High-Level QAM OFDM System Using DML for Low-Cost Short Reach Optical Communications

In this letter, we experimentally demonstrated a high level quadrature amplitude modulation (QAM) optical orthogonal frequency division multiplexing (OFDM) transmission system utilizing a cost-effective directly modulated laser. This experiment was enabled by intrasymbol frequency-domain averaging-based channel estimation, large fast Fourier transform size to enhance the resistance of intersymbol interference, and the discrete Fourier transform-spread technique to reduce peak-to-average power ratio. A 31.7-Gbit/s 2048QAM OFDM signal can be successfully transmitted over 20-km large effective area fiber under a 20% soft-decision forward-error-correction threshold (bit error rate of 2.4 × 10
^-2
).