A novel all-optical ultrawideband (UWB) signal generation scheme is proposed based on injection locking of Fabry-Perot laser diode (FP-LD). By injection locking the FP-LD with one wavelength signal light and two continuous probe light, multi-wavelength conversion is realized with two wavelength inverted signals output and one wavelength non-inverted signal output. After propagating through the fiber with a proper dispersion, time delay between different wavelengths output is introduced and the UWB signal pulse is generated. UWB signal is then obtained after the photo-detection. The operational principle of the proposed scheme is analyzed. Experimental investigation is carried out on the waveform and frequency spectrum characteristics of the UWB pulse. Differential UWB signals generation based on injecting 1.25 Gb/s non-veturn-to-zero (NRZ) signals to the FP-LD is then demonstrated. The experimental results show that the minimum full-width at half-maximum (FWHM) of the pulse is 83.3 ps, and the 10 dB spectral width is about 4.6 GHz with the fractional bandwidth of 107%.