A transceiver is a device composed of a transmitter and a receiver, which are combined and share common circuits or/and common housing. Transceivers are placed at the input of a network to launch modulated, encoded information to transmission medium (e.g. optical fibres) – a transceiver works as a transmitter, and at the termination of the network to decode, demodulate the signal – it operates as a receiver.
In case of transmission in both directions (e.g. duplex transmission), each transceiver transmits and receives data (e.g. alternately or at the same time in duplex).
A transmitter part can use lasers as a source of symbols in optical networks; a receiver contains a photodiode that converts an optical signal to electrical signal, which is further processed e.g. by a digital signal processor (DSP).
Each following binary symbol has phase shifted by π. A Mach-Zehnder modulator (MZM) is used to create the binary string, where pulses have the same shape and altered phase. The speed of this signal is the same as the speed of an information signal.
The information signal in a form of electronic pulses is sent to the modulator, and based on this “control” signal, the pulses with altering phase produced in the modulator are released or suppressed. The output signal is then a certain product of those two signals.