Direct-Detection Optical OFDM Transmission System Without Frequency Guard Band

Interleaver and turbo code techniques are used in high spectral-efficient direct-detection optical orthogonal frequency-division-multiplexing (OFDM) transmission systems allowing significant improvement of optical receiver sensitivity by mitigating the unbalanced noise distribution in subcarrier signals. The optical signal-to-noise ratio of 5.18 Gb/s, 7.77-Gb/s coded OFDM (5.18 Gb/s after decoding), and 7.77-Gb/s coded OFDM with interleaver (5.18 Gb/s after decoding) over 200-km single-mode fiber at a bit-error rate of 10
^-4
are 23.7, 18.0, and 17.1 dB, respectively.