Spectrometer operating in visible and near-infrared

2.2 Design of the component used for the experimentation
The first realization has been made by Le Coarer et al. [1]. Since the use of detectors that have small enough dimension (a sixth of the wavelength, approximately 100 nm in our case) was impossible, for the first realization a solution based on light scattering has been developed. The idea was to use nanometric scattering centres deposited on the waveguide surface to extract the stationary wave from the waveguide and thus make far field detection possible thanks to an optic system. Because of diffraction limit of the far field detection system used the minimum distance between two scattering centers was 2.7 μm. Thus the Shannon’s sampling criterion could not be satisfied. However, if the spectral range is relatively small, the restoration of the spectrum still remains possible. In this experimentation, we also use a solution based on light scattering, but unlike Le Coarer et al. [1] we have been able to fully sample the interferogram. In order to achieve that we scanned the interferogram by moving the position of the zero OPD (optical path difference) (see: 3.1). The component used for the following experimentation is a SWIFTS on glass substrate. It is composed of a single mode waveguide with nanowires of gold on top of it. The wave-guide has been produced by the ion K+ exchange technique. It is a 6 μm of diameter waveguide which is single mode at around 750 nm. With the nanowires of gold of 50 nm, it forms an original optical near-field detection in which nanowires of gold are used to directly sample the evanescent standing wave in the wave guide. This component is illustrated on figure 2, on the photograph one can see the waveguide and the nanowires of gold.



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[1] Le Coarer, E., Blaize, S., Benech, P., Stefanon, I., Morand, A., Lerondel, G., Leblond, G., Kern, P., F´ed´eli, J.-M., and Royer, P., “Stationary waves integrated fourier transform spectrometry (SWIFTS): towards an ultimate wavelength scalespectrometer,” Nature Photonics 8, 473–478 (2007).