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Aalto

Photonic Crystal Waveguides for Silicon Integrated Optics

Antti Säynätjoki

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Electronics, Communications and Automation for public examination and debate in Auditorium AS2 at Helsinki University of Technology (Espoo, Finland) on the 23rd of May, 2008, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9384-1)   [1260 KB]
Dissertation is also available in print (ISBN 978-951-22-9383-4)

Abstract

This thesis reports experimental and theoretical studies on photonic crystal waveguides in the silicon-on-insulator platform. The work presents a new variant of Fabry-Pérot method for waveguide characterization. In this method, the reflectivity at the ends of the waveguide under study is enhanced by lithographically patterned mirrors. The thesis also studies a new type of photonic crystal, where the planar photonic crystal lattice is defined with ring-shaped holes (RPhC). By choosing a suitable ring parameter, the RPhC waveguide exhibits low and quasi constant group velocity over a wavelength range of several nanometers. The effect of the modefield width on the dispersion properties of the waveguide is discussed. A short and efficient coupler between the slow mode in an RPhC waveguide and the mode in a conventional silicon waveguide is designed. A relationship between coupling efficiency and the phase match between the coupler mode and the slow mode is observed. These results and observations are important in designing slow-light devices for all-optical signal processing and communication systems. Use of RPhC waveguides in other applications, particularly in biosensing, is also studied. An electron beam writing method that minimizes the writing time of the RPhC lattice is presented. The experimental results on an RPhC waveguide are the first reported for such structure and they show slowdown factors of up to 22 for the group velocity, compared to the group velocity in vacuum.

This thesis consists of an overview and of the following 5 publications:

  1. A. Säynätjoki, M. Mulot, S. Arpiainen, J. Ahopelto, and H. Lipsanen. 2006. Characterization of photonic crystal waveguides using Fabry–Perot resonances. Journal of Optics A: Pure and Applied Optics, volume 8, pages S502-S506.
  2. M. Mulot, A. Säynätjoki, S. Arpiainen, H. Lipsanen, and J. Ahopelto. 2007. Slow light propagation in photonic crystal waveguides with ring-shaped holes. Journal of Optics A: Pure and Applied Optics, volume 9, pages S415-S418.
  3. A. Säynätjoki, M. Mulot, J. Ahopelto, and H. Lipsanen. 2007. Dispersion engineering of photonic crystal waveguides with ring-shaped holes. Optics Express, volume 15, number 13, pages 8323-8328. © 2007 Optical Society of America (OSA). By permission.
  4. A. Säynätjoki, M. Mulot, K. Vynck, D. Cassagne, J. Ahopelto, and H. Lipsanen. 2008. Properties, applications and fabrication of photonic crystals with ring-shaped holes in silicon-on-insulator. Photonics and Nanostructures – Fundamentals and Applications, volume 6, pages 42-46. © 2008 Elsevier Science. By permission.
  5. A. Säynätjoki, K. Vynck, M. Mulot, D. Cassagne, J. Ahopelto, and H. Lipsanen. 2008. Efficient light coupling into a photonic crystal waveguide with flatband slow mode. Photonics and Nanostructures – Fundamentals and Applications, in press, doi:10.1016/j.photonics.2008.03.001. © 2008 Elsevier Science. By permission.

Keywords: photonic crystals, optical waveguides, photonic integrated circuits, dispersion, silicon-on-insulator

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© 2008 Helsinki University of Technology

Last update 2011-05-26