Semiconductor lasers are very small (about the size of a grain of salt), very efficient electrically powered sources of coherent light. In the mid-1980s, their availability in large quantities and with long lifetimes enabled several applications, such as fiber optic communications, medical diagnostics and laser-based displays. Since then, technological advances in fiber optic components and dense wavelength division multiplexing (DWDM) have enabled the widespread deployment of high-speed optical networks. Low-cost laser sources and tunable components are critical for next-generation DWDM networks as the number of channels and data rates increase...