Scott M. Croom, Jon S. Lawrence, Joss Bland-Hawthorn, Julia J. Bryant, Lisa Fogarty, Samuel Richards, Michael Goodwin, Tony Farrell, Stan Miziarski, Ron Heald, D. Heath Jones, Steve Lee, Matthew Colless, Sarah Brough, Andrew M. Hopkins, Amanda E. Bauer, Michael N. Birchall, Simon Ellis, Anthony Horton, Sergio Leon-Saval, Geraint Lewis, A. R. Lopez-Sanchez, Seong-Sik Min, Christopher Trinh, Holly Trowland
Dec 14, 2011·astro-ph.CO·PDF We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The Sydney-AAO Multi-object IFS (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles ("hexabundles") to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly-fused multimode fibres with reduced cladding and yields a 75 percent filling factor. Each fibre core diameter subtends 1.6 arcseconds on the sky and each hexabundle has a field of view of 15 arcseconds diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R=lambda/delta(lambda) ~ 1700-13000) over the optical spectrum (3700-9500A). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z~0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially--resolved spectroscopic surveys of 10^4 to 10^5 galaxies.
Teresa Klinner-Teo, Marc-Antoine Martinod, Peter Tuthill, Simon Gross, Barnaby Norris, Sergio Leon-Saval
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 $1.4-1.7~μ$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.
Kevin Cook, John Canning, Sergio Leon-Saval, Zane Reid, Md Arafat Hossain, Jade-Edouard Comatti, Yanhua Luo, Gang-Ding Peng
A structured optical fibre is drawn from a 3D-printed structured preform. Preforms containing a single ring of holes around the core are fabricated using filament made from a modified butadiene polymer. More broadly, 3D printers capable of processing soft glasses, silica and other materials are likely to come on line in the not-so distant future. 3D printing of optical preforms signals a new milestone in optical fibre manufacture.
Janez Kos, Jane Lin, Tomaž Zwitter, Maruška Žerjal, Sanjib Sharma, Joss Bland-Hawthorn, Martin Asplund, Andrew R. Casey, Gayandhi M. De Silva, Ken C. Freeman, Sarah L. Martell, Jeffrey D. Simpson, Katharine J. Schlesinger, Daniel Zucker, Borja Anguiano, Carlos Bacigalupo, Timothy R. Bedding, Christopher Betters, Gary Da Costa, Ly Duong, Elaina Hyde, Michael Ireland, Prajwal R. Kafle, Sergio Leon-Saval, Geraint F. Lewis, Ulisse Munari, David Nataf, Dennis Stello, Chris G. Tinney, Gregor Traven, Fred Watson, Robert A. Wittenmyer
Aug 15, 2016·astro-ph.IM·PDF We present the data reduction procedures being used by the GALAH survey, carried out with the HERMES fibre-fed, multi-object spectrograph on the 3.9~m Anglo-Australian Telescope. GALAH is a unique survey, targeting 1 million stars brighter than magnitude V=14 at a resolution of 28,000 with a goal to measure the abundances of 29 elements. Such a large number of high resolution spectra necessitates the development of a reduction pipeline optimized for speed, accuracy, and consistency. We outline the design and structure of the Iraf-based reduction pipeline that we developed, specifically for GALAH, to produce fully calibrated spectra aimed for subsequent stellar atmospheric parameter estimation. The pipeline takes advantage of existing Iraf routines and other readily available software so as to be simple to maintain, testable and reliable. A radial velocity and stellar atmospheric parameter estimator code is also presented, which is used for further data analysis and yields a useful verification of the reduction quality. We have used this estimator to quantify the data quality of GALAH for fibre cross-talk level ($\lesssim0.5$%) and scattered light ($\sim5$ counts in a typical 20 minutes exposure), resolution across the field, sky spectrum properties, wavelength solution reliability (better than $1$ $\mathrm{km\ s^{-1}}$ accuracy) and radial velocity precision.
