Multiplex is a method to transmit signals simultaneously via the same medium, e.g. several telephone connections through one wire. "Wavelength multiplex" ties up to this by decoding the two or more optical channels of one image to allow a stereoscopic view. Stereoscopic images essentially need two overlapping pictures, each having a slightly different perspective for the left and right eye. The two perspectives are separated by special glasses. They may use different techniques like polarisation, rapid shutters, red-green glasses, or spectral grating. The latter method is suitable for stereoscopy in planetarium domes. It was invented by the German company "Infitec" in 1999.

Wavelength multiplex is based on the transmission of two frequency triplets in the light spectrum. The image information is coded in the primary colours blue, green and red -- they make up one frequency triplet. These monochromatic colours have a narrow-bandwith and an adequate spectral distance, such that the perceptors in the eye can distinguish the colours. The image would still be percepted in full colours. Now, taking two triplets with a small shift in frequency (such that the monochromatic colours of one triplet are more than the full-width half maximum apart from the second triplet), the filters inside the glasses would separate the colour triplets again. Each triplet carries only the information about one of the two pictures as seen by a deviating angle. Seen through the filter glasses, the left and right eye receives the light that is passed by the corresponding side. This wavelength multiplex enables a full colour image with spatial resolution (3D).

Further information: Jorke H. and Fritz M. in "Proceedings Electronic Displays" (2003).