An optical encoder includes an incoherent light source; a first grating, which is an amplitude grating having a first grating period, for spatial amplitude modulation of the incoherent light from the light source; a second grating, which is a phase grating having a second grating period, for spatial...http://www.google.de/patents/US20070187581?utm_source=gb-gplus-sharePatent US20070187581 - Optical encoder
