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Tunable Lasers in Optical Communications

Tunable Lasers in Optical Communications. By James Harper Instructor: P. Lui Department of Electrical Engineering University at Buffalo State University of New York Course Requirement for EE 566. Outline. Introduction Tuning Mechanisms Distributed Bragg Reflector Lasers

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Tunable Lasers in Optical Communications

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  1. Tunable Lasers in OpticalCommunications By James Harper Instructor: P. Lui Department of Electrical Engineering University at Buffalo State University of New York Course Requirement for EE 566

  2. Outline • Introduction • Tuning Mechanisms • Distributed Bragg Reflector Lasers • External Cavity Tunable Lasers • Vertical Cavity Surface Emitting Lasers • Types of Vertical Cavity Surface Emitting Lasers • Future Applications • Economical Impact

  3. Introduction • Most tunable lasers consist of a longitudinal integration of sections • Active section provides optical gain • Filter section provides a tunable frequency • Phase shifter section is for fine-tuning of the cavity resonance frequency • The problem of Metro Area Networks

  4. Tuning Mechanisms • Electric 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

  5. Distributed Bragg Reflector Laser • First 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 gain • The reflector has a higher bandgap, such that the material is transparent for laser light • The phase section can be adjusted electronically through current injection. Using this a cavity mode can be tuned to the Bragg frequency [1]

  6. External Cavity Tunable Laser • Consist 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 wavelength • Intel is one company that is working on external cavity tunable lasers Intel

  7. Vertical Cavity Surface Emitting Lasers (VCSEL) • VCSEL first proposed in 1977 and demonstrated in 1979 • In 1988 first continuous wave laser using GaAs material was demonstrated in 1988 • In 1999 production and extension of applications for VCSEL technology Honeywell

  8. Vertical Cavity Surface Emitting laser • Wavelength division multiplexing • Device fabrication • molecular beam epitaxy • Materials – GaAs has a natural wavelength emission of 873 nm, while InP emits a wavelength of 918nm.

  9. Vertical Cavity Surface Emitting laser • Key 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

  10. Vertical Cavity Surface Emitting Lasers Linnik 2002

  11. Tunable Vertical Cavity Surface Emitting Lasers • Tuning mechanisms • Temperature: 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 laser • Mechanical: most recent technique, uses micro-electro mechanical systems to adjust the wavelengths of the laser • Drawbacks

  12. Tunable VCSEL’s Cantilevers • How the cantilever works • Wavelength range is between 1530nm and 1610nm • The coupling efficiency of over 90% Chang-Hasnain 2001

  13. Tunable VCSEL’s Half Symmetric Type Chang-Hasnain 2000

  14. Tunable VCSEL’s Membrane Type Chang-Hasnian 2001

  15. 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 interconnects • Optical Sensing • Optical fiber sensing, Bar code readers, Encoders • Displays • Array light sources, Multi-beam search lights

  16. Economical Impact • Current Market Trends • Today as opto electronics become more commercial, this market generate about $ 15 billion a year • Future Market Projection • the world market for tunable lasers by 2007 should be about $ 2.4 billion a year

  17. REFERENCES • [1] Karim, A., Abraham, P., Lofgreen, D., Chiu, J., Bowers, Piprek, “Wafer Bonded 1.55μm 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

  18. Tunable VCSEL Cantilever Back

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