<p> Widely tunable lasers with fast tuning speeds have applications in dense wavelength division multiplexing (DWDM), optical sensing and optical packet switching. In DWDM, tunable lasers can greatly reduce inventory costs, increase manufacturing efficiency, and increase flexibility. For this application, tunable lasers must meet stringent requirements in terms of linewidth, SMSR, RIN, etc. As coherent detection moves to higher modulation formats to increase spectral efficiency, linewidths on the order of 100 kHz will be required. In FMCW LIDAR, the sensing range is directly coupled to the coherence length, i.e. linewidth, of the laser, and the resolution is determined by the tuning range of the laser. A laser with a 40 nm tuning range and 100 kHz linewidth can lead to a LIDAR system with 30 &micro;m of resolution at a 1.5 km range. The above motivations demonstrate the need for a laser that is widely tunable, with tuning speeds in the nanosecond regime, a 100 kHz linewidth and small form factor. Many different approaches have been taken to achieve a low linewidth laser, generally with the trade-off of slower tuning speeds or larger size. Typically, the widely tunable mirrors used to create a highly agile laser are noisy. In our approach we use negative feedback along with an InGaAsP/InP photonic integrated circuit (PIC) to reduce the linewidth of a widely tunable SG-DBR laser. The SG-DBR laser has a 40 nm tuning range, ns tuning speeds and is 1.5 mm long. Typically the linewidth is in the MHz range due to carrier induced frequency fluctuations. We use an asymmetric Mach Zehnder integrated on the same PIC to monitor and convert the laser frequency fluctuations to amplitude fluctuations. This error signal is fed back through a stabilizing loop filter to the phase tuning section of the SG-DBR laser to reduce the laser linewidth. Through integration of all the optical components, the loop delay is minimized and loop bandwidths upwards of 600 MHz have been achieved. Using this technique, we demonstrate an SG-DBR laser with the linewidth suppressed from 19 MHz to 150 kHz, which is the lowest linewidth yet for an SG-DBR laser. </p>

Using the focused ion beam sputtering capabilities of Scanning Ion Microscope with Polarization Analysis (SIMPA), arrays of regular shaped particles with sizes in the order of 10$\mu$m are produced from a 35nm thick $\rm Ni\sb{83}Fe\sb{17}$ film with in-plane uniaxial anisotropy, The aspect ratio of the particles range from bar-like (50:1) to island-like (1.4:1). Their magnetic properties are studied with longitudinal magneto-optical Kerr effect. Structures with different geometries are found to display fundamental differences in their magnetic behavior. Two types of geometry induced changes in the magnetization reversal process are discerned. These changes are found to agree with a theoretical model based on micromagnetic effects. Light is scattered into a regular diffraction pattern from these structures. The magneto-optical effects in the various spectral orders are examined; they are found to produce similar hysteresis curves as the specular beam.

<p> Digital Holography (DH) is an emerging tool for use in the structural investigation of temperature dependent material processes. DH is able to reveal deformations and topological details at ultrahigh sensitivity (a few tens of nanometers) for particular details such as point-like objects and interfacial structures, allowing for the investigation of a range of processes. However, while DH is able to provide high precision data, the height measurement range is limited by the probe wavelength. Therefore a 'synthetic' wavelength created from the superposition of two or more individual wavelengths is often required in order to increase the measurement range to a suitable value dependent upon the object dimensions. </p><p> The use of multiple wavelengths attached to one system thus allows for surface height measurements over a relatively long range. In addition as the complex wave-front of each wavelength can be captured simultaneously in one digital image, real-time performance is achievable. In this thesis a number of materials processes were investigated at differing temperatures. The structural changes associated with the martensite to austenite phase transformation were measured using dual-wavelength digital holography during thermal cycling of nickel-aluminum-platinum (NiAlPt) and single-crystal Fe-15Cr-15Ni alloys. Real-time in-situ measurements reveal the formation of striations within the NiPtAl alloy at &sim;70&deg;C, and the FeCrNi alloy at &sim;520&deg;C. The results demonstrate that digital holography is an effective technique for acquiring non-contact, high precision information of the 3D surface evolution of alloys at high temperatures.</p>

Cette thèse porte sur l'étude d'un composant optique à base de guides d'onde monomodes destiné à recombiner de manière cohérente les faisceaux provenant de quatre télescopes. L'architecture proposée permet de fournir une mesure instantanée de la visibilité et de la phase des tranges pour les six paires possibles de télescopes sur la bande H de transparence de l'atmosphère. A partir des résultats de caractérisation optique obtenus sur les dispositifs réalisés en technologie silice sur silicium, des composants plus complexes destinés aux projets d'instrumentation de seconde génération du VLTI (Very Large Telescope Interferometer) ont pu être étudiés. Il est notamment montré que l'architecture proposée est extensible aux bandes d'observation J et K et à la recombinaison de faisceaux issus de six voire huit télescopes, et peut être aussi avantageusement utilisée pour réaliser un suiveur de franges.

