We present experimental results concerning a new alloptical technique that multiplexes two binary signals into a quaternary one (4-ASK). The technique is based on parametric amplification. Values of the quaternary levels obtained experimentally, as a function of the extinction ratios of the binary input signals, show a rather good agreement with the simulated and the analytical results. The generated 4-ASK signals were propagated through 75 km of standard single-mode fiber and experienced eye penalties of only 0.5 dB. This indicates the robustness of the technique for practical applications in metropolitan area networks.