Overview

Thousand centuries completed, the opportunity will not be closed for anyone to contribute again. All future generations will still find something to discover. In any matter the beginning was far from the achievement, how many objects about which our age hasn't the slightest idea.

Seneque, Letters to Lucillius

"Many books and periodicals contain detailed writings on scientific topics and an increasing amount of technological gadgetry impinges on our daily lives" [1]. In this work, we tried to avoid exclusively giving the tricks of the trade. However we could not avoid being strongly focused on only a small part of the larger optical-telecommunications domain. It is sometimes difficult to step back and see the panorama. At this point we might ask: Where do we go from here? In our domain of DWDM, we have seen during the last few years a bandwagon effect of the business community, after much mistrust in the early 1980s. Today, many venture-capital firms have invested billions of dollars in DWDM and optical telecommunication. But there are likely false trails, on which we are going along, that will be abandoned. The problem is not, as sometimes asked, what will replace DWDM in the long-term? Analysis has shown that satellite communications including low-earth-orbit satellite communications are generally more expensive and capacity limited compared to fiber communications for long-distance highcapacity links. New concepts and new devices will be discovered in the ages to come but it is unlikely that the photonic technologies will be abandoned.