Category Archives: CATV systems

Optical Fiber CATV System Design

Analog AM fibre optic systems have begun to replace coax cable for local distribution within a CATV network, while digital systems are being used for headend or hub site elimination and for transmitting various data services. In the past, these simulations and digital transmission systems are operating independently of each other in a single optical fibre. In the past, these analog and digital transmissions systems are operated separately from each other over separate optical fibres.

However, as these CATV EDFA grow and expand, the current trend in CATV system design incorporates wavelength division multiplexing to combine both the analog and digital signals for transmission using the same fibre. This allows the system to expand by increasing the number of signal transmission in fibre is installed. With the growth of these systems, need no longer is the only path forward path transmission. Today’s CATV system may also need a return path network processing data from the Internet, through the cable modem. Figure 1 illustrates a typical system architecture including a super trunk. By transporting a high quality replica of the headend signals, this system reduced the number of cascaded amplifiers required.

In the early 1990’s, The CATV providers began using multichannel digital systems to transport large amounts of compression, digital video headends between channels. Still operating in the 1310 nm wavelength window, in this configuration, a previous separate headend is replaced by very high quality signals that are transported by a multichannel digital system from “master” headend. Figure 1 illustrates this configuration. The emergence of high performance outside 1550nm vestigial sideband modulation/AM transmitter and erbium-doped fibre amplifiers (EDFAs) changed the CATV system architecture design again. These 1550 nm links are used to transmit signals over long distances between a head end website, use as a series EDFA optical amplifier.

Figure 1- Hybrid Analog/Digital CATV Architecture

The high performance 1550 nm systems vary slightly in that a few additional optical components are required. Shown in Figure 2, the system also integrates optical splitters in addition to the EDFA. In this configuration, the transmitter is assumed for the output, a common feature, the new launcher. The first output of the 1550 nm transmitter feed a secondary head end 1310 nm transmitter. 1×2 for the second optical output in the beam splitter. The first output feeds directly into a 1550 nm receiver for distribution from the main headend to 1310 nm transmitter. The second output of the optical splitter feeds an EDFA. The signal is amplified optically and forwarded to the optical receiver which supplies a third headend located many miles away in the system.

Hybrid 1310 nm & 1550 nm VSB/AM CATV Architecture

The first three architecture without WDM components and are used to represent the complete simulation architecture. As the growth of CATV system, the need to increase transmission capacity of each optical fibre along with it. WDM allows both analog and digital signals to coexist in a single fibre. The figure 3 illustrates a unidirectional WDM AM CATV/Ditital transport system.

Figure 3 – Unidirectional Analog/Digital CATV Transport using WDM

In the configuration as shown in figure 4, the signal from the 1310 nm CATV AM transmitter and the 1550 digital transmitter is wavelength division multiplexed onto one fibre. At the receive, the signals are demultiplexed and output to the correct receivers. In order to maintain quality system, WDM must be a high isolation type, analog signal to prevent interference between 1310 nm and 1550 nm digital signal.