Fundamentals of laser modelling
Authors
Marcenac, Dominique David
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Description
This dissertation presents a new "time domain model" to design and invent advanced laser
diodes for optical fibre communications. It is securely based on quantum theory. This
new model describes the optical fields in the time domain, allowing it to simulate large
signal responses for Fabry-Perot and Distributed Feedback (DFB) lasers, in addition to
calculating the laser linewidth and the Relative Intensity Noise (RIN). The quantum basis
for this time domain model justifies the noise treatment of some other recent semiclassical
laser models. However, it indicates that these models are incapable of simulating lasers
with sub-Poissonian photon statistics (squeezing). The time domain model is implemented
with new algorithm, which uses a transfer matrix method to simulate DFB lasers with
much greater accuracy than previously.
New applications for two numerical methods are then introduced, providing tools to
study the spectra of lasers simulated by the time domain model. Firstly, the Wigner
distribution is shown to be the time-frequency representation, for modulated optical laser
signals, which has the highest resolution. Secondly, the maximum entropy method of
spectral estimation is shown to reduce noise and windowing effects, thus allowing small
features in the spectra of simulated lasers to be displayed, without being obscured as with
Fourier transform-based methods.
Comparisons of the time domain model are carried out. The first detailed comparison
of simulated multimode DFB lasers, under large signal modulation, is performed: the time
domain model and the Power Matrix Model show excellent agreement, increasing confidence
in the validity of both these models. A comparison of the time domain model, with
simulation results from the European COST laser workshop, further increases confidence
in the accuracy of the algorithm. Finally, the first detailed simulation of self-pulsating
DFB lasers is carried out. Its agreement with reported experimental results shows the
potential and power of the present model.
The time domain model is then extended, using a novel formalism, to allow the simulation
of intensity squeezed light: simulations for different laser structures are carried out.
A new analytic formula for the RIN in Fabry-Perot lasers is derived. Predictions of the
model are that low facet refiectivities and DFB structures make squeezing difficult, but
that lasers with a Distributed Bragg reflector are promising.
Finally, a new concept of spectrometer, which uses computer interpretation of twopinhole
diffraction patterns, is demonstrated experimentally. It uses the maximum entropy
method to resolve the spectrum of a two moded DFB laser, and is potentially a cheaper
and more robust alternative to commercial spectrometers which use diffraction gratings.
Date
Advisors
Keywords
Qualification
Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge