Light-induced Photonic Structures

In photorefractive media the refractive index can be modified by the influence of light. As a consequence, this allows not only for the excitation of solitary structures but for the preparation of periodic modulations exhibiting photonic properties.

 

 

 

 

 

 

 

 

 

 

Fig. 1: A gaussian beam (a) on the lattice (b) diffracts (c) and fokusses with higher power (d-f).

 

 

 

 

 

 

 

 

 

 

A periodic modulation of the refractive index is induced in a photorefractive material by means of periodic phase- or amplitude-modulated light waves. The Bloch waves that are able to propagate in such a structure are determined with the Bloch-Floquet-theorem and can be analyzed systematically both in numerics and experiment [1]. Even the formation of a complete two-dimensional bandgap gets possible, what is important for basic research on easily modifiable photonic structures. For example, we observed the anisotropic localzation of a specific Bloch wave getting possible through coupled effects [2].

To study such structures systematically different Bloch waves have to be excited independently [1]. In this case, we have applicated the corresponding Bloch waves for the points of high symmetry in the first Brillouin zone. As an example, in Figure 1 discrete diffraction and localization for higher power is visible.