Tantalum pentoxide integrated photonic devices

Abstract

This thesis investigates tantalum pentoxide (Ta₂O₅) as a material for realising integrated photonic devices on a silicon platform, as a basis for realising photonics integrated circuits with multiple functionalities on a single monolithic chip. In particular, achieving gain and lasing, and electro-optic functionalities were studied. To further investigate the integration of these functionalities onto a silicon platform, a grating-assisted coupler was explored.

Ta₂O₅ thin films were deposited on oxidised silicon wafer using RF sputtering and waveguides were realised using lithography and ion beam milling. An optimisation of the etching process to reduce waveguide sidewall roughness was performed.

Thulium-doped Ta₂O₅ was investigated to provide gain and lasing at around 2 μm by pumping at around 790 nm. With a thulium-doping concentration of 9x10²⁰ ions/cm³, the highest peak photoluminescence power and lifetime was achieved with sample annealed at 650 °C for 12 hours. The excited-state lifetime of this sample was 477 ± 40 μs. Emission centred around 1.85 μm and a high emission cross-section of 2.99x10^-20 cm² was attained. The absorption cross-section were 8.05x10^-21 cm² at 792 nm and 1.09x10^-20 cm² at a wavelength of 1756 nm.

Second-order nonlinearity was achieved in Ta₂O₅ by thermal poling, 0.46 and 0.34 pm/V was achieved with sodium-doped and undoped Ta₂O₅ respectively. The effect of sodium-doping and annealing on the induced second-order nonlinearity was studied.

A grating-assisted coupler was designed and fabricated to couple between 750 by 750 nm Ta₂O₅ and a 400 by 250 nm Si channel waveguides. Simulations show that a grating period of 2.361 μm was required for coupling to occur.

The results show that tantalum pentoxide is a promising medium for realising integrated lasers and amplifiers, electro-optic applications on a silicon platform.

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Identifiers

ORCID for Amy Sen Kay Tong: orcid.org/0000-0002-2026-2062

ORCID for James S. Wilkinson: orcid.org/0000-0003-4712-1697

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