Writing Bragg Gratings in Multicore Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

University of Sydney

Space missions currently on the drawing boards are expected to gather data at rates exceeding the transmission capabilities of today's telemetry systems by many orders of magnitude. Even on current missions, onboard data compression techniques are being implemented to compensate for lack of transmission speed. But while data compression can minimize the loss of data, it is no substitute for transmitting all of the data through a faster communications link. The transmission problem will soon reach crisis proportions and will affect astronomical, Earth resources, geophysical, meteorological, planetary and other space science missions. To overcome this communications bottleneck, the authors advocate the implementation of telemetry systems based on near-infrared laser transmission techniques. The fiber-optics communications industry has developed most of the basic components required for signal transmission in this wavelength band, which should make such a system affordable on scales relevant to the cost of anticipated space science missions.

Astronomy. Laser telemetry from space.

Astronomy. Near-field cosmology.

Recognizing computational science.

Astrophotonics lies at the interface of astronomy and photonics. This burgeoning field 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 within a multimode fibre; (v) planar waveguides to miniaturize astronomical spectrographs; (vi) large mode area fibres to generate artificial stars in the upper atmosphere for adaptive optics correction; (vii) liquid crystal polymers in optical vortex coronographs and adaptive optics systems. Astrophotonics, a field that has already created new photonic capabilities, is now extending its reach down to the Rayleigh scattering limit at ultraviolet wavelengths, and out to mid infrared wavelengths beyond 2500 nm.

Astrophotonics: a new era for astronomical instruments.

We demonstrate the fabrication of a high performance multi-mode (MM) to single-mode (SM) splitter or "photonic lantern", first described by Leon-Saval et al. (2005). Our photonic lantern is a solid all-glass version, and we show experimentally that this device can be used to achieve efficient and reversible coupling between a MM fiber and a number of SM fibers, when perfectly matched launch conditions into the MM fiber are ensured. The fabricated photonic lantern has a coupling loss for a MM to SM tapered transition of only 0.32 dB which proves the feasibility of the technology.

Efficient multi-mode to single-mode coupling in a photonic lantern.

Multimode fibres are widely used in astronomy because of the ease of coupling light into them at a telescope focus. The photonics industry has given rise to a broad range of products but these are almost exclusively restricted to single-mode fibres, although some can be adapted for use in fibres that allow several modes to propagate. Now that astronomical telescopes are moving toward diffraction-limited performance through the use of adaptive optics (AO), we address the problem of coupling light into a few-mode fibre (FMF). We find that fibres with as few as ~5 guided modes share important characterisitcs with multimode fibres, in particular high coupling efficiency.We anticipate that future astronomical instruments at an AO-corrected focus will be able to exploit a broad class of photonic devices.

Coupling light into few-mode optical fibres I: The diffraction limit.

Die &quot;Photonische Laterne,&quot; ein Glasfaser-Ger&auml;t, das aus dem Bereich der Astrophotonics, entstanden erm&ouml;glicht eine Singlemode-Photonische Funktion innerhalb einer Multimodefaser stattfinden. Wir untersuchen und bewerten das modale Verhalten der photonischen Laternen sowie die Voraussetzungen f&uuml;r einen verlustarmen zwischen einem multimode-LWL und einem &quot;nahe-Diffraction Limited&quot; Singlemode-System. Wir stellen auch eine intuitive Analogie des Verhaltens modal elektromagnetische Ausbreitung entlang der photonischen Laterne-&Uuml;bergang in Bezug auf das Kronig-Penney-Modell in der Quantenmechanik.

Photonische Laternen: eine Studie der Lichtausbreitung in Multimode Singlemode-Konverter.

La &quot;Lanterna fotonica,&quot; un dispositivo a fibra ottica che &egrave; emerso dal campo di astrophotonics, consente una funzione fotonica single-mode a prendere posto all&#39;interno di una fibra multimoda. Studiamo e valutare il comportamento modale di Lanterne fotoniche, nonch&eacute; le condizioni per il conseguimento di bassa perdita tra una fibra multimoda e un sistema single-mode &quot;vicino diffrazione limitata&quot;. Siamo presenti anche un&#39;analogia intuitiva del comportamento modale propagazione elettromagnetica lungo la transizione fotonici Lanterna in termini del modello di Kronig-Penney in meccanica quantistica.

Lanterne fotoniche: uno studio di propagazione di luce in multimode a convertitori single-mode.

