A　circular　sub-wavelength　radial　polarization　grating　(RPG)　is　designed　based　on　nanotechnology　in　this　paper.　It　is　capable　of　converting　a　Faraday　rotation　angle　into　synchronized　rotation　linearly,　so　it　can　be　employed　in　an　optical　current　transducer　to　achieve　a　linear　and　optical　power　independent　measurement.　The　Jones　matrix　and　the　rigorous　coupled　wave　theory　are　used　to　analyze　and　optimize　the　parameters　of　the　grating.　The　simulations　and　experiments　show　that　the　grating　has　a　TM　transmission　rate　being　greater　than　80%　and　an　extinction　ratio　being　more　than　100.　Moreover,　its　temperature　characteristics　have　been　studied　in　detail,　theoretically.　©　2019　IEEE.