UWB quadruplet signal generation based on a DP–QPSK modulator and a delay-line filter

A photonic ultra-wideband (UWB) quadruplet signal generation based on a dual-polarization quadrature phase shift keying (DP–QPSK) modulator is presented. A Gaussian sequence is split into four parts and input to the four driving ports of the DP–QPSK. Through polarization rotation and polarization combination, a pair of polarization-orthogonal, polarity-reversed doublet signals are generated from the output of the DP–QPSK modulator. Subsequently, they are injected into a balanced photodetector (BPD) for further differentiation. After the heterodyne detection, a UWB quadruplet signal can be obtained. In this system, four electrical amplifiers are incorporated into the four electrical driving paths to adjust the modulation indices of the DP–QPSK. To attain the optimal spectral power efficiency (SPE), a relationship among the SPE, pulse width, delay time, and the two main modulation indices is created. Consequently, the optimal point is found with an SPE of 53.46%. Then, several impairments brought by the nonideal devices are considered in the simulation system. The distortion caused by impairments is compensated by properly adjusting the devices. The generated spectrum has a SPE of 53.38% and efficiently complies with the Federal Communications Commission (FCC) mask without any low-frequency components exceeding the FCC mask. In addition, on–off keying and pulse position modulation are realized in the system.