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 Coupling in Space-division Multiplexed Systems

Even though fiber-optic communication systems have been engineered to nearly approach the Shannon capacity limit, they still cannot meet the exponentially-growing bandwidth demand of the Internet. Space-division multiplexing (SDM) has attracted considerable attention in recent years due to its potential to address this capacity crunch. In SDM, the transmission channels support more than one spatial mode, each of which can provide the same capacity as a single-mode fiber. To make SDM practical, crosstalk among modes must be effectively managed. This dissertation presents three techniques for crosstalk management for SDM. In some cases such as intra-datacenter interconnects, even though mode crosstalk cannot be completely avoided, crosstalk among mode groups can be suppressed in properly-designed few-mode fibers to support mode group-multiplexed transmission. However, in most cases, mode coupling is unavoidable. In free-space optical (FSO) communication, mode coupling due to turbulence manifests as wavefront distortions. Since there is almost no modal dispersion in FSO, we demonstrate the use of few-mode pre-amplified receivers to mitigate the effect of turbulence without using adaptive optics. In fiber-optic communication, multi-mode fibers or long-haul few-mode fibers not only suffer from mode crosstalk but also large modal dispersion, which can only be compensated electronically using multiple-input-multiple-output (MIMO) digital signal processing (DSP). In this case, we take the counterintuitive approach of introducing strong mode coupling to reduce modal group delay and DSP complexity

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

Three-dimensional femtosecond laser processing for lab-on-a-chip applications

AbstractThe extremely high peak intensity associated with ultrashort pulse width of femtosecond laser allows us to induce nonlinear interaction such as multiphoton absorption and tunneling ionization with materials that are transparent to the laser wavelength. More importantly, focusing the femtosecond laser beam inside the transparent materials confines the nonlinear interaction only within the focal volume, enabling three-dimensional (3D) micro- and nanofabrication. This 3D capability offers three different schemes, which involve undeformative, subtractive, and additive processing. The undeformative processing preforms internal refractive index modification to construct optical microcomponents including optical waveguides. Subtractive processing can realize the direct fabrication of 3D microfluidics, micromechanics, microelectronics, and photonic microcomponents in glass. Additive processing represented by two-photon polymerization enables the fabrication of 3D polymer micro- and nanostructures for photonic and microfluidic devices. These different schemes can be integrated to realize more functional microdevices including lab-on-a-chip devices, which are miniaturized laboratories that can perform reaction, detection, analysis, separation, and synthesis of biochemical materials with high efficiency, high speed, high sensitivity, low reagent consumption, and low waste production. This review paper describes the principles and applications of femtosecond laser 3D micro- and nanofabrication for lab-on-a-chip applications. A hybrid technique that promises to enhance functionality of lab-on-a-chip devices is also introduced

Rare-earth elements doped novel photonics sources

This thesis presents the work carried out on the development of novel photonic sources based in rare-earth doped ions. It discusses in detail the properties of rare earth ions and its applications. The three major components of this work, namely, rare-earth doped solid state hosts, rare-earth doped speciality fibres, and rare-earth doped waveguide lasers have been presented in different chapters. The host glasses for the rare-earth doped gain mediums have been prepared by the traditional melt-quenching technique and spectroscopic studies have been carried out on them. Experiments to realise multi-wavelength lasers operating in the visible range have been carried out on the samarium doped phosphate glasses, owing to samarium‟s unique multiple emission peaks at 561 nm, 596 nm, and 643 nm with violet-blue excitation. Due to the relatively low emission cross section value of trivalent samarium ions (3.911 X 10-22 cm2 at 596 nm), it requires a much higher pump power. Due to the lack of high pump power diodes in the violet wavelength range, laser action could not be demonstrated. Further spectroscopic investigations on the samarium doped glasses and crystals revealed that the presence of excited state absorption could be a factor as well which discourages the realisation of laser emission in the sample. Rare-earth doped multicore optical fibres have been designed and fabricated for the realisation of active multiplexer elements and multi-wavelength lasers. Optical fibres with six cores and two cores respectively have been fabricated. Each of the six cores of the fibre were doped with erbium with the aim to develop active multiplexer elements which could incorporate multiplexing and amplification together. The cores showed considerable gains, with the maximum gain of around 30 dB – 40 dB in the wavelength range of 1500 nm – 1600 nm. The cores of the two core fibre were doped with ytterbium and erbium/ytterbium with the aim to demonstrate simultaneous laser action at 1 μm and 1.5 μm. The fibre, upon cladding pumping at 976 nm, demonstrated simultaneous laser emissions at 1061 nm and 1536 nm from the ytterbium and erbium/ytterbium doped cores, respectively. The laser action was observed with Fresnel reflection from the parallel cleaved facets of the fibre. The slope efficiency of the emission for both the cores were ~1%, which is quite low, considering the Fresnel reflection lasing. CW modelocked waveguide laser has been demonstrated in ytterbium doped bismuthate glasses. The waveguides were inscribed by the ultrafast laser inscription technique. The waveguide laser operated at the repetition rate of around 1.94 GHz with the pulse duration of about 1.1 ps at the wavelength of 1029 nm

