Electro-Optic Waveguides

Abstract

Electro-optic waveguides are designed based on changing refractive index of the core layer with an external voltage. Materials used for electro-optic waveguides can be LiNbO3, LiTaO3, BaTiO3, electro-optic polymers, liquid crystal, and strained silicon. The LiNbO3 is a versatile material and used for various applications in guided wave optics, electro-optics, acousto-optics, and nonlinear optics. It has high electro-optic coefficient, optical damage resistance, and low losses. Stoichiometric lithium tantalate is good for applications at UV wavelengths as it is transparent down to 260 nm where most of the standard electro-optical materials, e.g., LiNbO3 or KNbO3, show large light absorption. The optical ferroelectrics in the form of highly transparent thin films are promising materials for communication. BaTiO3 is particularly an attractive candidate for thin film electro-optic modulators due to its large electro-optical coefficients, its high optical transparency and its favorable growth characteristics. Electro-optic (EO) polymers are unique materials having many advantages over inorganic materials for the wide range of applications from optical network components and optical interconnects to millimeter and microwave photonics. They have very large EO coefficients, low optical loss, and low dispersion of refractive index between optical frequencies and millimeter waves, as well as high bandwidth. They are easy to process and have relatively low cost. There is a broad range of EO devices that can be fabricated based on EO polymers having a waveguide structure as the main building block. Liquid-crystal electro-optic waveguide platform has exhibited unprecedented electro-optical phase delays, with very low loss and rapid response time. This technology is based upon a unique liquid-crystal waveguide geometry, which exploits the tremendous electro-optic response of liquid crystals while circumventing historic limitations of liquid crystals. The exceedingly large optical phase delays accessible with this technology enable the design and construction of a new class of previously unrealizable photonic devices. Strained silicon can be another electro-optic material. A significant linear electro-optic effect can be induced in silicon by breaking the crystal symmetry. The strain-induced linear electro-optic effect may be used to remove a bottleneck in modern computers by replacing the electronic bus with a much faster optical alternative. This chapter will give a brief review about various types of electro-optic waveguides, and their materials selection, optimum designs, as well as processing technologies depending on applications.