The Basic Optical Fiber Fiber optics is technology in which signals are converted from electrical into optical signals, transmitted through a thin glass fiber, and re-converted into electrical signals. The basic optical fiber consists of two concentric layers differing in optical properties, and a protective outer coating. Total internal reflection Light injected into the core and striking the core-to cladding interface at an angle greater than the critical angle will be reflected back in to the core. Since angles of incidence and reflection are equal, the light ray continues to zig-zag down the length of the fiber. The light is trapped within the core.
Light striking the interfaces at less than the critical angle passes into the classing ans is lost.
Ray of light do not travel randomly. They are channeled into modes, which are possible paths for a light ray traveling down the fiber. A fiber can support as few as one mode and as many as tens of thousands of modes. While we are normally not interested in modes per se, the number of modes in a fiber is significant because it helps determine the fiber's bandwidth. More modes typically mean lower bandwidth.