Photonic lantern behaviour and implications for instrument design
Anthony Horton, Robert Content, Simon Ellis, Jon Lawrence
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18 pages, 14 figures, presented at SPIE Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation 2014, to be published in Proc. SPIE 9151
Photonic lanterns are an important enabling technology for astrophotonics with a wide range of potential applications including fibre Bragg grating OH suppression, integrated photonic spectrographs and fibre scramblers for high resolution spectroscopy. The behaviour of photonic lanterns differs in several important respects from the conventional fibre systems more frequently used in astronomical instruments and a detailed understanding of this behaviour is required in order to make the most effective use of this promising technology. To this end we have undertaken a laboratory study of photonic lanterns with the aim of developing an empirical model for the mapping from input to output illumination distributions. We have measured overall transmission and near field output light distributions as a function of input angle of incidence for photonic lanterns with between 19 and 61 cores. We present the results of this work, highlight the key differences between photonic lanterns and conventional fibres, and illustrate the implications for instrument design via a case study, the design of the PRAXIS spectrograph. The empirical photonic lantern model was incorporated into an end-to-end PRAXIS performance model which was used to optimise the design parameters of the instrument. We describe the methods used and the resulting conclusions. The details of photonic lantern behaviour proved particularly important in selecting the optimum on sky field of view per fibre and in modelling of the instrument thermal background.
In an attempt to develop a streamlined astrophotonic instrument, we demonstrate the realization of an all-photonic device capable of both multimode to single mode conversion and spectral dispersion on an 8-m class telescope with efficient coupling. The device was a monolithic photonic spectrograph which combined an integrated photonic lantern, and an efficient arrayed waveguide grating device. During on-sky testing, we discovered a previously unreported type of noise that made spectral extraction and calibration extremely difficult. The source of the noise was traced to a wavelength-dependent …
Photonic lanterns allow the decomposition of highly multimodal light into a simplified modal basis such as single-moded and/or few-moded. They are increasingly finding uses in astronomy, optics and telecommunications. Calculating propagation through a photonic lantern using traditional algorithms takes $\sim 1$ hour per simulation on a modern CPU. This paper demonstrates that neural networks can bridge the disparate opto-electronic systems, and when trained can achieve a speed-up of over 5 orders of magnitude. We show that this approach can be used to model photonic lanterns with manufacturing…
Demonstration of a multimode-to-multimode photonic lantern for astronomy
Instituto de Astrofísica de Andalucía, CSIC（安达卢西亚天体物理研究所）；Sydney Astrophotonic Instrumentation Laboratories, School of Physics, The University of Sydney（悉尼大学物理学院悉尼天体光子学仪器实验室）；Centro Astronómico Hispano en Andalucía, Observatorio de Calar Alto（安达卢西亚西班牙天文中心卡拉阿尔托天文台）；Astrophotonics (innoFSPEC), Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿基米德天体物理研究所天体光子学部门）；Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）
The coupling of large telescopes to astronomical instruments has historically been challenging due to the tension between instrument throughput and stability. Light from the telescope can either be injected wholesale into the instrument, maintaining high throughput at the cost of point-spread function (PSF) stability, or the time-varying components of the light can be filtered out with single-mode fibers (SMFs), maintaining instrument stability at the cost of light loss. Today, the field of astrophotonics provides a potential resolution to the throughput-stability tension in the form of the ph…
