Liquid crystal fluctuations and device performance

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Performance specifications are very tight in telecommunications, mostly because network elements may cascade so that imperfections might combine pathologically. One source of 'noise' is the amount of light scattered into an outgoing fibre at a particular wavelength that is not supposed to be there - even levels 50dB below the signal level are problematic. Many optical devices employ liquid crystals to enable switching. Liquid crystals are optically anisotropic liquids, and thus enable switching of the optic axis with moderate switching fields. However, being liquid, they are also susceptible to fluctuations in the anisotropy axis. These fluctuations are called director fluctuations. Director fluctuations present themselves as optical noise to the signal. Liquid crystals also have properties characteristic of crystals: anisotropic elasticity. In addition, liquid crystals are usually made as thin sandwich-like films, therefore surface effects are important as well: all produce elastic distortions. Two distortion modes, one pertaining to molecular tilt at the surface and the other to the twist mode, are particularly important in thin liquid crystal cells. The goal of this proposal is to examine the source of optical noise in a particular liquid-crystal based optical device known as the LCOS cell. The dependencies of the optical noise on various liquid crystal parameters in LCOS cells will be studied, with a view to finding a solution that reduces or addresses how to reduce optical noise. This will enhance the quality of next-generation devices that the company makes, and ensure that revenues for these future devices are maximized.