Characterisation, emulation and by-emitter degradation analysis of high power semiconductor laser diodes

Amuzuvi, Christian Kwaku (2010) Characterisation, emulation and by-emitter degradation analysis of high power semiconductor laser diodes. PhD thesis, University of Nottingham.

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The characterisation, emulation and by-emitter degradation analysis of two types of high power semiconductor laser diodes are presented in this thesis as part of an European Union (EU) project. An attempt is made using an accurate laser simulator called Speclase to learn more about the degradation of high power semiconductor laser diodes. Speclase being a single emitter simulation tool was transformed to model a bar i.e. multiple emitters, which we have named Barlase, through an external control interface written in Labview. The concept of Barlase was based on the fact that a bar is a monolithic block of multiple emitters connected in parallel with each other with a common voltage connected across them.

This tool is capable of performing simulation in different modes of operation (i.e. constant current or constant power). The tool is designed to examine and emulate the degradation processes at both the laser bar and individual emitter levels of operation. It is known that, emitter degradation is faster for emitters within a bar than for identical single emitters due to a combination of packaging-induced strain and current competition between emitters amongst others.

This tool shows clear evidence of the benefits of using by-emitter degradation analysis for gaining detailed understanding of individual emitters operating in a bar and for determining bar degradation mechanisms. The tool complement to the by-emitter analysis, allowing the effects of certain factors that affect the degradation of laser bars to be investigated.

Various intervention measures were taken to improve upon the results of the emulation such as modifying the trap density through local heating and the use of the global thermal solver. The modification of the trap density allowed the acceptance of a spatially variable local trap density distribution that gave a more realistic and accurate simulation of the degradation behaviour. The introduction of the global thermal solver allowed the modelling of thermal cross-talk communication between the emitters, which brings about the frown shaped current/power profiles for the unaged bars (though not as pronounced as in the experiment).

An attempt was made to employ this tool in the emulation of experimentally observed degradation behaviour in a 975 nm, 16 emitter infrared tapered laser bar with each group of 4 mini-array emitters. The laser bar was first calibrated to achieve a reasonable agreement between the experimental P-I curves of unaged emitters assuming identical emitters with the simulated P-I curves. The simulated P-I curve was then used to perform simulations to emulate the degradation of the laser.

The simulated output power profile did not correspond well with the experimental power profile, but a good agreement was realised between the combined output powers of the bar. Better correlation was observed between the experimental and the simulated temperature profiles. This was expected since the experimental temperature was set as input for the heatsink temperature profile. This agreement therefore must not be over-emphasised.

The bar emulation model was enhanced by including a global thermal solver to model the thermal crosstalk between emitters. Emulations using this model showed a clearly defined frown shaped profile in the output current and power profiles but the change was minimal. As the emulation of laser bar degradation has not been attempted before, this work is still at a very early stage. Therefore, further work is needed to achieve better agreement in the output current/power profiles and to better the model.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Larkins, E.C.
Sujecki, S.
Keywords: Semiconductor lasers, diodes, semiconductor, high power lasers
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Electrical and Electronic Engineering
Item ID: 13102
Depositing User: EP, Services
Date Deposited: 14 Feb 2013 14:03
Last Modified: 14 Sep 2016 23:12

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