Abstract: The principle and experimental results of all-fibre optical heterodyne system, in which ordinary single mode fibres are used, are presented.Two novel fibre devices, fibre optic frequncy shifter and fibre optic polarization controller, are employed in this system.The principle and design method for the two key devices are described.In addition,this paper gives practical system,selection of electricoptic component,and alignment criterionfor optical configuration in detial.