Image processing now has a wide variety of applications and a large amount of algorithm development is required. Clearly, a convenient and easily used development system is a great advantage. Some preliminary work with an existing machine indicated that a carefully tailored interactive facility could provide such an environment. An image storage unit containing a novel, fast, method of accessing the window to be processed has been constructed. By delegating to the storage unit some of the tasks normally performed by image processing software a considerable increase in processing speed has been achieved. While the improvement is not sufficient for an industrial system, it does allow for the convenient investigation of algorithms of considerably greater complexity than has hitherto been found possible on a moderately priced machine. To make full use of the hardware and to provide a concise notation for the description of processing algorithms, a versatile computer language, PPL2, has been developed. PPL2 provides, in addition to an extensive range of operators, a very concise yet very efficient method of denoting image operations. A compiler for this language has been incorporated into a complete image processing system for fast interactive development and testing of programs. Use has been made of the system to investigate the possible application of the quadtree in image processing and also for the formation of the skeleton description of an object. In the latter application interest centered around the possible advantages of a 5 x 5 over a 3 x 3 pixel window. Awareness of the potential industrial applications of image processing has led to observations and comments on the hardware and software required for image processing. Conclusions are reached concerning the relative merits of parallel versus sequential algorithms and of various types of processors.

Whether in art or physics, two dimensions are better than one. And in this context, we consider the spatial shaping of optical fields and atomic polarisations. This work begins with a comprehensive review of how to accurately and arbitrarily modulate transverse beam profiles using six different methods. The methods are presented in the context of a general complex input beam and the shaping and measuring of the input beam with a single SLM is discussed and demonstrated. A simple setup is then considered that allows for the rapid switching between arbitrary profiles, using only a single holo- graphic component and an acousto-optical modulator (AOM). In this setup, a switching speed of approximately 10 kHz is demon- strated explicitly, limited by the current detection system, but where speeds of up to 20 MHz are estimated to be possible. The following discussion then concentrates on the spatial structure of atoms, reviewing the conceptual tools needed to measure and interpret an atomic cloud in the presence of a mag- netic field from fundamental concerns, both in theory and in practice: assuming a classical light field and a quantum atomic system. The specific implementation of both a magneto-optical trap and a holographically-shaped dynamic dark SpOT follows. The crux of the work then concerns how polarisation-structured light can be used to create spatial patterns of transparency (spa- tial EIT) within an atomic cloud. Beginning with a review of EIT in general, with particular focus on an F = 1 → F = 0 transition, the spatial modulation of absorption, dispersion, polarisation rotation and change in ellipticity is predicted for systems in the presence of a transverse magnetic field. The depth of this mag- netic field dependency is then explored in some detail, where the relationship between observed patterns and applied magnetic field suggests the possibility of a visual magnetometer. The final section then considers how linearly polarised light and a q-plate was used to demonstrate spatially dependent transparency in a real atomic cloud.

Terrestrial laser scanning (TLS) is a remote sensing tool that can record a large amount of accurate topographical information with a fine spatial resolution over a short period of time. It has been used increasingly for measuring ground surfaces (i.e. topographical survey) and monitoring surface movements, such as those caused by landslides. However, the capability of this technique in these applications has not been fully explored in the literature, and thus forms the focus of this thesis. A quantitative study has been carried out to investigate the major error sources that affect the accuracy of digital elevation models (DEMs) derived from TLS survey data, and the magnitude of deformation that can be detected by repeated TLS surveys, at a local scale. In this research, vegetation-induced elevation errors in TLS measurements and the ways in which they can be minimised have been investigated experimentally. The presence of short vegetation was found to be a significant limiting factor for TLS surveys of terrain surfaces, with the average grass-induced elevation error being roughly 65% of the grass height. A finer resolution scan with a lower incidence angle (greater visibility) can effectively reduce vegetation error, as will scanning the same area from multiple scanner locations. The influence of measurement errors in source data points (or a point cloud) on a triangulated irregular network (TIN) with linear interpolation has been analysed. Based on the law of error propagation, an analytical solution was derived to calculate the error variance at any location within a TIN model, due to vertical and horizontal errors in source data points. For the special case of equal and independent error variances in source data points, the maximum, average and minimum values of propagated error variance within a TIN were found to be equal to unity, a half and a third respectively of the error variance in source data points. Errors in DEMs created from the TLS data points representing four terrain surfaces of different characteristics have been quantified using a statistical resampling method. The results show that terrain surface complexity can considerably affect the accuracy of DEMs. The effects of data point density (equivalent point spacing) on the DEM errors have also been analysed. For the data point spacings (35-100 mm) considered in the analyses, the DEM errors increased almost linearly with increasing data point spacing. The results also show that the DEM errors can be decomposed into two parts: a noise-related part and a data-density dependent part. Repeat TLS surveys of some fixed objects have been carried out, to seek to empirically quantify the georeferencing-induced positional errors involved in repeated TLS surveys. The results indicate that repeated TLS surveys can measure millimetric deformations of smooth surfaces if a high georeferencing accuracy is achieved. The DEM errors, along with the georeferencing-induced positional errors, were used to infer the minimum magnitude of movements that can be measured by multi-temporal TLS surveys of rough terrain surfaces. In the case of the Newbury cutting considered in this study, the minimum level of detection was approximately 20 mm (at a 95% confidence level) for the data point spacing of 35 mm. The findings in this research can aid in assessing the fitness of TLS surveys of terrain surfaces for a particular project, and thus are of use in the survey planning. The methods presented in this thesis can be applied to analyse errors in DEMs for making more meaningful interpretations of DEMs or surface variations derived from repeated TLS surveys.

