中文摘要：

研究了基于周期极化反转铌酸锂光波导级联二阶非线性效应实现非归零码到归零码高速全光码型转换的新方案，使用的是马赫。曾德尔于涉仪结构。转换原理是非归零码信号光在级联倍频和差频过程中受到的放大作用引起马赫-曾德尔干涉仪的不平衡，进而通过干涉相消产生归零码信号光输出，首先从耦合波方程出发，数值模拟了非归零码到归零码码型转换过程。然后分析了波导长度、光功率、相对时延对消光比的影响并对码型转换进行了优化设计。最后分析了转换带宽，模拟计算表明信号光在90nm的3dB带宽内可调谐，进而可以实现多信道的同时转换。

英文摘要：

Based on the cascaded second-order nonlinear interactions in a periodically poled lithium niobate waveguide, a novel scheme of all-optical data format conversion from non-return-to-zero to return-to-zero is proposed, using a Mach-Zehnder interferometer structure. The conversion mechanism relies on the amplification effect induced on the signal field via cascaded second-harmonic generation and difference-frequency generation, which makes the Mach-Zehnder interferometer unbalanced and leads to the output of return-to-zero due to destructive interference. Fb~tly, the non-return-to-zero to return-to-zero conversion process is numerically simulated based on the coupled-wave equations. Secondly, the dependence of the extinction ratio on the waveguide length, optical power, and time-delay is analyzed and optimized. Finally, the conversion bandwidth is also discussed. It is found that the signal wavelength can be tuned in a wide wavelength range of approximately 90 nm, thus simultaneous multi- channel non-return-to-zero to return-to-zero data format conversion can potentially be implemented with the proposed scheme.