Page 115 - Optical Communications Essentials

Light Sources and Transmitters

Light Sources and Transmitters 105

cores. The FP laser is popular for short- and intermediate-distance (up to 15-km)
applications running at data rates of up to 622Mbps. Single-mode DFB lasers
are used extensively in high-speed transmission systems. A number of different
technologies are being considered for making tunable lasers, each having cer-
tain advantages and limitations with respect to tuning range, tuning speed,
power output, and control complexity. VCSELs were developed first at 850nm
for applications such as Gigabit and 10-Gigabit Ethernet in a LAN environ-
ment, but now also are available at longer wavelengths.
Transmitters for optical communications come in a wide range of complexity.
At the simple and inexpensive end, the small-form-factor package has been
standardized for moderate-speed (up to 622-Mbps), intermediate-distance appli-
cations. Dense WDM (DWDM) applications require a highly sophisticated laser
transmitter that includes a temperature controller to maintain a 0.02°C stabil-
ity, a wavelength-locking controller to stabilize the wavelength to a few picome-
ters, optical power level sensing and control functions, an alarm processor that
provides alerts for abnormal operation conditions, and optionally a built-in light
modulator.

Further Reading
1. G. Keiser, Optical Fiber Communications, 3d ed., McGraw-Hill, Burr Ridge, Ill., 2000, Chap. 4.
2. E. Garmire, “Sources, modulators, and detectors for fiber optic communication systems,” Chap. 4
in Fiber Optics Handbook, McGraw-Hill, New York, 2002.
3. R.-C. Yu, “Tunable lasers,” Fiberoptic Product News, vol. 16, pp. 28–33, February 2002 (www.
fpnmag.com).
4. H. Shakouri, “Wavelength lockers make fixed and tunable lasers precise,” WDM Solutions,
January 2002 (www.wdm-solutions.com).
5. H. Volterra, “Indium phosphide addresses 10-Gb/s metro demand,” Laser Focus World, vol. 38,
pp. 61–66, April 2002 (www.laserfocusworld.com).
6. T. Rahban, “PWM (pulse width modulation) temp controller for thermo-electric modules,”
Lightwave, vol. 19, pp. 81–84, August 2002 (www.lightwaveonline.com).

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