Comparison of Coherent WDMA and Hybrid WDMA/CDMA for the Multiplexing of Optical Signals

In this paper, we provide an accurate analysis of the performance of coherent dense wavelength-division multiple-access (WDMA) schemes introduced for use in high-capacity optical networks. In our analysis, the effects of interference from other signals due to the frequency overlap caused by the instability of the carrier frequency of laser, or to mistakes in frequency coordination and assignment, are taken into account. Phase noise and thermal noise are also taken into consideration. Dense WDMA is then coupled with spread-spectrum direct-sequence modulation in order to mitigate the effect of interference from other signals. The performance of this hybrid of WDMA and code-division multiple- access (CDMA) scheme is also analyzed and compared to that of pure WDMA.The average bit error probability of dense WDMA and WDMA/CDMA schemes is evaluated in integrating the characteristic function of other-user interference at the output of the matched optical filter. Gaussian approximation techniques are also employed. Time-synchronous and as asynchronous systems are analyzed in this context. Binary phase-shift-keying (BPSK) data modulation is considered. Our analysis quantifies accurately for first time the multiple-access capability of dense WDMA schemes and the advantages offered by employing hybrids of WDMA and CDMA