When an object is moved into the slot between the LED and phototransistor the light is interrupted and the phototransistor switches off. Opto activated switches are normally operated in saturation mode to provide definite on and off signals. This eliminates the need for manual fiber patch panels, a technique that has been used for years. Implementing this requires sophisticated software. For this application, switches with. Fiber-optic switches control light paths within fiber optics, ranging from simple on/off types to complex matrix configurations like 64×64. The simplest device is an on/off switch with one input and one output, which allows.