Study On Broadband Frequency Conversion In Nonlinear Photonic Crystal

Broadband frequency conversion technique is critical for a variety of application in all-optical conversion as the development of optical communications, ultra-short pulsed frequency conversion and so on. Nonlinear quadratic effect based on the second-order nonlinear susceptibility provides an effective way in the realization of all-optical conversion. By quasi-phase matching in periodic and quasi-periodic nonlinear photonic crystal, frequency conversion efficiency can be dramatically enhanced except with a limitation in broadband tunbility for multiple frequency conversions. While as the other side, it was showed that random nonlinear photonic crystals presented a large potential for simultaneously multiple frequency conversion with amounts of possession in continuous spectral space, but with pretty lower conversion efficiency limited for further applications.In this work, we will demonstrate new spacial modulation schemes of second-order susceptibility in one dimensional nonlinear photonic crystals combining periodic and disordered optimization of nonlinear photonic structures. The dependence of cascading effects on the spacial distribution in nonlinear photonic crystals will be dramatically studied, as an example of detailed study of effectively broadband triplet frequency conversion.By the detailed studies, the theoretical model between the effectively broadband cascading effect and the spacial modulation scheme will be established with an effective balance between bandwidth and efficiency.These research results will provide a new way for the designing of broadband optical devices.The mainly work can be included as follows:1.Firstly, we Introduces the process and current situation of the development of nonlinear optics, and then introduced the nonlinear effect, the Second harmonic generation and third harmonic generation, and gives the work arrangement.2.We theoretically and numerically properties of nonlinear frequency conversion of photonic crystal in the ordered ferroelectric domain structure.3.We theoretically and numerically study the second harmonic generation in the short-ranged ordered ferroelectric domain structure. The structure is composed with an alternative change of periodic poledferroelectric segments of certain length and random extended single domains. We study the effect of structure parameters on the acceptance bandwidth and conversion efficiency of the frequency conversion process and demonstrate that the conversion efficiency of the process can be enhanced by using a longer locally-ordered medium, while the acceptance bandwidth can be managed by the length of the periodic poled ferroelectric segment.4.We theoretically and numerically study cascaded third harmonic generation in a short-range ordered dual-periodic ferroelectric domain structure. The short-range ordered structure is composed with an alternative change of dual-periodic poled structures ferroelectric segments of certain length and random length-extended single domains. The effect of structure parameters on the acceptance bandwidth and conversion efficiency of the cascaded third harmonic process were analyzed. The results show that the acceptance bandwidth can be controlled by adjusting the length of the dual-periodic poled structure, and the conversion efficiency for cascaded third harmonic generation can be improved by increasing the interacted length of harmonic with the medium.5.Summarize the contents in this paper and put forward prospects for the future.