Scientists at Stanford University and Japan's National Institute of Informatics have created a new highly sensitive infrared spectrometer. The device converts light from the infrared part of the spectrum to the visible part, where the availability of superior optical detectors results in strongly improved sensing capabilities. The research will appear in the Nov. 24 issue of Optics Express, the Optical Society's open access journal. The new spectrometer is 100 times more sensitive than current commercial optical spectrum analyzers used in industrial applications such as optical communication, semiconductor microelectronics and forensic analysis.

Summary
Current spectrometers being used on the market today cover a wide spectral range, allow for moderately fast wavelength sweeps, have a good spectral resolution and don't require cryogenic cooling. However, the sensitivity of these instruments is limited, making them unsuitable for capturing single-photon-level spectra at telecommunication wavelengths. Cryogenic cooling can increase the sensitivity of these devices, yet reduces the usefulness for industrial applications. One possible solution is to up-convert near-infrared to visible light in a nonlinear medium. The up-converted photons can then be detected using a single-photon detector for visible light. The authors use a single-photon counting module, which results in 100 times better sensitivity. They implemented the frequency conversion via sum-frequency generation in a periodically poled lithium niobate waveguide, which can be thought of as combining two low-energy photons to get one high-energy photon.

Key Findings

• The up-conversion based spectrometer's sensitivity is 100 times higher compared to current commercial optical spectrum analyzers.
• Cryogenic cooling is not required for increased sensitivity, making the device practical for a variety of industrial applications.
• The cost and system complexity of the spectrometer is reduced because it only uses one single-photon detector instead of an array of detectors.