 core) and loop feeder or distribution environ- ment (metro access). However, the economic considerations for the deploy- ment of loop fiber have up to now mostly been based on supporting DSO voice applications over traditional digital loop carrier systems operating typically at an aggregated DS3 rate, rather than on supporting data appli- cations at some higher data rate. These traditional applications have COV- ered the feeder portion of the loop plant, connecting the central office (CO) Optics Primer Figure 2-1 Positioning of optical communication in the electromagnetic spectrum. Wavelength (Meters) 10-10 10-11 10-12 10-13 10-14 Frequency (Cycles Per Second) C =3x108 Used For Not Used For Public Telecommunications Public Telecommunications Today Today Chapter 2 Repeater/amplifier Figure 2-2 Fiber-optic system. Transmission Transmitter Transmitter Transmission multiplexing multiplexing equipment Receiver Receiver equipment Customer Fiber Customer interfaces interfaces (such as OCx or GbE) to the remote telco node. As another application, the cable TV industry has replaced in recent years some major portions of their distribution networks with a Fiber to the Node (FTTN) configuration. The economics of deploying fiber to support mid-range or broadband data applications to the home or office are just now receiving widespread attention. The bulk of this chapter focuses, however, on technology rather than on economics and cost- optimized network design. 2.1 Optical Fibers Optical fibers used in carrier applications are made predominantly from sil- ica (SiO2). Pure silica has a low optical signal loss in the infrared region of the electromagnetic/electro-optical spectrum. Infrared ranges from 0.80 to 1.60 um in terms of signal wavelength (800 to 1,600 nanometers). Refraction is one of the most important properties of interest in optical communication. The difference in the index of refraction gives the optical fiber its transmission (waveguide) properties. Refraction occurs because light moves faster through some mat