The device used to read the CD data is known as an optical pickup. The laser beam generated by a laser diode is passed through collimating lenses to render it as parallel rays, and then focused by an objective lens to a tiny spot that strikes the reflective layer. The beam reflected from the aluminum reflective layer is then divided by a polarizing beam-splitting prism and passed through a cylindrical lens to a photodetector array, where it is read as data.