La &laquo; lanterne photonique, &raquo; un dispositif de fibre optique qui a &eacute;merg&eacute; &agrave; partir du champ d&#39;astrophotonics, permet une fonction photonique monomode se d&eacute;rouler dans une fibre multimode. Nous &eacute;tudions et &eacute;valuer le comportement modal des lanternes photoniques ainsi que les conditions de r&eacute;alisation de faibles pertes entre une fibre multimode et un syst&egrave;me de mode unique de &laquo; pr&egrave;s de diffraction limited &raquo;. Nous pr&eacute;sentons aussi une analogie intuitive du comportement modal de la propagation &eacute;lectromagn&eacute;tique le long de la transition de la lanterne photoniques en fonction du mod&egrave;le de Kronig-Penney en m&eacute;canique quantique.

Lanternes photoniques : une &eacute;tude de la propagation lumineuse en multimode monomode convertisseurs.

&quot;&#x5149;&#x5B50;&#x706F;&#x7B3C;&#xFF0C;&quot;&#x57DF;&#x4E2D;&#x7684; astrophotonics&#xFF0C;&#x51FA;&#x73B0;&#x4E86;&#x7684;&#x5149;&#x7EA4;&#x8BBE;&#x5907;&#x5141;&#x8BB8;&#x5355;&#x6A21;&#x5149;&#x5B50;&#x51FD;&#x6570;&#x91C7;&#x7528;&#x591A;&#x6A21;&#x5149;&#x7EA4;&#x5185;&#x7684;&#x5730;&#x65B9;&#x3002;&#x6211;&#x4EEC;&#x7814;&#x7A76;&#x548C;&#x8BC4;&#x4F30;&#x7684;&#x6A21;&#x6001;&#x884C;&#x4E3A;&#x7684;&#x5149;&#x5B50;&#x7684;&#x706F;&#x7B3C;&#xFF0C;&#x4EE5;&#x53CA;&#x5B9E;&#x73B0;&#x4F4E;&#x635F;&#x8017;&#x591A;&#x6A21;&#x5149;&#x7EA4;&#x548C;&quot;&#x9644;&#x8FD1;&#x884D;&#x5C04;&#x6709;&#x9650;&#x516C;&#x53F8;&quot;&#x5355;&#x6A21;&#x5F0F;&#x7CFB;&#x7EDF;&#x4E4B;&#x95F4;&#x7684;&#x6761;&#x4EF6;&#x3002;&#x6211;&#x4EEC;&#x4E5F;&#x662F;&#x76F4;&#x89C2;&#x7684;&#x7C7B;&#x6BD4;&#xFF0C;&#x6CBF; Kronig Penney &#x6A21;&#x578B;&#x5149;&#x5B50;&#x5F69;&#x706F;&#x8FC7;&#x6E21;&#x7684;&#x6A21;&#x6001;&#x7535;&#x78C1;&#x4F20;&#x64AD;&#x884C;&#x4E3A;&#x7684;&#x91CF;&#x5B50;&#x529B;&#x5B66;&#x4E2D;&#x3002;

&#x5149;&#x5B50;&#x706F;&#x7B3C;&#xFF1A; &#x5355;&#x6A21;&#x5F0F;&#x8F6C;&#x6362;&#x5668;&#x591A;&#x6A21;&#x4E2D;&#x4EE5;&#x5149;&#x901F;&#x4F20;&#x64AD;&#x7684;&#x7814;&#x7A76;&#x3002;

The "photonic lantern," an optical fibre device that has emerged from the field of astrophotonics, allows for a single-mode photonic function to take place within a multimode fibre. We study and evaluate the modal behaviour of photonic lanterns as well as the conditions for achieving low-loss between a multimode fibre and a "near-diffraction limited" single-mode system. We also present an intuitive analogy of the modal electromagnetic propagation behaviour along the photonic lantern transition in terms of the Kronig-Penney model in Quantum Mechanics.

Photonic lanterns: a study of light propagation in multimode to single-mode converters.

