High-Speed Tunable Short-Wavelength VCSEL for Optical Interconnects

134 Pages·2015·4.08 MB·English

High-Speed Tunable Short-Wavelength VCSEL
for Optical Interconnects
Dem Fachbereich Elektrotechnik und Informationstechnik
der Technischen Universita¨t Darmstadt
zur Erlangung des akademischen Grades eines
Doktor-Ingenieurs (Dr. -Ing.)
genehmigte Dissertation
von
Dipl. -Ing. Hooman Abdollahzadeh Davani
geboren am 05.04.1981 in Teheran, I.R. Iran
Referent : Prof. Dr. -Ing. Peter Meißner
Korreferent : Prof. Dr. -Ing. Helmut F. Schlaak
Tag der Einreichung : 22.04.2014
Tag der mu¨ndlichen Prfu¨ng : 28.10.2014
D17
Darmstadt 2015

TomygrandmotherFatemehEnayatollah

Preface
This dissertation is a summary and a precious memory of my research in the Institute of Mi-
crowaveEngineeringandPhotonicsoftheTechnischeUniversita¨tDarmstadt.
FirstofallIwouldliketoexpressmygratitudetomysupervisorProf. Dr. -Ing. PeterMeißner.
Mysincereappreciationgoesalsotomyco-examiner Prof. Dr. -Ing. HelmutF.Schlaak.
Fortheinspiringdiscussionsandconstructivecooperation,myfellowcolleaguesintheInstitute
of Microwave Engineering and Optics are warmly thanked. Especially, I deeply appreciate Dr.
Christian Gierl, Karolina Zogal, Dr. Sandro Jatta, Dr. Benjamin Ko¨gel, Dr. Yuliang Zheng.
Dr. Mohsen Sazegar, Dr. Trung Q. Le, Dr. Tuomo von Lerber, Ali Emsia, Sujoy Paul, Peter
kiesslich, Andreas Semrad, Dr. Oktay Yilmazoglu, Dr. Chong Jin, Dr. Oleg Cojocari, Ion
Oprea,Dr. CezarySydlo,MariaKaiser,Dr. MichaelFeiginovandTraudelMicus.
Especially I would like to thank the Colleagues from institutions below involved in the Euro-
peanprojectSubtunebecauseofthegreatcollaborationsduring theproject:
Dr. Petter Westbergh, Dr. Johan Gustavsson, Dr. A˚sa Haglund und Prof. Anders Larsson from
ChalmersUniversityofTechnology.
Christian Grasse, Tobias Gruendl and Prof. Markus-Christian Amann from Walter Schottky
InstituteoftechnicalUniversity Munich.
Dr. PierluigiDebernardifrom IEIIT-CNRinTorino.
Dr. PierreFerdinandfromCEAList,Saclay,France.
AidanDalyandDr. BrianCorbettfrom TyndallNationalInstitute,Cork,Ireland
Finally i would like to thank my parents Farideh Dehdari and Hossein Abdollahzadeh Davani,
MywifeLuHuoandourSonKeyanAbdollahzadehDavanifortheirsupportsduringthiswork
andbelievinginme.

Erkla¨rung laut §9 PromO
Ich versichere hiermit, dass ich die vorliegende Dissertation allein und nur unter Verwendung
der angegebenen Literatur verfasst habe. Die Arbeit hat bisher noch nicht zu Pru¨fungszwecken
gedient.

Abstract
The forecast for serial transmission speed used in data communication systems is a continued
exponential increase with time. It is directly scaled in concert with silicon integrated circuits
andinresponsetothehumansociety’sperpetualhungerformassiveincreasesinthebandwidth.
This leads to an increase in the data rate of a single transmission channel and at the same time
toanefficientusageoftheexistingtransmissionmediumbyusingmethodssuchaswavelength
devision multiplexing (WDM). The electrical interfaces for a single channel using a bit rate
beyond 10 Gbit/s are being standardized for a variety of applications. As a result, the funda-
mental electro-magnetic limitations of copper wire-based links at a bit rate >10 Gbit/s make
fibre-based optics for data communication indispensable for distances >1 m. For shorter dis-
tances,problemsassociatedwithelectricaltransmissionlinesatsuchhighfrequencies,e. g. the
high power consumption, strong signal attenuation, signal distortions and the electromagnetic
interferences, lead to an unstoppable and progressive penetration of the optical communication
links into traditional copper interconnect markets [1]. This trend greatly expands the applica-
tions of vertical cavity surface emitting lasers (VCSELs), VCSEL arrays and tunable VCSELs
as inexpensive, efficient, reliable, readily manufacturable and compact laser light sources for
the next generation of fibre-optic, free-space, board-to-board, module-to-module, chip-to-chip
andon-chipinterconnectsandrelatedinformation systemsandnetworks.
Thisthesisreportsthedevelopmentofahigh-speedtunableshort-wavelengthVCSEL.Thegoal
ofourresearchisdevelopingadevice,suitableforopticalinterconnects.
Toachievethisgoal,thelongtraditionandexperienceinfabricationanddevelopmentofmicro-
electro-mechanical system- (MEMS-) mirrors for the long wavelength VCSELs in the Insti-
tute of Microwaves and Photonics of the Technische Universita¨t Darmstadt is combined with
the long tradition and experience in design and development of high-speed non-tunable short-
wavelength VCSELs at Chalmers University of Technology in Go¨teborg Sweden . The Walter
SchottkyInstituteofMunichhasprovidedwafersforsemiconductormirrorsandtheIEIIT-CNR
inTorinohassupporteduswithcold-cavity simulations.
The developed devices are made of a GaAs based half-VCSEL in combination with a MEMS-
mirror. They exhibit a maximum amplitude modulation bandwidth of up to 5 GHz, which was
the highest achieved amplitude modulation bandwidth among tunable GaAs based VCSELs at
the time of publication of our results according to our knowledge. These devices are also the
firstdevelopedhigh-speedtunableVCSELsintheshort-wavelengthrange. Theyexhibitawide
single-modecontinuoustuningrangeofupto37nm,whichisthehighestreportedtuningrange
around850nmachievedbyVCSELs.
Additionally to the results mentioned above, which have been achieved by means of bulk-
micromachining of the MEMS-mirror, a surface-micromachining technology has been suc-
cessfully developed and implemented. Additionally the polarization stability of the devices
is achieved by implementing a sub-wavelength grating (SWG). Further characteristics of the
devicessuchaslinewidth,farfield,tuningspeed,relativeintensitynoise(RIN)andlargesignal
IV
behaviorareinvestigated bymeansofmeasurements.