Photonic Generation of Ultra-Wideband Signal by Truncating a Continuous Wave into a Pulse

We propose and demonstrate a background-free millimeter-wave (MMW) ultra-wideband (UWB) signal generator using a dual-polarization dual-parallel Mach-Zehnder modulator. The MMW-UWB signal is generated by truncating a continuous-wave (CW) radio-frequency (RF) signal into an RF pulse. The upper dual-parallel Mach-Zehnder modulator (DPMZM1) is properly set to act as a phase modulator, while the lower DPMZM2 is well biased to generate a carrier-suppressed double-sideband (CS-DSB) modulated signal. By shifting the phase of the optical carrier through DPMZM1, a CW RF signal is truncated into a pulse one in a photodetector (PD). The baseband frequency components and local oscillator signal are well suppressed, since the optical power sent to the PD is constant. Moreover, there is no optical or electrical filters involved, which ensures a broad operation bandwidth and wide tunability. The proposed scheme is theoretically analyzed and experimentally verified. The generated background-free UWB signal at an RF carrier frequency of 26 GHz meets well the Federal Communications Commission spectral mask for outdoor UWB systems.