nonlinear pulse distortion (original) (raw)
Definition: distortion of the spatial, temporal or spectral characteristics of an optical pulse, resulting from optical nonlinearities
Categories: 
fiber optics and waveguides, 
nonlinear optics, 
optical amplifiers, 
light pulses
- optical effects
- nonlinear optical effects
* nonlinear frequency conversion
* self-phase modulation
* cross-phase modulation
* four-wave mixing
* soliton propagation
* modulational instability
* parametric amplification
* parametric fluorescence
* nonlinear pulse distortion
* self-focusing
* nonlinear polarization rotation
* self-steepening
* stimulated Raman scattering
* stimulated Brillouin scattering
* nonlinear absorption
* thermal lensing
* (more topics)
- nonlinear optical effects
Related: Raman Scattering in a Fiber AmplifiernonlinearitiesKerr effectpulse propagation modelingchirped-pulse amplification
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DOI: 10.61835/8cc Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn
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What is Nonlinear Pulse Distortion?
Optical pulses, in particular ultrashort pulses with pulse durations of picoseconds or femtoseconds, can have very high peak powers and peak intensities even when the pulse energy is moderate, e.g. in the microjoule regime. As a consequence, such pulses can be strongly influenced by nonlinearities during propagation in transparent media, such as in laser crystals or particularly in optical fibers. Nonlinear effects can result in distortions of various kinds:
- For propagation in homogeneous media (e.g. bulk optical crystals), the spatial properties can be affected. An example is self-focusing, which can in extreme cases lead to laser-induced breakdown. In less extreme cases, one still has the effect of an aberrative and time-dependent lens.
- Strong spectral distortions can result from, e.g., self-phase modulation: the optical spectrum can acquire strong modulations and broadening.
- The temporal shape of a pulse can also be distorted: The pulse may be broadened, may become asymmetric, or acquire temporal pedestals. In extreme cases, a pulse can break up into multiple pulses. An example is higher-order soliton fission in the process of supercontinuum generation. A related phenomenon is wave breaking. In many cases, the temporal distortion is not the direct impact of a nonlinearity, but rather the consequence of chromatic dispersion acting on a pulse with nonlinearly broadened optical spectrum. For example, self-phase modulation (in an approximation not containing the effect of self-steepening) or Raman scattering do not directly affect the temporal shape, but modify the optical spectrum so as to make a pulse significantly more susceptible to the effects of chromatic dispersion.
Simulations on Pulse Propagation
Pulses propagating in a fiber amplifier, for example, can undergo a complicated evolution. A suitable simulator is essential for getting complete insight — not only on the resulting output pulses, but also on the pulses at any location in your system. The RP Fiber Power software is an ideal tool for such work.
In amplifiers, the effect of gain saturation can also lead to substantial distortions of the temporal pulse shape: while the leading wing of the pulse experiences strong amplification, later parts are less strongly amplified as the gain is saturated already.
Figure 1: Temporal shape of a femtosecond pulse, which has been distorted during propagation in an optical fiber.
The nature of nonlinear pulse distortions depends strongly on the circumstances, i.e., the type and strength of nonlinearity and on the occurrence of other effects such as chromatic dispersion or waveguiding. It can be investigated with pulse propagation modeling.
Raman Scattering in a Fiber Amplifier
We investigate the effects of stimulated Raman scattering in an ytterbium-doped fiber amplifier for ultrashort pulses, considering three very different input pulse duration regimes. Surprisingly, the effect of Raman scattering always gets substantial only on the last meter, although the input peak powers vary by two orders of magnitude.
There are various methods for mitigating nonlinear pulse distortions, e.g. in amplifiers for ultrashort pulses. Examples are the use of thin (and highly doped) amplifier crystals, chirped-pulse amplification and divided-pulse amplification.
Frequently Asked Questions
This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).
What is nonlinear pulse distortion?
Nonlinear pulse distortion is any change in the spatial, spectral, or temporal characteristics of an optical pulse caused by nonlinearities during its propagation. It is particularly significant for ultrashort pulses with high peak powers.
How do nonlinearities change the temporal shape of a pulse?
Some effects, like gain saturation in an amplifier, directly distort the temporal pulse shape. Often, the effect is indirect: a nonlinearity like self-phase modulation first broadens the pulse's optical spectrum, and chromatic dispersion acting on this modified spectrum then causes temporal distortion.
How can nonlinear pulse distortions be controlled in high-power amplifiers?
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