Sergio Leon-Saval, Alexander Argyros, Joss Bland-Hawthorn
Photonic lanterns allow for a low-loss transformation of a multimode waveguide into a discrete number of single-mode waveguides and vice versa, thus, enabling the use of single-mode photonic technologies in multimode systems. In this review, we will discuss the theory and function of the photonic lantern, along with several different variants of the technology. We will also discuss some of its applications in more detail.
Samuel Nathan Richards, Sergio Leon-Saval, Michael Goodwin, Jessica Zheng, Jon Lawrence, Julia Bryant, Joss Bland-Hawthorn, Barnaby Norris, Nick Cvetojevic, Alexander Argyros
Jan 13, 2017·astro-ph.IM·PDF Imaging bundles provide a convenient way to translate a spatially coherent image, yet conventional imaging bundles made from silica fibre optics typically remain expensive with large losses due to poor filling factors (~40%). We present the characterisation of a novel polymer imaging bundle made from poly(methyl methacrylate) (PMMA) that is considerably cheaper and a better alternative to silica imaging bundles over short distances (~1 m; from the middle to the edge of a telescope's focal plane). The large increase in filling factor (92% for the polymer imaging bundle) outweighs the large increase in optical attenuation from using PMMA (1 dB/m) instead of silica (10^{-3} dB/m). We present and discuss current and possible future multi-object applications of the polymer imaging bundle in the context of astronomical instrumentation including: field acquisition, guiding, wavefront sensing, narrow-band imaging, aperture masking, and speckle imaging. The use of PMMA limits its use in low light applications (e.g. imaging of galaxies), however it is possible to fabricate polymer imaging bundles from a range of polymers that are better suited to the desired science.
Joss Bland-Hawthorn, Seong-Sik Min, Emma Lindley, Sergio Leon-Saval, Simon Ellis, John Lawrence, Martin Roth, Hans-Gerd Lohmannsroben, Sylvain Veilleux
For the past forty years, optical fibres have found widespread use in ground-based and space-based instruments. In most applications, these fibres are used in conjunction with conventional optics to transport light. But photonics offers a huge range of optical manipulations beyond light transport that were rarely exploited before 2001. The fundamental obstacle to the broader use of photonics is the difficulty of achieving photonic action in a multimode fibre. The first step towards a general solution was the invention of the photonic lantern (Leon-Saval, Birks & Bland-Hawthorn 2005) and the delivery of high-efficiency devices (< 1 dB loss) five years on (Noordegraaf et al 2009). Multicore fibres (MCF), used in conjunction with lanterns, are now enabling an even bigger leap towards multimode photonics. Until recently, the single-moded cores in MCFs were not sufficiently uniform to achieve telecom (SMF-28) performance. Now that high-quality MCFs have been realized, we turn our attention to printing complex functions (e.g. Bragg gratings for OH suppression) into their N cores. Our first work in this direction used a Mach-Zehnder interferometer (near-field phase mask) but this approach was only adequate for N=7 MCFs as measured by the grating uniformity (Lindley et al 2014). We have now built a Sagnac interferometer that gives a three-fold increase in the depth of field sufficient to print across N > 127 cores. We achieved first light this year with our 500mW Sabre FRED laser. These are sophisticated and complex interferometers. We report on our progress to date and summarize our first-year goals which include multimode OH suppression fibres for the Anglo-Australian Telescope/PRAXIS instrument and the Discovery Channel Telescope/MOHSIS instrument under development at the University of Maryland.
J. Gordon Robertson, Simon Ellis, Qingshan Yu, Joss Bland-Hawthorn, Christopher Betters, Martin Roth, Sergio Leon-Saval
Jun 18, 2021·astro-ph.IM·PDF Celestially, Positronium (Ps), has only been observed through gamma-ray emission produced by its annihilation. However, in its triplet state, a Ps atom has a mean lifetime long enough for electronic transitions to occur between quantum states. This produces a recombination spectrum observable in principle at near IR wavelengths, where angular resolution greatly exceeding that of the gamma-ray observations is possible. However, the background in the NIR is dominated by extremely bright atmospheric hydroxyl (OH) emission lines. In this paper we present the design of a diffraction-limited spectroscopic system using novel photonic components - a photonic lantern, OH Fiber Bragg Grating filters, and a photonic TIGER 2-dimensional pseudo-slit - to observe the Ps Balmer alpha line at 1.3122 microns for the first time.
