What is negative dispersion, and how it can be estimated when light is propagated through the fiber? is there any formula ?
Negative dispersion is associated with negative group velocity, indicating negative energy flux . A negative means, that w decreases with k.
Thank you Deshmukh Sir, can you explain your answer that w deceases with k.
Propagation of light in a negative dispersion regime (antiparallel phase and group velocities) may be attributed to either fast light or a backward wave. We show that by applying causality, only one of these is valid for each scenario.
In simple words, when light travels through any identical medium waveguide/ fiber, normally, red color light spectrum bent most, go faster and so, as blue is the slowest due to its material structure. This phenomenon is called positive dispersion (normal case).
But, when the blue light spectrum becomes fastest (velocity) than other colors, then it is called negative dispersion. (can be achieved by graded-index fiber, dispersion compensating fiber). It can be achieved by changing the physical structure (diameter), the refractive index of the waveguide. Normally, a negative dispersive system is used to cancel the effect of positive dispersion during long-distance communication, so that the dispersion remains very low at the time of receiving the optical signal (velocity of each color remains almost the same at the end ).
Negative dispersion: https://www.semanticscholar.org/paper/Controlling-the-sign-of-chromatic-dispersion-in-Arbabi-Arbabi/351013ad5ceb177fd23fd369518e56e3779e96db/figure/0
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