In　a　linear　optical　current　transducer　(OCT)　based　on　the　radial　grating　polarizer　detection,　the　faraday　rotation　angle　is　converted　into　synchronous　rotation　of　a　circular　facula.　Then,　a　charge　coupled　device　camera　(CCDC)　is　utilized　to　position　the　dark　stripe　of　the　facula　to　achieve　a　real　time　current　measurement.　The　linear　OCT　overcomes　some　issues　in　the　OCT　of　traditional　light　intensity　detection　mode,　such　as　small　dynamic　measurement　range,　nonlinear　detection,　light　intensity　dependence,　linear　birefringence　and　temperature　drift　etc.　However,　the　linear　OCT　still　has　some　shortcomings,　such　as　high　cost,　low　resolution,　big　algorithm　error,　and　not　being　capable　of　meeting　0.2S　accuracy　class,　especially　in　small　current　measurement.　In　order　to　fix　these　problems,　a　four-quadrant　detector　is　employed　to　sense　the　rotation　angle　of　the　circular　facular　with　the　advantages　of　low　cost,　simple　algorithm,　high-resolution　and　high-accuracy.　It　has　been　verified　that　the　resolution　of　measurement　is　increased　nearly　100-fold　by　theoretical　analysis　and　experimental　derivation　in　the　range　of　±40°of　the　faraday　rotation　angles.　The　accuracy　is　improved　from　0.5%　class　to　0.2S,　and　the　cost　of　picture　detection　unit　is　reduced　by　more　than　95%.　©　2017　Automation　of　Electric　Power　Systems　Press.