Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Flanged coaxial probes are widely used to conduct accurate, broadband permittivity measurements of various dielectric materials. A metrology study, discussed in [1], revealed that small perturbations in measured permittivity data, are due to escaping common-mode (CM) current that propagates onto exposed VNA feed cabling. This is not considered in published permittivity extraction algorithms, like the National Institute of Standards and Technology (NIST) full-wave code that assumes an infinite flange radius. To characterise this effect we validate a finite volume time domain (FVTD) CST simulation model of an SMA coaxial probe, by probing sensitive E-fields in a metallic shielding cylinder, placed around it. For this process, electro-optic (EO) E-field sensors are considered and a Mach-Zehnder type sensor is designed. Manufacturing difficulties discontinues this approach, but the revisited extended centre conductor E-field probing technique proves successful. The technique entails a high dynamic range, two-port VNA measurement. Through CST we gain knowledge of the physics behind the CM-problem and the behaviour of fields around the coaxial probe. Different shielding environments are simulated to establish their ability to impede CM-current coupling onto measurement cabling. To study the CM-effect on extracted permittivity results, the investigation is extended to Short-Open-Load (SOL) calibrated face-plane measurements of dielectric solids. A CST model, which considers escaping CM-energy, is used to generate open circuit (OC) calibration coefficients and to serve as an independent extraction method. We inspect the effect of different shielding environments and through CST, extract accurate permittivity results for e00, to a degree not previously achieved for such systems. This allows comment on the infinite-flange-radius assumption of the NIST method and proves the significance of the CM-effect. / AFRIKAANSE OPSOMMING: Geflensde koaksiale probes word algemeen in die praktyk gebruik om akkurate, wyeband permitiwiteitmetings van diëlektriese materiale te verrig. ’n Studie wat in [1] bespreek word, dui aan dat klein verskynsels in gemete resultate, verband hou met gemene-modus (GM) stroom, wat ontsnap en teenwoording is aan die buitekant van onbeskermde voerkabels. Hierdie verkynsel word nie deur huidige volgolf ekstraksie-algoaritmes, soos die van NIST wat ’n onëindige flensradius aanvaar, in ag geneem nie. Om die GM-effek te karakteriseer, verifieer ons ’n eindige-volume tyd-gebied CST simulasiemodel, deur sensitiewe metings binne ’n silidriese metaalskerm, wat om so ’n probe geplaas word. Vir hierdie meting word elektro-optiese E-veld probes eers oorweeg. In gevolg word ’n Mach-Zehnder-tipe probe ontwerp, maar vervaardigingsprobleme en tyd-oorwegings kniehalter hierdie benadering. Heroorweging van die verlengde koaksiale sentraalgeleier, E-veld-probe tegniek, wat hoë dinamiese bereik twee-poort netwerkanaliseerder metings behels, slaag uiteindelik in hierdie doel. CST maak dit nou moontlik om die GM stroomprobleem te simuleer en spesefieke veldgedrag te kan waarneem. Verskillende afskermingsmetodes se vermoë om GM-koppeling na kabels te beperk word ondersoek. Die GM studie word uitgebrei na SOL-gekalibreerde, flensvlakverwysde permitwiteitmetings van diëlektriese vastestowwe. ’n CST model, wat GM stroom in ag neem, word gebruik om oopgeslote kalibrasiekofisiënte te genereer en dien ook as ‘n alternatiewe permitiwiteit ekstraksiemetode. Die effek van die verskillende afskermingstegnieke word ondersoek en deur die CST metode te gebruik, word ’n aansienlike verbetering in akkuraatheid van e00 waardes verkry. Dit regverdig kommentaar oor die aannames wat in die NIST metode gemaak word en beklemtoon die belangrikheid om GM stroom in ag te neem.

