Abstract: The characteristic pass and rejection bands of an interference filter may be altered by changing the angle of incidence of light upon the filter. If the input beam is first collimated by a GRIN lens before it is transmitted to the interference filter, the characteristic wavelength bands of the filter can be altered by altering the distance of the input beam from the axis of the GRIN lens. Therefore, ferrules having imbedded therein input/output optical fibers may be provided to vary the distance of the input and output optical paths from the axis of the GRIN lens so that the desired spectral components in these paths are rejected or passed by the filter for performing multiplexing and demultiplexing.