A variety of self-organized patterns were observed in liquid crystal modulators, generated because of their large and controllable nonlinearity. In this work, we investigated some fatty acids and mixtures with cholesterol, which showed, under certain conditions, thermotropic mesomorphism and a large sensitivity to the optical field. Depending on the transverse profile of the laser beam, a self-phase modulation and external self-focusing - illustrating the nonlinear wave propagation - were observed. A ring pattern, due to the steady-state far-field diffraction intensity distribution of the Gaussian beam of a helium-neon laser, transmitted through the samples, was experimentally and computer studied. This is useful both for building new photonic devices and for explaining some processes from the biological membrane.