Transmission and Reflection Characterization of Polarizing Beam Splitters at Submillimeter Wavelengths

Abstract

This paper presents a comparison of the transmission and reflection performance of different free-standing wire grids and photolithographic polarizers. This study has been carried out in the frame of the development work of the submillimeter-wave instrument (SWI) as part of the JUpiter and ICy moons Explorer mission of the European Space Agency. SWI is a passive heterodyne radiometer that is operating in the frequency bands from 530 to 625 GHz and from 1080 to 1275 GHz. The optical coupling network of SWI includes a polarizing beam splitter to separate the signal into the two channels. Simulations of the transmittance and reflectance in co-polarization and in cross-polarization have been performed at different incidence angles and polarizations to support the selection of the optimum beam splitter for SWI. The nominal and actual design parameters of the investigated polarizing beam splitters, measured with a confocal laser microscope, have been considered in the simulations. Measurements of the transmission and reflection losses in co-and in cross-polarization have been performed at 636.5 GHz to validate these numerical calculations. The very low losses of the beam splitters in co-polarization were accurately measured by means of a free-space cavity resonator setup. These measurements are in very good agreement with the simulations and radiometric measurements of the transmission loss which were performed with a breadboard model of the SWI receiver unit at 590.0 GHz. The lowest transmission losses among the studied beam splitters are observed for a free-standing wire grid with a single plane of gold-coated wires. The highest reflectance in copolarization and the lowest levels of cross-polarization leakage are determined for the photolithographic polarizers. Index Terms-Electromagnetic transmission, electromagnetic reflection, submillimeter-wave measurements, submillimeter-wave components, polarizing beam splitters (PBS), wire grids. I. INTRODUCTION B ROADBAND and low-loss polarizing components operating at millimetre and submillimeter wavelengths are established in a variety of applications. In quasi-optical networks, polarizers are used as variable attenuators and reflectors, filters, and coupling elements [1]-[3]. Polarizing beam splitters (PBS) with a high polarization selectivity are frequently applied as Manuscript

Heterodyne Receiver for Origins

“…For a wire grid using 10 μm wire at 35-μm spacing, Defrance 23 calculates at 1.4 THz a transmission of 99.8% at 0°and 99.7% at 45°, for the reflections the numbers are slightly lower at 99.1% and 98.3%, respectively. Jacob et al 24 obtained a good agreement between their calculations with measurements at 640 GHz, where transmission and reflections were above 99% for nearly all grids tested. For the HERO calculations, we used the most pessimistic number of 98.3%.…”