&#x300C;&#x30D5;&#x30A9;&#x30C8;&#x30CB;&#x30C3;&#x30AF; &#x30E9;&#x30F3;&#x30BF;&#x30F3;&#x3001;&#x300D;astrophotonics&#x3001;&#x30D5;&#x30A3;&#x30FC;&#x30EB;&#x30C9;&#x304B;&#x3089;&#x6D6E;&#x4E0A;&#x3057;&#x3066;&#x3044;&#x308B;&#x5149;&#x30D5;&#x30A1;&#x30A4;&#x30D0;&#x30FC; &#x30C7;&#x30D0;&#x30A4;&#x30B9; &#x30D5;&#x30A9;&#x30C8;&#x30CB;&#x30C3;&#x30AF;&#x95A2;&#x6570;&#x306E;&#x5358;&#x4E00;&#x30E2;&#x30FC;&#x30C9;&#x306F;&#x3001;&#x30DE;&#x30EB;&#x30C1;&#x30E2;&#x30FC;&#x30C9;&#x5149;&#x30D5;&#x30A1;&#x30A4;&#x30D0;&#x30FC;&#x5185;&#x306E;&#x5834;&#x6240;&#x3092;&#x53D6;&#x308B;&#x3059;&#x308B;&#x3053;&#x3068;&#x304C;&#x3067;&#x304D;&#x307E;&#x3059;&#x3002;&#x79C1;&#x305F;&#x3061;&#x306F;&#x52C9;&#x5F37;&#x3057;&#x3001;&#x30D5;&#x30A9;&#x30C8;&#x30CB;&#x30C3;&#x30AF;&#x63D0;&#x706F;&#x3060;&#x3051;&#x3067;&#x306A;&#x304F;&#x3001;&#x30DE;&#x30EB;&#x30C1;&#x30E2;&#x30FC;&#x30C9;&#x5149;&#x30D5;&#x30A1;&#x30A4;&#x30D0;&#x30FC;&#x3068;&#x300C;&#x56DE;&#x6298;&#x8FD1;&#x304F;&#x9650;&#x5B9A;&#x300D;&#x30B7;&#x30F3;&#x30B0;&#x30EB; &#x30E2;&#x30FC;&#x30C9; &#x30B7;&#x30B9;&#x30C6;&#x30E0;&#x3068;&#x4F4E;&#x640D;&#x5931;&#x3092;&#x5B9F;&#x73FE;&#x3059;&#x308B;&#x305F;&#x3081;&#x306E;&#x6761;&#x4EF6;&#x306E;&#x30E2;&#x30FC;&#x30C0;&#x30EB;&#x6319;&#x52D5;&#x3092;&#x8A55;&#x4FA1;&#x3057;&#x307E;&#x3059;&#x3002;&#x307E;&#x305F;&#x91CF;&#x5B50;&#x529B;&#x5B66;&#x3067;&#x30E2;&#x30FC;&#x30C0;&#x30EB;&#x96FB;&#x78C1;&#x6CE2;&#x306E;&#x4F1D;&#x642C;&#x6319;&#x52D5;&#x30AF;&#x30ED;&#x30FC;&#x30CB;&#x30C3;&#x30D2; &#x30DA;&#x30CB;&#x30FC; &#x30E2;&#x30C7;&#x30EB;&#x306E;&#x89B3;&#x70B9;&#x304B;&#x3089;&#x30D5;&#x30A9;&#x30C8;&#x30CB;&#x30C3;&#x30AF; &#x30E9;&#x30F3;&#x30BF;&#x30F3;&#x9077;&#x79FB;&#x306B;&#x6CBF;&#x3063;&#x3066;&#x306E;&#x76F4;&#x611F;&#x7684;&#x306A;&#x30A2;&#x30CA;&#x30ED;&#x30B8;&#x30FC;&#x3092;&#x8FF0;&#x3079;&#x308B;&#x3002;

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&quot;&#xAD11;&#xD559; &#xB79C; &#xD134;,&quot; astrophotonics, &#xD544;&#xB4DC;&#xC5D0;&#xC11C; &#xB4F1;&#xC7A5; &#xD558;&#xB294; &#xAD11; &#xD30C;&#xC774;&#xBC84; &#xC7A5;&#xCE58; &#xB2E8;&#xC77C; &#xBAA8;&#xB4DC; &#xAD11;&#xD559;&#xC801; &#xAE30;&#xB2A5; &#xBA40;&#xD2F0; &#xBAA8;&#xB4DC; &#xD30C;&#xC774;&#xBC84; &#xB0B4;&#xC5D0;&#xC11C; &#xC790;&#xB9AC;&#xB97C; &#xCC28;&#xC9C0;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;. &#xC6B0;&#xB9AC;&#xAC00; &#xACF5;&#xBD80; &#xD558; &#xACE0; &#xBA40;&#xD2F0; &#xBAA8;&#xB4DC; &#xD30C;&#xC774;&#xBC84;&#xC640; &quot;&#xADFC;&#xCC98; &#xD68C;&#xC808; &#xC81C;&#xD55C;&quot; &#xB2E8;&#xC77C; &#xBAA8;&#xB4DC; &#xC2DC;&#xC2A4;&#xD15C; &#xC0AC;&#xC774;&#xC758; &#xB0AE;&#xC740; &#xAC10;&#xB7C9;&#xC744; &#xB2EC;&#xC131; &#xD558;&#xAE30; &#xC704;&#xD55C; &#xC870;&#xAC74;&#xC73C;&#xB85C; &#xAD11;&#xD559;&#xC801; &#xCD08; &#xB871;&#xC758; &#xBAA8;&#xB2EC; &#xD589;&#xB3D9;&#xC744; &#xD3C9;&#xAC00; &#xD569;&#xB2C8;&#xB2E4;. &#xC6B0;&#xB9AC;&#xB294; &#xB610;&#xD55C; &#xC591;&#xC790;&#xC5ED;&#xD559;&#xC5D0;&#xC11C; Kronig &#xD398;&#xB2C8; &#xBAA8;&#xB378; &#xAD11;&#xD559;&#xC801; &#xB79C; &#xD134; &#xC804;&#xD658; &#xB530;&#xB77C; &#xBAA8;&#xB2EC; &#xC804;&#xC790;&#xD30C; &#xC804;&#xD30C; &#xD589;&#xB3D9;&#xC758; &#xC9C1;&#xAD00;&#xC801;&#xC778; &#xBE44;&#xC720;&#xB97C; &#xC81C;&#xC2DC;.

