Experimental Demonstration of an IFFT FFT Size Efficient DFT-Spread OFDM for Short Reach Optical Transmission Systems

We experimentally demonstrate an IFFT/FFT size efficient discrete Fourier transform (DFT)-spread orthogonal frequency-division multiplexing (OFDM) based on complex-valued IFFT/FFT operations without Hermitian symmetry constraint at the input, for short-reach intensity-modulated and directly-detected optical fiber transmission systems. The only complex-valued IFFT-based OFDM has the similar peak-to-average power ratio (PAPR) and bit error rate (BER) performance, but with only half of the IFFT/FFT size as the conventional real IFFT-based OFDM. In this paper, the complex IFFT-based OFDM combined with DFT-spread technique is proposed and applied to reduce PAPR and IFFT/FFT size, and improve BER performance at the same time. The experimental results show that, with the help of PAPR reduction enabled by DFT-spread, more than 2-dB improvement in receiver sensitivity has been achieved after 20.62 km of single mode fiber transmission at a BER of 3.8 10 -3 (7% hard-decision forward error correction threshold). In addition, by using the DFT-spread technique, the BER performance comparison between complex IFFT-based OFDM and real IFFT-based OFDM is also performed. The results show that, the BER performance of the former is slightly worse than the latter, but has lower hardware complexity and less power consumption due to the reduced IFFT/FFT size.