Tunable Lasers in Optical Communications By James Harper

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 1

§ Introduction Outline § 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 2

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 3

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 4

Distributed Bragg Reflector Laser [1] § 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 5

External Cavity Tunable Laser Intel § 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 6

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

Vertical Cavity Surface Emitting laser § Wavelength division multiplexing § Device fabrication – molecular beam epitaxy § Materials – Ga. As has a natural wavelength emission of 873 nm, while In. P emits a wavelength of 918 nm. 8

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 9

Vertical Cavity Surface Emitting Lasers Linnik 2002 10

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 11

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

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

Tunable VCSEL’s Membrane Type Chang-Hasnian 2001 14

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 15

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 16

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. 979985 § [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 wavelengthon-demand in metro networks”, Compound Semiconductor, June 2001, pp. 1 -3 Selected Topics in Quantum § [6] WDM Technologies: Active Optical Components, Achyut Dutta, Niloy Dutta, Masahiko Fujiwara, Academic Press, pp. 116 -150, pp. 167 -205, 2002 17

Tunable VCSEL Cantilever Back 18