  In this paper, a systematic approach is employed to design a photonic crystal
with a boundary between positive and negative refraction to boost the
refractive properties of the crystal. Mathematical techniques are employed to
turn the process of EFC engineering into a nearly mechanical process free of
trial-and-error steps. The designed demultiplexers operational characteristics
are then further improved by adding a second photonic crystal with an oblique
boundary. The refracted beams in the first crystal impinge on an oblique
interface of the second photonic crystal to experience a change in Bloch
wavenumbers and even greater refraction angles so that a novel super-dispersive
two-step optical demultiplexer is made. A beam divergence of 161 degrees is
obtained for an input spectrum of {\lambda}= [1474nm, 1550nm].

Optics;Applied Physics