| 摘要 |
PROBLEM TO BE SOLVED: To improve saturation power in an active MMI type semiconductor optical amplifier and a semiconductor laser, and to achieve high power. SOLUTION: A basic mode waveguide region 1 is successively connected to first and second multimode waveguide regions 2 and 3. When waveguide widths are set to W1, W2, and W3 in the basic mode and first and second multimode waveguide regions 1, 2, and 3, respectively, the waveguide widths are set so that W1<W2 and at the same time W2<W3 can be met, and the waveguide width in the multimode waveguide regions becomes wider to the basic mode waveguide region 1 in steps, thus preventing the waveguide width from being changed all at once at the coupling section between the basic mode and multimode waveguide regions, and hence obtaining a high saturation power level.
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