Specifications

5-2
Cisco ONS 15530 Planning Guide
OL-7708-01
Chapter 5 Amplified Network Planning
About Variable Optical Attenuation
Figure 5-1 Erbium-Doped Fiber Amplifier Design
The key performance parameters of optical amplifiers are gain, gain flatness, noise level, and output
power. EDFAs are typically capable of gains of 30 dB or more and output power of 17 dBm or more. The
target parameters for an EDFA, however, are low noise and flat gain. Gain should be flat because all
signals must be amplified uniformly. While the signal gain provided with EDFA technology is inherently
wavelength-dependent, it can be corrected with gain flattening filters. Such filters are often built into
modern EDFAs.
Low noise is a requirement because noise, along with signal, is amplified. Because this effect is
cumulative, and cannot be filtered out, the signal-to-noise ratio is a limiting factor in the number of
amplifiers that can be concatenated and, therefore, the end-to-end reach of optical signals. That is
because the optical amplifier merely amplifies the signals and does not perform the 3R functions
(reshape, retime, retransmit).
Note The Cisco ONS 15530 interoperates with the Cisco ONS 15501 optical solutions amplifier. For
information about the Cisco ONS 15501 features, refer to the Cisco ONS 15501 User Guide.
About Variable Optical Attenuation
Optical attenuation is often needed to equalize all DWDM channel powers in an amplified ring network.
In a ring network, the pass through channels are typically weaker than the added channels. To equalize
the channel powers, the added channel powers are attenuated down to the power level of the pass through
channels. Power equalization is needed in an amplified network because of the input power limitation of
the EDFAs and to simplify network management.
The Cisco ONS 15530 supports two types of variable optical attenuation, per channel and per band. Per
channel attenuation equalizes the channel powers on a channel-by-channel basis, while the per band
attenuation achieves equalization by attenuating channels on a band-by-band basis.
VOA Modules
Variable optical attenuation on the Cisco ONS 15530 is provided by two types of VOA modules:
• PB-OE (per-band optical equalizer) modules
• WB-VOA (wide-band variable optical attenuator) modules
The VOA modules are half-height modules inserted into a carrier motherboard installed in a
Cisco ONS 15530 chassis slot.
Pump
laser
Pump
laser
Erbium-doped
fiber (10-50 m)
CouplerIsolator IsolatorCoupler
48093