Abstract
We propose a novel cross bowtie antenna using phase-shift lines to realize circular polarization (CP) in the infrared (IR) spectrum. The CP antenna consists of a vertical, a horizontal antenna, and two elliptical loops connecting adjacent tips of the antennas to create a 90° phase shift. The phase-shift lines are conceived to realize a single terminal of the antenna where a detecting material can be mounted and enable the detecting material to fully utilize the field enhancement from the antenna. In full-wave simulations, a nanometer-scale low-bandgap semiconductor, i.e., indium gallium arsenide antimonide (InGaAsSb) capable of detecting IR wave is loaded at the antenna terminal and the antenna structure is designed to achieve CP absorption at 180 THz. The antenna includes a transmission line-based impedance matching structure to compensate for the reactance of the InGaAsSb semiconductor load. To verify the CP detection of the antenna near 180 THz, we numerically show a higher field enhancement value and absorption rate in the antenna terminal in a specific CP case when the antenna is illuminated with incident waves with various polarization states. Also, we design 2 × 1 and 2 × 2 antenna arrays using the CP antennas connected with metallic traces and show that the CP absorption at 180 THz is maintained. Finally, an illustration of a focal plane array based on the proposed CP cross bowtie antennas coupled with the InGaAsSb for a full Stokes polarimeter is presented.
Highlights
Imaging polarimetry can measure the polarization state of a field emitted from a scene, as well as the intensity and color that can be detected by traditional infrared (IR) imagers
The final InGaAsSb-coupled circularly polarized (CP) antenna shows ∼6.5 of the field enhancement value and 25.88% of the absorption rate in the antenna terminal at 180 THz when a right-handed CP (RHCP) wave is incident; these values are higher than those for incident waves with different polarization states
This higher field enhancement and absorption of the antenna with the CP incident wave prove that the cross bowtie antenna coupled with the InGaAsSb can be utilized for a CP detector in the IR spectrum
Summary
Imaging polarimetry can measure the polarization state of a field emitted from a scene, as well as the intensity and color that can be detected by traditional infrared (IR) imagers. Compared to 3.71% absorption rate at 180 THz for the vertical polarization case, a significantly higher absorption rate of 25.88% is achieved for the RHCP case, which is much higher than the efficiencies (8.58% ∼ 13.7%) from a spiral-shaped structure which guides the CP incident wave to a central aperture [16] These results demonstrate that the designed cross-tapered bowtie antenna coupled with the InGaAsSb is capable of efficiently sensing the RHCP feature of the incident wave near 180 THz. In Fig. 9, it should be noted that the maximum field enhancement occurs at ∼165 THz for all polarization states of the incident wave. The highest field enhancement does not occur at the CP operation frequency, the InGaAsSb-coupled cross bowtie antenna can be used to construct a focal plane array for polarimetry because it is capable of achieving a higher field enhancement value and absorption rate in response to a particular CP incident wave near 180 THz
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