ln the last several years, considerable attention has been paid to the study of dispersion-flattened single-mode fibers which offer a high transmission capacity with low losses through a wide range of wavelengths. However, the existing designs are sensitive to bending and manufacturing tolerances, and are not truly single-mode at most wavelengths of interest. To remedy these problems a new series of broadband dispersion-flattened truly single-mode fiber designs are proposed. These fibers have both dispersion-shifted and dispersion-flattened features with low splice and bend losses. Results demonstrating a total dispersion of ±0.97 ps/km-nm over the entire spectral range between 1.31 μm to 1.66 μm are presented. Such dispersion-flattening is achieved while simultaneously maintaining a mode-field radius of 3 μm to 5 μm in the dispersion-flattened wavelength range. The most significant achievement is that the proposed muIti-clad fiber design is strictly single-mode and splice and bend losses are smaller than those of double-clad, triple-clad, and quadruple-clad fibers with the same value of dispersion. Ultralow dispersion fibers, whose chromatic dispersion and the first and second-order derivatives of the chromatic dispersion are zero at 1.5 μm or 1.55 μm, are described. This effectively increases the laser emission tolerance. Ultralow dispersion fibers open the way to wavelength multiplexing with currently available inexpensive multifrequency lasers, either in local or long distance networks. These fibers also have low splice and bend losses compared to double-clad, triple-clad, and quadruple-cIad fibers. An inverse waveguide synthesis program, which can trace multiple objective functions and optimize multiple parameters simultaneously, is developed. An objective function is applied, for the first time, to optimize the dispersion-flattened single-mode fiber index profile with respect to: (1) minimum dispersion, (2) the wavelengths of zero-dispersion, (3) maximum width of dispersion-flattened window, (4) maximum layer index difference less than 0.8%, and (5) layer thickness larger than 3.5 μm. The accuracy of chromatic dispersion calculations in dispersion-flattened fibers is evaluated. lt has been shown that the accuracy of approximate methods is influenced not only by the index differences, but also by their derivatives with respect to wavelength. The matrix method and direct numerical integration of the wave equation are used to compute the mode propagation constants, cutoff frequencies, field distributions, mode-field radius, and splice loss, and carry out production tolerance analysis for multi-clad step-index fibers and graded-index fibers, respectively. Detailed analysis and optimized fiber data are presented. / Ph. D.

Steady increases in the bandwidth requirements of access networks and local area networks have created a need for short-reach links supporting data rates of 10 Gb/s and larger. Server applications and data center applications too require such links. The primary challenge for these links lies in the reduction of the cost while retaining or improving the performance. Traditionally, multimode fiber (MMF) has satisfied these needs because of its low installation cost resulting from the alignment tolerance associated with the large core size. However, in view of the ever-increasing performance requirements, extraction of the best performance requires a holistic view of the channel that involves global optimization of transmitter, fiber, receiver performance and signaling strategies. The optimization results in a channel impairment mitigation technique that is a combination of optical, opto-electronic, and electronic methods. Both glass and plastic MMF links have been addressed in this work and many of the advances apply equally to both media. One example that applies strictly to glass MMF is the use of Raman amplification to not only combat attenuation but to reduce intersymbol interference (ISI). Raman amplification was demonstrated as an optical channel impairment mitigation technique enabling multi-km, multi-Gb/s transmission over glass-MMF. We demonstrated both numerically and experimentally that a power penalty reduction of 1.4 dBo can be achieved for 10 Gb/s transmission over 9 km of 62 micron glass MMF with a Raman pump power 250 mW. In recent years, plastic optical fiber (POF) has emerged as a potentially lower cost alternative to glass-MMF in enabling high performance links. The primary objective of this research is to explore the possibilities and develop low-cost, short-reach, high-data-rate POF-links. Using a comprehensive multimode fiber model, we showed that strong mode coupling, together with a reasonably accurate refractive index profile enables 40 Gb/s transmission over 200 m of graded-index POF. We experimentally demonstrated 40 Gb/s error-free transmission over 100 m of graded index perfluorinated POF (GI-PF-POF). We also demonstrated that even larger core (120 micron) GI-PF-POF can support >10 Gb/s over 100 m length. We numerically computed and experimentally measured the differential modal delay of GI-PF-POF to demonstrate that the available bandwidth is nearly independent of the launch conditions. Therefore, the alignment tolerance at the transmitter is increased resulting in a dramatically reduced packaging cost at the transmitter. However, the large-core POF increases the difficultly in capturing of the light efficiently onto a detector and results in optical power penalty and associated modal noise. To solve this, we have designed and developed a 10 Gb/s photoreceiver consisting of a large (100 micron diameter) GaAs PIN photodetector and a regulated cascade input based transimpedance amplifier (TIA) with low input impedance. Thus, a low-cost, alignment-tolerant, high-data-rate link is realized that uses a high-power, high-speed vertical cavity surface emitting laser (VCSEL) transmitter, large-core, high-speed GI-PF-POF, and the developed receiver.

