Dispersion-induced power fading in intensity modulated direct-detection systems degrades the higher frequency subcarriers' signal qualities. In layered/enhanced asymmetrically clipped optical OFDM (ACO-OFDM), which is a spectrally efficient version of ACO-OFDM, the error propagation in the iterative decoding can further degrade the performance, especially when a low bias current is used for the directly modulated laser. In this letter, we propose using pairwise coding within each layer to improve the bit error rate. We transmitted 5-GBb 16-QAM OFDM signals over a 19.8-km single mode fiber, and found a 3.6-dB improvement in the Q2-factor.
- asymmetrically clipped orthogonal frequency division multiplexing (ACO-OFDM)
- Direct modulation direct-detection (DM/DD)
- optical communications
- pairwise coding