GNOSIS: the first instrument to use fibre Bragg gratings for OH suppression

GNOSIS is a prototype astrophotonic instrument that utilizes OH suppression fibres consisting of fibre Bragg gratings and photonic lanterns to suppress the 103 brightest atmospheric emission doublets between 1.47-1.7 microns. GNOSIS was commissioned at the 3.9-meter Anglo-Australian Telescope with the IRIS2 spectrograph to demonstrate the potential of OH suppression fibres, 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 and excellent suppression of the skylines by the OH suppression fibres, surprisingly GNOSIS produced no significant reduction in the interline background and the sensitivity of GNOSIS and 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 fibres 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 fibres paired with a fibre-fed spectrograph will at least provide a real benefits at low resolving powers.Comment: 15 pages, 13 figures, accepted to A

Quantum information processing with space-division multiplexing optical fibres

The optical fibre is an essential tool for our communication infrastructure since it is the main transmission channel for optical communications. The latest major advance in optical fibre technology is spatial division multiplexing (SDM), where new fibre designs and components establish multiple co-existing data channels based on light propagation over distinct transverse optical modes. Simultaneously, there have been many recent developments in the field of quantum information processing (QIP), with novel protocols and devices in areas such as computing, communication and metrology. Here, we review recent works implementing QIP protocols with SDM optical fibres, and discuss new possibilities for manipulating quantum systems based on this technology.Comment: Originally submitted version. Please see published version for improved layout, new tables and updated references following review proces

Mode Evolution in Fiber Based Devices for Optical Communication Systems

Space division multiplexing (SDM) is the most promising way of increasing the capacity of a single fiber. To enable the few mode fiber (FMF) or multi-mode fiber (MMF) transmission system, several major challenges have to be overcome. One is the urgent need of ideal mode multiplexer, the second is the perfect amplification for all spatial modes, another one is the modal delay spread (MDS) due to group velocity difference of spatial modes. The main subject of this dissertation is to model, fabricate and characterize the mode multiplexer for FMF transmission. First, we designed a novel resonant mode coupler (structured directional coupler pair). After that, we studied the adiabatic mode multiplexer (photonic lantern). 6-mode photonic lantern using graded-index (GI) MMFs is proposed and demonstrated, which alleviates the adiabatic require-ment and improves mode selectivity. Then, 10-mode photonic lantern is demonstrated using novel double cladding micro-structured drilling-hole preform, which alleviates the adiabatic requirement and demonstrate a feasible way to scale up the lantern modes. Also, multi-mode photonic lantern is studied for high order input modes. In addition, for the perfect amplification of the modes, cladding pump method is demonstrated. The mode selective lantern designed and fabricated can be used for the characterization of few mode amplifier with swept wavelength interferometer (SWI). Also, we demonstrated the application of the use of the few mode amplifier for the turbulence-resisted preamplified receiver. Besides, for the reduction of MDS, the long period grating for introducing strong mode mixing is demonstrated

Optimizing astrophotonic spatial reformatters using simulated on-sky performance

One of the most useful techniques in astronomical instrumentation is image slicing. It enables a spectrograph to have a more compact angular slit, whilst retaining throughput and increasing resolving power. Astrophotonic components like the photonic lanterns and photonic reformatters can be used to replace bulk optics used so far. This study investigates the performance of such devices using end-to-end simulations to approximate realistic on-sky conditions. It investigates existing components, tries to optimize their performance and aims to understand better how best to design instruments to maximize their performance. This work complements the recent work in the field and provides an estimation for the performance of the new components.Comment: Conference proceedings in SPIE 2018 Austin Texa

Mode-dependent Loss and Gain Emulation in Coupled SDM Transmission

Space-division multiplexing (SDM) is currently the only solution to cope with the exponential growth of data traffic in optical transmission networks. The performance of long-haul SDM transmission is fundamentally limited by mode-dependent loss (MDL) and mode-dependent gain (MDG) generated in components and amplifiers. To enable the study of MDL/MDG effects in SDM systems as well as MDL/MDG estimation methods within the context of experimental setups, we evaluate an MDL/MDG emulator based on variable optical attenuators (VOAs) and photonic lanterns. We assess MDL/MDG emulation in different attenuation scenarios and demonstrate the capability of the emulator to artificially introduce a wide range of MDL/MDG in a short-reach 3-mode transmission system

Efficient detection and characterization of exoplanets within the diffraction limit: nulling with a mode-selective photonic lantern

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.Comment: 15 pages, 12 figure

Mode-Multiplexed Transmission over Conventional Graded-Index Multimode Fibers

We present experimental results for combined mode-multiplexed and wavelength multiplexed transmission over conventional graded-index multimode fibers. We use mode-selective photonic lanterns as mode couplers to precisely excite a subset of the modes of the multimode fiber and additionally to compensate for the differential group delay between the excited modes. Spatial mode filters are added to suppress undesired higher order modes. We transmit 30-Gbaud QPSK signals over 60 WDM channels, 3 spatial modes, and 2 polarizations, reaching a distance of 310 km based on a 44.3 km long span. We also report about transmission experiments over 6 spatial modes for a 17-km single-span experiment. The results indicate that multimode fibers support scalable mode-division multiplexing approaches, where modes can be added over time if desired. Also the results indicate that mode-multiplexed transmission distance over 300 km are possible in conventional multimode fibers