1) Optical component 
A retroreflector (sometimes called a retroflector or cataphote) is a device or surface that reflects light back to its source with a minimum of scattering. An electromagnetic wave front is reflected back along a vector that is parallel to but opposite in direction from the wave`s source. The angle of incidence at which the device or surface refle....
see corner-cube prism
a surface or device from which most of the reflected radiation is retroreflected