<p> Space-division multiplexing (SDM) has been extensively proposed to overcome the next capacity crunch with ever-increasing data and video traffic. Among several SDM approaches, mode-division-multiplexing (MDM) in few-mode fiber (FMF) is the most auspicious technology. One key challenge in FMF transmission systems is random mode coupling among different fiber modes, which can cause severe inter-modal crosstalk. Moreover, large accumulated differential mode group delay (DMGD) can induce significant inter-symbol interference (ISI). </p><p> The approach of adaptive multi-input multi-output (MIMO) digital signal processing (DSP) has been proposed and demonstrated to untangle the crosstalk between the spatial modes and compensate the DMGD. In FMF systems, compared with time-domain adaptive MIMO signal processing, the implementation of frequency domain method achieves much lower hardware complexity. In this dissertation, a single-stage adaptive MIMO equalizer is proposed to compensate both DMGD and chromatic dispersion (CD) simultaneously in order to further reduce the hardware complexity. </p><p> Except for hardware complexity, the convergence rate of adaptive MIMO equalizer is another essential concern. The adaptive MIMO equalizer with slower convergence speed requires longer training symbols, thus decreasing the system overall efficiency. In the dissertation, two advanced step size control methods are presented to increase the convergence rate of the conventional FD-LMS algorithm. The first approach is the signal power spectral density (PSD) dependent method, which adopts the step size for each frequency bin inverse to its power level in order to converge the estimated equalization error to zero, thus it is the optimal solution in the systems with noise-free channel. The other method is the noise PSD directed method, which adopts the frequency bin-wise step size to render the estimated error converge to the channel background noise, thus it is the optimum solution in the systems with additive white Gaussian noise channel.</p>

<p> The classical theory of plasmonics envisions spherical nanoparticles obeying classical electrodynamics. Modern colloidal synthesis of noble metal nanoparticles, in tandem with emerging methods of nanoparticle assembly, transcends the assumptions of this theory. First, strongly nonspherical particles give rise to optical spectra with complicated orientation dependence. An interpolation method is introduced to connect electrodynamic simulation results, generally carried out at fixed orientations, with experimental optical spectra, such as those of randomly oriented ensembles. Second, the ability to manipulate and arrange multiple spherical particles in solution with optical binding demands efficient calculation of the optical forces giving rise to their preferred geometries. A coupled-dipole model is developed to allow for rapid optical force calculations that predict many of the phenomena seen in the laboratory. Third, the prospect of attaching semiconductor quantum dots to metal nanoparticles in the electromagnetic near-field raises new questions about how the quantum behavior of localized surface plasmons affects the nonlinear optical response of the coupled system. Investigating such questions yields several new predictions about the optical response of plasmon-exciton systems. Under ultrafast pulsed illumination, a reversal of a Fano resonance is predicted, turning a dip into a spike in the pulsed optical spectrum. When two quantum dots are coupled to the same metal nanoparticle, it is found that their individual couplings to a quantized plasmon can give rise to coherence between the quantum dots, in particular a state enriched in an antisymmetric dark excitation that can be prepared with pulsed laser illumination. These theoretical tools and predictions, in addition to providing basic insight into plasmonic systems, will serve to guide further developments in colloidal synthesis, nanoparticle assembly, and optical applications.</p>

<p> Resonant devices are an integral component of the integrated silicon photonics platform, with applications in filters, switches, modulators, delays, sensors etc. High index contrast SOI waveguides can be used to form compact micro-ring resonators with bend radii on the order of micro-meters. This work describes the application of micro-ring resonators in linear and nonlinear silicon photonics. We describe the use of higher-order coupled resonators for use as ultra-high contrast pass-band filters with close to 100 dB extinction. Using the spontaneous four-wave mixing process, a third-order nonlinear Kerr effect, coupled resonator waveguides are shown to be a useful source of heralded single photons, as well as other unique quantum states of light. We also describe four-wave mixing results in silicon micro-resonators, where nonlinear loss effects are mitigated by reverse biased p-i-n diodes, showing potential for high-speed optical signal processing.</p>

<p> The present dual field of view flexible colonoscope can provide both forward view and radial or backward view of the colon to improve detection of cancerous polyps. The colonoscope has its own illumination that illuminates the parts of the colon viewed by imaging optics. The optical system, limited only by the diffraction effects at the exit pupil over the entire visible spectrum, can provide high resolution and is suitable for color imaging. The flexible colonoscope has an on-board sensor at the proximal end of the colonoscope to improve resolution. The proximal end of colonoscope measures only 8 mm in diameter and 20 mm in length. The present colonoscope has the potential to be scaled down to as small as 6 mm inner diameter from the present 8 mm. </p>

<p> The image captured by an imaging system is subject to constraints imposed by the wave nature of light and the geometry of image formation. The former limits the resolving power of the imager while the latter results in a loss of size and range information. The body of work presented in this dissertation strives to overcome the aforementioned limits. The suite of techniques and apparatus ideas disclosed in the work afford imagers the unique ability to capture spatial detail lost to optical blur, while also recovering range information. </p><p> A recurring theme in the work is the notion of imaging under patterned illumination. The Moir&eacute; fringes arising from the heterodyning of the object detail and the patterned illumination, are used to improve the resolving power of the imager. The deformations in the phase of the detected illumination pattern, aid in the recovery of range information. </p><p> The work furnishes a comprehensive mathematical model for imaging under patterned illumination that accommodates blur due to the imaging/illumination optics, and the perspective foreshortening observed at macroscopic scales. The model discloses the existence of a family of active stereo arrangements that jointly support super resolution (improvement of resolving power) and scene recovery (recovery of range information). </p><p> The work also presents a new description of the theoretical basis for super resolution. The description confirms that an improvement in resolving power results from the computational engineering of the imager impulse response. The above notion is explored further, in developing a strategy for engineering the impulse response of an imager, using patterned illumination. It is also established that optical aberrations are not an impediment to super resolution. </p><p> Furthermore, the work advances the state-of-the-art in scene recovery by establishing that a broader class of sinusoidal patterns may be used to recover range information, while circumventing the extensive calibration process employed by current approaches. </p><p> The work concludes by examining an extreme example of super resolution using patterned illumination. In particular, a strategy that overcomes the severe anisotropy in the resolving power of a single-lens imager is examined. Spatial frequency analysis of the reconstructed image confirms the effectiveness of lattice illumination in engineering a computational imager with near isotropic resolving power.</p>

