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It is 21 years since the first passive optical network (PON) was standardized as an asynchronous transfer mode passive optical network (APON) with same optical distribution network scheme as we know in current networks. A lot of PON networks were standardized in the following years and became an important part of telecommunication. The general principles of these PON networks are described in many papers and books, but only a little information about used lasers is available. The aim of this tutorial is to describe lasers used in PON networks and principles of their operation. The paper describes the principles of single longitudinal mode (SLM), multi longitudinal mode (MLM), distributed-feedback (DFB), and Fabry–Pérot (FP) lasers. Furthermore, the lasers are compared by their usage in optical line termination (OLT) for passive optical networks. The second part of this tutorial deals with activation process of optical network unit. The described principle is the same for connection of a new customer or blackout scenario. The end unit is not able to communicate until reach the operational state; each state is defined with physical layer operation and administration and maintenance (PLOAM) messages sequence and their processing.

Lasers in Passive Optical Networks and the Activation Process of an End Unit: A Tutorial