Signal regeneration techniques for advanced modulation formats

We review recent results on all-optical regeneration of phase encoded signals based on phase sensitive amplification achieved by avoiding phase-to-amplitude conversion in order to facilitate the regeneration of amplitude/phase encoded (QAM) signals

Statistical characterisation and stochastic modelling of 1-layer variable bit rate H.261 video codec traffic

The Integrated Services Digital Network(ISDN) is under re-design to provide flexibility which will ensure efficient network utilisation in the provision of broadband services. The main broadband services envisaged for provision on the Broadband ISDN(B-ISDN) are : Videophone; Videoconferencing; Television and High Definition TV. The B-ISDN will be a packet switched network where the packets(cells) will be transferred by the Asynchronous Transfer Mode(ATM) concept. Unlike voice and data services, the impact video services will have on the BISDN is unknown and hence loss of information is difficult to predict. Present videophone terminals are based on the CCITT H.261 Video Coding standard hence the picture quality is variable because video codec traffic is transmitted at a constant rate. To maintain a constant quality picture the codec output data must be transmitted at a variable rate or alternatively, for constant rate video codecs extra information must be made available to achieve constant picture quality. This latter technique is 2- Layer video coding where the first layer transmits at a constant rate and the second layer at a variable rate. The ATM B-ISDN promises constant picture quality video services, therefore to achieve this aim the impact variable rate video sources will have on the network must be determined by network simulation, thus variable rate video source models must be derived. To statistically characterise and stochastically model 1-Layer VBR(Variable Bit Rate) H.261 Video Codec traffic, here a videophone sequence is analysed by two alternative strategies : Talk-Listen and Motion Level. This analysis also found that 2-Layer H.261 Video Codec traffic can be stochastically modelled via a 1-Layer VBR H.261 Video Codec traffic model. Numerous hierarchical stochastic models with the ability to capture the statistical characteristics of long video sequences, in particular the short-term and long-term autocorrelations, are presented. One such model was simulated and the resulting simulated traffic was analysed to confirm the advantage hierarchical stochastic models have over non-hierarchical stochastic models in modelling video source traffic

Optical sampling and metrology using a soliton-effect compression pulse source

A low jitter optical pulse source for applications including optical sampling and optical metrology was modelled and then experimentally implemented using photonic components. Dispersion and non-linear fibre effects were utilised to compress a periodic optical waveform to generate pulses of the order of 10 picoseconds duration, via soliton-effect compression. Attractive features of this pulse source include electronically tuneable repetition rates greater than 1.5 GHz, ultra-short pulse duration (10-15 ps), and low timing jitter as measured by both harmonic analysis and single-sideband (SSB) phase noise measurements. The experimental implementation of the modelled compression scheme is discussed, including the successful removal of stimulated Brillouin scattering (SBS) through linewidth broadening by injection dithering or phase modulation. Timing jitter analysis identifies many unwanted artefacts generated by the SBS suppression methods, hence an experimental arrangement is devised (and was subsequently patented) which ensures that there are no phase modulation spikes present on the SSB phase noise spectrum over the offset range of interest for optical sampling applications, 10Hz-Nyquist. It is believed that this is the first detailed timing jitter study of a soliton-effect compression scheme. The soliton-effect compression pulses are then used to perform what is believed to be the first demonstration of optical sampling using this type of pulse source. The pulse source was also optimised for use in a novel optical metrology (range finding) system, which is being developed and patented under European Space Agency funding as an enabling technology for formation flying satellite missions. This new approach to optical metrology, known as Scanning Interferometric Pulse Overlap Detection (SIPOD), is based on scanning the optical pulse repetition rate to find the specific frequencies which allow the return pulses from the outlying satellite, i.e. the measurement arm, to overlap exactly with a reference pulse set on the hub satellite. By superimposing a low frequency phase modulation onto the optical pulse train, it is possible to detect the pulse overlap condition using conventional heterodyne detection. By rapidly scanning the pulse repetition rate to find two frequencies which provide the overlapping pulse condition, high precision optical pulses can be used to provide high resolution unambiguous range information, using only relatively simple electronic detection circuitry. SIPOD’s maximum longitudinal range measurement is limited only by the coherence length of the laser, which can be many tens of kilometres. Range measurements have been made to better than 10 microns resolution over extended duration trial periods, at measurement update rates of up to 470 Hz. This system is currently scheduled to fly on ESA’s PROBA-3 mission in 2012 to measure the intersatellite spacing for a two satellite coronagraph instrument. In summary, this thesis is believed to present three novel areas of research: the first detailed jitter characterisation of a soliton-effect compression source, the first optical sampling using such a compression source, and a novel optical metrology range finding system, known as SIPOD, which utilises the tuneable repetition rate and highly stable nature of the compression source pulses

