| 摘要 |
PURPOSE:To obtain a wide band by providing three waveguides having a roughly equal waveguide parameter, setting a coupling coefficient of first and third waveguides to a value being roughly equal to a coupling coefficient of the second and third waveguides, and setting the length of a coupling part to a prescribed value. CONSTITUTION:At least one section each of the first waveguide 8 and the second waveguide 9 having a roughly equal waveguide parameter is placed adjacently and in parallel, and between the first and the second waveguides 8, 9 of this section, the third waveguide 10 of prescribed length, which has a waveguide parameter being roughly equal to that of the first and the second waveguides 8, 9, and provided with a nonreflective end face is provided. In this state, a coupling coefficient between the first and the third waveguides 8, 10 is set to a value being roughly equal to a coupling coefficient between the second and the third waveguides 9, 10, and a value in wavelength lambda1 of is coupling coefficient, and a value in wavelength lambda2 (lambda2>lambda1) are denotes and xlambda1, and xlambda2, respectively and length l of a coupling part 11 and a positive integer (n) are derived. |
