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 a cost-effective hybrid system that achieves a signal-to-noise ratio higher than a standalone device fed by a single-mode fiber.
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…
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）
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…
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…
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…
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）
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…
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…
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）
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）
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…
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…
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）
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）
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）
Demonstration of a photonic lantern focal-plane wavefront sensor: measurement of atmospheric wavefront error modes and low wind effect in the non-linear regime
Linking a coronagraph instrument to a spectrograph via a single mode optical fiber is a pathway towards detailed characterization of exoplanet atmospheres with current and future ground- and space-based telescopes. However, given the extreme brightness ratio and small angular separation between planets and their host stars, the planet signal-to-noise ratio will likely be limited by the unwanted coupling of starlight into the fiber. To address this issue, we utilize a wavefront control loop and a deformable mirror to systematically reject starlight from the fiber by measuring what is transmitte…
For imaging faint exoplanets and disks, a coronagraph-equipped observatory needs focal plane wavefront correction to recover high contrast. The most efficient correction methods iteratively estimate the stellar electric field and suppress it with active optics. The estimation requires several images from the science camera per iteration. To maximize the science yield, it is desirable both to have fast wavefront correction and to utilize all the correction images for science target detection. Exoplanets and disks are incoherent with their stars, so a nonlinear estimator is required to estimate …
Adaptive optics (AO) is critical in astronomy, optical communications and remote sensing to deal with the rapid blurring caused by the Earth's turbulent atmosphere. But current AO systems are limited by their wavefront sensors, which need to be in an optical plane non-common to the science image and are insensitive to certain wavefront-error modes. Here we present a wavefront sensor based on a photonic lantern fibre-mode-converter and deep learning, which can be placed at the same focal plane as the science image, and is optimal for single-mode fibre injection. By measuring the intensities of …
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…
Vortex fiber nulling is a method for spectroscopically characterizing exoplanets at small angular separations, $\lesssimλ/D$, from their host star. The starlight is suppressed by creating an optical vortex in the system point spread function, which prevents the stellar field from coupling into the fundamental mode of a single-mode optical fiber. Light from the planet, on the other hand, couples into the fiber and is routed to a spectrograph. Using a prototype vortex fiber nuller (VFN) designed for monochromatic light, we demonstrate coupling fractions of $6\times10^{-5}$ and $>0.1$ for the sta…
As telescopes get larger, the size of a seeing-limited spectrograph for a given resolving power becomes larger also, and for ELTs the size will be so great that high resolution instruments of simple design will be infeasible. Solutions include adaptive optics (but not providing full correction for short wavelengths) or image slicers (which give feasible but still large instruments). Here we develop the solution proposed by Bland-Hawthorn and Horton: the use of diffraction-limited spectrographs which are compact even for high resolving power. Their use is made possible by the photonic lantern, …
Context. Direct imaging of exoplanets takes advantage of state-of-the-art adaptive optics (AO) systems, coronagraphy, and post-processing techniques. Coronagraphs attenuate starlight to mitigate the unfavorable flux ratio between an exoplanet and its host star. AO systems provide diffraction-limited images of point sources and minimize optical aberrations that would cause starlight to leak through coronagraphs. Post-processing techniques then estimate and remove residual stellar speckles such as noncommon path aberrations (NCPAs) and diffraction from telescope obscurations. Aims. We aim to dem…
The discovery of an Earth-mass exoplanet around the nearby star Proxima Centauri provides a prime target for the search for life on planets outside our solar system. Atmospheric characterization of these planets has been proposed by blocking the starlight with a stellar coronagraph and using a high-resolution spectrograph to search for reflected starlight off the planet. Due to the large flux ratio and small angular separation between Proxima b and its host star ($\lesssim10^{-7}$ and $\lesssim2.2λ/D$ respectively; at 750nm for an 8m-class telescope) the coronagraph needs to have a high starli…
The exoplanetary science through direct imaging and spectroscopy will largely expand with the forthcoming development of new instruments at the VLT (SPHERE), Gemini (GPI), Subaru (HiCIAO), and Palomar (Project 1640) observatories. All these ground-based adaptive optics instruments combine extremely high performance adaptive optics (XAO) systems correcting for the atmospheric turbulence with advanced starlight-cancellation techniques such as coronagraphy to deliver contrast ratios of about 10-6 to 10-7. While the past fifteen years have seen intensive research and the development of high-contra…
Extreme adaptive optics systems are now in operation across the globe. These systems, capable of high order wavefront correction, deliver Strehl ratios of 90% in the near-infrared. Originally intended for the direct imaging of exoplanets, these systems are often equipped with advanced coronagraphs that suppress the on-axis-star, interferometers to calibrate wavefront errors, and low order wavefront sensors to stabilize any tip/tilt residuals to a degree never seen before. Such systems are well positioned to facilitate the detailed spectroscopic characterization of faint substellar companions a…
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 Keck Planet Imager and Characterizer (KPIC) is an upgrade to the Keck II adaptive optics system that includes an active fiber injection unit (FIU) for efficiently routing light from exoplanets to NIRSPEC, a high-resolution spectrograph. Towards the end of 2019, we will add a suite of new coronagraph modes as well as a high-order deformable mirror. One of these modes, operating in $K$-band (2.2$μm$), will be the first vortex fiber nuller to go on sky. Vortex Fiber Nulling (VFN) is a new interferometric method for suppressing starlight in order to spectroscopically characterize exoplanets at…
