This document provides system design methodology guidance to users and suppliers of fibre optic transmission systems for telecommunications and broadband video distribution applications. The function of the fibre optic systems considered in this document is to interconnect signals between defined digital and analogue interfaces via a fibre optic link. In general, fibre optic systems are built-up from basic fibre optic systems (BFOS). As a result, it is necessary to consider only the BFOS, which transmits a single electrical signal between two points without intermediate regeneration. Thus, these guidelines are applicable to almost all design cases.