
line-shaped defect, it is possible to form an ultrasmall waveguide that permits
the transmission of light only along the defect. Light can be trapped at certain
points by introducing point defects, thereby forming photonic nanocavities.
By combining these line and point defects, it is possible to form ultrasmall
photonic circuits (or chips) with various functions. Furthermore, the band
gap itself makes it possible to suppress spontaneous emission, which is a
fundamental factor limiting the performance of various photonic devices.
(2) Band edge engineering: This type of engineering focuses on the band edge, where
the group velocity of light becomes