A method for the fabrication of a fiber optic coupler includes a step of fusing together two optical fibers along their longitudinal sections by heating them and a step of stretching the two optical fibers independently of one another with different conditions of tension and/or temperature so that the difference in their propagation constants varies. A desired splitting ratio of the fiber optic coupler can easily be achieved by making the above-said difference in propagation constant vary in the stretching step.