&#xAD11;&#xD559;&#xC801; &#xCD08; &#xB871;: &#xB2E8;&#xC77C; &#xBAA8;&#xB4DC; &#xCEE8;&#xBC84;&#xD130; &#xBA40;&#xD2F0;&#xC5D0;&#xC11C; &#xBE5B; &#xC804;&#xD30C;&#xC758; &#xC5F0;&#xAD6C;.

La &quot;linterna fot&oacute;nica,&quot; un dispositivo de fibra &oacute;ptica que ha surgido desde el campo de astrophotonics, permite una funci&oacute;n fot&oacute;nica monomodo tendr&aacute; lugar dentro de una fibra multimodo. Estudiamos y evaluar el comportamiento modal de linternas fot&oacute;nicas as&iacute; como las condiciones para el logro de baja p&eacute;rdida entre una fibra multimodo y un sistema de monomodo &quot;cerca de difracci&oacute;n limitada&quot;. Tambi&eacute;n presentamos una analog&iacute;a intuitiva del comportamiento modal de propagaci&oacute;n electromagn&eacute;tica a lo largo de la transici&oacute;n de la linterna fot&oacute;nicos en t&eacute;rminos del modelo de Kronig-Penney en mec&aacute;nica cu&aacute;ntica.

Linternas fot&oacute;nicas: un estudio de la propagaci&oacute;n ligera en multimodo a monomodo convertidores.

We demonstrate a novel imaging fiber bundle ("hexabundle") that is suitable for low-light applications in astronomy. The most successful survey instruments at optical-infrared wavelengths use hundreds to thousands of multimode fibers fed to one or more spectrographs. Since most celestial sources are spatially extended on the celestial sphere, a hexabundle provides spectroscopic information at many distinct locations across the source. We discuss two varieties of hexabundles: (i) lightly fused, closely packed, circular cores; (ii) heavily fused non-circular cores with higher fill fractions. In both cases, we find the important result that the cladding can be reduced to ~2 μm over the short fuse length, well below the conventional ~10λ thickness employed more generally, with a consequent gain in fill factor. Over the coming decade, it is to be expected that fiber-based instruments will be upgraded with hexabundles in order to increase the spatial multiplex capability by two or more orders of magnitude.

Hexabundles: imaging fiber arrays for low-light astronomical applications.

With the aim of utilizing arrayed waveguide gratings for multi-object spectroscopy in the field of astronomy, we outline several ways in which standard telecommunications grade chips should be modified. In particular, by removing the parabolic-horn taper or multimode interference coupler, and injecting with an optical fiber directly, the resolving power was increased threefold from 2400 ± 200 (spectral resolution of 0.63 ± 0.2 nm) to 7000 ± 700 (0.22 ± 0.02 nm) while attaining a throughput of 77 ± 5%. More importantly, the removal of the taper enabled simultaneous off-axis injection from multiple fibers, significantly increasing the number of spectra that can be obtained at once (i.e. the observing efficiency). Here we report that ~12 fibers can be injected simultaneously within the free spectral range of our device, with a 20% reduction in resolving power for fibers placed at 0.8 mm off-centre.

Developing arrayed waveguide grating spectrographs for multi-object astronomical spectroscopy.

