Chapter 11 Optical Network Leveling
Installation and Commissioning Manual
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Step 9
Measure and note the received optical power. This value should be
within the limits specified by the channel module spec for the intended
data rate and mode.
Step 10 Force laser on to RLS to disable the transmitter.
Step 11 If the received optical power is out of specification:
•
If turning on the Laser has not changed the power reading: Check
whether you really accessed the right transmitter module. If yes:
Search for the wiring error.
•
If the optical input power had been too high: Insert an attenuator
to correct this.
•
If the optical input power had been to low: Search the optical path
for the error, or replace an attenuator in the path. The
changed/removed attenuator might influence other optical paths,
so check for respective side effects.
Step 12 If the optical input power is within the spec limits: Insert the network
receiver fiber into the planned network receiver port.
End of Procedure
Measuring and Leveling Amplified Lines
When leveling an amplified line several aspects should be considered:
•
EDFAs have a limited dynamic range, i.e. minimum and maximum input lev-
els. Therefore you should level your line span by span from the network
transmitter on one side of the circuit to the network receiver on the other.
•
In EDFAs the signals can interact. If one transmitted signal saturates an
EDFA the other signal levels of the line are reduced. The distortion can
reduce the optical signal to noise ratio (OSNR) even further.
•
Especially pump power controlled EDFAs have no fixed gain. Therefore you
must measure at their input and cannot rely on a specific gain.
•
The most important measurement is optical signal noise ratio (OSNR): It is
no problem to amplify a signal, but you cannot improve the OSNR once it is
low.
•
For optimum transmission characteristics, the goal of leveling is to ensure
equal optical power levels across all of the active channels transported
through the system.