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Tunable Lasers in Tunable Lasers in OpticalOptical

CommunicationsCommunicationsByBy

James HarperJames Harper

Instructor: P. LuiInstructor: P. Lui

Department of Electrical EngineeringDepartment of Electrical Engineering

University at Buffalo State University of New YorkUniversity at Buffalo State University of New York

Course Requirement for EE 566Course Requirement for EE 566

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OutlineOutline IntroductionIntroduction

Tuning MechanismsTuning Mechanisms

Distributed Bragg Reflector LasersDistributed Bragg Reflector Lasers

External Cavity Tunable LasersExternal Cavity Tunable Lasers

Vertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting Lasers

Types of Vertical Cavity Surface Emitting LasersTypes of Vertical Cavity Surface Emitting Lasers

Future Applications Future Applications

Economical ImpactEconomical Impact

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IntroductionIntroduction Most tunable lasers consist of a longitudinal Most tunable lasers consist of a longitudinal

integration of sectionsintegration of sections

– Active section provides optical gain Active section provides optical gain

– Filter section provides a tunable frequencyFilter section provides a tunable frequency

– Phase shifter section is for fine-tuning of the cavity Phase shifter section is for fine-tuning of the cavity resonance frequencyresonance frequency

The problem of Metro Area NetworksThe problem of Metro Area Networks

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Tuning MechanismsTuning Mechanisms

Electric field-induce index changeElectric field-induce index change

– An electrical field is applied that changes the An electrical field is applied that changes the refractive index of the waveguiderefractive index of the waveguide

Thermally-induced index changeThermally-induced index change

– Heat is applied by a resistive method to the Heat is applied by a resistive method to the tuning section of the lasertuning section of the laser

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Distributed Bragg Reflector LaserDistributed Bragg Reflector Laser

First proposed tunable DBR laser was in 1977 for only the First proposed tunable DBR laser was in 1977 for only the active section and the reflectoractive section and the reflector

Consist of three integrated sectionsConsist of three integrated sections

– The active section has a matching bandgap for the desired emission The active section has a matching bandgap for the desired emission frequency which provides the optical gainfrequency which provides the optical gain

– The reflector has a higher bandgap, such that the material is transparent The reflector has a higher bandgap, such that the material is transparent for laser lightfor laser light

– The phase section can be adjusted electronically through current The phase section can be adjusted electronically through current injection. Using this a cavity mode can be tuned to the Bragg frequencyinjection. Using this a cavity mode can be tuned to the Bragg frequency

[1]

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External Cavity Tunable LaserExternal Cavity Tunable Laser

Consist of a laser chip and external reflectorConsist of a laser chip and external reflector

By using a grating as the external reflector, turning By using a grating as the external reflector, turning of the grating will lead to a tuning of the lasers of the grating will lead to a tuning of the lasers wavelengthwavelength

IntelIntel is one company that is working on external is one company that is working on external cavity tunable laserscavity tunable lasers

Intel

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Vertical Cavity Surface Emitting Vertical Cavity Surface Emitting Lasers (VCSEL)Lasers (VCSEL)

VCSEL first proposed in VCSEL first proposed in 1977 and demonstrated in 1977 and demonstrated in 19791979

In 1988 first continuous In 1988 first continuous wave laser using GaAs wave laser using GaAs material was demonstrated material was demonstrated in 1988in 1988

In 1999 production and In 1999 production and extension of applications extension of applications for VCSEL technologyfor VCSEL technology

Honeywell

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Vertical Cavity Surface Emitting Vertical Cavity Surface Emitting laserlaser

Wavelength division multiplexingWavelength division multiplexing

Device fabricationDevice fabrication

– molecular beam epitaxymolecular beam epitaxy

Materials – GaAs has a natural wavelength Materials – GaAs has a natural wavelength emission of 873 nm, while InP emits a wavelength emission of 873 nm, while InP emits a wavelength of 918nm.of 918nm.

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Vertical Cavity Surface Emitting Vertical Cavity Surface Emitting laserlaser

Key AdvantagesKey Advantages– low costlow cost– no noiseno noise– no frequency interruptionsno frequency interruptions– less power consumptionless power consumption– higher performance of transceivers for metro higher performance of transceivers for metro area networks area networks – high modulation bandwidthhigh modulation bandwidth

Beam Characteristics – The emitted laser can be controlled Beam Characteristics – The emitted laser can be controlled by selecting the number and thickness of mirror layersby selecting the number and thickness of mirror layers

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Vertical Cavity Surface Emitting Vertical Cavity Surface Emitting LasersLasers

Linnik 2002

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Tunable Vertical Cavity Surface Tunable Vertical Cavity Surface Emitting LasersEmitting Lasers

Tuning mechanismsTuning mechanisms

– Temperature: Increasing or decreasing the temperature of Temperature: Increasing or decreasing the temperature of the material changes the wavelength transmission of the the material changes the wavelength transmission of the laser laser

