Biomedical subjects
Publications and source records attributed to Umberto Bortolozzo.
We show experimentally that large matrices of localized structures can be stored as elementary pixels in a nematic liquid crystal cell. Based on optical feedback with phase modulated input beam, our system allows us to store, erase, and actualize the localized structures in the matrix.
In a nonlinear optical experiment we report a unique class of localized structures, which appears as localized peaks of a pattern nucleating over another pattern. We show that this occurs when the system is driven through three pattern branches of solutions, accompanied by the appearance of localized peaks with two different amplitudes. Spontaneous creation and motion of localized peaks are triggered by amplitude and phase fluctuations of the underlying pattern. The scenario is universal and applies whenever a subcritical bifurcation exists between two different pattern solutions.
Evidence of modulated dissipative structures with an intrinsic wavelength in a nonlinear optical system devoid of Turing instability is given. They are found in the transverse field distribution of an optical cavity containing a liquid crystal light valve. Their existence is related to a transition from flat to modulated fronts connecting the unstable middle branch of a bistability cycle and either of the two stable uniform states. We first analyze the cavity in the limit of nascent bistability, where a modified Swift-Hohenberg equation is derived. This allows for a simple analytical expression of the threshold associated with the transition as well as the wavelength of the emerging structure. Numerical simulations show development of ring-shaped modulated fronts and confirm analytical predictions. We then turn to the full model and find the same transition, both analytically and numerically, proving that this transition in not limited to nascent bistability regimes.