Audiovisual processing for sports-video summarisation technology

In this thesis a novel audiovisual feature-based scheme is proposed for the automatic summarization of sports-video content The scope of operability of the scheme is designed to encompass the wide variety o f sports genres that come under the description ‘field-sports’. Given the assumption that, in terms of conveying the narrative of a field-sports-video, score-update events constitute the most significant moments, it is proposed that their detection should thus yield a favourable summarisation solution. To this end, a generic methodology is proposed for the automatic identification of score-update events in field-sports-video content. The scheme is based on the development of robust extractors for a set of critical features, which are shown to reliably indicate their locations. The evidence gathered by the feature extractors is combined and analysed using a Support Vector Machine (SVM), which performs the event detection process. An SVM is chosen on the basis that its underlying technology represents an implementation of the latest generation of machine learning algorithms, based on the recent advances in statistical learning. Effectively, an SVM offers a solution to optimising the classification performance of a decision hypothesis, inferred from a given set of training data. Via a learning phase that utilizes a 90-hour field-sports-video trainmg-corpus, the SVM infers a score-update event model by observing patterns in the extracted feature evidence. Using a similar but distinct 90-hour evaluation corpus, the effectiveness of this model is then tested genencally across multiple genres of fieldsports- video including soccer, rugby, field hockey, hurling, and Gaelic football. The results suggest that in terms o f the summarization task, both high event retrieval and content rejection statistics are achievable

An optical phase quantiser exhibiting suppressed phase dependent gain variation

We experimentally demonstrate an all-optical phase quantiser based on phase-sensitive amplification which alleviates phase noise to amplitude noise conversion. Phase transfer functions are measured for the very first time using a novel scheme

Development and validation of the thermal diagnostics instrumentation in lisa pathfinder

This thesis focuses on the issues related to the thermal diagnostics aboard the space mission LISA Pathfinder (LPF). LPF is a technological mission devoted to put to test critical subsystems for the LISA mission. LISA will be the first space born gravitational wave (GW) observatory with the main objective of detecting GWs. GWs are ripples of the space-time geometry caused by acceleration of masses in an asymmetric way. Their detection requires put test masses (TMs) in an almost perfect inertial frame (or free fall).Non-inertial forces perturbing the TMs must be less than 6 fN/sqrt(Hz) in the frequency range of 0.1 mHz to 0.1 Hz and the noise in the measurement between the TMs (separated by 5 Gm) must be of 40 pm/sqrt(Hz) in the same band. To reduce the risks of a direct launch of LISA, ESA has decided to first launch LPF to put all the LISA technologies to test.The payload of LPF, the LISA Technology Package (LTP), contains two TMs placed in two cylinders inside a single spacecraft (SC) and an interferometric system that measures the relative distance between them. The SC isolates the TMs from the external disturbances but internal stray forces will still perturb the TMs. Their levels must be bounded not to challenge the free fall accuracy. One of these disturbances is temperature fluctuations and the aspects related to their measurement are the leitmotif of this thesis.In chapter 1 we have presented how temperature fluctuations couple into the key subsystems of the LTP to degrade their performance. The foreseen effects are radiation pressure, radiometer effect, temperature coefficient of optical components, etc. Onground estimations conclude that the temperature stability in the LTP must be less than 100 microK/sqrt(Hz) in the frequency range of 1 mHz to 30 mHz (LTP band). Since temperature fluctuations are an important issue in LPF and in LISA, a thermal diagnostic subsystem is needed aboard both missions.The task of the thermal diagnostics in the LTP is twofold: on the one hand, temperature fluctuations in different subsystems must be measured with noise levels of 10 microK/sqrt(Hz) in the LTP band. On the other hand, a set of heaters will generate heat pulses that in conjunction with temperature measurements will be used to estimate the actual coupling between temperature and systems performance. These actions will provide information on the behaviour of the system and will permit to identify the fraction of noise in the system coming from temperature issues. The main function of LPF, as precursor mission of LISA, is the understanding of all the noise sources in the system. This will provide clues to the final leap from LPF sensitivity to LISA one.The main investigations carried out during this thesis can be split into three main categories: (i) the design and validation of the LTP temperature measurement subsystem (TMS); (ii) the extension of the system to the LISA requirements; and (iii) the analysis of the in-flight thermal experiments in the LTP. The thesis is organised as follows: in chapter 2 we describe the designed electronics and the temperature sensors chosen. Aspects related to the coupling of the TMS with other subsystems nearby are discussed in chapter 3. Chapter 4 focuses on the design of the testbed needed for the validation of the TMS. Two different testbeds are described: one for the LTP measurement bandwidth (MBW) and another one for the LISA MBW, 0.1 mHz. In chapter 5 we present the results of the test campaigns: the prototype, the engineering model and the flight model systems were put to test. The results of the investigations in the LISA band are also shown. Chapter 6 contains investigations in view of LISA requirements to reduce excess noise at very low frequency and to reduce the floor noise of the measurement. Chapter 7 focuses on the thermal experiment on-board LPF: a set of thermal excitations are proposed to extract information of the thermal behaviour of the key subsystems of the LTP