Circularly Polarized, Long-Wave-Infrared Nanoantennas

Polarization information regarding solar radiation is not readily available in the mid- to far-infrared regimes. Conventional thermal IR detectors capture intensity with a loss of specific spectral and polarization information. Thermoelectrically coupled nanoantennas (TECNAs) capture infrared radiation by using an antenna that provides the capability for spectral, polarization, and angle-of-incidence selectivity. The nanoantenna resonantly absorbs the incident IR radiation and heats the hot junction of a nanothermocouple, which provides an output voltage that is proportional to the intensity. This is accomplished with minimal thermal mass, and provides las response times. Here we present 1LCNAs with log-spiral antennas that are capable of distinguishing left- and right-handed circular polarization (LHCP/RHCP) in the long-wave-infrared. The log-spiral TECNAs are suspended above quasi-hemispherical cavities etched into a Si substrate. The cavity thermally isolates the nanoantenna from the substrate and focuses the incident radiation onto it. Simulations show electromagnetic (EM) fields and resulting thermal distributions along the antennas for different polarizations. When the handedness of the EM polarization matches that of the antenna, the EM field is concentrated at the center of the antenna, while for opposite polarization it is concentrated toward the antenna leads. As a result, the temperature increase at the center of the nanoantenna for the two polarization directions is different. This provides an extinction ratio V-RHCP/V-LHCP similar to 4.