Design Of Wavelength Converter Based On Improved Quasi-Phase-Matched Structure

We design and research an improved quasi-phase matched wavelength converter.The conversion characteristics of the wavelength converter based on the sum + difference frequency generation in single-pass and double-pass configurations under different quasi-phase matched structures are studied.Firstly,the influence of the segmented quasi-phase matched grating structure on the characteristics of the wavelength converter based on the cascade sum frequency +difference frequency generation is analyzed.Studies show that for both of single-pass and double-pass configurations,high conversion efficiency,large conversion bandwidth,and good flatness can be achieved simultaneously by increasing the number of segments and optimizing the poling period of each segment.The conversion characteristics of the two configurations are compared under the same conditions,and compare them with the method of shifting the wavelength of one of the pump light in addition.Moreover,the effect of crystal length on the characteristics of a wavelength converter based on the segmented quasi-phase matched grating structure is also investigated.Secondly,a wavelength converter model under the sum + difference frequency generation is designed using the Bessel-chirp gratings.Not only analyze the design principle of Bessel-chirped gratings model but also research the characteristics of the wavelength converter based on this structure with the sum + difference frequency generation in the two configurations.The conversion bandwidth,maximum conversion efficiency,and flatness of the wavelength converters are compared in the single-pass and double-pass configurations by changing the crystal length and optimizing the design of the poling period.Finally,an improved quasi-phase matched structure is proposed and designed to achieve a wavelength conversion process based on the sum + difference frequency generation in the single-pass configuration.For a fixed crystal length,it can obtain high flatness and large conversion bandwidth by optimizing the quasi-phase matched structure parameters in a 55-nm pump wavelength difference.In addition,the effects on the wavelength conversion characteristics of different crystal lengths and crystal length manufacturing errors in the new quasi-phase matching structure wavelength converter are also studied.Eventually,the conversion characteristics of the wavelength converters to the ones using uniform grating-based devices with pump detuning and step chirped gratings are compared respectively under the same conditions.