Fig. 1. (a) Schematic diagram of the atomic structure of GeSe₂; (b) AFM image of GeSe₂ flake by mechanical exfoliation. The thickness of the sample is 88 nm; (c) polarization-dependent Raman spectrum. Four Raman peak positions are at 118, 212, 251, 307 cm^–1, respectively; (d)–(g) polar diagrams of the intensity of the four Raman peaks.

Fig. 2. Characterization of anisotropic bands of layered GeSe₂ by linear absorption spectrum: (a) Linear absorption spectrum with polarization directions from 0° to 180° with intervals of 15°; (b) the energy band of the 0° polarization direction is determined. The band position obtained indirectly from Tauc’s theorem, where the position of the intersection of the tangent and the abscissa is 2.717 eV; (c) determination of the energy band of the 90° polarization direction. The band position obtained indirectly from Tauc’s theorem, where the position of the intersection of the tangent and the abscissa is 2.7291 eV; (d) anisotropic energy bands of layered GeSe₂. The band gap in the b-axis direction is the largest, and the band gap in the a-axis direction is the smallest; (e) polar graph of anisotropic linear absorptivity of layered GeSe₂ at 400 nm; (f) polar graph of anisotropic linear absorption of layered GeSe₂ at 450 nm.

Fig. 3. Experimental results of superposition state absorption of different polarization directions under 400 nm non-resonant excitation: (a) Results of the I-scan experiment. The circles indicate the experimental data, and the solid lines indicate the excited state absorption curve; (b) polarization-dependent non-linear modulation depth polar plot; (c) polar plot of the change in polarization-dependent linear absorption coefficient α₀; (d) polarization diagram of polarization-dependent saturated absorption intensity I_1,s; (e) polarization diagram of the polarization-dependent excited state absorption coefficient β₀; (f) polarized graph of polarization-dependent saturation light intensity I_2,s absorbed by the excited state.

Fig. 4. Experimental results of superposition state absorption of different polarization directions under 450 nm non-resonant excitation: (a) Results of the I-scan experiment. The circles indicate the experimental data, and the solid lines indicate the excited state absorption curve: (b) polarization-dependent non-linear modulation depth polar plot: (c) polar plot of the change in polarization-dependent linear absorption coefficient α₀; (d) polarization diagram of polarization-dependent saturated absorption intensity I_1,s; (e) polarization diagram of the polarization-dependent excited state absorption coefficient β₀; (f) polarized graph of polarization-dependent saturation light intensityI_2,s absorbed by the excited state.

Fig. 5. Schematic diagram of GeSe₂ based polarized-dependent all-optical switching