Performance analysis of a hybrid optical CDMA/DWDM system against inter-symbol interference and four wave mixing

This paper reports the implementation and theoretical model for analyzing an optical CDMA/DWDM hybrid system to reduce two major problems, the Inter-Symbol Interference (ISI) and the Four-Wave Mixing (FWM) effects and improve the performance of optical subscriber access networks by using Zero Cross-Correlation (ZCC) optical codes, which helps to reduce the effect of the Multiple Access Interference (MAI). A squeezing method is used in the proposed hybrid system to completely suppress the ISI. In this method, the sequence interval of the signature code is squeezed into a duration of less than one-bit. The hybrid system is capable of accommodating 120 optical CDMA users carried by only 10 DWDM wavelengths spaced by 0.2 nm with 60 Gb/s/wavelength transmitted over 105.075 km of optical fiber. The result shows that the optimum interval of the code sequence is a quarter (i.e., 25%) of the bit duration. Moreover, the results reveal that the CDMA technology based on the spread spectrum is capable of increasing the nonlinear tolerance of the proposed hybrid system as the energy of bits is distributed over the chip sequence code. Also, the number of ones/weight and the positions between them have a significant effect on the performance of the proposed hybrid system.