The THz region is a burgeoning field of research with applications in spectroscopy, integrated circuit fabrication, bio-medicine, and communications. Until recently, the THz region was largely unexplored, mainly due to the technical difficulties involved in making efficient and compact sources and detectors. As these challenges are addressed, the focus of research has shifted to practical applications, such as sensing and imaging. The focus of this thesis is to investigate the characterization of parallel plate waveguide multimode propagation and periodically notched resonant structures for use in sensing and material parameter extraction applications. Broadband and narrowband measurements are presented and analyzed. Measurements are compared to finite difference time domain simulations and analytic solutions that use a Fourier transform mode-matching technique. Agreement is observed between simulation and measurement of radiation patterns. Weighted estimates of individual mode analytic solutions produce equivalent radiation patterns, which allows insight into the energy coupled into each respective mode. Results show that higher order modes contribute both a greater conductive attenuation and higher coupling loss. Agreement is also observed between measurements and simulated single and periodically notched resonant structures. Results demonstrate shifting of the resonant peak with respect to changes in plate separation for the periodically notched structure. For the single notch resonator, simulations indicate the resonant peak is dependent on notch depth until the depth-to-width ratio is greater than two. This work demonstrates that multimode propagation can be identified and the amount of energy coupled into each mode may be estimated using radiation patterns. Experiments using quasi-optical time domain spectroscopic and continuous wave vector network analyzer systems in the THz region have been demonstrated. Finite difference time domain simulations have validated measurements on both systems. The results presented will advance the field of THz research by aiding in the design and analysis of sensing and material parameter extraction systems

Taking inspiration from a variety of creatures found in nature, this thesis demonstrates a new class of materials designed for light capture and guidance. Through the facile method of waveguide self-inscription developed herein, the arrangement of these self-generated light channels can be influenced to produce complex architectures. Inspired by the arrangement of ommatidia found in arthropodal eyes, this was first demonstrated through the fabrication of a radial arrangement of waveguides. This resulted in a thin, polymer film which demonstrated a continuous, panoramic field of view (FOV) able to successfully control the light of a light emitting diode (LED). Moving to more complex architecture, waveguides self-generated in a conical geometry were fabricated. More closely reminiscent of the geometry seen in arthropodal eyes, this waveguide architecture demonstrated a seamless omnidirectional FOV and enhanced imaging capabilities in conjunction with a CMOS camera chip. Lastly, using the method of waveguide self-inscription with an electroactive hydrogel precursor, remote controllable light guiding architectures, as inspired by deep sea creatures, are designed and fabricated. The application of an electric field, in conjunction with the stimuli-responsive waveguides, allows for precise control of the waveguide structures and therefore control over the waveguided light. / Thesis / Doctor of Philosophy (PhD)

