SIMULATION OF LIGHTWAVE PROPAGATION IN PHOTONIC DEVICES

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Date
2010-06
Authors
MOHD YUSOFF, MOHD HANAPIAH
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Abstract
This dissertation focuses on the simulation of lightwave propagation in planar devices, which include investigation of single mode conditions in rib waveguide, designs of compact silica polarization rotator and splitters, investigation of multiple reflections in photonic crystal (PhC) multimode interference couplers and design of hybrid I-D and 2-D PhC wavelength division multiplexers and channels interleavers. In the design approach, we have adopted semi-analytical technique which allows us to incorporate fast optimization process. Global and local simplex search techniques were extensively used. In the investigation of single mode conditions in rib waveguide and the design of silica polarization rotator, full vectorial film mode matching and finite element methods were used. Propagation analysis in the silica polarization rotator was conducted using finite element eigen-mode expansion method. The quasi 2-D effective index method with eigen mode expansion method was used in the design of compact silica grating waveguide polarization splitter, investigation of multiple reflections in hybrid PhC multi mode interference coupler and design of hybrid PhC wavelength division multiplexers and channel interleavers. Basically all the objectives set in the thesis were achieved. In the investigation of single-mode gallium arsenide/aluminium gallium arsenide (GaAs/AIGaAs) rib waveguide, single-mode formulation for silicon on silica is shown to be equally applicable to GaAs/AIGaAs rib waveguide. A direct method of identifying vertical single-mode cut-off limit is also established by using power confinement factor in the waveguide. In the design and optimization of polarization controlling optical components, compact silica polarization rotator and polarization splitter were investigated. A compact silica polarization rotator of length 790 pm with slanted sidewall angle of 46° was designed. It has an overall conversion efficiency of 99%, with very low crosstalk value of -38 dB and a power transfer efficiency of about 81 %. As for the silica polarization splitter it consisted of a symmetric three channel directional coupler, with intermediate conventional waveguide at the center and two grating waveguides on the outside. a compact design was obtained with an overall length of 340 fJ.m and splitting ratio for the TE and TM polarized signals obtained at 36 dB and 15 dB respectively. Finally in this thesis, optical components based on hybrid I-D and 2-D photonic crystal structure were proposed and investigated. In the investigation of hybrid photonic crystal multimode interference coupler, the effect of multiple reflections is observed to be one of the main reasons why image periodicity in the couple departs from self-imaging principle. And in the proposed wavelength division multiplexer, an efficient design was proposed for 1.3111.55 pm wavelength, with a total device length of 12.33 pm. Its power transfer efficiency is 91 % and extinction ratios of -23.7 dB and -20.8 dB at wavelength l.31 fJ.m and 1.55 fJ.m respectively. For the channel interleaver, an interaction length of 2800 pm give a channel spacing of 0.8 nm wavelength, with output efficiency of 90%.
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Keywords
SIMULATION , DEVICES
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