 with electrical coils. The heat alters the refractive index of the glass, bending the light so that it enters one fiber or another (see Figure 11.9). An LCD switch, as shown in Figure 11.10, uses liquid to bend light. There are many issues to address with these evolving types of optical switches. Again, because we are in the early days of these technologies, we have not yet tested each of them under a full network load. We still have to address how well these technologies will scale. Carriers are looking for modular switches that can scale to thousands of ports. Switching speed is another consideration; routing traf- fic packet by packet will require switching speeds measured in nanoseconds. Bubble Channel Waveguide Light Beam No Bubble Fill Hole Figure 11.8 A bubble switch End-to-End Optical Networking Output 2 Beam Splitter Coupler Input Output 1 Heater Figure 11.9 A thermo-optic switch No Voltage Beam Displacer Polarized Light Liquid-Crystal Cell Voltage Beam Displacer Polarized Light Liquid-Crystal Cell Figure 11.10 An LCD switch Integrated Photonic Circuits Vendors are developing ways to make the optical equivalent of integrated circuits. The goal is to consolidate large numbers of separate optical devices into a single chip, customizing them for different applications and drastically reducing costs while improving performance. One of the key issues involved is the selection of materials. A wide variety of materials are being used for different applications, Chapter 11 Optical Networking including silica, silicon, polymer, and rare earths. Each material has unique advan- tages and disadvantages in terms of the performance of the chip and the ease and cost of manufacturing it. In these early days for this technology, vendors are pro- ducing relatively simple components, such as DWDM chips, small switch modules, and passive splitters. Indium phosphide (InP) is the material of choice for optoelectronic integra- tion. It is likely to revolutionize the communications industry, much as silicon rev- olutionized th