Multi-layer Modulation for Intensity-Modulated Direct-Detection Optical OFDM

Multi-layer modulation (MLM)-aided intensity-modulated direct-detection (IM/DD) DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) are considered. More explicitly, we propose a double turbo receiver (DTR) for jointly detecting the MLM and for compensating the clipping distortion. Additionally, a genetic-algorithm-aided weight optimization is pursued for seeking an increased MLM bits per symbol (BPS) throughput. Our numerical results demonstrate that for ACO-OFDM, at the throughput of η=3 BPS, a 3 dB gain was attained for Q=15 DTR iterations without requiring weight optimization. For DCO-OFDM, an even more significant gain of 12 and 8 dB was observed at the throughput of η=3 BPS and η=4 BPS, respectively, without any clipping distortion compensation.