In this thesis I describe work that I have done in two separate research areas. The first involves optical micro manipulation of nano-scale objects and their orientation. The second concerns the development of a semiconductor laser to provide high beam quality,average and peak power and short pulse durations. Optical tweezers are an excellent tool to manipulate nano scale objects in all three dimensions. An additional degree of control, the rotational alignment of assymetrical particles, is demonstrated by polarisation analysis of two photon induced fluorescence of the trapped and rotated semiconductor nanorods.Mode-locked vertical external-cavity surface emitting lasers (VECSELs) have recently achieved multi-watt average power levels. Nevertheless the need to optimize the gain structure design, in order to consistently obtain sub 200 fs pulse durations, still remains. The evolution of the intra-cavity power build-up transient is utilized for a novel spectro-temporal technique which allows for the extraction of the curvature of the gain spectrum during actual operation and enables the observation of the evolution of the gain spectrum during lasing build-up. In addition a method to obtain the total cavity loss via the combination of the power build-up transient and photo luminescence decline, during lasing onset is shown. The use of an amplified, femtosecond-pulsed and GHz repetition rate VECSEL to generate multi-watt average power supercontinuum in photonic crystal fibres (PCFs) is presented. Supercontinuum generation with GHz pulse repetition rates is of interest for frequency combs as the high repetition rate increases the mode spacing of the comb and energy per mode. Two different PCFs, one with an all-normal dispersion profile and one with a zero dispersion wavelength (ZDW) at 1040 nm, are pumped with the amplified VECSEL pulses generating spectral components over 200 nm and 500 nm, respectively. The thesis concludes with a proposal to use the advantages of both optical tweezers and VECSELs to analyse and resonantly excite the vibrational frequencies of single nano-scale objects.

It has been of major interest in recent research to produce faster optical processing for many telecommunications applications, as well as other applications of high performance optoelectronics. The combination of one-dimensional photonic crystal structures (PhC) and narrow photonic wire (PhW) waveguides in high refractive-index contrast materials such as silicon-on-insulator (SOI) is one of the main contenders for provision of various compact devices on a single chip. This development is due to the ability of silicon technology to support monolithic integration of optical interconnects and form fully functional photonic devices incorporated into CMOS chips. The high index contrast of the combination of a silicon core with a surrounding cladding of silica and/or air provides strong optical confinement, leading to the realization of more compact structures and small device volumes. In order to obtain a wide range of device functionality, the reduction of propagation losses in narrow wires is equally important, although there are still performance limitations determined by fabrication processes. Compact single-row PhC structures embedded in PhW waveguide micro-cavities could become essential components for wavelength selective devices, especially for possible application in WDM systems. The high quality factor, Q, and confinement of light in a small volume, V, are important for optical signal processing and filtering purposes, implying large Purcell factor values. In this thesis, one-dimensional photonic crystal/photonic wire micro-cavities have been designed and modeled using both 2D and 3D versions of the finite-difference time-domain (FDTD) approach. These devices were fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) for patterning of the silicon layer. The device structures were characterized with TE polarized light, using a tunable laser covering the range from 1480 nm to 1585 nm. Single-row periodic hole-type PhC mirrors consisting of identical and equally spaced holes were embedded in 500 nm wire waveguides. Two PhC hole mirrors were separated with a cavity spacer varying from 400 nm to 500 nm in length to form a micro-cavity. In contrast, several different cavity arrangements were also successfully investigated, - i.e. extended cavity and coupled micro-cavity structures. The experimental results on photonic crystal/photonic wire micro-cavity structures have demonstrated that further enhancement of the quality-factor (Q-factor) - up to approximately 149,000 at wavelengths in the fibre telecommunications range is possible. The Q factor values and the useful transmission levels achieved are due, in particular, to the combination of both tapering within and outside the micro-cavity, with carefully designed hole diameters and non-periodic hole placement within the tapered sections. On the other hand, a large resonance quality factor of approximately 18,500, together with high normalized transmission of 85% through the use of tapering on both sides of the hole-type PhC mirrors that formed the micro-cavity, has been obtained. For the extended cavity case, the multiple resonances excited within the stop band, together with substantial tuning capability of the resonances obtained by varying the cavity length has been demonstrated, together with a Q-factor value of approximately 74,000 at the selected resonance frequency with a normalised transmission of 40%. In addition, the coupled micro-cavity structures considered in this thesis have formed the basic building block for designing multiple cavity structures where the combination of several cavities splits the selected single cavity resonance frequency into a number of resonances that depends directly on the number of cavities used in the design. The coupling strength between the resonators and the Free Spectral Range (FSR) between the split resonance frequencies of the coupled cavity combination were controlled via the use of different numbers of periodic hole structures – and through the use of different aperiodic hole taper arrangements between the two cavities in the middle section of the mirrors.

