A light coupler between an optical fiber (6) and a waveguide is made on a semiconductor-on-insulator substrate (1), this substrate (1) comprising a thin layer of semiconducting material in which the waveguide is made. The coupler comprises a light injector (5) and an adiabatic collector (4) made up with an inverted nanotip formed from the thin layer of semiconducting material. The injector (5) is formed on the insulator (3) and has a face (7) for receiving an end of the optical fiber (6). The adiabatic collector (4) has a cross-section which increases from a first end located on the side of said end of the optical fiber (6) right up to a second end which is connected to the waveguide, the injector (5) covering the adiabatic collector (4) and having a rib waveguide shape.