A device for compensating modal dispersion during the transmission of information in a multimode optical fibre, the device being intended to be interposed between a source of a light radiation modulated digitally by the information and a receiver making it possible to demodulate this information, the device comprising a multimode optical fibre (MMF1, MMF2) and an optical component for modifying the spatial profile of the light beam placed upstream or downstream or inserted at an intermediate point of the fibre, this component comprising: - an input for receiving a multimode light beam, - a beam output, - at least two mirrors (20, 22) allowing a multiple reflection, and multiple free space paths, of the beam between the two mirrors, - and an optical phase-shifting structure, which can be one of the mirrors and which comprises several sets of multiple phase-shifting elementary areas, the individual phase-shifting patterns introduced by the phase-shifting elementary areas into each set generating an intermediate transformation of the spatial profile of the beam after the passage of the beam through this set, and the intermediate transformations generated by several sets combining, during the passages of the beam on the phase-shifting structure during multiple reflections between the mirrors, to form a global transformation, characterised in that the global transformation comprises: a) first a separation of the beam into several modes or groups of propagation modes having group speeds in different ranges of values, the deflections generated by the sets of phase-shifting areas being such that the beam portions corresponding to a mode or group of modes whose group speeds are in a first range of values undergo, as a result of these deflections, a number of reflections on the mirrors which is not the same as the number of reflections conferred on other parts of the beam corresponding to another mode or group of modes having group speeds in another range of values, b) then grouping the different parts of the beam after these reflections to direct the beam towards the output of the component. - an input for receiving a multimode light beam, - a beam output, - at least two mirrors (20, 22) allowing a multiple reflection, and multiple free space paths, of the beam between the two mirrors, - and an optical phase-shifting structure, which can be one of the mirrors and which comprises several sets of multiple phase-shifting elementary areas, the individual phase-shifting patterns introduced by the phase-shifting elementary areas into each set generating an intermediate transformation of the spatial profile of the beam after the passage of the beam through this set, and the intermediate transformations generated by several sets combining, during the passages of the beam on the phase-shifting structure during multiple reflections between the mirrors, to form a global transformation, characterised in that the global transformation comprises: a) first a separation of the beam into several modes or groups of propagation modes having group speeds in different ranges of values, the deflections generated by the sets of phase-shifting areas being such that the beam portions corresponding to a mode or group of modes whose group speeds are in a first range of values undergo, as a result of these deflections, a number of reflections on the mirrors which is not the same as the number of reflections conferred on other parts of the beam corresponding to another mode or group of modes having group speeds in another range of values, b) then grouping the different parts of the beam after these reflections to direct the beam towards the output of the component. a) first a separation of the beam into several modes or groups of propagation modes having group speeds in different ranges of values, the deflections generated by the sets of phase-shifting areas being such that the beam portions corresponding to a mode or group of modes whose group speeds are in a first range of values undergo, as a result of these deflections, a number of reflections on the mirrors which is not the same as the number of reflections conferred on other parts of the beam corresponding to another mode or group of modes having group speeds in another range of values, b) then grouping the different parts of the beam after these reflections to direct the beam towards the output of the component.