This thesis presents three distinct methodologies aimed at exploring pivotal aspects within the domain of fiber optics and piezoelectric materials. The first approach offers a comprehensive exploration of three pivotal aspects within the realm of fiber optics and piezoelectric materials. The study delves into the influence of voltage variation on piezoelectric displacement, examines the effects of bending multimode fiber (MMF) on data transmission, and scrutinizes the performance of an Autoencoder in MMF image reconstruction with and without additional noise. To assess the impact of voltage variation on piezoelectric displacement, experiments were conducted by applying varying voltages to a piezoelectric material, meticulously measuring its radial displacement. The results revealed a notable increase in displacement with higher voltage, presenting implications for fiber stability and overall performance. Additionally, the investigation into the effects of bending MMF on data transmission highlighted that the bending process causes the fiber to become leaky and radiate power radially, potentially affecting data transmission. This crucial insight emphasizes the necessity for further research to optimize data transmission in practical fiber systems. Furthermore, the performance of an Autoencoder model was evaluated using a dataset of MMF images, in diverse scenarios. The Autoencoder exhibited impressive accuracy in reconstructing MMF images with high fidelity. The results underscore the significance of ongoing research in these domains, propelling advancements in fiber optic technology.The second approach of this thesis entails a comparative investigation involving three distinct neural network models to assess their efficacy in improving image quality within optical transmissions through multimode fibers, with a specific focus on mitigating speckle patterns. Our proposed methodology integrates multimode fibers with a piezoelectric source, deliberately introducing noise into transmitted images to evaluate their performance using an autoencoder neural network. The autoencoder, trained on a dataset augmented with noise and speckle patterns, adeptly eliminates noise and reconstructs images with enhanced fidelity. Comparative analyses conducted with alternative neural network architectures, namely a single hidden layer (SHL) model and a U-Net architecture, reveal that while U-Net demonstrates superior performance in terms of image reconstruction fidelity, the autoencoder exhibits notable advantages in training efficiency. Notably, the autoencoder achieves saturation SSIM in 450 epochs and 24 minutes, surpassing the training durations of both U-Net (210 epochs, 1 hour) and SHL (160 epochs, 3 hours and 25 minutes) models. Impressively, the autoencoder's training time per epoch is six times faster than U-Net and fourteen times faster than SHL. The experimental setup involves the application of varying voltages via a piezoelectric source to induce noise, facilitating adaptation to real-world conditions. Furthermore, the study not only demonstrates the efficacy of the proposed methodology but also conducts comparative analyses with prior works, revealing significant improvements. Compared to Li et al.'s study, our methodology, particularly when utilizing the pre-trained autoencoder, demonstrates an average improvement of 15% for SSIM and 9% for PSNR in the worst-case scenario. Additionally, when compared to Lai et al.'s study employing a generative adversarial network for image reconstruction, our methodology achieves slightly superior SSIM outcomes in certain scenarios, reaching 96%. The versatility of the proposed method is underscored by its consistent performance across varying voltage scenarios, showcasing its potential applications in medical procedures and industrial inspections. This research not only presents a comprehensive and innovative approach to addressing challenges in optical image reconstruction but also signifies significant advancements compared to prior works. The final approach of this study entails employing Hermit Gaussian Functions with varying orders as activation functions within a U-Net model architecture, aiming to evaluate its effectiveness in image reconstruction. The performance of the model is rigorously assessed across five distinct voltage scenarios, and a supplementary evaluation is conducted with digit 5 excluded from the training set to gauge its generalization capability. The outcomes offer promising insights into the efficacy of the proposed methodologies, showcasing significant advancements in optical image reconstruction. Particularly noteworthy is the robust accuracy demonstrated by the higher orders of the Hermit Gaussian Function in reconstructing MMF images, even amidst the presence of noise introduced by the voltage source. However, a decline in accuracy is noted in the presence of voltage-induced noise, underscoring the imperative need for further research to bolster the model's resilience in real-world scenarios, especially in comparison to the utilization of the Rectified Linear Unit (ReLU) function.

