We theoretically and experimentally demonstrate a scheme to implement bipolar millimeter-wave (MMW) ultrawideband (UWB) monocycles using a nonlinear optical loop mirror (NOLM). A 20-GHz optical clock as the probe light and a Gaussian pulse as the pump light are launched into the NOLM for cross-phase modulation (XPM). At the reflection and transmission ports of the NOLM, a pair of polarity-reversed MMW-Gaussian pulses is generated due to constructive and destructive interferences. They are then mixed with proper time delay and orthogonal polarization states. Thus, a photonic MMW-UWB monocycle is obtained. By adjusting the time delay between the reflection and transmission ports of the NOLM, bipolar MMW-UWB pulses are generated.