Description: The optical signal power at the output of the Amplifier.
 The value of this attribute triggers the alarm, based on
 mean value and trigger as defined by 
 ons15501OutputSignalPowerMean and
 ons15501OutputSignalPowerTrigger.

 This value is internally calculated using the following
 formula.
  ons15501OutputSignalPower = ons15501OpticalPowerGain +
                                 ons15501InputOpticalPower
 At very low ons15501InputOpticalPower (below -16 dBm),
 the ons15501OutputSignalPower has significant difference
 from ons15501OutputOpticalPower while at higher input
 power (ons15501InputOpticalPower) they are closer.

 Following graph captures the difference (for a 17 dBm
 EDFA)
    (dashes '-'/'_' denote optical output power
     while dots '.' denote signal output power)

      ^
      |                               .-
      |                            .-
      |                         .-
+5 dBm   |                      .-
      |                   .-
Optical   |               _.-
power /   |         _  -.
Signal    |_  _  -   .
power     |       .
      |    .
      | .
-17 dBm +-----------------------+-------------->
     -29 dBm               -10 dBm
            Input Optical Power