We propose and demonstrate an approach for optical ultra-wideband (UWB) monocycle pulses generation by employing a phase modulator (PM) and twin-core fiber (TCF). Based on phase modulation to intensity modulation (PM-IM) conversion principle, multi-wavelength and polarity-reversed ultra-wideband (UWB) monocycle pulses are generated simply by making the optical carrier wavelength located at the positive or negative sloop of the periodic comb-transmission spectrum of TCF. The generated UWB monocycles with different optical carrier wavelengths are studied and analyzed. In addition, multiple modulation formats such as on-off keying (OOK), pulse position modulation (PPM) and binary phase shift keying (BPSK) are implemented. Simulation results show that the proposed scheme can offer a realistic solution to photonic UWB pulse generation and modulation for WDM systems.