The best way to build optical communication networks is the object of research by computer scientist Biswanath Mukherjee and electronic engineer Jonathan Heritage of the University of California, Davis. "We can create gadgets, but this is useless without understanding network architecture," said Mukherjee. Networks require repeaters and cross-connects that allow long-distance signals to pass through a junction point, while local traffic splits off. Mukherjee and Heritage use a computer modeling approach to work out how cross-connects should be positioned. "The question is, when should we stay in the optical domain and when should we go back to electronics to repair the signal?" said Heritage. To multiply the number of signals carried by a single fiber, engineers use wavelength division multiplexing (WDM). Each signal is allocated a slightly different wavelength of light. The UC Davis researchers are studying how best to assign wavelengths to signals, how to handle multiple wavelengths, and the best way to route the WDM signals across networks. Optical communications depend on advances in optics, electronic engineering, computer science and software development, said Mukherjee. The greatest payoff would come from merging the best of each field, rather than focusing on one area, he said. Mukherjee teaches a course in optical networks at UC Davis and has authored a textbook on the subject. He is a past chair of the Department of Computer Science and has acted as consultant for a number of communications companies. Heritage is currently chair of the Department of Electrical and Computer Engineering at UC Davis.