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Nonlinearities

Definition: optical phenomena involving a nonlinear response to a driving light field

More specific term: parametric nonlinearities

German: Nichtlinearitäten

Categories: fiber optics and waveguides, nonlinear optics

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Cite the article using its DOI: https://doi.org/10.61835/08e

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Lasers can be used for the generation of light with very high optical intensities. These can give rise to a number of nonlinear optical effects (→ nonlinear optics), the most important of which are the following:

There are also various other effects which are not directly based on optical nonlinearities, but are nevertheless affecting optical phenomena:

Usually, the strength of nonlinear effects is determined by the peak power. However, there are cases where stronger effects occur for lower peak powers, as explained in a Spotlight article.

Nonlinear Effects in Fiber Optics

In optical fiber technology, optical nonlinearities are of high interest. In fibers there is a particularly long interaction length combined with the high intensity resulting from a small mode area. Therefore, nonlinearities can have strong effects in fibers. Particularly the effects related to the <$\chi^{(3)}$> nonlinearity – Kerr effect, Raman scattering, Brillouin scattering – are often important, despite the relatively weak intrinsic nonlinear coefficient of silica: either they act as essential nonlinearities for achieving certain functions (e.g. pulse compression), or they constitute limiting effects in high-power fiber lasers and amplifiers.

Fibers usually not do not exhibit a <$\chi^{(2)}$> nonlinearity due to the symmetry properties of the used glass. Under certain circumstances, this can be changed, e.g. by poling the glass with a strong electric field.

Tutorials and Case Studies

See our tutorial Passive Fiber Optics, part 11.

The following case studies are available, which discuss various aspects of nonlinearities in optical fibers:

  • Pulse compression in a fiber
  • We explore how we can spectrally broaden light pulses by self-phase modulation in a fiber and subsequently compress the pulses using a dispersive element. A substantial reduction in pulse duration by more than an order of magnitude is easily achieved, while the pulse quality is often not ideal.
  • Parabolic pulses in a fiber amplifier
  • We explore the regime of parabolic pulse amplification in an Yb-doped single-mode fiber. We find reasonable operation parameters and investigate various kinds of limitations, e.g. concerning the nonlinear pulse compression.

Bibliography

[1]D. Castelló-Lurbe et al., “Nonlinearity measurement undergoing dispersion and loss”, Opt. Lett. 48 (2), 493 (2023); https://doi.org/10.1364/OL.481445
[2]G. P. Agrawal, Nonlinear Fiber Optics, 4th edn., Academic Press, New York (2007)
[3]R. Paschotta, tutorial on "Passive Fiber Optics", Part 11: Nonlinearities of Fibers

(Suggest additional literature!)

See also: nonlinear optics, effective nonlinear coefficient, laser-induced breakdown, nonlinear crystal materials, nonlinear frequency conversion, nonlinear polarization, nonlinear index, saturable absorbers, highly nonlinear fibers, spotlight 2007-09-01

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