Influence of structures on optical modulation in terahertz metamaterials

By utilizing optical pump terahertz probe spectroscopy, the optical modulated properties of three samples were investigated with terahertz subwavelength structures, which were derived from classical split ring resonators. The obtained results show in the metamaterials design, it is needed to avoid the same length bar in the middle of the symmetric samples due to the fact that the middle bar has less influence on the resonant property when the terahertz electric field vector is parallel to the bottom bar. However, the asymmetric samples exist coupling and splitting phenomenon in transmission spectra. For the different resonance mechanisms, it is found the LC resonance has higher sensitivity than the dipole resonance to the pump excitation. Although different designed structures will exhibit different resonant positions in frequency, the optical modulation behaviors of those samples have one same characterization. That is, when the terahertz electric field vector is parallel to the bilateral bar, there is only one transmission dip because of the structure design and this transmission dip from the dipole resonance is not sensitive to the pump excitation.