1. Introduction Since the late 1990, the transport capacities of ultra-long haul and long haul optical fiber communication systems has been significantly increased by the introduction of EDFA (Erbium Dropped Fiber Amplifier), DWDM, DCM (Dispersion Compensation Module), and FEC (Forward Error Correction) technologies. By utilizing these technologies, the universal on/off-keying (OOK) modulation along with direct […]