Patent ID: 7440658

Claim:
A photonic crystal coupling defect waveguide comprising: a photonic crystal including photonic crystal elements constituting a periodic structure and, for suppressing propagation of an electromagnetic field including light or a radio wave of a specific wavelength or in a specific frequency range; and a coupling waveguide including at least two waveguides, each of which includes a line defect that is a plurality of defects which are portions where the photonic crystal elements constituting the periodic structure of the photonic crystal are locally removed as line and forms the waveguide in the photonic crystal, and an input end or an output end for inputting and/or outputting the electromagnetic field and, which are mode-coupled to each other and, in which an electromagnetic field inputted to one of the waveguides causes an electromagnetic field to be propagated to the other waveguide, wherein by one of or more than one of (1) effectively changing a medium constant including one of or more than one of a dielectric constant, a refractive index, a conductivity and a magnetic permeability of the photonic crystal, (2) effectively changing size or shape of the photonic crystal elements, and (3) changing a lattice constant indicating a periodic interval of the photonic crystal elements, (a) band structures of an even mode and an odd mode of the coupling waveguide are shifted with respect to a normalized frequency, or (b) the band structures of the even mode and the odd mode of the coupling waveguide are respectively changed at different degrees; and by this, a difference in propagation constant between the even mode and the odd mode at a normalized frequency is made large, and a coupling length of a mode-coupled propagating electromagnetic wave which propagates in the coupling waveguide is made short, further wherein in the part of the photonic crystal including the part of or the whole of the coupling waveguide, the shape of the photonic crystal elements are not changed with respect to the another part, and the lattice constant and the size of the photonic crystal elements are changed similarly and at a same rate as compared with the another part.