Abstract
In this paper, we propose and experimentally demonstrate a radio frequency
(RF)-tone-assisted optical orthogonal frequency-division multiplexing (OFDM)
transmission. By inserting an RF tone at the edge of the signal band and biasing
the Mach–Zehnder modulator (MZM) at the null point, the proposed system
has a better sensitivity and chromatic dispersion (CD) tolerance compared
to the previous intensity-modulated single-sideband OFDM (SSB-OFDM). We show
analytically that the majority of the linear channel impairments, such as
the transmitter, CD, optical filtering, and receiver, can be compensated for
by a simple zero-forcing equalizer. Besides, the optimum value of the important
parameter, carrier-to-signal-power ratio (CSPR), is analytically obtained
and supported via the experimental results. We also observe that the relatively
worse sensitivity of the previous SSB-OFDM can be attributed to the limited
CSPR. We experimentally demonstrate a 10-Gb/s, 8 quadrature-amplitude modulation
(QAM) RF-tone-assisted OFDM transmission, and show that our system has a ${\sim}$5-dB better
sensitivity compared to the previous intensity-modulated SSB-OFDM and exhibits
a negligible transmission penalty after 260-km uncompensated standard single-mode
fiber (SSMF).
© 2008 IEEE
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