OPTICAL WAVEGUIDE TYPE FILTER

摘要

PROBLEM TO BE SOLVED: To provide an optical waveguide type filter which is good in wavelength branching characteristics and is low in insertion loss. SOLUTION: This filter has plural optical waveguides varying in optical path lengths from each other. The filter branches an input light to the plural optical waveguides and identifies the input light based on the wavelength by propagating the input light to the respective optical waveguides, then multiplexing and interfering the input light to and with each other. In such a case, the filter is constituted by providing the filter with a light absorption layer 15 as a light absorption region for absorbing the higher order mode component to be propagated near the core layer 13 of an InP lower clad layer 12, InGaAsP core layer 13 and InP upper clad layer 14 successively formed on an InP substrate 11 constituting the optical waveguides described above.