Orientadores: Luiz Carlos Barbosa, Cristiano Monteiro de Barros Cordeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T19:12:29Z (GMT). No. of bitstreams: 1 Santos_ElianeMourados_M.pdf: 4020531 bytes, checksum: 57766702771129e7f4bfe1d0c7852f67 (MD5) Previous issue date: 2007 / Resumo: Este trabalho apresenta estudos de como inserir fluidos (líquidos e gases) em fibras ópticas microestruturadas, especialmente fibras de cristal fotônico, também conhecidas como PCF¿s (do inglês Photonic Crystal Fibers). Estas fibras possuem buracos de ar que percorrem todo seu comprimento. Elas podem ser divididas em dois grandes grupos: as de núcleo sólido que guiam luz por reflexão interna total e as de núcleo oco que guiam luz por um mecanismo conhecido como photonic bandgap. Ambos os tipos de fibras permitem várias aplicações em áreas como óptica e fotônica e nos dedicamos aqui à área de sensoriamento a fibra. Nesta área, usamos os microburacos para inserir fluido e dessa maneira manipular as propriedades de guiamento (em fibras de núcleo líquido), deixar a fibra mais sensível a algum parâmetro externo ou para sensoriar o fluido em questão. Nos três casos, precisamos estudar os processos de preenchimentos de fibras microestruturadas. Para este fim, estudamos e desenvolvemos maneiras de inserir fluidos em fibras de núcleos sólidos ou ocos. Usando preenchimento seletivo, produzimos fibras com núcleo líquido, criando uma região de alta interação entre luz e material. Neste trabalho, estudamos diferentes técnicas de preenchimento. A primeira, para fibras de núcleo líquido, é um preenchimento seletivo que pode ser feito usando uma máquina de emendas (splicer) ou um polímero para bloquear os microburacos. O outro consiste em manter as pontas das fibras livres (para medidas ópticas) enquanto o preenchimento é feito. Por fim, usamos o conhecimento desses processos em aplicações como sensoriamento de fluidos ou parâmetros externos e manipulação de propriedades de guiamento da luz / Abstract: This work presents studies of how to insert fluids (liquid and gas) into microstructured optical fibers, especially photonic crystal fibers, also known as PCF¿s. These optical fibers possess air holes that run along its entire length. They can be divided into two major groups: solid core fibers that guide light by total internal reflection and hollow core fibers that guide light by photonic bandgap. Both types of fibers allow several applications in areas such as optics and photonics and we dedicated this work to the fiber-sensing field. In this area we use the micro holes to insert fluids and in this way to manipulate the guidance properties in liquid core fibers, to leave the fiber more sensitive to some external parameter or to sensing the fluid. In these three cases we need to study the filling procedures in microstructured fibers. For this purpose, we studied and developed ways of inserting fluids in hollow and solid core fibers. We produced liquid core fibers, creating a high light-material overlap, using a selective filling technique. In this work we studied different filling techniques. The first one, for liquid core fibers, is a selective filling, which can be done by using a splicer machine or a polymer to block the fiber micro holes. The last one consists of keeping the fiber tips free (for optical measurements) while the filling is done. And finally we used the filling process knowledge in applications like sensing of fluids or external parameters and manipulation of guidance properties / Mestrado / Física Geral / Mestre em Física

