Waveguide coupling structure

A coupling structure of waveguides to couple a line-defect waveguide in which light is guided along a line defect of a pillar photonic crystal and a wire waveguide in which light is guided along a thin wire, said coupling structure of the waveguides comprising:

• a line-defect waveguide portion configured to include said line defect waveguide;
• an electromagnetic-field-distribution-matching-portion configured to be connected to said line-defect waveguide portion and a first taper portion;
• the first taper portion configured to be connected to said electromagnetic-field-distribution-matching portion;
• and
• a wire waveguide portion configured to be connected to said first taper portion and have said wire waveguide, wherein said electromagnetic-field-distribution matching-portion includes:
• a matching portion line defect as the line defect of the pillar photonic crystal,
• wherein said matching portion line defect is connected to said line-defect waveguide,
• wherein said first taper portion includes:
• a first thin wire core, and
• a first line defect of the pillar photonic crystal arranged along at least one side of said first thin wire core,
• wherein said at least one of said first thin wire core and said first line defect is connected to said matching portion line defect,
• wherein said wire waveguide is connected to said first thin wire core.