High-Order Ultrawideband Pulse Generation from NRZ-DPSK Signals

A simple method to generate ultrawideband (UWB) doublet and triplet from nonreturn-to-zero (NRZ) differential phase shift keying (DPSK) signals is proposed and experimentally demonstrated. The proposed configuration consists of a Mach--Zehnder modulator (MZM) to generate NRZ-DPSK signals, a section of single-mode fibre to form a microwave bandpass filter, which is used to generate doublet pulses, and a Gaussian optical bandpass filter (OBF), which serves as a frequency discriminator to generate higher-order UWB pulses. A pair of polarity-reversed triplet pulses is achieved by locating the optical carrier at the positive and negative linear slopes of the OBF, where the OBF detuning is 0.12nm and -0.2nm, respectively. The spectra of the pair of UWB triplets have a central frequency of 5GHz and 5.6GHz, and have a -10dB bandwidth of 6.9GHz and 8.1GHz, respectively. The UWB pulses remain doublet shape when the light wavelength is located at the peak of the OBF. The spectrum of the doublet has a central frequency of 5.6GHz and a -10dB
bandwidth of 6.9GHz.