Quantum optics has been a frontier of physics in the last few decades. Integrated quantum photonics which prompts the concept of realizing quantum optics operation on a chip is crucial for any potential applications beyond the optical bench. This thesis focuses on two important material systems (diamond and GaN) which both have the potential for integration of single photon sources and detectors with integrated quantum circuits and at the same time can minimize the footprint of the integrated quantum circuits due to their high refractive index. We have proposed and realized two new masking methods to fabricating higher aspect ratio diamond microlenses through plasma etching. We have also proposed and demonstrated a new approach to fabricating large cross-section edge-coupled rib waveguides on free-standing thin diamond substrates by combining inkjet printing of photoresist with photolithographic patterning technique. Single-mode GaN directional couplers with transmission varying between 0.1:0.9 and 0.55:0.49 have been studied and two-photon interference was demonstrated in a 0.55:0.45 GaN directional coupler. This is the first demonstration of two-photon interference realized on a compound semiconductor chip. Our work opens up a new way to achieve sophisticated integrated quantum photonic circuits based on GaN and other suitable compound semiconductors. Integrated quantum photonics is a widespread research topic, currently undergoing explosive developments. Future options including an all-diamond platform, III-V semiconductors or a hybrid system between diamond and III- V semiconductors are discussed as perspectives.

Photonic clystals are an exciting component in the field of nanophotonics. They allow the control, confinement and manipulation of light at the nanometre scale. The ability to fabricate photonic clystals with semiconductor fabrication technology makes them a suitable building block of photonic integrated circuits. Photonic clystals offer sensitivity to surrounding materials and they can enhance light-matter interaction. This has motivated considerable research into their application in the area of chemical and biological sensing. Photonic clystals provide a versatile platform for lab-on-a-chip applications and the prospect of high integration density could benefit cost-sensitive applications such point-of-care diagnostics or environmental sensing. This thesis investigates the feasibility of creating photonic crystal sensors on gallium nitride. The maturity of GaN-based photonic devices, such as LEDs, makes it an ideal platform for lab-on-a-chip applications. Two types of GaN photonic clystals sensors are designed, fabricated and characterised in this work. The first type is a ID grating, which supports guided mode resonances. These are fabricated by electronbeam lithography and dlY etching on GaN membranes and on GaN-on-sapphire. The ability of membrane gratings to sense the refractive index of a liquid that is present at one side of the membrane is verified experimentally. GaN-on-sapphire gratings are presented as a method of enhancing fluorescence emission from molecules placed on the gratings through the guided mode resonances. The second structure analysed is a modified 2D photonic clystal L3 cavity. This novel structure possesses a central hole, which allows the positioning of fluorescent molecules in a region of high electric field density. It is shown by finite difference time domain calculations, that the resonant modes of the cavity significantly enhance the absorption and emission of the molecules. The fabrication and characterisation of those cavities, along with coupling to ridge waveguides, are shown as a first step towards an integrated sensor.

The aim of this thesis is to consistently fabricate low OH content silica solid-core photonic crystal fibres of different core diameters, identified as low spectral attenuation at 1383 nm. Three different methods are proposed. Two of them are focused on preventing the OH contamination of glass during fabrication whilst the third method is focused on obtaining low OH fibres by reducing the OH content of already contaminated glass. The local attenuation at the ends of these low OH fibres is notoriously worsen when they are exposed to the atmospheric water vapour, the levels of this attenuation depending very strongly with core diameter. The low OH levels achieved (0.19 ppm) in the small-core photonic crystal fibres open the scope to applications in non linear optics where standard levels of absorption are detrimental. In particular, the principle of a widely tunable source (across the OH absorption peak at 1383 nm) delivering femtosecond pulses beyond 2 μm is demonstrated experimentally.

A key problem in nanotechnology is the integration of individual components into larger networks capable of more complex processes. DNA based photonic wires are a promising solution as they have been shown to transmit light energy over 10 nm distances, but are limited by their problematic assembly and reliance on fluorophore labelled DNA. This thesis describes efforts to construct an improved photonic wire using functionalised DNA binding small molecules as proof of principle for a ‘mix and match’ approach to nanotechnology which delivers individual components to a specific site on DNA. Polyamides have been shown to bind to DNA with very high affinity and specificity which together with their modular nature makes them an ideal ‘delivery system’. To combine this with the versatility and efficiency of copper catalysed click chemistry, novel internally functionalised alkyne polyamides were synthesised using both solution and solid phase chemistry. A general route to produce these internally modified polyamides was developed and the synthesis of the standard polyamide building blocks was improved. Test click reactions on alkyne polyamide fragments showed up to 92% conversion, but the same reactions failed on the full length polyamides and previously reported modification methods were used to create a fluorophore labelled polyamide. A coumarin based fluorophore was selected to allow direct substitution into proven photonic wires, but when the DNA binding affinity of this polyamide was tested, it was found that only weak binding was observed with 1.5 equivalents of polyamide. Upon construction, the improved photonic wire transported energy over a distance of 6 nm with an overall efficiency of 9% which was attributed to the poor DNA affinity. This poor performance makes it difficult to assess the general potential for this ‘mix and match’ approach, but the non-applicability of click chemistry and improvements in the synthesis will inform future designs.

The detection of single photons is now commonplace in labs across the world. This was initially due to the invention of photomultiplier tubes (PMTs) and multichannel plates (MCPs) but the explosion in adoption was undoubtedly due to the developments in Single Photon Avalanche Photodiodes (SPADs), and most notably in silicon. The cost, bulk, weight, and complexity all dropped, and thus significantly expanded the application space. Today SPADs are found in biophotonics, sensing, rangefinding, quantum key distribution (QKD), quantum computing, and more This thesis investigates a relatively new class of single photon detectors, commonly referred to as shallow junction SPADs, and their applicability to a range of applications. These offer a further step reduction in cost and additionally allow for the creation of individually addressable arrays as well as integrated circuitry along side the detection areas.

Quantum information science provides new paradigms of communication, computation and measurement; such as perfectly secure quantum key distribution, intrinsic parallel computation and increased precision measurement by beating the standard quantum limit. The first implementation of optical quantum circuits whose performance exceeds that required for fault tolerance quantum computation is presented. Near- unit fidelity non-classical interference and entangling operations are demonstrated in integrated photonic waveguides fabricated on silica on silicon chips. Improvement of about 5% in the measured performance is the result of perfectly indistinguishable photon pairs produced from an SPDC source. These integrated devices, combined with high efficiency single photon sources and detectors, will be the building block for future demonstrations of quantum information. Operation of quantum optics circuits with superconducting nanowire single photon detectors (SNSPD) is reported. The lower jitter of SNSPDs compared to silicon single photon avalanche photodiodes (SPADs) enables the measurement of higher visibility non-classical interference on directional couplers, CNOT gates and Mach-Zehnder interferometer. SSPDs are fast, low noise and can detect single photons in a broad range of wavelengths. Recent studies show very high detection efficiency making these devices promising for future photonic quantum information processing. Quantum interference in multi-mode interference (MMI) devices is reported for the first time. These devices allow the design of NxM splitters with superior performances, excellent tolerance to polarization and wavelength variations and relaxed fabrication requirements compared to the other main beam splitting technology, the directional couplers. However, to date, there have been no demonstrations of quantum interference in MMI devices (one may be concerned that multi-mode operation could prevent or perturb such interference). It is found that that the quantum interference visibility is significantly lower than that of a directional coupler with the same source. A major reason for the reduced visibility is the coherence length of the photons, which is set by the large-band interference filters. Since the different modes see different effective refractive indices within the interferometer, a jitter is 'introduced which allows distinguishability between the photons. To overcome this problem a narrower filter was introduced in one of the channels between the device and the detector, i.e. not affecting the source. This quantum erasure technique increases the detected indistinguishability of the photons, showing a high visibility and confirming that timing jitter limits quantum interference with large filters. The first observation of quantum walks of two indistinguishable particles is reported. Quantum walks offer new tools for simulating physical, chemical and biological systems, performing universal quantum computation and studying generalized quantum interference. Experimental demonstrations to date have shown single particle quantum walks; the observable dynamics of which can be fully explained with classical wave mechanics and experimentally mimicked using, for example, bright laser light. To observe uniquely quantum mechanical correlations in quantum walks, the propagation of two single, indistinguishable photons in an array of 21 waveguides in a silicon oxynitride chip is measured. The simultaneous walk of two photons on a graph simulate the walk of a single photon on a larger graph; the graph growing exponentially when linearly increasing the number of photons. These results violate classical bounds and cannot be efficiently simulated or described using classical mechanics. It is shown that the output strongly depends on the input state. Previous quantum optical work has highlighted the promise of monolithic integrated optics for quantum information science. This demonstration takes advantage of the intrinsic stability of photonic waveguide circuits to perform two-photon interference on a large scale. The results presented in this Thesis demonstrate the potential of integrated quantum photonic technology for quantum information applications, in particular quantum computation and quantum simulation.

The subject of the thesis is the modelling, design, fabrication and characterisation of passive silicon photonic devices for near (NIR) and mid-infrared (MIR) applications. The NIR devices have been investigated with the aim to produce low temperature sensitive devices for optical interconnects, whilst the results obtained at AIR wavelengths promise great potential for a variety of applications such as sensing and biomedicine. Silicon photonics offers very promising prospects for meeting ever-increasing demands on data speed and bandwidth. Temperature sensitivity of resonant photonic devices is an important issue in the development of ultralow power optical interconnects. This research project reports on the design, fabrication, and characterisation of a low temperature sensitive strip silicon-an-insulator (SOI) racetrack resonators. A resonant wavelength shift of 0.2 pm/K at a 1550 mm wavelength is measured using polymer cladding. The influence of various parameters has been examined achieving a very good agreement with theoretical model. A significant reduction of waveguide propagation losses, improved racetrack resonator Q-value, and higher extinction ratio are obtained after overlaying the silicon waveguides with a polymer cladding. On the other side, MIR silicon photonics is gathering pace, driven mainly by the lure of possible applications such as sensing, free-space communications, thermal imaging and biomedicine. However, the field is still in its infancy and the first serious challenge is to find suitable material platforms for the MIR. The thesis reports experimental results for passive devices based on different material platforms such as SOl, silicon-an-sapphire and silicon-an-porous silicon. It is demonstrated that SOl is useful material for integrated group IV photonics in the 3-4 f.1,m wavelength range, where propagation losses of less than 1 dB/cm have been obtained. The design rules for single-mode and zero-birefringent SOl rib waveguides using stress engineering are also presented. Optical splitters and racetrack resonators based on SOl strip waveguides have been characterised in the 3.7-3.9 11m wavelength range.

Photonics is revolutionising the way we live in a similar way to what electronics historically did. The main aim of this PhD project was to investigate and develop fabrication techniques leading to the realisation of mid-infrared photonic components based entirely on chalcogenide glass compositions which were prepared in-house, here at the University of Nottingham, Nottingham, UK. Chalcogenide glasses are based on the chalcogen elements of Group XVI of the Periodic Table and were chosen over conventional silica glass in the work described in this thesis for their significant advantages such as: a wide transmission window, for wavelengths of light from O .5 ~tm up to 25~tm depending on the glass composition, low phonon energies, high non-linearities and high refractive indices. The chalcogenide glass systems of As-Se, Ge-As-Se and Te-As-Se were synthesised and a new quenching technique was developed to prevent ampoule failures. In addition, the distillation of Te-As-Se system was optimised via the use of temperature monitoring. Two simulations were developed using commercial software; the first led to a large mode area, endlessly single mode microstructured optical fibre design and the second verified the photonic band gaps of a photonic band gap fibre from the literature. In particular, a methodology leading to the automation of chalcogenide glass cane drawing, a hot-collapse rig for investigating hot-collapsing of a tube onto a rod and a stacking mechanism for stacking chalcogenide glass canes have all been established as part of fabrication route that has been d~veloped towards the realisation of a chalcogenide glass all-solid core microstructured optical fibre (MOF) comprising 37 core/clad canes based on the design parameters simulated. Furthermore, a robust method for obtaining for the first time multimode optical couplers based on core-clad chalcogenide glass fibre using the method of fibre sidepolishing has been demonstrated experimentally. A key feature is a novel and reproducible procedure developed for obtaining controlled side (D) polishing of chalcogenide glass fibre using an innovative polishing apparatus. These achievements are particularly noteworthy because chalcogenide glass fibre is "more toxic (requiring the use of fume extractors), requires inert atmosphere to prevent oxidation and complicated preparation methods, is difficult to handle and, due to the higher refractive indices, exhibits a higher degree of reflection at glass-air (~20%) interfaces than conventional silica glass fibre. Over the last few years, infrared rnicroscopy (IR) has gained interest and has been used to study cells and tissues for cancer diagnosis. The fabrication of IR-transmitting chalcogenide glass optical fibre tips has been investigated and tips exhibiting reproducible and controlled taper geometries have been demonstrated experimentally. f --- Additionally, methods for metal-coating the tips in a thermal evaporation chamber and cleaving the tips using a focused ion beam (FIB) have been successfully developed. Small diameter tips have been used as an IR probe in scanning near-field infrared microscopy (SNIM) and larger diameter tips for transflection spectroscopy in an attempt to obtain optical and topographical cell tissue data for cell IR fingerprint recognition of Chinese Hamster Ovary cells using synchrotron radiation by employing B22 Beamline of the Diamond Light Source, Oxford, UK. IR spectra was successfully collected and showed good indication of the amide I and amide II bands related with cell DNA.

