Spectrometer operating in visible and near-infrared

The current size, weight and complexity of spectrometers limit their use in medicine, space and many other applications.

Led by a team of French researchers, the SWIFTS project used stationary-wave integrated Fourier-transform (SWIFTS) technology to develop high-resolution miniature spectrometers for measuring wavelengths between 400-1100 nanometers, which extends from invisible light into the mid-infrared range.

“The spectrometer is half the size of a shoe box and replaces six tons of material. As the world's smallest spectrometer, it is easy to bring it out in the field. It also passed thermal and vibrations testing,” explained Etienne le Coarer, technical director at IPAG and co-inventor, to EETimes.

Le Coarer specified that the aerospace industry, including European Space Agency and CNES, had expressed interest.

Initial prototypes were developed from 2008 to 2011, and the first products are expected to reach the market this year. Measuring only 8.3 cm long and 12.6 cm wide, the devices are claimed to provide 100 times better resolution than other mini-spectrometers currently on the market.


A company, Resolution Spectra Systems, was created to commercialize the spectrometers. It anticipates the sale of 400 to 5,000 spectrometers by 2015, resulting in 8 million euro ($12.4 million) to 25 million euro ($38.8 million) revenues and the creation of 40 to 150 jobs.

The spectrometers will initially target the scientific instrumentation, spatial and metrology markets. Ultimately, SWIFTS technology could be used in telecommunications, imaging, and the detection of harmful gases.

The SWIFTS project gathered Joseph Fourier University, Troyes University e2v Semiconductors, Floralis, Teem Photonics. It is a 4 million euro ($4.9 million) project.

In a discussion with EETimes, Le Coarer agreed upon the publication of a design article on the stationary-wave integrated Fourier transform spectrometer. Although it was published a few years back, the article provides good technical background.  
Authors:
ETIENNE LE COARER (1), SYLVAIN BLAIZE (2), PIERRE BENECH (3), ILAN STEFANON (2), ALAIN MORAND (3), GILLES LE´ RONDEL (2), GREGORY LEBLOND (2), PIERRE KERN (1), JEAN MARC FEDELI (4) AND PASCAL ROYER (2)

1. Laboratoire d’Astrophysique de Grenoble, Université Joseph Fourier, CNRS, Grenoble, France
2. Laboratoire de Nanotechnologie et d’Instrumentation Optique, ICD, CNRS (FRE2848), Université Technologique de Troyes, France
3. Institut de Microélectronique d’Electromagnetisme et de Photonique, INPG-UJF-CNRS, Grenoble, France
4. CEA-LETI, Minatec, Grenoble, France

1. INTRODUCTION
SWIFTS (StationaryWave Integrated Fourier Transform Spectrometer) is a first step toward a new family of micro-Fourier-spectrometers. Because SWIFTS’s technology permits a drastic reduction of the size of spectrometers while conserving, even improving, their performances it opens spectroscopy capabilities to many applications. A SWIFTS component is an association of a single mode waveguide with a set of photosensitive elements that sample a stationary wave in the evanescent field of the guide. The concept allows a direct Fourier Transform measurement of the considered light spectrum over a wide spectral range in a really tiny volume without any moving part. After a first realization on silicon substrate we present in this work a SWIFTS operating in visible and near infrared on glass substrate. It is an original optical near-field detection in which nanowires of gold are used to directly sample the evanescent standing wave in the wave guide. With this first prototype we have been able to rebuild a spectrum with a resolution R=800.

2. PRESENTATION OF SWIFTS
2.1 Origin and principle
SWIFTS is an innovative way to achieve very compact spectrometers using nanodetectors coupled to the evanescent field of a dielectric integrated optics. The principle of SWIFTS is based on the Lippmann concept. In 1891, at the Académie des Sciences in Paris, Gabriel Lippmann presented his first interferential color photograph of the suns spectrum. Later, in 1894, he published an article on how his plate was able to record color information in the depth of photographic grainless gelatin and how the same plate after processing (development) could restore the original color image merely through light reflection.

He was thus the inventor of true interferential color photograph and received the Nobel Prize in 1908 for this breakthrough. Unfortunately, this principle was too complex to use for color photograph, but Lippmann concept remains nonetheless extremely interesting for spectroscopic applications. The basic principle underlying the spectrodetector is illustrated on figure 1. This design acts like a Fourier transform spectrometer with simultaneous recorded pattern, i.e. no moveable part is required to record the information needed to restore the spectrum. The light under test is coupled at the two extremities of a single mode waveguide. Nanoscaled detectors are placed in the evanescent field of the waveguide in order to extract only a small fraction of the guided energy. This peripheral detection approach allows proper sampling of the interferogram using small size detectors in comparison with the quarter wavelength of the guided light. In this way 74 percent of the whole energy is detected using a minimum number of detectors.