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Title: Waveguide lasers in ytterbium doped tantalum pentoxide for integrated photonic circuits
Author: Aghajani, Armen
ISNI:       0000 0004 5916 9820
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2015
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This thesis investigates ytterbium doped tantalum pentoxide as a material system for realising waveguide lasers on silicon substrate, as a basis to provide the next generation of mass-producible, low-cost planar devices with many interlocking photonic circuits for multi-functionality. Numerical modelling of symmetrical rib waveguide in Ta2O5 was carried out finding an optimum waveguide design for a near-circular mode profile with maximum confinement of light within the core with various etch depths and rib widths. A numerical study investigating the feasibility of integrated Kerr lens elements for future mode-locking was carried out, predicting that a Kerr lens slab with a length of 20 μm with input and out waveguides was able to achieve a 9% modulation depth for input intensity of 6 GW/m2. Thin films were fabricated by RF magnetron sputtering onto a silicon substrate with 2.5 μm silica layer from a powder pressed Yb:Ta2O5 target, with shallow rib waveguides realised using photolithography and ion beam milling. The excited-state lifetime of Yb:Ta2O5 was measured to be 0.25 ± 0.03 ms, and peak emission and absorption cross-sections were determined to be 2.9 ± 0.7×10-20 cm2 and 2.75 ± 0.2×10-20 cm2 respectively, with the fluorescence spectrum giving a broadband emission from 990 nm to 1090 nm. Finally a 10.8 mm long waveguide laser in Ta2O5 doped with ≈ 6.2×1020 Yb atoms/cm3 of ytterbium oxide was demonstrated with a laser cavity formed from a combination of high reflective mirrors with output couplers or reflections from the bare end-facets with Fresnel reflectivity of 12%. In a 5.4 μm wide waveguide, lasing was observed between 1015 nm and 1030 nm when end-pumped with a 977 nm laser diode with the highest output power of 25 mW at a wavelength of 1025 nm with an absorbed pump power of 120 mW for a cavity formed by a high reflector mirror and a bare end-facet at the output. In this case, the absorbed pump power threshold and slope efficiency were measured to be ≈ 30 mW and ≈ 26% respectively. The results presented in this thesis demonstrate that tantalum pentoxide has great potential for mass-producible, integrated optical circuits on silicon using conventional CMOS fabrication technologies.
Supervisor: Wilkinson, James Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available