We describe the first 16Gbit/s electronic multiplexer and use it to measure the characteristics of a high-speed directly modulated InGaAsP 1-3/wn-wavelength laser and a high-speed InGaAs/InP PIN photodetector. The laser rise and fall times are typically 35 ps and 40 ps, respectively. The largest eye opening occurs at an output power of 10mW with an optical extinction ratio of 2-3:1.