| 摘要 |
PURPOSE:To relax the wavelength dependency of the coupling rate of a dierctional coupler itself by generating a slight controlled optical path length difference between two optical waveguides which couple at least two directional couplers and operating them as the optical branching element. CONSTITUTION:The optical waveguides 1a and 1b arranged on a plane substrate 1 are put close to each other to constitute the directional couplers 2a and 2b, which have one-end sides 3a and 4a of the optical waveguides 1a and 1b as input ports and the other-end sides 3b and 4b as a main output port and a subordinate output port. The optical waveguides 1a and 1b between the two directional couplers 2a and 2b are made finely different in effective optical path length, and the fine difference in effective optical path length is set a slightly less than the value of the short-wavelength end of a desired operation wavelength range of the optical branching element. Consequently, a desired coupling rate with small wavelength dependency can be realized. |
