Liquid Crystal Optical Channel Waveguides With Strong Polarization-Dependent Mode Tunability

The electrically tunable liquid crystal (LC) optical channel waveguide with strong polarization-dependent mode tunability is demonstrated for the first time. When the applied voltage increases, the LC molecules encapsulated in the semicircular groove on the fused silica substrate gradually tilt upward and twist toward two sides. For TE polarization, the applied voltage slightly decreases the effective index and has a small effect on the field distribution of the guided mode. As to TM polarization, electrical tuning greatly enhances the effective index as larger as 2.234 ×10^-1 and causes an obvious variation of the mode size. The TM polarization has the lowest propagation loss 0.94 dB/cm up to date. It is attributed to high-optical quality substrate and smooth groove surface produced by chemical etching with the composite mask. The LC reorientation distribution and the full-vectorial guided mode characteristics at various voltages are calculated to explain the experimental results. The proposed LC-core channel waveguide owns the unique feature of strong polarization-dependent mode tunability and can be used as promising devices, such as ultrashort phase modulator, pulse-delayed device, and polarization controlling device.