Heterodyne detection in the infrared (IR) is one approach to the future detection of possible biochemical reactions on exoplanets, signaling life light years away. Now, a group of Russian scientists from Moscow State Pedagogical University and other institutes in Moscow has developed a fiber-coupled optical receiver for heterodyne IR spectroscopy operating at 1.5 μm; the device is based on a superconducting hot-electron bolometer (HEB). The measured noise for the device was 25 dB—only about 10 dB higher than the quantum noise limit. Previous to this demonstration at IR wavelengths (a frequency of around 200 GHz), the highest-frequency detection achieved by a HEB has been in the terahertz region at about 5.25 THz.
The sensitive area was about 7 μm square, chosen to closely match the 9-μm-diameter core of a standard single-mode fiber; the device has a bandwidth of about 2.5 GHz. The cryogenically cooled niobium nitride (NbN) superconducting detectors were enhanced with gold optical nanoantennas in a zebra-stripe pattern, which produced a 25% absorption efficiency for polarized light—three times that of an unpatterned NbN device. The 25 dB measured noise can likely be reduced by improving the optical coupling to the NbN receiver. In addition to astronomy, uses of the NbN HEB include quantum-optical tomography and fiber-optic sensing. Contact Yury Lobanov at [email protected].
