Patent ID: 6927758

Claim:
In an optical detection system housing a coherent light source for illuminating a surface, and an optical sensing assembly comprising at least one photosensitive array and at least one optical element, a method for detecting movement comprising: generating an illumination spot on the surface by lighting the surface with a coherent light beam from the coherent light source, the illumination spot providing optically back-scattered light off the surface; arranging each optical element to pass an image of the illumination spot onto each photosensor array associated with an optical element, the photosensor array having a plurality of pixels; and generating at least one image data signal from each photosensor array in response to the image on the plurality of pixels of that photosensor array, each image data signal comprising at least one image data point; storing a first image data signal and a second image data signal, the first image data signal comprises a first substantially random image data signal and the second image data signal comprises a second substantially random image data signal; and measuring similarility of images through the first image data signal and the second image data signal to obtain a displacement value, the displacement value indicative of detected movement, the similarity of the first image data signal to the second image data signal is measured at a multiple of a shift value, the first image data signal being shifted by a predetermined shift value prior to the measurement.