Flat band and dipolar discrete optics

摘要

In this talk, I will present our recent experimental results on weakly coupled waveguide arrays. We will review our experiments on Lieb photonic lattices, where we observed, for the first time ever, a at band linear localized mode and their linear combinations. Linear combinations of these zero dispersion modes form a completely coherent pattern which does not diffract at all. This observation allowed us to implement a distortion-free image transmission scheme: we codified numbers from 0 to 9 using ten different ring mode combinations and used this as an optical key mechanism. Localization without defects, disorder or nonlinearity is an important property of at band systems. I will discuss our recent experiments on these quasi one-dimensional lattices, where a at-band transition occurs for a very specific ratio between horizontal and diagonal coupling coefficients. I will show the tendency to localization, of a localized input beam, for a set of perfectly periodic linear Sawtooth lattices. Additionally, I will present our very recent theoretical findings on reflection properties on a square two-dimensional lattice possessing a Stub at band surface. I will show that a back-reflected wave is generated as a result of a special resonance with at band modes at the Stub border. By reducing the wavelength of the laser beam, we are able to excite dipolar modes in Silica waveguide arrays. We observe new phenomenology as a result of an effectively larger coupling coefficient and, even more interesting, the possibility to effectively tune the waveguide's interaction by changing the dipole orientation. We used a gaussian input condition, modulated in amplitude and phase, to reproduce the fundamental diffraction properties for single and dipolar modes. By comparing discrete diffraction patterns and gaussian beam propagation, we found a three times larger coupling constant for dipoles, at 532nm and a waveguide separation of 20 μm. We studied the transport properties of disordered lattices and found that while fundamental modes are already localized in space, dipolar modes are still able to propagate across the system. This could be used as a linear optical switch controlled by tuning the input condition.