Silicon based integrated circuits has been dominating the electronics technology industry in the last few decades. As the telecommunications and the computing industry slowly converges together, the need for a material to build photonics integrated circuits (PIC) that can be cost-effective and be produced in mass market has become very important. This thesis describes and outlines the characteristics of high index contrast waveguides as a building blocks that can be designed, fabricated and employed on devices in silicon photonics. Initially in this work, a fully vectorial H-field based finite element method has been used to obtain the modal characteristics of high index contrast bent waveguide to get a better understanding of the curved section. Through the beam propagation method, the propagation losses and the spot-size along the propagation distance are obtained when a mode from the straight guide is launched into a bent guide. It is also learnt that mode beating exists at the junction of a straight-to-bent waveguide, in which higher order modes will also be generated. It will be shown in this work that power do exchange between the two polarization states, therefore the polarization conversion, the power losses and the bending losses will be investigated. It will also shown in here that by applying lateral offsets with coupled waveguides of unequal widths, the insertion loss can be reduced. Secondly, for a high index contrast waveguide such as the silicon strip waveguide with a nanoscale cross-section, modes in such waveguide are not purely TE or TM but hybrid in nature, with all the six components of their E and H-fields being present. Therefore a detail analysis of the modal field profiles along with the Poynting vector profile will be shown. The effects of waveguide's width and height on the effective indices, the hybridness, the modal effective area and the power confinement in the core or cladding has been studied. Furthermore the modal birefringence of such strip waveguide will be shown. It will be presented that for a strip waveguide with height of 260 nm, single mode exists in the region of the width being 200 nm to 400 nm and that the modal effective is at its minimum when width is around 320 nm for both polarization states. Thirdly, a compact polarization rotator with an asymmetric waveguide structure design, suitable for fabrication that does not require a slanted side wall or curved waveguide is considered in this work. It will be shown in here that due to the hybrid nature of the asymmetric waveguide design, maximum polarization rotation (from TE to TM) will be achieve by enhancing the non-dominant field profile of both polarized fundamental mode. As the modal hybridness and the propagation constants of both polarized modes will be obtained, the half-beat length, polarization conversion and polarization cross-talk will be calculated by using the FEM and the least squares residual boundary method (LSBR). It is learnt that a compact single stage polarization rotator with a device length of 48 μm with more than 99% of polarization conversion is achieved in this work. Finally, a study of vertical and horizontal slot waveguide will be shown. Based on silicon strip waveguide, a detail modal characteristics of E and H-fields along with the Poynting vectors are presented. It will be shown that for slot waveguide, high power confinement and power density will be achieved in the slot area. It will be presented that by optimising the waveguide and slot dimension, the performance of the power confinement and power density in the slot region can be improved.

