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.

Supercontinuum Generation in Microstructured Fibers and Novel Optical Measurement Techniques

Goëry Genty

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 S4 at Helsinki University of Technology (Espoo, Finland) on the 12th of March, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7000-5)   [2481 KB]
Dissertation is also available in print (ISBN 951-22-6999-6)


Over the past few years microstructured fibers have shown potential for many practical applications and permitted significant progress in various domains such as nonlinear optics, medical science or telecommunications as the fabrication process allows for a great flexibility in the design of these fibers. In particular, small core microstructured fibers has proven to be the most efficient way for supercontinuum generation. Supercontinuum is one of the most spectacular outcome of nonlinear optics as it possesses the properties of a laser combined with an ultra-broad bandwidth spanning more than two octaves. The thesis provides a comprehensive review of the different physical mechanisms leading to the generation of these spectra in microstructured fibers.

Dispersion, which reflects the dependence of the refractive index of a material on the frequency of light plays a crucial role in the pulse propagation in optical fibers or components. A novel technique to characterize the anomalous dispersion of small core microstructured fibers using short optical pulses is demonstrated. The method presents several advantages over conventional techniques and relies on the spectral modulation resulting from the evolution of the input pulse into a soliton wave.

As the demand for capacity of optical networks increases, the requirements for the components employed in transmission systems becomes more stringent. In particular, the dispersion of fiber Bragg gratings or thin-film filters commonly employed in the links needs to be accurately evaluated as it may have a strong impact on the overall performance of the system. A novel method for improving the accuracy of dispersion measurements, based on the well-established phase-shift technique widely used in the characterization of optical components, is presented.

The performance of diode lasers can be greatly enhanced with the use of an external cavity configuration. The wavelength tunability of the diode is increased and its linewidth considerably reduced. The behavior of the linewidth of a grating cavity laser is both theoretically and experimentally explored as the oscillation frequency of the laser is varied. Surprisingly, large changes in the linewidth value are observed, which may have an impact in applications requiring lasers with a stable and narrow linewidth.

The fabrication of integrated silica-based optical components performing active functionalities is an exciting prospect for obvious reasons. Poling of silica glass is a very promising technique for the development of this type of component as it allows for the introduction of an effective second-order nonlinearity essential for performing active functions. A new technique based on the inscription of Bragg gratings for measuring the second-order nonlinearity induced by negative thermal poling is demonstrated.

This thesis consists of an overview and of the following 7 publications:

  1. Genty G., Lehtonen M., Ludvigsen H., Broeng J. and Kaivola M., 2002. Spectral broadening of femtosecond pulses into continuum radiation in microstructured fibers. Optics Express 10, number 20, pages 1083-1098. © 2002 Optical Society of America (OSA). By permission.
  2. Lehtonen M., Genty G., Ludvigsen H. and Kaivola M., 2003. Supercontinuum generation in a highly birefringent microstructured fiber. Applied Physics Letters 82, number 14, pages 2197-2199. © 2003 American Institute of Physics. By permission.
  3. Genty G., Ludvigsen H., Hansen K. P. and Kaivola M., Measurement of anomalous dispersion in microstructured fibers using spectral modulation. Optics Express, submitted for publication (accepted in February 2004).
  4. Genty G., Niemi T. and Ludvigsen H., 2002. New method to improve the accuracy of group delay measurements using the phase-shift technique. Optics Communications 204, number 1-6, pages 119-126. © 2002 Elsevier Science. By permission.
  5. Genty G., Gröhn A., Talvitie H., Kaivola M. and Ludvigsen H., 2000. Analysis of the linewidth of a grating-feedback GaAlAs laser. IEEE Journal of Quantum Electronics 36, number 10, pages 1193-1198. © 2000 IEEE. By permission.
  6. Genty G., Kaivola M. and Ludvigsen H., 2002. Measurements of linewidth variations within external-cavity modes of a grating-cavity laser. Optics Communications 203, number 3-6, pages 295-300. © 2002 Elsevier Science. By permission.
  7. Marckmann C. J., Ren Y., Genty G. and Kristensen M., 2002. Strength and symmetry of the third-order nonlinearity during poling of glass waveguides. IEEE Photonics Technology Letters 14, number 9, pages 1294-1296. © 2002 IEEE. By permission.

Errata of publications 1 and 2

Keywords: supercontinuum, microstructured fibers, dispersion measurements, linewidth, external cavity laser, poling

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© 2004 Helsinki University of Technology

Last update 2011-05-26