78 research outputs found

    High-multiplicity space-division multiplexed transmission systems

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    High-multiplicity space-division multiplexed transmission systems

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    Generation and characterization of cylindrical vector beams in few-mode fiber

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    For the past many decades, the Gaussian laser beam has driven major scientific discoveries that revolutionized the world of optics and photonics. In recent years, there is a burgeoning transformation where significant research has been dedicated in discovering the complex properties of cylindrical vector beams (CVBs). Increasingly, a beam of light with its intensity profile taking the shape of a single doughnut ring has attracted attention of several researchers the world over. Particularly, the so-called CVBs exhibit unique properties when focused owing to their radial and azimuthal distribution of polarization. In comparison to conventional (Gaussian-like) beams inheriting homogeneous polarization, CVBs provide unique light-matter interactions. For example, a radially polarized beam can enhance the imaging resolution of the system significantly with their spatial inhomogeneous polarization by imparting a symmetric and high numerical aperture focus. Moreover, CVBs with their phase and intensity singularities have found broad applications in quantum optics, optical micro/nano-manipulation, surface plasmon polariton, super-resolution imaging, and high-capacity fiber-optic communication. The studies of most widely used CVBs have been explored both in free space optics as well as in guided fiber optics. Further developments will require reliable techniques to generate these CVBs with strong coupling efficiency, high mode purity and high-power handling. For the past few years, the design, fabrication and study of optical fibers that supports CVBs, vortex and orbital angular momentum (OAM) beams have come to the forefront of research in this area. This is true in a sense that mode division multiplexing (MDM) is considered as a preeminent solution to the data capacity limitations faced by the standard single-mode fiber. In addition, vector beams in optical fibers constitute the fundamental basis set of linearly polarized (LP) modes (within the scalar approximation) as well as modes carrying OAM which represent another potential approach for implementing MDM based communications. Therefore, fundamental information and control over the vector beams is key to unravel future fiber communication links and CVB based fiber-optic sensors. For this purpose, it is essential to develop efficient methods to generate these CVBs. Some of the current methods reported for the generation of CVBs employ spiral phase plate, spatial light modulator (SLM), and offset fiber coupling. This thesis elucidates the generation as well as the optical characterization of such propagating cylindrical vector beams in a few-mode fiber. The ultimate purpose would be to develop simple, flexible and cost-effective photonic devices that will allow the efficient generation and stable propagation of the CVB while reducing the overall losses incurred by the system. Most of the methods reported earlier were limited to the measurements of the scalar LP mode groups of a FMF, thus neglecting the underlying vector beams that require delicate spectral and spatial control in order to be detected. In this thesis, three different techniques have been utilized for the generation of CVBs and OAM beams with high output purity. Initially, a tunable mechanical mode converter has been fabricated to demonstrate the generation of cylindrical vector beams supported by FMF in the telecom spectral range. This photonic device is utilized to demonstrate the non-destructive nonlinear characterization of CVB by utilizing the phenomenon of stimulated Brillouin scattering for the first time. We showed how the Brillouin gain spectra of the vector beams in some specialty fibers can be independently identified, measured, and subsequently exploited to probe the corresponding effective refractive indices of the vector beam retrieved from the data. This new characterization method of individual vector beam will have an impact in both light-wave and FMF-based optical sensing applications, which at present, mostly rely on the scalar LP modes. Further, a simple and low-cost technique to generate CVBs via long period fiber grating (LPFG) with very small grating pitch is reported. This work demonstrates that the cost-effective electric arc writing method for the fabrication of LPFGs is open to specialty few-mode fiber that often calls for very small pitch values. Finally, the generation of perfect cylindrical vector beams (PCVB) is demonstrated whose beam profile (i.e. transverse intensity profile) can be easily and precisely controlled. The latter novel method was used in-order to increase the free space coupling efficiency demanded by some specialty FMFs. The tailoring of the beam width and radius is performed via an iris and a diffractive phase mask implemented on a programmable SLM. The technique proposed towards the generation of PCVBs is highly adaptable for its robust nature to generate any arbitrary PCBs as well as perfect vortex beams with any topological order, using the same experimental setup. This experimental analysis is supported and validated via a rigorous theoretical framework that is in concordance with the results obtained

    Techniques émergentes de codage espace-temps pour les systèmes de communications optiques

