Fig. 1. (a) Schematic illustration of the ultrafast THz polarization-dependent metamaterial device configuration for OPTP spectral measurement. (b) Schematic of the metamaterial unit cell. The geometric parameters are listed as follows: Lx=120  μm, Ly=50  μm, lxx=26  μm, lxy=25  μm, lyx=50  μm, lyy=15  μm, w=5  μm, g=5  μm, d=5  μm, h=200  nm. (c) Optical microscopy image of the metadevice. The inset shows the surface morphology measured by the atomic force microscope (AFM).

Fig. 2. Experimentally measured spectral dispersion of transmission spectra for the polarization-related metadevice in THz (a) x-polarized and (b) y-polarized pumps, considering a series of selected fluences. The corresponding numerically simulated transmission spectra for THz (c) x-polarized and (d) y-polarized light, with the labeled conductivity of the Ge film representing the pump level.

Fig. 3. Numerically calculated z-component field distributions in the transverse plane of a metamaterial unit at 0.79 THz, in the case of THz x polarization, accounting for Ge conductivity varying from 0 to 1600 S/m.

Fig. 4. Experimentally measured group delay spectra of the polarization-related metadevice for THz (a) x polarization and (b) y polarization, in the case of a series of selected fluences. The corresponding numerical results for (c) x polarization and (d) y polarization, with the conductivity of Ge film representing the pump level.

Fig. 5. Color map showing the transient evolution of THz transmission amplitude against frequency and time delay pumped with fluence of 1000  μJ/cm2 over an entire on-off photoswitching cycle.

Fig. 6. Negative differential transmission of 125 nm thick Ge film coated on quartz substrate pumped for a series of selected powers (as labeled). The experimental measurement is fitted using a single exponential function. These plots are vertically arranged for distinct comparison.

Fig. 7. Transmission spectra of SRR resonators and CRR resonators for (a) x polarization and (b) y polarization, with conductivity of 0 S/m.

Fig. 8. Relative modulation depth as a function of pump power.

Fig. 9. Numerically calculated z-component field distributions in the transverse plane of a unit of the metamaterial for the THz y polarization, accounting for the conductivity of Ge varying from 0 to 1600 S/m.

Fig. 10. Contour map showing the transient evolution of THz group delay against frequency and time delay over an entire on-off photoswitching cycle, under a pump fluence of 1000  μJ/cm2.

Table 1. Exponential Decay Time of the Relative Change of Fitted THz Transmission in Quartz Substrate Coated by Ge, Pumped by a Series of Exterior Lasers^a