Visual observation of Zener tunneling.

We experimentally investigate photonic Zener tunneling between the bands of a waveguide array by directly monitoring the propagating light inside this structure. For strong transverse index gradients we observe Zener breakdown as regular outbursts of radiation escaping from the Bloch oscillations. Tunneling to higher order photonic bands and Bloch oscillations in different bands have been detected.

Formation of micro-optical structures by self-writing processes in photosensitive polymers.

A local exposure of UV-sensitive polymers leads to a local curing. This corresponds to a saturable and irreversible nonlinear change of the refractive index, which evidently leads to a filamentation of the hardening polymer. This paper investigates the physical background of these effects and analyzes how the different influencing factors could be used for a steered, partly self-written formation of micro-optical structures. The structure formation is simulated on the basis of an iterative beam propagation method with consideration of a set of process parameters, e.g., the photoinitiator concentration or the exposure intensity. It is shown theoretically as well as experimentally that a variation of material- and exposure-specific process parameters gives opportunities for a controlled structure formation. The experimental realization of a configuration by use of a beam shaper within a UV contact exposure process is presented by means of the preparation of high-aspect-ratio conic structures.

Tailoring guided modes in waveguide arrays.

The formation of localized states or modes at defects in waveguide arrays is investigated both, theoretically and experimentally. If the effective index or the coupling of the defect guide to its neighbors is varied the number and character of respective modes bound to the defect can be altered. Waveguide arrays may be considered as tailor-made or metamaterials with new and unexpected properties as e.g. guiding staggered modes bound to defects with reduced index. Although the symmetric defect waveguide becomes multimode for increased coupling it does not support antisymmetric modes. All theoretical predictions are confirmed in excellent agreement with experimental observations in polymer waveguide arrays.