The increasing demand for high power laser sources with excellent beam quality operating in the visible and near-infrared electromagnetic radiation spectrum has prompted significant research effort into developing robust, reliable and efficient diode-pumped solid-state lasers (DPSSLs). The scope of this thesis is to study the planar waveguide laser (PWL) architecture, with semiconductor diode lasers (SDLs) pumping, along with the spectroscopic investigation of promising materials with embedded trivalent rare earth (RE) ions that may enable upconversion (UC) lasers of the future. The PWL architecture has distinct advantages over their bulk counterparts in terms of exceptional thermal management, compatibility with SDLs, typically high figures of merit regarding the intensity-interaction length product, leading to the possibility of enabling weak optical transitions. Several experiments are detailed in this thesis in order to point out unique properties of PWLs. The first, a demonstration of a Tm:Y2O3 PWL with a maximum output power of 35mW at 1.95 µm and slope efficiency of 9 %, with respect to the incident pump power. A 12 µm thick active film was grown by the pulsed laser deposition (PLD)technique on top of undoped Y3Al5O12 (YAG) crystal. That was the first demonstration at its kind,i.e. in terms of a sesquioxides PWL, one operating with Tm3+ as the optically active ion and in the 2 micron wavelength regime. Despite waveguide propagation losses on the order of 2 dB/cm, the efficiency was respectable, demonstrating the potential of these PLD films. The second PWL experiment was conducted with a state of the art double-clad Nd:YAG structure fabricated by Adhesive-Free Bonding technique, operating on a weak optical transition of this material, this is, at a wavelength of 1.83 µm, with an output laser power in excess of 1W in a near diffraction-limited optical beam. The main goal of this thesis, however, is to investigate the suitability of several different solid-state gain materials for generation of laser radiation in UV and purple-blue optical spectrum by means of the upconversion process via a sequential step pumping scheme. Nd- and Tm-doped crystals have been investigated for their spectroscopic properties associated with the pump absorption bands, emission strengths, and lifetimes of the main intermediate energy level of Tm3+, which would be likely a reservoir for the first excitation step. These comprehensive spectroscopic studies have been carried out in order to develop rate equations and gain analysis for prospective UC lasers from different host media. The prior literature results of upconversion lasers have been gathered for comparison with herein data and some general guidelines have been pointed out towards the future work. High resolution, absolute excited-state absorption (ESA) spectra, at room temperature,for the long-lived thulium and neodymium metastable levels (the 3F4 and 4F3/2 manifolds, respectively) were measured using a bespoke purpose built spectrophotometer based upon diodes and a dual lock-in amplifier technique. The aim of that investigation was to determine the strength of ESA channels at wavelengths addressable by commercially available SDLs operating around 630-680 nm and 440-470 nm wavelength. From those measurements, for Tm3+, the effective stimulated emission cross-sections were derived and used in the modelling of the potential gain for the UC transitions (wavelength below 500 nm) in a variety of hosts, including Y3Al5O12, YAlO3, LiYF4 and KY(WO4)2. Waveguides ordered for this project were not delivered. Notwithstanding, preparation of SDL pump sources for the double-excitation method, and the necessary optical components, was undertaken. With the gain studies, and initial hardware preparations, the ground has been laid that will enable the demonstration of new class of UV or purple-blue UC laser architecture in the near future.

