Single-mode operation in laterally coupled cavity semiconductor lasers

Single-mode semiconductor lasers are desirable for fiber-optic communications because their narrow spectrum translates into minimal pulse spreading in a dispersive fiber. Unfortunately, simple Fabry-Perot semiconductor lasers tend to oscillate in several longitudinal modes, particularly under high-frequency modulation. To combat this problem, more complicated laser structures have been proposed, including distributed feedback lasers, distributed Bragg reflectors, and coupled cavity lasers.1 These last are of particular interest due to their relative ease of fabrication. Thus far, most work has focused on longitudinally coupled lasers. In these devices, the gap between the lasers plays a critical role in determining gain selectivity, and it must be altered mechanically. Recently, we demonstrated operation of a laterally coupled laser pair, in which the coupling between two lasers of dissimilar lengths occurs via the evanescent fields of the individual lasers.2 In this paper we solve for the threshold gains of a laterally coupled cavity (LC2) laser and present experimental verification of single-mode operation.