A method of automatically coupling between a fiber and an optical waveguide is disclosed. Such a scheme is achieved by the property of the different etching rate in the various wafer direction on a semiconductor material, especial silicon, and the shrinking property of the glass soot formed by a flame hydrolysis deposition technique during a high temperature consolidation process, for improving aligning accuracy. The manufacturing process of the method is described below. First, a waveguide buffer layer is formed on a semiconductor substrate, then a waveguide layer is formed on the semiconductor substrate and the waveguide buffer layer. A part of the waveguide is manipulated to the planar optical waveguide, meanwhile, several windows which lead to the I/O end of the planar waveguide are formed on the other waveguide layer. The semiconductor substrate beneath the windows is etched anisotropically to form several aligning grooves. The lateral faces of these grooves and the surface of the semiconductor substrate can constitute a fixed angle.