Researchers at SRON and TU Delft have made bolometer detectors using flat lenses on a silicon wafer, solving a major bottleneck in building large cameras. Bolometers form the heart of far-infrared spectrometers that can distinguish colors up to one-millionth of their wavelength. This is needed to observe astrophysical processes such as the birth of stars and galaxies from gas and dust clouds.
Current bolometer detectors, known as hot electron bolometer (HEB) mixers, require bulky, individually machined silicon elliptical lenses for each pixel. Aligning and assembling these lenses into arrays larger than ten pixels is a complex, manual process, which especially involves a cryogenic temperature measurement, making larger arrays impractical.
flat surface
Researchers from SRON and TU Delft have now demonstrated a solution. They have replaced the traditional elliptical lenses with a planar metalens—a flat surface etched with microstructures that bend light like a curved lens. This metalens is fabricated directly onto a silicon wafer, which can then be perfectly aligned and bonded to a second wafer containing an array of HEB detectors in a single step.
first successful integration
The team now reports in a publication in Applied Physics Letters the first successful experimental integration of a flat lens with a superconducting detector. The system achieves enough sensitivity to be viable for future space missions.
‘This team effort is a marriage of two disciplines: optics and detectors,’ says team leader Jian-Rong Gao. ‘This demonstration proves that metalenses are not just a laboratory curiosity but a practical solution for real-world far-infrared astronomy.’
Publication
D. Ren, J. R. G. Silva, S. Cremasco, Z. Zhao, W. Ji, J. de Graaff, A. J. L. Adam, and J. R. Gao, ‘Meta-lens coupled terahertz NbN hot electron bolometer mixer’, Applied Physics Letters