We investigate the use of "photonic lanterns" as adiabatic mode converters for space-division multiplexing (SDM) systems to interface multiple single-mode fibers to a multi-mode fiber. In a SDM system, minimizing the coupling loss and mode-dependent loss best utilizes all spatial modes of the fiber which increases the capacity, the transmission distance, and minimizes the outage probability. We use modal analysis, the beam propagation method, and a transfer matrix technique to analyze the lanterns throughput along with its mode dependent loss and show that unitary coupling between single-mode fibers and a multi-mode fiber is only possible by optimizing the arrangements of the cores. Results include simulations for three, 12, 15, and 51 core lanterns to couple to six, 24, 30, and 102 spatial and polarization modes, respectively.

Geometric requirements for photonic lanterns in space division multiplexing.

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; (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) with a spectral resolution of 0.055 nm (R~30,000) using a 1 × 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.

Beating the classical limit: a diffraction-limited spectrograph for an arbitrary input beam.

We demonstrate a 3x1 fiber-based photonic lantern spatial-multiplexer with mode-selectivity greater than 6 dB and transmission loss of less than 0.3 dB. The total insertion loss of the mode-selective multiplexers when coupled to a graded-index few-mode fiber was < 2 dB. These mode multiplexers showed mode-dependent loss below 0.5 dB. To our knowledge these are the lowest insertion and mode-dependent loss devices, which are also fully compatible with conventional few-mode fiber technology and broadband operation.

Mode-selective photonic lanterns for space-division multiplexing.

We demonstrate an 11 port count wavelength selective switch (WSS) supporting spatial superchannels of three spatial modes, based on the combination of photonic lanterns and a high-port count single-mode WSS.

1x11 few-mode fiber wavelength selective switch using photonic lanterns.

We demonstrate a general method for the first order compensation of singularity splitting in a vortex beam at a single plane. By superimposing multiple forked holograms on the SLM used to generate the vortex beam, we are able to compensate vortex splitting and generate beams with desired phase singularities of order ℓ = 0, 1, 2, and 3 in one plane. We then extend this method by application of a radial phase, in order to simultaneously compensate the observed vortex splitting at two planes (near and far field) for an ℓ = 2 beam.

Correcting vortex splitting in higher order vortex beams.

The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo-three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB research.

Interstellar medium. Pseudo-three-dimensional maps of the diffuse interstellar band at 862 nm.

Fiber Bragg gratings in multicore fibers have significant potential as compact and robust filters for research and commercial applications. With the aid of an innovative, flat-fielded Mach-Zehnder interferometer, we demonstrate deep (>30 dB) narrow (100 pm at 3 dB; 90 pm at 10 dB) notches in the outer 6 cores of a 7-core fiber at a constant wavelength ( ± 15 pm). This is a crucial step in the development of FBGs operating within multimode fibers that carry an arbitrary number of spatial modes.

Demonstration of uniform multicore fiber Bragg gratings.

In recent years, there have been a series of proposals to exploit the orbital angular momentum (OAM) of light for astronomical applications. The OAM of light potentially represents a new way in which to probe the universe. The study of this property of light entails the development of new instrumentation and problems which must be addressed. One of the key issues is whether we can overcome the loss of the information carried by OAM due to atmospheric turbulence. We experimentally analyze the effect of atmospheric turbulence on the OAM content of a signal over a range of realistic turbulence strengths typical for astronomical observations. With an adaptive optics system we are able to recover up to 89% power in an initial non-zero OAM mode (ℓ = 1) at low turbulence strengths (0.30″ FWHM seeing). However, for poorer seeing conditions (1.1″ FWHM seeing), the amount of power recovered is significantly lower (5%), showing that for the terrestrial detection of astronomical OAM, a careful design of the adaptive optics system is needed.

Joss Bland-Hawthorn

Sydney Institute for Astronomy,
School of Physics,
Institute of Photonics and Optical Science,
Sydney Institute for Astronomy, School of Physics,
Institute of Photonics and Optical Science, School of Physics

University of Sydney

Writing Bragg Gratings in Multicore Fibers

Joss Bland-Hawthorn

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Sydney Institute for Astronomy,School of Physics,Institute of Photonics and Optical Science,Sydney Institute for Astronomy, School of Physics,Institute of Photonics and Optical Science, School of Physics

University of Sydney

Writing Bragg Gratings in Multicore Fibers

Sydney Institute for Astronomy,
School of Physics,
Institute of Photonics and Optical Science,
Sydney Institute for Astronomy, School of Physics,
Institute of Photonics and Optical Science, School of Physics