An electrochemical detection method based on long range surface plasmon waveguides is proposed and demonstrated in this integrated article thesis. This dissertation uses CYTOP gold (Au) waveguides supporting long range surface plasmon polaritons (LRSPPs) in conjunction with grating couplers as well as Au waveguides embedded on a one-dimensional photonic crystal (1DPC) supporting Bloch LRSPPs integrated grating couplers. Grating couplers for Au stripe waveguides embedded in Cytop are demonstrated and analyzed. Grating couplers are used in a broadside coupling scheme where a laser beam incident on a stripe of Au on Cytop. The use of gratings for excitation of LRSPPs simplifies optical alignment and does not require high-quality input and output edge facets. Over a broad operating wavelength range, optical experiments are performed to demonstrate coupling loss and determine the efficiency of grating coupling using both a cleaved bow-tie PM fiber and a lensed PM fiber. The coupling loss and grating coupling efficiency of both types of fibers are also calculated numerically. Fluoropolymers with refractive indices close to water, such as CYTOP, are widely used to make waveguide biosensors today. Due to its low glass transition temperature, CYTOP presents limitations to fabrication processes. A truncated 1D photonic crystal may replace a low-index polymer cladding such as CYTOP to support Bloch LRSPPs within the bandgap of the 1DPC over limited wavenumbers and wavelength range. As a result of the high sensitivity of Au stripe Bloch LRSPP waveguide biosensors and their compatibility with high levels of integration, microelectrode systems that can be integrated with such optical biosensors are examined. A chip bearing a Au LRSPP waveguide that can also function as a working electrode (WE), a Pt counter electrode (CE), and Pt/Cu electrical contact pads, is used to demonstrate the electrochemical performance of LRSPPs waveguides. The cyclic voltammetry measurements were performed at different scan rates and concentrations of potassium ferricyanide as the redox species on Au LRSPPs waveguides. By fitting our experimental data to the Randles-Sevcik equation, we find the diffusion coefficient of potassium ferricyanide. The results from CV measurements obtained from chips are compared with commercial macroscopic electrodes. The CV measurements are also compared with theoretical results computed using the Butler-Volmer equation to determine the rate constant of the redox species at zero potential. A waveguide containing a stripe of Au that propagates infrared surface plasmon polaritons (SPPs), acting simultaneously as an electrode in a three-electrode electrochemical cell is also examined. Under SPP excitation, cyclic voltammetry was measured as a function of incident optical power and wavelength (1350 nm). In oxidation and reduction reactions, energetic electrons are separated from energetic holes. Under SPP excitation, redox current densities increase by 10×. With the SPP power, the oxidation, reduction, and equilibrium potentials drop by as much as 2× and separate in correlation with the photon energy. According to electrochemical impedance spectroscopy, charge transfer resistance dropped by almost 2× under SPP excitation. During SPP excitation, the temperature of the working electrode is monitored in situ and independent control experiments are performed to isolate thermal effects. Measurements of chronoamperometry with SPPs modulated at 600 Hz yield a rapid current response modulated at the same frequency, ruling out thermally enhanced mass transport. The observation is attributed to the opening of optically controlled non-equilibrium redox channels associated with the energetic carrier transfer to the redox species. During CV and chronoamperometry measurements, convolutional voltammetry is performed by monitoring the SPP output power versus the applied voltage. Using both experimental and theoretical methods, we demonstrate that the SPP output power is proportional to the electrochemical current convolution. A SPP voltammogram confirms that signal changes are mainly caused by differences in refractive index between reduced and oxidized forms of redox species. In addition, we demonstrate that energetic carriers resulted from SPP absorption significantly improved electrochemical sensitivity. As a complementary electrochemical technique, convolutional voltammetry is useful since the signal is related directly to the concentration of electroactive species on the working electrode (WE) and independent of the scan rate. As a probe of electrochemistry taking place in waveguides, surface plasmon polaritons (SPPs) propagating along one are sensitive. In such a waveguide, the optical output power is proportional to the time convolution of the electrochemical current density, eliminating the need to calculate the latter a posteriori via numerical integration. It is demonstrated that a waveguide WE provide an optical response that can be experimentally validated by chronoamperometry and cyclic voltammetry measurements under SPP excitation for a few potassium ferricyanide (redox species) concentrations in potassium nitrate (electrolyte) and various scan rates. Cyclic voltammetry measurements taken under increasing SPP power produce a regime where SPPs no longer act solely as the probe, but also act as a pump, producing energetic electrons and holes via their absorption in the WE. The energetic carriers enhance (10×) redox current densities as well as the convolution signal measured directly as the optical output power over time.

Results of research on surface emission from a waveguide due to second-harmonic generation are presented. This concept has been applied and demonstrated here in the InP-InGaAsP material system for the first time, using a fundamental wavelength of 1.32 |im and a harmonic surface emission at 660 nm. The surface emission is the result of the nonlinear mixing of two counterpropagating modes in a waveguide. The theory of nonlinear optics that produces this effect is explained, leading up to a model that describes the behaviour of the surface emitting waveguide (SEWG). This model is then used to design a pseudo-optimized structure that was subsequently grown, characterized and tested. Device performance and behaviour are compared with theoretical predictions. / Thesis / Master of Engineering (ME)

