photonic crystal transfer function

hi
i am simulating photonic crystal (PhC) slab lenses. the structure consists of a triangular lattice of cylindrical holes with radius r=0.4a in dielectric with permittivity e=12.96. in this PhC slab at frequency f=0.3, PhC exhibits negative effective index. These application of this type of PhC slabs as negative index lenses is investigated in lots of references.
one diagram (that i intend to obtain) is the transfer function of the PhC slab lens vesus Kx (transverse component of wave vector (transverse with respect to lateral interface of slab )). i don't know how should i calculate such a diagram).
i have attached a sample diagram from paper (influence of surface termination to the point imaging by a photonic crystal slab with negative refraction, applied physics letters, volume 85, number 19, (2004))

figure caption : transfer functions of photonic crystal slab (as an imaging system) for different surface terminations (dx represents surface termination)

thanks and regards
Sohrab