M.Ing. / Lightwave systems used in the core transport network of telecommunication systems operate in the second transmission window. The 1550 nm wavelength region exhibits the lowest attenuation coefficient, thus expanding the repeater distance in the network. However, the influence of the large dispersion coefficient associated with the second transmission window limits the operating speed of the network to 2.5 Gbit/s or less. In order for the network to operate at higher bit-rate, a dispersion management scheme is needed. In this research, the performance of negative dispersion fibre used as a dispersion compensating module is investigated. The negative dispersion fibre used in this study was the AVANEX PureForm DCM. The dispersion coefficient of the DCM measured at 1525 nm, 1545 nm and 1565 nm were given as -918 , -987 and -1047 respectively. The optimal operating condition of the DCM was obtained by considering various dispersion management configurations i.e. post-compensation, pre-compensation and symmetric compensation. The DCM was tested on a single span, single channel system operating at a speed of 10 Gbit/s with the transmitting wavelength of 1551.2 nm, over 60 km of convention single mode fibre. Furthermore, the performance of the system at 55 km and 65 km were also used to examine the results for the over- and under compensation links respectively. The results obtained for 100% dispersion cancellation for the pre-, post- and symmetric configuration showed an increase in the extinction ratio of 2.09 dB, 2.72 dB and 2.37 dB respectively. Similarly, the Q-factor was estimated to equal 13.67, 11.296 and 13.167 respectively. The results indicate similar performance for all the configurations considered, analysis of the eye-diagrams reveals that the post-compensation configuration would ultimately yield the best results. This is due to the fact that eye diagram recovered from this setup has minimal deformation. The experiments for an extremely over-compensated link, i.e. 40 km, showed an increase from 9.49, obtained with no compensation, to 10.63. However, for the extremely under-compensated link i.e. 80 km, the extinction ratio only manages to improve from 4.88 dB to 8.63 dB.

This Dissertation describes how I used a three nanograting Mach-Zehnder atom beam interferometer to precisely measure a wavelength of light, known as a tune-out wavelength, that causes zero energy shift for an atom. I also describe how such measurements can be remarkably sensitive to rotation rates. It is well known that atom interferometry can be used to measure accelerations and rotations, but it was a surprise to find out that tune-out wavelength measurements can under certain conditions be used to report the absolute rotation rate of the laboratory with respect to an inertial frame of reference. I also describe how we created conditions which improve the accuracy of tune out wavelength measurements. These measurements are important because they serve as a benchmark test for atomic structure calculations of line strengths, oscillator strengths, and dipole matrix elements. I present a new measurement of the longest tune-out wavelength in potassium, λzero = 768.9701(4) nm. To reach sub-picometer precision, an optical cavity surrounding the atom beam paths of the interferometer was used. Although this improved the precision of our experiment by increasing the light-induced phase shifts, the cavity also brought several systematic errors to our attentions. For example, I found that large ±200 pm shifts in tune-out wavelengths can occur due to the Earth's rotation rate. To solve this problem, I demonstrated that controlling the optical polarization, the magnetic field, and the atom beam velocity distribution can either suppress or enhance these systematic shifts. Suppressing these systemic shifts in tune-out wavelengths is useful for precision measurements used to test atomic structure calculations. By enhancing these systematic shifts, the interferometer can be a gyroscope that utilizes tune-out wavelengths.