Στην παρούσα διδακτορική διατριβή παρουσιάζεται η δυνατότητα ανάπτυξης νέων αισθητήρων με χρήση μιας καινοτόμας οπτικής ίνας, γνωστή ως Ίνα Φωτονικών Κρυστάλλων (ΙΦΚ) - (Photonic crystal fiber) σε συνδυασμό με νέα και λειτουργικά υλικά. Η ΙΦΚ αποτελείται από μια περιοδική συνήθως εξαγωνική δομή οπών που δρα ως τον μανδύα της ίνας και τις περισσότερες φορές κατασκευάζεται από γυαλί (SiO2) ή πολυμερές (PMMA, TOPAS, κτλ). Η αλλαγή στην διάμετρο των οπών και της απόστασης μεταξύ τους δίνει πολύ μεγάλη ευελιξία για διαχείριση των οπτικών ιδιοτήτων της. Εδώ παρουσιάζεται πώς η διήθηση νέων υλικών στις οπές της ΙΦΚ είναι μια αποδοτική μέθοδος για ενεργοποίηση της ΙΦΚ σε εξωτερικές παρεμβολές χωρίς να απαιτείται η κατασκευή μιας νέας ίνας από την αρχή. / This PhD thesis presents the possibility of development of new sensors using a novel optical fiber, called as photonic crystal fiber (PCF) in combination with new functional materials. PCF is consisted by a periodical, usually hexagonal structure of holes which acts as the cladding of the fiber and most of the times this fiber is made of glass (SiO2) or polymer (PMMA, TOPAS, etc.). The hole diameter and the pitch size of these fibers provides great flexibility for manipulation of their optical properties. Here, it is presented how the infiltration of new materials inside the holes of PCF constitutes an efficient method to sensitize the fiber to external perturbations without the need of a new fiber.

The quantity and length of optical fibers required for the Hobby-Eberly Telescope Dark Energy eXperiment (HETDEX) create unique fiber handling challenges. More than 33,000 optical fibers will enable the Hobby-Eberly Telescope (HET) to collect data on at least one million galaxies that are 9 billion to 11 billion light-years away, yielding the largest map of the universe ever produced [1,2]. The design advantages made possible by optical fibers also forms challenges to prevent damage to the fragile fibers that can lead to Focal Ratio Degradation (FRD) [3]. Therefore, a life cycle test must be conducted to study fiber behavior and measure FRD as a function of time. This thesis describes the design and design methodology of an electro-mechanical test apparatus for accelerated life testing of optical fiber assemblies. The design methodology summarizes the development of functional requirements and constraints that drove the design. The test apparatus design utilizes six linear actuators to replicate the movement of the fiber system deployed on HETDEX for over 65,000 accelerated cycles, simulating five years of actual operation. The electro-mechanical test apparatus will provide insight into the effects of load history on the performance of optical fibers which published data has thus far been lacking. Performance of the electro-mechanical test apparatus will be demonstrated through simulation, modeling and calculations. The test results that will be generated from the accelerated life test will be of great interest to designers of robotic fiber handling systems for major telescopes. / text

A new interferometric method which indirectly measures the total chromatic dispersion of a single mode fiber is demonstrated. The technique utilizes a short length of fiber, an unmodulated broadband source, simple low frequency electronics, and a standard interferometer. The concept of this measurement is based on the behavior of the uncorrelated individual bursts of light from the elemental emitters that constitute a thermal source. Their propagation through a dispersive media, e.g., silica fiber, which is placed in one arm of the interferometer, is delayed and broadened. They will interfere with their counterpart from the other arm, generating a train of time-varying fringes as one mirror of the interferometer is uniformly translated. The local frequency of the fringes at a given position of the moving mirror is a direct measure of the instantaneous wavelength, while the mirror position itself demarks the corresponding relative delay. A colinearly launched HeNe laser beam is used as a reference to calibrate the other source's fringe width and location of the mirror. In this experiment, an edge-emitting LED of λo = 830 nm and Δλ = 60 nm was used. The tested fibers had a length of 27.9 cm and 38.3 cm, which made the width of the crosscorrelation function approximately 100 times greater than the source's coherence length. The speed of the mechanically driven mirror set the frequency of the HeNe fringes to approximately 800 Hz with an r.m.s. fluctuation around the mean of 0.2%. The SNR of the HeNe fringes was four times larger than the LED's. Ten different runs for each fiber were executed. Data from the two sets of simultaneous measurements of delay versus wavelength were used to fit the best linear and quadratic polynomials with a minimum residual mean error square. The derivative of this function with respect to wavelength gave the dispersion relation. The accuracy of measured delay and wavelength were 0.1 ps and 6 nm, respectively. The dispersion value and its standard error for the best linear fit was approximately 117 ∓ 2 ps/km nm. The standard error for the quadratic fit was much larger due to the high noise level accompanying signal. A thorough investigation of the noise sources, accuracies, standard error of the polynomial's coefficient, and SNR analysis is conducted. This measurement is simple and has the potential of achieving substantially higher accuracy--especially for the longer wavelength region where dispersion is minute.

