Pérez Quintián, FernandoAlonso Fernández, JoséAtencia Carrizo, JesúsBernabeu Martínez, Eusebio2023-06-202023-06-202003-12-011559-128X10.1364/AO.42.006797https://hdl.handle.net/20.500.14352/51207© 2003 Optical Society of America. We thank M. Quintanilla for useful comments and discussions. This research has been supported by projects DPI 2001-1238 and DPI 2001-1369 of the Spanish Ministry for Science and Technology.An optical method for generating a reference signal for an incremental displacement measurement system is proposed. We achieved this zero reference signal by comparing two speckle patterns arriving from two symmetric diffusers, which are used as natural random codes that are identical only when the reading head is located equidistantly between the diffusers. The comparison of the speckles is obtained either by interference, as in a Michelson interferometer, or by intensity correlations.engjournal articlehttp://dx.doi.org/10.1364/AO.42.006797http://www.opticsinfobase.orgopen access535ReflectionEncoderÓptica (Física)2209.19 Óptica Física