Silica optical fibres are renowned for the framework they have set in modern communications systems, sensors, and biotechnology. One particular trend in current research aims to investigate materials with enhanced optical functionality, high optical effciency, robustness, and a small device footprint. Amongst the many material choices, semiconductors are emerging as a promising route. In this work, optical fibres and semiconductors are elegantly unified to create a hybrid structure with the potential of seamless integration into current fibre infrastructures. Silica capillaries form the fibre templates in which amorphous semiconductor materials such as silicon and/or germanium are impregnated. This thesis will present the first comprehensive description of the fabrication, characterisation, and the implementation of silicon optical fibres for all-optical signal processing. The fibres are fabricated via a novel high pressure chemical deposition procedure. Each fibre is analysed to determine the exact material composition, uniformity, and more importantly the optical quality. Linear and nonlinear optical characterisations are performed experimentally and supported by intensive numerical studies to validate the results. The high nonlinearity of silicon is exploited for all-optical signal processing. Several investigations have been performed to determine key nonlinear coeffcients that were previously unknown in these fibres. Nonlinear absorption experiments allowed for the determination of the degenerate and non-degenerate two-photon absorption coeffcients, free carrier cross sections, and free carrier lifetimes of a number of silicon fibres. Nonlinear refraction investigations were then used to establish the Kerr nonlinearity. The strength of this parameter allowed for demonstration of strong self-phase and cross-phase modulation effects. With the insight gained in nonlinear absorption and refraction in silicon optical fibres, all-optical amplitude modulation and wavelength switching was demonstrated at ultrafast sub-picosecond speeds.

This thesis reports how the performance of a Vertical-External-Cavity Surface-Emitting Laser (VECSEL) can be significantly improved by cooling the active region to cryogenic temperatures. Also presented is the development of a room temperature, stable, high power, wavelength-tuneable, mode locked VECSEL and its subsequent implementation as a pump laser in a system designed to generate single photons. The VECSEL is a type of semiconductor laser capable of producing high output power in near diffraction-limited beams. The semiconductor gain region is highly temperature sensitive and the output power of a VECSEL is limited by non-radiative Auger recombination. Previous research has shown that by cooling the gain chip the gain per carrier is increased, the carrier density at the point of threshold lasing is reduced and the onset of Auger-recombination induced thermal rollover is delayed. This thesis presents a VECSEL that uses a gain chip cooled to 83 K. The device exhibited a 53% x 10% reduction in the incident pump power required to reach laser threshold, a 4-fold increase in incident pump power tolerated prior to the onset of thermal rollover, and an increase in output power of more than an order of magnitude when its performance was compared to operation at 293 K. A mode locked VECSEL using a gain chip held at 143 K is also reported. Prior to this research the coldest temperature at which a VECSEL gain chip had been operated was 248 K. This work shows that cryogenic temperatures can significantly improve VECSEL performance and begins a new direction in VECSEL research. The mode locked VECSEL has surpassed the performance of other types of mode locked semiconductor laser and is now approaching the performance of fibre and solidstate lasers. It has yet to be commercialised and so, to demonstrate that the mode locked VECSEL is now a mature, reliable technology, this thesis reports the development and implementation of a mode locked VECSEL as a pump laser in a single photon generation system. The system generates coincidental pairs of photons and, by detecting one photon in the pair, the presence of the companion will be heralded. The wavelength exibility, excellent beam quality and high pulse repetition rate make the mode locked VECSEL ideal for both quantum state engineering and heralded single photon generation.

Semiconductor microcavities represent a rich playground for the investigation and exploitation of fundamental light{matter interaction as well as opto{electronic devices. Due to strong interaction of confined photons with electronic excitations new quasiparticles are formed, known as exciton{polaritons. These new eigenstates play a key role in a various number of intriguing effects like Bose-Einstein condensation and superfluidity due to their light-matter duality which unifies at the same time small effective mass and strong inter-particles interaction. Meanwhile, research achievements in the study of organic light emitting diodes and organic trasistors combined with strong advancements of the fabrication technologies has propelled the organic photonic and electronic field. In the present thesis the physics of organic microcavities is explored with particular attention at the limiting factors which prevent from the observation of cooperative non-linear phenomena. Such structural and material issues are addressed by following new engineeristic approaches. The inclusion of different organic dyes in the cavity active region is demonstrated to enhance polariton population density by direct intracavity pumping or either provide new efficient channels for particles relaxation. Inspired by a similar design, an hybrid organic{inorganic microcavity which exploits coupling of organic with inorganic quantum well excitons (Frenkel and Wannier{Mott) in a light emitting diode scheme is presented. Within this system, the optical cavity mode simultaneously couples to both excitonic transitions for the formation of mixed polariton states. The new bosonic eigenstates which arise from photon{mediated hybridiazation of Frenkel and Wannier-Mott excitons are predicted to exhibit large radius, small saturation density and large oscillator strength. Results from the optical characterization enlighten the enhancement of nonlinear properties of such hybrid polaritons while observation of strong coupling regime under electrical injection suggests the possibility for an effective exploitation of such unique polaritonic features in a electro-optic device.

