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In this paper for tlie ffrst time a basic theory of optical code division multiple access (CDMA) is presented. Based on the detection principle of photodiodes and the coherence time of optical sources a general receiver model is deduced. From this model 9 elemcirtary structures can be found, enabliiig tlie theoretical ;uialysis of all known schemes. Moreover, we derive geiieral rules for the utilization of suitable code families for possible structures.*K. Iversen is now with the tleiiil-icli-Hei-tz-InstitiiT. fiir 'The term (dense) WDhlA is used ill tire chairire1 spacing is in the order of 1 nm. The t~erin FDMA is eir~ploycrl if t . 1~ clranirel spacing approximately correspoiids t,o the signal haiitlwicl~.lr. In this case normally t,he heterodyne principle is used.