Introduction

Abstract

A passive optical network (PON) is an optical network without any additional electronic or opto-electronic devices. A PON may thus consist of optical fibre, optical splitters and combiners, directional couplers, lenses, gratings, optical filters, phase masks etc. PONs have several advantages over networks with active components: they do not require an electric power supply and are consequently not sensitive to power failures; PONs are not EMI sensitive; and, what is important for the cost of operation: PONs are highly reliable and require no maintenance, because there is no degradation as there would be with active components. The optical fibre used will generally be a single-mode fibre for broadband networks. One important aspect of a multi-user PON is its physical topology, i.e. the way in which fibre parts are connected to form a network. For the application as a subscriber access network the logical structure requires one bidirectional point-to-point connection between the optical line termination (OLT) and each optical network unit (ONU). This can be accomplished by different physical topology types.