Investigation of nonlinear processes and device designs applicable to the creation of a compact, broadly tunable laser based on a tantalum pentoxide planar lightwave circuit platform

摘要

Nonlinear photonic devices utilize phase-matched parametric wavelength conversion in a nonlinear medium to create a widely tunable pulsed laser source. Currently most of nonlinear lasers are based on bulk optics or photonic fibres. Lasers based on bulk optics utilizing nonlinear crystals in conjunction with high intensity pulsed laser pumps, which are very powerful and often used as pump lasers for nonlinear experiments, but they are very large in size, and expensive to purchase. Although marketed as ‘turn key’ solutions, they require expert alignment, are difficult to use and are not suitable for deployment to environments other than environmentally stable optics labs. The photonic crystal fibres based lasers are very useful for optical communication purposes, but they are not as powerful as the bulk optics lasers and hard to be integrated with semiconductor devices due to their cylindrical structures. This thesis investigates the viability of creating an alternative widely tunable laser in a planar lightwave circuit (PLC) format. The overall aim of this project was to investigate the viability of creating a functional on-chip tunable laser, develop some of the key components, the base technologies required to do this job.Required sub-components include efficient: supercontinuum generation, harmonic generation, and parametric wavelength conversion devices, all of which should ideally be powered by a compact, low cost, solid state pump source. To complicate matters further, requirements for parametric conversion include precise phase-matching of up to four participating beams, each of which may have a different wavelength. Furthermore, to provide broadband tunability, phase-matching condition must be maintained as the wavelengths of all participating beams are tuned. Hence the parametric conversion must take place in a device supporting ‘variable phasematching’.One of the key sub-components of a broadband tunable laser is a supercontinuum (SC) source. Supercontinuum (SC) generation is a nonlinear optical phenomenon that generates a spectrum across a wide range of frequencies. The SC component is itself very useful for many optical applications including: optical coherence tomography(OCT), frequency metrology, pulse compression, wavelength division multiplexing (WDM) and hence, attracts great research interests. Up to now, about 99% of the SC devices are based on optical fibres or nonlinear crystals. This thesis starts an in depth investigation of the generation of SC in planar waveguides reviewing the key linear and nonlinear optical effects associated with SC generation, making comparisons to prior literature.All devices studied in this thesis were based on rib and ridge waveguides consisting of a tantalum pentoxide ( 2 5 Ta O ) core and silicon dioxide ( 2 SiO ) cladding materials. The simulated dispersion properties of such planar waveguides are presented. The experimental results on frequency tripling, SC generation and parametric effects along the waveguides are demonstrated. Further optimization procedures and potential applications are suggested subject to the current results and the nonlinear properties obtained from the 2 5 Ta O waveguide samples.