A de-multiplexer 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 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 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 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. <EOS>