Sub-wavelength multimode tunable plasmonic terahertz lenses and detectors

We report on sub-wavelength THz plasmonic lenses based on 2 dimensional electron gas (2DEG) at AlGaN/GaN interface and also on few-layer graphene sheets. Circular gratings investigated in this study concentrate THz electric field into deep sub-wavelength scale by plasmonic excitations polarization independently. Propagation of a broadband pulse of EM waves in 0.5-10 THz was simulated by using a commercial FDTD simulation tool. The results show that concentric plasmonic grating structures can be used to concentrate THz into deep sub-wavelength down to lambda/350 spot size and achieve very large field enhancements by plasmonic confinement which can be used for THz detection and possibly for sub-wavelength imaging. Electric field intensity under the central point can be orders of magnitude higher than the outer grating area. Moreover, plasmonic lens modes supported by system can be tuned with an applied voltage to gratings.