Equilibrium mode distribution
- Equilibrium mode distribution
The equilibrium mode [power] distribution of light travelling in an optical waveguide or fiber, is the distribution of light that is no longer changing with fibre length or with input modal excitation. This phenomenon requires both mode filtering and mode mixing to occur in the fibre to produce a state that is independent of the mode power distribution launched by the light source. At propagation distances exceeding the equilibrium length, intramodal pulse distortion increases (bandwidth decreases) as the square root of length.
The term "equilibrium length" is sometimes used to describe a "stationary" mode distribution, which is the length of multimode optical fiber necessary to attain a static mode distribution from a specific excitation condition. Equilibrium length is, strictly, the longest such length, as would result from a widely variable range of input excitation. Other terms for equilibrium length are "equilibrium coupling length" and "equilibrium mode distribution length".
Equilibrium mode [power] distributions were reported in early multimode transmission systems at propagation distances as short as a few hundred metres. However, as fibre manufacturing improved, the minute waveguide dimensional and structural changes that produce mode-mixing have been greatly reduced. The length of fibre required to attain true equilibrium is now much greater than the length of practical multimode transmission systems, which makes the term effectively obsolete.
In the absence of strong mode-mixing, high order mode filtering is the primary remaining mechanism for potential change of an input mode power distribution. If a well-aligned laser is the optical source, the mode power distribution is highly concentrated in the lowest order modes, and remains essentially unchanged with distance due to the lack of mode-mixing. If an optical source that overfills the fibre is used, only the highest order guided mode group experiences excess attenuation, and the mode power distribution becomes slightly filtered as a result. (Mandrel wrapping is a viable method to artificially create this state.) Such mode power distributions are stationary; neither changes with fibre length, but equilibrium does not exist in either case because the distributions remain dependent on the input power distribution.
ee also
*Mode volume
*Mode scrambler
*Stationary mode power distribution
References
* Federal Standard 1037C
* MIL-STD-188
Wikimedia Foundation.
2010.
Look at other dictionaries:
Equilibrium — is the condition of a system in which competing influences are balanced and it may refer to:cienceBiology* Equilibrioception, the sense of balance present in humans and animals * Homeostasis, the ability of an open system, especially living… … Wikipedia
Mode scrambler — In telecommunications, a mode scrambler or mode mixer is a device for inducing mode coupling in an optical fiber, or a device that, itself, exhibits a uniform output intensity profile independent of the input mode volume or modal excitation… … Wikipedia
Mode volume — In fiber optics, mode volume is the number of bound modes that an optical fiber is capable of supporting. The mode volume M is approximately given by and , respectively for step index and power law index profile fibers, where g is the profile… … Wikipedia
Transverse mode — A transverse mode of a beam of electromagnetic radiation is a particular electromagnetic field pattern of radiation measured in a plane perpendicular (i.e., transverse) to the propagation direction of the beam. Transverse modes occur in radio… … Wikipedia
Maxwell–Boltzmann distribution — Maxwell–Boltzmann Probability density function Cumulative distribution function parameters … Wikipedia
Trip distribution — (or destination choice or zonal interchange analysis), is the second component (after trip generation, but before mode choice and route assignment) in the traditional four step transportation forecasting model. This step matches tripmakers’… … Wikipedia
Normal distribution — This article is about the univariate normal distribution. For normally distributed vectors, see Multivariate normal distribution. Probability density function The red line is the standard normal distribution Cumulative distribution function … Wikipedia
Pareto distribution — Probability distribution name =Pareto type =density pdf cdf Pareto cumulative distribution functions for various k with x m = 1. The horizontal axis is the x parameter. parameters =x mathrm{m}>0, scale (real) k>0, shape (real) support =x in [x… … Wikipedia
Tfm distribution — est une société de distribution de film opérant sur la marché français et de capitaux franco américains, fondée en 2001 par Miramax et TF1[1]. Sommaire 1 Liste de films distribués en France … Wikipédia en Français
TFM Distribution — est une société de distribution de film opérant sur la marché français et de capitaux franco américains, fondée en 2001 par Miramax et TF1[1]. Sommaire 1 Liste de films distribués en France 1.1 … Wikipédia en Français
