IR polarimetry using compact circular polarized IR antennas integrated with InGaAsSb Nano-load

Abstract

Summary form only given. The imaging polarimetry can measure the polarization status of the scene in addition to the intensity and color which the traditional imager can detect. The polarization information can show the surface roughness and shading of target material and the distinct contrast image which is uncorrelated with intensity and color (J. S. Tyo, D. L. Goldstein, D. B. Chenault, and J. Straw, Appl. Opt, 45, 5453-5469). Detecting the circular polarization (CP) is a key factor for the IR imaging polarimetry. The traditional IR imagers to detect CP have implemented a quarter-wave plate integrated with a linear polarizer (K. A. Bachman, J. J. Peltzer, P. D. Flammer, T. E. Furtak, R. T. Collins, and R. E. Hollingsworth, Opt. Express, 20(2), 1308-1319). Instead of the traditional polarization plates, antennas with different polarizations loaded with the IR detectors can be used to measure the polarization of the received IR signals. The spiral antenna has been introduced as a typical antenna structure for CP in IR frequency regime (F. J. Gonzalez, B. Ilic, J. Alda, and G. D. Boreman, IEEE J. Sel. Topics Quantum Electron., 11, 117-120). However the structure requires the multiple circular or rectangular turns and thus it would require much space within a polarimetric detector cell. In this study, a compact CP antenna operating in IR spectrum is designed using a cross dipole shaped structure where a vertical and horizontal dipole are connected through a pair of elliptical-shaped loops. The dimension and shape of the loop is designed in such a way to achieve circular polarization at the antenna boresight. The placement of the loops in first and third, or the second or fourth quadrant of the cross loop structure can produce right-handed CP (RHCP) or left-handed CP (LHCP). In the proposed IR detector element, a nanometer-sized semiconductor PN junction material, Indium Gallium Arsenide Antimonide (InGaAsSb) with Eg = 0.52 eV is mounted at the terminal of the antenna structure, and the material dimension needs to be optimized for the impedance matching to the antenna's input impedance. This optimization ensures the maximum power transfer between the antenna and the semiconductor. This impedance matching of the antennas in IR frequencies is problematic due to the high capacitance of the semiconductor. However the loops in the cross dipole antenna could provide an adequate inductance which can compensate the high capacitance from a semiconductor for the PN junction. Finally, a combination of a vertical dipole, a horizontal dipole, a LHCP cross dipole, and a RHCP cross dipole all within a single imager pixel allows determination of the Stokes vector of the incoming IR signal.