The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Modeling Transmitters, Amplifiers and Nonlinear Circuits for the Next Generation Optical Networks

Jani Oksanen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium TU1 at Helsinki University of Technology (Espoo, Finland) on the 13th of December, 2006, at 12 noon.

Overview in PDF format (ISBN 951-22-8305-0)   [1025 KB]
Dissertation is also available in print (ISBN 951-22-8304-2)

Abstract

In the current optical networks nonlinear interaction of optical signals with matter is often a nuisance in the operation of amplifiers, optical fibers and other linear devices. The next generation optical networks, on the other hand, need nonlinear optical components with signal processing capabilities. To create components that meet the demands of tomorrow, it is necessary to understand, control, exploit and enhance the available weak nonlinearities.

In this thesis the dynamic properties of quantum dot lasers and linear optical amplifiers are investigated. Additionally, optical memories and logic ports exploiting a new type of nonlinearity based on gain clamped optical amplifiers and interferometers are proposed. The properties of quantum dot lasers are studied by using a parametrized model for the bandstructure of the dots and the surrounding layers. The model is used to calculate the absorption spectrum, refractive index and other properties of the lasers at different excitation levels.

The properties of linear optical amplifiers, conventional gain clamped amplifiers and semiconductor optical amplifiers are described by a stochastic traveling wave rate equation model. The gain clamped optical amplifiers used together with interferometers are shown to provide a new fast nonlinearity, which can be used to construct coherent nonlinear optical circuits, including optical regenerators, flip-flop memories and logic gates.

The speed of the nonlinear devices presented in this thesis is limited by the modulation response of the gain clamped optical amplifiers above the laser threshold in the regime where there always is a large photon population in the laser mode. The speed may therefore reach values in excess of 100 GHz, or even higher values if the level of optical technologies evolves closer to the level of silicon technology. In principle the flip-flop structure developed in this thesis is suitable for integration.

This thesis consists of an overview and of the following 6 publications:

  1. J. Oksanen and J. Tulkki, Linewidth enhancement factor and chirp in quantum dot lasers, Journal of Applied Physics 94, pp. 1983-1989 (2003). © 2003 American Institute of Physics. By permission.
  2. J. Oksanen and J. Tulkki, On crosstalk and noise in an optical amplifier with gain clamping by vertical laser field, Journal of Lightwave Technology 21, pp. 1914-1919 (2003). © 2003 IEEE. By permission.
  3. J. Oksanen and J. Tulkki, Fast 2R regeneration by coherent laser amplifiers, IEEE Journal of Quantum Electronics 41, pp. 1075-1082 (2005). © 2005 IEEE. By permission.
  4. J. Oksanen and J. Tulkki, Fast coherent all-optical flip-flop memory, Applied Physics Letters 88, pp. 181118-1-181118-3 (2006). © 2006 American Institute of Physics. By permission.
  5. J. Oksanen and J. Tulkki, Fast all-optical flip-flop memory exploiting the electric field nonlinearity of coherent laser amplifiers, IEEE Journal of Quantum Electronics 42, pp. 509-516 (2006). © 2006 IEEE. By permission.
  6. J. Oksanen and J. Tulkki, Coherent optical logic by laser amplifiers with feedback, Journal of Lightwave Technology 24 (2006), accepted for publication. © 2006 IEEE. By permission.

Keywords: semiconductor lasers and amplifiers, optical memories, nonlinear optical components

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© 2006 Helsinki University of Technology

Last update 2011-05-26