Gaussian pulse mixing by nonlinear photonic crystals

The properties of mixing and scattering of two non-collinear Gaussian pulses with different centre frequencies and lengths, incident on the finite nonlinear periodic layered dielectric structures, have been analysed. It is shown that at the backward emission grows with the number of layers and can reach the level of the forward emission in the direction of combinatorial frequency scattering.

Tomographic characterisation of correlations in a photonic tripartite state

Starting from a four-partite photonic hyper-entangled Dicke resource, we report the full tomographic characterization of three-, two-, and one-qubit states obtained by projecting out part of the computational register. The reduced states thus obtained correspond to fidelities with the expected states larger than 87%, therefore certifying the faithfulness of the entanglement-sharing structure within the original four-qubit resource. The high quality of the reduced three-qubit state allows for the experimental verification of the Koashi-Winter relation for the monogamy of correlations within a tripartite state. We show that, by exploiting the symmetries of the three-qubit state obtained upon projection over the four-qubit Dicke resource, such relation can be experimentally fully characterized using only 5 measurement settings. We highlight the limitations of such approach and sketch an experimentally-oriented way to overcome them.

Tuneable magneto-optical metamaterials based on photonic resonances in nickel nanorod arrays

We investigate the magneto-optical properties of a nanostructured metamaterial comprised of arrays of nickel nanorods embedded in an anodized aluminum oxide template. The rods are grown using a self-assembly bottom-up technique that provides a uniform, quasi-hexagonal array over a large area, quickly and at low cost. The tuneability of the magneto-optic response of the material is investigated by varying the nanorod dimensions: diameter, length and inter-rod spacing as well as the overall thickness of the template. It is demonstrated that the system acts as a sub-wavelength light trap with enhanced magneto-optical properties occurring at reflectivity minima corresponding to photonic resonances of the metamaterial. Changes in dimensions of the nickel rods on the order of tens of nanometers cause a spectral blue-shift in the peak magneto-optical response of 270 nm in the visible range. A plasmonic enhancement is also observed at lower wavelengths, which becomes increasingly damped with larger diameters and increased volume fraction of nickel inclusions. This type of structure has potential applications in high density magneto-optical data storage (up to 1011–12 rods per square inch), ultrafast magneto-plasmonic switching and optical components for telecommunications.

The effect of pH on the photonic efficiency of the destruction of methyl orange under controlled periodic illumination with UV-LED sources

The nature of photon interaction and reaction pH can have significant impacts on semiconductor photocatalysis. This paper describes the effect of pH on the photonic efficiency of photocatalytic reactions in the aqueous phase using TiO2 catalysts. The reactor was irradiated using periodic illumination with UV-LEDs through control of the illumination duty cycle (γ) through a series of light and dark times (Ton/Toff). Photonic efficiencies for methyl orange degradation were found to be comparable at high γ irrespective of pH. At lower γ, pH effects on photonic efficiency were very distinct across acidic, neutral and alkaline pH indicating an effect of complementary parameters. The results suggest photonic efficiency is greatest as illumination time, Ton approaches interfacial electron-transfer characteristic time which is within the range of this study or charge-carrier lifetimes upon extrapolation and also when electrostatic attraction between surface-trapped holes, {TiIVOH}ads+ and substrate molecules is strongest.

Effect of controlled periodic-based illumination on the photonic efficiency of photocatalytic degradation of methyl orange

The use of controlled periodic illumination with UV LEDs for enhancing photonic efficiency of photocatalytic decomposition processes in water has been investigated using methyl orange as a model compound. The impact of the length of light and dark time periods (T _ON/T _OFF times) on photodegradation and photonic efficiency using a UV LED-illuminated photoreactor has been studied. The results have shown an inverse dependency of the photonic efficiency on duty cycle and a very little effect on T _ON or T _OFF time periods, indicating no effect of rate-limiting steps through mass diffusion or adsorption/desorption in the reaction. For this reactor, the photonic efficiency under controlled periodic illumination (CPI) matches to that of continuous illumination, for the same average UV light intensities. Furthermore, under CPI conditions, the photonic efficiency is inversely related to the average UV light intensity in the reactor, in the millisecond time regime. This is the first study that has investigated the effect of controlled periodic illumination using ultra band gap UV LED light sources in the photocatalytic destruction of dye compounds using titanium dioxide. The results not only enhance the understanding of the effect of periodic illumination on photocatalytic processes but also provide a greater insight to the potential of these light sources in photocatalytic reactions. 

Photonic devices for optical and RF signal processing

O presente trabalho tem por objectivo o estudo de novos dispositivos fotónicos aplicados a sistemas de comunicações por fibra óptica e a sistemas de processamento de sinais RF. Os dispositivos apresentados baseiam-se em processamento de sinal linear e não linear. Dispositivos lineares ópticos tais como o interferómetro de Mach-Zehnder permitem adicionar sinais ópticos com pesos fixos ou sintonizáveis. Desta forma, este dispositivo pode ser usado respectivamente como um filtro óptico em amplitude com duas saídas complementares, ou, como um filtro óptico de resposta de fase sintonizável. O primeiro princípio de operação serve como base para um novo sistema fotónico de medição em tempo real da frequência de um sinal RF. O segundo princípio de operação é explorado num novo sistema fotónico de direccionamento do campo eléctrico radiado por um agregado de antenas, e também num novo compensador sintonizável de dispersão cromática. O processamento de sinal é não linear quando sinais ópticos são atrasados e posteriormente misturados entre si, em vez de serem linearmente adicionados. Este princípio de operação está por detrás da mistura de um sinal eléctrico com um sinal óptico, que por sua vez é a base de um novo sistema fotónico de medição em tempo real da frequência de um sinal RF. A mistura de sinais ópticos em meios não lineares permite uma operação eficiente numa grande largura espectral. Tal operação é usada para realizar conversão de comprimento de onda sintonizável. Um sinal óptico com multiplexagem no domínio temporal de elevada largura de banda é misturado com duas bombas ópticas não moduladas com base em processos não lineares paramétricos num guia de ondas de niobato de lítio com inversão periódica da polarização dos domínios ferroeléctricos. Noutro trabalho, uma bomba pulsada em que cada pulso tem um comprimento de onda sintonizável serve como base a um novo conversor de sinal óptico com multiplexagem no domínio temporal para um sinal óptico com multiplexagem no comprimento de onda. A bomba é misturada com o sinal óptico de entrada através de um processo não linear paramétrico numa fibra óptica com parâmetro não linear elevado. Todos os dispositivos fotónicos de processamento de sinal linear ou não linear propostos são experimentalmente validados. São também modelados teoricamente ou através de simulação, com a excepção dos que envolvem mistura de sinais ópticos. Uma análise qualitativa é suficiente nestes últimos dispositivos.

Reconfigurable photonic logic architecture

The amorphous silicon photo-sensor studied in this thesis, is a double pin structure (p(a-SiC:H)-i’(a-SiC:H)-n(a-SiC:H)-p(a-SiC:H)-i(a-Si:H)-n(a-Si:H)) sandwiched between two transparent contacts deposited over transparent glass thus with the possibility of illumination on both sides, responding to wave-lengths from the ultra-violet, visible to the near infrared range. The frontal il-lumination surface, glass side, is used for light signal inputs. Both surfaces are used for optical bias, which changes the dynamic characteristics of the photo-sensor resulting in different outputs for the same input. Experimental studies were made with the photo-sensor to evaluate its applicability in multiplexing and demultiplexing several data communication channels. The digital light sig-nal was defined to implement simple logical operations like the NOT, AND, OR, and complex like the XOR, MAJ, full-adder and memory effect. A pro-grammable pattern emission system was built and also those for the validation and recovery of the obtained signals. This photo-sensor has applications in op-tical communications with several wavelengths, as a wavelength detector and to execute directly logical operations over digital light input signals.

Évaluation d’un prototype de détecteur de glucose dans le tissu interstitiel sans aiguille, le PGS (Photonic Glucose Sensor)

Objectif : Déterminer la fiabilité et la précision d’un prototype d’appareil non invasif de mesure de glucose dans le tissu interstitiel, le PGS (Photonic Glucose Sensor), en utilisant des clamps glycémiques multi-étagés. Méthodes : Le PGS a été évalué chez 13 sujets avec diabète de type 1. Deux PGS étaient testés par sujet, un sur chacun des triceps, pour évaluer la sensibilité, la spécificité, la reproductibilité et la précision comparativement à la technique de référence (le Beckman®). Chaque sujet était soumis à un clamp de glucose multi-étagé de 8 heures aux concentrations de 3, 5, 8 et 12 mmol/L, de 2 heures chacun. Résultats : La corrélation entre le PGS et le Beckman® était de 0,70. Pour la détection des hypoglycémies, la sensibilité était de 63,4%, la spécificité de 91,6%, la valeur prédictive positive (VPP) 71,8% et la valeur prédictive négative (VPN) 88,2%. Pour la détection de l’hyperglycémie, la sensibilité était de 64,7% et la spécificité de 92%, la VPP 70,8% et la VPN : 89,7%. La courbe ROC (Receiver Operating Characteristics) démontrait une précision de 0,86 pour l’hypoglycémie et de 0,87 pour l’hyperglycémie. La reproductibilité selon la « Clark Error Grid » était de 88% (A+B). Conclusion : La performance du PGS était comparable, sinon meilleure que les autres appareils sur le marché(Freestyle® Navigator, Medtronic Guardian® RT, Dexcom® STS-7) avec l’avantage qu’il n’y a pas d’aiguille. Il s’agit donc d’un appareil avec beaucoup de potentiel comme outil pour faciliter le monitoring au cours du traitement intensif du diabète. Mot clés : Diabète, diabète de type 1, PGS (Photonic Glucose Sensor), mesure continue de glucose, courbe ROC, « Clark Error Grid».

