refractive index of the glass, bending the light SO that it enters one fiber or another. Liquid crystal display (LCD) switches-LCDs use liquid to bend light. Tunable lasers-Tunable lasers pump out light at different wavelengths, and they can switch from one wavelength to another very quickly. MEMS-based optical switches were among the first technology to be deployed (see Figure 11.7), with several companies offering a new generation of optical high-capacity switches. Unfortunately, the market for optical switches in general has been fraught with difficulties, with service providers yet to make big, bold commitments to adopt the technology. However, developments and announce- ments are continuing. For example, in early 2006, Lambda OpticalSystems (www. lambdaopticalsystems.com) unveiled its LambdaNode 2000, an all-optical switch Optical Fibers Imaging Lenses Reflector Mirrors Figure 11.7 A MEMS switch Chapter 11 Optical Networking that scales as large as 256 x 256 ports in one bay and is the first all-optical switch to combine switching and transport functions in one system. Another approach in optical switches, bubble switches, involves using inkjet printer technology to switch packets in optical switches. In inkjet printers, tiny enclosures are filled with gas, and they sit behind the ink in a printer. In front of each enclosure is a minute nozzle. When a character is called for, the gas behind the nozzles that form the letters is heated, and the ink is shot onto the paper (see Figure 11.8). Bubble switches work in a similar manner but use liquid as well as gas. If a packet is supposed to stay on the same network, the liquid remains cool, and the packet passes through unscathed. If a switch is required, the liquid is heated and turns to gas. If the gas has the correct reflective properties and if the cavity is precisely positioned, the light is bounced in the right direction. Yet another optical switching approach involves thermo-optic switches. Light is passed through glass that is then heated up or cooled down