The first demonstration of narrowband spectral filtering of multimode light on a 3D integrated photonic chip using photonic lanterns and waveguide Bragg gratings is reported. The photonic lanterns with multi-notch waveguide Bragg gratings were fabricated using the femtosecond direct-write technique in boro-aluminosilicate glass (Corning, Eagle 2000). Transmission dips of up to 5 dB were measured in both photonic lanterns and reference single-mode waveguides with 10.4-mm-long gratings. The result demonstrates efficient and symmetrical performance of each of the gratings in the photonic lantern.…
In ground-based astronomy, starlight distorted by the atmosphere couples poorly into single-mode waveguides but a correction by adaptive optics, even if only partial, can boost coupling into the few-mode regime allowing the use of photonic lanterns to convert into multiple single-mode beams. Corrected wavefronts result in focal patterns that couple mostly with the circularly symmetric waveguide modes. A mode-selective photonic lantern is hence proposed to convert the multimode light into a subset of the single-mode waveguides of the standard photonic lantern, thereby reducing the required numb…
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）
The PolyOculus technology produces large-area-equivalent telescopes by using fiber optics to link modules of multiple semi-autonomous, small, inexpensive, commercial-off-the-shelf telescopes. Crucially, this scalable design has construction costs which are > 10x lower than equivalent traditional large-area telescopes. We have developed a novel photonic lantern approach for the PolyOculus fiber optic linkages which potentially offers substantial advantages over previously considered free-space optical linkages, including much higher coupling efficiencies. We have carried out the first laborator…
Instrumental artifacts in photonic lantern spectroastrometry and their mitigation with PLred
University of California, Los Angeles（加州大学洛杉矶分校）；University of Hawai’i at Hilo（夏威夷大学希洛分校）；University of Hawai’i（夏威夷大学）；University of Arizona（亚利桑那大学）；Subaru Telescope, National Astronomical Observatory of Japan（日本国立天文台昴星团望远镜）；Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台、巴黎文理研究大学、索邦大学、巴黎西岱大学、CY塞吉-蓬图瓦兹大学、法国国家科学研究中心）；California Institute of Technology（加州理工学院）
Envisioning more compact and cost accessible astronomical instruments is now possible with existing photonic technologies like specialty optical fibres, photonic lanterns and ultrafast laser inscribed chips. We present an original design of a multicore fibre (MCF) terminated with multimode photonic lantern ports. It is designed to act as a relay fibre with the coupling effciency of a multimode fibre, modal stability similar to a single-mode fibre and low loss in a wide range of wavelengths (380 nm to 860 nm). It provides phase and amplitude scrambling to achieve a stable near field and far fie…
FIRST-PL: Commissioning the first visible photonic lantern spectrograph for sub-diffraction-limit astronomy on Subaru/SCExAO
University of Hawai‘i（夏威夷大学）；University of Hawaii at Manoa（夏威夷大学马诺阿分校）；Subaru Telescope, National Astronomical Observatory of Japan（昴星团望远镜，日本国立天文台）；Observatoire de Paris, Université PSL（巴黎天文台，巴黎文理研究大学）；Steward Observatory, University of Arizona（斯图尔德天文台，亚利桑那大学）；Astrobiology Center（天体生物学中心）；Univ. Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，IPAG）；University of California, Los Angeles（加州大学洛杉矶分校）；Sydney Institute for Astronomy, School of Physics, The University of Sydney（悉尼天体物理研究所，悉尼大学物理学院）；Optical Sharpeners（光学锐化器）；California Institute of Technology（加州理工学院）；Sydney Astrophotonic Instrumentation Laboratory, School of Physics, The University of Sydney（悉尼天体光子仪器实验室，悉尼大学物理学院）；Astralis, School of Physics, University of Sydney（Astralis，悉尼大学物理学院）；University of Texas, San Antonio（得克萨斯大学圣安东尼奥分校）
Photonic lanterns rely on a close packed arrangement of single mode fibers, which are tapered and fused into one multi-mode core. Topologically optimal circle packing arrangements have been well studied. Using this, we fabricate PLs with 19 and 37 SMFs showing tightly packed, ordered arrangements with packing densities of 95 % and 99 % of theoretically achievable values, with mean adjacent core separations of 1.03 and 1.08 fiber diameters, respectively. We demonstrate that topological circle packing data is a good predictor for optimal PL parameters.