Long-range surface plasmon-polaritons are transverse-magnetic polarized optical surface waves formed through the interaction of photons with free electrons at the surface of metal slabs or stripes. They play important roles in a variety of field such as integrated optics, amplifiers and lasers, optical sensing, modulation, etc. Due to their longer propagation length and deeper penetration depth compared to those of single-interface surface plasmon-polaritons, they have become increasingly promising in optical sensing. In sensing applications, it is necessary to reduce the noise level in order to obtain a lower detection limit. One way to achieve this is to use dual- or triple-output Mach-Zehnder interferometers so that the common perturbations among the outputs can be suppressed. The objective of this thesis is to provide deeper insights on the performances of dual- and triple-output Mach-Zehnder interferometers in thermo-optic and optical bulk sensing applications, theoretically and experimentally, and to demonstrate their ability to suppress common perturbations and lower the detection limit. On the theoretical side, the objective is approached by constructing a model for the transfer characteristic. For dual-output Mach-Zehnder interferometers, the plane-wave model is used to develop a general model for thermo-optic sensing and an unbalanced model for optical bulk sensing. For triple-output ones, local normal mode theory is used with modal analysis for the 3×3 coupler portion of the structure. Quantitative methods to analyze and compare different detection schemes are developed. The minimum detectable phase shift is determined for the case of thermo-optic sensing while the detection limit is determined for optical bulk sensing. On the experimental side, the objective is approached by providing a direct experimental demonstration of the transfer characteristics at an optimized operating wavelength for the coupler portion of the device, then comparing to theory. Time traces are carried out and various detection schemes are applied to suppress common perturbations among the outputs, and to improve the minimum detectable phase shift or the detection limit.

Gas sensing is essential for safety and maintenance operations in many industries, including power generation, petrochemical, capture and storage technologies, and the food-processing sector. The properties of fiber-optic sensors make them a superior choice for environmental monitoring applications, especially in extreme conditions, and particularly when compared against conventional electro-optical sensors. Their advantageous properties include immunity to electromagnetic radiation, high temperature durability, high sensitivity and the ability for high resolution detection, as well as multifunctional sensing capabilities such as temperature, humidity, pressure, strain, and corrosion. Among different types of interferometers, Mach-Zehnder Interferometers (MZI) have received significant attention because they are robust, compact, and have high levels of precision. In this dissertation, we present an in-line and compact MZI point sensor designed for sensing refractive index. In comparison with various types of interferometers, fiber MZI based RI sensing was selected based on its enhanced sensitivity and fabrication simplicity. The MZI sensor is developed using photonic crystal fiber and demonstrated for high sensitivity detection and measurement of pure gases. The transmission spectrum of MZI sensors is formed by interference between the cladding and core modes. To construct the device, the sensing element fiber was placed and aligned between two single-mode fibers with air gaps at each side. Two linear-translation micro stages were used to accurately differ and adjust gap lengths from 0 to 5mm. Great measurement repeatability was shown in the cyclic test for the detection of various gases such as methane and helium. A high RI measurement resolution of 2.1 E-7 and a sensitivity of 4629 nm/RIU was achieved, which is among the highest reported. Results show that the sensitivity of the fabricated MZI increases from 3000 nm/RIU to 4600 nm/RIU when the length of the sensing element fiber decreases from 5 mm to 3.3 mm. Furthermore, the device was packaged to demonstrate the laboratory-scale monitoring, as well as leakage detection of different concentrations of CO2 in both subsurface soil and aqueous environments. Two water resistant but gas permeable membranes were used to package the sensor, to achieve a good balance of CO2 permeability and water resistance. The experimental study of this work reveals the great potential of the fiber-optic approach for environmental monitoring of CO2. This study also explores other potential applications. Three types of sensors were fabricated using the proposed configuration employing 4 mm stub of (i) solid core Photonic Crystal Fiber (PCF), (ii) 10 µm Hollow core PCF (HC-PCF), and (iii) 20 µm HC-PCF as the sensing elements. We compared the performance of these sensors for detecting and measuring the quantity of gas present. As the transmission signals correspond to the frequency components in the sensor’s Fast Fourier Transform (FFT) spectrum, the effect of gap distance on the number and amplitude distribution of the modes was examined in an effort to optimize the design elements. The MZI sensors are highly sensitive to low percentages of CH4 and CO2, making them suitable for greenhouse gas measurement. / Graduate

The purpose of this thesis is the theoretical study of interference and correlation effects in multimode and continuum mode quantum systems. We are concerned with interference effects in multiport devices which in a sense are generalised Mach-Zehnder interferometers. It is shown how these multimode devices can be employed for the study of negative result and interaction free measurements. Interference and coherence effects are also studied in relation to the radiation fields generated by atoms through the process of spontaneous emission. Besides first order interference, higher order coherence effects are investigated with the aid of Glauber's photodetection theory and it is found that detectors that lie in spacelike regions may display nonclassical correlations under certain conditions. It is well known that the vanishing of field commutators between regions that cannot be connected by subluminal signals reflects the locality of quantum field theory. But is it possible that these spacelike regions exhibit correlations that violate Bell type inequalities? This is the main question and principal concern of the thesis and the answer is affirmative, nonclassical correlations between spacelike regions are indeed possible. A scheme of four detectors that lie in spacelike points was also studied. In this case we do not consider the radiation field but a free scalar field in vacuum state. Nevertheless the virtual quanta of this field may induce nonclassical correlations if the intervals between the detectors are spacelike but small enough. The fundamental reason for this fact is the nonvanishing of the Feynman propagator outside the light cone. Since this propagator is decaying expotentially with the distance it is demonstrated that for large spacelike intervals field correlations obey classical inequalities. We should also note that different inertial observers will agree on the violation or not of these inequalities since the results are manifestly Lorentz invariant.

