Optimising Output Characteristics of (edgeemitting) Light Emitting Diodes (eeLEDs)

  • Xizi Chen

Student thesis: Doctoral ThesisMPhil

Abstract

Stripe contact (edgeemitting)LEDs have been found to be suitable for many applications in present day optical/photonics devices and systems. Polarised light (i.e., light with dominantly a single polarisation direction) is required for various applications. Semiconductor LASERs generate polarized light but such sources may not be suitable due to other reasons such as the ‘speckle’ effect that occurs due to the highly coherent LASER light; also, if the source is to be part of a monolithically integrated optical circuit it will be expensive to produce the two reflective planes needed for the LASER to operate. Unlike semiconductor Lasers, however, stripecontact TM ASE, and yet be easy to fabricate.Rays and Rate Equations analysis is used to model the device. A computationally efficient model for stripe contact semiconductor optical devices is designed and used to obtain design guidelines for the “V”geometrydevice, which is taking benefits and advantages to design a polarisationselectiveeeLEDdevice. Simulation results from the model are shown.edgeemittingLEDs in bulk active layer semiconductor material tend to produce nearly unpolarised light. LED sources but with polarised output are attractive for various applications such as in Optical Coherence Tomography (OCT).The objective of this project is to design a simple, inexpensive device structure to achieve polarisation enhanced output by using stripecontactedgeemittingLEDs in bulk active layer semiconductor material, with multilayer, DoubleHeterostructure(DH), as commonly used for semiconductor Lasers and LEDs. As is well known light in the material is primarily generated by spontaneous emission. If the material is ‘pumped’ sufficiently then there will be net stimulated emission which corresponds to having optical gain; in that case the spontaneously emitted light will experience optical emission as it progresses through the material resulting in Amplified Spontaneous Emission (ASE). In this condition of operation the eeLEDis often referred to as the Superluminescent LED (SLED). It is also well known that in bulk active layer semiconductors spontaneous emission occurs uniformly in all polarisations and that the material gain is also polarisation independent. Hence the generated ASE is equally distributed in TE & TM polarisations. The challenge, therefore, is to find a scheme which that would generate dominantly TE or dominantly
Date of Award1 Dec 2009
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorFederica Causa (Supervisor) & Jayanta Sarma (Supervisor)

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