Optical-Guided-Wave Modulators

Abstract

Planar optical-guided-wave devices have been in existence for over 20 years. Two interesting, informative articles can be found in References 1 and 2. Much of the early work in guided-wave optics was on passive devices, but this was also when much of the theoretical understanding of optical-guided-wave (OGW) devices was developed. This theoretical understanding applies to active devices as well. It's interesting to note that the commercialization of passive, glass-based guided-wave devices has just occurred with product introductions by Corning & Nippon Sheet Glass. Active OGW devices (i.e., ones where the light properties can be altered with an applied voltage) have been reported since about 1975. In 1985, Crystal Technology, Inc. announced the first commercially available product—a high-speed, efficient, intensity modulator. Throughout the ten years in between, a huge amount of technical literature has been generated. Most of the work has centered on the Ti:LiNbO3 waveguide technology although several other material systems have been demonstrated as well.Materials upon which optical-guided-wave modulators have been fabricated include: dielectrics such as lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and potassium titanyl phosphate (KTP); the III-V semiconductor compounds, gallium arsenide (GaAs) and indium phosphide (InP); and a variety of organic polymers. Of these materials, waveguides on LiNbO3 are clearly the most developed and are offered for sale commercially. For this reason I will concentrate on this material system while making comparisons to the other material systems when appropriate.