Core (optical fiber)
1. Core 9, 50, or 62.5 μm diameter
2. Cladding 125 μm dia.[1]
3. Coating 250 μm dia.[1]
4. Buffer or jacket 900 μm dia.[1]
The core of a conventional optical fiber is the part of the fiber that guides the light. It is a cylinder of glass or plastic that runs along the fiber's length.[2] 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 greater than the critical angle.[3] As a result, the fiber transmits all rays that enter the fiber with an angle to the fiber's axis smaller than the acceptance angle.[4] Light rays confined by the core/cladding boundary are called guided rays.
The core is differentiated primarily by its diameter of which the resulting cross-sectional area determines various fiber characteristics.[5][6] The core's diameter should be uniform with a perfectly circular cross-section, but due to manufacturing tolerance and defects 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; allowing for deviations from circularity.[7]
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/e2 ≈ 13.5%).[7] 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 industry standard core sizes[1] for fiber optic communication cables are:
- 9 μm diameter (single-mode)
- 50 μm diameter (multi-mode)
- 62.5 μm diameter (multi-mode)[8]
See also
[edit]References
[edit]- 1 2 3 4 "Fiber Optic Cable Size & Diameter Chart: Core Sizes". DYS Fiber Optic. 2026-07-15. Retrieved 2026-10-03.
- ↑ Insulation/circuits. Lake Publishing Corporation. 1978.
- ↑ "The FOA Reference For Fiber Optics - Total Internal Reflection In Optical Fiber". www.thefoa.org. Retrieved 2026-10-02.
- ↑ Peter Starmer GCGI(LM), GCGI(HR), BA, ILM, icalculator.com. "Acceptance Angle in Optical Fibre Calculator". iCalculator™ - Acceptance Angle in Optical Fibre Calculator. Archived from the original on 2025-10-09. Retrieved 2026-10-02.
{{cite web}}: CS1 maint: multiple names: authors list (link) - ↑ "Fiber Optic Cable Size & Diameter Chart: Core Sizes". DYS Fiber Optic. 2026-07-15. Retrieved 2026-10-02.
- ↑ "Fiber Cross Sectional Area Integration: Interpreting Empirical Platform Frameworks". www.flyriver.com. Retrieved 2026-10-02.
- 1 2 Fiorentino, John (2020-04-15). "Single-Mode Optical Fiber Geometries". Lightera. Retrieved 2026-10-03.
- ↑ "The FOA Reference For Fiber Optics - Optical Fiber". www.thefoa.org. Retrieved 2016-04-10.
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