| 摘要 |
PROBLEM TO BE SOLVED: To provide a waveguide type optical branching element provided with a low PDL(polarization dependent loss), wavelength non-dependency and different branching ratios in which the temperature dependency of the branching ratio is small. SOLUTION: When light is inputted from one input port 40, almost only an even numbered mode is excited in a waveguide 45 on the side of the input port. When the light is inputted from the other input port 41, almost only an odd numbered mode is excited in the waveguide 46 on the side of the input port. Only the even numbered mode or the odd numbered mode is present on the input side of a coupling part 47, and since a core width is gently changed in the coupling part 47, coupling between the even and odd numbered modes hardly occurs. By attaining a smooth structure where the boundary line La between a core and a clad is changed according to a sine function or a cosine function especially, the coupling between the even and odd numbered modes is suppressed and an unrequired mode is hardly generated. |
