In previous post, about Step 1, where we discussed dawn of fiber communication links we saw, that main problems that engineers met at that time was distance limitations, and they needed add signal re-generators in middle of fiber distances, and needed thus convert back and forth signal from optical to electrical.
That was not effective and expensive.
What happened at Step 2 of this optical revolution? Optical Amplifiers were introduced, and schemes we discussed in previous post came to such concept:
Figure1 : Increasing transmission distance by introducing optical amplifiers.
Be sure to compare with schemes in Step 1.
So, what can clearly see here is that while technologically it was more complex, in reality scheme looks more simple now and these devices now starts to amplify signal compensate power loss.
Another important thing is that these devices already does not needed convert signal back from optical to electrical. Examples of such devices are Raman amplifiers, EDFA’s, or Semiconductor Optical Amplifier.
Now testing is even more easy, it is enough to connect testing equipment at the end of those segments, where you need to compensate power loss value, and measure proper value.
However, it’s important to note, that while adding optical amplifiers compensates power lost, that is caused by attenuation, and can be also calculated if you know how many db you lose per km in your fiber cable, then optical amplifiers could not do anything with optical dispersion. This is why Dispersion Compensation Modules, or DCM’s where introduced along with Optical Amplifiers.
DCM’s can reduce the width of optical pulses transmitted into optical cable.