Analysis and optimization of photonic crystal components for optical telecommunications

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Doctoral thesis (article-based)
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70, [app]
Report / Helsinki University of Technology, Laboratory of Computational Engineering. B, 51
Photonic crystals are periodic dielectric structures where the period is of the same order of magnitude than the wavelength of light. As a result of interference, there exist band gaps for light, i.e., light of certain range of frequencies is not allowed to exist inside the photonic crystal, which can be used to control and confine light. In this thesis, photonic crystals were studied with computer simulations and concepts of new components for optical telecommunications were proposed. An all-optical switch, based on the properties of a Kerr-nonlinear one-dimensional photonic crystal, was investigated. The band gap was shown to change as a function of light intensity inside the nonlinear photonic crystal. Thus, it performs an all-optical switching function, where one signal can be dynamically reflected depending on another signal. Two parallel waveguides in a two-dimensional photonic crystal were considered. In general, adjacent waveguides are coupled and a light pulse traveling in one waveguide will oscillate between the waveguides. We found complete decoupling between the waveguides for certain geometries. This can be utilized in integrated optics when cross-talk between contiguous channels is not desired. The band gap of a thin slab of two-dimensional photonic crystal was shown to depend strongly on the material on top/below the slab, and thus a new type of waveguide was proposed. Instead of the conventional defect waveguide, a waveguide can be made by patterning the photonic crystal slab by a suitable material. The waveguiding was shown to be due to band gap difference in some cases and due to average refractive index difference in others. Microstructure and dual-core fibers were optimized to achieve large negative dispersion and large mode area simultaneously. Negative dispersion fibers are needed for dispersion compensation and pulse compression. They usually have small mode areas and are highly nonlinear, which is a problem for high-intensity applications. This can be avoided with the fiber geometries proposed in this thesis. The effect of the wavelength dependence of gain, nonlinearity and dispersion to the propagation of short pulses in high-gain efficiency photonic crystal fiber amplifiers was studied. It resulted in asymmetric spectrum and chirp, and reduction of the pulse broadening. Wavelength dependence of the nonlinearity was demonstrated to have the most effect, compared to that of dispersion or gain.
all-optical switching, photonic crystal waveguides, dispersion compensation, photonic crystal fiber amplifier
Other note
  • A. Huttunen and P. Törmä, Band structures for nonlinear photonic crystals, Journal of Applied Physics 91, 3988-3991 (2002). [article1.pdf] © 2002 American Institute of Physics. By permission.
  • T. Koponen, A. Huttunen, and P. Törmä, Conditions for waveguide decoupling in square-lattice photonic crystals, Journal of Applied Physics 96, 4039-4041 (2004). [article2.pdf] © 2004 American Institute of Physics. By permission.
  • A. Huttunen, K. Varis, K. Kataja, J. Aikio, and P. Törmä, Guiding and reflecting light by boundary material, Optics Communications 244, 147-152 (2005). [article3.pdf] © 2005 Elsevier Science. By permission.
  • A. Huttunen and P. Törmä, Optimization of dual-core and microstructure fiber geometries for dispersion compensation and large mode area, Optics Express 13, 627-635 (2005). [article4.pdf] © 2005 Optical Society of America (OSA). By permission.
  • A. Huttunen and P. Törmä, Effect of wavelength dependence of nonlinearity, gain, and dispersion in photonic crystal fiber amplifiers, Optics Express 13, 4286-4295 (2005). [article5.pdf] © 2005 Optical Society of America (OSA). By permission.
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