Este trabalho relata um estudo numÃrico das caracterÃsticas Ãpticas de um interferÃmetro Mach-Zehnder disposto em uma configuraÃÃo com quatro estÃgios e um ressonador Ãptico em anel. O interferÃmetro Mach-Zehnder foi construÃdo numa versÃo com fibra comum e outra com fibra de dispersÃo decrescente considerando um perfil de dispersÃo linear. O ressonador Ãptico em anel foi constuÃdo com um guia de onda cujo o Ãndice de refraÃÃo nÃo linear foi moldado com um perfil linear crescente. A transmissÃo e o fator de compressÃo dos pulsos de saÃda sÃo analisados nos regimes de soliton e quasi-soliton para ambos os dispositivos. Os resultados mostraram que a transmissÃo do interferÃmetro Mach-Zehnder à fortemente dependente da potÃncia de entrada em ambos os regimes. O nÃvel de crosstalk tambÃm à dependente da potÃncia de entrada e da dispersÃo da fibra. Para potÃncias de entrada altas, o nÃvel de crosstalk à mais baixo para o dispositivo com fibra de dispersÃo decrescente no regime de soliton. Para esta configuraÃÃo, o nÃvel de crosstalk mÃnimo encontrado (-22 dB) foi para a potÃncia normalizada de entrada P = 2,7. No regime de quasi-soliton, em geral, o nÃvel de crosstalk mÃnimo à mais baixo para o interferÃmetro Mach-Zehnder com fibra de dispersÃo decrescente em potÃncias de entrada altas, mas com a possibilidade de se obter um nÃvel de crosstalk menor para o dispositivo utilizando fibra comum. A razÃo de extinÃÃo à tambÃm muito dependente da potÃncia de entrada e sofre degeneraÃÃo quando a potÃncia de entrada aumenta. Para potÃncias de entrada baixas, o interferÃmetro Mach-Zehnder apresenta uma razÃo de extinÃÃo melhor em potÃncias de entrada mais altas no regime de soliton. No regime de quasi-soliton, a melhor razÃo de extinÃÃo à obtida para o interferÃmetro Mach-Zehnder com fibra comum em potÃncias de entrada altas. Pode-se dizer que a operaÃÃo do dispositivo como uma chave Ãptica nÃo melhora com o uso de fibra de dispersÃo decrescente. Entretanto, para operaÃÃo de multiplex/demultiplex, o interferÃmetro Mach-Zehnder construÃdo com fibra de dispersÃo decrescente mostrou melhoramentos no nÃvel de crosstalk no regime de soliton e, dependendo da potÃncia de entrada, tambÃm no regime de quasi-soliton. No estudo do ressonador Ãptico em anel foi encontrado que a perda do guia de onda que forma a cavidade anelar diminui a transmissÃo em ambos os regimes, mas mantÃm o mesmo comportamento nÃo linear. O uso de um Ãndice de refraÃÃo nÃo linear com um perfil linear crescente leva à compressÃo ou alargamento temporal, dependendo da potÃncia de entrada, no regime de soliton. No regime de quasi-soliton nÃo foi observado deformaÃÃo temporal dos pulsos de saÃda. Isto indica que, em mÃdia, os pulsos de saÃda estÃo com a mesma duraÃÃo temporal que os pulsos de entrada. Os resultados tambÃm mostraram que hà um aumento da transmissÃo quando um Ãndice de refraÃÃo nÃo linear com um perfil linear crescente à usado. Assim, o decrÃscimo na transmissÃo associado à perda do guia de onda pode ser evitado. As caracterÃsticas de transmissÃo e a forma dos pulsos Ãpticos de saÃda do interferÃmetro Mach-Zehnder e do ressonador Ãptico em anel serÃo de interesse em circuitos Ãpticos e sistemas de comunicaÃÃes totalmente Ãpticos no futuro.

