PHASED ARRAY WAVEGUIDE DIFFRACTION GRATING

PROBLEM TO BE SOLVED: To provide a phased array waveguide diffraction grating which has a wide passing band while transmission spectrum characteristics of respective wavelengths have flat tops. SOLUTION: The output side of a 1st star coupler and the input side of a 2nd star coupler are connected by a light waveguide diffraction grating. The light waveguide diffraction grating 30 is constituted by combining the 1st array 33 and 2nd array 36 of arms 3 of light waveguides. The 1st array 33 is an array of arms 33 which are based upon an arm having initial length L1 and obtd. by adding increments in length which are integral multiples of ΔL1 in order. The 2nd array 36 is an array of arms 3 which are based upon an arm having initial length L2 and obtd. by adding increments in length which are integral multiples of ΔL2 in order. Here, ΔL1 and ΔL2 are so set that signals of respective wavelengths are separated and the difference between L1 and L2 is so determined that signals of the same wavelength are focused while overlapping partially with each other.