Starlight corrupted by atmospheric turbulence cannot couple efficiently into astronomical instruments based on integrated optics as they require light of high spatial coherence to couple into their single-mode waveguides. Low-order adaptive optics in combination with photonic lanterns offer a practical approach to achieve efficient coupling into multiplexed astrophotonic devices. We investigate, aided by simulations and an experimental testbed, the trade-off between the degrees of freedom of the adaptive optics system and those of the input waveguide of an integrated optic component leading to…
The photonic lantern (PL) is a tapered waveguide that can efficiently couple light into multiple single-mode optical fibers. Such devices are currently being considered for a number of tasks, including the coupling of telescopes and high-resolution, fiber-fed spectrometers, coherent detection, nulling interferometry, and vortex-fiber nulling (VFN). In conjunction with these use cases, PLs can simultaneously perform low-order focal-plane wavefront sensing. In this work, we provide a mathematical framework for the analysis of the photonic lantern wavefront sensor (PLWFS), deriving linear and hig…
The Photonic Lantern Nuller: from concept to laboratory and on-sky demonstrations
Caltech（加州理工学院）；Sterrewacht Leiden（莱顿天文台）；University of California, Los Angeles（加利福尼亚大学洛杉矶分校）；NASA Ames Research Center（NASA艾姆斯研究中心）；Subaru Telescope, National Astronomical Observatory of Japan（日本国立天文台昴星望远镜）；University of Hawai’i（夏威夷大学）；The University of Sydney（悉尼大学）；University of Central Florida（中佛罗里达大学）；University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；University of California, Santa Cruz（加利福尼亚大学圣克鲁兹分校）
We present a new way to mitigate focal-ratio degradation (FRD) when using optical fibers to transport multimode light. Our approach exploits a custom multicore fiber (MCF) with six dissimilar cores that are single mode at ~1550 nm wavelength and minimally coupled over 7 m. We fabricated adiabatic mode-selective photonic lanterns (PLs) at each end of the MCF to create a fiber link with multimode ports, the PLs coupling each spatial mode of the multimode ports to a specific core of the MCF and vice versa. The PL-MCF-PL link exhibits superior FRD behavior compared to a conventional multimode fibe…
Towards High-Throughput Visible Photonic Lanterns for the EMARCOT Project
Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿基米德天体物理研究所）；Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas（安达卢西亚天体物理研究所，西班牙高等科学研究委员会）；Centro Astronómico Hispano en Andalucía (CAHA), Observatorio de Calar Alto（安达卢西亚西班牙天文中心，卡萨拉托天文台）；Institute of Photonics and Optical Science, School of Physics, University of Sydney（悉尼大学物理学院光子学与光学科学研究所）
Empirical verification of principal mode orthogonality and relative phase calibration in photonic lanterns
Sydney Institute for Astronomy, School of Physics, The University of Sydney（悉尼大学物理学院天体物理学研究所）；Sydney Astrophotonics Instrumentation Laboratory, School of Physics, The University of Sydney（悉尼大学物理学院天文光子学仪器实验室）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）
Overcoming the low signal-to-noise problem for hybrid mode-selective photonic lantern-based wavefront correction using machine learning
University of Sydney（悉尼大学）；Sydney Institute for Astronomy (SIfA)（悉尼天文研究所）；School of Physics, University of Sydney（悉尼大学物理学院）；Sydney Astrophotonics Instrumentation Laboratories（悉尼天体光子学仪器实验室）；Observatoire de la Cote d’Azur（蔚蓝海岸天文台）；Université Côte d’Azur（蔚蓝海岸大学）；Leiden University（莱顿大学）
We demonstrate the use of an optimized 5 core photonic lantern (PL) to simultaneously measure tip/tilt errors at the telescope focal plane, while also providing the input to an instrument. By replacing a single mode (SM) fiber with the PL we show that it is possible to stabilize the input PSF to an instrument due to non-common path tip/tilt aberrations in an adaptive optics system. We show the PL in two different regimes, (i) using only the outer cores for tip/tilt measurements while feeding an instrument with the central core and, (ii) using all cores to measure tip/tilt when used in an instr…
Demonstrating the integration of a photonic lantern with an all-fiber-based nulling interferometer
Univ. of California, Santa Cruz（加州大学圣克鲁兹分校）；Univ. of California, Los Angeles（加州大学洛杉矶分校）；NASA Ames Research Center（NASA艾姆斯研究中心）；NASA Glenn Research Center（NASA格伦研究中心）；Univ. of Central Florida（中佛罗里达大学）
Spectroscopy using a visible photonic lantern at the Subaru telescope: Laboratory characterization and first on-sky demonstration on Ikiiki (α Leo) and `Aua (α Ori)
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…
Combining spectroscopy and wavefront control at deep contrast with photonic lanterns
University of Texas-San Antonio（德克萨斯大学圣安东尼奥分校）；Subaru Telescope, National Astronomical Observatory of Japan（昴星团望远镜，日本国立天文台）；Astrobiology Center（天体生物学中心）；Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院悉尼天体物理学研究所）；The University of Sydney, Sydney Astrophotonic Instrumentation Laboratory（悉尼大学悉尼天体光子仪器实验室）；California Institute of Technology（加州理工学院）；Space Science and Engineering Initiative, College of Engineering, Institute for Astronomy, University of Hawai’i（夏威夷大学天体物理学院工程学院太空科学与工程倡议）；University of California Los Angeles（加州大学洛杉矶分校）
