Tiny electromechanical systems on a silicon chip. MEMS comprise integrated mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technologies, including the micromachining of the mechanical elements. MEMS are employed in optical projectors as well as in purely optical switches used in fiber optics transmission systems (FOTS), and actually are more along the lines of optical cross-connects. As purely optical devices, they do not require that the incoming optical signal be converted to an electrical signal for processing and then be reconverted to an optical signal. In other words, MEMS are optical-optical-optical (OOO), rather than optical-electrical-optical (OEO). See also cross-connect, FOTS, and switch.