Visible light communication is a developing technology making use of light-emitting diodes (LEDs) and laser diodes in the visible spectrum for communication purposes. This thesis looks at the use of gallium nitride (GaN) devices for high speed measurements in free space, through fibre and underwater. Micro-pixellated LEDs (micro-LEDs) have been used as a source for these measurements and the different ways to drive these devices is explored. LEDs are limited in how fast they can be driven and therefore laser diodes are also considered for these high speed measurements. The frequency responses of such devices are measured and data transmission experiments are conducted.However, these devices can be used for more than just free-space communication. Laser diodes are much more powerful than their LED counterparts and can be modulated much faster making them ideal for fibre communications and underwater communications, where eye-safety is not an issue. By using these devices, a study of step-index plastic optical fibre (SI-POF) and multi-core fibre is carried out, analysing their dispersion properties and transmission characteristics.Further high speed measurements were conducted under the water as the need to communicate with unmanned vehicles under the ocean continues to be an important issue. Many security and defence companies and oil and gas industries are interested in this technology for that purpose, as the current setup is complex, expensive and limited in bandwidth.High modulation bandwidths and high data transmission rates are achieved, with some of the leading results in the field presented here. These results highlight the importance of the topic of visible light communication and show the attractiveness of using these visible GaN devices for this purpose.
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High speed systems using GaN visible LEDs and laser diodes
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