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Reduction of multimode effects in an SOI-based etched diffraction grating demultiplexer
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.ORCID iD: 0000-0002-3401-1125
2005 (English)In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 247, no 4-6, 281-290 p.Article in journal (Refereed) Published
Abstract [en]

Multimode effects in the free propagation region (FPR) of a silicon-on-insulator (SOI)-based etched diffraction grating (EDG) demultiplexer are analyzed. In a conventional design, the power coupled to the higher order modes is considerable, which introduces a significant excess loss and crosstalk. It is shown that the multimode effects in an SOI EDG demultiplexer are much more detrimental than in an arrayed waveguide grating demultiplexer. Several methods for reducing the multimode effects are discussed. In particular, a laterally tapered structure between the FPR and the input/output waveguides is proposed as a simple and effective method for reducing the power coupled to the higher order modes and consequently reducing the multimode effects. The taper width is optimized to minimize the crosstalk.

Place, publisher, year, edition, pages
2005. Vol. 247, no 4-6, 281-290 p.
Keyword [en]
multimode effect, taper, silicon-on-insulator, etched diffraction grating, insertion loss, crosstalk, demultiplexer
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-5159DOI: 10.1016/j.optcom.2004.11.080ISI: 000228112800006OAI: oai:DiVA.org:kth-5159DiVA: diva2:7961
Note
QC 20100928Available from: 2005-05-27 Created: 2005-05-27 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Designs and simulations of silicon-based microphotonic devices
Open this publication in new window or tab >>Designs and simulations of silicon-based microphotonic devices
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The characteristics of a silicon-on-insulator (SOI) rib waveguide, including the bending loss of a multimode bent waveguide and the birefringence of a rib waveguide, are analyzed by using a finite-difference method (FDM). Based on a detailed analysis for a multimode bent waveguide, an appropriately designed multimode bent waveguide for reducing effectively the bending loss of the fundamental mode is realized. The slab height and the rib width of an SOI rib waveguide are normalized with the total height of the silicon layer and a general relation between these two normalized parameters for a nonbirefringent SOI rib waveguide is established. Using this general relation, one can easily design a nonbirefringent SOI rib waveguide. The issue of multimode effect in the SOI-based microphotonic devices such as arrayed-waveguide gratings (AWGs), etched diffraction gratings (EDGs), and multimode interference (MMI) couplers is discussed in detail. Two kinds of taper structures are proposed for reducing the multimode effects in EDGs or MMI couplers. A bi-level taper is introduced to eliminate effectively the multimode effects in an EDG or an MMI coupler. The bi-level taper is very appropriate for an EDG demultiplexer since the Si layer is etched through simultaneously for both the grating and the bottom taper structure, and thus no additional fabrication process is required. For the simulation of an AWG demultiplexer, a fast simulation method based on the Gaussian approximation is proposed and two kinds of effective and accurate three-dimensional (3D) simulation modeling are developed. The first 3D model is based on Kirchhoff-Huygens diffraction formula. To improve the computational speed, the 3D model is reduced to a two-dimensional (2D) one by integrating the corresponding field distributions in the AWG demultiplexer along the vertical direction under an assumption that the power coupled to the higher order modes in the free propagation region (FPR) is negligibly small. The equivalent 2D model has an almost the same accuracy as the original 3D model. Furthermore, a reciprocity theory is introduced for the optimal designof a special structure used for flattening the spectral response of an AWG demultiplexer. In the second 3D simulation method, we combine a beam propagation method (BPM) and the Kirchhoff-Huygens diffraction formula. In this method, a 3D BPM in a polar coordinate system is used for calculating the light propagation in the region connecting the first FPR and the arrayed waveguides, and thus the coupling coefficient of each arrayed waveguide is calculated conveniently and accurately. In the simulation of the second FPR, due to the uniform arrangement of arrayed waveguides, only several arrayed waveguides are needed in the BPM window and thus the computational efficiency is improved.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 61 p.
Series
TRITA-TET/DA, ISSN 0349-7836 ; 2005:01
Keyword
Electronics, waveguide, silicon-on-insulator (SOI), arrayed waveguide grating (AWG), Elektronik
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-226 (URN)91-7178-076-9 (ISBN)
Public defence
2005-06-03, sal E3, Osquars backe 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101004Available from: 2005-05-27 Created: 2005-05-27 Last updated: 2010-10-04Bibliographically approved

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