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Study on electroabsorption modulators and grating couplers for optical interconnects
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. (Photonics and Microwave Engineering)
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.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610
Keyword [en]
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
Telecommunications
Research subject
SRA - ICT
Identifiers
URN: urn:nbn:se:kth:diva-24178OAI: oai:DiVA.org:kth-24178DiVA: diva2:344663
Public defence
2010-09-27, sal 438, Isafjordsgatan 39, Kista, Stockholm, Forum, KTH, 10:00 (English)
Opponent
Supervisors
Note
QC 20100906Available from: 2010-09-06 Created: 2010-08-19 Last updated: 2011-08-30Bibliographically approved
List of papers
1. Modeling and Optimization for Segmented Transmission-Line Electroabsorption Modulators with Asymmetrical Electrodes
Open this publication in new window or tab >>Modeling and Optimization for Segmented Transmission-Line Electroabsorption Modulators with Asymmetrical Electrodes
2008 (English)In: AOE 2007: ASIA OPTICAL FIBER COMMUNICATION & OPTOELECTRONIC EXPOSITION & CONFERENCE, CONFERENCE PROCEEDINGS, AOE , 2008, 525-527 p.Conference paper, Published paper (Refereed)
Abstract [en]

Normalized RF link gain is derived for a segmented transmission-line electroabsorption modulator. Genetic algorithm is used to optimize the electrode structures which are asymmetrical and non-periodic. Performance of the optimized EAM design is analyzed.

Place, publisher, year, edition, pages
AOE, 2008
Keyword
Engineering, Electrical & Electronic, Optics
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24349 (URN)10.1109/AOE.2007.4410863 (DOI)000265048200179 ()2-s2.0-50049100233 (Scopus ID)978-0-9789217-3-6 (ISBN)
Conference
Asia Optical Fiber Communication and Optoelectronic Exposition and Conference, Shanghai, PEOPLES R CHINA, OCT 17-19, 2007
Note

QC 20100903

Available from: 2010-09-03 Created: 2010-09-03 Last updated: 2016-12-19Bibliographically approved
2. Design and optimization of an arbitrarily segmented traveling wave electrode for an ultrahigh speed electroabsorption modulator
Open this publication in new window or tab >>Design and optimization of an arbitrarily segmented traveling wave electrode for an ultrahigh speed electroabsorption modulator
Show others...
2008 (English)In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 281, no 20, 5177-5182 p.Article in journal (Refereed) Published
Abstract [en]

The modulation response of an arbitrarily segmented traveling wave electroabsorption modulator (TW-EAM) with a non-periodic electrode layout is analyzed with an effective approach based on the transmission line theory. An optimization method based on a genetic algorithm is used to optimize the segmented electrode with additional capacitive pads for a TW-EAM. Optimized electrode structures are given for 165 mu m-length devices under standard 50 Omega RF termination condition and 210 mu m-length devices with smaller integrated resistors. Great enhancement of performances in modulation response is achieved as compared to the periodic design reported previously. The simulation with the parameters extracted from measurement results suggests that a 3 dB-bandwidth over 100 GHz could be achieved. The eye diagram from the simulation demonstrates that such devices would be competent for a 100Gb/s optical network.

Keyword
Electroabsorption, Electrodes, Genetic algorithm, Optical intensity, modulation, Transmission line theory, Traveling wave (TW) devices, Waveguide modulators, optical modulators
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-17879 (URN)10.1016/j.optcom.2008.07.014 (DOI)000259940700018 ()2-s2.0-50449109737 (Scopus ID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2016-12-19Bibliographically approved
3. Proposal for a Grating Waveguide Serving as Both a Polarization Splitter and an Efficient Coupler for Silicon-on-Insulator Nanophotonic Circuits
Open this publication in new window or tab >>Proposal for a Grating Waveguide Serving as Both a Polarization Splitter and an Efficient Coupler for Silicon-on-Insulator Nanophotonic Circuits
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.

Keyword
Grating couplers, integrated optics, polarization splitters, silicon-on-insulator (SOI) technology, waveguides, compact, diversity
Identifiers
urn:nbn:se:kth:diva-18186 (URN)10.1109/lpt.2008.2010528 (DOI)000263480100077 ()2-s2.0-77049105875 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2013-11-19Bibliographically approved
4. Ultracompact low-loss coupler between strip and slot waveguides
Open this publication in new window or tab >>Ultracompact low-loss coupler between strip and slot waveguides
Show others...
2009 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 10, 1498-1500 p.Article in journal (Refereed) Published
Abstract [en]

We present both theoretical and experimental results of an ultracompact waveguide coupler that is capable of highly efficient coupling of light from strip waveguides to slot waveguides, and vice versa. By optimizing the geometrical parameters, it is possible to achieve extremely low-loss coupling. A coupling efficiency of 97% has been obtained experimentally while keeping the overall size down to the range below 10 mu m. Further analysis shows that the proposed coupler has relatively high tolerance to fabrication errors and is wavelength insensitive. (C) 2009 Optical Society of America