The intersection of silicon technology with the rapidly growing field of nanoplasmonics, provides a fertile ground for development of synergistic technologies. The optical and electrical properties of silicon are well understood and well characterized. In this thesis we explore the interactions of plasmonic nanostructures with both passive and active silicon substrates. In the case of a passive silicon substrate, we characterize the properties of propagating surface plasmon waves supported by copper and silver gratings on silicon. We simulate the properties of gold colloid, nanoshells and dielectric particles on lightly doped n-type substrates, through the use of the finite element method. In the case of active silicon substrates, we deposit gold colloid, nanoshells, and dielectric particles on an embedded p+n diode structure. We examine the influence of parameters such as nanoparticle size and plasmon resonance position on the photocurrent measured, in the visible and near infrared wavelength regimes. Both ensemble and local photocurrent measurements are made experimentally. Dielectric particles and Au nanospheres enhance the photocurrent in the 500 nm to 980 nm wavelength range, with a maximum enhancement of 10% observed in the case of both types of nanoparticles. Au nanoshells exhibit a more complex size and wavelength dependent photocurrent alteration pattern, decreasing the photocurrent at wavelengths of 532 and 633 nm, and enhancing photocurrent at wavelengths of 780 and 980 nm. The maximum photocurrent enhancement of 19% was observed for a nanoshell with an inner radius of 96 nm and a outer radius of 116 nm, at a wavelength of 980 nm.

The generation of substantial electrical conductivity in high temperature polymers and thin film C$\sb{60}$ by means of KrF (248 nm) excimer laser irradiation has been investigated. Formation of both laser ablated surface structures and laser induced electrically conducting wires in polymers with nanometer dimensions is also demonstrated. The electrical conductivity of polymers has been changed by up to 18 orders of magnitude by laser irradiation, obtaining values exceeding 10 $\Omega\sp{-1}$ cm$\sp{-1}$. The conducting material consists of graphitized carbon clusters whose size varies from 2-50 nm. The conduction mechanism is phonon assisted variable range hopping. The large change in the electrical conductivity is an example of a three dimensional percolative metal-insulator phase transition. The critical volume fraction is determined to be $\Phi\sb{\rm c}$ = 0.30 $\pm$ 0.05 and the critical exponent is t = 2.2 $\pm$ 0.4. The electrical conductivity of thin film C$\sb{60}$ has been altered by more than seven orders of magnitude with laser irradiation, obtaining values of 1 $\Omega\sp{-1}$ cm$\sp{-1}$. The threshold for KrF laser ablation of C$\sb{60}$ is determined to be 20 $\pm$ 2 mJ/cm$\sp2.$ Modification of the surface morphology and the electrical conductivity of polymers with high spatial resolution using excimer lasers has also been achieved. Using holographic techniques with a KrF excimer laser, periodic lines structures with periods ranging from 166 nm to 950 nm were ablated into polyimide (Kapton$\sp{\rm TM})$ and polybenzimidazole (PBI). The nonlinear nature of laser ablation permits linewidths as small as 30 nm to be obtained, exceeding the resolution expected from linear optics. These experiments establish a new spatial resolution limit for laser ablation and illustrate the dependence of resolution on material properties. This technique was combined with the ability to modify the electrical conductivity of polymers to produce an array of permanently electrically conducting wires in polyimide with a 0.5 $\mu$m width and a 0.9 $\mu$m period. The electrical conductivity of these submicron wires exceeded 1 $\Omega\sp{-1}$ cm$\sp{-1}.$

The application of diode-laser-pumped tunable IR sources to trace gas detection in air is discussed. The design and technology issues of CW tunable mid-infrared difference-frequency generation are addressed. Feasibility experiments are reported in which the detection of CH$\sb4$, and CO was performed at low pressure and in air using two laser sources near 3.2 $\mu$m, and 4.7 $\mu$m, respectively. They were based on difference-frequency mixing in AgGaS$\sb2$ at room temperature. Pump sources used were a diode-pumped Nd:YAG laser at 1064 nm, a laser diode at 693 nm, and a tunable fiber-coupled Ti:Sapphire laser near 795 nm, and 813 nm. Detection limits of 2.4 ppb*m/$\rm\sqrt{Hz}$ for CO, and 9.0 ppb*m/$\rm\sqrt{Hz}$ for CH$\sb4$ in air are estimated for 0.1 $\mu$W of IR probe power based upon the performance of the sources and detector.

Highly oriented polycrystalline thin films of lithium niobate on (012), (100), and (110) sapphire single crystal substrates, (111) silicon and SiO$\sb2$/(100)Si wafers were grown by magnetron rf sputtering and metallo-organic decomposition techniques. A novel technique of photo-induced metallo-organic decomposition (PIMOD) is proposed and implemented to eliminate inter-diffusion and cracking which are commonly observed in MOD-derived films. Results of XRD, TEM, and ion beam spectrometry confirm that highly oriented, polycrystalline, stoichiometric lithium niobate thin films have been successfully grown on a variety of substrates. Prism coupling has been used to excite the guided modes in the optical thin film waveguides. The optical and electrooptic properties, including the refractive index, propagation losses, and electrooptic coefficient, were investigated. Finally, an electrooptic phase modulator was implemented.

In this dissertation we study the dynamic Franz-Keldysh effect (DFKE) in GaAs. We observe the salient features of DFKE viz., below bandgap absorption and oscillations above the band gap, in our experiments. We also report the first observation of a large photoinduced transparency which represents a novel coherent phenomenon based on the DFKE and agrees well with the theoretical predictions. Finally we propose schemes making use of this effect to realize all-optical wavelength conversion required in high speed optical networks based on wavelength division multiplexing (WDM).

Design, development, and application of novel all-solid-state spectroscopic gas sensors is reported. These compact instruments employ mid-infrared difference-frequency generation pumped by room-temperature semiconductor lasers, and are capable of real-time selective measurement of trace gases in ambient air with better than 1 ppb precision (part per billion, by mole fraction). Their features and performance in the laboratory and field environment are examined and compared to that of traditional spectroscopic sensors.