NIST researchers model anti-reflection structures for photon number resolving optical detectors.

NIST researchers have successfully modeled antireflection structures that could be used with tungsten superconducting transition-edge sensors (TES) to increase the quantum efficiency of detection of a 1.55 [micro]m photon from 20% to 98.5%. By using a reflecting layer underneath the detector metal layer (tungsten) and a single layer anti-reflection coating above the tungsten, the quantum efficiency of a photon being absorbed in the tungsten can be significantly enhanced. After carefully measuring the optical properties of thin films of tungsten, silicon oxide, and silicon nitride fabricated in a NIST cleanroom, optical measurements of anti-reflection structures agreed with numerical calculations for their performance. A structure with >98.5% absorption of photons in a tungsten film was fabricated. In principle, >99% absorption should be possible with better control of thicknesses of the various films.

Improvements in the quantum efficiency of detection for tungsten films fabricated into TES sensors will have a significant impact on several areas of research, including metrology for quantum key distribution systems, quantum optics, and linear optical quantum computing.

CONTACT: Sae Woo Nam, [phone]; [e-mail].