– Current: Multiple current injections are used in the device to Current: Multiple current injections are used in the device to change the wavelengths of the laserchange the wavelengths of the laser

– Mechanical: most recent technique, uses micro-electro Mechanical: most recent technique, uses micro-electro mechanical systems to adjust the wavelengths of the lasermechanical systems to adjust the wavelengths of the laser

DrawbacksDrawbacks

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Tunable VCSEL’s CantileversTunable VCSEL’s Cantilevers

How the cantilever worksHow the cantilever works

Wavelength range is between 1530nm and 1610nmWavelength range is between 1530nm and 1610nm

The coupling efficiency of over 90%The coupling efficiency of over 90%

Chang-Hasnain 2001

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Tunable VCSEL’sTunable VCSEL’s Half Symmetric Type Half Symmetric Type

Chang-Hasnain 2000

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Tunable VCSEL’sTunable VCSEL’s Membrane Type Membrane Type

Chang-Hasnian 2001

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Future Applications Future Applications Optical Cross Connects (OXCs)Optical Cross Connects (OXCs)

– used to switch wavelengths in Metro area networks, it used to switch wavelengths in Metro area networks, it regulates traffic throughout the network.regulates traffic throughout the network.

Computer OpticsComputer Optics

– Computer links, optical interconnectsComputer links, optical interconnects

Optical SensingOptical Sensing

– Optical fiber sensing, Bar code readers, EncodersOptical fiber sensing, Bar code readers, Encoders

DisplaysDisplays

– Array light sources, Multi-beam search lights Array light sources, Multi-beam search lights

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Economical ImpactEconomical Impact

Current Market TrendsCurrent Market Trends

– Today as opto electronics become more Today as opto electronics become more commercial, this market generate about $ 15 commercial, this market generate about $ 15 billion a yearbillion a year

Future Market ProjectionFuture Market Projection

– the world market for tunable lasers by 2007 the world market for tunable lasers by 2007 should be about $ 2.4 billion a yearshould be about $ 2.4 billion a year

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REFERENCESREFERENCES [1][1] Karim, A., Abraham, P., Lofgreen, D., Chiu, J., Bowers, Piprek, Karim, A., Abraham, P., Lofgreen, D., Chiu, J., Bowers, Piprek,

“Wafer Bonded 1.55μm Vertical Cavity Laser Arrays for wavelength “Wafer Bonded 1.55μm Vertical Cavity Laser Arrays for wavelength Division Multiplexing”, IEEE Journal Electronics, Vol. 7, No. 2, Mar/Apr Division Multiplexing”, IEEE Journal Electronics, Vol. 7, No. 2, Mar/Apr 2001, pp. 178-1832001, pp. 178-183

[2][2] Shinagawa, Tatsuyuki, Iwai, Norihrio, Yokouchi, Noriyuki, “Vertical Shinagawa, Tatsuyuki, Iwai, Norihrio, Yokouchi, Noriyuki, “Vertical Cavity Surface Emitting Semiconductor Laser Device”, United States Patent Cavity Surface Emitting Semiconductor Laser Device”, United States Patent Application, Mar 2003, pp.1-11Application, Mar 2003, pp.1-11

[3][3] Chung-Hasnain, Connie, J., “Tunable VCSEL”, IEEE Journal on Chung-Hasnain, Connie, J., “Tunable VCSEL”, IEEE Journal on Selected Topics in Quantum Electronics, Vol. 6, No. 6, Dec 2000, pp. 979-Selected Topics in Quantum Electronics, Vol. 6, No. 6, Dec 2000, pp. 979-985985

[4][4] Derbyshire, Katherine, “Prospects Bright for Optoelectronics”, Derbyshire, Katherine, “Prospects Bright for Optoelectronics”, Semiconductor magazine, Vol. 3, No.3, Mar 2002, pp 1-5Semiconductor magazine, Vol. 3, No.3, Mar 2002, pp 1-5

[5][5] Chang-Hasnain, Connie, J., “Tunable VCSELs: enabling Chang-Hasnain, Connie, J., “Tunable VCSELs: enabling wavelength-on-demand in metro networks”, Compound Semiconductor, wavelength-on-demand in metro networks”, Compound Semiconductor, June 2001, pp. 1-3Selected Topics in Quantum June 2001, pp. 1-3Selected Topics in Quantum

[6][6] WDM Technologies: Active Optical Components, Achyut Dutta, WDM Technologies: Active Optical Components, Achyut Dutta, Niloy Dutta, Masahiko Fujiwara, Academic Press, pp. 116-150, pp. 167-Niloy Dutta, Masahiko Fujiwara, Academic Press, pp. 116-150, pp. 167-205,2002205,2002

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Tunable VCSEL CantileverTunable VCSEL Cantilever