The use of optical fiber is of great interest in developing extensive, high-speed networking infrastructures. Optical fiber provide many advantages over traditional copper cables and wireless links. Among them are high security, low electromagnetic interference, extremely low loss and high bandwidths, light weight and manageability. However, the very small wavelengths associated with optical radiation requires very small waveguide dimensions. Waveguide dimension of single mode fiber (SMF) are < 10µm, resulting in relatively poor yield in device manufacturing. For residential and other last-mile networks topologies, cost constraints limit the appeal of SMF. Multimode fiber (MMF) allow for less restrictive manufacturing tolerances; however, the distortion that results from the dispersion in propagation among the many modes can be prohibitively large for data rates approaching and exceeding 1 Gb/s. To improve the deployability of MMF, a method of dispersion compensation that maintains the ease-of-use characteristic of MMF is required This dissertation demonstrates an opto-electronic method of dispersion compensation by the use of a multisegment photodetector. It is shown the modes of the fiber can be seperated such that when the individual photodetector signals are combined, the resulting temporal response of the fiber link is improved from that of a conventional fiber link. This method is extremely robust to system variation and is independent of data rate and transmission format, allowing it to be employed in a wide variety of optical links. More importantly, the implementation demonstrated is comparable, in simplicity and alignment tolerance, to a conventional photodetector. System performance is shown using both temporal and frequency response as well as real bit error rate and eye diagram measurements.

Few mode fibers and multimode fibers (MMFs) are traditionally regarded as unsuitable for important applications such as communications and sensing. A major challenge in using MMFs for aforementioned applications is how to precisely control the waveguide modes propagating within MMFs. In this thesis, we experimentally demonstrate a generic method for controlling the linearly polarized (LP) modes within a two-mode fiber (TMF). Our method is based on adaptive optics (AO), where one utilizes proper feedback signals to shape the wavefront of the input beam in order to achieve the desired LP mode composition. In the first part of this thesis, we demonstrate the feasibility of AO-based mode control by using the correlation between the experimentally measured field distribution and the desired mode profiles as feedback for wavefront optimization. Selectively excitation of pure LP modes or their combinations at the distal end of a TMF are shown. Furthermore, we demonstrate that selective mode excitation in the TMF can be achieved by using only 5×5 independent phase blocks. Afterwards, we extend our AO-based mode control method to more practical scenarios, where feedback signals are provided by all-fiber devices such as a directional fiber coupler or fiber Bragg gratings (FBGs). Using the coupling ratio of a directional coupler as feedback, we demonstrate adaptive control of LP modes at the two output ports of the directional coupler. With feedback determined by the relative magnitude of optical power reflected by a FBG and the transmitted power, selective excitations of the LP01 and the LP11 modes are experimentally shown. As the final component of this thesis, we experimentally combine the AO-based mode control with time-division-multiplexing. By choosing reflected pulses with appropriate arrival time for mode control, we can selectively excite the LP11 mode at different FBG locations within the TMF, based on the ratio of optical signals reflected by FBGs in the TMF and the transmitted signal. Using two lasers set at the two FBG peak reflection wavelengths associated with the LP01 and the LP11 modes, we can accomplish AO-based mode control within a TMF by using only the reflection signals from the FBG. By using the ratio of the reflected signals of two lasers as feedback, we demonstrate selective excitation of almost pure LP01 or LP11 mode at the FBG location within the TMF. The method developed in this thesis is generic and can be extended to many other applications using appropriately chosen feedback signals. It is possible to generalize the AO-based mode control method to MMF as well. This method may find important applications in MMF-based communication, sensing and imaging et. al. in the future. / Ph. D.

This thesis deals with the possibilities of energy transmission by optical fiber for the purpose of powering of electronic systems. It comprises issues of electrical energy conversion to optical energy, coupling the power into the optical fiber, coupling between fiber and opto-electric transducer, conversion of optical energy to electrical energy, and transformation on required voltage levels. The principles of such Power-Over-Fiber are discussed in the first part of the work. Various technologies for the implementation of key system parts and their effectivity are discussed. In the next part, several Power-Over-Fiber commercial devices are compared. Subsequently, systems for Power-Over-Fiber experimental implementations are proposed. They are based on the utilization of semiconductor laser, multimode fiber, photovoltaic cell and related electronic circuits. The final part of the thesis deals with the construction of experimental systems and measurement of parameters of transmitted power and efficiency.

