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Real-time Fourier transformation in a laser system

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Calculating the Fourier transform of an input time signal (i.e. its spectrum) usually requires several steps including data acquisition and numerical data processing. However it is possible in some systems, to generate an output signal whose temporal variations reproduce the spectrum of the input signal (Frequency to time mapping).

For example in optics, propagation through a dispersive medium showing group velocity dispersion leads to a temporal separation of the different frequency components of the input signal, enabling analog real-time Fourier transformation. However the frequency resolution in this case is relatively limited (10 GHz). In the frame of a collaboration with INRS in Montreal, we have shown that frequency-shifted-feedback lasers developed by OPTIMA, lead to the same property, but with a frequency resolution improved by orders of magnitude (down to 30 kHz). Moreover the latency time is optimal (equal to the inverse of the frequency resolution). These results have just been published in Optica.