A polaric modulator is a device that can dilute a subatomic particle stream, similar to how a carburetor dilutes gasoline with air.
While working on a coaxial warp ship in 2374, Tom Paris suggested to Steth that they use a polaric modulator to dilute the particle stream of a coaxial warp drive, thus preventing the particles from destabilizing the coaxial core. Paris later prevented the shapeshifting alien previously posing as Steth from making a coaxial warp jump by targeting his polaric modulator with a chromoelectric pulse. (VOY: "Vis à Vis")