An example of a hybrid system. Coherent optical system with costas loop in receiver-system for transmission in baseband

The possibility of hybrid system construction is considered in this paper, The coherent optical system is the constituent part of this system, The first part of the system is constructed in passband (optical cable is transmission medium), and the second part of the system is constructed in baseband, The heterodyne optical receiver is used as optical receiver. Estimation is not done just after demodulation, but it is done at the end of the section in baseband, Taking into account shot noise of photodetectors, laser phase noise (transmitter laser and local laser) and noise which is generated during transmission by means of the section in baseband, we determine the performances of the proposed system.