Abstract
The purpose of this paper is to demonstrate the potential of an electrical
signal processing technique to mitigate the effect of intersymbol
interference in metro optical networks, using optical coherent detection.
Intersymbol interference in fiber-optic systems can severely degrade the
system performance and subsequently limit both the maximum transmission
distance and data rate. The main sources of intersymbol interference include
chromatic dispersion (CD) and polarization mode dispersion (PMD).The typical reach for 10 Gb/s metro optical systems is on the order of 300
km. To bridge this distance either with or without repeaters, we demonstrate
the potential use of 10 Gb/s differential phase-shift keying (DPSK)
modulation format in conjunction with an optical coherent receiver with a
built-in switchable electrical dispersion compensator. The overall
performance of the optical coherent receiver is compared with that of the
corresponding direct detection (DD) receiver based on Mach–Zehnder
delay interferometer.The optical signal-to-noise (OSNR) required to operate the optical
coherent receiver at the enhanced forward error correction (EFEC) threshold
of $2.1\times 10^{-3}$ is 6 dB/0.1 nm resolution bandwidth. The optical coherent
receiver outperforms in absolute required OSNR by 0.5 dB at the EFEC
threshold when compared to a DD receiver. A four position switchable CD
compensator compensates up to ${\pm}5100$ ps/nm of CD, using the method of heterodyne detection. The
optical coherent receiver has a first-order PMD tolerance of 36.2 ps for 1
dB OSNR penalty.The utility of our optical coherent receiver is demonstrated by doing
transmission experiments over 304 km of standard single-mode fiber (SSMF) in
both repeatered (multiple spans) and repeaterless (single span) to measure
the self-phase modulation (SPM) tolerance of 10 Gb/s nonreturn-to-zero
(NRZ)-DPSK. The measured SPM tolerance of NRZ-DPSK over 304 km of SSMF in
three spans of ${\sim}100$ km each is ${+}8.8$ dBm fiber launch power for 1.5 dB OSNR penalty. In addition, the
best Q factor of ${\sim}12$ dB is obtained for the fiber launch power of ${+}18$ dBm over single repeaterless span of 304 km of SSMF, which gives ${\sim}3$ dB of system margin at the second generation EFEC threshold of
9.1 dB.
© 2010 IEEE
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