Research On Dual Wavelengthand Wideband Frequency-doubling Characteristics Based On Quasi-Phase Matching

Second-order nonlinear optical frequency conversion has important applications in the fields of spectroscopy,ultra-short pulse multiplication,signal processing and optical communication.To achieve broadband frequency conversion,phase matching and group velocity matching are indispensable conditions.Among them,the quasi-phase matching(QPM)technique can realize the phase matching simply and effectively.Meanwhile,a new optical superlattice structure is proposed in this paper,on the basis of which dual-wavelength simultaneous multiplication is achieved,Wavelengths can be modulated in any ratio.Taking 1mol% and 5mol% lithium magnesium oxide niobateas an example,the dispersion characteristics were analyzed and the method of double wavelength doubling was described.In the mode of operation,dual-wavelength frequency conversion is realized.For example,for a SHG process,1mol% of MgO-doped periodically poled lithium niobate is used under the ee-e type QPM at a temperature of 114 ° C at 0.86 ?m and 1.06 ?m at the same time to achieve any proportionally adjustable octave.In order to further study the frequency doubling and double fundamental wavelength spacing and reduce the difficulty of crystal fabrication,we propose a new method of designing polarized crystals,redesigning the tapered nested structure as a segmented nested structure,There is a limit to any ratio of multiples output.Under the action of ee-e type QPM,the double-wavelength interval is larger,so we extend the polarization state of the input and output light waves and find that when the polarization states are different,the double fundamental wave can be multiplied and the wavelength interval can be adjusted.In this structure we study the dichromatic wavelength spacing and the frequency conversion characteristics.The paper also discusses the physical meaning of the relatively efficient nonlinear coefficient dreff(?)and uses it to measure the conversion efficiency.The results show that when the temperature is 130 ?,the crystal of 5mol% MgO doped periodically poled lithium niobate is used.The two wavelengths are in the ee-o and oo-o in the polarizationmode,double wavelength doubling of 1.31 um and 1.3149 um.When the temperature or domain length changes,the wavelength spacing of the two fundamental waves can be adjusted to achieve a shorter wavelength double fundamental frequency multiplication and to switch the output intensity of the frequency doubling light.Finally,the article discusses the structure of a stepped germanium crystal.The bandwidth frequency conversion characteristics of the central wavelength of 1.55 um are studied in detail.Analyzed and compared different schemes for realizing the extended bandwidth by changing the parameter structure of the step germanium crystal.The quasi-phase matching technology and the group velocity matching point are used to realize the 3.44 um wideband infrared frequency.