3 research outputs found
Advances in Optical Amplifiers
Optical amplifiers play a central role in all categories of fibre communications systems and networks. By compensating for the losses exerted by the transmission medium and the components through which the signals pass, they reduce the need for expensive and slow optical-electrical-optical conversion. The photonic gain media, which are normally based on glass- or semiconductor-based waveguides, can amplify many high speed wavelength division multiplexed channels simultaneously. Recent research has also concentrated on wavelength conversion, switching, demultiplexing in the time domain and other enhanced functions. Advances in Optical Amplifiers presents up to date results on amplifier performance, along with explanations of their relevance, from leading researchers in the field. Its chapters cover amplifiers based on rare earth doped fibres and waveguides, stimulated Raman scattering, nonlinear parametric processes and semiconductor media. Wavelength conversion and other enhanced signal processing functions are also considered in depth. This book is targeted at research, development and design engineers from teams in manufacturing industry, academia and telecommunications service operators
Roadmap on all-optical processing
The ability to process optical signals without passing into the electrical domain has always attracted the attention of the research community. Processing photons by photons unfolds new scenarios, in principle allowing for unseen signal processing and computing capabilities. Optical computation can be seen as a large scientific field in which researchers operate, trying to find solutions to their specific needs by different approaches; although the challenges can be substantially different, they are typically addressed using knowledge and technological platforms that are shared across the whole field. This significant know-how can also benefit other scientific communities, providing lateral solutions to their problems, as well as leading to novel applications. The aim of this Roadmap is to provide a broad view of the state-of-the-art in this lively scientific research field and to discuss the advances required to tackle emerging challenges, thanks to contributions authored by experts affiliated to both academic institutions and high-tech industries. The Roadmap is organized so as to put side by side contributions on different aspects of optical processing, aiming to enhance the cross-contamination of ideas between scientists working in three different fields of photonics: optical gates and logical units, high bit-rate signal processing and optical quantum computing. The ultimate intent of this paper is to provide guidance for young scientists as well as providing research-funding institutions and stake holders with a comprehensive overview of perspectives and opportunities offered by this research field
All-optical processing systems based on semiconductor optical amplifiers
Doutoramento em Engenharia ElectrotécnicaNesta tese investigam-se e desenvolvem-se dispositivos para processamento
integralmente óptico em redes com multiplexagem densa por divisão no
comprimento de onda (DWDM). O principal objectivo das redes DWDM é
transportar e distribuir um espectro óptico densamente multiplexado com sinais
de débito binário ultra elevado, ao longo de centenas ou milhares de
quilómetros de fibra óptica. Estes sinais devem ser transportados e
encaminhados no domínio óptico de forma transparente, sem conversões
óptico-eléctrico-ópticas (OEO), evitando as suas limitações e custos. A
tecnologia baseada em amplificadores ópticos de semicondutor (SOA) é
promissora graças aos seus efeitos não-lineares ultra-rápidos e eficientes, ao
potencial para integração, reduzido consumo de potência e custos.
Conversores de comprimento de onda são o elemento óptico básico para
aumentar a capacidade da rede e evitar o bloqueio de comprimentos de onda.
Neste trabalho, são estudados e analisados experimentalmente métodos para
aumentar a largura de banda operacional de conversores de modulação
cruzada de ganho (XGM), a fim de permitir a operação do SOA para além das
suas limitações físicas. Conversão de um comprimento de onda, e conversão
simultânea de múltiplos comprimentos de onda são testadas, usando
interferómetros de Mach-Zehnder com SOA.
As redes DWDM de alto débito binário requerem formatos de modulação
optimizados, com elevada tolerância aos efeitos nefastos da fibra, e reduzida
ocupação espectral. Para esse efeito, é vital desenvolver conversores
integramente ópticos de formatos de modulação, a fim de permitir a
interligação entre as redes já instaladas, que operam com modulação de
intensidade, e as redes modernas, que utilizam formatos de modulação
avançados. No âmbito deste trabalho é proposto um conversor integralmente
óptico de formato entre modulação óptica de banda lateral dupla e modulação
óptica de banda lateral residual; este é caracterizado através de simulação e
experimentalmente. Adicionalmente, é proposto um conversor para formato de
portadora suprimida, através de XGM e modulação cruzada de fase.
A interligação entre as redes de transporte com débito binário ultra-elevado e
as redes de acesso com débito binário reduzido requer conversão óptica de
formato de impulso entre retorno-a-zero (RZ) e não-RZ. São aqui propostas e
investigadas duas estruturas distintas: uma baseada em filtragem desalinhada
do sinal convertido por XGM; uma segunda utiliza as dinâmicas do laser
interno de um SOA com ganho limitado (GC-SOA).
Regeneração integralmente óptica é essencial para reduzir os custos das
redes. Dois esquemas distintos são utilizados para regeneração: uma estrutura
baseada em MZI-SOA, e um método no qual o laser interno de um GC-SOA é
modulado com o sinal distorcido a regenerar.
A maioria dos esquemas referidos é testada experimentalmente a 40 Gb/s,
com potencial para aplicação a débitos binários superiores, demonstrado que
os SOA são uma tecnologia basilar para as redes ópticas do futuro.This thesis investigates and develops all-optical processing devices for
wavelength division multiplexing networks (DWM) of the future. The ultimate
goal of optical networks is to transport and deliver a densely multiplexed
spectrum, populated by ultra-high bit rate signals over hundreds or thousands
of kilometers of optical fiber. Such signals should be transported and routed
transparently in the optical domain, without recurring to optic-electro-optic
(OEO) conversions, avoiding its limitations and costs. Semiconductor optical
amplifier (SOA) based technology is a promising building block due to its
inherent ultra-fast and efficient non-linear effects, potential for integration, low
power consumption and cost.
Wavelength converters are the basic optical functionality to increase the
network throughput and avoid wavelength blocking. Methods to increase the
operation bandwidth of cross-gain modulation (XGM) converters are studied
and experimentally assessed to enable operation beyond the physical
constraints of SOA. Single and multi-wavelength conversion exploiting crossphase
modulation (XPM) in Mach-Zehnder interferometer with semiconductor
optical amplifiers (MZI-SOA) is tested.
High bit rate DWDM networks require optimized modulation formats with
enhanced tolerance to fiber impairments and reduced spectral tolerance. As a
consequence, it is crucial to develop all-optical modulation formats between
legacy on-off-keying networks and networks employing advanced modulation
formats. An all-optical format converter between optical double sideband
(ODSB) and optical vestigial sideband (OVSB) based on SOA self-phase
modulation is proposed and thoroughly characterized by simulations and
experimental tests. A converter, which uses a mix of XGM and XPM to allow
simultaneous pulse and modulation format conversion to the carrier
suppressed format, is proposed.
The interface between ultra-high bit rate transport networks and lower bit rate
access networks requires optical pulse format conversions between return-tozero
(RZ) and non-return-to-zero (NRZ). Two different structures are proposed
and investigated. The first is based on detuned filtering of XPM converted
signal; while the second uses the dynamics of the internal laser of a gainclamped
SOA.
All-optical regeneration is one of the most sought functionalities to reduce
network costs. Regeneration is achieved in this work through two simple
setups: a MZI-SOA based structure, and a method in which the internal laser
from a GC-SOA is modulated with the input distorted signal.
Most applications are experimentally validated at 40 Gb/s, with potential for
even higher bit rates, demonstrating that SOA can be one of the key elements
for the next generation of optical networks