In optics

Optics

Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...

, a nematicon is a spatial optical soliton

Soliton (optics)

In optics, the term soliton is used to refer to any optical field that does not change during propagation because of a delicate balance between nonlinear and linear effects in the medium. There are two main kinds of solitons:...

 in a nematic liquid crystal

Liquid crystal

Liquid crystals are a state of matter that have properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of LC phases, which can be...

. The name was invented in 2003 by G. Assanto . Nematicons are generated by the special type of optical nonlinearity

Nonlinear optics

Nonlinear optics is the branch of optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light...

 that is present in nematic LCs: the optical field induced director reorientation. This nonlinearity arises from the fact that the liquid crystal director (i.e. the average molecular orientation) tends to align along the optical electric field. Nematicons are very easy to generate (with a few mW of optical power

Optical power

Optical power is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device. The dioptre is the most common unit of measurement of optical power...

) because the nonlinearity has the following properties:

• A very large nonlinear coefficient : the nonlinearity is typically eight orders of magnitude larger than that of carbon disulfide
  Carbon disulfide
  Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non-polar solvent...
  
  . This means that much lower optical power
  Optical power
  Optical power is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device. The dioptre is the most common unit of measurement of optical power...
  
   is necessary for obtaining the same refractive index
  Refractive index
  In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
  
   variation.
• The nonlocal response : nonlocality means that the nonlinear response is not limited to the exact location of the optical field
  Optical field
  The optical field is a term used in physics and vector calculus to designate the electric field shown as E in the electromagnetic wave equation which can be derived from Maxwell's Equations...
  
  . Instead the nonlinear response is spread out. A high nonlocality leads to a stable soliton propagation. A higher and lower power than the ideal soliton power will lead to breathing solitons.

• The saturability: the director of the liquid crystal tends to align along the optical electric field. For very strong optical fields the director is aligned along the optical field and no further reorientation is possible.

External links

• Spatial optical solitons in liquid crystals, a short introduction (Ghent University).