Core ( optical fiber ) - Wikipedia Core ( optical fiber ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( July 2017 ) The structure of a typical single - mode fiber. 1. Core 8 μm diameter 2. Cladding 125 μm dia. 3. Buffer 250 μm dia. 4. Jacket 400 μm dia. Light propagating in a multi-mode fiber The core of a conventional optical fiber is a cylinder of glass or plastic that runs along the fiber 's length. The core is surrounded by a medium with a lower index of refraction, typically a cladding of a different glass, or plastic. Light travelling in the core reflects from the core - cladding boundary due to total internal reflection, as long as the angle between the light and the boundary is less than the critical angle. As a result, the fiber transmits all rays that enter the fiber with a sufficiently small angle to the fiber 's axis. The limiting angle is called the acceptance angle, and the rays that are confined by the core / cladding boundary are called guided rays. The core is characterized by its diameter or cross-sectional area. In most cases the core 's cross-section should be circular, but the diameter is more rigorously defined as the average of the diameters of the smallest circle that can be circumscribed about the core - cladding boundary, and the largest circle that can be inscribed within the core - cladding boundary. This allows for deviations from circularity due to manufacturing variation. Another commonly quoted statistic for core size is the mode field diameter. This is the diameter at which the intensity of light in the fiber falls to some specified fraction of maximum ( usually 1 / e ≈ 13.5 % ). For single - mode fiber, the mode field diameter is larger than the physical diameter of the core, because the light penetrates slightly into the cladding as an evanescent wave. The three most common core sizes are : 9 μm diameter ( single - mode ) 50 μm diameter ( multi-mode ) 62.5 μm diameter ( multi-mode ) See also Buffer ( optical fiber ) References Jump up ^ Insulation / circuits. Lake Publishing Corporation. 1978. Jump up ^ `` The FOA Reference For Fiber Optics - Optical Fiber ''. www.thefoa.org. Retrieved 2016 - 04 - 10. This article related to telecommunications is a stub. You can help Wikipedia by expanding it. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Core_(optical_fiber)&oldid=811212183 '' Categories : Fiber optics Telecommunications stubs Hidden categories : Articles needing additional references from July 2017 All articles needing additional references All stub articles Talk About Wikipedia فارسی Edit links This page was last edited on 20 November 2017, at 05 : 31. About Wikipedia

Question: the core of an optical fiber has a
Answer: cylinder of glass or plastic that runs along the fiber's length