Page 41 - Optical Communications Essentials

Optical Communication Systems Overview

Optical Communication Systems Overview 31

an electrical back to an optical format. The motivation behind this concept is to
extend the versatility of communication networks beyond architectures such as
those provided by high-bandwidth point-to-point SONET light pipes. So far
most of these types of all-optical networks are only concepts, since the technology
still needs to mature. In particular, as described in Chap. 17, an optical cross-
connect switch is one of the key elements needed to deploy agile optical net-
works. Developing such a component is a major challenge since it needs to
switch optical signals at line rates (e.g., at 10-Gbps OC-192 or 40-Gbps OC-768
rates) without optical-to-electrical conversion, thereby providing lower switching
costs and higher capacities than the currently used electrical cross-connects.

2.7. Standards for Optical Communications
When people travel from one country to another, they need to bring along an
electrical adapter that will match up the voltage and plug configurations of
their personal appliances to those of the other country. Even when you do this,
sometimes you are greeted by sparks and black smoke as you plug something
into a foreign electric socket. If the hotel personnel or clerks in stores do not
speak the same language as you do, there is another interface problem. To avoid
similar situations when trying to interface equipment from different manufac-
turers, engineers have devised many different types of standards so that diverse
equipment will interface properly. However, since many people like to do things
their own way, sometimes the standards in one country do not quite match
those of another. Nevertheless, international standards for a wide range of com-
ponent and system-level considerations have made life a lot easier.
There are three basic classes of standards for fiber optics: primary standards,
component testing standards, and system standards.
Primary standards refer to measuring and characterizing fundamental phys-
ical parameters such as attenuation, bandwidth, operational characteristics of
fibers, and optical power levels and spectral widths. In the United States the
main organization involved in primary standards is the National Institute of
Standards and Technology (NIST). This organization carries out fiber optic and
laser standardization work, and it sponsors an annual conference on optical fiber
measurements. Other national organizations include the National Physical
Laboratory (NPL) in the United Kingdom and the Physikalisch-Technische
Bundesanstalt (PTB) in Germany.
Component testing standards define relevant tests for fiber optic component
performance, and they establish equipment calibration procedures. Several dif-
ferent organizations are involved in formulating testing standards, some very
active ones being the Telecommunication Industries Association (TIA) in asso-
ciation with the Electronic Industries Association (EIA), the Telecommunication
Standardization Sector of the International Telecommunication Union (ITU-T),
and the International Electrotechnical Commission (IEC). The TIA has a list of
over 120 fiber optic test standards and specifications under the general desig-
nation TIA/EIA-455-XX-YY, where XX refers to a specific measurement technique

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