Patent ID: 7751669

Claim:
A waveguide comprising a three-dimensional photonic crystal including: a first layer including columnar structures arranged at a predetermined interval; a second layer including columnar structures arranged at the interval so as to extend in a direction different from the longitudinal direction of the columnar structures of the first layer; a third layer including columnar structures arranged at the interval so as to extend in the longitudinal direction of the columnar structures of the first layer, the columnar structures of the third layer being shifted from the columnar structures of the first layer by half the interval in a direction perpendicular to the longitudinal direction thereof; a fourth layer including columnar structures arranged at the interval so as to extend in the longitudinal direction of the columnar structures of the second layer, the columnar structures of the fourth layer being shifted from the columnar structures of the second layer by half the interval in a direction perpendicular to the longitudinal direction thereof; a first linear defect disposed at part of the columnar structures, the first linear defect comprising a medium different from the columnar structures; and a second linear defect disposed at part of the columnar structures extending in the longitudinal direction of the first linear defect, the second linear defect comprising a medium having a refractive index different from that of the medium used for the columnar structures, the second linear defect being separated from the first linear defect by a distance between about 0.5 times and about 1.5 times the out-of-plane lattice period of the three-dimensional photonic crystal in a direction in which the layers are stacked, the second linear defect controlling a frequency of a mode in which light propagates through the waveguide so as to guide the light in a single mode in a desired frequency range.