An optical coupler (also referred to as OC) is also known as an opto-isolator or optocoupler, referred to as an optocoupler. It is a device that transmits electrical signals by means of light. Generally, an illuminator (infrared light emitting diode (LED)) and a light receiver (photosensitive semiconductor tube) are packaged in the same package. When the input terminal is powered, the illuminator emits light, and after receiving the light, the photocurrent is generated and flows out from the output end, thereby realizing the "electric-optical-electrical" conversion. The optocoupler that couples the input signal to the output end with light as a medium, because of its small size, long life, no contact, strong anti-interference ability, insulation between output and input, one-way transmission of signals, etc. Widely used on circuits. Optocouplers can be divided into nonlinear optocouplers and linear optocouplers.
The optical coupler transmits electrical signals in light as a medium. It has good isolation for input and output electrical signals, so it is widely used in various circuits. Optocouplers have become one of the most versatile and versatile optoelectronic devices. An optical coupler generally consists of three parts: light emission, light reception, and signal amplification. The input electrical signal drives a light-emitting diode (LED) to emit a certain wavelength of light, which is received by the photodetector to generate a photocurrent, which is further amplified and output. This completes the electro-optical-electrical conversion, thereby functioning as input, output, and isolation. Since the input and output of the optocoupler are isolated from each other, the electrical signal transmission has the characteristics of unidirectionality, and thus has good electrical insulation capability and anti-interference ability. Therefore, it can greatly improve the signal-to-noise ratio as a terminal isolation component in long-line transmission information. As a signal isolation interface device in computer digital communication and real-time control, the reliability of computer work can be greatly improved.
Moreover, since the input end of the optocoupler belongs to a low-resistance component of current type operation, it has strong common mode suppression capability.
The optical coupler has the characteristics of small size, long life, no contact, strong anti-interference ability, isolation between output and input, and one-way transmission of signals, and sometimes it can replace relays, transformers, choppers and the like.  Widely used in electrical insulation, level shifting, interstage coupling, drive circuits, switching circuits, choppers, multivibrators, signal isolation, interstage isolation, pulse amplifier circuits, digital meters, long range Signal transmission, pulse amplification, solid state relay (SSR), instrumentation, communication equipment and computer interfaces. In the monolithic switching power supply, the optocoupler feedback circuit can be constructed by using a linear optical coupler, and the duty ratio is changed by adjusting the current of the control terminal to achieve the purpose of precision voltage regulation.