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00925njm 22002777a 4500 dc Saez Landete, José author Alonso Fernández, José author Sánchez Brea, Luis Miguel author Morlanes Calvo, Tomás author Bernabeu Martínez, Eusebio author 2009-09-01 Two-grating measurement systems are routinely employed for high-resolution measurements of angular and linear displacement. Usually, these systems incorporate zero reference codes (ZRCs) to obtain a zero reference signal (ZRS), which is used as a stage-homing signal. This signal provides absolute information of the position to the otherwise relative information provided by the two-grating incremental subsystems. A zero reference signal is commonly obtained illuminating the superposition of two identical pseudorandom codes and registering the transmitted light by means of a photodiode. To increase the resolution of the system, a reduction of the grating period and the ZRC widths is required. Due to this reduction, the diffractive effects produce a widening of the ZRS and, in turn, a loss of the measuring accuracy. In this work, we propose a method to narrow the distorted signal obtained with a Lau-based encoder, reinstating the accuracy of the ZRS. The method consists of the inclusion of a correlation mask on the detector. A theoretical model to design the mask has been developed, and experimental results have been obtained that validate the proposed technique. 1084-7529 10.1364/JOSAA.26.001901 https://hdl.handle.net/20.500.14352/44293 http://dx.doi.org/10.1364/JOSAA.26.001901 http://www.opticsinfobase.org Correlation technique for the compensation of diffraction widening of optical reference signals