 From the late 1960s, Li engaged in pioneering research on lightwave technologies and systems, which are now ubiquitously deployed in the telecommunications industry.In the late 1980s, when the whole world's attention on optical communication was still focused on a single-channel high speed solution, he and his team developed the world's first (sparse channel) WDM (Wavelength Division Multiplexing) system at AT&T Bell Labs.With the understanding that a technique that can only be put into real use if it remains backwards-compatible with existing technology, he (and his team) proposed and studied the use of optical amplifiers in WDM systems, which utilized the existing embedded base to create virtual fibers by putting more channels onto a single fibre.