Thesis

III-nitride LEDs and lasers for underwater wireless optical communications

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Awarding institution
  • University of Strathclyde
Date of award
  • 2023
Thesis identifier
  • T16880
Person Identifier (Local)
  • 201651437
Person Identifier (ORCID)
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • This thesis delves into the deployment of III-nitride micro-LED and laser-based devices for Underwater Wireless Optical Communications (UWOC), an emerging field with considerable potential for underwater data transfer. UWOC offers a compelling solution owing to the vast bandwidth available in the visible spectrum (hundreds of THz), the substantial modulation bandwidth of micro-GaN-based devices (hundreds of MHz), and the underwater “window” characterised by low light attenuation at visible wavelengths. Throughout this thesis, extensive experiments were conducted within a 1.5 m water tank, employing various transmitters (Tx’s) and receivers (Rx’s). The results showcase error-free data transmission rates in the gigabits per second (Gb/s) and megabits per second (Mb/s) range, even in the presence of varying water turbidity levels and attenuation lengths (ALs). Notably, data rates of 4.92 Gb/s and 1.32 Gb/s were achieved using a series-connected micro-LED array of 6 pixels, spanning distances of 1.5 m and 4 m, respectively, and achieved 15 Mb/s over 5.33 ALs. Different underwater conditions, influenced by water turbidity, lead to distinct light attenuation minima underwater. Consequently, I highlight the applicability of wavelength division multiplexing (WDM) in real UWOC scenarios. Using transfer-printed (TP) dual-colour micro-LED arrays, data rates of 200 Mb/s were demonstrated over 8.5 ALs. In most UWOC scenarios, establishing a reliable point-to-point underwater link is challenging due to the unpredictable subsea environment and terrestrial weather conditions. To mitigate this, I introduced the deployment of a diffusing fibre coupled with a laser diode, functioning as a Tx for omnidirectional data transmission (underwater “beacon”). This approach circumvented the alignment restrictions between the Tx and Rx, and data at 5 Mb/s were successfully transmitted over 11.81 ALs, showcasing the robustness of this solution.
Advisor / supervisor
  • Dawson, Martin
Resource Type
DOI

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