Date of Award

2023

Thesis Type

PhD

Document Type

Thesis

Divisions

Faculty of Science

Department

Department of Physics

Institution

Universiti Malaya

Abstract

This thesis aims to study the phase change characteristic of Ge2Sb2Se4Te1 (GSST) using 1550 nm pulsed laser as excitation source, and to explore its potential in multilevel nonvolatile photonic memory application. Firstly, the amorphous to crystalline state phase transition of GSST using 1550 nm pulsed laser as optical excitation source is investigated. The threshold laser pulse duration to achieve crystallization are 190 ns, 140 ns, 100 ns and 70 ns for laser intensities of 0.46 GW/cm2, 0.61 GW/cm2, 0.76 GW/cm2 and 0.85 GW/cm2, respectively. However, it is found that the phase change tolerance of GSST is very stringent (phase transition window is in few ns range) when using 1550 nm pulsed laser as optical stimuli due to its high transparency and this wavelength and large contrast between its amorphous and crystalline states. Thus, a second optical material, graphene oxide (GO) is used to enhance the phase change tolerance of GSST, owing to its polarization dependent absorption and large photothermal effect. The complex refractive index of GO is first determined using a novel optical characterization technique, and the values are measured to be 1.71+0.09i and 1.58+0.05i for TE- and TM-polarized light, respectively. Then, GO is integrated with GSST using sequential coating process. The optical phase change characteristics of GSST-GO duo-layer is studied and it is found that the phase change tolerance of the GSST-GO duo-layer is significantly improved compared to GSST layer only. Finally, the GSST-GO duo-layer is integrated on both planar optical waveguide and standard single mode optical fibre to study their performance as all-optical multilevel nonvolatile photonic memory. The maximum achievable readout contrast for GSST-GO functionalized planar optical waveguide and single mode fibre are found to be 25 % and 32 %, respectively. Multilevel photonic switching has also been achieved using these hybrid waveguide structures, which opens up the potential of using these structures as basic building blocks for high level optical signal processing.

Initial

khm

Additional Information

Thesis (PhD) - Faculty of Science, Universiti Malaya, 2023.

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