Optoelectronic synergistic terahertz fiber modulator for free-electron laser compatibility.

Free-electron laser (FEL) operating in the terahertz (THz) spectral regime has found significant applications in diverse research fields. Nevertheless, fiber-based THz modulators based on FEL systems remain relatively underexplored. This study proposes a THz modulator based on side-polished fiber integrated with GaAs/Au nanoparticles (Nps) that demonstrates effective compatibility with the China Academy of Engineering Physics' THz FEL system. The modulator operates under high-power THz pulses (3 W) and achieves effective amplitude modulation across a broad frequency range from 1.6 to 3.0 THz. Owing to structural mode resonance, the modulator reaches the maximum modulation depth at 2.7 THz. The modulation depth was further enhanced by simultaneously applying optical and electrical modulation, i.e., optoelectronic synergistic optimization. Under a pump laser power of 235 mW, the peak modulation depth increases from 58.56% (at 0 V) to 67.11% (under 2.0 V). This investigation provides a solid foundation for the future application of fiber-based THz modulators in materials science, atomic physics, and biomedical studies, demonstrating their potential to advance the development of THz technology.