Terahertz Broadband Polarization Conversion for Transmitted Waves Based on Graphene Plasmon Resonances

We applied the harmonic oscillator model combined with the transfer matrix method to study the polarization conversion for transmitted waves in metallic grating/plasmon-excitation layer/metallic grating structure in the terahertz (THz) region. By comparing the calculated spectra and the simulated (by the finite-difference-time-domain method) ones, we found that they correspond well with each other. Both methods show that the Drude background absorption and the excited plasmon resonances are responsible for polarization conversion. The transmission is close to 0 when the distance between the top/bottom metallic gratings and gated graphene is an integer multiple of half the wavelength of the incident wave (in the dielectrics), at which points the plasmon resonances are greatly suppressed by the destructive interference between the backward/forward electromagnetic waves and that reflected by the top/bottom metallic gratings. Away from these points, the transmission can be higher than 80%. The electron density and the excitation efficiency of the plasmon-excitation layer were found to be important for the bandwidth of the polarization conversion window, while the scattering rate was found to influence mainly the polarization conversion rate. Multi-broadband polarization conversion is realized by exciting plasmon modes between the 0 transmission points in the THz region.

PHOTOCURRENT ENHANCEMENT IN A MID-INFRARED QUANTUM DOT PHOTODETECTOR COUPLED WITH A HYBRID METAL-DIELECTRIC GRATING STRUCTURE

Many studies are dedicated to the problem of optical anomalies, focusing mainly on the case of metallic gratings. In the mean time, there is an increasing interest in resonant all-dielectric elements, as they offer a low-loss alternative to plasmonic structures.