Edge-Triggered Bi-Phase Modulation for the Generation and Modulation of UWB Pulses

We propose and demonstrate a novel scheme called edge-triggered bi-phase modulation for the generation and modulation of ultra-wideband (UWB) pulses in the optical domain. The proposed system consists of a laser diode, a Mach-Zehnder modulator (MZM), and a photodetector. An input data sequence with either return-to-zero or nonreturn-to-zero format is sent to the MZM via its radio-frequency port. The MZM is biased at the quadrature point; for an input pulse having a pulse amplitude equal to the two times the half-wave voltage of the MZM, a pair of UWB mono- cycles is generated with opposite polarities corresponding to the rising and falling edges of the input pulse. A proof-of-concept experiment is performed. A UWB monocycle sequence is generated when a square-wave with a frequency of 680 MHz is applied to the MZM. The generated UWB pulse has a 10-dB bandwidth of 5 GHz with a fractional bandwidth of 165%.