Microwatt power optically controlled spatial solitons in azobenzene liquid crystal

摘要

We study the phenomena of laser beam propagation in azobenzene liquid crystals (azo LCs) in waveguiding configuration. We found that spatial solitons can be formed at microwatt power levels of a He-Ne laser beam. We have observed several well-known processes of nonlinear propagation such as undulation of solitons, their interaction and merging. In addition, we have shown that due to the memory of the nonlinear waveguide in azo NLC, the solitons are steered following mechanical displacement of the LC cell, a phenomenon that can be used for stabilized coupling of radiation into optical fibers. Cis-trans isomerization of azobenzene molecules and related change in the LC order parameter is the underlying mechanism of optical nonlinearity that makes possible formation of solitons. This mechanism is present in the mesophase as well as in the photoinduced isotropic phase of the material. We have shown that the photoinduced isotropic phase may be locally induced to form a waveguide that steers the solitons to large angles without noticeable attenuation of the beam at distances ～1 cm. We have presented a simple 3-level theory for describing the complexity of the effects of laser beams on azo LCs.