A phototransistor optocoupler is formed by an infrared light emitter device (IR-LED) (Gallium Arsenide (GaAs)) and a light detector device (phototransistor), both optically coupled and typically encapsulated in a 4-pin package, which is offered in different mechanical dimensions and. A phototransistor optocoupler is formed by an infrared light emitter device (IR-LED) (Gallium Arsenide (GaAs)) and a light detector device (phototransistor), both optically coupled and typically encapsulated in a 4-pin package, which is offered in different mechanical dimensions and. Optocouplers (also called Photocouplers, Optoisolators, and Optical Isolators) are available at Mouser Electronics from industry leading manufacturers. Mouser is an authorized distributor for many optocoupler manufacturers including Broadcom, onsemi, Renesas, Toshiba, Vishay & more. Optocouplers. An optocoupler—also known as an optoisolator or photocoupler—is an electrical component designed to transmit signals between two isolated circuits using light. It typically consists of a light-emitting diode (LED) on the input side and a photodetector (usually a phototransistor, photodiode, or. Optocouplers are used in many electronic devices, from mobile electronics to household electronics. As we have already learnt about transistors, an ideal transistor will not.