中文摘要：

利用龙格-库塔法分析了阶梯分段准相位匹配结构对基于差频效应的波长转换器的转换带宽、转换效率及平坦性的影响.当晶体长度不变时,增加阶梯段数,设计合理的起始段极化周期及合理的阶梯变化量,可以同时获得高平坦性、大转换带宽和高转换效率的波长转换.分析了结构参数对波长转换特性的影响.对于3cm长的晶体,在保证平坦度低于0.2dB的前提下,得到166nm的转换带宽和-0.55dB的最大转换效率.对比分析了阶梯分段结构的波长转换器与正弦啁啾光学超晶格和分段光栅结构的波长转换器的特性,结果表明阶梯分段结构与正弦啁啾光学超晶格相比在转换效率、带宽和平坦度方面都占优势;与分段光栅结构相比,转换带宽稍小,但转换效率和平坦度都更大.

英文摘要：

Flattop broadband wavelength conversions based on difference frequency generation were fulfilled by utilizing step-segmented quasi-phase matched gratings.For the same waveguide length,high conversion efficiency,flat response and broad signal bandwidth can be obtained simultaneously by adding the segment number of quasi-phase matched grating and optimizing the poling period of the first segment and the period shifts between adjacent sections.Analysis of the structure parameters on conversion efficiency,signal bandwidth and response flatness is performed as well.The conversion bandwidth in a 3-cm-long waveguide reaches 166 nm,which is over the whole conventional band and long-wavelength band,meanwhile the maximum efficiency is-0.55 dB and the peak-to-peak ripples less than 0.2dB.In addition,the comparison among step-segmented gratings,sinusoidally chirped optical superlattices and segmented gratings is carried out,the step-segmented gratings shows higher conversion efficiency and flatter response than the other two gratings,and has much broader bandwidth than sinusoidally chirped optical superlattices.