Multilevel phase modulation formats with coherent detection enable a new generation of high-speed optical transport platform. We demonstrate 12 x 160 Gbps (1.92 Tb/s) WDM Optical systems employing super channel concept. Each super channel comprises of four subcarriers, with subcarrier spacing of 80 GHz. Each sub carrier transmits at a transmission rate of 160 Gbps using PDM-QPSK modulation format. The analysis is carried out for 12 x 160 Gb/s (1.92 Tb/s) PDM-QPSK WDM optical systems with and without inline DCF at long transmission reach from 4000 km to 9000 km. Coherent detection with DSP is used for both the systems at receiving end. Extensive Simulations are carried out to assess symbol error rate, error vector magnitude and Q-factor in each case. Simulation results are verified with analytical results for a system without inline DCF at 4000 km. Improvement of 3 dB to 4.5 dB is noted in Q-factor for a system with inline DCF in comparison with a system without DCF for long reach. EVM values are found 21% to 31% lower in a system with DCF. Log of Estimated symbol error (ESE) is almost half in system with inline DCF at 9000 km. The results clearly show that a WDM optical system with inline DCF gives better performance.