What optical device is mainly used for the transmission of light over long distances?

The optical device primarily used for the transmission of light over long distances is an optical fiber. Optical fibers are thin strands of glass or plastic that carry light signals through a principle known as total internal reflection. This allows light to travel through the fiber with minimal loss of intensity, making them exceptionally efficient for long-distance communication.

Optical fibers are used in various applications, including telecommunications and internet data transmission, where they can send large amounts of data quickly and over distances that would degrade the signal if transmitted through traditional electrical cables. The ability of optical fibers to maintain signal quality over long stretches makes them vital in modern communication technologies.

In contrast, while concave lenses, prisms, and plane mirrors can manipulate and direct light, they do not serve the same function as optical fibers when it comes to transmitting light over extended distances. Concave lenses can focus light but do not transmit it over long distances effectively. Prisms can disperse light into its component colors but are not designed for distance transmission. Plane mirrors reflect light but do not facilitate transmission of light through space. Thus, optical fibers represent the optimal choice for long-distance light transmission.