| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to increase and stabilize the quantity of the light output from a multiplexing/branching element even if the wavelength of a light oscillation source fluctuates by providing this element with an expanded part input waveguide for expanding the mode distribution of an input waveguide near a first end face more in a waveguide transverse direction than the mode distribution of an ordinary part input waveguide. SOLUTION: The input waveguide 12 has an ordinary part input waveguide 12a and an expanded part input waveguide 12b. The expanded part input waveguide 12b is connected to the first end face 4a of an input side plane waveguide 14. While the waveguide widths of the input waveguide 12 are respectively constant, the waveguide width of the expanded part input waveguide 12b is made larger than the waveguide width of the ordinary part input waveguide 12a. The mode distribution of the expanded part input waveguide 12b, therefore, spreads more to the waveguide transverse direction than the mode distribution of the ordinary part input waveguide 12a. The waveguide length of the expanded part input waveguide 12b is so set that the light has the two peaks in the waveguide direction when this light is inputted to the input side plane waveguide 14 from the expanded part input waveguide 12b. |
