In this thesis, the approach of the distributed-amplifier based transversal filter for multi-Gbit/s Optical CDMA systems is addressed. Of particular interest is the research into circuits that enable handling high rate sequences for high-speed system applications. Different distributed transversal filter structures were considered, in particular those that allow extending the range of filtering functions by including positive and negative tap gain weight control. A novel transversal filter topology that enables operations at multi-Gbit/s application is designed and its behaviour is studied. The work demonstrates that pulse generation and correlation functions in the electrical domain can be accomplished using the designed versatile and reconfigurable transversal filters. The newly developed filter is dubbed the triple-line transversal filter in reference to the filter cell design that distributes the parasitic capacitances of the devices along three artificial transmission lines; a common-input line and two output drain lines. It is demonstrated that this topology can be designed for chip rates exceeding 40 Gbit/s. The practicalities of the triple-line transversal filter were assessed using a 0.2 mum-gate length HEMTs and following the design rules of a commercially available MMIC foundry process. A new tap gain weight control technique was specifically designed for the triple-line filter topology. A special bias level calculation technique was developed and used so that the filter can be modelled and operated with constant distributed characteristics. Wideband delay transmission lines were modelled and designed for filter implementations. An assessment of the MMIC transversal filter is provided via computer simulations in the time and frequency domains. A novel framework based on differential-mode scattering parameters was derived to investigate the various frequency responses of the triple-line structure. The filter satisfies the first Nyquist criterion and is suitable for decoders and encoders of CDMA systems. Overall, this thesis addresses design issues that provide an insight into the practicality of receivers and transmitters for multi-Gbit/s CDMA systems.

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This thesis investigates advanced optical performance monitoring approaches for future all-optical networks using the synchronous sampling technique. This allows for improved signal quality estimation, fault management and resource allocation through improved control of transmission at the physical layer level. Because of the increased transparency in next generation networks, it is not possible to verify the quality of the signal at each node because of the limited number of optical-electrical-optical conversions, and therefore new non-intrusive mechanisms to achieve signal quality monitoring are needed. The synchronous sampling technique can be deployed to estimate the bit error rate, considered an important quality measure, and hence can be utilised to certify service level agreements between operators and customers. This method also has fault identification capabilities by analysing the shapes of the obtained histograms. Each impairment affects the histogram in a specific way, giving it a unique shape that can be used for root cause analysis. However, chromatic dispersion and polarisation mode dispersion (PMD) can have similar signatures on the histograms obtained at decision times. A novel technique to unambiguously discriminate between these two sources of degradation is proposed in this work. It consists of varying the decision times so that sampling also occurs at both edges of the eye diagram. This approach is referred to as three-section eye sampling technique. In addition, it is shown that this method can be used to accurately assess first order polarisation mode dispersion and can simultaneously estimate the differential group delay (DGD) and the power splitting ratio between the two states of polarisation. Since synchronous sampling is employed, the effect of PMD on the sampling times is also investigated. For the first time, closed form relationship between the shift in sampling time, the DGD and the power splitting ratio between the polarisation states is obtained. Three types of high-Q filter based clock recovery circuits are considered: without pre-processing circuits that can be used for RZ format and with an edge detector or a squarer pre-processing circuits suitable for NRZ format. Moreover, this technique can be used to monitor chromatic dispersion and a large monitoring range of more than 1750ps/nm is experimentally demonstrated at 10Gbit/s. Since it can monitor PMD and dispersion, this method can be deployed to control dynamic PMD or dispersion compensators. Furthermore, this technique offers easy and quick inline eye mask testing and timing jitter assessment.

This thesis describes an investigation of technologies and sub-systems required for physical layer implementation of a range of dynamic wavelength-routed optical networks with a specific focus on acknowledged optical-burst-switching (OBS) architectures where burst lengths are expected to be in the millisecond regime. The key sub-systems are identified and examined both individually and in terms of their interoperability. The feasibility of existing systems is investigated and new control systems are developed where appropriate. The initial focus is the tuneable transmitter required to provide wavelength agility at the network edge. The available laser technology is identified and the switching operation of fast widely tuneable lasers in the context of dynamic optical networks is investigated. Using novel probe channel BER measurements, it is shown that additional control systems are required to provide adequate wavelength stability and prevent crosstalk caused by spurious modes excited during the switching process. Based on these findings, a tuneable burst transmitter using SOA blanking and a wavelength locking control loop is developed and its performance described. Next, the reception of the transmitted bursts is explored and the operation and characterisation of the first 10Gb/s digital burst-mode receiver is described. The receiver uses an AC-coupled photodiode, asynchronous digital sampling at 20GS/s and digital signal processing for clock and data recovery. The investigation reveals that the burst-to-burst dynamic range is ultimately limited by quantization noise and methods to improve the dynamic range are investigated and implemented. In the core network, an experimental investigation of optically gain-clamped erbium-doped-fiber-amplifers shows that them optimum feedback cavity designs depends on a trade off between gain transient suppression and reduced signal gain. Cascaded operation is investigated using an experimental OBS link model comprising burst-mode transmitter, receiver, amplifier and router within a recirculating transmission loop. These experiments reveal the importance of network size in feedback cavity design and that, for small networks, the use of the adaptive threshold receiver may negate all gain clamping requirements and allow maximum signal gain.

As bit rates of optical fibre communication are increased, chromatic dispersion increasingly becomes a problem. Optical means of compensation have been traditionally used. However, the rapid increase in available electronic processing power has made electronic chromatic dispersion compensation a viable option leading to an adaptive, low cost integrated solution which avoids additional optical losses. The aim of this thesis is to explore the maximum transmission distance over standard single mode fibre (SSMF) which can be achieved using only electronic signal processing while minimising complexity in the optical domain. The use of feed-forward and decision feedback equalisers in the receiver of an existing intensity-modulated direct-detection (IM/DD) optical link is explored. An increase in the 10 Gb/s transmission distance from 70 to 112 km of SSMF is demonstrated. However, it is shown that this approach is limited by the loss of the optical field phase information after direct detection. Techniques for overcoming this limit by control or measurement of the optical field are reviewed. The rest of the thesis explores the transmission limits of one such technique: electronic predistortion (EPD). Firstly, limits due to the fundamental transmission properties of EPD signals in non-linear fibre are considered. Secondly, the design of the high speed digital signal processing (DSP) for EPD is described, showing the effect of DSP compensator structure, DAC resolution and sample rate on transmission performance. EPD is shown to be capable of ultra-long haul DWDM operation over SSMF. The design of an experimental 10.7 Gb/s transmitter with real time digital signal processing implemented on FPGAs is described. Transmission over 1200 km of SSMF is demonstrated and the performance is assessed in comparison with simulation results. Finally, conclusions concerning the benefits of EPD transmission in comparison with competing technologies are provided. Areas for further research are identified.

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