Polarization-modulable ASE light source using Bi2O2S thin film as modulator

We report an all-fiber polarization-modulable amplified spontaneous emission (ASE) light source, enabled by the thermo-optic effect of a Bi2O2S thin film. By coupling a 980 nm laser diode as the control signal and allowing it to interact with linearly polarized ASE light, photon-to-photon modulation is achieved through localized photothermal heating in the Bi2O2S thin film. The induced refractive index variation generates a controllable phase delay between orthogonal polarization components, resulting in continuous rotation of the polarization azimuth degree. Experimental results show a linear polarization tuning behavior, with a maximum azimuth rotation of 28.44° and a rotation efficiency of 0.0825°/mW (R² = 0.9773). Importantly, the ASE spectrum remains unchanged during modulation, confirming stable wavelength operation and purely polarization-based control. The fully fiber-integrated, compact, and alignment-free configuration provides a practical and highly stable platform for implementing tunable polarization control in broadband light sources. This polarization-modulable ASE source offers potential for applications in lidar sensing, optical coherence tomography, coherent detection, and other polarization-sensitive photonic systems.