Abstract
We demonstrate an optically reconfigurable grating with enhanced transmission of TE-polarized waves in the terahertz (THz) waveband. This kind of grating is realized by projecting a grating image onto a thin Si wafer with a digital micromirror device (DMD). The enhanced transmission is caused by a resonance of the electromagnetic fields between the photoexcited strips. The position of the transmission peak shifts with the variation of the period and duty cycle of the photoinduced grating, which can be readily controlled by the DMD. Furthermore, a flattened Gaussian model was applied to describe the distribution of the photoexcited free carriers in the Si wafer, and the simulated transmittance spectra are shown to be in good agreement with the experimental results. In future, the photoexcited carriers could also be used to produce THz diffractive elements with reconfigurable functionality.
Highlights
Terahertz (THz) radiation occupies the region between infrared and microwave radiation in the electromagnetic spectrum
The transmittance spectrum is defined as the ratio of the intensity of the transmitted THz wave through a photoinduced grating to the intensity of the transmitted THz wave through the Si wafer without optical illumination
The cases corresponding to transverse electric (TE) and transverse magnetic (TM) polarizations are displayed in Figs. 2(a) and 2(b), respectively
Summary
Terahertz (THz) radiation occupies the region between infrared and microwave radiation in the electromagnetic spectrum. The surface excitations are not allowed.[11] This kind of resonance behaves differently from the TM polarization resonances Researchers realized such plasmonless EOT by combining a subwavelength slit or hole arrays with a thin dielectric slab. Some active THz devices[22,23,24,25,26] have been proposed to modulate THz waves in real time These active devices consist of metallic structures and semiconductors and are triggered by means of electricity, light, or temperature. Some photoinduced THz devices have been proposed to overcome these limitations These all-optical devices, which offer better flexibility than standard lithography, rely on grating patterns,[27,28,29] chiral patterns,[30] and subwavelength antennas[31] to realize the modulation of the THz spectrum. Our results are supported by simulations performed using the finite-difference timedomain (FDTD) method
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