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Design of quantum dot electroabsorption modulators for next-generation data and telecommunications​

Mahoney, Joe 2023. Design of quantum dot electroabsorption modulators for next-generation data and telecommunications​. PhD Thesis, Cardiff University.
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The work presented in this thesis investigates the characterisation and optimisation of InAs quantum dots for the purpose of electro-absorption modulators. The modulator is a crucial component of the next generation of integrated circuits using photonics for lower power-consumption and faster data transfer speeds. Initial studies measuring the quantum confined Stark effect in undoped and p-modulation doped InAs QD stacks highlighted an enhanced red-shift and increase in ground state absorption strength in the p-doped structure due to carrier blocking effects. The potential modulation performance was quantified with a standard figure of merit. The figure of merit, defined as the change in absorption for a given voltage swing over the absorption at 1V showed that the p-doped QD stacks had an improvement of as much as four times that of the undoped QD when applying a 9V swing between 21 to 100 degrees Celsius. The same level of improvement was observed in the p-doped sample using a 4V swing at -73 degrees Celsius. This suggests the suitability of p-doped QDs for modulation in high or low temperature environments. Further optimisation of the QD electro-absorption modulator was carried out using various simulation techniques. Schrodinger-Poisson models were used to get initial agreements between the model and the aforementioned measurement results. This model was then used to adjust various aspects of the QD stack to determine the optimum configuration for the modulator. The optimal configuration was found to use 7 QD layers, with a stepped doping profile within the p and n-cladding. This configuration led to an estimated 20 percent improvement in RC-bandwidth whilst having a negligible effect on the QCSE of the stack. This will enable high performance, low power consumption modulators for next generation data-communications. A brief study into using total-internal reflection (TIR) mirrors to couple light from the QD III-V stacks to Silicon waveguides was carried out. The work showed potential for efficient, compact coupling of the light. Simulations produced using 3D FDTD found that the optimised system involved using 45 degree angled reflectors for both the active and passive sections. The effect misalignment of the TIR's in both the x and y-axis on coupling performance showed a reasonable degree of tolerance when considering accuracy of typical fabrication techniques to both the overlap and relative confinement within the QD core compared to the expected TE mode profile.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: InAs Quantum dot Modulator Silicon Photonics p-type modulation doping Quantum confined Stark effect
Funders: EPSRC
Date of First Compliant Deposit: 9 January 2024
Last Modified: 10 Jan 2024 17:24

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