Optical grooming switch with regenerative functionality for transparent interconnection of networks

We demonstrate a regenerative optical grooming switch for buffer-less interconnection of metro/access and metro/core ring networks with switching functionality in time, space and wavelength domain. Key functionalities of the router are the traffic aggregation with time-slot interchanging (TSI) functionality, the WDM-to-ODTM multiplexing and the OTDM-to-WDM demultiplexing of high-speed channel into lower bit-rate tributaries as well as multi-wavelength all-optical 2R regeneration of several higher-speed signals. BER and Q-factor measurements of different switching scenarios show excellent performance with no error floor and Q-factors above 21 dB.

An all-optical grooming switch for interconnecting access and metro ring networks

A regenerative all-optical grooming switch for interconnecting 130 Gbit/s on-off keying (OOK) metro/core ring and 43 Gbit/s-OOK metro/access ring networks with switching functionality in time, space, and wavelength domains is demonstrated. Key functionalities of the switch are traffic aggregation with time-slot interchanging functionality, optical time division multiplexing (OTDM) to wavelength division multiplexing (WDM) demultiplexing, and multi-wavelength 2R regeneration. Laboratory and field demonstrations show the excellent performance of the new concept with error-free signal transmission and Q-factors above 20 dB.

Advanced UV inscribed fibre grating structures and applications in optical sensing and laser systems

This thesis presents detailed investigation of UV inscribed fibre grating based devices and novel developments in the applications of such devices in optical sensing and fibre laser systems. The major contribution of this PhD programme includes the systematic study on fabrication, spectral characteristics and applications of different types of UV written in-fibre gratings such as Type I and IA Fibre Bragg Gratings (FBGs), Chirped Fibre Bragg Gratings (CFBGs) and Tilted Fibre Gratings (TFGs) with small, large and 45º tilted structures inscribed in normal silica fibre. Three fabrication techniques including holographic, phase-mask and blank beam exposure scanning, which were employed to fabricate a range of gratings in standard single mode fibre, are fully discussed. The thesis reports the creation of smart structures with self-sensing capability by embedding FBG-array sensors in Al matrix composite. In another part of this study, we have demonstrated the particular significant improvements made in sensitising standard FBGs to the chemical surrounding medium by inducing microstructure to the grating by femtosecond (fs) patterning assisted chemical etching technique. Also, a major work is presented for the investigation on the structures, inscription methods and spectral Polarisation Dependent Loss (PDL) and thermal characteristics of different angle TFGs. Finally, a very novel application in realising stable single polarisation and multiwavelength switchable Erbium Doped Fibre Lasers (EDFLs) using intracavity polarisation selective filters based on TFG devices with tilted structures at small, large and exact 45° angles forms another important contribution of this thesis.

All-optical regenerative memory using a single device

In recent years the optical domain has been traditionally reserved for node-to-node transmission with the processing and switching achieved entirely in the electrical domain. However, with the constantly increasing demand for bandwidth and the resultant increase in transmission speeds, there is a very real fear that current electronic technology as used for processing will not be able to cope with future demands. Fuelled by this requirement for faster processing speeds, considerable research is currently being carried out into the potential of All-optical processing. One of the fundamental obstacles in realising All-optical processing is the requirement for All-optical buffering. Without all-optical buffers it is extremely difficult to resolve situations such as contention and congestion. Many devices have been proposed to solve this problem however none of them provide the perfect solution. The subject of this research is to experimentally demonstrate a novel all-optical memory device. Unlike many previously demonstrated optical storage devices the device under consideration utilises only a single loop mirror and a single SOA as its switch, whilst providing full regenerative capabilities required for long-term storage. I will explain some of the principles and characteristics of the device, which will then be experimentally demonstrated. The device configuration will then be studied and investigated as to its suitability for Hybrid Integrated Technology.