Rigorous numerical simulations have been carried out by using the Finite Element Method (FEM) in order to calculate bending and leakage losses of Photonic Crystal Fibres (PCF). A modal solution approach including the implementations of the conformal transformation and the Perfectly Matched Layer (PML) were undertaken to determine the bending and leakage losses of several designs of Photonic Crystal Fibres. This was carried out by varying key parameters such as the pitch (Λ), diameter (d) and air-filling fraction (d/Λ). Output modal parameters including the effective indices, spot sizes, leakage and bending losses as well as the mode field profiles were obtained. These output parameters were obtained by varying the bending radius (R) from very large values to very low values for different dimensions of the PCF, with results being obtained for Transverse Magnetic and Transverse Electric (quasi-TM and quasi-TE) polarizations. These parameters were calculated by solving the Maxwell’s equations using the H-field vector formulation and with the inclusion of PML to solve complex eigenvalue equations. Generally, it was observed that for all Λ, d/Λ and the polarization considered, as R is reduced from a very high value to lower values, the bending losses increase and there is a sharp increase at some lower values of R. At some very low values of R, some oscillatory behaviour was observed in the curves obtained for the fibre losses, where further investigations were carried out. These oscillations appeared due to degeneration of the fundamental mode with the cladding modes. In most of the cases investigated, there was a correlation in the variation of effective indices the loss values and also in the variation of spot sizes. PCFs with non-identical air-holes were also investigated in which case the d ≠ d2 (diameter of 4 larger air-holes in the first ring) and knowing the values for TM and TE polarizations, it was possible to determine the birefringence, which is the difference between the effective indices for the TM and TE modes and also the loss ratio, which is the ratio of TM loss to that of the TE loss. All the input and output parameters that were considered with the symmetric air-holes were also considered in the case with fibre with asymmetric air-holes study. The results obtained are very important in the design of Single Mode Single Polarization PCF. Results have also been obtained from the studies done of asymmetric arrangement of air-holes which lead to the design of Single Mode Single Polarization PCF. Work was carried out on the design of a tapered PCF that could be efficiently coupled to a single mode fibre, SMF. This was achieved by increasing the number rings up to 10 rings of air-holes in the cladding and having the outermost ring with larger air-holes, the inner rings were near cutoff. This fibre was coupled to a conventional SMF to allow for better tolerance to fabrication errors. There has also been work carried out in polymer fibre namely Teflon and TOPAS in the terahertz regime. The conventional hexagonal arrangement of PCF was simulated and compared to spiral PCF in THz. An improved PCF design having a porous core with hexagonal arrangement and cladding was designed and analysed and low-loss guidance in THz was achieved. Thus overall a number of different PCF designs were considered and their properties evaluated and detailed knowledge has been obtained on potential performance of such fibres.

Photons have proven to be an effective test-bed for the fundamental concepts and elements of quantum-enhanced technologies. As systems become increasingly complex, however, practical considerations make the traditional approach of bulk optics and free-space propagation progressively more difficult. The major obstacles are the physical space necessary to realise and operate such a complex system, its stability, and maintaining low losses. In order to address these issues, quantum optical technologies can take a cue from their classical counterparts and look towards an integrated architecture to provide miniaturisation, greatly enhanced stability, less alignment, and low loss interfaces between different system components. In this thesis the feasibility of chip-based waveguides as a platform for metrology and information processing will be explored. In Part I, the necessary criteria for a metrology system to out-perform its classical counterpart will be investigated. It will be found that loss is a major barrier to this aim and, critically, that it is unlikely to have been achieved to date by any experiment which consumes resources of a fixed photon number. The issue of loss will be addressed by developing a scalable heralded source of a class of entangled photonic states which are both robust to losses and practically feasible to prepare. A novel tomographic technique will be developed to characterize these states and it will be explicitly demonstrated how it is possible to beat some bounds on classical performance without being able to out-perform a comparable classical system. Finally, a proof of principle demonstration of a waveguide-based interferometer with an integrated phase-shifter will be undertaken. It will be shown that the device preserves quantum interference, making it suitable for use in quantum-enhanced metrology applications. In Part II, integrated optics in the context of information processing will be discussed. First, a novel characterization technique will be developed which enables the behaviour of complex circuits to be predicted. The technique is independent of loss in the device being characterized. A method of simulating these circuits will be outlined that takes advantage of the computational speed-up available from parallelisation and sparse matrix operations. A key increase in complexity for integrated photonic systems will be demonstrated by showing quantum interference of three photons from two separate sources in eight spatial modes. The resulting interference has a visibility which beats all possible classical interference visibilities for similar circuits. Finally, a fully integrated waveguide-coupled photon-number-resolving detector will be developed and demonstrated. This proof of concept demonstration will show good resolution of different photon number events. The device will be modelled and routes to high efficiency operation will be explored.

