A packet switch (10, 40, 60) comprising: a first plurality of wavelength tuneable optical transmitters each arranged to receive at least one electrical signal packet to be switched, each said optical transmitter being arranged to convert said at least one received electrical signal packet into a corresponding optical signal packet at one of a second plurality of input wavelengths; an optical switch fabric (14, 42, 62) arranged to receive said at least one optical signal packet and comprising: an ingress stage (22, 44, 64) comprising a third plurality of wavelength selective routers (20, 46, 72); and an egress stage (24, 50, 68) comprising a fourth plurality of wavelength selective routers (34, 54, 76) and a fifth plurality of wavelength tuneable wavelength converters each respectively provided before an input port of a said wavelength selective router, each said wavelength tuneable wavelength converter being arranged to receive an optical signal at a respective said input wavelength and to output a corresponding optical signal at a respective output wavelength; a sixth plurality of optical detectors each arranged to receive an optical signal packet from said egress stage and to convert said optical signal packet into an output electrical signal packet; and a controller arranged to configure a path across said optical switch fabric connecting a said optical transmitter to a respective said optical detector, said controller being arranged to set said input wavelength for said optical transmitter and to set said output wavelength for a respective said wavelength converter in said path. a first plurality of wavelength tuneable optical transmitters each arranged to receive at least one electrical signal packet to be switched, each said optical transmitter being arranged to convert said at least one received electrical signal packet into a corresponding optical signal packet at one of a second plurality of input wavelengths; an optical switch fabric (14, 42, 62) arranged to receive said at least one optical signal packet and comprising: an ingress stage (22, 44, 64) comprising a third plurality of wavelength selective routers (20, 46, 72); and an egress stage (24, 50, 68) comprising a fourth plurality of wavelength selective routers (34, 54, 76) and a fifth plurality of wavelength tuneable wavelength converters each respectively provided before an input port of a said wavelength selective router, each said wavelength tuneable wavelength converter being arranged to receive an optical signal at a respective said input wavelength and to output a corresponding optical signal at a respective output wavelength; an ingress stage (22, 44, 64) comprising a third plurality of wavelength selective routers (20, 46, 72); and an egress stage (24, 50, 68) comprising a fourth plurality of wavelength selective routers (34, 54, 76) and a fifth plurality of wavelength tuneable wavelength converters each respectively provided before an input port of a said wavelength selective router, each said wavelength tuneable wavelength converter being arranged to receive an optical signal at a respective said input wavelength and to output a corresponding optical signal at a respective output wavelength; a sixth plurality of optical detectors each arranged to receive an optical signal packet from said egress stage and to convert said optical signal packet into an output electrical signal packet; and a controller arranged to configure a path across said optical switch fabric connecting a said optical transmitter to a respective said optical detector, said controller being arranged to set said input wavelength for said optical transmitter and to set said output wavelength for a respective said wavelength converter in said path.