Abstract
We analytically and experimentally demonstrate a linearly field-modulated,
direct-detected virtual single-sideband orthogonal frequency-division
multiplexing (VSSB-OFDM) system that employs a tunable frequency gap and an
iterative detection technique. The VSSB-OFDM that uses no frequency gap,
which is referred to as the gapless VSSB-OFDM, is proposed as a spectrally
efficient format. Compared with the intensity-modulated SSB-OFDM, the
gapless VSSB-OFDM saves half the electrical bandwidth (BW), and exhibits
better receiving sensitivity and more robust tolerance against fiber
chromatic dispersion (CD). Furthermore, by incorporating a tunable frequency
gap between the optical carrier and the OFDM data sideband, the calculating
burden of the iterative detection is greatly alleviated and the system
performance can be flexibly improved within moderate iterations. The width
of the optimum frequency gap is found to be ${\sim} {\hbox {0.35}}$ sideband BW, which is reached by trading the levels of
signal–signal beat interference and the residual image beat
interference. Such a gapped VSSB-OFDM system requires fewer iterations to
extract the desired data from the interfered signal and exhibits greater
robustness against the carrier-to-signal-power ratio (CSPR) variation,
compared with the gapless VSSB-OFDM. In this paper, the analytical model of
the proposed gapped VSSB-OFDM system will be addressed. In addition, we also
successfully conduct a gapped VSSB-OFDM signal transmission over 1600 km of
uncompensated standard single-mode fiber (SSMF) with only ${\sim} {\hbox {3}}$ dB optical SNR (OSNR) penalty, and obtain a significant OSNR
sensitivity improvement of ${\sim} {\hbox {8}}$ dB, compared with the gapless VSSB-OFDM, after such a 1600-km
fiber link.
© 2009 IEEE
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