New Device Concepts in Polymer Optical Fibers

The fact that light induces a refractive index change in a material is the basis of an all-optical switching or logic device - where one beam of light affects its own propagation or the propagation of a second beam of light. There are many mechanisms that result in such a light- induced refractive index change. The heating mechanisms, for example, results when the refractive index changes in response to the density change that accompanies thermal heating when light energy is absorbed by a material. By virtue of the conductive nature of heating, the thermal effects are slow (approximately ≈ Is time scale). The fast electronic mechanism, on the other hand, results in refractive index changes due to electronic cloud deformation. When the excitations are far off any material resonances, electron cloud distortion does not result in real excitations of the atoms or molecules and is thus a fast response (≈ 10-15s).