Optical multiplexer/demultiplexer

An optical multiplexer/demultiplexer comprising:

• a substrate;
• first and second slab waveguides, provided on said substrate, each having a predetermined slab length;
• one or more input waveguides, disposed on said substrate, each having one end connected to said first slab waveguide;
• a plurality of output waveguides, provided on said substrate, each having one end connected to said second slab waveguide, said output waveguides being provided so as to correspond to individual signals having respective channel wavelengths set as signal channels with a predetermined wavelength spacing;
• and
• a plurality of channel waveguides, provided on said substrate, each having one end connected to said first slab waveguide such that said first slab waveguide is sandwiched between said input waveguide and said channel waveguides, and the other end connected to said second slab waveguide such that said second slab waveguide is sandwiched between said channel waveguides and said output waveguides, said channel waveguides having lengths different from each other;
• wherein at least the slab lengths in said first and second slab waveguides and the channel waveguide intervals at respective connection end faces of said first and second slab waveguides are adjusted such that, in a power spectrum indicating a wavelength-transmission characteristic concerning an output light component from selected one of said output waveguides, a second channel wavelength adjacent a first channel wavelength corresponding to said selected one in said channel wavelengths of signals exists within a wavelength region yielding an output light power lower than that at said first channel wavelength by 20 dB or more.