Keyword
ring resonators, confining light, fibers
Identifiers
urn:nbn:se:kth:diva-13074 (URN)10.1364/OL.34.001498 (DOI)000267064500003 ()2-s2.0-66349112883 (Scopus ID)
Note
QC20100702Available from: 2010-07-02 Created: 2010-05-26 Last updated: 2013-11-19Bibliographically approved
5. Experimental demonstration of a high efficiency polarization splitter based on a one-dimensional grating with a Bragg reflector underneath
Open this publication in new window or tab >>Experimental demonstration of a high efficiency polarization splitter based on a one-dimensional grating with a Bragg reflector underneath
2010 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 22, no 21, 1568-1570 p.Article in journal (Refereed) Published
Abstract [en]

A one-dimensional grating serving both as a polarization beam splitter and a vertical coupler for silicon photonic circuits is designed, fabricated, and characterized. Bragg reflectors are employed to improve greatly the coupling efficiency. Over 50% efficiency for both polarizations are achieved experimentally, and the extinction ratio between them is also high (-20 dB).

Keyword
Bragg reflector, grating coupler, integrated optics, polarization splitter, silicon-on-insulator (SOI)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-13930 (URN)10.1109/LPT.2010.2070792 (DOI)000283368700005 ()2-s2.0-77957733646 (Scopus ID)
Available from: 2010-07-02 Created: 2010-07-02 Last updated: 2013-11-19Bibliographically approved
6. High efficiency nonuniformgrating coupler by utilizing the lag effect in the dry etching process
Open this publication in new window or tab >>High efficiency nonuniformgrating coupler by utilizing the lag effect in the dry etching process
2010 (English)In: 2010 Conference on Optical Fiber Communication, Collocated National Fiber Optic Engineers Conference, OFC/NFOEC 2010, 2010, 5465672- p.Conference paper, Published paper (Refereed)
Abstract [en]

Utilizing the lag effect in dry etching, a nonuniform silicon-on-insulator grating coupler is designed and fabricated. Over 80% (>-1dB) coupling efficiency is theoretically obtained and experimental coupling efficiency of 55% is achieved for TE polarization.

Keyword
Nanophotonic Wave-Guides, Optical-Fiber
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24371 (URN)000287574100506 ()2-s2.0-77953917743 (Scopus ID)978-1-55752-884-1 (ISBN)
Conference
2010 Conference on Optical Fiber Communication, Collocated National Fiber Optic Engineers Conference, OFC/NFOEC 2010; San Diego, CA; United States; 21 March 2010 through 25 March 2010
Note

QC 20100906

Available from: 2010-09-06 Created: 2010-09-06 Last updated: 2014-08-21Bibliographically approved
7. Highly efficient nonuniform grating coupler for silicon-on-insulator nanophotonic circuits
Open this publication in new window or tab >>Highly efficient nonuniform grating coupler for silicon-on-insulator nanophotonic circuits
Show others...
2010 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 35, no 8, 1290-1292 p.Article in journal (Refereed) Published
Abstract [en]

We present design, fabrication, and characterization of a silicon-on-insulator grating coupler of high efficiency for coupling between a silicon nanophotonic waveguide and a single mode fiber. By utilizing the lag effect of the dry etching process, a grating coupler consisting of nonuniform grooves with different widths and depths is designed and fabricated to maximize the overlapping between the upward wave and the fiber mode. The measured waveguide-to-fiber coupling efficiency of 64% (−1.9 dB) for the transverse electric polarization is achieved by the present nonuniform grating coupler directly defined on a regular silicon-on-insulator wafer.

Identifiers
urn:nbn:se:kth:diva-13073 (URN)10.1364/OL.35.001290 (DOI)000276861100059 ()2-s2.0-77954911525 (Scopus ID)
Note

QC 20100906

Available from: 2010-05-26 Created: 2010-05-26 Last updated: 2014-09-24Bibliographically approved
8. Silicon-based photonic crystals and nanowires
Open this publication in new window or tab >>Silicon-based photonic crystals and nanowires
2008 (English)In: Photonic Crystals: Physics and Technology / [ed] Sibilia, C.; Benson, T.M.; Marciniak, M.; Szoplik, T., Springer, 2008, 149-169 p.Chapter in book (Refereed)
Abstract [en]

This Chapter highlights issues related to dense photonic integration based on silicon platform and reviews two alternatives to achieve this goal within the diffraction limit; photonic nanowires and photonic crystal waveguides. Examples of the device concepts and demonstrators, as well as the fabrication techniques for passive Si based mesostructures, are presented. Promising prospects and recent breakthroughs in heterogeneous integration of silicon with optically active materials are indicated.

Place, publisher, year, edition, pages
Springer, 2008
Keyword
Photonic crystal, nanowire waveguide, integrated optics, silicon-on-insulator
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - ICT
Identifiers
urn:nbn:se:kth:diva-13931 (URN)10.1007/978-88-470-0844-1_9 (DOI)2-s2.0-84892213111 (Scopus ID)978-354024431-8 (ISBN)
Conference
2009 Asia Communications and Photonics Conference and Exhibition, ACP 2009; Shanghai; 2 November 2009 through 6 November 2009
Note

QC 20100702

Available from: 2010-07-02 Created: 2010-07-02 Last updated: 2014-04-23Bibliographically approved

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Citation style
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  • ieee
  • modern-language-association-8th-edition
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  • en-US
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Output format
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