Optical modulation of terahertz behavior in silicon with structured surfaces

Optically modulated terahertz (THz) transmittance through Si with various resistivities, in particular the high-resistivity samples with a structured surface showing nanosized pillars or split-ring resonators (SRRs), was investigated. The samples with nanosized pillars display an increased transmittance and an accordingly reduced modulation depth. With SRRs on the surface, strongly selective modulation can be realized at the resonant frequencies where the transmittance is vanishingly small, whereas at the non-resonant frequencies, where the transmittance is large, the modulation depth is much greater. These results demonstrate an alternative route for the modulation of THz wave in the all-optical devices.