| Summary: | 博士 === 國立臺灣大學 === 電機工程學研究所 === 89 === In this paper, Ti-diffused ridge LiNbO3 waveguides are analyzed to show the effects of the ridge on optical propagation characteristics, such as propagation index, electric field, and coupling length. An anisotropic semivectorial polarized finite difference method with a shift inverse power method and a simultaneous iteration scheme is used for the numerical calculation. The validity and accuracy of the calculated results by this method are assessed by comparing with those published. Waveguide devices with the ridge structure are then considered to provide design rules for the improvement of efficiency of Ti-diffused Er:LiNbO3 waveguide laser and the tuning of coupling length of directional coupler. By incorporating the ridge structure, the effective pump area of coaxially pumped Ti-diffused Er:LiNbO3 waveguide laser is decreased such that the threshold pump power of the laser is significantly lowered. The results show that the reduction of the threshold pump power can be as large as about 40%, while the slope efficiency is not obviously changed. Next, two kinds of groove structure for shortening and broadening the coupling lengths of Ti:diffused LiNbO3 directional couplers are presented. The coupling lengths as functions of the depth, width, and spacing of the grooves were numerically calculated. The results show that the maximum shortening of coupling length is up to 43%, and the maximum broadening is even larger depending on the groove depth. This method can be efficiently applied to the analysis of any longitudinally invariant waveguide devices.
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