Patent ID: 7715016

Claim:
An image invariant optical speckle capturing device, comprising: a light source, which emits a beam of highly coherent light to illuminate a surface and to produce a plurality of scattered lights; a light restrictive module, which confines the incident angular field of view to the scattered light, and produces a plurality of diffracted lights from the scattered lights so that the diffracted lights interfere with each other to produce a plurality of speckles, wherein the light restrictive module has a optical axis arranged in the direction of 90°>θr≧θi+10° or 0°<θr≦θi−10°,where θr is the angle between the optical axis of the light restrictive module and a normal direction of the surface, and θi is the angle between a direction of the incident light and a normal direction of the surface; and an optical sensor, which receives the speckles to generate a first speckle image, wherein a second speckle image is generated after the light restrictive module and the sensor move with respect to the surface, and the direction and distance of the motion are determined by comparing the first speckle image with the second speckle image; and a pre-stage light restrictive elements, disposed in between the light restrictive module and the surface, which blocks secondary scattered lights of the scattered lights to enter the optical sensor.