Application of SOA-NOLM in all-optical processing

This thesis presents experimental investigations of the use of semiconductor optical amplifiers in a nonlinear loop mirror (SOA-NOLM) and its application in all-optical processing. The techniques used are mainly experimental and are divided into three major applications. Initially the semiconductor optical amplifier, SOA, is experimentally characterised and the optimum operating condition is identified. An interferometric switch based on a Sagnac loop with the SOA as the nonlinear element is employed to realise all-optical switching. All-optical switching is a very attractive alternative to optoelectronic conversion because it avoids the conversion from the optical to the electronic domain and back again. The first major investigation involves a carrier suppressed return to zero, CSRZ, format conversion and transmission. This study is divided into single channel and four channel WDM respectively. The optical bandwidth which limits the conversion is investigated. The improvement of the nonlinear tolerance in the CSRZ transmission is shown which shows the suitability of this format for enhancing system performance. Second, a symmetrical switching window is studied in the SOA-NOLM where two similar control pulses are injected into the SOA from opposite directions. The switching window is symmetric when these two control pulses have the same power and arrive at the same time in the SOA. Finally, I study an all-optical circulating shift register with an inverter. The detailed behaviour of the blocks of zeros and ones has been analysed in terms of their transient measurement. Good agreement with a simple model of the shift register is obtained. The transient can be reduced but it will affect the extinction ratio of the pulses.

Symmetric operating point for increasing the extinction ratio of semiconductor based optical loop mirrors

Terahertz optical asymmetric demultiplexors (TOADs) use a semiconductor optical amplifier in an interferometer to create an all-optical switch and have potential uses in many optical networking applications. Here we demonstrate and compare experimentally a novel and simple method of dramatically increasing the extinction ratio of the device using a symmetrical configuration as compared to a ‘traditional’ configuration. The new configuration is designed to suppress the occurrence of self-switching in the device thus allowing signal pulses to be used at higher power levels. Using the proposed configuration an increase in extinction ratio of 10 dB has been measured on the transmitted port whilst benefiting from an improved input signal power handling capability.

Embedded fibre Bragg grating array sensors in aluminium alloy matrix by ultrasonic consolidation

Fibre Bragg Grating (FBG) array sensors have been successfully embedded in aluminium alloy matrix by ultrasonic consolidation (UC) technique. The temperature and loading responses of the embedded FBG arrays have been systematically characterised. The embedded grating sensors exhibit an average temperature sensitivity of ~36pm/°C, which is three times higher than that of normal FBGs, and a loading responsivity of ~0.1nm/kg within the dynamic range from 0kg to 3kg. This initial experiment clearly demonstrates that FBG array sensors can be embedded in metal matrix together with other passive and active fibres to fabricate smart materials to monitor the operation and health of engineering structures.

Field experiments with a grooming switch for OTDM meshed networking

Field experiments of 42.7/128.1 Gb/s wavelength-division multiplexed, optical time-division multiplexed (WDM-OTDM) transmultiplexing and all-optical dual-wavelength regeneration at the OTDM rate are presented in this paper. By using the asynchronous retiming scheme, we achieve error-free bufferless data grooming with time-slot interchange capability for OTDM meshed networking. We demonstrate excellent performance from the system, discuss scalability, applicability, and the potential reach of the asynchronous retiming scheme for transparent OTDM-domain interconnection.

Integration of a 3D hydrogel matrix within a hollow core photonic crystal fibre for DNA probe immobilization

In this paper, we demonstrate the integration of a 3D hydrogel matrix within a hollow core photonic crystal fibre (HC-PCF). In addition, we also show the fluorescence of Cy5-labelled DNA molecules immobilized within the hydrogel formed in two different types of HC-PCF. The 3D hydrogel matrix is designed to bind with the amino groups of biomolecules using an appropriate cross-linker, providing higher sensitivity and selectivity than the standard 2D coverage, enabling a greater number of probe molecules to be available per unit area. The HC-PCFs, on the other hand, can be designed to maximize the capture of fluorescence to improve sensitivity and provide longer interaction lengths. This could enable the development of fibre-based point-of-care and remote systems, where the enhanced sensitivity would relax the constraints placed on sources and detectors. In this paper, we will discuss the formation of such polyethylene glycol diacrylate (PEGDA) hydrogels within a HC-PCF, including their optical properties such as light propagation and auto-fluorescence.

Multiplexers and demultiplexers based on fibre Bragg gratings and optical circulators for DWDM systems

Two different architectures of multiplexers/demultiplexers based on 4×1 and 1×4 configurations are discussed. These architectures are implemented using apodized fibre Bragg gratings as optical filters and optical circulators. The spectral characteristics of the devices for channel separations of 100 GHz and 50 GHz are analysed and their performance is evaluated. Optical switch and cross-connect configurations are also demonstrated.