This thesis presents studies of novel terahertz photonic devices, including photoconductive optoelectronic devices and guided-wave components, aimed at the development of next-generation terahertz systems. In chapter 2, a scalable interdigitated THz transmitter is designed to increase the output power and compared with a conventional 50 μm coplanar transmitter. In chapter 3, we compare four different receivers with different antenna geometries in terms of bandwidth and sensitivity. Then we describe a photoconductive near-field detector with a subwavelength aperture and its system integration and characterization. In chapter 4, a parallel metal plate waveguide is designed with an integrated step inside the waveguide that can couple to higher order TM modes efficiently from the TEM mode. In this chapter, we also experimentally and numerically study a 2-dimensionally tapered parallel plate waveguide, by which a free-space THz beam can be focused into a deep subwavelength-scale volume. In chapter 5, a parallel thin dielectric film waveguide is used to explore the guiding mechanism of an antiresonant optical reflection waveguide. Cylindrical silica single capillaries and a microstructured capillary, which guide in a similar way, are characterized in terms of mode profiles and attenuation. In chapter 6, we study oblique transmission through freestanding thin nickel films, which are perforated with periodic conical hole arrays. Surface modes can be supported by both metallic surfaces with different nonlinear dispersion curves, which results in spectral interferences in a near-field region when the surface modes couple out of the waveguide into free space.

La technique Lidar Radar est couramment utilisée pour la détection de cibles immergées dans des eaux peu profondes inférieures à quelques dizaines de mètres. Cette technique repose sur l’envoi d’un signal modulé associé, à la réception avec un filtre passe bande autour de la fréquence de modulation. Cette technique requiert ainsi un signal optique bleu vert, intense, modulé à des fréquences radar. Nous présentons dans cette thèse de nouvelles architectures de modulateur parfaitement adaptées à cette technique. La 1ère architecture est constituée d’une cavité externe comportant un doubleur intracavité. Cette architecture est couplée à une source laser picoseconde infrarouge (1064 nm). Les résultats ont montré que ce modulateur permet de générer un signal vert (532 nm), intense (5 mJ) et stable en fréquence. Grâce à la source utilisée, le signal modulé en sortie de l’émetteur (source laser et modulateur) ne dure que quelques nanosecondes. Ceci permet d’utiliser la méthode de « range-gating » pour obtenir une précision sur la localisation de la cible. Néanmoins, ce dispositif présente l’inconvénient d’avoir une bande passante du signal émis fixe. Nous avons donc développé une deuxième architecture du modulateur, permettant d’accorder facilement la bande passante du signal émis. Cette configuration repose sur le comportement polarimétrique des composants optiques afin de changer la largeur de bande passante du signal. Nous avons montré que ce modulateur permet de délivrer, un signal intense (jusqu’à 2,9 mJ), court (quelques nanosecondes), à 532 nm, modulé à des fréquences radar, stable en fréquence et accordable en bande passante. / The Lidar Radar technique is commonly used for submerged target detection in shallow waters less than a few tens of meters. This technique is based on sending a modulated signal, associated with a bandpass filter around the modulation frequency after detection. This technique requires an intense blue-green optical signal modulated at radar frequencies. We present in this thesis new modulator architectures perfectly adapted to this technique. The first architecture consists of an external cavity with an intracavity SHG stage. This architecture is coupled to an infrared picosecond laser source (1064 nm). The results showed that this modulator makes it possible to generate a green signal (532 nm), intense (5 mJ) and stable in frequency. Thanks to the source used, the signal modulated at the output of the transmitter (laser source and modulator) lasts only a few nanoseconds. This makes it possible to use the "range-gating" method to precisely locate the target.Nevertheless, this device has the disadvantage of a fixed bandwidth. We have therefore developed a second architecture of the modulator, allowing to easily tune the bandwidth of the transmitted signal. This configuration is based on the polarimetric behavior of the optical components in order to change the bandwidth of the signal. We have shown that this modulator can deliver , an intense signal (up to 2.9 mJ), short (a few nanoseconds), at 532 nm, modulated at mirowave frequencies, stable in frequency and tunable in bandwidth.

