Application research on 4-pulsed amplitude modulation in 10Â Gb/s passive optical access systems

A novel scheme which can realize high-speed bidirectional optical signals transmission and reception by using 4-pulsed amplitude modulation (4-PAM) and demodulation in 10 Gb/s passive optical access systems, is introduced in this paper. In this scheme, a PAM sequence generator module, a M-ary pulse generator module and one Mach-Zehnder intensity Modulator (MZM) are employed for generating the 10 Gb/s optical 4-PAM signals. The generated optical 4-PAM signal is achieved full-duplex transmission over 20 km single mode fiber (SMF) for both downstream (DS) and upstream (US) access links application. The electrical spectrum diagrams, optical spectrum diagrams, and eye-diagrams are obtained, and the receiver sensitivities of 10 Gb/s 4-PAM signals before and after bidirectional transmission are analyzed. The simulation results demonstrate that, while the 4-PAM signal is adopted in passive optical access systems as bidirectional transmission signal, it can be received effectively with the BER below the forward-error-correction (FEC) limit value.