Optical routing switches incorporating ferroelectric liquid crystals for use in photonic networks (Invited Paper)

ABSTRACT Optical switching allows us to make the photonic network flexible and expandable. We have been studying two types ofoptical switches incorporating ferro-electric liquid crystals (FLCs). One type of them is a polarization-controlled free-space optical switch whose operation principle is based on the polarization switching by FLC cells. It has a novelintegrated structure consisted with FLC polarization control devices (FLC-PCDs), thin-film beam-splitters and mirrors.The FLC-PCD with a metal mirror electrode is the key element in this switch. The design theory for the FLC-PCD toachieve an accurate 90-degree polarization switching for the oblique incident light has been developed and verified byexperiments. 2x2 and 4x4 optical switches were fabricated for optical communication wavelengths of 1300 and1550nm and their feasibility was demonstrated. The other switch type is a waveguide switch composed of an optical waveguide having FLC claddings. The FLCs inthe cladding layer change their effective refractive index corresponding to the applied voltage polarity, providing thephase shift of the travelling lightwave in the waveguide. The operation principle of the switch has been confirmed by anexperimental Si waveguide Mach-Zehnder interferometer (MZI) having FLC claddings.Keywords: Optical switch, waveguide switch, FLC, polarization switch, photonic network