{HEAD ~ The photonic band gap material} may be characterized by periodicity of dielectric properties in two or three dimensions, and may comprise holes, defects, cavities, or other elements in {TAIL ~ layers} of dielectric materials that give rise to the band gap behavior 
{ HEAD ~ The photonic band gap material } may be characterized by periodicity of dielectric properties in two or three dimensions , and may comprise holes , defects , cavities , or other elements in { TAIL ~ layers } of dielectric materials that give rise to the band gap behavior
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH