An optical system comprises a light emitter, an optical waveguide, and a lens that optically couples the light emitter to the optical waveguide. The lens has a long axis and a plurality of surfaces surrounding the long axis, the plurality of surfaces including a convex surface and a flat surface. The convex surface faces the light emitter such that light emitted by the light emitter enters the lens through the convex surface. In some examples, the lens serves as a fast axis collimation (FAC) lens. In some examples, the flat surface serves as a mounting surface to mount the lens on a substrate such that the convex surface faces the light emitter and an output surface of the lens opposite the convex surface faces the optical waveguide. In some examples, the convex surface includes an anti-reflection coating.