optical transceivers used in data communications equipment are typically bidirectional and require two - way communications in order to maintain their operability . however , in some applications such as cable television , the traffic is highly unbalanced with very high bandwidth requirements in one direction and minimal bandwidth requirements in the opposite direction . hence for such efficient and cost effective one - way communication applications , unidirectional fiber optic transceivers are useful . there is provided here a unidirectional transceiver provided internally with a keep - alive signal generator to enable unidirectional transmissions . the keep alive signal is , for instance , idle characters for a gigabit ethernet communication system , or any other suitable handshake signal which provides the desired operability .