Recent experiments with optical fibers have reached a remarkable development for optical communication spectroscopy as well as a medical technology. Hollow optical fibers are required for optical communications. The measurement of the transmission of light through fibers can provide information about the fiber quality and about the far-field energy which radiates from the fiber end. We used five flexible hollow fused quartz fibers to study laser beam propagation down the fiber axis. Five different refractive index fluids were prepared and inserted into the fiber core to measure the transmitted intensity as a function of core property. The plots of the normalized, relative transmitted intensity measured as a function of the beam insertion point show the dependence of the transmitted intensity as a function of fiber diameter and refractive index fluid.

We report on the scrambling performance and focal-ratio-degradation (FRD) of various octagonal and rectangular fibers considered for MAROON-X. Our measurements demonstrate the detrimental effect of thin claddings on the FRD of octagonal and rectangular fibers and that stress induced at the connectors can further increase the FRD. We find that fibers with a thick, round cladding show low FRD. We further demonstrate that the scrambling behavior of non-circular fibers is often complex and introduce a new metric to fully capture non-linear scrambling performance, leading to much lower scrambling gain values than are typically reported in the literature (<1000 compared to 10,000 or more). We find that scrambling gain measurements for small-core, non-circular fibers are often speckle dominated if the fiber is not agitated.

We are developing a stable and precise spectrograph for the Large Binocular Telescope (LBT) named "iLocater." The instrument comprises three principal components: a cross-dispersed echelle spectrograph that operates in the YJ-bands (0.97-1.30 mu m), a fiber-injection acquisition camera system, and a wavelength calibration unit. iLocater will deliver high spectral resolution (R similar to 150,000-240,000) measurements that permit novel studies of stellar and substellar objects in the solar neighborhood including extrasolar planets. Unlike previous planet-finding instruments, which are seeing-limited, iLocater operates at the diffraction limit and uses single mode fibers to eliminate the effects of modal noise entirely. By receiving starlight from two 8.4m diameter telescopes that each use "extreme" adaptive optics (AO), iLocater shows promise to overcome the limitations that prevent existing instruments from generating sub-meter-per-second radial velocity (RV) precision. Although optimized for the characterization of low-mass planets using the Doppler technique, iLocater will also advance areas of research that involve crowded fields, line-blanketing, and weak absorption lines.

Lee Chun Ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leave 45). / List of Figures --- p.iii / List of Tables --- p.iv / Acknowledgement --- p.v / Abstract --- p.vi / Chapter I --- Introduction --- p.1 / Chapter II --- Architecture of The Proposed Lightwave Backbone Network --- p.4 / Chapter III --- Wavelength Conflicts Problem --- p.8 / Chapter IV --- Network Dimensioning Problem --- p.10 / Chapter A. --- Integer Programming Formulation --- p.10 / Chapter V --- Capacity Apportionment (CA) Problem --- p.17 / Chapter A. --- Integer Programming Formulation --- p.17 / Chapter B. --- Heuristic Algorithm --- p.19 / Chapter C. --- An Illustrative Example For The Hueristic Algorithm --- p.21 / Chapter VI --- Wavelength Channel Assignment Problem --- p.24 / Chapter A. --- Wavelength Channel Assignment Strategies --- p.24 / Chapter B. --- Dynamic Wavelength Channel Assignment Algorithms --- p.25 / Chapter C. --- Performance Results By simulation --- p.33 / Chapter D. --- Comparison Of Blocking Performance Between Static And Dynamic Wavelength Channel Assignment Scheme --- p.40 / Chapter VII --- Conclusion --- p.42 / References --- p.45 / Appendix A Wavelength channel assignment plan generated by the heuristic algorithm for the illustrative example in section V --- p.46