<p> This thesis investigates the fundamental nanoscale near-field light matter interaction between a probe tip and plasmonic antenna nanostructures. The thesis is focused on polarization control of metallic plasmon modes using scattering-type scanning near-field optical microscopy (s-SNOM). Part of the thesis is dedicated to spectroscopic near-field comparison of coated and bare single plasmonic particles in the infrared wavelength range (&lambda;= 9&ndash;11 &micro;m) using s-SNOM. By tuning the wavelength of the incident light, we have acquired information on the spectral polarization dependence plasmon modes and plasmon/phonon&ndash;polariton resonant near-field interactions. The enhanced near-field coupling between the probe tip and high index Au nanostructures and Au-core thin silica coating (thickness &ap;10 nm) is described and quantified. </p>

<p> This thesis investigated the science behind polarimetric road ice detection systems. Laboratory Mueller matrix measurements of a simulated road under differing surface conditions were collected searching for a discriminatory polarization property. These Mueller matrices were decomposed into depolarization, diattenuation, and retardance. Individual sample surface polarization properties were then calculated from these three unique matrices and compared. Specular and off-specular reflection responses of each sample were collected. Four polarization properties stood out for having high separation between dry and iced measurements: Depolarization Index, Linear Diattenuation, Linear Polarizance, and Linear Retardance. </p><p> Through our investigation polarimetric ice detection is possible. Continued research of the polarization properties of road ice can result in the development of a road ice detection system. Proposed deployment methods of such a system have been outlined following the analysis of the data collected in this experiment. </p>

Free-space optical interconnects (FSOIs) promise to deliver tremendous gains in connectivity and architectural freedom in future computing systems, especially at the backplane level. However, a critical hurdle that must be overcome for FSOIs to deliver on their promise is that of optical packaging. The objective of optical packaging in FSOIs is to implement an optical design within the specified alignment budget and support the associated optoelectronics. It is a multidisciplinary field combining aspects of mechanical, optical and electrical engineering. This thesis explores optical packaging issues for FSOIs such as: type of optical interconnect, impact of device technology, environmental effects, and fabrication issues. Approaches taken to address these issues in previous optical systems described in the literature are then studied; key points are the importance of improving diagnostic techniques and the benefits of microoptic/optoelectronic device integration. To further study these aspects, the optical packaging for a four-stage hybrid macrolens/lenslet FSOI backplane is designed, built, and characterized. A non-obtrusive, in-situ alignment diagnostic system which uses dedicated alignment beams running parallel to the main link is also designed, implemented and characterized. An analysis of optical crosstalk and signal-to-crosstalk ratio considerations due to misalignment is then presented and it is shown that crosstalk can be exploited to yield alignment diagnostic information at the expense of few additional components. A novel approach for simplifying prealignment of microoptics and optoelectronics during fabrication is then presented. This consists of using on-die reflective diffractive structures to generate reference marks for use during alignment and fabrication of integrated microoptic/optoelectronic packages. Future avenues of research are then discussed.

Multi-wavelength laser sources have attracted much interest in the last decade as new photonic technologies have enabled the realization of such sources with much improved characteristics. Tunable continuous-wave multi-wavelength fiber lasers may now offer, for example, the ability to tune the wavelength spacing between the lasing lines and, also at times, the possibility to control the individual output peak powers. The more flexible and low-cost solutions benefiting from higher optical spectrum bandwidths also attract the most interest for future applications. These lasers find clients in so many fields such as optical test and measurement, optical communications, sensing, and processing like microwave photonic filtering. The search for such a flexible, stable and affordable laser source has fueled the investigation presented in this thesis. We first analyze the different approaches taken in the past for the implementation of tunable continuous-wave multi-wavelength lasers and follow with the development of a novel, relatively low-cost, tunable multi-wavelength semiconductor fiber laser (SFL). All the design steps are clearly explained and characterized. The final SFL is then used for the demonstration of two applications: chromatic dispersion measurements in long fiber spools, and the new design of a photonic microwave filter.

This thesis investigates the application of a recently developed numerical technique, the Flexible Local Approximation Method (FLAME) to compute the resonances of 2D photonic crystal (PC) cavities, formed by a defect in a regular array of dielectric rods. FLAME is a finite-difference-like method which is ideally suited to problems consisting of large numbers of identical structures. / The anisotropic perfectly matched layer (PML) is used as an artificial absorbing layer to truncate the computational domain. The parameters of the PML are chosen carefully to provide adequate absorption without a large computational cost. / FLAME method and PML boundaries are applied to cavities with 3x3, 5x5 and 7x7 arrays of rods. The resonant modes, field distribution, and quality factor are computed and compared with previously-published results. Good agreement is obtained. However, the matrix eigenproblem generated by FLAME is of a kind for which sparse-matrix algorithms are not available and dense-matrix software had to be used. This limitation will have to be overcome if FLAME is to be widely used for PC cavities.