Frequency Conversion And Performance Research Based On Strip Lithium Niobate Waveguide

Second harmonic generation,which is widely used in nonlinear optics,plays an important role in fields such as spectroscopy,signal processing,ultra-short pulse doubling,and optical communication.In order to achieve effective wavelength conversion in waveguides,strict phase matching between the interacting waves is required.Mode dispersion phase matching（MDPM）technology is used,through careful design of the waveguide geometry and dispersion,to match the fundamental mode with higher order modes,making the effective refractive index of the two beams equal,and achieving perfect phase matching in a simple and effective manner,thus enabling efficient frequency conversion.Based on the theory of optical waveguides and the principle of phase matching,a new type of strip waveguide structure（Si O₂-Li Nb O₃-Si O₂）is studied in the visible-light communication and near-infrared range.By studying the influence of the parameters of the Si O₂ covering layer on the phase matching point of the fundamental frequency light and second harmonic light,it is found that the sensitivity of the phase matching point to the width of the Si O₂ covering layer is significantly smaller than that to the height.Therefore,width is selected as the influencing factor while keeping the height constant,which provides a basis for the parameter design of practical waveguide devices.When the width of the waveguide covering layer is 1600 nm and the height is 400 nm,a pump wavelength（1740 nm）that satisfied the dispersion requirement is obtained,and second harmonic generation is successfully achieved.For a waveguide device with a length of 50μm,a theoretically normalized conversion efficiency of over 455.99%W^-1cm^-2 is achieved,demonstrating high nonlinear optical properties.In addition,the response of the broadband supercontinuum generated by the 1740 nm pump source to the peak power and pulse width is also studied.It is found that a broadband supercontinuum covering the visible-light communication and mid-infrared range can be achieved when the peak power is 900 W and the pulse width is 6 fs,which is of great significance for the development of all-optical communication.In order to further investigate the second harmonic generation characteristics of the waveguide,the research scope is expanded to the visible-light communication and mid-infrared range.Under certain waveguide structures with a covering layer width of 1600 nm,dual-wavelength second harmonic generation output is successfully achieved,and the dual-wavelength second harmonic generation characteristics of different waveguide structures are further explored.The optimal waveguide structure parameters for various dual-wavelength second harmonic generations are proposed.The study shows that as the width of the waveguide increased,fewer waveguide structures satisfy the dual-wavelength second harmonic generation condition.When the covering layer width is 1100 nm,the structure can achieve the most dual-wavelength second harmonic generation.Based on the number of transition points and their transition ranges,the structure is most stable when the width is 1400 nm.When the widths are 1100 nm,1200 nm,and 1300 nm,dual-wavelength second harmonic generations with a continuous adjustable wavelength interval are achieved.By studying the characteristics of different waveguide structures,it is found that when the width is 1100 nm and the height is 390 nm,a broadband supercontinuum covering the visible-light communication and mid-infrared range can also be achieved using dual-pump sources of 1.528μm and 3.252μm.Compared with a single-pump source,the peak power and pulse width are only 900m W and 10 fs,respectively,indicating important application value.