36?per cent, but this could be improved to 46?per cent with a more optimal design. We measure strong suppression of the OH lines, confirming that OH suppression with fibre Bragg gratings will be a powerful technology for low-resolution spectroscopy. The integrated OH suppressed background between 1.5 and 1.7 mu m is reduced by a factor of 9 compared to a control spectrum using the same system without suppression. The potential of low-resolution OH-suppressed spectroscopy is illustrated with example observations of Seyfert galaxies and a low-mass star. The GNOSIS background is dominated by detector dark current below 1.67 mu m and by thermal emission above 1.67 mu m. After subtracting these, we detect an unidentified residual interline component of 860 +/- 210 photons s-1 m-2?arcsec-2?mu m-1, comparable to previous measurements. This component is equally bright in the suppressed and control spectra. We have investigated the possible source of the interline component, but were unable to discriminate between a possible instrumental artefact and intrinsic atmospheric emission. Resolving the source of this emission is crucial for the design of fully optimized OH suppression spectrographs. The next-generation OH suppression spectrograph will be focused on resolving the source of the interline component, taking advantage of better optimization for a fibre Bragg grating feed incorporating refinements of design based on our findings from GNOSIS. We quantify the necessary improvements for an optimal OH suppressing fibre spectrograph design. KW - atmospheric effects KW - instrumentation: miscellaneous KW - infrared: general Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2966.2012.21602.x SN - 0035-8711 VL - 425 IS - 3 SP - 1682 EP - 1695 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Trinh, Christopher Q. A1 - Ellis, Simon C. A1 - Bland-Hawthorn, Joss A1 - Lawrence, Jon S. A1 - Horton, Anthony J. A1 - Leon-Saval, Sergio G. A1 - Shortridge, Keith A1 - Bryant, Julia A1 - Case, Scott A1 - Colless, Matthew A1 - Couch, Warrick A1 - Freeman, Kenneth A1 - Löhmannsröben, Hans-Gerd A1 - Gers, Luke A1 - Glazebrook, Karl A1 - Haynes, Roger A1 - Lee, Steve A1 - O'Byrne, John A1 - Miziarski, Stan A1 - Roth, Martin M. A1 - Schmidt, Brian A1 - Tinney, Christopher G. A1 - Zheng, Jessica T1 - Gnosis - the first instrument to use fiber bragg gratings for OH suppression JF - The astronomical journal N2 - The near-infrared is an important part of the spectrum in astronomy, especially in cosmology because the light from objects in the early universe is redshifted to these wavelengths. However, deep near-infrared observations are extremely difficult to make from ground-based telescopes due to the bright background from the atmosphere. Nearly all of this background comes from the bright and narrow emission lines of atmospheric hydroxyl (OH) molecules. The atmospheric background cannot be easily removed from data because the brightness fluctuates unpredictably on short timescales. The sensitivity of ground-based optical astronomy far exceeds that of near-infrared astronomy because of this long-standing problem. GNOSIS is a prototype astrophotonic instrument that utilizes "OH suppression fibers" consisting of fiber Bragg gratings and photonic lanterns to suppress the 103 brightest atmospheric emission doublets between 1.47 and 1.7 mu m. GNOSIS was commissioned at the 3.9 m Anglo-Australian Telescope with the IRIS2 spectrograph to demonstrate the potential of OH suppression fibers, but may be potentially used with any telescope and spectrograph combination. Unlike previous atmospheric suppression techniques GNOSIS suppresses the lines before dispersion and in a manner that depends purely on wavelength. We present the instrument design and report the results of laboratory and on-sky tests from commissioning. While these tests demonstrated high throughput (approximate to 60%) and excellent suppression of the skylines by the OH suppression fibers, surprisingly GNOSIS produced no significant reduction in the interline background and the sensitivity of GNOSIS+IRIS2 is about the same as IRIS2. It is unclear whether the lack of reduction in the interline background is due to physical sources or systematic errors as the observations are detector noise dominated. OH suppression fibers could potentially impact ground-based astronomy at the level of adaptive optics or greater. However, until a clear reduction in the interline background and the corresponding increasing in sensitivity is demonstrated optimized OH suppression fibers paired with a fiber-fed spectrograph will at least provide a real benefit at low resolving powers. KW - atmospheric effects KW - infrared: diffuse background KW - instrumentation: miscellaneous Y1 - 2013 U6 - https://doi.org/10.1088/0004-6256/145/2/51 SN - 0004-6256 VL - 145 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER -