An optical sensor that includes a light source and a detector is located within a cavity in a polishing pad so as to face the surface that is being polished. Light from the light source is reflected from the surface being polished and the detector detects the reflected light. The electrical signal produced...http://www.google.es/patents/US7083497?utm_source=gb-gplus-sharePatente US7083497 - Polishing pad with built-in optical sensor
