| 摘要 |
PROBLEM TO BE SOLVED: To obtain an optical branching and coupling unit which has its branching rate set almost to 50% by reducing variation in the branching rate to a production error and a polarized wave, etc. SOLUTION: The optical branching and coupling unit has 1st, 2nd, 3rd, and 4th directional coupling parts 3 to 6 in which intermediate parts of 1st and 2nd light guides 1 and 2 are formed closely to one another at four places so thatΔL1=ΔL2=-ΔL3=λ/4 are satisfied, whereΔL1 is the optical path length difference between the 1st and 2nd light waveguides 1 and 2 in the rang between the 1st and 2nd directional coupling parts 3 and 4,ΔL2 is the optical path length difference between the 1st and 2nd light guides 1 and 2 in the range between the 3rd and 4th directional couplers 5 and 6, andΔL3 is the optical path length difference between the 1st and 2nd light guides 1 and 2 in the range between the 3rd and 4th directional coupling parts 5 and 6. |