This PhD thesis investigates the optical properties of colloidal semiconductor nanocrystals and evaluates concepts regarding the development of novel photonic devices. Spectroscopic studies of the exciton dynamics in colloidal lead sulfide (PbS) quantum dots (QDs) by tuning the temperature are presented. The lowest exciton splitting for a range of PbS QDs sizes is calculated and a transfer of the oscillator strength from dark to bright states as the size increases is demonstrated. Hybrid structures with PbS QDs deposited on silicon substrates were also studied in order to explore whether excitons can be created in this material by means of resonant energy transfer. Furthermore, elongated asymmetric cadmium selenide/cadmium sulfide (CdSe/CdS) quantum rods are used as gain medium for the development of whispering gallery mode microlasers. Single-mode operation of hybrid lasers based on colloidal CdSe/CdS core/shell QRs in silica microspheres is for the first time reported. Laser-emission tunability over a range of 2.1 nm is also demonstrated, by heating the microsphere cavity with a 3.5-μm laser. In the last part of this thesis, unstructured and micro structured LiNbO3 are presented as excellent substrates for cell culture. Two commonly used neuron-like cells have been successfully proliferated and differentiated on both polar (±z) faces of LiNbO3 crystal substrates. Spatially selective attachment of neuron-like cells onto the domain engineered micro-structured substrates is also shown, providing the opportunity for the development of functional materials for the study of neuronal networks.

The thesis presented here entitled “Structural and Optoelectronic Properties of Rare Earth Doped Silicon Photonic Materials” for the degree of Doctor of Philosophy is submitted to the University of Manchester by Hang Li in December 2012.The original work presented in this thesis concentrates on the origin of the luminescence and the possible radiative loss mechanisms in rare earth (RE) and silicon nanocrystals (Si-NCs) co-doped SiO2. The optoelectronic properties of these materials were studied by employing laser or Xe lamp correlated photoluminescence (PL) and time-resolved PL spectroscopy and the structural and compositional characterisation was carried out using transmission electron microscopy (TEM) and scanning TEM (STEM).The pressure dependence of the band-gap of Si-NCs is strongly correlated to the co-doped erbium (Er) concentration. A conventional diamond anvil cell (DAC) was used for applying the hydrostatic pressure. A strong quenching and a non-linear red-shift of the PL of Si-NCs were obtained with increasing pressure, which was attributed to the quantum confinement effect. The rate of the red-shift as a function of pressure (pressure coefficient) increases with increasing Er concentration. We propose that this is the result of a reduction in the surface tension of Si-NCs when Er ions gather at their surface.Er is present as the trivalent oxide (Er2O3) in silicon rich silicon oxide (SRSO). Large Er2O3 clusters are formed when silicon excess is low as silicon is considered as a competitor for oxygen. Under the indirect excitation, the PL of Er3+ at 1.54 μm is highly dependent on the sensitization by Si-NCs. The decay lifetime of this emission contains a slow component of about 10 ms and a fast component of the order of μs. We found that the fast component became considerably faster with increasing Er2O3 cluster size. This is an indication of strong Er3+ ion-ion interactions in large clusters, which give rise to the non-radiative recombination of excitons.A novel fabrication of RE doped SiO2 was developed by implanting RE ions into silicon wafer directly and followed by the thermal oxidation and rapid thermal annealing (RTA) in contrast to the conventional procedure, in which the ion implantation was carried out after the oxidation of silicon wafer. TEM images showed that RE ions were distributed close to the surface of SiO2 film via the novel method but via the conventional method they were located at certain depth below the surface. Ce3+ doped SiO2 prepared via both methods has a broad blue PL ranging from around 380 to 470 nm attributed to the 5d-4f transitions and Eu3+ has a red PL with several narrow bands in the range of 570 to 700 nm attributed to the intra-4f transitions. Concentration quenching is one of the limiting factors for the conventional fabrication whilst it is successfully minimised by the novel method. A new phase of Ce silicate (Ce2Si2O7) may grow after the high temperature RTA via the novel method and leads to a remarkable enhancement of the Ce3+ luminescence.