Information limits of photonic lantern wavefront sensing: a Fisher- and quantum-Fisher-information framework and its relation to Fourier-filtering sensitivity limits
Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）
Analysis of Angular-Differential Post-Processing Algorithms for Exoplanet Direct Detection with a Photonic Lantern Nuller
California Institute of Technology（加州理工学院）；University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；Leiden Observatory（莱顿天文台）；University of California, Los Angeles（加州大学洛杉矶分校）
Experimentally-determined performance limits for joint imaging and wavefront sensing with a photonic lantern
University of California, Santa Cruz（加州大学圣克鲁兹分校）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Laboratoire d’Astrophysique de Marseille（马赛天体物理学实验室）；University of California, Los Angeles（加州大学洛杉矶分校）；The College of Optics & Photonics, University of Central Florida（中佛罗里达大学光学与光子学院）
Demonstration of a photonic lantern focal-plane wavefront sensor: measurement of atmospheric wavefront error modes and low wind effect in the non-linear regime
This paper reports on the modal noise characterisation of a hybrid reformatter. The device consists of a multicore-fibre photonic lantern and an ultrafast laser-inscribed slit reformatter. It operates around 1550 nm and supports 92 modes. Photonic lanterns transform a multimode signal into an array of single-mode signals, and thus combine the high coupling efficiency of multimode fibres with the diffraction-limited performance of single-mode fibres. This paper presents experimental measurements of the device point spread function properties under different coupling conditions, and its throughp…
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 de…
One of the well-known problems of producing instruments for Extremely Large Telescopes is that their size (and hence cost) scales rapidly with telescope aperture. To try to break this relation alternative new technologies have been proposed, such as the use of the Integrated Photonic Spectrograph (IPS). Due to their diffraction limited nature the IPS is claimed to defeat the harsh scaling law applying to conventional instruments. The problem with astronomical applications is that unlike conventional photonics, they are not usually fed by diffraction limited sources. This means in order to reta…
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 milliarcs…
Astrophotonics lies at the interface of astronomy and photonics. This burgeoning field -- now formally recognized by the optics community -- has emerged over the past decade in response to the increasing demands of astronomical instrumentation. Early successes include: (i) planar waveguides to combine signals from widely spaced telescopes in stellar interferometry; (ii) frequency combs for ultra-high precision spectroscopy to detect planets around nearby stars; (iii) ultra-broadband fibre Bragg gratings to suppress unwanted background; (iv) photonic lanterns that allow single-mode behaviour wi…
The next generation of Extremely Large Telescopes (ELT), with diameters up to 39 meters, will start opera- tion in the next decade and promises new challenges in the development of instruments. The growing field of astrophotonics (the use of photonic technologies in astronomy) can partly solve this problem by allowing mass production of fully integrated and robust instruments combining various optical functions, with the potential to reduce the size, complexity and cost of instruments. In this paper, we focus on developments in integrated micro-spectrographs and their potential for ELTs. We ta…
The characterisation of exoplanets is critical to understanding planet diversity and formation, their atmospheric composition and the potential for life. This endeavour is greatly enhanced when light from the planet can be spatially separated from that of the host star. One potential method is nulling interferometry, where the contaminating starlight is removed via destructive interference. The GLINT instrument is a photonic nulling interferometer with novel capabilities that has now been demonstrated in on-sky testing. The instrument fragments the telescope pupil into sub-apertures that are i…
Recently, we demonstrated how an astrophotonic light reformatting device, based on a multicore fibre photonic lantern and a three-dimensional waveguide component, can be used to efficiently reformat the point spread function of a telescope to a diffraction-limited psuedo-slit [arXiv:1512.07309]. Here, we demonstrate how such a device can also efficiently mitigate modal noise -- a potential source of instability in high resolution multi-mode fibre-fed spectrographs). To investigate the modal noise performance of the photonic reformatter, we have used it to feed light into a bench-top near-infra…
One of the problems of producing instruments for Extremely Large Telescopes is that their size (and hence cost) scales rapidly with telescope aperture. To try to break this relation alternative new technologies have been proposed, such as the use of the Integrated Photonic Spectrograph (IPS). Due to their diffraction-limited nature the IPS is claimed to defeat the harsh scaling law applying to conventional instruments. In contrast to photonic applications, devices for astronomy are not usually used at the diffraction limit. Therefore to retain throughput and spatial information, the IPS requir…
