WAVEGUIDE TYPE OPTICAL BRANCHING/COUPLING ELEMENT AND OPTICAL LINE USING THE ELEMENT

摘要

PROBLEM TO BE SOLVED: To reduce the loss of test light and the mixing of returned test light into a communication port and to make the element function in the wide wavelength band of communication light. SOLUTION: Optical couplers 3, 4 having different coupling rates in a first and a second wavelength bands are successively arranged in series on two optical guides 1, 2, a branching/coupling characteristic in the first wavelength band is made to be flat and a loss in the second wavelength band is removed. A phase shift area is provided between the optical couplers 3, 4 and the coupling rate of a Mach-Zehnder interferometer is set at a constant value in the first wavelength band over a wide region by using the difference of effective optical path lengths.