Performance optimization of optical switches in ferroelectric liquid crystals and polymers operating at 1550 nm

A multilayer structure realizing an optical switch with ferroelectric liquid crystal, polymeric buffers and waveguides has been analyzed at the wavelength of 1550 nm, focusing on fabrication and design tolerances. The used liquid crystal FELIX-M4851-025 from Clariant is aligned by Nylon6 and embedded between two polymeric waveguides. ITO is deposited on quartz substrates to apply voltage to the cell and polymeric buffers are employed to reduce ITO absorption losses. The polymers consisted of poly(pentafluorostyrene-co-glycidyl methacrylate). Light is switched between the optical waveguides by reorienting the liquid crystal. Optimization in terms of optical losses and extinction ratios was carried out by varying layer thicknesses, refractive indices of waveguides and buffers, and the angle a between the normal to the smectic layers and the propagation direction. An optimized device with α = 51°, refractive indices of 1.475 and 1.462, thicknesses of 3 and 6 μm for waveguides and buffer, respectively and 4.4 μm for the liquid crystal layer, exhibits an extinction ratio of 59.6 dB with losses as low as 0.8 dB for a length of only 174 μm. A device design using single mode channel waveguides for optical switching matrices has been also carried out.