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*Tunable Lasers in OpticalCommunicationsByJames Harper
Instructor: P. LuiDepartment of Electrical EngineeringUniversity
at Buffalo State University of New YorkCourse Requirement for EE
566
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*OutlineIntroductionTuning MechanismsDistributed Bragg Reflector
LasersExternal Cavity Tunable LasersVertical Cavity Surface
Emitting LasersTypes of Vertical Cavity Surface Emitting
LasersFuture Applications Economical Impact
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*Introduction Most tunable lasers consist of a longitudinal
integration of sectionsActive section provides optical gain Filter
section provides a tunable frequencyPhase shifter section is for
fine-tuning of the cavity resonance frequency The problem of Metro
Area Networks
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*Tuning MechanismsElectric field-induce index change
An electrical field is applied that changes the refractive index
of the waveguide
Thermally-induced index change
Heat is applied by a resistive method to the tuning section of
the laser
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*Distributed Bragg Reflector LaserFirst proposed tunable DBR
laser was in 1977 for only the active section and the reflector
Consist of three integrated sections
The active section has a matching bandgap for the desired
emission frequency which provides the optical gainThe reflector has
a higher bandgap, such that the material is transparent for laser
lightThe phase section can be adjusted electronically through
current injection. Using this a cavity mode can be tuned to the
Bragg frequency[1]
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*External Cavity Tunable LaserConsist of a laser chip and
external reflector
By using a grating as the external reflector, turning of the
grating will lead to a tuning of the lasers wavelengthIntel is one
company that is working on external cavity tunable lasers
Intel
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*Vertical Cavity Surface Emitting Lasers (VCSEL)VCSEL first
proposed in 1977 and demonstrated in 1979In 1988 first continuous
wave laser using GaAs material was demonstrated in 1988In 1999
production and extension of applications for VCSEL
technologyHoneywell
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*Vertical Cavity Surface Emitting laserWavelength division
multiplexingDevice fabricationmolecular beam epitaxy
Materials GaAs has a natural wavelength emission of 873 nm,
while InP emits a wavelength of 918nm.
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*Vertical Cavity Surface Emitting laserKey Advantages low cost
no noise no frequency interruptions less power consumption higher
performance of transceivers for metro area networks high modulation
bandwidth
Beam Characteristics The emitted laser can be controlled by
selecting the number and thickness of mirror layers
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* Vertical Cavity Surface Emitting LasersLinnik 2002
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*Tunable Vertical Cavity Surface Emitting LasersTuning
mechanismsTemperature: Increasing or decreasing the temperature of
the material changes the wavelength transmission of the laser
Current: Multiple current injections are used in the device to
change the wavelengths of the laserMechanical: most recent
technique, uses micro-electro mechanical systems to adjust the
wavelengths of the laserDrawbacks
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*Tunable VCSELs Cantilevers
How the cantilever worksWavelength range is between 1530nm and
1610nmThe coupling efficiency of over 90%
Chang-Hasnain 2001
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*Tunable VCSELs Half Symmetric TypeChang-Hasnain 2000
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* Tunable VCSELs Membrane TypeChang-Hasnian 2001
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*Future Applications Optical Cross Connects (OXCs) used to
switch wavelengths in Metro area networks, it regulates traffic
throughout the network.Computer Optics Computer links, optical
interconnectsOptical SensingOptical fiber sensing, Bar code
readers, EncodersDisplaysArray light sources, Multi-beam search
lights
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*Economical Impact
Current Market TrendsToday as opto electronics become more
commercial, this market generate about $ 15 billion a yearFuture
Market Projection the world market for tunable lasers by 2007
should be about $ 2.4 billion a year
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*REFERENCES[1]Karim, A., Abraham, P., Lofgreen, D., Chiu, J.,
Bowers, Piprek, Wafer Bonded 1.55m Vertical Cavity Laser Arrays for
wavelength Division Multiplexing, IEEE Journal Electronics, Vol. 7,
No. 2, Mar/Apr 2001, pp. 178-183[2]Shinagawa, Tatsuyuki, Iwai,
Norihrio, Yokouchi, Noriyuki, Vertical Cavity Surface Emitting
Semiconductor Laser Device, United States Patent Application, Mar
2003, pp.1-11[3]Chung-Hasnain, Connie, J., Tunable VCSEL, IEEE
Journal on Selected Topics in Quantum Electronics, Vol. 6, No. 6,
Dec 2000, pp. 979-985[4]Derbyshire, Katherine, Prospects Bright for
Optoelectronics, Semiconductor magazine, Vol. 3, No.3, Mar 2002, pp
1-5[5]Chang-Hasnain, Connie, J., Tunable VCSELs: enabling
wavelength-on-demand in metro networks, Compound Semiconductor,
June 2001, pp. 1-3Selected Topics in Quantum [6]WDM Technologies:
Active Optical Components, Achyut Dutta, Niloy Dutta, Masahiko
Fujiwara, Academic Press, pp. 116-150, pp. 167-205,2002
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*BackTunable VCSEL Cantilever