chapter 1, WDM, Fiber to the X, and HFC Systems: A Technical Review

Excerpt

1.1 Introduction

Fiber optics is mature technology. It was used at the beginning of the eighties for computers' local networking using light emitting diodes (LEDs). One of its major advantages over traditional “copper lines” and “coax lines” is the virtually infinite bandwidth of the fiber line, which translates into a higher data rate capacity and therefore more users per line. This advantage can be expanded when several wavelengths are transmitted through the same fiber, where each wavelength carries wide band data. This method is called wavelength division multiplexing or WDM. The second main advantage of a fiber optics line over a regular “copper line” is its low-loss nature, traditionally 0.15 dB∕km. The traditional coax will lose half of the input power within a few hundred meters. In comparison, a good-quality fiber will lose half of its input power after 15 to 20 km. This means less retransmit and fewer nodes required to amplify the signal. It is known that the transmitted distance depends on the input power to the fiber losses and the receiver sensitivity. An additional advantage of fibers is their immunity to any kind of magnetic interference from the outside. Hence, there will be fewer problems related to surge protection to take care of during deployment. Furthermore, since the fiber does not emit any electromagnetic radiation, it is considered to be an ideal line that cannot be tapped. One more advantage over the coax is the fiber diameter of 10–50 microns. Thus, one fiber cable, which contains many fibers, results in a higher data rate per cable and higher data capacity.

As optics and dedicated integrated circuits (IC) technology progressed, more applications and content could be designed and implemented using fiber optics. Traditional “community access TV” (CATV: cable TV) shifted to fiber optics; other applications, such as slow data transport “return path” for “video on demand” (VOD) charging, fast data transport such as the Internet, and digital data and multimedialike video-over-internet protocol, created a need for different kinds of receivers and transmitters with MUX∕deMUX blocks. low optical x-talk and bulk optics, while size reduction effort was on both electronics and optics. Mixed signal design strategies were emerging in order to reduce costs, shrink size using system-on-package (SOP) technology and penetrate the market. Mature cost effective building blocks for optics and signal conversion from modulated light to electrical signal, and vice versa, resulted in optical deployments. These deployments are: fiber to the curb (FTTC), fiber to the home (FTTH), fiber to the business (FTTB) fiber to the premises (FTTP), or in general, fiber to the “x” (FTTx) implemented by a passive optical network (PON), ethernet passive optical network (EPON), gigabit passive optical network (GPON), broadband passive optical network (BPON), and asynchronous transfer mode (ATM) passive optical network (APON).