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