Specialty Optical Fiber

Specialty optical fiber is modified, usually by doping, for a specialized function. It consists of one or more transparent fibers enclosed in a protective covering. Both single mode and multimode specialty optical fiber is available. Single mode fiber has a core diameter that is only a few times the wavelength of the light transmitted. By contrast, multimode fiber has a core diameter that is much larger than the wavelength of light transmitted. This larger diameter allows many modes to propagate. Typically, single mode fibers are used with laser sources for high speed, long distance links. Multimode fiber is used commonly with light emitting diode (LED) sources for lower speed, shorter distance links. 

There are many types of specialty optical fiber. Examples include attenuating, bare, double-clad, erbium-doped, fiber laser, graded index, high NA, metallized, mid-infrared photonic crystal, photosensitive, polarization maintaining, and yterrbium-doped fibers. Attenuating fibers are used at the ends of optical fiber links to adjust the transmitted signal to a controlled degree of attenuation, or to provide reflection-free termination. Bare specialty optical fiber can be either single mode or multimode and consists of a fiber optic core and cladding.  Double-clad fiber is used in high power applications. Erbium-doped fiber amplifiers (EDFA) are used widely in optical fiber telecommunications because they allow transmission transparency. EDFAs include power amplifiers, pre-amplifiers and in-line amplifiers for C- and L-bands. Some EDFAs are also doped with yterrbium. Fiber lasers use a lasing medium that consists of an optical fiber doped with low levels of rare-earth halides. With graded index fibers, the refractive index of the core takes the form of a parabolic curve that decreases toward the cladding. High NA fibers capture more input with very low, bend-induced attenuation. Metallized fibers are coated with metals for increased temperature resistance, ease of soldering, and suitability for harsh environments. Mid-infrared (mid-IR) fiber is designed to provide ultra-low loss optical transmission in the mid-infrared spectrum (2 to 10 microns).  Photosensitive fibers exhibit uniform and controlled photosensitivity to conventional UV radiation techniques.

Selecting specialty optical fiber requires an analysis of performance specifications such as wavelength, numerical aperture, maximum attenuation, bending radius, and operating temperature. Typically, the wavelength for which specialty optical fiber is designed is measured in nanometers (nm). Numerical aperture (NA) measures an optical fiber's light-gathering ability. NA is the maximum angle to the fiber axis at which light is accepted and propagated through the fiber. Maximum attenuation, the decrease in signal strength caused by absorption and scattering, is expressed in decibels per kilometer (dB/km). Bending radius is the smallest radius that an optical fiber or fiber cable can bend before increased attenuation or breakage occurs. Operating temperature is the full required range of ambient operating temperature.

• Specialty Optical Fibers Handbook
  Specialty Optical Fibers Handbook Including essential facts and details at the beginning of each chapter, this book aims to describe and explain the design, fabrication, operating characteristics,...
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• Low Speed Carbon Deposition Process for Hermetic Optical Fibers
  For optical fibers used in adverse environments, a carbon coating is frequently deposited on the fiber surface to prevent water and hydrogen ingression that lead respectively to strength degradation...
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• Machine Vision Industry Focus: Putting Light to Work
  Special fiber optics now let spectroscopy migrate out of the laboratory and into inhospitable environments. Spectrometers and other sophisticated light-measurement equipment once were consigned to...
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