Multilevel dynamic control of surface plasmon propagation direction using phase-change materials

The surging demand for AI-driven massive data transmission has rendered optical communication increasingly vital, necessitating smaller devices capable of sub-diffraction-limit operation. Surface plasmons, capable of overcoming the diffraction limit to achieve nanoscale light manipulation, represent a novel approach for producing high-density integrated photonic chips. Here, we demonstrate a novel approach for actively manipulating plasmon generation using asymmetric nanogrooves integrated with the phase-change material Ge₂Sb₂Te₅. The phase transition modulates the coupling of plasmonic fields, which enables tunable directional excitation. By exploiting the contrasting optical properties of Ge₂Sb₂Te₅ in its amorphous and crystalline phases, we demonstrate active multilevel control of SPP launching with a high extinction ratio (ER) contrast, enabling both one-way and two-way nanosecond switching. The one-way switching achieves high ER values of -15.4 dB (on) and -0.42 dB (off), while the two-way switching exhibits an ER of -10.8 dB (rightward) in the amorphous state and an ER of 5.0 dB (leftward) in the crystalline state. The extinction ratio contrast reaches 15 dB, resulting in a modulation efficiency of up to 96.8%. This approach for surface plasmon manipulation paves the way for ultra-compact plasmonic devices, such as modulators and optical switches, advancing the miniaturization of photonic components.