La Tomographie Optique Diffuse (TOD) est une nouvelle technique d'imagerie médicale permettant de reconstruire les propriétés optiques des tissus biologiques dans le but de détecter des tumeurs cancéreuses. Il s’agit, toutefois, d’un problème inverse mal-posé et sous-déterminé. Le travail de cette thèse s’articule autour de la résolution de ce problème en utilisant l’équation du transfert radiatif comme modèle de propagation de la lumière (modèle direct). L’analyse de sensibilité a montré que le facteur d’anisotropie g de la fonction de phase de Henyey-Greenstein est le paramètre le plus influant sur la sortie du modèle direct suivi du coefficient de diffusion µs puis du coefficient d’absorption µa. Dans un premier temps, un algorithme de Gauss-Newton a été implémenté en utilisant les fonctions de sensibilités. Toutefois, ce dernier ne permet d’estimer qu'un nombre très limité de paramètres optiques (supposés constants en espace). Dans un second temps, un algorithme de Quasi-Newton a été développé pour reconstruire les distributions spatiales des propriétés optiques. Le gradient de la fonction objectif a été calculé efficacement par la méthode adjointe à travers le formalisme de Lagrange avec une approche Multi-fréquences. Les reconstructions sont obtenues à partir des données simulées en surface. Le facteur g est reconstruit comme un nouvel agent de contraste en TOD. Le problème de diaphonie entre µs g a été donc mis en évidence dans cette thèse. Notre algorithme a permis de reconstruire en 2D et 3D une ou plusieurs inclusions tumorales présentant différentes formes. La qualité des images reconstruites a été examinée en fonction du nombre de fréquences, de la diaphonie, du niveau de contraste (Inclusion/Fond), du niveau de bruit et de la position des inclusions tumorales / Diffuse Optical Tomography (DOT) is a new medical imaging technique used to reconstruct the optical properties of biological tissues in order to detect cancerous tumors. However, this is an ill-posed and under-determined inverse problem. The work of this thesis deals with the resolution of this problem using the radiative transfer equation as a forward model of light propagation. The sensitivity analysis showed that the anisotropy factor g of the Henyey-Greenstein phase function is the most sensitive parameter of the forward model followed by the scattering coefficient µs and then the absorption coefficient µa. In a first step, a Gauss-Newton algorithm was implemented using the sensitivity functions. However, this algorithm allows to estimate a very limited number of the optical parameters (assumed to be constant in space). In a second step, a Quasi-Newton algorithm was developed to reconstruct the spatial distributions of the optical properties. The gradient of the objective function was efficiently computed by the adjoint method through the Lagrangian formalism with a Multi-frequency approach. The reconstructed images were obtained from simulated boundary data. The g factor was reconstructed as a new optical contrast agent in DOT and the crosstalk problem between this factor and µs has been studied. The results showed that the algorithm is efficient to reconstruct in 2D and 3D one or several tumor inclusions having different shapes. The quality of the reconstructed images was examined according to several parameters: the number of frequencies, the crosstalk, the contrast and the noise levels