A Cost-Effective and Efficient Scheme for Optical OFDM in Short-Range IM/DD Systems

We propose a cost-effective and efficient modulation scheme for intensity-modulated and direct-detection (IM/DD) optical orthogonal frequency division multiplexing (O-OFDM) systems, which combines complex-to-real transform (C2RT) and fast Hartley transform (FHT), named as fast-fast Fourier transform (FFT). The proposed scheme can modulate the complex constellation by the real-valued operations. Compared with the FFT method, the same OFDM signal can also be generated by fast-FFT, but the computational complexity nearly halved. Meanwhile, compared with the FHT scheme, fast-FFT can modulate the complex constellations by adding a simple C2RT module for a wide applicable range. The transmission experiment of over 50-km standard single-mode fiber (SSMF) has been implemented to verify the feasibility of fast-FFT-based IM/DD O-OFDM systems, including asymmetrically clipping and DC-bias O-OFDM systems. It reveals that fast-FFT shares the same bit-error-rate (BER) performance as FFT, but fast-FFT shows superiority on computational complexity.