THz Metal-Mesh Bandpass Filters With Diamond-Shaped Apertures for Sensitive THz Receivers

In this letter, we present high-performance terahertz (THz) metal-mesh bandpass filters developed to mitigate direct detection effects in sensitive THz receivers based on superconducting hot-electron bolometer (HEB) mixers. These metal-mesh filters are freestanding 5-μm-thick sheets of copper perforated with a periodic array of diamond-shaped apertures. The simple aperture design minimizes the effect of fabrication (rounding) errors on filter performance, allowing precise engineering of the center frequency (1.5–5.5 THz) while maintaining high (>90%) peak power transmission at normal incidence and a relatively narrow bandwidth of 5%–15%. Based on finite-element method simulation results, we provide simple design equations that can be used for rapid design with high accuracy. The measured transmission profiles of 1.9-, 2.5-, and 4.7-THz filters show excellent agreement with the simulation results. These filters are compatible with cryogenic operation and can substantially reduce the direct detection effects in HEB mixers.