Abstract: Attachment of an optical fibre (22) to a planar substrate (17) having a major face and an edge surface (14) perpendicular to the major face, the optical fibre (22) being positioned in a groove (18) provided in the major face of the substrate (17) and extending over the edge of the substrate, a mechanical restraint (24) such as a transparent apertured disc being affixed to the edge surface (19) of the substrate, e.g. by a light-cured adhesive (17) to resist movement of the optical fibre (22) in a direction substantially perpendicular to the major face.