Delta-sigma-modulated IFoF transmission system assisted by a correlative-level encoding technique.

A delta-sigma-modulated intermediate-frequency-over-fiber (IFoF) transmission system assisted by a correlative-level coding technique is proposed and experimentally demonstrated. Unlike conventional delta-sigma IFoF systems with multiple output levels to achieve higher signal quality or larger capacity, a correlative-level encoder is exploited as a second modulator preceded by the delta-sigma modulator. The encoder compresses the bandwidth of the delta-sigma modulated signal by creating a correlation between adjacent signal symbols. As a result, the sampling frequency of the delta-sigma modulator in the proposed system can be increased beyond the transmission bandwidth of the IFoF system, considerably improving the in-band signal quality and the transmission capacity over the conventional multi-level approach. This is because the quantization noise from the delta-sigma modulation in the proposed scheme is more aggressively pushed away from the signal bandwidth with the high sampling frequency. According to experimental results, the proposed link provides at least a 40% larger transmission capacity for similar in-band signal quality or 2.1% better average EVM performance for the same capacity than the conventional four-level pulse-amplitude-modulation delta-sigma IFoF systems.