Optically Implemented Broadband Blueshift Switch in the Terahertz Regime

We experimentally demonstrate, for the first time, an optically implemented blueshift tunable metamaterial in the terahertz (THz) regime. The design implies two potential resonance states, and the photoconductive semiconductor (silicon) settled in the critical region plays the role of intermediary for switching the resonator from mode 1 to mode 2. The observed tuning range of the fabricated device is as high as 26% (from 0.76 THz to 0.96 THz) through optical control to silicon. The realization of broadband blueshift tunable metamaterial offers opportunities for achieving switchable metamaterials with simultaneous redshift and blueshift tunability and cascade tunable devices. Our experimental approach is compatible with semiconductor technologies and can be used for other applications in the THz regime.

Figure 1

Schematic of our design for a broadband blueshift tunable metamaterial device. Left: Sketch of experimental pump-probe configuration for the measurement of THz transmissions through the fabricated metamaterial device. Right: Top view to the unit cell of the designed structure showing the geometry and dimensions of the device: $a=50\mu \mathrm{m}$, $d=36\mu \mathrm{m}$, $l=4\mu \mathrm{m}$, $w=2\mu \mathrm{m}$, and $g=2\mu \mathrm{m}$. Photoconductive silicon (red part) is put within two side gaps of the gold ELC resonator (yellow part) and the substrate is made by sapphire (blue part).

Figure 2

Optical microscopy images of the fabricated metamaterial device. (a) Large area of the device with an array of hybrid metamaterials; (b) Close view of the unit cell.

Figure 3

Normalized transmission amplitude of the THz beam for the metamaterial device as shown in Figs. 1, 2 (a) Results of experimental measurements as a function of energy flux of pump beam; (b) Results of simulations as a function of conductivity of silicon.

Figure 4

Distribution of surface current density at resonance frequency. (a) Surface current at $f=0.7\mathrm{THz}$ for ${\sigma }_{\mathrm{Si}}=1\mathrm{S}/\mathrm{m}$ (case without pump); (b) Surface current at $f=0.96\mathrm{THz}$ for ${\sigma }_{\mathrm{Si}}=1\times {10}^5\mathrm{S}/\mathrm{m}$ (case with highest pump intensity). The red parts within the gaps of two side paths are silicon.