Ultrawideband pulse generation based on overshooting effect in gain-switched semiconductor laser

We demonstrate an alternative procedure to achieve ultrawideband (UWB) radio-frequency (RF) doublet impulses. It is based on the overshooting effect appearing by biasing a semiconductor laser close to the threshold with a large-amplitude signal. Specifically, with an optical bandpass filter and an electrical lowpass filter, we easily obtain doublet-like impulses whose RF spectrum meets the UWB regulations. Furthermore, we have been able to propagate such signals through an optical fiber link of 118-km length. Though the technique is not flexible in terms of waveform generation, our method constitutes a reliable, easy, and low-cost alternative for RF UWB impulse generation.