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 GaAs
material was demonstrated
in 1988
 In 1999 production and
extension of applications
for VCSEL technology
Honeywell
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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.
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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 1530nm and 1610nm
 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.
1-3Selected 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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Tunable VCSEL Cantilever
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