Broadband Ultrafast Polarization Switching in ZnO With Distortion‐Free Waveform Preservation

ABSTRACT As silicon electronics approaches the picoseconds wall, light polarization stands alone as a carrier that multiplexes amplitude, phase, and space. However, electronically driven active polarization control is fundamentally constrained to gigahertz (GHz) speeds by inherent electronic circuitry limitations, creating the “last‐mile” bottleneck for terahertz (THz) and ultimately petahertz (PHz) information processing. Here, we demonstrate all‐optical quarter‐ and half‐wave plates that operate within zinc‐oxide (ZnO) crystals at about 100 femtoseconds switching speed over a 600–880 nm bandwidth while preserving the temporal waveform. These phenomena are independent of material‐intrinsic relaxation, eliminating the conventional trade‐off between modulation depth and response time. This advance shifts ultrafast photonics from intensity modulation to full vector‐field control, offering an excellent foundation for ultrafast photonic circuits, quantum‐state manipulation, and attosecond science.