The demand for faster data transmission is ever increasing. Wavelength division multiplexing (WDM) presents as a viable solution to increase the data transmission rate significantly. WDM systems are based on the ability to transmit multiple wavelengths simultaneously down the fibre. Unlike time division multiplexing (TDM) systems, WDM systems do not increase the data transfer by increasing the transmission rate of a single channel. In WDM systems the data rate per channel remains the same, only multiple channels carry data across the link. Dense wavelength division multiplexing (DWDM) promises even more wavelengths packed together in the same fibre. This multiplication of channels increases the bandwidth capacity rapidly. Networks are looking into making use of technology that will ensure no electronic signal regeneration at any point within the DWDM network. Examples are; reconfigurable optical add/drop multiplexers (ROADM) and optical cross connect (OXC) units. These components essentially enable network operators to split, combine and multiplex optical signals carried by optical fibre. WDM allows network operators to increase the capacity of existing networks without expensive re-cabling. This provides networks with the flexibility to be upgraded to larger bandwidths and for reconfiguration of network services. Further, WDM technology opens up an opportunity of marketing flexibility to network operators, where operators not only have the option to rent out cables and fibres but wavelengths as well. Cross phase modulation (XPM) poses a problem to WDM networks. The refractive index experienced by a neighbouring optical signal, not only depends on the signal’s intensity but on the intensity of the co-propagating signal as well. This effect leads to a phase change and is known as XPM. This work investigates the characteristics of XPM. It is shown that, in a two channel WDM network, a probe signal’s SOP can be steered by controlling a high intensity pump signal’s SOP. This effect could be applied to make a wavelength converter. Experimental results show that the degree of polarization (DOP) of a probe signal degrades according to a mathematical model found in literature. The pump and probe signals are shown to experience maximum interaction, for orthogonal probe-pump SOP vector orientations. This may be problematic to polarization mode dispersion compensators. Additionally, experimental results point out that the SOP of a probe signal is much more active in the presence of a high intensity pump, as compared to the single signal transmission scenario.

Clusters of atoms have remarkable optical properties that were exploited since the antiquity. It was only during the late 20th century though that their production was better controlled and opened the door to a better understanding of matter. Lasers are the tool of choice to study these nanoscopic objects so scientists have been blowing clusters with high intensities and short duration laser pulses to gain insights on the dynamics at the nanoscale. Clusters of atoms are an excellent first step in the study of bio-molecules imaging. New advancements in laser technology in the shape of Free Electron Lasers (FEL) made shorter and shorter wavelengths accessible from the infrared (IR) to the vacuum and extreme ultra-violet (VUV and XUV) to even X-rays. Experiments in these short wavelengths regimes revealed surprisingly high energy absorption that are yet to be fully explained. This thesis tries to increase the global knowledge of clusters of rare-gas atoms interacting with short duration and high intensity lasers in the VUV and XUV regime. Theoretical and numerical tools were developed and a novel model of energy transfer based on excited states will be presented. The first part describes the current knowledge of laser-cluster interaction in the short wavelength regime followed by the description of the new model. In the second part of the thesis the different tools and implementations used throughout this work are presented. Third, a series of journal articles (of which four are published and one to be submitted) are included where our models and tools were successfully used to explain experimental results.

L’objet de cette thèse est l’étude de la distribution quantique de clés, une primitive cryptographique qui permet à deux utilisateurs distants de générer une quantité arbitraire de clé secrète et cela y compris en présence d’un espion, sous réserve qu’ils partagent un secret initial. Nous restreignons notre étude aux protocoles employant des variables continues et démontrons expérimentalement une implémentation entièrement fibrée fonctionnant à 80 km sur une fibre dédiée en prenant en compte toutes les imperfections expérimentales connues. Pour atteindre une telle distance de fonctionnement, nous avons mis au point des codes correcteurs d’erreurs spécifiques fonctionnant près de la limite théorique de Shannon dans des régimes de faible rapport signal à bruit. Nous envisageons également la possibilité d’attaques par canaux cachés qui ne sont donc pas prises en compte dans la preuve de sécurité du système et proposons des contre-mesures. Enfin, nous étudions la compatibilité de notre système avec des canaux de communication intenses qui se propagent sur la même fibre optique. / This thesis focuses on a cryptographic primitive that allows two distant parties to generate an arbitrary amount of secret key even in the presence of an eavesdropper, provided that they share a short initial secret message. We focus our study on continuous-variable protocols and demonstrate experimentally an all-fiber system that performs distribution of secret keys at 80 km on a dedicated fiber link while taking into account all known imperfections. We could extract secret keys at such a distance bydesigning specific error correcting codes that perform very close to Shannon’s bound for low signal to noise ratios. We also consider side-channel attacks that are not taken into account into the system security proof and propose some countermeasures. Finally, we study our system compability with intense communication channels that propagate on the same optical fiber.

