Enhanced Pre/Post Compensation of Fiber Link Nonlinear Distortion by a Stepwise Parameter Profiled Fiber and Phase Conjugation Module

Compensation of nonlinear distortion in long distance communication links from the power induced Kerr effect is demonstrated by inserting at the transmitter or receiver a module combining optical phase conjugation (OPC) and propagation in a stepwise parameter profiled fiber (SPF). The SPF tailored with an increasing nonlinearity and decreasing dispersion parameter on average with distance as well as Raman gain induces a distortion more closely matching that of the link to improve propagation symmetry for enhancing overall distortion cancellation by OPC. Measurements show inserting the module at the transmitter or receiver with a 60 km long SPF comprising of three different fibers enables increasing the
Q
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-factor by 2.3 and 1.7 dB, respectively, compared to without for transmitting 5 channel WDM dual polarization 12 Gbaud 16-QAM signals in 2 × 160 km fiber spans that include dispersion compensation. Similarly, recirculating loop transmission of the same signal over 18 × 80 km (1440 km) shows improved
Q
²
-factors of 1.9 and 1.3 dB, respectively. This corresponds to extending the transmission reach by 125 and 80%, respectively, for matched performance at equal launch power, highlighting the greater nonlinear distortion tolerance achievable with advanced OPC designs.