Patent ID: 6937797

Claim:
A planar lightwave circuit comprising: an input waveguide and an output waveguide formed on a substrate herein each of said input waveguide and said output waveguide are formed by a core and a cladding which covers said core, and a refractive index of said core is higher than a refractive index of said cladding, wherein a core width of each of an input end side of said input waveguide and an output end side of said output waveguide decreases gradually toward an end face of said substrate, so that a spotsize of each of said input waveguide and said output waveguide is widened, wherein said core continues to said end face of said substrate, and wherein the core width at the end face of the substrate is W 1 , a core width at a position apart from the end face is W 2 , a length of a region where a core width decreases gradually toward an end face of the substrate is L, a mean taper angle θ in the region is defined as θ=tan −1 (W 2 −W 1 )·( 2 L) −1 ), and assuming that a dicing position error amount at an end of the substrate is x, the mean taper angle θ is determined such that a=x·tan θ is smaller than a permissible amount of a core width forming error.