Electroabsorption modulators and laser diodes for free space optics and on-chip applications

Maglio, Benjamin Cosimo 2022. Electroabsorption modulators and laser diodes for free space optics and on-chip applications. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Theoretical predictions corroborated with experimental observations of III-V compound semiconductor normal-incidence electroabsorption modulators and edge-coupled modulators and lasers are described. Application of such devices to free space optical communication and photonic integrated circuits respectively are considered. These are of interest collectively for extending present capabilities in wireless and on-chip communication techniques. Free space optical communication offers a high-speed, secure alternative to wireless radio frequency communication, without spectrum licensing nor excessive infrastructure requirements. Laser transceivers, although presently in operation in ground-satellite and satellite-satellite communication cannot be supported in miniaturized systems due to size, weight, and power constraints. Quantum well modulating retroreflectors offer an alternative, though few studies have considered optimization of the epi-structures for this particular application. Monolithic integration of III-V alloys on silicon substrates is currently being explored as a method of increasing on-chip optoelectronic integration. Active photonic components such as lasers and modulators are required. Quantum dot lasers offer low threshold current densities, temperature insensitivity, and resilience to dislocation induced degradation from lattice mismatch between III-V alloys and silicon. Nevertheless, doping strategies (p-type modulation and n-type direct) are required to correct carrier occupation imbalances and enhance performance. A modelling routine for calculating absorption in quantum well and dot heterostructures is corroborated with experimental measurements. Measurement validated predictions of the quantum confined Stark effect in quantum wells are used to propose novel epi-structures, for application to retroreflective free space optics. Expected improvements in the extinction ratio and insertion loss are reported. Predictions of gain and the quantum confined Stark effect in InAs quantum dots show potential improvements through p-type modulation doping in lasers and modulators operating at 1310nm. Calculations of n-type direct doped InAs quantum dots highlight possible mechanisms of enhanced laser operation, with further enhancements using both p-type modulation and n-type direct doping, so-called “co-doped” quantum dot devices.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Quantum wells, quantum dots, electroabsorption, laser, modulator, quantum confined Stark effect, gain, free space communication, free space optics, photonic integration, photonic integrated circuits, modulation doping, direct doping, co-doping, dual-doping, III-V compound semiconductors, monolithic integration
Funders:	EPSRC, AIRBUS
Date of First Compliant Deposit:	17 November 2022
Last Modified:	17 Nov 2023 02:30
URI:	https://orca.cardiff.ac.uk/id/eprint/154270

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