There are three layers to the traditional hybrid fiber/coax (HFC) CATV distribution system. Supertrunks carry signals over long distances. Distances of 100+ km may be achieved with high signal fidelity, with a single fiber link. Second, feeder links typically span a shorter distance and connect a fiber hub (supertrunk termination) to a fiber node. Nodes are the point in a network at which fiber is converted back to RF – this amplified RF is typically fed over coaxial cable to a number of CATV set top boxes.
Basic applications include the following:
- Campus/Enterprise CATV Distribution – Fiber is used to distribute CATV over distances that are greater than can be achieved with high fidelity over coaxial cable. Loss of fidelity in copper systems primarily results from the use of nonlinear RF amplifiers required for signal amplification over the higher signal attenuating copper. Such fiber distribution systems can employ splitters in either the optical or RF domain, or both.
- Passive optical network (PON) and RF-over-glass (RFoG) architectures have extended fiber penetration all the way to residential and business premises. Optical transmitters have evolved to meet the high launch power, high split ratios, and high stimulated Brillouin scattering (SBS) requirements of FTTx architectures. Likewise optical receivers have evolved to facilitate better noise performance at lower optical received power.
- Supertrunk Links – 1550 nm fiberoptic transmission facilitates the use of erbium doped fiber amplifiers (EDFAs) to accomplish fiber launch powers of up to +21 dBm. This high launch power is useful in systems requiring transmission up to 100 km or systems requiring the optical signal to be split to multiple fiberoptic nodes. 1550 nm transmission also accommodates the use of dense wavelength division multiplexing (DWDM) as a means of transmitting multiple optical signals over a single fiber.
- Multi Mode Fiber Links – A limited number of CATV channels may be transmitted over linear multi mode fiber links. Such links may be useful if multi mode plant is already installed, and may be used for RF video distribution within buildings.