Injection Lasers for High Data Rate Optical Communications. Volume II.

Abstract : An outline is given of the basic parameters which control the operation and life expectancy of cw laser diodes. This includes a different approach to the laser design problem than that generally used and leads to a modified expression for the threshold current density. Results of this analysis are used to develop a cw laser structure that combines a low threshold with a low vertical beam spread, the latter being essential to the achievement of low coupling losses needed in fiber-optic communication systems. Other design requirements are reviewed, and electrical and optical performance data of lasers developed under this contract are presented. Based on extensive experimental measurements, the reliability aspects of cw lasers are discussed. Facet erosion is shown to be a major failure mode, and methods are given for limiting the influence of this effect. With a suitable coating applied to the facet, lasers fabricated during this contract have accumulated 6000 hours of life without significant output decrease. Similar lasers, without facet protection, have accumulated more than 10,000 hours of operating time with output decreasing gradually, as a consequence of facet erosion. A laser system has been developed, which includes thermal stabilization utilizing thermoelectric coolers and fan coooling for heat removal from the hot end of the thermoelectric module. Convection cooling for that purpose has been demonstrated to be adequate under less extreme ambients.