Methods for the fabrication of dense wavelength division multiplexors (DWDM) are disclosed. In one embodiment, an array of micro membranes and an array of cavities for optical fibers are etched in a substrate. The distance between major surface of adjacent micro membranes is controlled during the etching step. Multilayer narrow band pass filters are then deposited on all micro membranes simultaneously by vacuum deposition methods. Due to the controlled separation between adjacent micro membranes, the central wavelength of transmission either increases or decreases from one membrane to another. In another embodiment, a micro machined structure containing a plurality of cavities and a slot for variable narrow band pass filter is fabricated. The variable narrow band pass filter is aligned with respect to the optical fibers to obtain a WDM.