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

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

Mode division multiplexing using an orbital angular momentum mode sorter and MIMO-DSP over a graded-index few-mode optical fibre

Mode division multiplexing (MDM)– using a multimode optical fiber’s N spatial modes as data channels to transmit N independent data streams – has received interest as it can potentially increase optical fiber data transmission capacity N-times with respect to single mode optical fibers. Two challenges of MDM are (1) designing mode (de)multiplexers with high mode selectivity (2) designing mode (de)multiplexers without cascaded beam splitting’s 1/N insertion loss. One spatial mode basis that has received interest is that of orbital angular momentum (OAM) modes. In this paper, using a device referred to as an OAM mode sorter, we show that OAM modes can be (de)multiplexed over a multimode optical fiber with higher than −15 dB mode selectivity and without cascaded beam splitting’s 1/N insertion loss. As a proof of concept, the OAM modes of the LP11 mode group (OAM−1,0 and OAM+1,0), each carrying 20-Gbit/s polarization division multiplexed and quadrature phase shift keyed data streams, are transmitted 5km over a graded-index, few-mode optical fibre. Channel crosstalk is mitigated using 4 × 4 multiple-input-multiple-output digital-signal-processing with <1.5 dB power penalties at a bit-error-rate of 2 × 10−3

Characterization of a Fiber-Coupled 36-Core 3-Mode Photonic Lantern Spatial Multiplexer

A fiber-coupled 108-port photonic lantern spatial-MUX is characterized with a spatially-diverse optical vector network analyzer. Insertion loss, mode-dependent losses, and time response are measured, showing significant mode mixing at a fiber splice

Novel Fibers and Components for Space Division Multiplexing Technologies

Passive devices and amplifiers for space division multiplexing are key components for future deployment of this technology and for the development of new applications exploring the spatial diversity of light. Some important devices include photonic lantern (PL) mode multiplexers supporting several modes, fan-in/fan-out (FIFO) devices for multicore fibers (MCFs), and multimode amplifiers capable of amplifying several modes with low differential modal gain penalty. All these components are required to overcome the capacity limit of single mode fiber (SMF) communication systems, driven by the growing data capacity demand. In this dissertation I propose and develop different passive components and amplifiers for space division multiplexing technologies, including PL mode multiplexers with low insertion loss and low mode dependent loss to excite different number of modes into few mode fibers (FMFs). I demonstrate a PL with a graded index core that better matches the mode profiles of a graded index FMF supporting six spatial modes with mode dependent loss (MDL) ranging from 2- to 3-dB over the entire C-band. Multicore fibers can alleviate the capacity limit of single mode fibers by placing multiple single mode cores within the same fiber cladding. However, interfacing single mode fibers to MCFs can be challenging due to physical limitations, in this dissertation I develop and fabricate different types of FIFO devices to couple light into MCFs with high efficiency and having up to 19 cores. I demonstrate high coupling efficiency with insertion loss below 0.5 dB per FIFO into a 4-core MCF and below 1 dB for a 19-core MCF. Multimode erbium doped fiber (EDF) amplifiers are required to amplify each mode within the few mode transmission fiber, the main challenge is to provide an amplifier with low differential modal gain, in this dissertation I present the first coupled-core amplifier concept compatible with FMFs. A 6-core coupled-core EDF can be spliced with low insertion and low MDL to a FMF supporting 6 spatial modes via a slight taper transition. The amplifier introduces 1.8 MDL with gain variation over the entire C-band below 1-dB

Optical Fibers for Space-Division Multiplexed Transmission and Networking

Single-mode fiber transmission can no longer satisfy exponentially growing capacity demand. Space-division multiplexing (SDM) appears to be the only way able to dramatically improve the transmission capacity, for which, novel optical fiber is one of the key technologies. Such fibers must possess the following characteristics: 1) high mode density per cross-sectional area and 2) low crosstalk or low modal differential group delay (DMGD) to reduce complexity of digital signal processing. In this dissertation, we explore the design and characterization of three kinds of fibers for SDM: few-mode fiber (FMF), few-mode multi-core fiber (FM-MCF) and coupled multi-core fiber (CMCF) as well as their applications in transmission and networking. For the ultra-high density need of SDM, we have proposed the FMMCF. It combines advantages of both the FMF and MCF. The challenge is the inter-core crosstalk of the high-order modes. By applying a hole-assisted structure and careful fiber design, the LP11 crosstalk has been suppressed down to -40dB per km. This allows separate transmission on LP01 and LP11 modes without penalty. In fact, a robust SDM transmission up to 200Tb/s has been achieved using this fiber. To overcome distributed modal crosstalk in conjunction with DMGD, supermodes in CMCFs have been proposed. The properties of supermodes were investigated using the coupled-mode theory. The immediate benefits include high mode density and large effective area. In supermode structures, core-to-core coupling is exploited to reduce modal crosstalk or minimize DMGD. In addition, higher-order supermodes have been discovered in CMCFs with few-mode cores. We show that higher-order supermodes in different waveguide array configurations can be strongly affected by angle-dependent couplings, leading to different modal fields. Analytical solutions are provided for linear, rectangular and ring arrays. Higher-order modes have been observed for the first time using S2 imaging method. Finally, we introduce FMF to gigabit-capable passive optical networks (GPON). By replacing the conventional splitter with a photonic lantern, upstream combining loss can be eliminated. Low crosstalk has been achieved by a customized mode-selective photonic lantern carefully coupled to the FMF. We have demonstrated the first few-mode GPON system with error-free performance over 20-km 3-mode transmission using a commercial GPON system carrying live Ethernet traffic. We then scale the 3-mode GPON system to 5-mode, which resulted in a 4dB net gain in power budget in comparison with current commercial single-mode GPON systems

