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Echoes is a project of a spaceborne Doppler Spectro-Imager (DSI) which has been proposed as payload to the JUICE mission project selected in the Cosmic Vision program of the European Space Agency (ESA). It is a Fourier transform spectrometer which measures phase shifts in the interference patterns induced by Doppler shifts of spectral lines reflected at the surface of the planet. Dedicated to the seismology of Jupiter, the instrument is designed to analyze the periodic movements induced by internal acoustic modes of the planet. It will allow the knowledge of the internal structure of Jupiter, in particular of the central region, which is essential for the comprehension of the scenario of the giant planets' formation. The optical design is based on a modified Mach-Zehnder interferometer operating in the visible domain and takes carefully into account the sensitivity of the optical path difference to the temperature. The instrument produces simultaneously four images in quadrature which allows the measurement of the phase without being contaminated by the continuum component of the incident light. We expect a noise level less than 1 cm²s -²μHz -1 in the frequency range [0.5 -10] mHz. In this paper, we present the prototype implemented at the Observatoire de la Côte d'Azur (OCA) in collaboration with Institut d'Astrophysique Spatiale (IAS) to study the real performances in laboratory and to demonstrate the capability to reach the required Technology Readiness Level 5.