-
Description
Kerr-induced distortions can be squeezed in the imaginary part of the
optical field by designing the transmission line so that it presents a
real-valued nonlinear transfer function [1]. This condition is roughly
met in nondispersion-managed links with 50% precompensation. This
nonlinear noise squeezing enables dramatic reduction of Kerr-induced
impairments for modulation formats encoded in the real part of the
optical field (e.g. BPSK) [1].
Furthermore, Kerr-induced distortions can be, in principle, canceled for
links with real-valued nonlinear transfer function when the signal
tributaries in the orthogonal polarizations are complex-conjugated
(i.e., Ey=Ex*) [2]. This specific configuration of the polarization
tributaries is referred to as Twin Waves.
-
Typical Results
The principle of nonlinear noise cancellation is illustrated in this
example by considering the transmission of 50-Gb/s single-polarization
(SP) QPSK and 50-Gb/s Twin Waves QPSK over 2000 km of uncompensated spans.
Digital frequency pre- and postcompensation is performed at the
transmitter and receiver respectively (see
).
In VPItransmissionMaker Twin Wave signals are handled as a special kind of arbitrary
4D modulation format, whose bit-to-symbol mapping can be specified by the user via a
text file (see
).
In order to focus on the impact of Kerr nonlinearities, the EDFA-induced optical
noise has been switched off in the simulation. The constellations of SP DPQSK
without electronic precompensation and with 50% precompensation can be observed in
and
for 0 dBm input power. For comparison, the constellation of the twin-wave signal
(50% precompensation) is reported in
for the same input power. Kerr-induced distortion is considerably reduced but
not completely suppressed because of random polarization effects.
-
Further Information
Keywords: Polarization Division Multiplexing (PDM), Quadrature Phase-Shift Keying (QPSK), QPSK, PDM QPSK, coded modulation, 4D modulation, BER, Kerr, Twin Waves
Similar demonstrations are available in VPItransmissionMaker Optical Systems and on the VPIphotonics Forum.
[1] X. Liu et al. '406.6Gb/s PDM-BPDK Superchannel Transmission over 12.800-km TWRS Fiber via Nonlinear Noise Squeezing', OFC 2012, paper PDP5B
[2] X. Liu et al. 'Phase-conjugated twin waves for communication beyond the Kerr nonlinearity limit', Nature photonics, May 2013 DOI: 10.1038/NPHOTON.2013.109