Philosophiae Doctor - PhD / We present a new sample of distant powerful radio galaxies, in order to study their host-galaxy properties and provide targets for future observations of Hi absorption with new radio telescopes. We cross-match the Sydney University Molonglo Sky Survey radio catalogue at 843 MHz with the VISTA Hemisphere Survey near-infrared catalogue using the Likelihood Ratio technique, producing contour plots as a way to inspect by eye a subset of bright sources to validate the automated technique. We then use the Dark Energy Survey optical and near-infrared wavelength data to obtain photometric redshifts of the radio sources. We find a total of 249 radio sources with photometric redshifts over a 148 square degree region. By fitting the optical and near-infrared photometry with spectral synthesis models, we determine the stellar masses and star-formation rates of the radio sources. We find typical stellar masses of 1011−1012 M for the powerful high-redshift radio galaxies. We also find a population of low-mass blue galaxies. We then report results from the first search for associated Hi 21 cm line absorption with the new MeerKAT radio telescope (shared-risk early science programme). We used a 16-antenna sub-array of MeerKAT to carry out a survey for Hi absorption in the host galaxies of nine powerful (L1.4 GHz > 1026 W Hz−1 ) radio galaxies at cosmological distances (z = 0.29 to 0.54). We found no evidence of absorption with 5σ optical depth detection limits. We only obtain a tentative absorption towards a radio source 3C 262 at z = 0.44 with significant ongoing star formation at a rate of 10.5 M yr−1 . The source consists of two radio lobes separated by 28.5 kpc with no evidence of a compact core. If the absorption arises from neutral gas from an extended disc, the line is redshifted by 79(21) km s−1 with respect to the nucleus and has an average Hi column density across the source of NHI ∼ 7 × 1019−20 cm−2 , which is consistent with the rate of star formation. But after further tests, we find that the Hi detection towards 3C 262 is likely to be an artefact. We conclude that the new correlator with 32 k channel resolution will be needed before searching for its associated absorption in MIGHTEE data.

Thesis / Master of Science (MS)

Gas chromatography (GC) and gas chromatography olfactometry (GCO) was used to determine the effect of specific light wavelengths on light oxidation in milk. The most damaging wavelengths to milk quality appear to be the UV (200-400 and 395 nm) and short visible (463 nm) wavelengths. However, exposure to 610 nm also appears to be damaging. GC and GCO were also used to look at the efficacy of film over-wraps made from iridescent films. Single-layer over-wraps were not as effective in reducing light oxidation as multi-layer film over-wraps. Single-layer over-wrap treatments had higher numbers of odor-active compounds than multi-layer over-wrap treatments with a number of odor-active compounds detected consistently in single-layer over-wrap treatments but not in the multi-layer over-wrap treatments. Concentrations of volatile compounds were slightly lower in the multilayer treatments. Multi-layer film over-wrap treatments were tested for light oxidation flavor intensity with a balanced incomplete block multi-sample difference test using a ranking system and a trained panel. Packaging over-wraps limited the production of light oxidation flavor in milk over time but not to the same degree as the complete light block. Blocking all visible riboflavin excitation wavelengths was better at reducing light oxidation flavor than blocking only a single visible excitation wavelength. A method to determine light oxidation in oil using Fourier Transform Infrared (FTIR) spectroscopy was established and preliminary data is presented. / Ph. D.

The Long Wavelength Array (LWA) is a large multi-purpose radio telescope, operating in frequencies between 10 and 88 MHz, designed for both long-wavelength astrophysics and ionospheric science. The LWA will eventually consist of 53 "stations", each consisting of 256 pairs of crossed-dipole antennas whose signals are formed into beams. The Monitoring and Control System (MCS), a subsystem of each LWA station, controls the station's subsystems and also monitors their status. This thesis addresses the interface-related features of MCS. The physical interface of the MCS with each subsystem is a Gigabit Ethernet connection and the interface protocol is User Datagram Protocol (UDP). An analysis of the throughput obtained through the interface using UDP is compared to that achieved using Transmission Control Protocol (TCP). It is seen that the throughput with UDP is 15\% better than with TCP, and that UDP is a better choice for the given requirements. Implementation of a new ionospheric calibration scheme requires that the MCS be capable of repointing between astronomical sources on a 5 ms time scale. The rate at which beams can be repointed is analyzed. It is confirmed that MCS is at least 2 orders of magnitude faster than necessary, and is limited by the ethernet network throughput. Python software that facilitates the development and testing of MCS and other subsystems have been developed, and are described. / Master of Science

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