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Title: Quantum dot lasers and modulators for optical telecommunications
Author: Chu, Y.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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In this thesis, spectral effects of QD lasers including injection locking of QD lasers and their linewidth enhancement factor measurement are first studied. Experimental studies show that the QD laser performance can be greatly improved by injection locking. Linewidth enhancement factor measurement reveals that chirp of QD lasers under moderate bias is inherently smaller than typical QW lasers. Large alpha factor values up to 6.3 induced by the excited-state carrier effect are observed under high bias current operation. In addition, a novel optical injection gain-tuning method is invented for easy implementation of linewidth enhancement factor measurement. In addition, applications of QD lasers for multi-mode fibre (MMF) transmission are investigated. Beam profiling is employed to achieve spot size reduction and single transverse mode operation of a 980 nm QD vertical-cavity surface-emitting laser (VCSEL). Furthermore, error-free operation of 10 Gb/s data transmission over 300 m of MMF is demonstrated using the post-processed QD VCSEL. Finally, applications of QD Febry-Perot (FP) lasers and modulators for single mode fibre (SMF) transmission are demonstrated. A directly modulated QD laser at 10 Gb/s is applied for both SMF and MMF data transmission. Error-free transmission is achieved over 4 km of SMF and 300 m of MMF. The potential application of 2.5 Gb/s QD electro-absorption modulator (EAM) is investigated. Substantial quantum-confined Stark shifts (QCSE) are observed in QD material subject to reverse bias. Based on the QCSE observed, a high speed QD EAM is mounted and demonstrated for 2.5 Gb/s error-free back-to-back modulation. This is the first time that the QD material has been shown to be applicable for semiconductor EAMs, and QD EAMs have the potential advantages of low insertion loss, high saturation power and short response time.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available