Novel QPSK modulation technique for DWDM free space optical communication system

A novel 1.28Tbps dense wave length division multiplexing system for free-space optical communication is proposed. The system is a line-of-sight configuration and uses coherent optical quadrature phase shift keying (QPSK) modulation technique. The system consists of 32-channels, with bit-rate of 40-Gbps/channel and adjacent channel spacing of 200GHz. The system is analyzed for various modulation formats; such as return-to-zero, non-return-to-zero and coherent-optical QPSK modulation technique. The performance of the proposed system is analyzed in terms of bit-error-rate, Q-factor, eye opening etc. For an input power level of 10dBm and employing coherent optical QPSK modulation technique, the coverage distance observed is 1360km.