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Title: Measuring small values of internal optical mode loss in laser diodes
Author: Pascoe, Robert
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2016
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Improvements in fabrication processes have yielded a steady reduction in the Internal Optical Mode Loss, αᵢ , of semiconductor laser devices in recent decades. Hence, uncertainty in the determination of αᵢ (roughly ±1.0 cm⁻¹) has become insufficient. The aim of this work is to reduce the uncertainty within this method to ±0.1 cm⁻¹. The modulated multisection method - in which the absorbing length within a device is alternated rapidly compared with the timescales of systemic drift - was introduced to combat errors associated with such drifts in the standard method. Experimental data demonstrated that systemic drift correlates with substantial systematic errors and that these errors are made negligible by application of this modulated method. A systematic error - due to divergence within the waveguide of broad area devices - of 3.2 cm⁻¹ was identified and a method for its correction was developed. Error associated with injection efficiency of the multisection contact geometry was identified. This error is sufficiently small for drive currents greater than 22 mA at device temperatures of 300 Kelvin and greater. By characterising measurement precision, experimental conditions were established in which drift-associated error and imprecision were small with respect to the project uncertainty aim. In optimised conditions, repeated measurements of optical loss below the absorption edge had an associated average deviation of ±0.017 cm⁻¹. This low uncertainty was applied to a systematic investigation of optical loss spectra in an InP Quantum Dot device as a function of device temperature. The temperature dependence of αᵢ was characterised with an uncertainty (approximately ±0.05 cm⁻¹) that would be impossible using conventional methods. A feature with a peak magnitude of 0.2 cm⁻¹ was identifi�ed and associated with the occurrence of very large quantum dots. The improved uncertainty demonstrated in this project presents an opportunity for more detailed study of αᵢ .
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics