Liquid crystal applications in photonics

Abstract

We developed new optical switches based on nematic and ferroelectric liquid crystal (LC) cells for photonics applications. Certain new LC switches based on the effect of total internal reflection in nematic LC and deformed helix ferroelectric effect ferroelectric LC with very fast response time were developed. Fast bistable optical switches of the light polarization based on ferroelectric liquid crystal cells were proposed. The switches are characterized by 100μs switching time and 26dB crosstalk at the wavelength of 632.8nm and bistable, i.e., required zero power consumption in the switch state.
High frequency hysteretic free electrically controlled 0–2π phase modulation of light has been proposed using a very short helix pitch (less than 400nm) deformed helix ferroelectric liquid crystal. The electrically controlled 0–2π hysteretic free phase modulation was achieved at the driving voltage frequency up to 4kHz and the voltage amplitude of 32V. The application of fast V-shaped deformed helix ferroelectric ferroelectric LC (DHF-FLC) for new active-matrix liquid crystal display (LCD) and optical data processing devices is envisaged.
Photoalignment technology can be very useful for the new generation of liquid crystal devices as well as in new photovoltaic, optoelectronic and photonic devices based on highly ordered thin organic layers. We have investigated the LC photoalignment in superthin tubes, which are basic elements of switchable photonic crystal/liquid crystal structures and obtained the order parameter comparable with usual homogeneous nematic LC cells. We studied LC alignment on silicon surfaces with submicrometer-sized straight and curved waveguide profiles. The liquid crystal cladding refractive index was then varied according to the applied voltage, and subsequently the microresonator resonance wavelengths were tuned. Based on our initial measurements, the free spectral range (FSR) wavelength shift within the range of 20nm was obtained, which is comparable with a thermooptic effect. The new voltage controllable Si-based add drop filters are envisaged based on this principle.