Page 182 - Optical Communications Essentials

Active Optical Components

172 Chapter Ten

10.9. Summary
Dynamically tunable devices are essential for high-performance WDM networks.
Their functions include tunable optical sources, variable optical attenuators,
optical switches, optical filters, dynamic gain equalizers, add/drop multiplexers,
dispersion-compensating modules, polarization controllers, and optical per-
formance monitors. Table 10.3 gives a summary of some typical tunable devices
and indicates where they are described in this book.

TABLE 10.3. Summary of Some Tunable Devices, Their Functions, and in Which Chapter to
Find Application Details
Tunable device Function Chapter
Tunable laser diode Emits optical power at a precisely tunable 6
frequency (wavelength) over a certain
spectral band
Wavelength locker Precisely maintains the output from a laser 12
diode at a predefined ITU-T frequency
External modulator Allows the optical output from a laser diode 6
to be modulated external to the source at
rates greater than 2.5Gbps
Optical amplifier Operates completely in the optical domain 11
to boost the power level of optical signals
Variable optical attenuator Used in multiple-wavelength links to adjust 10
the power levels of individual wavelengths
Optical filter Selects a specific narrow wavelength range 9,10,12
for data receipt or performance monitoring
Dynamic gain equalizer Provides dynamic gain equalization or 10
blocking of individual channels
Optical add/drop multiplexer Adds and/or drops selected wavelengths at a 10,17
designated point in an optical network
Polarization controller Dynamically adjusts any incoming state of 10
polarization to an arbitrary output state
Chromatic dispersion compensator Optically restores signals that have become 10,15
degraded by chromatic dispersion
Optical performance monitor Tracks optical power, wavelength, and 18
optical signal-to-noise ratio to check
operational performance trends
Optical switch Operates completely in the optical domain 17
to switch an incoming signal from an
input to an output port
Wavelength converter Transforms one incoming wavelength to a 11
different outgoing wavelength in WDM
links

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