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Abstract. In this letter, a novel scheme which can realize high-speed optical signals transmission and reception by using 4-pulsed amplitude (4-PAM) modulation and demodulation in 10 Gb/s free-space optical (FSO) systems. In this scheme, one PAM sequence generator module, one M-element pulse generator (MPG) module and one Mach-Zehnder Modulator are used to generate 10Gb/s 4-PAM optical signals. And then, the generated optical signal is transmitted in free space. Finally, it is directly detected and demodulated (IM/DD). We measure time-domain sequential waveform curves, optical spectrum curves, eye diagrams, and analyze the reception performance of 10Gb/s 4-PAM signals before and after transmission.

In this letter, a novel optical duobinary (ODB) downlink access scheme using low pass filter was proposed. The ODB downlink signal was generated by one continuous-wave (CW) laser, one pseudo-random binary sequence (PRBS) generator, one NRZ generator, one precoder, one Mach-Zehnder modulator and one low pass Bessel filter. The downlink signal can be transmitted over 20km singlemode fiber (SMF) and successfully received. We analyzed the time-domain waveforms, optical spectrum and eye diagrams before and after downstream transmission. The simulation results show that, compared to the traditional downlink scheme, this scheme has the advantages of high bandwidth efficiency, resistance to dispersion and good reception performance.