An optical communication system 100 is configured to provide optical communication between a transmitter 200 and a receiver 300. The transmitter 200 is configured to transmit a multiplexed optical signal 235. The transmitter 200 includes at least one optical signal generator 210 configured to generate at least one optical signal 215, a modulator 220 configured to encode data onto the at least one optical signal 215, and a multiplexer 230 configured to combine the at least one optical signal 215 into a multiplexed optical signal 235. A receiver 300 is configured to receive a multiplexed optical signal 390. The receiver 300 comprises a de-multiplexer 330 configured to separate the received multiplexed optical signal 390 into at least one optical signal 335, an opto-electronic element 370 configured to convert the at least one optical signal 335 into at least one electrical signal, and a de-modulator 320 configured to decode the at least one electrical signal. At least one of the transmitter 200 and receiver 300 are configured to be operated under water. Also described herein is a system 100 comprising the transmitter 200 and receiver 300 apparatuses, and methods of transmitting 400 and receiving 500 an optical signal, for example, using the transmitter 200 and receiver 300 apparatuses.