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a b s t r a c tIn order to optimize the performance of three level code division multiplexing (3LCDM) at 2×20 Gb/s data rate, signal level spacing technique is investigated in this paper. The 3LCDM performance is improved considerably using both electrical and optical level spacing optimization configurations. The results demonstrate that by optimization, in conditions of the optical signal-to-noise ratio, an improvement of around 4.5 dB can be achieved in both approaches as well as 3.3 dB in the electrical configuration and 3.5 dB in the optical configuration can be accomplished for the 3LCDM in terms of the receiver sensitivity.

In this research, performance of Three Level Code Division Multiplexing (3LCDM) technique is investigated for high-speed optical fiber communication systems. It is shown that 40 Gb/s (2×20 Gb/s) 3LCDM system perform s better than the conventional 40 Gb/s non return to zero (NRZ-OOK) in term the dispersion tolerance. At 40 Gb/s, the lower level displays a nearly analogous behaviour of positive and negative chromatic dispersions tolerance which stands about ±98 ps/nm while the upper level has chromatic dispersion tolerance of ±81 ps/nm at BER of 10-9. These values are higher than that of 40 Gb/s conventional NRZ, which is approximately ±49 ps/nm.

A new dispersion map is designed for threelevel code division multiplexing (3LCDM) of a 40 Gb/s (2×20 Gb/s) over 500 km (5×100 km) standard single mode fiber. The results show that an 87.5 % dispersion compensation ratio was the optimum map for the 3LCDM system. The system performance is improved by 6 dB in optical signal-tonoise ratio, 6 dB in receiver sensitivity and 3 dB in self-phase modulation threshold. Based on these improvements, the 3LCDM performance is comparable to the available multiplexing and modulation techniques while offering simpler transmitter and receiver architecture.