1.25–1.57 THz Dual-Polarization Receiver Optics Based on Corrugated Horns

High-performance dual-polarization receiver optics is a key component of terahertz applications with stringent requirements, such as radio astronomy or planetary exploration. Usually, such optics use corrugated horns due to their excellent wideband performance. However, this kind of horns is difficult to fabricate for frequencies higher than 1 THz. Traditionally, the performance of optics at frequencies over 1 THz is thus limited by the choice of feed horn, usually a diagonal or smooth-wall horn. This choice limits the effective maximum aperture efficiency or bandwidth achievable, respectively. Recently, we successfully fabricated direct-machined terahertz corrugated horns with good beam characteristics and low cross polarization. Based on these horns, we have designed full receiver optics for a possible future ALMA band 11 (1.25-1.57 THz) receiver. The polarization separation is achieved by means of a wire grid. A prototype has been fabricated and tested on a near-field beam scanner. It shows aperture efficiency above 85% and polarization efficiency above 99.6% at all measured frequencies. This complies with the stringent requirements of the ALMA telescope for frequencies between 35 and 950 GHz. To our knowledge, these are the highest aperture and polarization efficiencies achieved over such a wide bandwidth at around 1.4 THz.