A polaric modulator was a device capable of diluting a particle stream.
In 2374, USS Voyager helmsman Tom Paris conceived of the idea of using a polaric modulator to overcome the instability of a coaxial warp drive. Drawing inspiration from a carburetor, a 20th century device used to supply an automobile's engine with a mixture of vaporized fuel and air, Paris realized that a modulator could perform much the same function with a coaxial drive, diluting the particle stream being drawn into the drive, thereby solving the problem of engine overload caused by particle instability.
When a hostile alien later attempted to escape aboard a Starfleet shuttlecraft which had been installed with a coaxial drive, Paris was able to target the modulator with a chromoelectric pulse, disrupting the shuttle's engines and preventing the alien's escape. (VOY: "Vis à Vis")