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Proposal for a Grating Waveguide Serving as Both a Polarization Splitter and an Efficient Coupler for Silicon-on-Insulator Nanophotonic Circuits
KTH, School of Information and Communication Technology (ICT), Optics and Photonics. 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.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.ORCID iD: 0000-0002-3401-1125
2009 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 21, no 1-4, 242-244 p.Article in journal (Refereed) Published
Abstract [en]

A grating waveguide is introduced and designed to serve as both a polarization splitter and an efficient vertical coupler between a fiber and a silicon-on-insulator (SOI) nanophotonic waveguide. Through this grating waveguide, the light from the fiber can be efficiently coupled into an SOI chip where the two orthogonally polarized waves are separated to travel towards the opposite directions along the waveguide. According to our simulations, the optimized structure can give a high coupling efficiency of about 50% for both polarizations, as well as a large bandwidth of over 70 nm and a very low polarization crosstalk below -22 dB at the output ports.

Place, publisher, year, edition, pages
2009. Vol. 21, no 1-4, 242-244 p.
Keyword [en]
Grating couplers, integrated optics, polarization splitters, silicon-on-insulator (SOI) technology, waveguides, compact, diversity
URN: urn:nbn:se:kth:diva-18186DOI: 10.1109/lpt.2008.2010528ISI: 000263480100077ScopusID: 2-s2.0-77049105875OAI: diva2:336232
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2013-11-19Bibliographically approved
In thesis
1. Study on electroabsorption modulators and grating couplers for optical interconnects
Open this publication in new window or tab >>Study on electroabsorption modulators and grating couplers for optical interconnects
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Decades of efforts have pushed the replacement of electrical interconnects by optical links to the interconnects between computers, racks and circuit boards. It may be expected that optical solutions will further be used for inter-chip and intra-chip interconnects with potential benefits in bandwidth, capacity, delay, power consumption and crosstalk. Silicon integration is emerging to be the best candidate nowadays due to not only the dominant status of silicon in microelectronics but also the great advantages brought to the photonic integrated circuits (PICs). Regarding the recent breakthroughs concerning active devices on silicon substrate, the question left is no longer the feasibility of the optical interconnects based on silicon but the competitiveness of the silicon device compared with other alternatives.

This thesis focuses on the study of two key components for the optical interconnects, both especially designed and fabricated for silicon platform. One is a high speed electroabsorption modulator (EAM), realized by transferring an InP-based segmented design to the hybrid silicon evanescent platform. The purpose here is to increase the speed of the silicon PICs to over 50  Gb/s or more. The other one is a high performance grating coupler, with the purpose to improve the optical interface between the silicon PICs and the outside fiber-based communication system.

An general approach based on the transmission line analysis has been developed to evaluate the modulation response of an EAM with a lumped, traveling-wave, segmented or capacitively-loaded configuration. A genetic algorithm is used to optimize its configuration. This method has been applied to the design of the EAMs on hybrid silicon evanescent platform. Based on the comparison of various electrode design, segmented configuration is adopted for the target of a bandwidth over 40 GHz with as low as possible voltage and high extinction ratio.

In addition to the common periodic analysis, the grating coupler is analyzed by the antenna theory assisted with an improved volume-current method, where the directionality of a grating coupler can be obtained analytically. In order to improve the performance of the grating coupler, a direct way is to address its shortcoming by e.g. increasing the coupling efficiency. For this reason, a nonuniform grating coupler with apodized grooves has been developed with a coupling efficiency of 64%, nearly a double of a standard one. Another way is to add more functionalities to the grating coupler. To do this, a polarization beam splitter (PBS) based on a bidirectional grating coupler has been proposed and experimentally demonstrated. An extinction ratio of around -20 dB, as well as a maximum coupling efficiency of over 50% for both polarizations, is achieved by such a PBS with a Bragg reflector underneath.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xii, 80 p.
Trita-ICT/MAP AVH, ISSN 1653-7610
Photonic integrated circuit, optical interconnect, transmission line, traveling-wave, electro-absorption modulator, hybrid silicon evanescent platform, grating coupler, vertical coupling scheme, optical antenna, lag effect, polarization beam splitter
National Category
Research subject
urn:nbn:se:kth:diva-24178 (URN)
Public defence
2010-09-27, sal 438, Isafjordsgatan 39, Kista, Stockholm, Forum, KTH, 10:00 (English)
QC 20100906Available from: 2010-09-06 Created: 2010-08-19 Last updated: 2011-08-30Bibliographically approved

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Tang, YongboDai, DaoxinHe, Sailing
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