*Tunable Lasers in OpticalCommunicationsByJames Harper

Instructor: P. LuiDepartment of Electrical EngineeringUniversity at Buffalo State University of New YorkCourse Requirement for EE 566

*OutlineIntroductionTuning MechanismsDistributed Bragg Reflector LasersExternal Cavity Tunable LasersVertical Cavity Surface Emitting LasersTypes of Vertical Cavity Surface Emitting LasersFuture Applications Economical Impact

*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

*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

*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]

*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

*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

*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.

*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

* Vertical Cavity Surface Emitting LasersLinnik 2002

*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

*Tunable VCSELs Cantilevers

How the cantilever worksWavelength range is between 1530nm and 1610nmThe coupling efficiency of over 90%

Chang-Hasnain 2001

*Tunable VCSELs Half Symmetric TypeChang-Hasnain 2000

* Tunable VCSELs Membrane TypeChang-Hasnian 2001

*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

*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

*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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