This part of IEC 61757 is a generic specification covering optical fibres, components and subassemblies as they pertain specifically to fibre optic sensing applications. It has been designed to be used as a common working and discussion tool by the vendor of components and subassemblies intended to be integrated in fibre optic sensors, as well as by designers, manufacturers and users of fibre optic sensors independent of any application or installation. The objective of this generic specification is to define, classify and provide the framework for specifying fibre optic sensors, and their specific components and subassemblies. The requirements of this standard apply to all related sectional, family, and detail specifications. Sectional specifications will contain requirements specific to sensors for particular quantities subject to measurement. Within each sectional specification, family and detail specifications contain requirements for a particular style or variant of a fibre optic sensor of that sectional specification. A fibre optic sensor contains an optical or optically powered sensing element in which the information is created by reaction of light to a measurand. The sensing element can be the fibre itself or an optically powered element inserted along the optical path. In a fibre optic sensor, one or more light parameters are directly or indirectly modified by the measurand somewhere in the optical path, contrary to an optical data link where the information is merely transmitted from the transmitter to the receiver. Generic tests or measurement methods are defined for specified attributes. Where possible, these definitions are by reference to an IEC standard – otherwise the test or measurement method is outlined in the relevant sectional, family and/or detail specification. Annex A gives examples of fibre optic sensors to better illustrate the classification scheme. The examples given are illustrative only and are not limitative, nor do they constitute a recommendation or endorsement of a particular transduction principle.