A system comprising: a plurality of first forward error correction, FEC, code encoders (204-1, 204-2... 204-k), each of said first FEC code encoders being configured to encode an associated input signal (203-1,..., 203-k) using a first FEC code and provide an associated first FEC code encoded output (205-1,..., 205-k); an interleaver coupled to said plurality of first FEC code encoders (204-1, 204-2... 204-k) and configured to provide a plurality of interleaved outputs, each of said interleaved outputs comprising at least a portion of said associated first FEC code encoded output of at least one of said plurality of first FEC code encoders (204-1, 204-2... 204-k); a second FEC code encoder coupled to said interleaver and configured to encode a first group of said interleaved outputs (207-1, 207-2... 207-i) with a second FEC code; a mapper coupled to said second FEC code encoder; and a modulator coupled to said mapper and configured to modulate an optical signal in response to a mapped output of said mapper, to provide a modulated output signal, characterised in that said second FEC code encoder provides a plurality of second FEC code encoder outputs associated with said first group of said interleaved outputs, wherein said mapper is also coupled to said interleaver and is configured to alternately map said plurality of second FEC code encoder outputs and a second group of said interleaved outputs (209-1, 209-2...209-n) to associated symbols for establishing said mapped output, said second group of interleaved outputs being ones of said plurality of interleaved outputs that are not encoded with said second FEC code. a plurality of first forward error correction, FEC, code encoders (204-1, 204-2... 204-k), each of said first FEC code encoders being configured to encode an associated input signal (203-1,..., 203-k) using a first FEC code and provide an associated first FEC code encoded output (205-1,..., 205-k); an interleaver coupled to said plurality of first FEC code encoders (204-1, 204-2... 204-k) and configured to provide a plurality of interleaved outputs, each of said interleaved outputs comprising at least a portion of said associated first FEC code encoded output of at least one of said plurality of first FEC code encoders (204-1, 204-2... 204-k); a second FEC code encoder coupled to said interleaver and configured to encode a first group of said interleaved outputs (207-1, 207-2... 207-i) with a second FEC code; a mapper coupled to said second FEC code encoder; and a modulator coupled to said mapper and configured to modulate an optical signal in response to a mapped output of said mapper, to provide a modulated output signal, characterised in that said second FEC code encoder provides a plurality of second FEC code encoder outputs associated with said first group of said interleaved outputs, wherein said mapper is also coupled to said interleaver and is configured to alternately map said plurality of second FEC code encoder outputs and a second group of said interleaved outputs (209-1, 209-2...209-n) to associated symbols for establishing said mapped output, said second group of interleaved outputs being ones of said plurality of interleaved outputs that are not encoded with said second FEC code.