Fig. 1. Fabrication process and resultant metasurfaces of GSBT micro-nano gratings. (a) The schematic diagram of the fabrication process of GSBT gratings. Inset: the SEM images of (b) 1D-cGSBT grating and (c) 2D-cGSBT grating.

Fig. 2. Parameterization of laser power and pulse width in GSBT morphology. (a) A standard checkerboard pattern used for initial experimental setup via LDW. (b) The optical microscope image of the morphological evolution of GSBT under various laser powers and pulse durations.

Fig. 3. SEM analysis of etching progression over time. (a)–(c) At 75 s, 80 s, and 83 s, the early stage of etching shows the aGSBT material largely unetched, with no significant structural features evident. (d) By 85 s, the cGSBT grating structures reach optimal definition, showcasing effective material transformation. (e), (f) At 87 s and 90 s, the onset of over-etching becomes apparent, leading to the beginning loss of structural integrity.

Fig. 4. Comparative analysis of graphene-based plasmonic nanostructures and their effects on laser output. The incident continuous-wave light for (a) the time and (b) frequency domains. The light interacts with various graphene configurations: (c) bare graphene, (d) Au grating-Gr, (e) SiO2 grating-Gr, and (f) 1D cGSBT-Gr metamaterial. The pulse outputs from these structures are captured in (g)–(j) for the time and in (k)–(n) for the frequency domains, respectively. Among them, (g), (k) correspond to bare graphene, (h), (l) to metallic grating-graphene, (i), (m) to dielectric film grating- graphene, and (j), (n) to 1D cGSBT-Gr metamaterial. The vdW heterostructure of 1D cGSBT-Gr metamaterial’s mode-locking capability is evident from its distinctive pulse and spectral features, showcasing the unique plasmonic modulation achieved.

Fig. 5. Characterization of GSBT structures and their graphene composites. (a) XRD patterns of as-deposited GSBT and cGSBT. (b) Raman spectra of aGSBT and cGSBT. (c) Raman spectra of aGSBT-Gr and cGSBT-Gr. (d) Absorption spectra of aGSBT, aGSBT-Gr, cGSBT, and cGSBT-Gr. AFM images of (e) aGSBT, (f) cGSBT, (g) aGSBT-Gr, and (h) cGSBT-Gr.

Fig. 6. Simulated electric field distributions of cGSBT and graphene-integrated grating metasurfaces. (a) displays the field distribution in 1D cGSBT grating. (b) shows the enhanced field in a 1D cGSBT-Gr, demonstrating the effect of graphene integration. (c) depicts the complex field interactions in a 2D cGSBT-Gr. (d) zooms in on the cross-sectional electric field in the 2D cGSBT-Gr, highlighting the augmented plasmonic interaction. Accompanying schematics for (e) the 1D GSBT grating, (f) the 1D cGSBT-Gr, and (g) the 2D cGSBT-Gr and (h) detail of the cross-sectional view of the 2D cGSBT-Gr. Note: the illustrations of 1D/2D pattern and graphene are not shown to scale.

Fig. 7. The diagram illustrates the mechanism of a cGSBT-Gr hybrid metasurface, highlighting its structural evolution and plasmonic functionalities. (a) showcases aGSBT with Sb (Bi) atoms forming the apexes of triangular pyramids by three Sb-Te bonds and Ge atoms centered in tetrahedrons by four Ge-Te bonds. (b) displays 1D cGSBT-Gr where Sb (Bi) and Ge atoms are octahedrally coordinated by six Sb-Te and Ge-Te bonds, respectively. (c) illustrates the 2D cGSBT-Gr metasurface fabricated via LDW along both x and y axes, retaining the atomic coordination of 1D cGSBT-Gr and introducing LSPs effects. (d) depicts the 2D cGSBT-Gr metasurface acting as an SA, where plasmonic interactions transform continuous light into pulsed light, incorporating SPPs effects. The magnified section of (d) highlights the GPs and LSPs. Note: the illustrations of 1D/2D pattern and graphene are not shown to scale.

Fig. 8. The nonlinear optical characteristics of different GSBT samples. (a) presents the setup of the nonlinear optical system used for testing. The nonlinear optical characteristic of (b) aGSBT, (c) cGSBT, (d) aGSBT-Gr, (e) cGSBT-Gr, (f) 1D cGSBT-Gr, and (g) 2D cGSBT-Gr.

Fig. 9. Modulation depth and absorption trends for a series of samples (S1–S6): aGSBT, cGSBT, aGSBT-Gr, cGSBT-Gr, 1D cGSBT-Gr, and 2D cGSBT-Gr.

Fig. 10. Schematic and results of the mode-locked fiber laser system. (a) Configuration of the mode-locked fiber laser integrating GSBT-Gr as the SA. (b) Demonstrated output power as a function of the pump power. (c) Temporal sequence of emitted pulses in a train. (d) Optical spectrum of the mode-locked laser. (e) Radiofrequency (RF) spectrum highlighting pulse repetition stability. Inset: broadband RF spectrum exhibiting overall system stability. (f) Autocorrelation trace detailing the temporal pulse width. (g) Long-term optical spectrum stability, showcasing the robustness of the laser operation.

Fig. 11. Schematic illustration of the fabrication process for bare graphene, Au grating-Gr, SiO₂ grating-Gr, and 1D cGSBT-Gr metamaterials.

Fig. 12. aGSBT films across different thicknesses and their morphological evolution.

Fig. 13. Simulated magnetic field intensity distributions for (a) 1D cGSBT grating, (b) 1D cGSBT-Gr, and (c) 2D cGSBT-Gr configurations.

Fig. 14. Optical microscope images of the morphological evolution of GSBT under varying laser powers of 22 mW (top), 25 mW (middle), and 28 mW (bottom).

Fig. 15. Three-dimensional AFM images of (a) aGSBT, (b) aGSBT-Gr, (c) cGSBT, and (d) cGSBT-Gr.

Fig. 16. Local configurations of Ge, Sb, and Bi atoms in aGSBT and cGSBT.

Fig. 17. Modulation depth and absorption for a series of samples.