10-Mode Photonic Lanterns Using Low-Index Micro-Structured Drilling Preforms

We demonstrate low mode-dependent loss 10-mode photonic lanterns using low-index micro-structured drilling preforms. The adiabaticity requirement for lantern tapering can be alleviated by the proposed solution leading to improved performances

10-Mode Photonic Lanterns Using Low-Index Micro-Structured Drilling Preforms

We demonstrate low mode-dependent loss 10-mode photonic lanterns using low-index micro-structured drilling preforms. The adiabaticity requirement for lantern tapering can be alleviated by the proposed solution leading to improved performances

10-mode photonic lanterns using low-index micro structured drilling preforms

We demonstrate low mode-dependent loss 10-mode photonic lanterns using low-index micro-structured drilling preforms. The adiabaticity requirement for lantern tapering can be alleviated by the proposed solution leading to improved performances

Direct laser writing of a new type of optical waveguides and components in silver containing glasses

"Thèse en cotutelle, Doctorat en physique; Université Laval, Québec, Canada et Université de Bordeaux, Talence, France"L'inscription laser directe est un domaine de recherche en croissance depuis ces deux dernières décennies, fournissant un moyen efficace et robuste pour inscrire directement des structures en trois dimensions (3D) dans des matériaux transparents tels que des verres en utilisant des impulsions laser femtosecondes. Cette technique présente de nombreux avantages par rapport à la technique de lithographie, qui se limite à la structuration en deux dimensions (2D) et implique de nombreuses étapes de fabrication. Cela rend la technique d’inscription laser directe bien adaptée aux nouveaux procédés de fabrication. Généralement, l’inscription laser dans les verres induit des changements physiques tels qu'un changement permanent de l'indice de réfraction localisé. Ces modifications ont été classées en trois types distincts:(type I, type II et type III). Dans ce travail, nous présentons un nouveau type de changement d'indice de réfraction, appelé type A qui est basé sur la création d’agrégats d'argent photo-induits. En effet, dans des verres dans lesquels sont incorporés des ions argent Ag+, lors de leur synthèse, l’inscription laser directe induit la création d’agrégats d’argent fluorescents Agmx+ au voisinage du voxel d’interaction. Ces agrégats modifient localement les propriétés optiques comme la fluorescence, la non-linéarité et la réponse plasmonique du verre. Ainsi, différents guides d'ondes, un séparateur de faisceau 50-50, ainsi que des coupleurs optiques ont été inscrits en se basant sur ce nouveau type A et complétement caractérisés. D'autre part, une étude comparative entre les deux types de guides d'ondes (type A et type I) est présentée, tout en montrant qu’en ajustant les paramètres laser, il est possible de déclencher soit le type I soit le type A. Enfin, en se basant sur des guides d’ondes de type A inscrits proche de la surface du verre, un capteur d'indice de réfraction hautement sensible a été inscrit dans une lame de verre de 1 cm de long. Ce capteur miniaturisé peut présenter deux fenêtres de détection d’indice, ce qui constitue une première mondiale. Les propriétés des guides d'ondes inscrits dans ces verres massifs ont été transposées à des fibres en forme de ruban, du même matériau contenant de l'argent. Les résultats obtenus dans ce travail de thèse ouvrent la voie à la fabrication de circuits intégrés en 3D et de capteurs à fibre basés sur des propriétés optiques originales inaccessibles avec des guides d’onde de type I standard.Direct Laser Writing (DLW) has been an exponentially growing research field during the last two decades, by providing an efficient and robust way to directly fabricate three dimensional (3D) structures in transparent materials such as glasses using femtosecond laser pulses. It exhibits many advantages over the lithography technique, which is mostly limited to two dimensional (2D) structuring and involves many fabrication steps. This competitive aspect makes the DLW technique suitable for future technological transfer to advanced industrial manufacturing. Generally, DLW in glasses induces physical changes such as permanent local refractive index modifications that have been classified under three distinct types: (Type I, Type II & Type III). In silver containing glasses with embedded silver ions Ag+, DLW induces the creation of fluorescent silver clusters Agmx+ at the vicinity of the interaction voxel. In this work, we present a new type of refractive index change, called type A occurring in the low pulse energy regime that is based on the creation of the photo-induced silver clusters allowing the creation of new linear and nonlinear optical waveguides in silver containing glasses. Various waveguides, a 50- 50 Y beam splitter, as well as optical couplers, were written based on type A modification inside bulk glasses and further characterized. In addition, a comparitive study between type A and type I waveguides is presented, showing that finely tuning the laser parameters allows the creation of either type A or type I modifications inside silver containing glasses. Finally, based on type A near-surface waveguides, a highly sensitive refractive index sensor is created in a 1 cm glass chip, which could exhibit a pioneer demonstration of double sensing refractive ranges. The waveguiding properties observed and reported in the bulk of such silver containing glasses were transposed to ribbon shaped fibers of the same material. Those results pave the way towards the fabrication of 3D integrated circuits and fiber sensors with original fluorescent, nonlinear and plasmonic properties that are not accessible using the standard type I modification

Development of optical fibre curvateure sensors for subsea instrumentation

The experimental results presented in this thesis were part of a bigger research project (LAkHsMI) funded by the European Union (Horizon 2020). The overall project’s aim is to monitor sea flow speeds for different applications with electrical and optical fibre sensors. Here, the fabrication of the sensors which exploit Fibre Bragg Grating (FBG) using conventional, as well as novel optical fibres is presented. Two different curvature sensors were produced for the purposes of the project. The first one was fabricated using four single mode fibres (SMFs) bundled together, while the second used one Multicore fibre (MCF) with four optical cores. The structure of both permitted their curvature to be determined in two dimensions. The first type of optical fibre curvature sensor was also used for the fabrication of a FBG Attitude sensor, where the orientation of a platform in two planes could be determined with accuracy of ±2°. The main priority of the studies presented here was the fabrication and performance of the MCF curvature sensors. The transmittance and reflectance (using inscribed FBGs) of the light into the MCF is explored, where an interface device between the MCF to SMF is required. Two different cases are reported, the first uses a silica inscribed waveguide fan-out device, while the second uses a tapered MCF fan-out device. In the first case the temperature sensitivity of the silica waveguide fan-out device is detected. This sensitivity can be diminished with the use of the tapered MCF fan-out device and discussed. Moreover, in the second case coupling of light from one core of the MCF to all four cores is required. Hence, inscription of different FBGs into the cores of the MCF was achieved so that the overlap of the FBGs spectra would be avoided. The challenges that arose during the fabrication and performance of these sensors are reported. Moreover, their temperature sensitivity as well as the strengths and weaknesses over several aspects are reported. Finally, a comparison between the curvature sensors is included and states which sensor can be used for subsea flow measurements and which has the potentials for further development