science officer Mike Shlesinger, who oversees the research. "It pro- vides a definite advantage over direct encoding of polarization, leaving an eavesdropper only chaotic static and no means to extract the signal." 4.5 OPTICAL COMMUNICATIONS VIA CDMA A new generation of light-based communications devices is the goal of engi- neers at the University of California, Davis, and the Lawrence Livermore National Laboratory. The researchers will build chip-sized devices that use code division multiple access (CDMA), a method already in use in some mobile phones, to transmit and receive optical signals. Optical fibers and lasers send messages as streams of light pulses. In current technology, different messages are separated with a method called wavelength division multiplexing (WDM), where each message uses a different wavelength of light. In contrast, optical CDMA encodes each pulse or bit of information across a spread of wavelengths. The receiver uses a key to decode the signal and recreate the original pulse. "You don't need a wavelength for each user," says Ben Yoo, an associate professor of electrical engineering at UC Davis. Optical CDMA devices would provide fast, secure links to telecommuni- cations networks that already use an optical fiber backbone, Yoo notes. Currently, users access the network backbone over slower electronic or wire- less connections. CDMA also makes it difficult for eavesdroppers to tune in as the frequencies used change rapidly. Even if a snoop can tap into a con- versation, they can't understand it without knowing the key. "Security-wise, there are strong advantages to optical CDMA because you can change the code at any time," says UC Davis electrical engineer Zhi Ding. 4.6 LIGHT EMITTERS Optical networks are all about light. So it's only natural that researchers are working hard to create light sources that are bright, smaller, and less power hungry. 4.6.1 Smallest Light Emitter IBM researchers have created the world's smallest solid-state light emitter. The device, the first electricall