Zeitschriftenaufsätze

We demonstrate a method for creating a three-dimensional (3D) array of focal spots by combination of a multi-focal diffractive lens and a two-dimensional multi-value phase grating. The multi-focal Fresnel-based lens is created by means of encoding special nonlinearities into the phase structure of a Fresnel zone plate and is represented as a mathematical superposition of this phase function with a refractive lens. The imposed nonlinearity type enables the creation of multiple focal spots with uniform intensity along the optical axis. We demonstrate the example of a 3D multi-value phase grating, which creates five focal planes with a 5×5 transverse array of focal spots with equal energy distribution in each plane. Experimental results are included to verify the theoretical outcomes, where the phase pattern of a 3D multi-value phase grating is encoded onto a spatial light modulator.

Optical microdisk cavities with certain asymmetric shapes are known to possess unidirectional far-field emission properties. Here, we investigate arrays of these dielectric microresonators with respect to their emission properties resulting from the coherent behavior of the coupled constituents. This approach is inspired by electronic mesoscopic physics where the additional interference effects are known to enhance the properties of the individual system. As an example, we study the linear arrangement of nominally identical Lima¸con-shaped cavities and find mostly an increase of the portion of directional emitted light while its angular spread is largely diminished from 20 deg for the single cavity to about 3 deg for a linear array of 10 Lima¸con resonators, in fair agreement with a simple array model. Moreover, by varying the intercavity distance, we observe windows of reversion of the emission directionality and superdirectionality that can be interesting for applications like optical sensing or interconnects. We introduce a generalized array factor model that takes the coupling into account.