Le projet FUI12 RLDO – dans le cadre duquel s’inscrit cette thèse – préconise une solution de réseau de topologie en étoile passive pour la montée en débit des réseaux domestiques. Cette solution de réseau rencontre des difficultés dans son implémentation avec la non-uniformité des puissances des ports de sortie des coupleurs multimodes. L’analyse de ce point nous a permis de comprendre que les propriétés des modes de propagation dans les éléments du réseau jouent un rôle clé dans les problèmes rencontrés. Pour caractériser la propagation dans le réseau, nous avons développé un banc de réflectométrie optique complexe dans le domaine fréquentiel. Les phénomènes limitant la sensibilité à la phase – liés en particulier à la non-linéarité du balayage en fréquence de la source laser – sont étudiés pour contribuer à une meilleure compréhension des mécanismes. Puis les performances de la mesure en intensité et en phase de l’instrument que nous avons mis en place sont testées. Nous avons aussi étudié les conditions de résolution optimales pour caractériser les modes d’un guide multimode et analysé l’incertitude sur la dispersion chromatique dans le cas où il est impossible de déterminer si on a accès à un mode ou plusieurs modes dans un diagramme de dispersion donné. Nous introduisons par la suite une méthode d’analyse temps-fréquence adaptative, permettant d’obtenir les courbes de dispersions avec une résolution optimale. Cette méthode nous a permis de montrer le caractère quasi-monomode, en condition d’excitation monomode, de la fibre multimode spéciale RLDO à 1310 nm et à 1550 nm. L’analyse de la propagation dans les fibres optiques, associée au modèle que nous avons développé pour comprendre le fonctionnement des coupleurs multimodes, a permis d’expliquer les difficultés rencontré avec les premières expérimentations de la topologie de réseau en étoile passive multimode et d’envisager des pistes de réalisation d’un prototype de réseau fonctionnel / In order to develop high capacity future-proof home network, the FUI 12 RLDO project suggests passive star network topology using multimode couplers. This topology encounters implementation difficulties due to the non-uniformity of the power distribution in the output ports of multimode couplers. Analyzing this problem shows that the properties of modes propagating in the network elements plays a key role in this non-uniform characteristics of multimode couplers. In order to characterize these modes propagating in the network, we have developed a complex optical frequency domain reflectometry (OFDR) setup. The phenomena limiting the sensitivity to the phase in OFDR – in fact, those related to the non-linear frequency tuning of the laser source - are investigated to contribute to a better understanding of the limiting mechanisms. Then we have tested the intensity and phase measurement performance of the developed setup. Later, we studied the optimal resolution conditions to characterize the modes in a multimode waveguide. We have also analyzed the uncertainty of the measurement of the chromatic dispersion of modes in case where it is impossible to determine whether one or several modes are present in a given dispersion curve. Additionally, we have introduced an adaptive time-frequency method, to obtain the dispersion curves with optimal resolution. This method allows us to show the versatility of the special RLDO multimode fiber (single-mode behavior under single-mode excitation at 1310 nm and 1550 nm). The analysis of the propagation in the optical fibers, associated with a model we have developed to study the behavior of multimode couplers, has permitted to explain encountered difficulties with the experiments of the multimode passive star network topology. This also gives insights to develop a functional prototype of network

Cavity ring-down spectroscopy has been used over the last twenty years as a highly sensitive absorption spectroscopic technique to measure light attenuation in gases, liquids, and solid samples. An optical cavity is used as a multi-pass cell, and the decay time of the light intensity in the cavity is measured, thereby rendering the techniques insensitive to light intensity fluctuations. Optical waveguides are used to build the optical cavities presented in this work. The geometries of such waveguides permit the use of very small liquid sample volumes while retaining the advantages of cavity ring-down spectroscopy. In this thesis cavity ring-down measurements are conducted, both, in the time domain and by measuring phase-shifts of sinusoidally modulated light, and the two methods are theoretically connected using a simple mathematical model, which is then experimentally confirmed. A new laser driver, that is compatible with high powered diode lasers, has to be designed to be able to switch from time domain to frequency domain measurements. A sample path length enhancement within the optical cavity is explored with the use of liquid core waveguides. The setup was optimised with respect to the matrix liquid, the geometrical matching of waveguide geometries, and the shape of liquid core waveguide ends. Additionally, a new technique of producing concave lenses at fibre ends has been developed and the output of a general fibre lens is simulated. Finally, liquid core waveguides are incorporated into a fibre-loop ring-down spectroscopy setup to measure the attenuation of two model dyes in a sample volume of <1 µL. The setup is characterized by measuring concentrations of Allura Red AC and Congo Red from 1 µM to a limit of detection of 5 nM. The performance of the setup is compared to other absorption techniques measuring liquid samples. / Thesis (Ph.D, Chemistry) -- Queen's University, 2013-04-23 14:08:16.33

The master theses deals with a detailed analysis of optical fiber sensors. Specifically, there are discussed optical fibers, various types of sensors and realization optical fiber senzor and senzor system that has been optimized and processed data in real time. In master theses also describes the LabView programming enviroment and uses components, including the entire sensor systém of a sensors system that sends measured data