Nonlinear Noise Cancellation Using Phase-Conjugated Twin Waves

  • 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 Figure 1). 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 Figure 2). 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 Figure 3 and Figure 4 for 0 dBm input power. For comparison, the constellation of the twin-wave signal (50% precompensation) is reported in Figure 5 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

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