High power fiber lasers have several applications thanks to their outstanding features such as good beam quality, all fiberized compact device size, robustness, wavelength tuning, high wall-plug efficiency, and low cost. Due to these features high power fiber lasers are replacing other solid-state lasers for several applications. Fiber lasers are being used commercially for several applications such as surgery, material processing (cutting, drilling, polishing etc.), oil and gas sensing, pumping several other lasers, and space communication etc. However, nonlinear effects restrict the output power level of fiber lasers. Although reducing power density by using large core diameter fibers can increase the threshold of non-linear effects, however large core diameter leads to multimode behavior and is prone to bend-induced effective area reduction. Several novel large mode area fibers have been proposed to scale the output power level. However, the advantages of all-fiberized device and low cost disappear as most of these fibers involve complex fabrication and cannot be spliced to optical components such as conventional pump fibers. This thesis deals with novel large mode area fibers which are suitable for mass scale production and can offer low cost production compared to other competitive fiber designs thanks to their simple design. These novel fibers are all-solid and can be easily spliced to other fibers, thus can lead to an allfiberized device. Moreover, some of the novel fibers proposed in this thesis offer the delocalization of powers of the higher order modes outside the core. This delocalization of the higher order modes can be useful to ensure an effective single mode operation in a double clad configuration. The proposed novel fibers offer better or competitive mode area scaling performance compared to other competitive fibers. In this thesis, firstly conventional step-index fibers have been exploited for mode area scaling by reducing the refractive index of the actively doped core with respect to the cladding. Prior to this thesis, the lowest reported NA of a Yb-Al doped fiber was 0.048 corresponding to 0.0008 refractive index of core with respect to cladding. In this thesis, optimized solution doping process leads to a NA of 0.038 for a Yb and Al doped core corresponding to 0.0005 refractive index of core with respect to cladding. This reduction in NA of core leads to an effective area increase from ~450μm2 to ~700μm2 at 32cm bend diameter ensuring effective single mode operation. This is the lowest NA ever reported using cost-effective solution doping process to the best of author’s knowledge, which is widely used in manufacturing of rare-earth doped fiber. Further, in a 4%-4% laser configuration, a 35μm core diameter 0.038 NA fiber shows high laser efficiency (~81%) with good M2 (~1.1) value of output beam at 1040nm. Thesis also reports a novel fiber design known as single trench fiber, where a passive Ge-doped ring has been added around the core. This ring known as resonant ring facilitates the suppression of the higher order modes thanks to resonant coupling between modes of core and ring. The combination of ultra-low NA (~0.038) and a surrounding ring can lead to an effective single mode operation of fiber having a core diameter as large as of 50μm offering an effective area of ~1,500μm2 at ~40cm bend diameter. A 40μm core diameter single trench fiber has been successfully fabricated in house and shows robust effective single mode behavior. Further, a 30μm single trench fiber has been tested in a master oscillator power amplifier configuration delivering ~23.5ps pulses at 13.5MHz repetition rate carrying up to ~3.8μJ pulse energy corresponding to >160kW peak power and ~52.3W of average power, while maintaining ~76% slope efficiency. Numerical Performance of STF has also been reported at other wavelengths such as 1550nm and 2000nm. A detailed comparative analysis has been performed with other competitive fiber designs showing the advantages of single trench fiber over other fiber designs. Further, another fiber design known as multi trench fiber has also been proposed. Multi trench fiber can scale effective area as large as of 12,000μm2 in a rod-type configuration. Multi-trench fibers offer several advantages such as easy cleaving and splicing thanks to the all solid structure; however refractive index of active core has to be same as of passive cladding. Nevertheless, this fiber has shown a strong potential for applications in ultrafast rod-type fiber lasers. A 90μm core diameter passive fiber has been fabricated in house using rod-in-tube technique in conjunction with modified chemical vapour process. Experiments ensure an effective single mode operation. Furthermore, this fiber also shows the potential to be used for beam delivery applications with a small core diameter thanks to effective single mode operation over a wide range of bend radii. MTFs of 30μm and 20μm core diameter have been successfully fabricated and both ensure robust single mode operation over a wide range of bend radii at 1060nm and 632nm respectively. Numerical simulations show the possibility of a 10μm fiber to be effectively single moded at a wavelength of 300nm.