Design, Fabrication and Characterization of Passive and Active Polymer Photonic Devices

The rapid developments in fields such as fibre optic communication engineering and integrated optical electronics have expanded the interest and have increased the expectations about guided wave optics, in which optical waveguides and optical fibres play a central role. The technology of guided wave photonics now plays a role in generating information (guided-wave sensors) and processing information (spectral analysis, analog-to-digital conversion and other optical communication schemes) in addition to its original application of transmitting information (fibre optic communication). Passive and active polymer devices have generated much research interest recently because of the versatility of the fabrication techniques and the potential applications in two important areas – short distant communication network and special functionality optical devices such as amplifiers, switches and sensors. Polymer optical waveguides and fibres are often designed to have large cores with 10-1000 micrometer diameter to facilitate easy connection and splicing. Large diameter polymer optical fibres being less fragile and vastly easier to work with than glass fibres, are attractive in sensing applications. Sensors using commercial plastic optical fibres are based on ideas already used in silica glass sensors, but exploiting the flexible and cost effective nature of the plastic optical fibre for harsh environments and throw-away sensors. In the field of Photonics, considerable attention is centering on the use of polymer waveguides and fibres, as they have a great potential to create all-optical devices. By attaching organic dyes to the polymer system we can incorporate a variety of optical functions. Organic dye doped polymer waveguides and fibres are potential candidates for solid state gain media. High power and high gain optical amplification in organic dye-doped polymer waveguide amplifier is possible due to extremely large emission cross sections of dyes. Also, an extensive choice of organic dye dopants is possible resulting in amplification covering a wide range in the visible region.

Z-scan and Degenerate Four Wave Mixing Studies in Certain Photonic Materials

International School of Photonics, Cochin University of Science & Technology

Laser Induced Photothermal Investigations on Thermal and Transport Properties of Certain Selected Photonic Materials

Discovery of coherent optical sources four decades ago has revolutionized all fields of scientific development. One of the path breaking applications of lasers is the emergence of various thermo optic techniques to unravel some of the mysteries of light matter interactions.Thermo optic technique is a valuable tool to evaluate optical and thermal properties of materials in solid,liquid and gaseous states .This technique can also be employed effectively in nondestructive quality evaluation. In this doctoral thesis , the use of photothermal techniques based on photoacoustic and photothermal deflection phenomena for the study of certain class of photonics materials such as semiconductors, nano metal dispersed ceramics, composites of conducting polymers and liquid crystals is elaborated.

Studies on Electrical and Thermal Properties of Certain Selected Photonic Materials

The present thesis is centered around the study of electrical and thermal properties of certain selected photonic materials.We have studied the electrical conduction mechanism in various phases of certain selected photonic materials and those associated with different phase transitions occurring in them. A phase transition leaves its own impressions on the key parameters like electrical conductivity and dielectric constant. However, the activation energy calculation reveals the dominant factor responsible for conduction process.PA measurements of thermal diffusivity in certain other important photonic materials are included in the remaining part of the research work presented in this thesis. PA technique is a promising tool for studying thermal diffusivities of solid samples in any form. Because of its crucial role and common occurrence in heat flow problems, the thermal diffusivity determination is often necessary and knowledge of thermal diffusivity can intum be used to calculate the thermal conductivity. Especially,knowledge of the thermal diffusivity of semiconductors is important due to its relation to the power dissipation problem in microelectronic and optoelectronic devices which limits their performances. More than that, the thermal properties, especially those of thin films are of growing interest in microelectronics and microsystems because of the heat removal problem involved in highly integrated devices. The prescribed chapter of the present theis demonstrates how direct measurement of thermal diffusivity can be carried out in thin films of interest in a simple and elegant manner using PA techniques. Although results of only representative measurements viz; thermal diffusivity values in Indium, Aluminium, Silver and CdS thin films are given here, evaluation of this quantity for any photonic and / electronic material can be carried out using this technique in a very simple and straight forward manner.

Investigations on Nonlinear and Radiative Properties of Certain Photonic Materials

International School of Photonics, Cochin University of Science & Technology

Synthesis and Laser induced Studies of nanosized ZnO for Photonic Applications

Over the past few years, a little word with big potential has been rapidly entering into the world's consciousness-'nano'. Nanoscience and technology is a multidisciplinary field, involving the fabrication and understanding of matter at the finest level of a few nanomters.This thesis is about the synthesis and laser induced studies of nanosized ZnO,a versatile material with a wide range of applications.After synthesizing colloids and films of nano ZnO,the samples are studied using different optical methods.Interactions of intense laser beams with nanosized particles are found to open up many interesting scenarios with possible applications in the field of photonics.