Yinzi Xin, Daniel Echeverri, Nemanja Jovanovic, Dimitri Mawet, Sergio Leon-Saval, Rodrigo Amezcua-Correa, Stephanos Yerolatsitis, Michael P. Fitzgerald, Pradip Gatkine, Yoo Jung Kim, Jonathan Lin, Barnaby Norris, Garreth Ruane, Steph Sallum
Photonic lantern nulling (PLN) is a method for enabling the detection and characterization of close-in exoplanets by exploiting the symmetries of the ports of a mode-selective photonic lantern (MSPL) to cancel out starlight. A six-port MSPL provides four ports where on-axis starlight is suppressed, while off-axis planet light is coupled with efficiencies that vary as a function of the planet's spatial position. We characterize the properties of a six-port MSPL in the laboratory and perform the first testbed demonstration of the PLN in monochromatic light (1569 nm) and in broadband light (1450 nm to 1625 nm), each using two orthogonal polarizations. We compare the measured spatial throughput maps with those predicted by simulations using the lantern's modes. We find that the morphologies of the measured throughput maps are reproduced by the simulations, though the real lantern is lossy and has lower throughputs overall. The measured ratios of on-axis stellar leakage to peak off-axis throughput are around 10^(-2), likely limited by testbed wavefront errors. These null-depths are already sufficient for observing young gas giants at the diffraction limit using ground-based observatories. Future work includes using wavefront control to further improve the nulls, as well as testing and validating the PLN on-sky.
Michael Goodwin, Belen Alcalde, Samuel Richards, Jessica Zheng, Jon Lawrence, Sergio Leon-Saval, Alexander Argyros
Jul 18, 2014·astro-ph.IM·PDF The ability to position multiple miniaturized wavefront sensors precisely over large focal surfaces are advantageous to multi-object adaptive optics. The Australian Astronomical Observatory (AAO) has prototyped a compact and lightweight Shack-Hartmann wavefront-sensor that fits into a standard Starbug parallel fibre positioning robot. Each device makes use of a polymer coherent fibre imaging bundle to relay an image produced by a microlens array placed at the telescope focal plane to a re-imaging camera mounted elsewhere. The advantages of the polymer fibre bundle are its high-fill factor, high-throughput, low weight, and relatively low cost. Multiple devices can also be multiplexed to a single low-noise camera for cost efficiencies per wavefront sensor. The use of fibre bundles also opens the possibility of applications such as telescope field acquisition, guiding, and seeing monitors to be positioned by Starbugs. We present the design aspects, simulations and laboratory test results.
Julia J. Bryant, Joss Bland-Hawthorn, Jon Lawrence, Scott Croom, David Brown, Sudharshan Venkatesan, Peter R. Gillingham, Ross Zhelem, Robert Content, Will Saunders, Nicholas F. Staszak, Jesse van de Sande, Warrick Couch, Sergio Leon-Saval, Julia Tims, Richard McDermid, Adam Schaefer
Aug 12, 2016·astro-ph.IM·PDF Hector will be the new massively-multiplexed integral field spectroscopy (IFS) instrument for the Anglo-Australian Telescope (AAT) in Australia and the next main dark-time instrument for the observatory. Based on the success of the SAMI instrument, which is undertaking a 3400-galaxy survey, the integral field unit (IFU) imaging fibre bundle (hexabundle) technology under-pinning SAMI is being improved to a new innovative design for Hector. The distribution of hexabundle angular sizes is matched to the galaxy survey properties in order to image 90% of galaxies out to 2 effective radii. 50-100 of these IFU imaging bundles will be positioned by 'starbug' robots across a new 3-degree field corrector top end to be purpose-built for the AAT. Many thousand fibres will then be fed into new replicable spectrographs. Fundamentally new science will be achieved compared to existing instruments due to Hector's wider field of view (3 degrees), high positioning efficiency using starbugs, higher spectroscopic resolution (R~3000-5500 from 3727-7761A, with a possible redder extension later) and large IFUs (up to 30 arcsec diameter with 61-217 fibre cores). A 100,000 galaxy IFS survey with Hector will decrypt how the accretion and merger history and large-scale environment made every galaxy different in its morphology and star formation history. The high resolution, particularly in the blue, will make Hector the only instrument to be able to measure higher-order kinematics for galaxies down to much lower velocity dispersion than in current large IFS galaxy surveys, opening up a wealth of new nearby galaxy science.
