Effect of Read-Out Interconnects on the Polarization Characteristics of Nanoantennas for the Long-Wave Infrared Regime

We report experimental and simulation studies of the effect of interconnects on the polarization characteristics of nanoscale dipole antennas. In the long-wave infrared (LWIR) regime, isolation of the postdetection dc circuit and the optical-frequency antenna currents is difficult because the wavelength of the incident radiation is comparable to the dimensions of the isolating elements, and because metal and dielectric losses limit the quality factor of reactive elements at LWIR frequencies. Thus, these “dc” interconnects can also contribute to the radiation pattern of the antenna, and affect the polarization characteristics of the antenna. Antenna-coupled metal-oxide-metal diodes (ACMOMD) based on planar half-wave dipole antennas with different detector read-out interconnect geometries are fabricated adjacent to each other on the same die. ACMOMDs with geometrically-different read-out interconnects have different associated polarization ellipses. 3-D, full-wave simulations in Ansoft high-frequency structure simulator (HFSS) are performed to obtain the polarization tilt angles for different read-out interconnect geometries. The relative shifts in polarization axes are measured experimentally and compared to the relative tilt angles of the polarization ellipses obtained through simulations. The simulated relative shifts in the polarization axes are in good agreement with the measured values.