Structured light illumination for order sorting in Echelle spectrometers.

We report on the operation of an echelle spectrometer under structured light illumination. Each diffraction order of the spectrometer is encoded with a certain periodic structure allowing for order sorting by numerical analysis after detection. In contrast to cross-dispersed echelle spectrometers, in this approach the orders overlap at the detection plane so that the spectral calibration can be performed easily with a single reference wavelength. This operational simplification makes it possible to measure simultaneously the light source under study and the calibration wavelength giving rise to a self-calibrated echelle spectrometer. In this way the device compensates for the spectral drift due to temporal changes of environmental conditions in real time. Our proposal can be useful in a large number of applications requiring moderate, high or very high resolving power for a wide bandwidth in a non-isolated environment.