Specifications

CHAPTER
5-1
Cisco ONS 15530 Planning Guide
OL-7708-01
5
Amplified Network Planning
The Cisco ONS 15530 topologies might require signal amplification because of the distance between
nodes and the optical loss of channels as they pass through nodes in the network. This chapter discusses
the amplification and attenuation features supported by the Cisco ONS 15530. This chapter contains the
following sections:
• Optical Amplification Overview, page 5-1
• About Variable Optical Attenuation, page 5-2
• VOA Modules, page 5-2
• Amplified Network Planning Considerations, page 5-6
• Amplified Network Planning Guidelines, page 5-7
Optical Amplification Overview
Due to attenuation caused by the physical characteristics of the network topology, such as the distance
between nodes and the optical loss for channels passing through nodes, there are limits to how far a
signal can propagate with integrity before it has to be regenerated. The optical amplifier makes it
possible to amplify all the wavelengths at once without any optical-electrical-optical (O-E-O)
conversion. Besides being used on optical links, optical amplifiers also can be used to boost signal power
after multiplexing (post-amplification), or before demultiplexing (preamplification).
Erbium-Doped Fiber Amplifiers
The EDFA (erbium-doped fiber amplifier) is a key enabling technology that extends the range of DWDM
networks. Erbium is a rare-earth element that, when excited, emits light around 1.54 micrometers—the
low-loss wavelength for optical fibers used in DWDM. Light at 980 nm or 1480 nm is injected into the
fiber using a pump laser. This injected light stimulates the erbium atoms to release their stored energy
as additional 1550-nm light. As this process continues down the fiber, the signal on the fiber grows
stronger. The spontaneous emissions in the EDFA also add noise to the signal, which is a limiting factor
for an EDFA. Figure 5-1 shows a simplified diagram of an EDFA.