LIMA, José Luiz Sousa. Estudo do desempenho de filtros ópticos interferométricos: interferômetro Mach-Zehnder de fibra óptica e ressonador óptico em anel. 2006. 96 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2006. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-05T20:15:39Z No. of bitstreams: 1 2006_tese_jlslima.pdf: 688113 bytes, checksum: 11efdee52324ab34ae806b2466f4f088 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-07T14:27:12Z (GMT) No. of bitstreams: 1 2006_tese_jlslima.pdf: 688113 bytes, checksum: 11efdee52324ab34ae806b2466f4f088 (MD5) / Made available in DSpace on 2015-05-07T14:27:12Z (GMT). No. of bitstreams: 1 2006_tese_jlslima.pdf: 688113 bytes, checksum: 11efdee52324ab34ae806b2466f4f088 (MD5) Previous issue date: 2006

La conversion de fréquence est une fonction clef présente dans divers contextes, particulièrement dans les systèmes mixtes photoniques-hyperfréquences. Aujourd’hui, la suprématie des réseaux optiques pour le transport de données à haut débit sur de grandes distances incite à l’intégration de telles fonctions dans le domaine optique afin de bénéficier des faibles pertes, larges bandes passantes, faibles poids et tailles propres aux technologies optiques. Dans ce travail, nous étudions un mélangeur tout-optique utilisant un composant SOA-MZI (Semiconductor Optical Amplifier Mach-Zehnder Interferometer) et une technique d’échantillonnage permettant la conversion vers les hautes et les basses fréquences. Le principe du mélange exploite les caractéristiques spectrales d’un signal échantillonné pour lequel des répliques du signal d’origine existent à différentes autres fréquences. Utiliser une telle technique pour la conversion de fréquences offre deux avantages : la conversion vers les hautes et les basses fréquences utilise la même configuration du mélangeur et la fréquence de l’oscillateur local peut être inférieure à la gamme des fréquences visées.L’implémentation d’une telle technique d’échantillonnage nécessite un interrupteur optique contrôlé optiquement.Comme cela est montré dans ce travail, un SOA-MZI peut jouer ce rôle. Selon la phase relative entre ses bras, un interféromètre Mach-Zehnder (MZI) peut transmettre ou non un signal optique d’entrée. En plaçant un SOA dans chaque bras de la structure MZI, la modulation croisée de la phase qui existe au sein d’un SOA est mise à profit pour contrôler l’état de l’interféromètre. Contrôlé par une source impulsionnelle optique, cet interrupteur optique permet d’échantillonner un signal optique porteur de données à modulation complexe. La conversion de fréquence de signaux mono et multi-porteuses dans le domaine 0,5-39,5 GHz a été obtenue avec succès. Par utilisation d’une configuration différentielle du SOA-MZI, des conversions vers les hautes et les basses fréquences jusqu’à un débit de 1 Gb/s ont pu être réalisées. / Frequency mixing is a key function existing in different systems, especially in mixed photonic-microwave ones. Today, the supremacy of optical networks to carry high bitrate data over large distances motivates the optical implementation of such functions to benefit from the low loss, high bandwidth, low size and weight of optical technologies. In this work, we study a photonic mixer based on a SOA-MZI (Semiconductor Optical Amplifier Mach-Zehnder Interferometer) device and a sampling technique allowing both conversion towards high and low frequencies.The involved mixing principle exploits the spectral characteristics of a sampled signal in which replicas of the original spectrum exist at different other frequencies. Basing the frequency conversion on a sampling technique gives two advantages: the photonic mixer configuration is the same for up and down conversions, and the frequency of the local oscillator can be less than the addressed frequency range.The implementation of such a sampling technique needs an optically-controlled high-frequency optical switch. As shown in this work, a SOA-MZI can play this role. Depending on the relative phase between its arms, an interferometric structure (MZI) can transmit or cancel an optical input signal. By locating one SOA in each arm of the MZI structure, the cross-phase modulation that exists inside an SOA is exploited to optically control the optical switch state of the MZI.Controlled by an optical pulse source, this optical switch is able to sample an optical input signal carrying complexmodulated data. Frequency conversions of mono and multi-carrier signals in the range 0.5-39.5 GHz have been successfully achieved. By using a differential configuration of the SOA-MZI, both up and down conversions at bitrates up to 1 Gb/s are reached.

