In a
single-mode optical fiber
In fiber-optic communication, a single-mode optical fiber, also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode (electromagnetism), mode of light - the transverse mode. Modes are the possible solutio ...
, the zero-dispersion wavelength is the
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
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 by restricting the transmission of energy to one direction. Common types of waveguides include acoustic waveguides which direct sound, optical waveguides which direct light, and radio-frequency w ...
dispersion cancel one another. In all
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...
-based
optical fiber
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...
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 val ...
. 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 (laboratory), a highly specialized shared research resource
* Core (manufacturing), used in casting and molding
* Core (optical fiber ...
and
cladding. 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 fibers or
photonic crystal fiber
Photonic-crystal fiber (PCF) is a class of optical fiber based on the properties of Photonic crystal, 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 c ...
s (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 ...
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 optics, 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 effec ...
(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 ...
,
soliton
In mathematics and physics, a soliton is a nonlinear, self-reinforcing, localized wave packet that is , in that it preserves its shape while propagating freely, at constant velocity, and recovers it even after collisions with other such local ...
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 800 Gbit/s. Multi-mode fiber has a fairly ...
. 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.
See also
*
Nonzero dispersion shifted fiber
References
*
*Govind P. Agrawal, ''Nonlinear Fiber Optics'', 3rd ed. (Academic Press, San Diego, CA, USA, 2001), {{ISBN, 0-12-045143-3
Fiber optics