Patent ID: 8169599

Claim:
A device for measuring moving material, which includes: a processor and operating software associated therewith; light source means for emitting at least two polarized light beams in a manner wherein said beams cross thereby creating an interference region and generate a set of fringes; a sensor aligned relative to said interference region wherein the fringes have a predetermined orientation to the directional movement of the material and wherein the sensor is operably equipped to receive scattered light emanating from said interference region and provide a time varying signal to said processor such that said processor can manipulate and convert said signal to speed and distance; and an optical isolator having circular polarizers and a polarized beam splitter operably associated with said sensor in a manner to substantially preclude reflected polarized light from said interference region back to said sensor and configured to let light pass through the optical isolator and prevent such light, when reflected, from returning through said optical isolator back to the light source means such that the light is circularly polarized when reflecting off a surface changing direction and goes back through one of said circular polarizers in an opposite direction and becomes linearly polarized perpendicular to said emitted light beams.