What is an optical coupling?

Optical coupling occurs when a remote control communicates with a television.

Optical coupling is a method of interconnecting two devices to transfer an optical signal using light waves in the field of optoelectronics. In practice, an optical coupling can be a simple connection between two optical cables using a coupling device, or it can be a complex system that links two separate actions via optical devices to make them dependent or reactive on each other. In a broader sense, it can refer to making any connection using light waves between two or more devices. For example, when a television remote control sends an infrared signal to the infrared receiver on the television set, the television and remote are momentarily optically coupled.

When configuring optics-based electronic systems, it is often necessary to connect two or more fiber optic cables. This is done using a device called an optocoupler. Optical couplers are passive devices that allow light to travel from one fiber optic cable to another, while preventing them from coming into direct contact with each other. This isolation allows optocouplers to connect small fiber optic cables to large cables, large cables to small cables, or even one cable to multiple cables.

In fiber optic computer networks, optical coupling is a key concept. Optical couplers can accept signals transmitted as light waves from a computer on a fiber optic cable and branch them to many computers over many cables, thus distributing the information throughout the network. Likewise, they can collect data from many different source cables and combine them into a single fiber optic cable, which can be connected to the network server or other components such as printers or data backup devices.

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There are different types of optocouplers to provide optical coupling for many special tasks. For example, the United States federal government monitors the Internet using a special optocoupler based on a mirrored prism design. This coupler receives information from an Internet access point through a fiber optic cable in the form of light waves and then, through a prism, splits the light waves into two copies of the original. A copy of the information continues to its destination on the Internet with no more interference or delay than would exist if it passed through a simple optocoupler used to connect two fiber optic cables. The other copy of the information is transmitted to a government agency for review.

Many common electronic devices use closed internal optical coupling systems. Some power transistors work by taking an electronic signal, converting it into light, and directing that light to an internal photosensor. As soon as the sensor detects the light source, the transistor turns on and begins to conduct power. By using light to switch the transistor in response to electronic signals, rather than using the electrical signals directly, the transistor can react to inputs at much faster speeds. Also, because the input signal and the output signal are isolated from each other by the internal optocoupler, these transistors can send or transfer signals very different from those they receive.

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