Fundamentals of laser modelling
Marcenac, Dominique David
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.
Doctor of Philosophy (PhD)
University of Cambridge