Study on Single-Polarized Holey Fibers with Double-Hole Unit Cores for Cross-Talk Free Polarization Splitter

A single-polarization single-mode (SPSM) photonic crystal fiber (PCF) based on double-hole unit core is proposed in this paper for application to cross-talk free polarization splitter (PS). Birefringence of the PCF is obtained by adopting double-hole unit cells into the core to destroy its symmetry. With an appropriate cladding hole size, single x- or y-polarized PCF can be achieved by arranging the double-hole unit in the core along the x- or y-axis, respectively. Moreover, our proposed SPSM PCF has the potential to be applied to consist a cross-talk free PS. The simulation result by employing a vectorial finite element beam propagation method (FE-BPM) demonstrates that an arbitrary polarized incident light can be completely separated into two orthogonal single-polarized components through the PS. The structural tolerance and wavelength dependence of the PS have also been discussed in detail

Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications

Specialty Fiber Lasers and Novel Fiber Devices

At the Dawn of the 21st century, the field of specialty optical fibers experienced a scientific revolution with the introduction of the stack-and-draw technique, a multi-steps and advanced fiber fabrication method, which enabled the creation of well-controlled micro-structured designs. Since then, an extremely wide variety of finely tuned fiber structures have been demonstrated including novel materials and novel designs. As the complexity of the fiber design increased, highly-controlled fabrication processes became critical. To determine the ability of a novel fiber design to deliver light with properties tailored according to a specific application, several mode analysis techniques were reported, addressing the recurring needs for in-depth fiber characterization. The first part of this dissertation details a novel experiment that was demonstrated to achieve modal decomposition with extended capabilities, reaching beyond the limits set by the existing mode analysis techniques. As a result, individual transverse modes carrying between ~0.01% and ~30% of the total light were resolved with unmatched accuracy. Furthermore, this approach was employed to decompose the light guided in Large-Mode Area (LMA) fiber, Photonic Crystal Fiber (PCF) and Leakage Channel Fiber (LCF). The single-mode performances were evaluated and compared. As a result, the suitability of each specialty fiber design to be implemented for power-scaling applications of fiber laser systems was experimentally determined. The second part of this dissertation is dedicated to novel specialty fiber laser systems. First, challenges related to the monolithic integration of novel and complex specialty fiber designs in all-fiber systems were addressed. The poor design and size compatibility between specialty fibers and conventional fiber-based components limits their monolithic integration due to high coupling loss and unstable performances. Here, novel all-fiber Mode-Field Adapter (MFA) devices made of selected segments of Graded Index Multimode Fiber (GIMF) were implemented to mitigate the coupling losses between a LMA PCF and a conventional Single-Mode Fiber (SMF), presenting an initial 18-fold mode-field area mismatch. It was experimentally demonstrated that the overall transmission in the mode-matched fiber chain was increased by more than 11 dB (the MFA was a 250 ?m piece of 50 ?m core diameter GIMF). This approach was further employed to assemble monolithic fiber laser cavities combining an active LMA PCF and fiber Bragg gratings (FBG) in conventional SMF. It was demonstrated that intra-cavity mode-matching results in an efficient (60%) and narrow-linewidth (200 pm) laser emission at the FBG wavelength. In the last section of this dissertation, monolithic Multi-Core Fiber (MCF) laser cavities were reported for the first time. Compared to existing MCF lasers, renown for high-brightness beam delivery after selection of the in-phase supermode, the present new generation of 7-coupled-cores Yb-doped fiber laser uses the gain from several supermodes simultaneously. In order to uncover mode competition mechanisms during amplification and the complex dynamics of multi-supermode lasing, novel diagnostic approaches were demonstrated. After characterizing the laser behavior, the first observations of self-mode-locking in linear MCF laser cavities were discovered

Recent Progress in Optical Fiber Research

This book presents a comprehensive account of the recent progress in optical fiber research. It consists of four sections with 20 chapters covering the topics of nonlinear and polarisation effects in optical fibers, photonic crystal fibers and new applications for optical fibers. Section 1 reviews nonlinear effects in optical fibers in terms of theoretical analysis, experiments and applications. Section 2 presents polarization mode dispersion, chromatic dispersion and polarization dependent losses in optical fibers, fiber birefringence effects and spun fibers. Section 3 and 4 cover the topics of photonic crystal fibers and a new trend of optical fiber applications. Edited by three scientists with wide knowledge and experience in the field of fiber optics and photonics, the book brings together leading academics and practitioners in a comprehensive and incisive treatment of the subject. This is an essential point of reference for researchers working and teaching in optical fiber technologies, and for industrial users who need to be aware of current developments in optical fiber research areas

Sensing and interferometry, including design and characterisation of special optical fibres

This thesis presents my work in the area of optical fibre sensing, and optical fibre design and characterisation along with the interferometric and signal processing techniques that were developed along the way

Sensing and interferometry, including design and characterisation of special optical fibres

This thesis presents my work in the area of optical fibre sensing, and optical fibre design and characterisation along with the interferometric and signal processing techniques that were developed along the way

Novel approaches to power scaling of single-frequency photonic crystal fiber amplifiers

This dissertation presents experimental and theoretical studies of high power, single-frequency, ytterbium-doped photonic crystal fiber amplifiers. The objective of this effort is to identify issues which limit power scaling and develop novel techniques to overcome these limitations. Historically, stimulated Brillouin scattering (SBS) has been the primary obstacle in the realization of high power single-frequency fiber amplifiers. A novel acoustically tailored photonic crystal fiber design, having a reduced Brillouin gain coefficient of 1.2x10-11 m/W, is demonstrated. The fiber design is such that it may be used in conjunction with other SBS mitigation techniques, which increases the nonlinear threshold beyond the current state of the art. In the successful suppression of SBS, a new regime of single-frequency photonic crystal fiber amplifier power scaling is explored. Instabilities in the transverse mode is observed at increasing output powers. Mitigation of this effect is demonstrated experimentally. This empirical data is used as the basis for a theoretical treatment of the problem, which provides direction for future fiber amplifier designs. The culmination of this work results in the successful utilization of the acoustically tailored photonic crystal fiber in a single-frequency counter-pumped amplifier configuration, yielding close to 500 W output power and near diffraction-limited beam quality

Sonic and Photonic Crystals

Sonic/phononic crystals termed acoustic/sonic band gap media are elastic analogues of photonic crystals and have also recently received renewed attention in many acoustic applications. Photonic crystals have a periodic dielectric modulation with a spatial scale on the order of the optical wavelength. The design and optimization of photonic crystals can be utilized in many applications by combining factors related to the combinations of intermixing materials, lattice symmetry, lattice constant, filling factor, shape of the scattering object, and thickness of a structural layer. Through the publications and discussions of the research on sonic/phononic crystals, researchers can obtain effective and valuable results and improve their future development in related fields. Devices based on these crystals can be utilized in mechanical and physical applications and can also be designed for novel applications as based on the investigations in this Special Issue

Subsystems for High bit-rate Optical Networks

Questa tesi contiene parte del lavoro svolto negli ultimi tre anni presso i laboratori congiunti del CNIT e della la Scuola Superiore Sant'Anna di Pisa, dove ho lavorato nel gruppo di Sistemi Ottici sotto la supervisione del prof. Ernesto Ciaramella, ed in parte presso il Dipartimento di Fisica dell'Università di Pisa, sotto la supervisione del prof. Niccolò Beverini. Durante questi anni ho avuto l'opportunità di lavorare su vari filoni di ricerca (studio di sorgenti laser impulsate, esperimenti di processamento dei segnali tutto ottico, sistemi di protezione dei guasti di rete,...) inquadrati in differenti progetti di ricerca, ed anche in Università straniere (Massachussetts Intitute of Technology MIT di Boston, USA). In questa tesi verrà comunque descritta solo una parte dei risultati sviluppati. In particolare, verrà discussa la ricerca svolta mirata alla realizzazione di sotto-sistemi che possono essere impiegati nei sistemi di comunicazione ottica (o, più in generale nelle Reti Ottiche) basate su trassmissioni di dati alla frequenza di cifra di 40 Gb/s. Ogni sottos-sistema sarà presentato seguendo un ordine che riproduce quello in cui questi sotto-sistemi sono impegati effettivamente: inizierò descrivendo una sorgente di impulsi ottici ad altissimo bit-rate da impiegare nei sistemi ottici multiplati a divisione di tempo (OTDM); si passerà poi alla descrizione di vari convertitori di lunghezza d'onda che sono utilizzati nei nodi di rete; per concludere, verrà discussa una unità tutta ottica per i recupero del sincronisimo, che è tipicamente impiegata alla fine di un sistema di trasmissione ed è usata per affiancare i ricevitori veri e propri. Tutte queste funzionalità sfruttano le proprietà ottiche non lineari di dispositivi tra i più comunemente usati nei sistemi di comunicazione ottici: le fibre ottiche e gli amplificatori ottici a semiconduttore. Oltre che dalla natura "tutto-ottica", tutti questi dispositivi (o funzionalità) sono accumunati dalla ricerca di semplicità sia realizzativa che progettuale: come verrà mostrato caso per caso, ogni sotto-sistema è stato realizzato cercando di ricorrere al minor numero possibile di dispositivi per ridurre la complessità globale. Questo è un punto fondamentale per dimostrare che le tecnologie "tutto-ottiche" possono rappresentare un'alternativa all'elettronica. Ogni "sotto-sistema" verrà trattato separatamente in un capitolo. Ogni capitolo contiene una breve discussione sulle novità introdotte, rispetto a soluzioni simili presentate in letteratura o in commercio. Benchè il lavoro riportato in questa tesi è essenzialmente di carattere sperimentale, per migliorarne la comprensione e la completezza ogni capitolo contiene dei paragrafi in cui l'argomento viene illustrato dal punto di vista teorico. La tesi è divisa in 4 capitoli secondo lo schema seguente: Una panoramica sui sistemi di comunicazione basati su fibra ottica: un capitolo introduttivo per spiegare l'evoluzione e la struttura e possibili scenari delle Reti Ottiche ed introdurre i motivi fondanti della ricerca riportata nella tesi. Una sorgente solitonica, nel capitolo 2. Questo capitolo contiene una discussione sulla progettazione e la realizzazione di una sorgente laser da impiegare in sistemi OTDM. La sorgente è progetatta per produrre impulsi di durata inferiore al picosecondo ad una frequenza di ripetizione di 40 GHz repetition rate. La sorgente è studiata per essere utilizzata direttamente nei sistemi di comunicazione, senza la necessità di dover ricorrere a stadi di processamento successivi (come la risagomatura degli impulsi, la loro compressione o la rimozione di piedistallo). Gli impulsi sono generati tramite un fenomeno di propagazione in regime non-lineare controllato in una fibra ottica particolare. Benchè la sorgente sia stata progettata per essere impiegata in sistemi OTDM, dato il suo spettro ottico largo e periodico potrebbe essere utilizzata anche in altri ambiti, come verrà discusso più volte nel corso della tesi. Esperimenti di conversione di lunghezza d'onda (includendo anche espeimenti di conversione di lunghezza d'onda multipla), nel capitolo 3. In questo capitolo, la conversione di lunghezza d'onda (ovvero il trasferimento della modulazione contenuta su un segnale ottico ad uno su una portante a lughezza d'onda differente) è dimostrata attraverso diverse tecniche, principalmente ricorrendo alle dinamiche veloci non-lineari deli amplificatori a semiconduttore. In tutti questi esperimenti, verrà trattata in dettaglio anche la realizzazione della conversione di lunghezza d'onda simultaneamente su più canali: in particolare questa funzionalità è ritenuta molto importante per le reti di accesso di prossima generazione.. Uno circuito tutto ottico per l'estrazione del segnale di sincronia da un segnale modulato nel capitolo 4. Lo schema presentato in questo capitolo per i recupero del sincronismo rappresenta un notevole passo in avanti rispetto ai circuiti presentati precedentemente in letteratura, sia in termini di efficienza che di compattezza. Il dispositivo è basato sull'implementazione tutta-ottico del Tank-Circuit (largamente utilizzato in elettronica). Questo circuito si è dimostrato molto versatile: in particolare è stato dimostrato il suo impiego con diversi formati di modulazione, sia con traffico continuo che a pacchetti. Il circuito inoltre è adatto per un'integrazione fotonica ibrida

All-fibre wavelength versatile short pulsed laser sources

Pulsed lasers operating in the picosecond or femtosecond regimes find a wide range of applications in optical sciences, such as spectroscopy, laser surgery, material processing and optical communications. Among the existing sources of short-pulses, mode-locked fibre lasers play an important role mainly due to their robust and compact nature, and also due to their ability to generate outputs over a wide range of repetition-rates, pulse durations, pulse shapes, peak powers and optical wavelengths. Considering the case of wavelength versatility, Raman amplification can be used to fill the spectral gaps that are not covered by the emission band of traditional rare-earth doped elements such as ytterbium and erbium, allowing the generation of light at unconventional wavelengths. Additionally, another contribution has come from the recent development of new nanomaterials such as graphene and carbon nanotubes that can be used as saturable absorbers over a broadband wavelength range. The experimental work reported in this thesis is mainly focused in combining the wavelength versatility allowed by Raman gain and carbon nanotubes and graphene to generate short-pulsed fibre lasers at different wavelengths. High power ytterbium and erbium lasers and also a high power Raman laser operating at 1450 nm are used as pump sources to seed the Raman gain and carbon nanotubes and graphene are the saturable absorbers used as mode-lockers. All the fibres utilized in the oscillators are highly non-linear single mode silica fibres doped with GeO2. The lasers operate in the dissipative soliton regime, generating chirped pulses with durations on the order of hundred of picosecond that are suitable for external compression. We demonstrate for example an erbium-pumped Raman oscillator generating 500 ps pulses that are linearly compressed to 2 ps. The results presented in this document are a contribution towards making fibre based lasers more universal devices in terms of wavelength operation.Open Acces