Lightwave communications networks may require highly reliable optical switches for multimode fibers. Such switches should have low loss, low cross talk, low power consumption, and low operating voltages. Three types of switch have been proposed: mechanical: electrooptic; and liquid crystal. Mechanical switches, which operate by moving either the fibers or other optical components, are the most widely used. Alternatives to mechanical switches have been sought because these switches require high driving power (>20 mW) and are subject to wear. Electrooptic switches eliminate these problems and are significantly faster. However, both insertion losses and cross talk are higher than for mechanical switches, and their use with multimode fibers requires large voltages. Liquid crystal switches are low voltage devices, but their cross-talk performance is relatively poor, and the long term stability of liquid crystals in field conditions is not established.