The last few decades have a wide spread use of optical fibre sensors in many applications. Optical fibre sensors have significant benefits over existing conventional sensors such as; high immunity to electromagnetic interference, the ability to transmit signal over long distance at high bandwidth, high resolution, usage in hazardous environments and no need for isolation when working at high voltages. The measurement of high voltages is essential for electrical power systems as it is used as a source of electrical information for Relay Protection Systems (RPS) and load management systems. Electrical Power Systems need to be protected from faults. Faults can range from short circuits, voltage dips, surges, transients etc. The Optical High Voltage sensor developed is based on the principle that the Lead Zirconate Titanate (PZT) electrostriction displacement changes when a voltage is applied to it. The displacement causes the fibre (FBG) which is bonded to the PZT material to have a resultant change in the wavelength. An optical fibre sensor prototype has been developed and evaluated that measures up to 250 V DC. Simulation using ANSYS software has been used to demonstrate the operational capability of the sensor up to 300kV AC. This sensor overcomes some of the challenges of conventional sensors issues like electromagnetic interference, signal transmission, resolution etc. R BASHOUR 2 A novel optical fibre high voltage based on the Kerr effect has been demonstrated. The The Kerr effect was determined using Optsim (R-Soft) software and Maxwell software was used to model an optical Kerr Cell. Maxwell software is an electromagnetic/electric field software used for simulating, analysing, designing 2D and 3D electromagnetic materials and devices. It uses highly accurate Finite Element techniques to solve time varying, static, frequency domain electric and electromagnetic fields. A Relay Protection System on electrical networks was discussed in detail. Keywords: Fibre Bragg Grating, Fibre Optics Sensors, Piezoelectricity, Kerr effect, Relay Protection Systems.

Modern manufacturing processes require better quality control of the manufactured products at a faster rate, for achieving good throughput. This is increasing the need for process-oriented precision metrology capable of providing faster inspection and yielding valuable feedback to the manufacturing system for quality control of the manufactured products. Over the past twenty years optical sensors have emerged as a preferred method for the measurement applications in manufacturing automation, owing to some inherent advantages, such as high speed, high resolution, non-contact operation, and low cost. Improved online optical sensors for surface measurement would enable incorporating measuring systems into production processes and machines, improving the production performance and the quality of products, which is highly desired in many high/ultraprecision manufacturing applications. This thesis presents a novel spatially dispersed short coherence interferometry (SDSCI) sensor system for online surface measurement applications on the nanoscale. The SDSCI sensor system uses a low-cost broadband super-luminescent diode (SLD) with an emission bandwidth of 25 nm. Two measurement methods, phase shifting interferometry and Fourier transform for surface profile measurements, have been investigated in this study. The metrology sensor system incorporated the Michelson interferometer configuration with an optical probe in the measurement arm, while the reference arm had a mirror with a piezo-electric transducer. The technique involves surface scanning by spatially dispersing the broadband light using a reflective grating and a scan lens, and recording the resulting interferogram by using a high-speed spectrometer. The first measurement method involved investigations of implementation of phase shifting interferometry and the Carré algorithm for phase retrieval from the measured phase-shifted interferograms for profile measurements. Standard diamond turned multi-stepped and NPL artefact samples with 550-nm and 100-nm-high steps, respectively, were measured and confirmed the capability of the measurement sensor. The measurement speed of this technique was limited by the spectrometer speed and by the piezo-electric transducer movement. The optimised system has a measurement time of 1s. The second method was then investigated based on the Fourier transform profilometry technique for further increasing the measurement speed of the sensor device, as it required a single-shot interferogram, alleviating the need of any phase shifting. With increased measurement speed, this technique further reduced the problem of environmental noise inherent to all interferometer-based systems. Similar artefacts were measured by using this technique for evaluating its applicability for surface profile measurements. Once the sensor system was optimised and calibrated, the resulting open-space system could be further miniaturised into a compact sensor system by using optical fibres with a remote probe connected via a fibre link for use in embedded metrology applications. This method will be very beneficial in online inspection of samples in rollto-roll manufacturing processes, where the measurand is constantly moving. An example of such a measurement challenge is detection of defects on vapour barrier films formed by depositing an aluminium oxide layer several tens of nanometres thick on a flexible polymer substrate. Effective detection and characterisation of defects in this layer requires a single-shot approach with nanometre-scale vertical resolution.