Waveguides in large bandgap materials for lasers and quantum photonics

• Main Author: McKnight, Loyd James
• Published: University of Strathclyde 2012
• Subjects: 621.36
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.576294

The spatial confinement of light with a waveguide offers the possibility for improved performance of many optical devices including lasers and nonlinear frequency converters. Furthermore, waveguide devices may be combined together to increase functionality reliably, in a field known as integrated optics. One application that may benefit from integration is quantum photonics: working with single photons for quantum logic. The work presented in this thesis studies the development of waveguides for these aforementioned applications in three materials for which few waveguide devices have been previously reported: diamond, gallium nitride (GaN) and stoichiometric potassium ytterbium double tungstate (KYbW). Each material platform offers properties that are highly suited to the selected photonics application. Diamond is a suitable material for quantum photonics and as a Raman laser gain material. A large-cross-sectional-area diamond rib waveguide has been designed, fabricated and charac terised optically. Diamond waveguides of varying cross-section are considered for a Raman waveguide laser. A fully analytical model is developed incorporating scattering losses to optimise the design of such a laser system. GaN has a range of material properties that are suited to the application of integrated quantum photonics. A directional coupler was designed and optimised for a small footprint with contact lithography. Devices were fabricated and optically characterised including for propagation loss. Two-photon interference was measured within a GaN directional coupler highlighting the suitability for quantum photonics. KYbW is an atypical laser gain material with very high Yb3+ concentrations. The short absorption-length at a wavelength of 980 nm has been used in combination with a high nonlinear polarisability to form an optically-induced waveguide. Mode profiles have been characterised and transient analysis has been carried out at 633 nm. This pump-induced waveguide is used within a laser cavity to create laser action at 1080 nm, using the pumped region of the crystal to define the stability.