We　design　a　four　InAs　quantum　dot　system　in　which　two　leads　are　irradiated　by　terahertz　light　fields.　The　average　current　through　the　system　is　obtained　by　means　of　non-equilibrium　Green＇s　function　theory.　Typical　photon-assisted　tunneling　is　observed　in　the　current　energy　spectrum.　100%　polarization　can　be　achieved　by　adjusting　the　intensity　of　Zeeman　magnetic　field　or　the　amplitude　of　terahertz　light　field.　As　the　frequency　of　terahertz　light　field　is　invariant,　a　zero　current　can　be　obtained　by　adjusting　the　amplitude　of　the　terahertz　light　field,　indicating　an　optically　controlled　quantum　switch　device.　The　spin　polarization　can　be　converted　between　0　and　1　by　tuning　the　energy　level　of　quantum　dots,　suggesting　a　physical　scheme　of　a　polarization　pulse　device.　Moreover,　the　system　can　be　constructed　as　a　terahertz　detector　due　to　the　oscillation　properties　of　spin　polarization.　The　present　work　sheds　lights　onto　the　design　of　quantum　computing　and　spin-dependent　quantum　devices.　©　2022　Elsevier　B.V.