An optical demultiplexor utilizes a single optical interference filter disposed between an input end and an output end of the device. The filter is preferably housed wi thin a cavity in a glass block having an upstanding input end, endwall. The optical filter is a wavelength selective means having a wavelength characteristic dependent upon an angle of in cidence. The device has a plurality of reflective surfaces disposed at the input end for reflecting light reflected from the filter, back to the filter at different predetermined angles. Each different predetermined incident angle allows a different predetermined wavelength of ligh t to pass through the filter to an output end being spatially separated from other predete rmined wavelengths that pass through the filter. The reflective surfaces are preferably formed in the upstanding endwall of the glass block. Sixteen channels can be separated by this demultiplexor.
