Page 29 - Optical Communications Essentials

Basic Concepts of Communication Systems

Basic Concepts of Communication Systems 19

One particular tool from the VPIsystems suite is VPItransmissionMaker, which
is a design and simulation tool for optical devices, components, subsystems, and
transmission systems. This has all the tools needed to explore, design, simulate,
verify, and evaluate active and passive optical components, fiber amplifiers, dense
WDM transmission systems, and broadband access networks. Familiar measure-
ment instruments offer a wide range of settable options when displaying data from
multiple runs, optimizations, and multidimensional parameter sweeps. Signal pro-
cessing modules allow data to be manipulated to mimic any laboratory setup.
An abbreviated version of this simulation module is available for noncom-
mercial educational use. This version is called VPIplayer and contains predefined
component and link configurations that allow interactive concept demonstra-
tions. Among the demonstration setups are optical amplifier structures, simple
single-wavelength links, and WDM links. Although the configurations are fixed,
the user has the ability to interactively change the operational parameter values
of components such as optical fibers, light sources, optical filters, and optical
amplifiers. This can be done very simply by using the mouse to move calibrated
slider controls. Results are shown in a format similar to the displays presented
by laboratory instruments and show, for example, link performance degradation
or improvement when various component values change.
VPIplayer can be downloaded from www.VPIphotonics.com. In addition, at
www.PhotonicsComm.com there are numerous examples of optical communica-
tion components and links related to topics in this book that the reader can
download and simulate. As noted above, predefined component parameters in
these examples may be modified very simply via calibrated slider controls.

1.11. Summary

This chapter provides some fundamental operational concepts and definitions of
terminology related to wired telecommunication systems. This “wiring” encom-
passes copper wires and optical fibers. Some key concepts include the following:
■ Section 1.1 gives basic definitions of metric prefixes, terms used in communi-
cations (e.g., information, message, and signal), waveform characteristics, and
digital signal formats.
■ Section 1.9 defines the concepts of decibels and the relative power unit dBm
that is used extensively in optical communication systems.
■ Although most signals occurring in nature are of an analog form, in general
they can be sent more easily and with a higher fidelity when changed to a dig-
ital format.
■ A common digital signal configuration is the binary waveform consisting of
binary 0 and binary 1 pulses called bits.
■ The SONET/SDH multiplexing hierarchy defines a standard synchronous
frame structure for sending multiplexed digital traffic over optical fiber trans-
mission lines.

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