It is known to couple a collimated beam of light into the end of an optical fibre with a graded index lens having an angled facet at the lens/fibre interface to reduce the amplitude of Fresnel retroreflected power. The expense incurred in providing angled facets is avoided by using a two-part compound lens. One part is a graded index lens part having an axial length shorter than a quarter period. To this is bonded a cylindrical uniform refractive index lens part whose index is matched with the effective refractive index of the fibre. This reduces the amplitude of the retroreflection power by causing the displacement of the Fresnel reflection from the lens focus.