11 March 2015

Frequency comb light sources extended towards mid-IR using silicon photonics technology

Belgium's Ghent University (UGent) and nanoelectronics R&D center Imec in Leuven have joined forces with the Max Planck Institute in Garching, Germany and New Zealand's Auckland University to realize a frequency comb light source in the mid-infrared wavelength band (B. Kuyken et al, 'An octave spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide', Nature Communications, 6(6310), (2015)). Frequency comb light sources with an extended spectrum can be used for real-time, extremely high-resolution spectroscopy, for example to measure the presence and concentration of gas molecules in analytes.

A frequency comb source is a light source with a spectrum containing thousands of laser lines. Their development has allowed the construction of a link between the optical part of the electromagnetic spectrum and the radio frequency part, allowing researchers to determine optical frequencies with an unprecedented precision. Frequency comb light sources have also been used in optical clocks, enabling precise time keeping. The impact of frequency comb light sources on science was highlighted in 2005, when the Nobel Prize for physics was awarded to professor T. Haensch and professor J. Hall for their work on optical frequency metrology using frequency combs.

Lately, frequency combs have been used to target more real-life applications. Several experiments have shown that the specific properties of the sources can be used to do fast, high-resolution spectroscopy over a broad spectrum. However, traditional comb sources are not at the right wavelength spectrum for doing spectroscopy.

Ghent University, Imec, the Max Planck Institute for Quantum Optics in Garching and the Auckland University in New Zealand have developed mid-infrared frequency combs, working in the mid-IR molecular fingerprinting region of the electromagnetic spectrum. In this wavelength region, many molecules have specific absorption bands that can be used in spectroscopy to determine the presence and concentration of these molecules in samples.

The researchers realized the broad frequency combs by combining the strong light-matter interaction in silicon with its broad transparency window. By fabricating nanowire silicon photonics waveguides to confine the light in a very small-area waveguide, they further enhanced the strong light-matter interaction, allowing them to broaden the spectrum of the frequency combs into the mid-infrared. The achievements were possible through the use of a unique pump laser source, previously developed by Spain's Institut de Ciences Fotoniques Barcelona (ICFO).

The results are reckoned to be an important step towards a small-footprint chip-scale mid-IR frequency comb source. Such sources could act as sensitive cheap gas sensors in the mid-infrared. These would be important for example for environmental monitoring for measuring air-pollution or in medical diagnostics as a cheap tool for breath analysis.

The reported work is the result of collaboration between three European Research Council (ERC) grants: Multicomb, Miracle and InSpectra.

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Ghent University and Imec demonstrate interaction between light and sound in nanoscale waveguide

Tags: Nanophotonics silicon photonics IMEC

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