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Fiber Optics

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Definition: optics based on optical fibers

German: Faseroptik

Category: fiber optics and waveguides

How to cite the article; suggest additional literature

Fiber optics is the technology based on optical fibers, i.e., on mostly flexible waveguides for light. The article on fibers describes the core technology, including various types of glass fibers (e.g. silica fibers and fluoride fibers) but also plastic optical fibers. Apart from the basic materials, fibers can differ in many other respects, particularly concerning the propagation characteristics of light in their fiber cores. For example, there are

and various kinds of specialty fibers. Some belong to the important group of photonic crystal fibers (or microstructure fibers), which contain tiny air holes running along the fiber core.

launching light into a glass fiber

Figure 1: Light can be launched into a fiber, where it can propagate with a constant beam radius until it leaves the fiber. One can also combine multiple fiber-optic elements. In all-fiber setups, the light may entirely stay within fiber waveguides.

Fiber Cables

Fibers are often used in the form of optical fiber cables, where the actual fiber is embedded into a supporting structure, which protects it mostly against mechanical stress and moisture. Fiber cables are often terminated with fiber connectors, so that they can be plugged in a similar way as electrical cables, although fiber-optic connections are tentatively more delicate.

Fiber cables can differ in many respects:

More details can be found in the article on fiber cables.

Fiber-optic Components

Apart from the fibers, there are various types of fiber-optic elements, which may be connected with each other using optical fibers. Some of these are essentially made of fibers, whereas others consist of utterly different materials but are coupled to fibers, i.e., they offer fibers for input and output purposes. Some examples for fiber-optical components:

Fiber-optic Setups

One may combine multiple fiber-optical elements to obtain all-fiber setups with complex functionality. For example, one can assemble diode-pumped (fiber lasers, see below) from fiber-coupled laser diodes, rare-earth-doped fibers and fiber couplers. Additional elements such as fiber-coupled saturable absorbers and fibers for dispersion compensation allow one to obtain mode-locked operation, where the laser emits a train of ultrashort pulses. One can also use elements for Q switching, power stabilization, wavelength tuning and various other purposes.

Fiber Amplifiers and Lasers

In laser-active fibers, which are in most cases rare-earth-doped fibers, one can perform laser amplification processes based on stimulated emission. The laser-active ions, e.g. Yb3+, Er3+ or Tm3+, are pumped with some typically shorter-wavelength pump light injected into the fiber, and can then amplify some signal light. Fiber amplifiers based on that technology can easily provide a power gain of several tens of decibels. High-power versions based on double-clad fibers can generate average output powers of hundreds or even thousands of watts. By incorporation of reflectors such as fiber Bragg gratings, or by building ring resonators, one can also realize fiber lasers.

figure-of-eight laser

Figure 2: A figure-of-eight laser setup, as explained more in detail in the article on mode-locked fiber lasers. Multiple fiber-optic components are combined to a complex setup.

Due to high laser gain, effects of amplified spontaneous emission, the quasi-three-level behavior of typical laser-active ions in fibers, strong gain saturation effects etc., the operation details of fiber amplifiers and lasers are often more complicated than those of bulk lasers. Therefore, detailed laser modeling is particularly important in this area in order to obtain a clear understanding, based on which device designs can be optimized.

Comparison of Bulk Optics and Fiber Optics

Traditional bulk-optical setups comprise discrete optical elements such as mirrors, lenses, polarizers, filters, etc., whereas fiber optics may be use to make all-fiber setups.

The different technological approaches can differ in many respects:

Of course, bulk and fiber technologies are also used in mixed forms, where the light partly travels through air and bulk-optical elements and partly through fibers. One may then obtain advantages of both technologies, but also disadvantages of both. For example, the robustness of a fiber-optical solution may be lost entirely if a setup contains only a single free-space beam path. (Note that re-launching light into a single-mode fiber requires a more sensitive alignment than that in many bulk-optical setups.)

Important Applications of Fiber Optics

Fiber optics have become a very important area of photonics technology. In the following, we briefly discuss some particularly important areas of application:

Modeling of Fiber Devices

Physical modeling is often crucial for analyzing and optimizing the operation details of fiber-optic devices. Many different aspects can be the subject of such modeling:

For many such aspects, fiber simulation software is used – particularly for various kinds of numerical simulations.

Bibliography

[1]W. A. Gambling, “The rise and rise of optical fibers”, IEEE J. Sel. Top. Quantum Electron. 6 (6), 1084 (2000) (an informative review on the development of glass fibers)
[2]A. W. Snyder, “Guiding light into the millennium”, IEEE J. Sel. Top. Quantum Electron. 6 (6), 1408 (2000)
[3]R. Paschotta, tutorial on "Passive Fiber Optics"
[4]R. Paschotta, tutorial on "Modeling of Fiber Amplifiers and Lasers"
[5]A. W. Snyder and J. D. Love, Optical Waveguide Theory, Chapman and Hall, London (1983)
[6]J. Hecht, City of Light, The Story of Fiber Optics, Oxford University Press, New York (1999)
[7]J. A. Buck, Fundamentals of Optical Fibers, Wiley, Hoboken, New Jersey (2004)
[8]W. Koechner, Solid-State Laser Engineering, 6th edn., Springer, Berlin (2006)
[9]F. Mitschke, Fiber Optics: Physics and Technology, Springer, Berlin (2010)
[10]R. Paschotta, Field Guide to Optical Fiber Technology, SPIE Press, Bellingham, WA (2010)

(Suggest additional literature!)

See also: fibers, fiber cables, fiber connectors, fiber collimators, cleaving of fibers, silica fibers, plastic optical fibers, rare-earth-doped fibers, double-clad fibers, single-mode fibers, multimode fibers, LP modes, photonic crystal fibers, large mode area fibers, specialty fibers, mode size converters, tapered fibers, polarization-maintaining fibers, optical fiber communications, dispersion-decreasing fibers, dispersion-shifted fibers, fiber Bragg gratings, fiber-optic sensors, power over fiber, fiber lasers, fiber joints, fiber simulation software
and other articles in the category fiber optics and waveguides

In the RP Photonics Buyer's Guide, 278 suppliers for fiber optics are listed.

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