Fiber Optic Wiki

The fiber fuse

October 12, 2011

At high optical intensities, above 2 megawatts per square centimeter, when a fiber is subjected to a shock or is otherwise suddenly damaged, a fiber fuse can occur. The reflection from the damage vaporizes the fiber immediately before the break, and this new defect remains reflective so that the damage propagates back toward the transmitter at 1–3 meters per second (411 km/h, 2–8 mph).

Power transmission

October 12, 2011

Optical fiber can be used to transmit power using a photovoltaic cell to convert the light into electricity. While the efficiency is not nearly that of electricity (the efficiency of the photovoltaic is around 40 to 50%), it is especially useful in situations where it is desirable not to have a metallic conductor as in the case of use near MRI machines, which produce strong magnetic fields.

Preform

October 12, 2011

A preform is a piece of glass used to draw an optical fiber. The preform may consist of several pieces of a glass with different refractive indices, to provide the core and cladding of the fiber. The shape of the preform may be circular, although for some applications such as double-clad fibers another form is preferred.56 In fiber lasers based on double-clad fiber, an asymmetric shape improves the filling factor for laser pumping.

Manufacturing

October 8, 2011

Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses as well as crystalline materials like sapphire, are used for longer-wavelength infrared or other specialized applications. Silica and fluoride glasses usually have refractive indices of about 1.5, but some materials such as the chalcogenides can have indices as high as 3. Typically the index difference between core and cladding is less than one percent.

Silica exhibits fairly good optical transmission

October 8, 2011

Silica exhibits fairly good optical transmission over a wide range of wavelengths. In the near-infrared (near IR) portion of the spectrum, particularly around 1.5 μm, silica can have extremely low absorption and scattering losses of the order of 0.2 dB/km. A high transparency in the 1.4-μm region is achieved by maintaining a low concentration of hydroxyl groups (OH). Alternatively, a high OH concentration is better for transmission in the ultraviolet (UV) region.

Fluorides glass

October 8, 2011

Fluoride glass is a class of non-oxide optical quality glasses composed of fluorides of various metals. Because of their low viscosity, it is very difficult to completely avoid crystallization while processing it through the glass transition (or drawing the fiber from the melt). Thus, although heavy metal fluoride glasses (HMFG) exhibit very low optical attenuation, they are not only difficult to manufacture, but are quite fragile, and have poor resistance to moisture and other environmental attacks. Their best attribute is that they lack the absorption band associated with the hydroxyl (OH) group (3200–3600 cm), which is present in nearly all oxide-based glasses.

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