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Ultrasmall Si-nanowire-based polarization rotator
KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
2008 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, Vol. 25, no 5, 747-753 p.Article in journal (Refereed) Published
Abstract [en]

A polarization rotator based on asymmetrical Si nanowires is presented and optimized for high polarization rotation efficiency (almost 100%). The present polarization rotator has a very small conversion length (similar to 10 mu m) and consequently becomes very compact. The analysis of the wavelength dependence shows the present polarization rotator has a broad bandwidth (similar to 120 nm) for high conversion efficiency (> 97%). The tolerance to various fabrication errors is also numerically studied. To compensate the fabrication error, a post-compensation method is introduced by modifying the refractive index of the up-cladding. (c) 2008 Optical Society of America.

Place, publisher, year, edition, pages
2008. Vol. 25, no 5, 747-753 p.
Keyword [en]
URN: urn:nbn:se:kth:diva-13934ISI: 000256323200007OAI: diva2:328360
QC20100702Available from: 2010-07-02 Created: 2010-07-02 Last updated: 2012-03-19Bibliographically approved
In thesis
1. Investigation of New Concepts and Solutions for Silicon Nanophotonics
Open this publication in new window or tab >>Investigation of New Concepts and Solutions for Silicon Nanophotonics
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nowadays, silicon photonics is a widely studied research topic. Its high-index-contrast and compatibility with the complementary metal-oxide-semiconductor technology make it a promising platform for low cost high density integration. Several general problems have been brought up, including the lack of silicon active devices, the difficulty of light coupling, the polarization dependence, etc. This thesis aims to give new attempts to novel solutions for some of these problems. Both theoretical modeling and experimental work have been done.

Several numerical methods are reviewed first. The semi-vectorial finite-difference mode solver in cylindrical coordinate system is developed and it is mainly used for calculating the eigenmodes of the waveguide structures employed in this thesis. The finite-difference time-domain method and beam propagation method are also used to analyze the light propagation in complex structures.

The fabrication and characterization technologies are studied. The fabrication is mainly based on clean room facilities, including plasma assisted film deposition, electron beam lithography and dry etching. The vertical coupling system is mainly used for characterization in this thesis. Compared with conventional butt-coupling system, it can provide much higher coupling efficiency and larger alignment tolerance.

Two novel couplers related to silicon photonic wires are studied. In order to improve the coupling efficiency of a grating coupler, a nonuniform grating is theoretically designed to maximize the overlap between the radiated light profile and the optical fiber mode. Over 60% coupling efficiency is obtained experimentally. Another coupler facilitating the light coupling between silicon photonic wires and slot waveguides is demonstrated, both theoretically and experimentally. Almost lossless coupling is achieved in experiments.

Two approaches are studied to realize polarization insensitive devices based on silicon photonic wires. The first one is the use of a sandwich waveguide structure to eliminate the polarization dependent wavelength of a microring resonator. By optimizing the multilayer structure, we successfully eliminate the large birefringence in an ultrasmall ring resonator. Another approach is to use polarization diversity scheme. Two key components of the scheme are studied. An efficient polarization beam splitter based on a one-dimensional grating coupler is theoretically designed and experimentally demonstrated. This polarization beam splitter can also serve as an efficient light coupler between silicon-on-insulator waveguides and optical fibers. Over 50% coupling efficiency for both polarizations and -20dB extinction ratio between them are experimentally obtained. A compact polarization rotator based on silicon photonic wire is theoretically analyzed. 100% polarization conversion is achievable and the fabrication tolerance is relatively large by using a compensation method.

A novel integration platform based on nano-epitaxial lateral overgrowth technology is investigated to realize monolithic integration of III-V materials on silicon. A silica mask is used to block the threading dislocations from the InP seed layer on silicon. Technologies such as hydride vapor phase epitaxy and chemical-mechanical polishing are developed. A thin dislocation free InP layer on silicon is obtained experimentally.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xii, 79 p.
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2010:4
Planar integrated circuit, silicon photonics, slot waveguide, finite-difference time-domain, waveguide grating coupler, ring resonator, polarization diversity scheme, polarization beam splitter, polarization rotator, hybrid silicon laser, epitaxial lateral overgrowth, chemical-mechanical polishing.
National Category
Atom and Molecular Physics and Optics
urn:nbn:se:kth:diva-13029 (URN)
Public defence
2010-06-11, C1, Electrum 1, Isafjordsgatan 26, Kista, 13:47 (English)
QC20100705Available from: 2010-05-26 Created: 2010-05-24 Last updated: 2011-08-30Bibliographically approved

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