Abstract
The impact of the phase-to-intensity conversion of the laser phase noise due to
the optical band selector (BS) used for band extraction on the performance of
direct-detection (DD) optical multiband orthogonal frequency-division multiplexing
(MB-OFDM) networks employing single-sideband (SSB) modulation is assessed. Compared to
conventional double-sideband DD systems, in which the amplitude shape of the optical
filter is quasi-symmetric relative to the centre of the signal spectrum, ultra-dense
optical SSB-MB-OFDM networks employing virtual carrier-assisted DD are differently
affected by the phase-to-intensity conversion. This is due to the detuned BS required by
these networks, which modify the converted phase noise (CPN) features. A reduction of
the power spectral density of the CPN achieving 30 dB can occur along the frequency
range in which the BS bandwidth and detuning lead to a filtering attenuation that is
similar in both sides of the virtual carrier. For single band, when the ratio between
the BS detuning and bandwidth increases from 0% to 28%, an error vector magnitude
improvement of 7 dB due to the CPN reduction is observed. The optical signal-to-noise
ratio (OSNR) penalty due to the laser phase noise in 112-Gb/s SSB-MB-OFDM networks
comprising 12 OFDM bands and employing an ultra-dense band spacing of 3.125 GHz is lower
than 1 dB for external cavity lasers and is 1.6 dB for distributed feedback lasers.
These OSNR penalties are obtained for an optimized ratio between the BS detuning and
bandwidth of 14%.
© 2015 IEEE
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