Patent ID: 7268875

Claim:
A method for optically measuring absolute displacement using a polarized light detection system I and a polarized light detection II, comprising: with respect to polarized light detection system I, converting a linear displacement being measured by polarized light detection system I, using a mechanical device, to an angular displacement which consequently causes a first polarizer to rotate; passing a light from a light source through the first polarizer and then two parts of a dual analyzer assembly to reach two photoelectric detectors; and controlling a step motor through comparison of the magnitude of light intensity signals from the said two photoelectric detectors to drive the dual analyzer to trace the rotation of the first polarizer so that the number of control pulses from the step motor becomes an accurate value for the displacement being measured in a single rotation; and with respect to polarization light detection system II, maintaining the rotation of a second polarizer proportional to the rotation of the first polarizer in the polarization light detection system I while a light from a light source is passing through the second polarizer and then an analyzer assembly wherein a certain included angle is formed between polarization axes of the adjacent analyzers of the analyzer assembly to reach a plurality of photoelectric detectors respectively so that the number of rotations of the first polarizer and step motor is ascertained, thereby measuring the absolute displacement in the polarized light detection system I.