An optical switching arrangement, comprising: a plurality of input waveguides (110, 120, 160, 210, 310), each of the input waveguides (110, 120, 160, 210, 310) having a first plurality of 1x2 optical switches (120, 170, 220) associated therewith and extending therealong; a plurality of output waveguides (110, 120, 160, 210, 310), each of the output waveguides (110, 120, 160, 210, 310) having a second plurality of 1x2 optical switches (120, 170, 220) associated therewith and extending therealong; each of the optical switches (120, 170,220) in the first and second plurality of optical switches (120, 170, 220) being selectively switchable between first and second states such that in a first state each optical switch (120, 170, 220) allows light propagating in the input or output waveguide with which it is associated to continue propagating therethrough undisturbed without encountering any intervening mode perturbing structures between adjacent ones of the 1x2 switches (120, 170, 220) and in a second state each optical switch (120, 170, 220) couples light into or out of the input or output waveguide (110, 120, 160, 210, 310) with which it is associated; and wherein each of the first plurality of optical switches (120, 170, 220) associated with each of the input waveguides (110, 120, 160, 210, 310) is optically coupled to one of the second plurality of optical switches (120, 170, 220) in a different one of the output waveguides (110, 120, 160, 210, 310) when both optical switches (120, 170, 220) are in the second state, further comprising a first planar lightwave or photonic integrated circuit in which the plurality of input waveguides (110, 120, 160, 210, 310) and the first plurality of 1x2 optical switches (120, 170, 220) are integrated, characterised by the optical switching arrangement further comprising a second planar lightwave or photonic integrated circuit in which the plurality of output waveguides (110, 120, 160, 210, 310) and the second plurality of 1x2 optical switches (120, 170, 220) are integrated, wherein the first and second planar lightwave or photonic integrated circuits are stacked on top of one another, and further comprising a plurality of vertical couplers (130, 180) each optically coupling one of the first plurality of optical switches (120, 170, 220) associated with each of the input waveguides (110, 120, 160, 210, 310) to one of the second plurality of optical switches associated with one of the output waveguides (110, 120, 160, 210, 310) when both optical switches (120, 170, 220) are in the second state. a plurality of input waveguides (110, 120, 160, 210, 310), each of the input waveguides (110, 120, 160, 210, 310) having a first plurality of 1x2 optical switches (120, 170, 220) associated therewith and extending therealong; a plurality of output waveguides (110, 120, 160, 210, 310), each of the output waveguides (110, 120, 160, 210, 310) having a second plurality of 1x2 optical switches (120, 170, 220) associated therewith and extending therealong; each of the optical switches (120, 170,220) in the first and second plurality of optical switches (120, 170, 220) being selectively switchable between first and second states such that in a first state each optical switch (120, 170, 220) allows light propagating in the input or output waveguide with which it is associated to continue propagating therethrough undisturbed without encountering any intervening mode perturbing structures between adjacent ones of the 1x2 switches (120, 170, 220) and in a second state each optical switch (120, 170, 220) couples light into or out of the input or output waveguide (110, 120, 160, 210, 310) with which it is associated; and wherein each of the first plurality of optical switches (120, 170, 220) associated with each of the input waveguides (110, 120, 160, 210, 310) is optically coupled to one of the second plurality of optical switches (120, 170, 220) in a different one of the output waveguides (110, 120, 160, 210, 310) when both optical switches (120, 170, 220) are in the second state, further comprising a first planar lightwave or photonic integrated circuit in which the plurality of input waveguides (110, 120, 160, 210, 310) and the first plurality of 1x2 optical switches (120, 170, 220) are integrated, characterised by the optical switching arrangement further comprising a second planar lightwave or photonic integrated circuit in which the plurality of output waveguides (110, 120, 160, 210, 310) and the second plurality of 1x2 optical switches (120, 170, 220) are integrated, wherein the first and second planar lightwave or photonic integrated circuits are stacked on top of one another, and further comprising a plurality of vertical couplers (130, 180) each optically coupling one of the first plurality of optical switches (120, 170, 220) associated with each of the input waveguides (110, 120, 160, 210, 310) to one of the second plurality of optical switches associated with one of the output waveguides (110, 120, 160, 210, 310) when both optical switches (120, 170, 220) are in the second state.