An optical label extractor (10) comprising a non-linear optical element (12), a pump source (14) and optical filter apparatus (16). Said non-linear optical element (12) is arranged to receive optical data packets (18) at data signal wavelengths. Each said data packet comprises at least one data bit and at least one label bit. Said pump source (14) is arranged to pump said non-linear optical element such that any non-zero label bit experiences a non-linear optical effect on propagation through said non-linear optical element and an output label bit (20) comprising a respective further wavelength is thereby generated. Said optical filter apparatus (16) is arranged to receive any said output label bit from said non-linear optical element and being further arranged to prevent transmission of a part of said output label at said respective data signal wavelength and to transmit a part of said output label bit at said respective further wavelength.