Cube corner retro-reflector

Patent Granted A set of three mutually perpendicular reflective surfaces, placed to form the corner of a cube, work as a retroreflector. The three corresponding normal vectors of the corner's sides form a basis (x, y, z) in which to represent the direction of an arbitrary incoming ray, [a, b, c]. When the ray reflects from the first side, say x, the ray's x component, a, is reversed to -a while the y and z components are unchanged. Therefore as the ray reflects first from side x then side y and finally from side z the ray direction goes from [a,b,c] to [-a,b,c] to [-a,-b,c] to [-a,-b,-c] and it leaves the corner with all three components of motions exactly reversed.