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Abstract A buried hybrid waveguide with large angle bend utilizing Fresnel refraction is presented. The waveguide device consists of a polymer core buried in SiO2 cladding on a Si substrate. Large angle bend of the waveguide is achieved based on Fresnel refraction by inserting a low index region into the bend structure. The buried hybrid waveguide was fabricate by dry etching a trench into the SiO2 cladding using Cr as the etch mask. Benzocyclobutene (BCB) polymer was then coated on to the sample to planarize the surface and was used as the guiding core. Etch back was performed to remove the polymer outside the guiding region. The device was completed by passivating the surface with a thin layer of spin on glass (SOG). The normalized transmission loss of the hybrid waveguide with two 8¢X angle bends is 75%. The propagation loss of the waveguide is 0.6 dB/cm. In addition, a theoretical model of the bend waveguide is proposed. BPM-CAD is used to calculate the bending loss of the waveguide with different bending angles. The calculated results suggest that a large angle bend can be obtained for a large index different the core and the cladding.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1961. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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Due to the increased demand for high-operating-speed systems and ultra-compact optical devices, nanophotonic waveguides such as plasmonic waveguides have been a subject of intense interest over the past few years. The ability of plasmonic waveguides to guide light within nano-scale structures beyond the diffraction limit has driven researchers in different fields to exploit their unique features. Even though plasmonic waveguides have shown a strong mode confinement at nano-scale dimensions, they have high propagation loss. Consequently, many geometries and structures have been proposed to investigate ways to reduce this loss. The most recent type of plasmonic waveguide that shows high mode confinement and low propagation loss compared with the other types is the hybrid plasmonic waveguide (HPW). An HPW consists of a low-index dielectric layer sandwiched between a high-index dielectric material and a metal layer; the mode is predominantly confined within the low-index layer. This thesis addresses the use of HPWs for nonlinear applications such as optical switching devices based on the nonlinear phenomenon known as the Kerr effect, where the sub-wavelength dielectric layer has a pronounced nonlinear response. Using Finite Element Method analysis, the nonlinear hybrid plasmonic waveguide (NLHPW) is modeled, and the performance of the NLHPW has been investigated by using appropriate figures of merit to measure the Kerr nonlinearity of the NLHPW with and without the linear loss of the waveguide. These are shown to compare favourably with those of alternate waveguiding geometries. Moreover, the NLHPW has been shown a good balance between mode confinement and loss; small effective mode areas of 0.04 – 0.15 µm2 at a wavelength of λ=1.55 µm and relatively long propagation lengths of 30 to 160 µm can be realized, which make NLHPWs promising candidates for nonlinear applications. As a result, a nonlinear ring resonator with a radius of 1 µm based on the NLHPW is designed and investigated numerically by using frequency domain simulations. It is found that the field intensity in the ring is enhanced four times higher than the field intensity in the input waveguide, and that a nonlinear resonance shift is realized when changing the intensity of the data signal.

Due to the increased demand for high-operating-speed systems and ultra-compact optical devices, nanophotonic waveguides such as plasmonic waveguides have been a subject of intense interest over the past few years. The ability of plasmonic waveguides to guide light within nano-scale structures beyond the diffraction limit has driven researchers in different fields to exploit their unique features. Even though plasmonic waveguides have shown a strong mode confinement at nano-scale dimensions, they have high propagation loss. Consequently, many geometries and structures have been proposed to investigate ways to reduce this loss. The most recent type of plasmonic waveguide that shows high mode confinement and low propagation loss compared with the other types is the hybrid plasmonic waveguide (HPW). An HPW consists of a low-index dielectric layer sandwiched between a high-index dielectric material and a metal layer; the mode is predominantly confined within the low-index layer. This thesis addresses the use of HPWs for nonlinear applications such as optical switching devices based on the nonlinear phenomenon known as the Kerr effect, where the sub-wavelength dielectric layer has a pronounced nonlinear response. Using Finite Element Method analysis, the nonlinear hybrid plasmonic waveguide (NLHPW) is modeled, and the performance of the NLHPW has been investigated by using appropriate figures of merit to measure the Kerr nonlinearity of the NLHPW with and without the linear loss of the waveguide. These are shown to compare favourably with those of alternate waveguiding geometries. Moreover, the NLHPW has been shown a good balance between mode confinement and loss; small effective mode areas of 0.04 – 0.15 µm2 at a wavelength of λ=1.55 µm and relatively long propagation lengths of 30 to 160 µm can be realized, which make NLHPWs promising candidates for nonlinear applications. As a result, a nonlinear ring resonator with a radius of 1 µm based on the NLHPW is designed and investigated numerically by using frequency domain simulations. It is found that the field intensity in the ring is enhanced four times higher than the field intensity in the input waveguide, and that a nonlinear resonance shift is realized when changing the intensity of the data signal.

A theoretical investigation of one-dimensional planar photonic crystal waveguides is carried out. These waveguides consist of a dielectric layer sandwiched between two semiinfinite periodic dielectric structures. Using a novel approach, exact analytical solutions for guided modes in such waveguides are presented. The se rigorous solutions allow one to distinguish clearly between the index-guiding regime and guidance due to the photonic crystal effect. In the first part of this investigation, a rigorous analysis of the reflection of uniform plane waves from a semi- infinite periodic dielectric structure is undertaken. Both parallel and perpendicular polarizations for the incident plane wave are considered. Exact expressions for the reflection coefficients corresponding to two polarization cases are obtained using an impedance approach. The results for the reflection coefficient are then used to study propagation properties of guided modes in one-dimensional photonic crystal waveguides with semiinfinite periodic cladding regions. Characteristic equations, from which propagation constants of guided modes can be obtained, and solutions for electromagnetic fields of these modes are derived. Solutions for both TE (transverse electric) and TM (transverse magnetic) modes are presented. Numerical results for the propagation constant and field distributions of several lower-order modes are presented. The solutions unique to photonic crystal waveguides are emphasized. / Master of Science

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