We study the conversion bandwidth of the cross-polarization-modulation (XPoIM)-based wavelength conversion scheme with a dispersion-flattened highly nonlinear photonic-crystal fiber for signals with a nonreturn-to-zero (NRZ) modulation format. Both theoretical and experimental results show that the conversion bandwidth can be extended to cover a very wide band, including S-, C-, and L-bands for $10\mathrm{Gbit}∕\mathrm{s}$ NRZ signals (a total bandwidth of $120\mathrm{nm}$ is experimentally demonstrated). We also study the theoretical bandwidth limit for $40\mathrm{Gbit}∕\mathrm{s}$ NRZ signals. A significant extension of the conversion bandwidth using the XPoIM approach compared with the four-wave mixing approach previously reported is demonstrated.