Combination of graphene plasmons and surface plasmons in a crystalline Ge₂Sb_1.5Bi_0.5Te₅ metasurface structure for laser mode-locking

Owing to the dynamic tunability and strong confinement, graphene plasmons (GPs) have emerged as an excellent candidate for the manipulation of light–matter interaction. Surface plasmons (SPs) have been admitted as another effective way allowing strong confinement of light at the nanoscale. The combination of GPs and SPs like localized surface plasmons (LSPs) and propagating surface plasmon polaritons (SPPs) will lead to a synergistic effect that could remarkably improve light–matter interactions, showing great potential for many applications for the improvement of solar cell efficiency, biosensor sensitivity, and the performance of photonic devices. In this study, the GPs were activated by placing graphene film onto a two-dimensional (2D) phase-changing crystalline Ge 2 Sb 1.5 Bi 0.5 Te 5 (cGSBT) nanograting structure, which also acts as an original source generating LSPs. The SPPs originated by laying the above structure onto an Au mirror. The combined effects of GPs, LSPs, and SPPs are epitomized in such a simple Gr/2D cGSBT gratings/Au heterostructure, which allows easy realization of an ultrafast mode-locked laser quite stable working at 1550 nm range due to the strong nonlinear optical absorption capability. This approach overcomes the heat and energy loss in metallic gratings or a Gr-based heterostructure, exhibiting great potential for applications in the design and fabrication of photonic devices.