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. 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. Optocouplers, also known as opto-isolators, uses infrared light to transfer electrical signals between two electrically isolated circuits and are commonly classified by their photosensitive output device What is an Optocoupler? An optocoupler (also called an opto-isolator, photo-coupler, or optical. An optocoupler (or opto-isolator) is a component that transfer signals between circuits using light. In this guide, you'll learn how they work and how you can use one in your own projects. Optocouplers are very useful when you need to isolate different sections of a circuit, for example in power. An optocoupler, also known as photocoupler or opto-isolator, is a device which can transfer an electrical signal across two galvanically-isolated circuits by way of optical coupling. Opto-isolators prevent high voltages from affecting the system receiving the signal. Commercially. There are many different applications for optocoupler circuits, so there are many different design requirements, but a basic design for an optocoupler providing isolation for example between two circuits, simply involves the choice of appropriate resistor values for the two resistors R1 and R2. Optocouplers become specifically useful where an electrical signal is required to be sent across two circuit stages, but with an extreme degree of electrical isolation across the stages. Optocoupling devices work as logic level changeovers between two circuits, It has the ability to block noise.