Research On Spatial Self-phase Modulation Effect Based On Cylindrical Lens Focusing

The invention of laser has promoted the progress of modern optics and the development of science and technology.The interaction of intense laser beam with matter produces many nonlinear optical phenomena,which also makes the research of nonlinear optics develop rapidly.With the in-depth study of nonlinear optical phenomena,photonic devices based on nonlinear optical effects,such as optical limiters,all-optical switches,and photonic diodes,have received widespread attention.The spatial self-phase modulation effect is an important third-order nonlinear optical effect,which exists widely in most nonlinear optical materials.In this thesis,the black phosphorus in N-methyl-2-pyrrolidone(NMP)solution is used as the nonlinear optical sample to study the spatial self-phase modulation and its application in nonlinear photonic devices.The main innovations are as follows:(1)the influencing factors of the spatial self-phase modulation effect and the quality of the ring formation are studied;(2)By introducing the cylindrical lens focusing a laser beam,the dynamic formation process of self-diffraction ring is adjustable,and all-optical switches and all-optical information converters are designed based on multi-beam spatial cross-phase modulation experiments.The main research contents of this thesis are as follows:1.The factors affecting the imaging quality of self-diffraction rings and the effects of different factors on the spatial self-phase modulation are studied.As a novel two-dimensional material,black phosphorus nanosheets were prepared and characterized.According to the experimental results of spatial self-phase modulation in black phosphorus dispersions,it is found that the formed self-diffraction rings are divided into thin rings and thick rings,and the physical mechanism of spatial self-phase modulation is analyzed.It is proved by different approaches that the thin ring comes from the optical Kerr nonlinearity,while the thick ring is caused by the thermally induced nonlinearity.The nonlinear refractive index and the thermo-optical coefficient can be obtained from the optical Kerr nonlinear effect and the thermally induced nonlinearity,respectively.2.Taking black phosphorus in NMP solution as the optical nonlinear sample and using the cylindrical lens focusing laser beams,the spatial self-phase modulation phenomenon with adjustable ring-forming process is designed.By controlling the light intensity and the effective area of thermal convection,the dynamic process of the spatial self-phase modulation process can be relatively manipulated.It is verified that the asymmetric thermal convection promoted by gravity is the main cause of the distortion of the self-diffraction ring.It is found that the size of the effective thermal convection area directly affects the dynamic process of ring formation.The effective area of asymmetric thermal convection can be controlled by using different orientation angles of cylindrical lens.Based on the transmission matrix and the Collins formula,the numerical simulations of the spatial self-phase modulation effect using the cylindrical lens and the convex lens are carried out.The simulation results are consistent with the experimental measurements.3.Based on the multi-beam spatial cross-phase modulation experiments,the nonlinear photonic devices are designed and investigated.Using the degenerate and non-degenerate multi-beam spatial cross-phase modulation experiments,the influence of multi beams on the self-diffraction ring is studied,based on the beam splitter and grating,respectively.It is demonstrated that the distortion of self-diffraction ring is due to the spatial change of refractive index in the sample.The self-diffraction rings generated by the identical phase change are the same,and the number of self-diffraction rings with long wavelength will be less than that with short wavelengths.Based on the non-degenerate multi-beam spatial cross-phase modulation experiments and the introduction of cylindrical lens,the all-optical switch and all-optical information converter which can relatively control the response time are designed.