Hybrid GaN-based optoelectronics for visible light communications

  • Joao Miguel Melo Santos

Student thesis: Doctoral Thesis

Abstract

Development of light-emitting diode technology is driven mainly by the need for efficient solid-state lighting, but it is also creating opportunities for new applications such as visible light communications (VLC). Here, the solid-state visible light sources are used to transmit data with the added requirement of a short excited-state lifetime so that sources can be modulated at high speed. This research focuses on hybrid optical sources for visible light communications with an emphasis on novel formats of colour-converters for multi-wavelength photoluminescence as well as white-light generation. Such converters include red and green colloidal quantum dots, the organic semiconductor BBEHPV andII-VI / III-V epitaxial structures.Solution-processable and environmentally stable polymeric films based on red and green colloidal quantum dots are demonstrated. Modulation bandwidth up to 24 MHz, photoluminescence quantum yields up to 61% and peak emission tunability across the visible spectrum makes these materials interesting as colour-converters for VLC. Free-space data transmission was demonstrated in this case with data rates up to 400 Mbit/s and 500 Mbit/s using 2-PAM modulation scheme for green and red quantum dots, respectively.Hybrid sources consisting of 450nm InGaN LEDs with capillary-bonded micron-thick ZnCdSe/ZnCdMgSe multi-quantum-well colour-converting membranes with peak emission at 540 nm are reported. After processing, the membrane was capillary bonded onto the sapphire side of the μLED resulting in a maximum converted average power of 37 μW. The -3dB optical modulation bandwidth of the bare LED, hybrid device and II-VI were 79 MHz, 51 MHz and 145 MHz, respectively.Visible light communication using both InGaN LEDs and a InGaN laser diode, down-converted by a red-emitting AlInGaP multi-quantum-well nanomembrane are also reported. Similarly to the previous devices, the AlInGaP nanomembrane was bonded onto the μLED array. For the down-converted laser diode approach, the nanomembrane can be sandwiched between a sapphire lens and optionally onto a distributed feedback reflector. The down-converter structure is remotely excited by the laser diode. Data transmission up to 870 Mb/s using M-PAM andOFDM modulation schemes is demonstrated for the μLED integrated nanomembrane. ODFM transmission at 1.2Gb/s is achieved for the laser diode pumped sample.
Date of Award1 Oct 2015
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorMartin Dawson (Supervisor) & Robert Martin (Supervisor)

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