Abstract
We experimentally demonstrate compensation of nonlinear distortion caused by the Kerr effect in a 3 × 32-Gbaud quadrature phase-shift keying (QPSK) wavelength-division multiplexing (WDM) transmission system. We use optical phase conjugation (OPC) produced by four-wave mixing (FWM) in a 7-mm long silicon nanowire. A clear improvement in Q-factor is shown after 800-km transmission with high span input power when comparing the system with and without the optical phase conjugation module. The influence of OSNR degradation introduced by the silicon nanowire is analysed by comparing transmission systems of three different lengths. This is the first demonstration of nonlinear compensation using a silicon nanowire.
Highlights
Coherent systems are becoming increasingly used in optical communications since they enable compensation of dispersive transmission impairments in the digital domain and make it possible to use advanced modulation formats such as quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM) to increase the spectral efficiency and provide enhanced capacity
We experimentally demonstrate compensation of nonlinear distortion caused by the Kerr effect in a 3 × 32-Gbaud quadrature phaseshift keying (QPSK) wavelength-division multiplexing (WDM) transmission system
It has been shown that higher conversion efficiencies lead to higher improvement in Q–factor at high span input powers
Summary
Coherent systems are becoming increasingly used in optical communications since they enable compensation of dispersive transmission impairments in the digital domain and make it possible to use advanced modulation formats such as quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM) to increase the spectral efficiency and provide enhanced capacity. Nano-engineered waveguides fabricated on the silicon-on-insulator (SOI) platform, so-called nanowires, have been intensively investigated as key components for nonlinear silicon photonics These nanowires may not exhibit SBS, offer the possibility for widely tunable dispersion engineering enabling large conversion bandwidths and, due to strong confinement, show large nonlinear coefficients. The drawback of silicon waveguides is the presence of twophoton absorption (TPA) induced free-carrier absorption (FCA) that causes nonlinear loss limiting the total power that can be launched into the waveguide, the efficiency of the parametric processes This issue can be solved by implementing reverse-biased p-i-n diode structures across the waveguides, leading to high conversion efficiencies, and values as high as −1 dB have so far been demonstrated [19]. When 13 dBm of signal power is launched into each transmission span of the 800-km link, the performance of the system without OPC is below the standard forward-error-correction (FEC) limit (corresponding to a Q-factor of 9.8 dB), while when OPC is introduced in the system, the measured Q-factor is significantly enhanced, reaching values as high as 13.3 dB
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