We propose a layered asymmetrically clipped optical fast orthogonal frequency division multiplexing (ACO⁃FOFDM) scheme for intensity⁃modulated and direct⁃detected (IM/DD) systems. Layered ACO⁃FOFDM can compensate the weakness of conventional ACO⁃FOFDM in low spectral efficiency. For FOFDM system, the utilization of discrete cosine transform (DCT) instead of fast Fourier transform (FFT) can reduce the computational complexity without any influence on bit error rate (BER) performance. At transmitter, the superposition of multiple layers is performed in frequency domain, and the iterative receiver is used to recover transmitted signals by subtracting the clipping noise of each layer. We compare the BER performance of the proposed layered ACO⁃FOFDM system and DC⁃offset FOFDM (DCO⁃FOFDM) system with optimal DC⁃bias at the same spectral efficiency. Simulation results show that in terms of optical bit energy to noise power ratio, the layered ACO⁃OFDM system has 1.23 dB, 2.77 dB, 3.67 dB and 0.78 dB improvement at the forward error correction (FEC) limit compared with DCO⁃FOFDM system when the spectral efficiencies are 1 bit/s/Hz, 2 bits/s/Hz, 3 bits/s/Hz and 4 bits/s/Hz. The layered ACO⁃FOFDM system with zero DC⁃bias is more suitable for adaptive system, so this system also has potential for application in IM/DD systems.
FOFDM; ACO⁃FOFDM; DCT; spectral efficiency; IM/DD