Investigations on birefringence effects in polymer optical fiber Bragg gratings

Step-index polymer optical fiber Bragg gratings (POFBGs) and microstructured polymer optical fiber Bragg gratings (mPOFBGs) present several attractive features, especially for sensing purposes. In comparison to FBGs written in silica fibers, they are more sensitive to temperature and pressure because of the larger thermo-optic coefficient and smaller Young's modulus of polymer materials. (M)POFBGs are most often photowritten in poly(methylmethacrylate) (PMMA) materials using a continuous-wave 325 nm HeCd laser. For the first time to the best of our knowledge, we study photoinduced birefringence effects in (m)POFBGs. To achieve this, highly reflective gratings were inscribed with the phase mask technique. They were then monitored in transmission with polarized light. For this, (m)POF sections a few cm in length containing the gratings were glued to angled silica fibers. Polarization dependent loss (PDL) and differential group delay (DGD) were computed from the Jones matrix eigenanalysis using an optical vector analyser. Maximum values exceeding several dB and a few picoseconds were obtained for the PDL and DGD, respectively. The response to lateral force was finally investigated. As it induces birefringence in addition to the photo-induced one, an increase of the PDL and DGD values were noticed. © 2014 Copyright SPIE.

Effects of crosstalk in WDM optical label switching networks due to wavelength switching of a tunable laser

Crosstalk caused by switching events in fast tunable lasers in an optical label switching (OLS) system is investigated for the first time. A wavelength-division-multiplexed OLS system based on subcarrier multiplexed labels is presented which employs a 40-Gb/s duobinary payload and a 155-Mb/s label on a 40-GHz subcarrier. Degradation in system performance as the transmitters switch between different channels is then characterized in terms of the frequency drift of the tunable laser.

Enabling transparent technologies for the development of highly granular flexible optical cross-connects

Flexible optical networking is identified today as the solution that offers smooth system upgradability towards Tb/s capacities and optimized use of network resources. However, in order to fully exploit the potentials of flexible spectrum allocation and networking, the development of a flexible switching node is required capable to adaptively add, drop and switch tributaries with variable bandwidth characteristics from/to ultra-high capacity wavelength channels at the lowest switching granularity. This paper presents the main concept and technology solutions envisioned by the EU funded project FOX-C, which targets the design, development and evaluation of the first functional system prototype of flexible add-drop and switching cross-connects. The key developments enable ultra-fine switching granularity at the optical subcarrier level, providing end-to-end routing of any tributary channel with flexible bandwidth down to 10Gb/s (or even lower) carried over wavelength superchannels, each with an aggregated capacity beyond 1Tb/s. © 2014 IEEE.

Embedded fibre Bragg grating array sensors in aluminium alloy matrix by ultrasonic consolidation

Fibre Bragg Grating (FBG) array sensors have been successfully embedded in aluminium alloy matrix by ultrasonic consolidation (UC) technique. The temperature and loading responses of the embedded FBG arrays have been systematically characterised. The embedded grating sensors exhibit an average temperature sensitivity of ~36pm/°C, which is three times higher than that of normal FBGs, and a loading responsivity of ~0.1nm/kg within the dynamic range from 0kg to 3kg. This initial experiment clearly demonstrates that FBG array sensors can be embedded in metal matrix together with other passive and active fibres to fabricate smart materials to monitor the operation and health of engineering structures.

100-Gb/s point-to-point solutions for long-reach passive optical networks in sparse rural and urban areas

Long reach-passive optical networks (LR-PON) are being proposed as a means of enabling ubiquitous fiber-to-the-home (FTTH) by massive sharing of network resources and therefore reducing per customer costs to affordable levels. In this paper, we analyze the chain solutions for LR-PON deployment in urban and rural areas at 100-Gb/s point-to-point transmission using dual polarization-quaternary phase shift-keying (DP-QPSK) modulation. The numerical analysis shows that with appropriate finite impulse response (FIR) filter designs, 100-Gb/s transmission can be achieved with at least 512 way split and up to 160 km total distance, which is sufficient for many of the optical paths in a practical situation, for point-to-point link from one LR-PON to another LR-PON through the optical switch at the metro nodes and across a core light path through the core network without regeneration.