Frequency-stable semiconductor laser for DWDM

Abstract

A frequency stable semiconductor laser source based on InGaAsP distributed feedback (DFB) laser technology is described. The device enables tight tolerances to be maintained on the absolute accuracy and long-term stability of laser sources for the next generation of wavelength division multiplexed (WDM) fiber optic networks. The improved DFB laser frequency stability is achieved by utilizing electrical feedback to stabilize the optical frequency relative to the transmission peak of a Fabry-Perot reference cavity. The novel design achieves stable loop operation while resolving fundamentally incompatible loop gain and bandwidth requirements imposed by the respectively high gain and wide linewidth of the free-running laser. Laboratory measurements of the resulting laser spectrum are presented, demonstrating the impact of the electrical feedback on the short and long-term laser frequency stability. Heterodyne measurements are presented depicting relative laser frequency stability including the Allan variance of the long-term spectral drift.