The Photonic Lantern

Photonic lanterns are made by adiabatically merging several single-mode cores into one multimode core. They provide low-loss interfaces between single-mode and multimode systems where the precise optical mapping between cores and individual modes is unimportant.Comment: 45 pages; article unchanged, accepted for publication in Advances in Optics and Photonic

Orbital angular momentum in optical fibers

Thesis (Ph.D.)--Boston UniversityInternet data traffic capacity is rapidly reaching limits imposed by nonlinear effects of single mode fibers currently used in optical communications. Having almost exhausted available degrees of freedom to orthogonally multiplex data in optical fibers, researchers are now exploring the possibility of using the spatial dimension of fibers, via multicore and multimode fibers, to address the forthcoming capacity crunch. While multicore fibers require complex manufacturing, conventional multimode fibers suffer from mode coupling, caused by random perturbations in fibers and modal (de)multiplexers. Methods that have been developed to address the problem of mode coupling so far, have been dependent on computationally intensive digital signal processing algorithms using adaptive optics feedback or complex multiple-input multiple-output algorithms. Here we study the possibility of using the orbital angular momentum (OAM), or helicity, of light, as a means of increasing capacity of future optical fiber communication links. We first introduce a class of specialty fibers designed to minimize mode coupling and show their potential for OAM mode generation in fibers using numerical analysis. We then experimentally confirm the existence of OAM states in these fibers using methods based on fiber gratings and spatial light modulators. In order to quantify the purity of created OAM states, we developed two methods based on mode-image analysis, showing purity of OAM states to be 90% after 1km in these fibers. Finally, in order to demonstrate data transmission using OAM states, we developed a 4-mode multiplexing and demultiplexing systems based on free-space optics and spatial light modulators. Using simple coherent detection methods, we successfully transmit data at 400Gbit/s using four OAM modes at a single wavelength, over 1.1 km of fiber. Furthermore, we achieve data transmission at 1.6Tbit/s using 10 wavelengths and two OAM modes. Our study indicates that OAM light can exist, and be long lived, in a special class of fibers and our data transmission demonstrations show that OAM could be considered an additional degree of freedom for data multiplexing in future optical fiber communication links. Our studies open the doors for other applications such as micro-endoscopy and nanoscale imaging which require fiber based remote delivery of OAM light

Space Division Multiplexing in Optical Fibres

Optical communications technology has made enormous and steady progress for several decades, providing the key resource in our increasingly information-driven society and economy. Much of this progress has been in finding innovative ways to increase the data carrying capacity of a single optical fibre. In this search, researchers have explored (and close to maximally exploited) every available degree of freedom, and even commercial systems now utilize multiplexing in time, wavelength, polarization, and phase to speed more information through the fibre infrastructure. Conspicuously, one potentially enormous source of improvement has however been left untapped in these systems: fibres can easily support hundreds of spatial modes, but today's commercial systems (single-mode or multi-mode) make no attempt to use these as parallel channels for independent signals.Comment: to appear in Nature Photonic

Multiplexage par division modale pour les applications à courte distance

Le multiplexage par division de mode (MDM) a reçu une attention considérable de la part des chercheurs au cours des dernières années. La principale motivation derrière l'utilisation de différents modes de fibre optique est d'augmenter la capacité des réseaux de transport. Les expériences initiales ont montré une grande complexité dans le traitement de signal (DSP) du récepteur. Dans cette thèse, nous étudions la viabilité et les défis de la transmission de données sur des fibres à quelques modes (FMF) pour des systèmes MDM à complexité de DSP réduite. Nos études comprennent à la fois une transmission de données cohérente et non cohérente. Dans notre première contribution, nous démontrons, pour la première fois, la transmission de données sur 4 canaux dans une nouvelle fibre OAM sans démultiplexage de polarisation optique. Nous utilisons une complexité de DSP réduite: deux jeux d'égaliseurs MIMO (multiple-input multiple-output) 2 × 2 au lieu d'un bloc égaliseur MIMO 4 × 4 complet. Nous proposons un nouveau démultiplexeur de mode permettant de recevoir simultanément deux polarisations d'un mode et de réaliser électriquement un démultiplexage de polarisation dans le récepteur DSP. Nous étudions également la pénalité OSNR due aux imperfections dans le démultiplexeur de mode et nous examinons la vitesse de transmission maximum accessible pour notre système. Dans notre deuxième contribution, nous étudions les dégradations modales dans les systèmes OAM-MDM, en nous concentrant sur leur effet sur la performance et la complexité du récepteur. Dans notre étude expérimentale, nous discutons pour la première fois de l'impact de deux modes non porteurs de données sur les canaux de données véhiculés par les modes OAM. Deux types différents de fibres OAM sont étudiés. Nous caractérisons notre liaison MDM en utilisant les techniques de mesure du temps de vol et de réponse impulsionnelle. Nous discutons des conclusions des résultats de caractérisation en étudiant l'impact des interactions modales sur la complexité de l'égaliseur du récepteur pour différents scénarios de transmission de données. Dans le troisième chapitre, nous étudions un nouveau FMF à maintien de polarisation et conduisons deux séries d'expériences de transmission de données cohérentes et de radio sur fibre (RoF). Nous démontrons pour la première fois, la transmission de données sans MIMO sur six et quatre canaux dans les systèmes cohérents et RoF, respectivement. Nous démontrons également, pour la première fois, la transmission de données RoF sur deux polarisations d'un mode dans une FMF. Nous discutons de la dégradation des performances due à la diaphonie dans de tels systèmes. Nous étudions également l'impact de la courbure sur cette fibre dans un contexte de RoF. La propriété de maintien de polarisation de cette fibre sous courbure est étudiée à la fois par des expériences de caractérisation et de transmission de données.Mode division multiplexing (MDM) has received extensive attention by researchers in the last few years. The main motivation behind using different modes of optical fiber is to increase the capacity of transport networks. Initial experiments showed high complexity in DSP of the receiver. In this thesis, we investigate the viability and challenges for data transmission over specially designed few mode fibers (FMF) for MDM systems with reduced DSP. Our studies include both coherent and non-coherent data transmission. In our first contribution, we demonstrate, for the first time, data transmission over 4 channels in a novel OAM fiber without optical polarization demultiplexing. We use reduced DSP complexity: two sets of 2×2 multiple-input multiple-output (MIMO) equalizers instead of a full 4×4 MIMO equalizer block. We propose a novel mode demultiplexer enabling us to receive two polarizations of a mode simultaneously and conducting polarization demultiplexing electrically in receiver DSP. We also investigate the OSNR penalty due to imperfections in the mode demultiplexer and we examine the maximum reachable baud rate for our system. In our second contribution, we study the modal impairments in OAM-MDM systems, focusing on their effect on receiver performance and complexity. In our experimental study, for the first time, we discuss the impact of two non-data carrying modes on data channels carried by OAM modes. Two different types of OAM fibers are studied. We characterize our MDM link using time-of-flight and impulse response measurement techniques. We discuss conclusions from characterization results with studies of the impact of modal interactions on receiver equalizer complexity for different data transmission scenarios . In the third contribution, we study a novel polarization-maintaining FMF and conduct two sets of coherent data transmission and non-coherent radio over fiber (RoF) experiments. We demonstrate for the first time, MIMO –Free data transmission over six and four channels in coherent and RoF systems, respectively. We also demonstrate, for the first time, RoF data transmission over two polarizations of a mode in a FMF. We discuss the performance degradation due to crosstalk in such systems. We also study the impact of bending on this fiber in RoF context. The polarization maintaining property of this fiber under bending is studied both via characterization and data transmission experiments