Research On Nonlinear Optical Phenomena And Modulation Effects In Nonlinear Photonic Crystals And Interface Structures

The nonlinear photonic crystal is a kind of crystal in which the second-order non-linear coefficient is periodically modulated in different spatial directions.With the development and maturity of artificial micro-nano processing technology,the design and construction of material microstructures in sub-micron and even nano-scale can be realized.On this basis,nonlinear photonic crystals would also be fabricated and re-alize similar modulation in space.So that the study of domain poling techniques in sub-micron-scale ferroelectric domain inversion has aroused great interest.The electron beam direct write polarization process is expected to realize the domain inversion of any pattern on the submicron level in ferroelectric crystal film.Consequently,the fabrication of complex structure in nonlinear photonic crystal will be achieved in the condition of the combination with all kinds of poling techniques.Meanwhile,the fabrication of poling techniques in two-dimensional or even three-dimensional nonlinear photonic crystals has been initially achieved,which puts forward a higher demand for the theoretical study of nonlinear optical phenomena in nonlinear photonic crystals with different structures.In this paper,we explored and developed the electron beam direct write poling technique,realizing submicron domain inversion of arbitrary patterns on lithium niobate thin film that contains gold electrode on a limited scale.Subsequently,comparing the existing domain poling techniques,we proposed a potential method for the joint use of different techniques to achieve domain poling pattern of small size,complex structure and wide area in the future.Secondly,this research built a standard model of three-dimensional nonlinear pho-tonic crystals to analyze the second order frequency conversion process.The universal equation that describes the behavior of second harmonic wave in nonlinear photonic crystals of different dimension is derived,which includes a unified phase-matching con-dition that containing different second harmonic generation in bulk,one-dimensional,two-dimensional and three-dimensional nonlinear photonic crystals.In addition,we analyzed the characteristics of the single-layer of nonlinear interface with periodic?^?2?modulation extracted from the standard model of nonlinear photonic crystal.The generalized nonlinear Snell's law in second-order nonlinear frequency conversion process is obtained.The nonlinear interface has an enhanced effect on the generation of harmonic waves.Besides,multiple orders of second harmonic waves get emitted under the generalized nonlinear Snell's law.Based on such properties,we subsequently proposed a few applications.According to generalized nonlinear Snell's law,nonlinear metasurface is constructed which modulates the behavior of harmonic wave artificially.it is also possible to achieve anomalous nonlinear refraction and reflection in the condition of proper modulation.Combining the structure of nonlinear interface with a metal layer,surface plasmon polaritons will be generated under proper conditions.In-depth study of the characteristics of the nonlinear interface makes the traditional phase matching no longer subject to the shackles of the simple periodic modulation structure,which shall overcome the limitation of the nonlinear frequency conversion process in the bulk material medium.