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Table Of Contents
1.2 Wavelength Protection Switching
Applications
This manual describes how to install and operate the Cisco Optical Network System (ONS) 15216 Erbium-Doped Fiber Amplifier 2 (EDFA2). The ONS 15216 EDFA2 is an optical amplifier that enables the migration to next-generation all-optical networks. It features bandwidth-on-demand and wavelength protection switching that extend dense wavelength division multiplexing (DWDM) links by hundreds of kilometers.
With the ONS 15216 EDFA2, optical signals from a span in a DWDM network can be added or dropped without negatively affecting (degrading) other optical signals on the same span.
1.1 Bandwidth On Demand
The ONS 15216 EDFA2 is a technology for bandwidth-on-demand wavelength services. Depending on the settings and the input power, every wavelength in a ONS 15216 EDFA2 is guaranteed to be amplified by 13 to 22 dB. With the ONS 15216 EDFA2's gain control technology, amplification for each wavelength remains constant at all times as wavelengths are added or dropped from an optical fiber. As long as the total (composite) input power of all wavelengths is between 4 dBm and -27 dBm, any number of wavelengths can be amplified.
1.2 Wavelength Protection Switching
The ONS 15216 EDFA2 uses wavelength protection switching to restore wavelengths that are lost in the event of a fiber cut or other loss of signal. Figure 1-1 shows an example of wavelength protection switching. In this example, two wavelengths are routed clockwise around a metro ring, and two wavelengths are routed counter-clockwise around the same ring. Of the two counter-clockwise wavelengths, only one transits the span linking locations D and C. If a fiber cut occurred on this span, the affected wavelength could be restored by rerouting it (clockwise) around the ring to location D. Wavelength protection switching minimizes the amount of bandwidth allocated for restoration because only the affected wavelength is restored, not the entire fiber.
Figure 1-1 Wavelength Protection Switching
After a protection switch occurs, the number of wavelengths on each fiber changes. In the example, the number of clockwise wavelengths increases to three,while the number of counter-clockwise wavelengths decreases to one.
1.3 Key Features
Figure 1-2 shows a block diagram of the ONS 15216 EDFA2.
Figure 1-2 ONS 15216 EDFA2 Block Diagram
The ONS 15216 EDFA2 has the following key features:
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Adjustable constant gain of 13 to 22 dB
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1.3.1 Constant Gain
Constant amplification (gain) per wavelength is important for ensuring that variations in power between channels at the receivers is minimized. As wavelengths are added/dropped from an optical fiber, small variations in gain between channels in a span can cause large variations in the power difference between channels at the receivers. The ONS 15216 EDFA2 enables bandwidth-on-demand services by guaranteeing that every wavelength is amplified by a value that can be set between 13 and 22 dB, no matter how many wavelengths are being amplified.
Constant gain is achieved using an automatic control circuit that adjusts pump power when changes in input power are detected. The ONS 15216 EDFA2 operates in Constant Gain Temperature Compensated mode by default, but since there may be applications where other operating modes may be required, the ONS 15216 EDFA2 can be set to operate in any one the following pump control modes:
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1.3.2 Gain Flattening
Figure 1-3 illustrates the effect of the gain flattening filter in the ONS 15216 EDFA2. Fiber (a) in the figure shows a set of channels with equal powers being input to a cascaded network of amplifiers that produce vastly different power levels and optical signal-to-noise ratios (OSNR) at the output. In contrast, fiber (b) shows how the EDFAs effectively reduce this effect by introducing a gain flattening filter within each amplifier.
Figure 1-3 Gain Flattening Filter
1.3.3 Transient Suppression
Transients in the performance of optical amplifiers are inevitable whenever the number of signals, or the relative power of signals, changes. The ONS 15216 EDFA2 uses transient suppression to reduce the amount of time required by an amplifier to recover from a change. This indicates the suitability of the amplifier for add/drop applications like those described earlier.
1.3.4 Low Noise
Whenever there is gain in an optical system, noise also occurs. The predominant source of noise in EDFAs is amplified spontaneous emission (ASE). The ONS 15216 EDFA2 has a low noise figure of less than 7 dB at -5 dBm input.
1.3.5 SNMP MIBs
The ONS 15216 EDFA2 SNMP MIBs contain definitions of management information that allows network systems to be remotely monitored, configured, and controlled.
1.3.6 TL1
The ONS 15216 EDFA2 has a TL1 interface available to the network operator and craftsperson.
Posted: Sun Apr 2 01:59:51 PST 2006
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