Abstract: Lack of versatility and efficiency in optical multiplexing/demultiplexing is countered by progressing incident light along a wavelength selective holographic reflection filter which reflects different wavelengths at different positions along the filter. Light from a fibre optic input cable is directed by mirrors to make successive passes at the filter at respective different positions therealong and detectors receive the respectively reflected wavelengths. The filter preferably varies the reflected wavelength continuously and progressively as the incident light progresses along the filter.