Joss Bland-Hawthorn, Janez Kos, Christopher Betters, Gayandhi De Silva, John O'Byrne, Rob Patterson, Sergio Leon-Saval
Apr 27, 2017·astro-ph.IM·PDF We demonstrate a new approach to calibrating the spectral-spatial response of a wide-field spectrograph using a fibre etalon comb. Conventional wide-field instruments employed on front-line telescopes are mapped with a grid of diffraction-limited holes cut into a focal plane mask. The aberrated grid pattern in the image plane typically reveals n-symmetric (e.g. pincushion) distortion patterns over the field arising from the optical train. This approach is impractical in the presence of a dispersing element because the diffraction-limited spots in the focal plane are imaged as an array of overlapping spectra. Instead we propose a compact solution that builds on recent developments in fibre-based Fabry-Perot etalons. We introduce a novel approach to near-field illumination that exploits a 25cm commercial telescope and the propagation of skew rays in a multimode fibre. The mapping of the optical transfer function across the full field is represented accurately (<0.5% rms residual) by an orthonormal set of Chebyshev moments. Thus we are able to reconstruct the full 4Kx4K CCD image of the dispersed output from the optical fibres using this mapping, as we demonstrate. Our method removes one of the largest sources of systematic error in multi-object spectroscopy.
Joss Bland-Hawthorn, Sergio Leon-Saval
Jun 16, 2017·astro-ph.IM·PDF Since its emergence two decades ago, astrophotonics has found broad application in scientific instruments at many institutions worldwide. The case for astrophotonics becomes more compelling as telescopes push for AO-assisted, diffraction-limited performance, a mode of observing that is central to the next-generation of extremely large telescopes (ELTs). Even AO systems are beginning to incorporate advanced photonic principles as the community pushes for higher performance and more complex guide-star configurations. Photonic instruments like Gravity on the Very Large Telescope achieve milliarcsec resolution at 2000 nm which would be very difficult to achieve with conventional optics. While space photonics is not reviewed here, we foresee that remote sensing platforms will become a major beneficiary of astrophotonic components in the years ahead. The field has given back with the development of new technologies (e.g. photonic lantern, large area multi-core fibres) already finding widespread use in other fields; Google Scholar lists more than 400 research papers making reference to this technology. This short review covers representative key developments since the 2009 Focus issue on Astrophotonics.
Yinzi Xin, Nemanja Jovanovic, Garreth Ruane, Dimitri Mawet, Michael P. Fitzgerald, Daniel Echeverri, Jonathan Lin, Sergio Leon-Saval, Pradip Gatkine, Yoo Jung Kim, Barnaby Norris, Steph Sallum
Sep 15, 2022·astro-ph.IM·PDF Coronagraphs allow for faint off-axis exoplanets to be observed, but are limited to angular separations greater than a few beam widths. Accessing closer-in separations would greatly increase the expected number of detectable planets, which scales inversely with the inner working angle. The Vortex Fiber Nuller (VFN) is an instrument concept designed to characterize exoplanets within a single beam-width. It requires few optical elements and is compatible with many coronagraph designs as a complementary characterization tool. However, the peak throughput for planet light is limited to about 20%, and the measurement places poor constraints on the planet location and flux ratio. We propose to augment the VFN design by replacing its single-mode fiber with a six-port mode-selective photonic lantern, retaining the original functionality while providing several additional ports that reject starlight but couple planet light. We show that the photonic lantern can also be used as a nuller without a vortex. We present monochromatic simulations characterizing the response of the Photonic Lantern Nuller (PLN) to astrophysical signals and wavefront errors, and show that combining exoplanet flux from the nulled ports significantly increases the overall throughput of the instrument. We show using synthetically generated data that the PLN detects exoplanets more effectively than the VFN. Furthermore, with the PLN, the exoplanet can be partially localized, and its flux ratio constrained. The PLN has the potential to be a powerful characterization tool complementary to traditional coronagraphs in future high-contrast instruments.
