In this paper we present a review of different micro-lenses we have developed at the end of single-mode fibers for improving optical coupling efficiency in communication systems. These micro-lenses find their applications in laser-diodes or integrated waveguides to single mode fibers, fiber to detector coupling, or fiber-to-fiber interconnecting. More generally, the applications concern active or passive components to single mode fiber coupling. Three kinds of micro-lenses are considered whose fabrication process has been designed to be very simple and low cost. Some of them are produced by companies in Lannion such as IDIL Fibers Optiques.