Structure of an Optical Fiber

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[edit] Structure of an Optical Fiber

Typical optical fibers are composed of core, cladding and buffer coating. The core is the inner part of the fiber, which guides light. The cladding surrounds the core completely. The refractive index of the core is higher than that of the cladding, so light in the core that strikes the boundary with the cladding at an angle shallower than critical angle will be reflected back into the core by total internal reflection.
Typical optical fibers are composed of core, cladding and buffer coating. The core is the inner part of the fiber, which guides light. The cladding surrounds the core completely. The refractive index of the core is higher than that of the cladding, so light in the core that strikes the boundary with the cladding at an angle shallower than critical angle will be reflected back into the core by total internal reflection.

Typical optical fibers are composed of core, cladding and buffer coating.

The core is the inner part of the fiber, which guides light. The cladding surrounds the core completely. The refractive index of the core is higher than that of the cladding, so light in the core that strikes the boundary with the cladding at an angle shallower than critical angle will be reflected back into the core by total internal reflection.

An optical fiber guides light waves in distinct patterns called modes. Mode describes the distribution of light energy across the fiber. The precise patterns depend on the wavelength of light transmitted and on the variation in refractive index that shapes the core. In essence, the variations in refractive index create boundary conditions that shape how light waves travel through the fiber, like the walls of a tunnel affect how sounds echo inside.
An optical fiber guides light waves in distinct patterns called modes. Mode describes the distribution of light energy across the fiber. The precise patterns depend on the wavelength of light transmitted and on the variation in refractive index that shapes the core. In essence, the variations in refractive index create boundary conditions that shape how light waves travel through the fiber, like the walls of a tunnel affect how sounds echo inside.

For the most common optical glass fiber types, which includes 1550nm single mode fibers and 850nm or 1300nm multimode fibers, the core diameter ranges from 8 ~ 62.5 µm. The most common cladding diameter is 125 µm. The material of buffer coating usually is soft or hard plastic such as acrylic, nylon and with diameter ranges from 250 µm to 900 µm. Buffer coating provides mechanical protection and bending flexibility for the fiber.

For the most common optical glass fiber types, which includes 1550nm single mode fibers and 850nm or 1300nm multimode fibers, the core diameter ranges from 8 ~ 62.5 µm. The most common cladding diameter is 125 µm. The material of buffer coating usually is soft or hard plastic such as acrylic, nylon and with diameter ranges from 250 µm to 900 µm. Buffer coating provides mechanical protection and bending flexibility for the fiber.
For the most common optical glass fiber types, which includes 1550nm single mode fibers and 850nm or 1300nm multimode fibers, the core diameter ranges from 8 ~ 62.5 µm. The most common cladding diameter is 125 µm. The material of buffer coating usually is soft or hard plastic such as acrylic, nylon and with diameter ranges from 250 µm to 900 µm. Buffer coating provides mechanical protection and bending flexibility for the fiber.


[edit] What is Fiber Mode?

An optical fiber guides light waves in distinct patterns called modes. Mode describes the distribution of light energy across the fiber. The precise patterns depend on the wavelength of light transmitted and on the variation in refractive index that shapes the core. In essence, the variations in refractive index create boundary conditions that shape how light waves travel through the fiber, like the walls of a tunnel affect how sounds echo inside.

We can take a look at large-core step-index fibers. Light rays enter the fiber at a range of angles, and rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding interface at an angle larger than critical angle. These rays are different modes.

Fibers that carry more than one mode at a specific light wavelength are called multimode fibers. Some fibers have very small diameter core that they can carry only one mode which travels as a straight line at the center of the core. These fibers are single mode fibers. This is illustrated in the following picture.


[edit] Optical Fiber Index Profile

Index profile is the refractive index distribution across the core and the cladding of a fiber. Some optical fiber has a step index profile, in which the core has one uniformly distributed index and the cladding has a lower uniformly distributed index. Other optical fiber has a graded index profile, in which refractive index varies gradually as a function of radial distance from the fiber center. Graded-index profiles include power-law index profiles and parabolic index profiles. The following figure shows some common types of index profiles for single mode fibers and multimode fibers.


[edit] Also see


[edit] Reference

  • Optical Fiber Tutorial [1]

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