MTHOD AND DEVICE FOR INCREASING THE RESOLUTION IN AN INTERFEROMETER BASED ON CODE COUNTING ASSOCIATED WITH INTERFERENCE FRINGES

摘要

The invention relates to a method and a device for increasing the resolution of displacement measurement in an interferometer based on encoding interference fringes in phase quadrature, obtained at the optical output of the interferometer in order to carry out the fringe counting. The claimed method consists in using a number of five analog signals (sin, cos, -sin, -cos, and sigma) generated, starting from two electric signals (sin and cos) corresponding to some interference fringes in phase quadrature, while, by a corresponding electronic processing, the five signals generate eight logic binary functions (F) whose results define the structure of some associated counting codes. During a period T= λ /2 there are registered 16 such codes with a distinct structure for each T/16 = λ /32 and a different succession for the displacement direction "forwards" and "backwards", respectively, the consecutive bidirectional reading of these 16 codes allows the discrimination of the displacement direction and the corresponding generation of the incremental/decremental command for a reversible counter whose content represents the displacement length (in λ /32 multiples). The claimed device comprises two photodetectors (FD1 and FD2) for detecting the optical fringes, two current-voltage converters (A1 and A2) at whose outputs there are obtained the two electrical signals (sin and cos), two inverse amplifiers (A3 and A4) producing at the output other two signals (-sin and - cos), a balanced adder-reverser ( &Sgr; ) which gives at the output the fifth signal ( &sgr; ) and a chain of analog comparators (C1...C8) which generate at the output the logical statuses corresponding to the logic functions (F).