Ce mémoire de thèse présente les travaux effectués pour la réalisation de sources optiques fibrées d’impulsions picosecondes cadencées à 40 GHz dans la bande C des télécommunications. Dans une première partie, nous présentons des études numériques et expérimentales mises en place pour la génération d’un train d’impulsions cadencé à 40 GHz par la compression non-linéaire d’un battement sinusoïdal via un processus de mélanges à quatre ondes multiples. Afin d’obtenir des impulsions stables, le battement sinusoïdal initial est obtenu par la modulation en intensité d’un signal continu grâce à un modulateur Mach-Zehnder piloté au point nul de transmission. Nous démontrons également l’amélioration de la qualité des impulsions générées par la suppression de la diffusion Brillouin stimulée grâce à la mise en place d’isolateurs optiques dans la ligne fibrée de la source. Nous présentons ensuite la génération d’impulsions ultra-courtes grâce à un compresseur non-linéaire composé de quatre étages fibrés. Le train d’impulsions obtenu est alors codé puis multiplexé jusqu’à un débit optique de 160 Gbit/s. Dans la dernière partie, nous présentons les démarches mises en place en vue d’un transfert technologique, telles que la réalisation d’un prototype de la source, la recherche d’antériorité et l’étude de marché. / This thesis presents the work carried out on the realization of fibered 40-GHz picosecond optical pulse sources in the telecommunications C-band. In the first part, we present a numerical and experimental study of the generation of 40-GHz pulse trains thanks to the nonlinear compression of an initial beat-signal by multiple Four-Wave Mixing process. Enhanced temporal stability is achieved by generating the sinusoidal beating thanks to a Mach-Zehnder modulator driven at its zero-transmission working point. In order to improve the quality of the generated pulses, we also demonstrate the suppression of stimulated Brillouin back-scattering by inserting several optical isolators into the compression line. In the next part, we present the generation of low duty-cycle pulse trains by using a nonlinear compressor line based on 4 segments of fiber. The generated pulse trains have been encoded and then multiplexed to achieve a high bit rate signal (160 Gb/s). In the last part, we present the technology transfer steps of this optical source, such as creating a prototype of the source, prior art search and market research.

We have harnessed the power of programmable photonics devices for an interferometric measurement technique. Laser interferometers are widely used for flow velocity measurements, since they offer high temporal and spatial resolutions. However, often optical wavefront distortions deteriorate the measurement properties. In principle, adaptive optics enables the correction of these disturbances. One challenge is to generate a suitable reference signal for the closed loop operation of the adaptive optics. An adaptive Mach Zehnder interferometer is presented to measure through a dynamic liquid-gas phase boundary, which can lead to a misalignment of the interfering laser beams. In order to generate the reference signal for the closed loop control, the Fresnel reflex of the phase boundary is used as Laser Guide Star (LGS) for the first time to the best of the authors’ knowledge. The concept is related to the generation of artificial stars in astronomy, where the light transmitted by the atmosphere is evaluated. However, the adaptive interferometric flow velocity measurements at real world experiments require a different concept, since only the reflected light can be evaluated. The used LGS allows to measure the wavefront distortions induced by the dynamic phase boundary. Two biaxial electromagnetically driven steering mirrors are employed to correct the wavefront distortions. This opens up the possibility for accurate flow measurements through a dynamic phase boundary using only one optical access. Our work represents a paradigm shift in interferometric velocity measurement techniques from using static to dynamic optical elements.

Este trabalho apresenta uma análise de natureza teórica de um dispositivo RF-Photonic denominado de Oscilador de Microondas Optoeletrônico. Este dispositivo, realizado utilizando-se conceitos de óptica integrada, converte a energia contínua de uma fonte laser em sinais na faixa espectral de Microondas ou de Rádio Freqüência (RF). Os sinais gerados por este oscilador são considerados mais estáveis e espectralmente puros do que aqueles gerados pelos tradicionais osciladores eletrônicos que utilizam o cristal de quartzo como seu meio ressonante. Este oscilador, referido pelo acrônimo de OEO, consiste de uma fonte laser e um circuito de realimentação constituído por um modulador eletroóptico de amplitude, uma linha de atraso a fibra óptica, um fotodetector, um amplificador e um filtro. Neste trabalho, abordam-se dispositivos optoeletrônicos nos quais as características de sinais ópticos são controladas por sinais de microondas, por meio do efeito eletroóptico. Desenvolve-se uma análise detalhada do interferômetro de tipo Mach-Zehnder, o qual é utilizado para implementar o modulador eletroóptico existente no OEO. Faz-se um desenvolvimento completo e detalhado de um enlace óptico analógico com a finalidade de constituir uma sólida base teórica. Emprega-se uma teoria quase linear para analisar o limiar de oscilação e determinar os valores de amplitude e freqüência de oscilação do OEO. Apresenta-se uma configuração em malha dupla, a qual resolve a dificuldade na implementação de filtros de RF altamente seletivos, requeridos pelo OEO.