1.5 mm [53]. This experiment represented the first successful propagation of light
in a fiber optic wavelength region in 3D crystals. Currently, the number of layers
that have been stacked is about nine, so the propagation loss is still relatively large,
but it is expected that an increase in the numb er of layers will cause the propaga-
tion loss to decrease exponentially.
13.3 BAND EDGE ENGINEERING
13.3.1 Outline of Resonance Action at the Band Edge
As is well know n, distributed feedback semiconductor lasers have a 1D periodic
lattice. The propagating waves undergo Bragg diffraction from this lattice and are
diffracted in the opposite direction. As a result, the propagating waves merge with
the diffracted waves, which in turn causes a standing