a wavelength - division multiplex component for an optical broadband isdn network with monomode transmission fibers is an uncomplicated component for bi - directional optical wavelength - divison multiplex transmission composed of a rod lens , a wavelength selective filter planarly applied to a front surface of the rod lens , and a plug member surrounding the rod lens and the filter . monomode and multimode light waveguides are held in the plug member and are butt - coupled to a back surface of the rod lens . the monomode light waveguide fiber is preferably aligned to the optical axis of the rod lens and the front end face of the rod lens is preferably inclined slightly relative to the optical axis so that the multimode light waveguide , which extends parallel to the monomode light waveguide , can be offset laterally therefrom .