a coupler is disclosed for properly positioning the endface of an optical waveguide filament with respect to an optoelectronic device in a repeatable fashion . three elongated rods of deformable material are disposed in mutually contacting relationship within a bore which terminates at the device . after a filament is inserted into the aperture between the rods so that its endface is disposed adjacent to the device , an elastomeric washer is caused to deform inwardly against the rods , thereby causing them to engage the filament . since the ends of the rods adjacent to the device are secured in the bore , the filament may be replaced by other filaments , the endfaces of which will be precisely positioned with respect to the optoelectronic device .