This thesis describes the design, fabrication and characterisation of an infrared optical waveguide phase modulator. The modulator was fabricated in GaAs utilizing a carrier-concentration-reduction rib waveguide structure with a Schottky diode contact to allow the application of an electric field across the waveguide region. Measurements of the phase modulation are presented with results agreeing with the theoretical predictions of an electrooptic coefficient of 1.2 x 10-12 m/V at 1.15 //m. Fabrication techniques and problems are thoroughly discussed. The second part of this thesis consists of measurements of the quantum confined stark shift in an AlGaAs-GaAs multiple quantum well p-i-n diode structure. The results show useful changes in absorption with applied electric field. Transmission measurements as a function of applied field are presented for TE polarized light in a waveguiding geometry as well as photocurrent measurements in the same geometry and with light incident perpendicular to the MQW layers. Reasonable agreements for the relative field induced shifts of the excitonic feature are found but the absolute position of the feature is blue shifted by 7 meV with respect to the theoretically predicted position. / Thesis / Master of Engineering (ME)

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The family of III-V semiconductors is of high significance in photonics for two main reasons. First, not only they are the most practical material platforms for active photonic devices but also they are suitable for monolithic integration of passive and active photonic devices. Second, some III-V compounds exhibit high values of second and third-order nonlinear coefficients – the property useful in all-optical signal processing and wavelength conversion. This Ph.D. thesis explores the above perspectives with two candidates from the group III-V family, namely AlGaAs and InGaAsP. The dissertation consists of two main parts. The first part is dedicated to the theoretical modelling of nonlinear bianisotropic AlGaAs metasurfaces, while the second part focuses on the experimental studies of the nonlinear optical performance of InGaAsP waveguides. Concerning the first part, due to the high confinement of light supported by the Mie resonances, AlGaAs nanoantennas and metasurfaces with both high refractive index and high nonlinear susceptibility have found a unique place in planar nonlinear optics, where not only the presence of high intensity of light is of significant matter, but also the optically thin thickness of the entities releases the device from phase matching. We first describe the linear optical properties of AlGaAs meta-atoms and metasurfaces such as relatively high scattering cross-sections and the bianisotropic effect. Also, we derive and explain all required analytic formulas for this purpose. Bianisotropic metasurfaces with magnetoelectric coupling and asymmetric optical properties have sparked considerable interest in linear meta-optics. However, further in this thesis, we explore the nonlinear features of bianisotropic AlGaAs metasurfaces. In particular, we explore a second-harmonic generation in a bianisotropic AlGaAs metasurface based on the multipolar interference inside the meta-atoms and the nonlinear polarization current. We theoretically demonstrate that it is possible to obtain several orders of magnitude secondharmonic power differences for the forward and backward illuminations by adjusting the geometrical parameters of the meta-atoms in such a way that quasi-bound states in the continuum (quasi-BICs) are achievable. This research paves the way for the generation of directional higher-order waves. Concerning the second part, the research is focused on exploring nonlinear material platforms for monolithic integration of active and passive devices on the same chip. In this regard, we explore InGaAsP/InP waveguides of different geometries. First, we provide the theoretical background such as the nonlinear Schrodinger equation and four-wave mixing (FWM) equations in a nonlinear waveguide, then we solve the set of FWM equations using MATLAB to observe the qualitative behavior of the signal, idler, and the pump inside a nonlinear waveguide. Furthermore, we design and employ two waveguide geometries i.e. half-core and nanowire waveguides. We first design these waveguides so that achieving zero group velocity dispersion is possible through a suitable material composition and certain geometrical dimensions. However, for the rest of the work, we continued with the waveguides of different dimensions compared to the designed ones (due to some limitations in fabrication). We demonstrate self-phase modulation (SPM) and FWM for the half-core waveguides. For the case of the nanowire waveguides, we also demonstrate the FWM effect. We measured and extracted the effective value of the nonlinear refractive index of InGaAsP/InP waveguides to be n2 = 1.9 × 10−13 cm2/W through the relation between the idler and the pump power when the phase mismatch is negligible. Finally, we experimentally observe the two-photon absorption effect in our waveguides through the nonlinear characteristics of input and output powers of the waveguides from which the two-photon absorption coefficient of 19 cm/GW is calculated.