Optical rectification is analogous to the electric rectification effect produced by diodes, wherein an AC signal can be converted ("rectified") to DC. However, it is "not" the same thing. A diode can turn a sinusoidal electric field into a DC current, while optical rectification can turn a sinusoidal electric field into a DC polarization, but not a DC current. On the other hand, a "changing" polarization is a kind of current. Therefore, if the incident light is getting more and more intense, optical rectification causes a DC current, while if the light is getting less and less intense, optical rectification causes a DC current in the opposite direction. But again, if the light intensity is constant, optical rectification cannot cause a DC current.