Optical QPSK modulated signal receiver - processes optical signal in electrical part with IF as separation of local and transmitter laser

摘要

The modulated transmitter wave is coupled to the one input of an optical 90 deg. hybrid, and the local laser to the other. The two outputs are coupled to respective photodiodes and photocurrent amplifiers. The output of the first amplifier is coupled to first multiplication places, and of the second amplifier to second multiplication places. The outputs of these feed respective summers whose outputs form in-phase and quadradture channels, and are coupled to a circuit distinguishing data and deriving a phase difference. The phase difference signal operates a four output VCO via a loop filters, each output being coupled to the respective multiplication points via respective filters. ADVANTAGE - Simplified circuits.