of the triangle formed by the three lower selenium atoms. [18,19] Since the atomicscale thin InSe has been successfully stripped by mechanical methods, [20,21] it has been prepared by chemical vapor transport (CVT), [22,23] colloidal ligand template, [24] and pulsed laser deposition (PLD). [25] The bulk InSe is a direct bandgap, and the bandgap value is suitably 1.25 eV, which is suitable for making a lightemitting device. [26] In addition, experiments and theories have proved that due to the quantum confinement effect, as the number of InSe layers is reduced to few layers, it will undergo a transition from the direct bandgap to the indirect bandgap, and the bandgap value increases to 2.6 eV, [27][28][29] which makes it have a broad prospect in the application of optoelectronics. Hybridization of the In and Se atomic orbitals results in a relatively light electron effective electron mass (0.143 m 0 ) [30] in the plane of the layer, which results in a field effect transistor fabricated using multiple layers of InSe with high electron mobility rate (10 3 cm 2 V −1 s −1) ) [20] and on/off current ratio (10 8 ) [31] over the transition metal disulfide at room temperature. In addition, 2D layered semiconductor InSe is used to fabricate, photodetectors, image sensors, heterojunction devices, and the like. [32][33][34] Although InSe-based devices and theories are developing rapidly, experimental investigations of the interaction between light and InSe have rarely been reported.Spatial self-phase modulation (SSPM) is a third-order nonlinear phenomenon in which the phase of incident light is modulated by its own intensity, [35] which has become an effective method for characterizing the nonlinear characteristics of 2D materials. The nonlinear refractive index coefficients of a large number of materials have been measured by this method, including graphene, [36] MoS 2 , [37] black phosphorus (BP), [38] Mxene, [39] etc. Cross-phase modulation (XPM) occurs because the signal light undergoes additional phase accumulation or variation caused by another co-propagating switched beam. [40] In this contribution, XPM refers to the change in optical phase of the beam caused by the interaction of two beams in a nonlinear medium (InSe). Nonreciprocal light propagation is of great significance for the field of optical communication and integrated photonics. Currently implemented methods include photons with specially designed waveguides, optomechanical systems, interband transitions, etc. [41][42][43][44] Some selenides also have NLO properties, such as GeSe, SnSe, and NbSe 2 , [45][46][47] where the SSPM effect of GeSe and NbSe 2 has been reported. [47,48] The nonlinear optical response of 2D materials has attracted wide attention in the recent year due to their strong nonlinearity and broadband characteristics. A new optical scheme is presented enabling the implementation of the broadband nonlinear optical response and their all-optical applications of few-layered InSe nanosheets. First, few-layer InSe nanosheets are synthesized by u...
