Research On Modal Phase Matching Frequency Conversion Method In Semiconductor Optical Waveguides

Since the 90 s of last century,the nonlinear frequency conversion in the waveguide has received more and more attention.The frequency conversion based on the second-order and third-order nonlinear effects has caused a lot of researches.The frequency conversion can be applied in many aspects,including wavelength converters of all-optical networks,tunable optical combs,infrared light sources,all-optical frequency-coded binary adders,high-purity entangled photon pairs and so forth.This paper proposes a method to increase the frequency conversion efficiency of the waveguide by increasing the spatial overlap area between the modes.Thre e waveguide structures that increase the spatial overlap area are designed and verified by simulation.This paper firstly analyzes the factors that affect the frequency conversion efficiency of the waveguide based on modal phase matching,and obtains the influence of the spatial overlapping area between the modes.Phase matching is a necessary condition for implementing waveguide frequency conversion.This paper selects modal phase matching because it does not require the waveguide material to have birefringence properties,and the manufacturing process is much less difficult than quasi-phase matching,but its disadvantage is that the space overlap area between modes limits the frequency conversion efficiency.Then the factors that affect the spatial overlapping area between modes are analyzed,and the method of increasing the spatial overlapping area between modes by changing the nonlinear coefficient of the crystal is proposed,so as to improve the frequency conversion efficiency of the waveguide.Based on the theoretical analysis,this paper designs three kinds of waveguides that change the nonlinear coefficient of the crystal.They are the inversion type,the suppression type,and the coating type waveguide.Inverted waveguides are waveguides that change the sign of the crystal nonlinearity coefficient by inverting the structure of the waveguide part,which can maximize the overlap area between the modes.Suppression type waveguides use quantum well mixing technology to suppress the crystal nonlinear coefficient of the waveguide structure,reducing the electric field cancellation between the modes,and increas ing the overlap area between the modes.The coated waveguide replaces the waveguide structure with a material that does not have a non-linear effect,and the crystal nonlinear coefficient is reduced to zero,which is the limit of a suppressed waveguide.Finally,this paper uses Matlab software to simulate and verify these waveguides.The simulation results show that the inverted waveguide structure has the best effect in improving the frequency conversion efficiency,followed by the coated waveguide structure,which illustrates that the larger overlap area is,the higher the frequency conversion efficiency in the waveguide is.And the method proposed in this paper to improve the frequency conversion efficiency of the waveguide is verified.Using the method proposed in this paper can greatly improve the frequency conversion efficiency based on modal phase matching waveguides,and provide theoretical guidance for manufacturing waveguides based on modal phase matching.