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.

Fabrication of Microphotonic Waveguide Components on Silicon

Kimmo Solehmainen

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 20th of April, 2007, at 12 o'clock noon.

Overview in PDF format (ISBN 978-951-38-7000-3)   [6872 KB]
VTT Publications 630, ISSN 1455-0849

Dissertation is also available in print (ISBN 978-951-38-6999-1)
Copyright © 2007 VTT Technical Research Centre of Finland
VTT Publications 630, ISSN 1235-0621


This thesis reports on the development of silicon-based microphotonic waveguide components, which are targeted in future optical telecommunication networks. The aim of the work was to develop the fabrication of silicon microphotonics using standard clean room processes which enable high volume production. The waveguide processing was done using photolithography and etching. The default waveguide structure was the rib-type, with the waveguide thickness varying from 2 to 10 µm. Most of the work was done with silicon-on-insulator (SOI) wafers, in which the waveguide core was formed of silicon. However, the erbium-doped waveguides were realised using aluminium oxide grown with atomic layer deposition. In the multi-step processing, the basic SOI rib waveguide structure was provided with additional trenches and steps, which offers more flexibility to the realisation of photonic integrated circuits.

The experimental results included the low propagation loss of 0.13 and 0.35 dB/cm for SOI waveguides with 9 and 4 µm thicknesses, respectively. The first demonstration of adiabatic couplers in SOI resulted in optical loss of 0.5 dB/coupler and a broad spectral range. An arrayed waveguide grating showed a total loss of 5.5 dB. The work with SOI waveguides resulted also in a significant reduction of bending loss when using multi-step processing. In addition, a SOI waveguide mirror exhibited optical loss below 1 dB/90° and a vertical taper component between 10 and 4 µm thick waveguides had a loss of 0.7 dB. A converter between a rib and a strip SOI waveguides showed a negligible loss of 0.07 dB. In the Er-doped Al2O3 waveguides a strong Er-induced absorption was measured. This indicates potential for amplification applications, once a more uniform Er doping profile is achieved.

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

  1. K. Solehmainen, T. Aalto, J. Dekker, M. Kapulainen, M. Harjanne, K. Kukli, P. Heimala, K. Kolari, and M. Leskelä, Dry-etched silicon-on-insulator waveguides with low propagation and fiber-coupling losses, Journal of Lightwave Technology, Vol. 23, No. 11, pp. 3875-3880, 2005. © 2005 IEEE. By permission.
  2. K. Solehmainen, T. Aalto, J. Dekker, M. Kapulainen, M. Harjanne, and P. Heimala, Development of multi-step processing in silicon-on-insulator for optical waveguide applications, Journal of Optics A: Pure and Applied Optics, Vol. 8, No. 7, pp. S455-S460, 2006. © 2006 Institute of Physics Publishing. By permission.
  3. K. Solehmainen, M. Kapulainen, M. Harjanne, and T. Aalto, Adiabatic and multimode interference couplers on silicon-on-insulator, IEEE Photonics Technology Letters, Vol. 18, No. 21, pp. 2287-2289, 2006. © 2006 IEEE. By permission.
  4. G. Przyrembel, B. Kuhlow, K. Solehmainen, T. Aalto, P. Heimala, and L. Moerl, AWG based DWDM multiplexers combined with attenuators on SOI, Proceedings of the 32nd European Conference on Optical Communication (ECOC 2006), paper We3.P.40, 2 p., September 2006, Cannes, France. © 2006 La Société de l'Electricité et de l'Electronique et les technologies de l'information et de la communication (SEE). By permission.
  5. T. Aalto, K. Solehmainen, M. Harjanne, M. Kapulainen, and P. Heimala, Low-loss converters between optical silicon waveguides of different sizes and types, IEEE Photonics Technology Letters, Vol. 18, No. 5, pp. 709-711, 2006. © 2006 IEEE. By permission.
  6. K. Solehmainen, M. Kapulainen, P. Heimala, and K. Polamo, Erbium-doped waveguides fabricated with atomic layer deposition method, IEEE Photonics Technology Letters, Vol. 16, No. 1, pp. 194-196, 2004. © 2004 IEEE. By permission.

Keywords: inductively coupled plasma etching, integrated optics, microphotonics, optical device fabrication, optical losses, silicon-on-insulator waveguides, waveguide bends

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© 2007 Helsinki University of Technology

Last update 2011-05-26