Sergio G. Leon-Saval, Christopher H. Betters, Joss Bland-Hawthorn
Aug 15, 2012·astro-ph.IM·PDF We present a proof of concept compact diffraction limited high-resolution fiber-fed spectrograph by using a 2D multicore array input. This high resolution spectrograph is fed by a 2D pseudo-slit, the Photonic TIGER, a hexagonal array of near-diffraction limited single-mode cores. We study the feasibility of this new platform related to the core array separation and rotation with respect to the dispersion axis. A 7 core compact Photonic TIGER fiber-fed spectrograph with a resolving power of around R~31000 and 8 nm bandwidth in the IR centered on 1550 nm is demonstrated. We also describe possible architectures based on this concept for building small scale compact diffraction limited Integral Field Spectrographs (IFS).
Christopher Q. Trinh, Simon C. Ellis, Joss Bland-Hawthorn, Anthony J. Horton, Jon S. Lawrence, Sergio G. Leon-Saval
We analyse the near-infrared interline sky background, OH and O2 emission in 19 hours of H band observations with the GNOSIS OH suppression unit and the IRIS2 spectrograph at the 3.9-m AAT. We find that the temporal behaviour of OH emission is best described by a gradual decrease during the first half of the night followed by a gradual increase during the second half of the night following the behaviour of the solar elevation angle. We measure the interline background at 1.520 microns where the instrumental thermal background is very low and study its variation with zenith distance, time after sunset, ecliptic latitude, lunar zenith angle and lunar distance to determine the presence of non-thermal atmospheric emission, zodiacal scattered light and scattered moonlight. Zodiacal scattered light is too faint to be detected in the summed observations. Scattered moonlight due to Mie scattering by atmospheric aerosols is seen at small lunar distances (< 11 deg), but is otherwise too faint to detect. Except at very small lunar distances the interline background at a resolving power of R~2400 when using OH suppression fibres is dominated by a non-thermal atmospheric source with a temporal behaviour that resembles atmospheric OH emission suggesting that the interline background contains instrumentally-scattered OH. However, the interline background dims more rapidly than OH early in the night suggesting contributions from rapid dimming molecules. The absolute interline background is 560 +/- 120 photons s^-1 m^-2 micron^-1 arcsec^-2 under dark conditions. This value is similar to previous measurements without OH suppression suggesting that non-suppressed atmospheric emission is responsible for the interline background. Future OH suppression fibre designs may address this by the suppression of more sky lines using more accurate sky line measurements taken from high resolution spectra.
