Impact of Optical Power in the Guard-Band Reduction of an Optimized DDO-OFDM System

A multiobjective optimization on the parameters of direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems in short-range links is proposed. Based on genetic algorithms, the optimization process takes into account the influence of optical power in the guard-band reduction of such multicarrier systems with 4and 16-quadratic-amplitude modulation (QAM) subcarrier mapping and for propagation in 40 km of standard single-mode fiber (SSMF). Simulation results show that the parameters optimization is responsible for a gain of approximately 2.5 dB [≈ 1.8 dB] in the required optical power for bit-errorrate ≤10^-3, for DDO-OFDM system transmission over 40 km of uncompensated SSMF, with a guard band B_G equals to 50% of the signal bandwidth B_w and 16-QAM [4-QAM] subcarrier mapping. For an extremely reduced guard band of only 1% of B_w, the gain reduced to ≈ 0.5 dB and ≈ 1.5 dB for 16and 4-QAM mapping, respectively. The optimization process is experimentally validated under the transmission of the optimized DDO-OFDM systems in optical back-to-back (B2B) configuration and 40 km of uncompensated SSMF. A fair performance comparison is discussed in the experimental results considering B_G/B_w = 0.5 and B_G/B_w = 0.01 in the range of the optimized optical powers. It is shown that a maximum optical power penalty of approximately 2 dBm is registered according to a guard-band reduction from 50% to 1% of the useful bandwidth, for transmission over the 40 km of SSMF, considering 16-QAM subcarrier mapping.