A de-multiplexer (1, 21, 41, 61, 71) for separating two co-propagating modes of electromagnetic radiation ( Ê in), wherein the electric fields of the two modes of electromagnetic radiation are orthogonal to each other, wherein the de-multiplexer (1, 21, 41, 61, 71) comprises: a volume comprising a path therethrough for receiving electromagnetic radiation ( Ê in); an input for directing two co-propagating modes of electromagnetic radiation ( Ê in) to be incident upon the volume, wherein the electric fields of the two modes of electromagnetic radiation ( Ê in) are orthogonal to each other; a control source (12, 32, 33, 48) of optical or microwave electromagnetic radiation arranged to generate a time-dependent control field ( R (t), R 1 (t), R 2 ( t), Ĉ j), wherein the time-dependent control field ( R (t), R 1 (t), R 2 (t), Ĉ j) from the control source is arranged to be incident upon the volume and to overlap both contemporaneously and spatially with the two co-propagating modes of electromagnetic radiation ( Ê in); wherein the volume is arranged and the time-dependent control field ( R (t), R 1 (t), R 2 ( t), Ĉ j) is shaped such that, when the two co-propagating modes of electromagnetic radiation ( Ê in) and the time-dependent control field ( R (t), R 1 (t), R 2 ( t), Ĉ j) are incident upon the volume contemporaneously, the time-dependent control field ( R (t), R 1 (t), R 2 ( t), Ĉ j) causes the volume to accept one of the two modes of electromagnetic radiation ( Ê in) onto a mode of the volume without any parametric non-linear optical interaction taking place and to reflect or transmit the other of the two modes of electromagnetic radiation ( Ê in), so to spatially and/or temporally separate the two modes of electromagnetic radiation ( Ê in) from each other. a volume comprising a path therethrough for receiving electromagnetic radiation ( Ê in); an input for directing two co-propagating modes of electromagnetic radiation ( Ê in) to be incident upon the volume, wherein the electric fields of the two modes of electromagnetic radiation ( Ê in) are orthogonal to each other; a control source (12, 32, 33, 48) of optical or microwave electromagnetic radiation arranged to generate a time-dependent control field ( R (t), R 1 (t), R 2 ( t), Ĉ j), wherein the time-dependent control field ( R (t), R 1 (t), R 2 (t), Ĉ j) from the control source is arranged to be incident upon the volume and to overlap both contemporaneously and spatially with the two co-propagating modes of electromagnetic radiation ( Ê in); wherein the volume is arranged and the time-dependent control field ( R (t), R 1 (t), R 2 ( t), Ĉ j) is shaped such that, when the two co-propagating modes of electromagnetic radiation ( Ê in) and the time-dependent control field ( R (t), R 1 (t), R 2 ( t), Ĉ j) are incident upon the volume contemporaneously, the time-dependent control field ( R (t), R 1 (t), R 2 ( t), Ĉ j) causes the volume to accept one of the two modes of electromagnetic radiation ( Ê in) onto a mode of the volume without any parametric non-linear optical interaction taking place and to reflect or transmit the other of the two modes of electromagnetic radiation ( Ê in), so to spatially and/or temporally separate the two modes of electromagnetic radiation ( Ê in) from each other.