A low-loss silicon optical diplexer for millimeter and submillimeter radio astronomy

Simultaneous dual polarization observations at multiple frequencies are crucial for understanding time-varying astronomical phenomena. To achieve this, it is necessary to separate the main radio telescope beam into different frequency components to feed various receivers. This paper presents our innovative optical diplexer design, based on the layering of dielectric materials. By stacking nine periodic layers of low-loss High Resistivity Silicon (HR-Si) and Low-Density Polyethylene (LDPE), we have developed a diplexer that separates frequency bands centered around 220 GHz and 350 GHz. This diplexer design has applications in the wideband Submillimeter Array (wSMA). Future optical diplexer designs utilizing dielectric stacks will enable dual polarization multi-band observations with the next generation Event Horizon Telescope (ngEHT) and the Black Hole Explorer (BHEX).