Christian Schwab, Sergio G. Leon-Saval, Christopher H. Betters, Joss Bland-Hawthorn, Suvrath Mahadevan
Dec 19, 2012·astro-ph.IM·PDF The 'holy grail' of exoplanet research today is the detection of an earth-like planet: a rocky planet in the habitable zone around a main-sequence star. Extremely precise Doppler spectroscopy is an indispensable tool to find and characterize earth-like planets; however, to find these planets around solar-type stars, we need nearly one order of magnitude better radial velocity (RV) precision than the best current spectrographs provide. Recent developments in astrophotonics (Bland-Hawthorn & Horton 2006, Bland-Hawthorn et al. 2010) and adaptive optics (AO) enable single mode fiber (SMF) fed, high resolution spectrographs, which can realize the next step in precision. SMF feeds have intrinsic advantages over multimode fiber or slit coupled spectrographs: The intensity distribution at the fiber exit is extremely stable, and as a result the line spread function of a well-designed spectrograph is fully decoupled from input coupling conditions, like guiding or seeing variations (Ihle et al. 2010). Modal noise, a limiting factor in current multimode fiber fed instruments (Baudrand & Walker 2001), can be eliminated by proper design, and the diffraction limited input to the spectrograph allows for very compact instrument designs, which provide excellent optomechanical stability. A SMF is the ideal interface for new, very precise wavelength calibrators, like laser frequency combs (Steinmetz et al. 2008, Osterman et al. 2012), or SMF based Fabry-Perot Etalons (Halverson et al. 2012). At near infrared wavelengths, these technologies are ready to be implemented in on-sky instruments, or already in use. We discuss a novel concept for such a spectrograph.
Theodoros Anagnos, Mareike Trappen, Blaise C. Kuo Tiong, Tobias Feger, Stephanos Yerolatsitis, Robert J. Harris, Julien Lozi, Nemanja Jovanovic, Tim A. Birks, Sébastien Vievard, Olivier Guyon, Itandehui Gris-Sánchez, Sergio G. Leon-Saval, Barnaby Norris, Sebastiaan Y. Haffert, Phillip Hottinger, Matthias Blaicher, Yilin Xu, Christopher H. Betters, Christian Koos, David W. Coutts, Christian Schwab, Andreas Quirrenbach
May 12, 2021·astro-ph.IM·PDF By combining IFS with ExAO we are now able to resolve objects close to the diffraction-limit of large telescopes, exploring new science cases. We introduce an IFU designed to couple light with a minimal platescale from the SCExAO facility at NIR wavelengths to a SM spectrograph. The IFU has a 3D-printed MLA on top of a custom SM MCF, to optimize the coupling of light into the fiber cores. We demonstrate the potential of the instrument via initial results from the first on-sky runs at the 8.2 m Subaru Telescope with a spectrograph using off-the-shelf optics, allowing for rapid development with low cost.
Bo Zhang, Jianfeng Sun, Chenzhe Lao, Christopher H Betters, Alexander Argyros, Yu Zhou, Sergio G. Leon-Saval
A multimode optical receiver for free space optical communications (FSOC) based on a photonic lantern and adaptive optics coherent beam combining (CBC) of the lantern's single-mode outputs is proposed and demonstrated for the first time. The use of optical coherent combining in fiber serves to increase the signal to noise ratio compared to similar receivers based on electrically combined signals, and represents an all-fiber approach to low-order adaptive optics. This optical receiver is demonstrated using a photonic lantern with three outputs, fibre couplers and active phase locking, and further investigated under atmospheric conditions with and without turbulence.
Christopher H. Betters, Sergio G. Leon-Saval, J. Gordon Robertson, Joss Bland-Hawthorn
Oct 17, 2013·astro-ph.IM·PDF We demonstrate a new approach to classical fiber-fed spectroscopy. Our method is to use a photonic lantern that converts an arbitrary (e.g. incoherent) input beam into N diffraction-limited outputs. For the highest throughput, the number of outputs must be matched to the total number of unpolarized spatial modes on input. This approach has many advantages: (i) after the lantern, the instrument is constructed from 'commercial off the shelf' components; (ii) the instrument is the minimum size and mass configuration at a fixed resolving power and spectral order (~shoebox sized in this case); (iii) the throughput is better than 60% (slit to detector, including detector QE of ~80%); (iv) the scattered light at the detector can be less than 0.1% (total power). Our first implementation operates over 1545-1555 nm (limited by the detector, a 640$\times$512 array with 20$μ$m pitch) with a spectral resolution of 0.055nm (R~30,000) using a 1$\times$7 (1 multi-mode input to 7 single-mode outputs) photonic lantern. This approach is a first step towards a fully integrated, multimode photonic microspectrograph.