Study on RZ-4PAM downstream signals with duty cycles of 33% and 50% for optical access system application

4-ary pulse amplitude modulation(4PAM) signals with 33% and 50% return-to-zero(RZ) clocks are generated for passive optical network(PON). We demonstrate that RZ-4PAM signals with duty cycles of 33% and 50% after transmission over 20-km-long single mode fiber(SMF) at 10 Gbit/s can be directly detected by using one photo detector,and the original data can also be restored by one M-ary threshold detector and one 4PAM sequence decoder. The optical spectra of 33% and 50% RZ-4PAM signals are measured,and their eye-diagrams before and after transmission are also analyzed. Simulation results show that 33% and 50% RZ-4PAM downlink signals can be received effectively,and the received power values are-15.1 d Bm and-13.8 d Bm when the bit error rate(BER) is 10^(-6). Moreover,33% RZ-4PAM optical signals have better reception performance than 50% RZ-4PAM optical signals.

A full-duplex optical access system with hybrid 64/16/4QAM-OFDM downlink

A full-duplex optical passive access scheme is proposed and verified by simulation, in which hybrid 64/16/4-quadrature amplitude modulation(64/16/4QAM) orthogonal frequency division multiplexing(OFDM) optical signal is for downstream transmission and non-return-to-zero(NRZ) optical signal is for upstream transmission. In view of the transmitting and receiving process for downlink optical signal, in-phase/quadrature-phase(I/Q) modulation based on Mach-Zehnder modulator(MZM) and homodyne coherent detection technology are employed, respectively. The simulation results show that the bit error ratio(BER) less than hardware decision forward error correction(HD-FEC) threshold is successfully obtained over transmission path with 20-km-long standard single mode fiber(SSMF) for hybrid downlink modulation OFDM optical signal. In addition, by dividing the system bandwidth into several subchannels consisting of some continuous subcarriers, it is convenient for users to select different channels depending on requirements of communication.

Simultaneous generation of 3G and millimeter-wave signals using a dual-electrode MZM in ROF systems

A novel radio-over-fiber(ROF) scheme to simultaneously generate and transmit the 3rd generation telecommunication(3G) and millimeter-wave(MMW) signals by using a single dual-electrode Mach-Zehnder modulator(MZM) is proposed.There is no apparent nonlinearity induced by the ROF system.By employing this analog ROF signal transmission technique,highly transparent fiber-wireless convergence networks can be realized,which are ideal for multi-standard wireless system operation.