In a

single-mode optical fiber In fiber-optic communication, a single-mode optical fiber (SMF), also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode of light - the transverse mode. Modes are the possible solutions of the Helmholtz ...

, the zero-dispersion wavelength is the

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...

or wavelengths at which material

dispersion Dispersion may refer to: Economics and finance * Dispersion (finance), a measure for the statistical distribution of portfolio returns * Price dispersion, a variation in prices across sellers of the same item *Wage dispersion, the amount of variat ...

and

waveguide A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...

dispersion cancel one another. In all

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

-based

optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a mea ...

s, minimum material dispersion occurs naturally at a wavelength of approximately 1300 nm. Single-mode fibers may be made of silica-based glasses containing dopants that shift the material-dispersion wavelength, and thus, the zero-dispersion wavelength, toward the minimum-loss window at approximately 1550 nm. The engineering tradeoff is a slight increase in the minimum

attenuation coefficient The linear attenuation coefficient, attenuation coefficient, or narrow-beam attenuation coefficient characterizes how easily a volume of material can be penetrated by a beam of light, sound, particles, or other energy or matter. A coefficient valu ...

. Such fiber is called dispersion-shifted fiber. Another way to alter the dispersion is changing the core size and the refractive indices of the material of

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

and

cladding Cladding is an outer layer of material covering another. It may refer to the following: *Cladding (boiler), the layer of insulation and outer wrapping around a boiler shell *Cladding (construction), materials applied to the exterior of buildings ...

. Because fiber optic materials are already highly optimized for low scattering and high transparency alternative ways to change the refractive index were investigated. As a straightforward solution tapered fibers and

holey fiber Photonic-crystal fiber (PCF) is a class of optical fiber based on the properties of photonic crystals. It was first explored in 1996 at University of Bath, UK. Because of its ability to confine light in hollow cores or with confinement charact ...

s or photonic crystal fibers (PCF) were produced. Essentially they replace the cladding by air. This improves the contrast of refractive indices by a factor of 10. Therefore, the effective index is changed, especially for longer wavelengths. This type of refractive index change versus wavelength due to different geometry is called waveguide dispersion. As these narrow waveguides (~1-3 μm core diameter) are combined with

ultrashort pulse In optics, an ultrashort pulse, also known as an ultrafast event, is an electromagnetic pulse whose time duration is of the order of a picosecond (10−12 second) or less. Such pulses have a broadband optical spectrum, and can be created by m ...

s at the zero-dispersion wavelength pulses are not instantly destroyed by dispersion. After reaching a certain peak power within the pulse the non-linear refractive index starts to play an important role leading to frequency generation processes like

self-phase modulation Self-phase modulation (SPM) is a nonlinear optical effect of light–matter interaction. An ultrashort pulse of light, when travelling in a medium, will induce a varying refractive index of the medium due to the optical Kerr effect. This variatio ...

(SPM),

modulational instability In the fields of nonlinear optics and fluid dynamics, modulational instability or sideband instability is a phenomenon whereby deviations from a periodic waveform are reinforced by nonlinearity, leading to the generation of spectral-sidebands and t ...

soliton In mathematics and physics, a soliton or solitary wave is a self-reinforcing wave packet that maintains its shape while it propagates at a constant velocity. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medi ...

generation and soliton fission, cross phase modulation (XPM) and others. All these processes generate new frequency components, meaning that input light with narrow bandwidth expands into a wide range of new colours, through a process called supercontinuum generation. The term is also used, more loosely, in

multi-mode optical fiber Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 100 Gbit/s. Multi-mode fiber has a fairly large ...

. There, it refers to the wavelength at which the material dispersion is minimum, ''i.e.'' ''essentially'' zero. This is more accurately called the minimum-dispersion wavelength.

Zero-dispersion slope

The rate of change of dispersion with respect to wavelength at the zero-dispersion point is called the zero-dispersion slope. Doubly and quadruply clad single-mode fibers have two zero-dispersion points.

References

* *Govind P. Agrawal, ''Nonlinear Fiber Optics'', 3rd ed. (Academic Press, San Diego, CA, USA, 2001), {{ISBN, 0-12-045143-3 Fiber optics

Zero-dispersion slope

See also

References