Spatially integrated erbium-doped fiber amplifiers enabling space-division multiplexing

L'augmentation exponentielle de la demande de bande passante pour les communications laisse présager une saturation prochaine de la capacité des réseaux de télécommunications qui devrait se matérialiser au cours de la prochaine décennie. En effet, la théorie de l’information prédit que les effets non linéaires dans les fibres monomodes limite la capacité de transmission de celles-ci et peu de gain à ce niveau peut être espéré des techniques traditionnelles de multiplexage développées et utilisées jusqu’à présent dans les systèmes à haut débit. La dimension spatiale du canal optique est proposée comme un nouveau degré de liberté qui peut être utilisé pour augmenter le nombre de canaux de transmission et, par conséquent, résoudre cette menace de «crise de capacité». Ainsi, inspirée par les techniques micro-ondes, la technique émergente appelée multiplexage spatial (SDM) est une technologie prometteuse pour la création de réseaux optiques de prochaine génération. Pour réaliser le SDM dans les liens de fibres optiques, il faut réexaminer tous les dispositifs intégrés, les équipements et les sous-systèmes. Parmi ces éléments, l'amplificateur optique SDM est critique, en particulier pour les systèmes de transmission pour les longues distances. En raison des excellentes caractéristiques de l'amplificateur à fibre dopée à l'erbium (EDFA) utilisé dans les systèmes actuels de pointe, l'EDFA est à nouveau un candidat de choix pour la mise en œuvre des amplificateurs SDM pratiques. Toutefois, étant donné que le SDM introduit une variation spatiale du champ dans le plan transversal de la fibre, les amplificateurs à fibre dopée à l'erbium spatialement intégrés (SIEDFA) nécessitent une conception soignée. Dans cette thèse, nous examinons tout d'abord les progrès récents du SDM, en particulier les amplificateurs optiques SDM. Ensuite, nous identifions et discutons les principaux enjeux des SIEDFA qui exigent un examen scientifique. Suite à cela, la théorie des EDFA est brièvement présentée et une modélisation numérique pouvant être utilisée pour simuler les SIEDFA est proposée. Sur la base d'un outil de simulation fait maison, nous proposons une nouvelle conception des profils de dopage annulaire des fibres à quelques-modes dopées à l'erbium (ED-FMF) et nous évaluons numériquement la performance d’un amplificateur à un étage, avec fibre à dopage annulaire, à ainsi qu’un amplificateur à double étage pour les communications sur des fibres ne comportant que quelques modes. Par la suite, nous concevons des fibres dopées à l'erbium avec une gaine annulaire et multi-cœurs (ED-MCF). Nous avons évalué numériquement le recouvrement de la pompe avec les multiples cœurs de ces amplificateurs. En plus de la conception, nous fabriquons et caractérisons une fibre multi-cœurs à quelques modes dopées à l'erbium. Nous réalisons la première démonstration des amplificateurs à fibre optique spatialement intégrés incorporant de telles fibres dopées. Enfin, nous présentons les conclusions ainsi que les perspectives de cette recherche. La recherche et le développement des SIEDFA offriront d'énormes avantages non seulement pour les systèmes de transmission future SDM, mais aussi pour les systèmes de transmission monomode sur des fibres standards à un cœur car ils permettent de remplacer plusieurs amplificateurs par un amplificateur intégré.The exponential increase of communication bandwidth demand is giving rise to the so-called ‘capacity crunch’ expected to materialize within the next decade. Due to the nonlinear limit of the single mode fiber predicted by the information theory, all the state-of-the-art techniques which have so far been developed and utilized in order to extend the optical fiber communication capacity are exhausted. The spatial domain of the lightwave links is proposed as a new degree of freedom that can be employed to increase the number of transmission paths and, subsequently, overcome the looming ‘capacity crunch’. Therefore, the emerging technique named space-division multiplexing (SDM) is a promising candidate for creating next-generation optical networks. To realize SDM in optical fiber links, one needs to investigate novel spatially integrated devices, equipment, and subsystems. Among these elements, the SDM amplifier is a critical subsystem, in particular for the long-haul transmission system. Due to the excellent features of the erbium-doped fiber amplifier (EDFA) used in current state-of-the-art systems, the EDFA is again a prime candidate for implementing practical SDM amplifiers. However, since the SDM introduces a spatial variation of the field in the transverse plane of the optical fibers, spatially integrated erbium-doped fiber amplifiers (SIEDFA) require a careful design. In this thesis, we firstly review the recent progress in SDM, in particular, the SDM optical amplifiers. Next, we identify and discuss the key issues of SIEDFA that require scientific investigation. After that, the EDFA theory is briefly introduced and a corresponding numerical modeling that can be used for simulating the SIEDFA is proposed. Based on a home-made simulation tool, we propose a novel design of an annular based doping profile of few-mode erbium-doped fibers (FM-EDF) and numerically evaluate the performance of single stage as well as double-stage few-mode erbium-doped fiber amplifiers (FM-EDFA) based on such fibers. Afterward, we design annular-cladding erbium-doped multicore fibers (MC-EDF) and numerically evaluate the cladding pumped multicore erbium-doped fiber amplifier (MC-EDFA) based on these fibers as well. In addition to fiber design, we fabricate and characterize a multicore few-mode erbium-doped fiber (MC-FM-EDF), and perform the first demonstration of the spatially integrated optical fiber amplifiers incorporating such specialty doped fibers. Finally, we present the conclusions as well as the perspectives of this research. In general, the investigation and development of the SIEDFA will bring tremendous benefits not only for future SDM transmission systems but also for current state-of-the-art single-mode single-core transmission systems by replacing plural amplifiers by one integrated amplifier