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    Research in the field of optical fiber communications is advancing at a rapid pace in order to meet the growing needs for higher data rates. The main driving forces behind these advancements are the availability of multiple degrees of freedom in the optical fiber allowing for multiplexing more data: amplitude, phase and polarization state of the optical field, along with time and wavelength are already used in the deployed optical transmission systems. Yet, these systems are approaching their theoretical capacity limits and an extra dimension "space" is investigated to achieve the next capacity leap. However, packing several data channels in the same medium brings with it differential impairments and crosstalk that can seriously deteriorate the performance of the system. In this thesis, we focus on recent optical MIMO schemes based on polarization division multiplexing (PDM) and space division multiplexing (SDM). In both, we assess the performance penalties induced by non-unitary crosstalk and loss disparities among the channels arising from imperfections in the used optical components (fibers, amplifiers, multiplexers...), and suggest novel MIMO coding techniques known as Space-Time (ST) codes, initially designed for wireless multi-antenna channels, to mitigate them.La recherche dans le domaine des communications sur fibres optiques avance à un rythme rapide afin de satisfaire des demandes croissantes de communications à débits élevés. Les principaux moteurs de ces avancements sont la multitude de degrés de liberté offerts par la fibre permettant ainsi la transmission de plus de données: l'amplitude, la phase et l'état de polarisation du champ optique, ainsi que le temps et la longueur d'onde sont déjà utilisés dans les systèmes de transmission optique déployés. Pourtant, ces systèmes s'approchent de leur limite fondamentale de capacité et un degré supplémentaire: "la dimension spatiale" est étudié pour réaliser un saut qualitatif majeur en termes de capacité de transmission. Cependant, l'insertion de plusieurs flux de données dans le même canal de propagation induit également des pertes différentielles et de la diaphonie entre les flux, ce qui peut fortement réduire la qualité du système de transmission. Dans cette thèse, nous nous concentrons sur les systèmes de transmission optique de type MIMO basés sur un multiplexage en polarisation ou en modes de propagation. Dans les deux cas, nous évaluons la dégradation de la performance provoquée par une interférence inter-canaux non-unitaire et des disparités de gain entre les canaux engendrées par des imperfections dans les composants optiques utilisés (fibres, amplificateurs, multiplexeurs...), et proposons pour les combattre, de nouvelles techniques de codage pour les systèmes MIMO nommées "codes Spatio-Temporels" (ST), préalablement conçues pour les systèmes radios multi-antennaires

    Optical performance monitoring in optical packet-switched networks

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    Para poder satisfacer la demanda de mayores anchos de banda y los requisitos de los nuevos servicios, se espera que se produzca una evolución de las redes ópticas hacia arquitecturas reconfigurables dinámicamente. Esta evolución subraya la importancia de ofrecer soluciones en la que la escalabilidad y la flexibilidad sean las principales directrices. De acuerdo a estas características, las redes ópticas de conmutación de paquetes (OPS) proporcionan altas capacidades de transmisión, eficiencia en ancho de banda y excelente flexibilidad, además de permitir el procesado de los paquetes directamente en la capa óptica. En este escenario, la solución all-optical label switching (AOLS) resuelve el cuello de botella impuesto por los nodos que realizan el procesado en el dominio eléctrico. A pesar de los progresos en el campo del networking óptico, las redes totalmente ópticas todavía se consideran una solución lejana . Por tanto, es importante desarrollar un escenario de migración factible y gradual desde las actuales redes ópticas basadas en la conmutación de circuitos (OCS). Uno de los objetivos de esta tesis se centra en la propuesta de escenarios de migración basados en redes híbridas que combinan diferentes tecnologías de conmutación. Además, se analiza la arquitectura de una red OPS compuesta de nodos que incorporan nuevas funcionalidades relacionadas con labores de monitorización y esquemas de recuperación. Las redes ópticas permiten mejorar la transparencia de la red, pero a costa de aumentar la complejidad de las tareas de gesión. En este escenario, la monitorización óptica de prestaciones (OPM) surge como una tecnología capaz de facilitar la administración de las redes OPS, en las que cada paquete sigue su propia ruta en la red y sufre un diferente nivel de degradación al llegar a su destino. Aquí reside la importancia de OPM para garantizar los requisitos de calidad de cada paquete.Vilar Mateo, R. (2010). Optical performance monitoring in optical packet-switched networks [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8926Palanci

    Radio beam steering in indoor fibre-wireless networks

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