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Subwavelength-diameter Silica Wire for Light In-coupling to Silicon-based Waveguide
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC. KTH, School of Computer Science and Communication (CSC).
Department of Optical Engineering, Zhejiang University.
2007 (English)In: Chinese optics letters, ISSN 1671-7694, Vol. 5, no 10, 577-579 p.Article in journal (Refereed) Published
Abstract [en]

Coupling between subwavelength-diameter silica wires and silicon-based waveguides is studied using the parallel three-dimensional (3D) finite-different time-domain method. Conventional butt-coupling to a silica-substrated silicon wire waveguide gives above 40% transmission at the wavelength range from 1300 to 1750 nm with good robustness against axial misalignments. Slow light can be generated by counter-directional coupling between a silica wire and a two-dimensional (2D) silicon photonic crystal slab waveguide. Through dispersion-band engineering, 82% transmission is achieved over a coupling distance of 50 lattice constants. The group velocity is estimated as 1/35 of the light speed in vacuum.

Place, publisher, year, edition, pages
2007. Vol. 5, no 10, 577-579 p.
Keyword [en]
Alignment, Finite difference time domain method, Optical waveguides, Parallel algorithms, Silicon, Three dimensional, Axial misalignments, Silicon based waveguides, Subwavelength diameter silica wires
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-8024ISI: 000255024400006Scopus ID: 2-s2.0-36248989245OAI: oai:DiVA.org:kth-8024DiVA: diva2:13233
Note
QC 20100923Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2010-09-23Bibliographically approved
In thesis
1. Silicon-based Photonic Devices: Design, Fabrication and Characterization
Open this publication in new window or tab >>Silicon-based Photonic Devices: Design, Fabrication and Characterization
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The field of Information and Communication Technologies is witnessing a development speed unprecedented in history. Moore’s law proves that the processor speed and memory size are roughly doubling each 18 months, which is expected to continue in the next decade. If photonics is going to play a substantial role in the ICT market, it will have to follow the same dynamics. There are mainly two groups of components that need to be integrated. The active components, including light sources, electro-optic modulators, and detectors, are mostly fabricated in III-V semiconductors. The passive components, such as waveguides, resonators, couplers and splitters, need no power supply and can be realized in silicon-related semiconductors. The prospects of silicon photonics are particularly promising, the fabrication is mostly compatible with standard CMOS technology and the on-chip optical interconnects are expected to increase the speed of microprocessors to the next generation.

This thesis starts with designs of various silicon-based devices using finite-difference time-domain simulations. Parallel computation is a powerful tool in the modeling of large-scale photonic circuits. High Q cavities and resonant channel drop filters are designed in photonic crystal platform. Different methods to couple light from a single mode fiber to silicon waveguides are studied by coupled-mode theory and verified using parallel simulations. The performance of waveguide grating coupler for vertical radiation is also studied.

The fabrication of silicon-based photonic devices involves material deposition, E-beam or optical lithography for pattern defining, and plasma/wet-chemistry etching for pattern transfer. For nanometer-scaled structures, E-beam lithography is the most critical process. Depending on the structures of the devices, both positive resist (ZEP520A) and negative resist (maN2405) are used. The proximity and stitch issues are addressed by careful dose correction and patches exposure. Some examples are given including photonic crystal surface mode filter, micro-ring resonators and gold grating couplers. In particular, high Q (2.6×105), deep notch (40 dB) and resonance-splitting phenomenon are demonstrated for silicon ring resonators.

It is challenging to couple light into photonic integrated circuits directly from a single-mode fiber. The butt-coupled light-injecting method usually causes large insertion loss due to small overlap of the mode profiles and large index mismatch. Practically it is not easy to cleave silicon sample with smooth facet where the waveguide exposes. By adding gold gratings to the waveguides, light can be injected and collected vertically from single-mode fiber. The coupling efficiency is much higher. There is no need to cleave the sample. The access waveguides are much shortened and the stitch problem in E-beam lithography is avoided.

In summary, this thesis introduces parallel simulations for the design of modern large-scale photonic devices, addresses various issues with Si-based fabrication, and analyses the data from the characterization. Several novel devices using silicon nanowire waveguides and 2D photonic crystal structures have been demonstrated for the first time.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 58 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:5
Keyword
Photonic Devices, Silicon Photonics, Parallel Computation, Nanofabrication, Electron Beam Lithography, Optical Characterisation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-4647 (URN)
Public defence
2008-03-07, N1, Electrum 3, Isafjordsgatan 28, Kista, 10:00
Opponent
Supervisors
Note
QC 20100923Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2010-09-23Bibliographically approved

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