LED fundamentals: Comparison of front- and edge-emitting diodes

We establish a criterion for the maximum amount of power that can be launched into an optical fiber relative to a front-emitting diode of given active layer (junction) thickness. According to this criterion it should be possible to obtain 7.5 times the amount of power from a light-emitting diode (LED) of optimum design relative to a front-emitting LED whose active layer of equal intrinsic brightness is 2.5 μm thick. We also discuss the performance of edge-emitting diodes and find that the LED's of our examples are capable of providing approximately 50 percent of the power expected from the ultimate diode configuration.