Abstract
Feature
Issue on Optical Performance Monitoring (OPM). A new technique
for monitoring the signal-to-noise ratio (SNR) of a randomly modulated optical data
signal is proposed and demonstrated. The signal is detected and then subjected to a
narrowband rf demodulation at precisely half the data clock frequency. Because of
symmetries present in the modulation spectrum at the half-clock frequency, the
demodulated signal is confined to a single dimension in the recovered phase space.
In contrast, the noise power is distributed isotropically within the phase space,
and the SNR is measured by taking the ratio of the power recovered along the signal
dimension to the power recovered along the orthogonal dimension. The narrowband
nature of the measurement makes it highly sensitive. The technique is demonstrated
for return-to-zero modulated data at 10 Gbits/s, where it accurately tracks OSNR
variations from 10 to 26 dB with only -24 dBm of optical input. The measurement is
also shown to be sensitive to chromatic dispersion and can be made to track OSNR
variations in the presence of large amounts of chromatic dispersion with vestigial
sideband optical filtering. These properties make this technique an ideal candidate
for optical performance monitoring in transparent optical networks, where a
sensitive, low-cost monitoring solution is needed for effective fault
localization.
© 2003 Optical Society of America
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