Erbium-doped fiber amplifier History of engineering & technology KTP PDOS TE TM acoustic metamaterial angular filtering anti-counterfeiting arbitrarily anisotropic materials autocloning auxetic structure band gap band tunability beam shaping bubble resonance colloidal photonic crystals complete PBG coupled elastic waves coupling characteristics cylindrical lens defect bands defect modes differential quadrature method direct laser writing dispersion curves dual-core photonic crystal fiber effective medium electrical boundaries energy harvesting