Smart Modulator for Line of Sight Communications PhD Project

Lead Research Organisation: Cardiff University
Department Name: School of Physics and Astronomy

Abstract

The main objective is to design a modulator that can be fitted to an unmanned aerial vehicle (UAV) to provide an optical datalink that is fast, secure and robust.
There has been a significant amount of research conducted into free space optical communication systems in the last decade alone and a modulating retro-reflector system is the best solution for a lightweight and efficient modulator. The bulk of this work has focussed on cat's eye retro-reflector (CER) systems, rather than the simpler corner-cube retro-reflector (CCR), due to limitations on size and speed that come with the larger CCR. CER systems are generally less robust than CCR due to high precision required in lens positioning, potential optical aberrations and quite severe limitations on field of view. The primary aim for this project is to utilize modern manufacturing and fabrication techniques to construct a large, pixelated electro absorption CCR modulator.
Advances in manufacturing techniques have created more possibilities in type-II semiconductor systems and these will form the basis for further research, modelling and testing. Antimony based compounds show great potential for application at 1.55um wavelength. Manufacturing and fabrication developments allow for the construction of precise type-II multiple quantum well heterostructures that can be engineered to this specific use. The material system which appears to be the most applicable combines GaSb quantum wells with AlGaSb barriers. This multiple quantum well active region will then be fabricated within a P-I-N diode structure. Type-II materials have strong confinement of electrons and holes with spatial separation, thus generally holes are confined to the well material and electrons to the barrier material. This can lead to very large shifts in the optical absorption of the material when under an electrical bias. This is ideal for providing a high extinction ratio.
Furthermore, by pixelating this material, high speed data transmission can be achieved without compromising the field of view of the retro-reflector. Another aim for the project is to create 'smart' pixels that will only be active upon incident light of wavelength 1.55um. This will greatly reduce the overall power consumption of the modulator. Other considerations to optimise the system will be the temperature stability of the material, contrast ratio and insertion loss.
The intention is that the PhD will also characterise the performance of as-grown structures.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R511882/1 01/10/2017 30/09/2022
2036167 Studentship EP/R511882/1 01/04/2018 31/03/2022 Benjamin Maglio