In Step 4, WDM concept, that took off in Step 3, evolved further to multiple wavelengths, that now was not only more over same fiber, but also much more closely spaced. So, DWDM – (Dense Wavelength Division Multiplexing) technology was started to see a light, and by means of this technology service providers could send wavelengths over same fiber as dense as separated by 0.4 nm only!
Now, that’s already real re-use of fiber infrastructure!
Figure 1: DWDM (Dense Wavelength Division Multiplexing) technology principle
According to ITU G.692 standard, DWDM technology multiplexing equipment can make up to 200 wavelengths sent over same fiber and not mix with each other. And it seems only sky is the limit to DWDM technology, because according to this article, Bell Labs did an experiment, where they could send 1000 wavelengths in same fiber, and this article is 15 years old! Imagine, what is possible now…
What are conditions that are required for successful sending so many wavelengths over same fiber?
– Stable wavelength;
– Minimum dispersion;
– Narrow spectral width lasers;
– Limitation of total power in core of fiber;
Also, laser modules and DWDM fiber modules that are used in these systems needs to be carefully designed to control a temperature, and subsequent wavelength drift, because as a result of such drifts usually are interference between 2 channels.
And yes – adding EDFA, can increase a distance of whole DWDM transmission system:
Figure 2: adding EDFA to increase DWDM system distance
Testimonials
Lomoveishiy – Finland
I needed those to connect my PC on the third floor to have internet access in that room, and ISP installed their modem on the first floor only. After dropping fiber patch cables, plugged in all cables into these media converters at both sides, and link came up instantly. Was much easier than I thought!
