Error-free detection of ultrashort-pulse CDMA signals in a hybrid optical WDM-CDMA system

Summary form only given.Ultrashort-pulse code-division multiple-access (CDMA) communications based on spectral phase encoding and decoding of coherent pulses has been studied by several groups recently. We report experiments on a hybrid WDM-CDMA fiber communication system, in which ultrashort pulse CDMA signals are spectrally overlaid with a wavelength-division-multiplexing (WDM) data stream. Because the broadband CDMA signals utilize the bandwidth occupied by the guard bands between WDM channels, the overall system-bandwidth efficiency is increased. The CDMA channels provide additional transmission bandwidth for WDM systems already operating at capacity or can be used to support bursty network traffic. Because WDM signals and CDMA signals coexist in both spectral and temporal domains, one of the key issues in the hybrid system is to reject WDM interference for CDMA detection. We demonstrate the complete rejection of a WDM channel for the error-free detection of CDMA signals by the use of a narrow-band spectral notch filter and a fiber nonlinear thresholder. We also perform experiments that indicate the feasibility of scaling to multiple WDM channels while maintaining error-free CDMA operation.