Spatial Self‐Phase Modulation in SnSe 2 Nanosheets: Wavelength Nonreciprocity for All‐Optical Switching and Modulation

ABSTRACT Based on spatial self‐phase modulation (SSPM) in emerging two‐dimensional nanomaterials, researchers have developed various passive nonlinear photonic devices, such as all‐optical switches, modulators, and information converters. However, the influence of wavelength nonreciprocity on their performance remains underexplored. Here, we fabricate and characterize SnSe 2 nanosheets, investigate their SSPM behavior, and exploit them for two‐color all‐optical switching and modulation. Owing to the material's nonlinear dispersion, the measured third‐order nonlinear susceptibility of monolayer SnSe 2 is 3.20 × 10 −8 esu at 532 nm and 1.41 × 10 −8 esu at 671 nm, with corresponding SSPM ring formation times of ∼0.33 s and ∼0.50 s at ∼200 W/cm 2 , respectively. Whereas previously reported two‐color all‐optical switches and modulators employ a short‐wavelength laser as the pump beam and a long‐wavelength beam as the probe beam, this study systematically investigates the influence of wavelength nonreciprocity on the performance of such devices. The results show that the pump beam plays a decisive role in determining both the switching time and modulation depth, revealing wavelength‐dominated nonlinear dynamical nonreciprocity in SSPM‐based devices. This flexible regulation of all‐optical switching and modulation performance via wavelength interchange provides a new route to break through the conventional intensity‐only control approach and to realize tunable, broadband, and multifunctional nonlinear photonic devices.