Photonic Integration Based on Liquid Crystals for Low Driving Voltage Optical Switches

This paper reports on optical waveguides using liquid crystals (LC) as core. Such optical waveguides have the advantage to be controlled by a low voltage electric field or by using an optical beam by exploiting the highly efficient electro-optic or nonlinear optical effects, respectively. Optical switches based on LC embedded in silicon grooves have been reported with on–off contrast over 40 dB by applying about 8 V. Recently, a novel technology based on LC embedded in polydimethysiloxane (LC:PDMS) have been also developed to make photonic devices based on electro-optic waveguides on flexible substrates for telecom and sensor applications. An interesting feature of this guiding structure is that propagation is polarization independent. This technology has been employed to design a 2 × 2 optical switch based on a zero-gap electro-optical controlled directional coupler able to switch light from one output port to another by applying less than 1.8 V with an extinction ratio better than 16 dB.