Theoretical Analysis of Modulation Bandwidth of InP-Based Strained-Layer Multiple-Quantum-Well Lasers

Abstract

InP-based strained-layer quantum-well (SL-QW) lasers have attracted much interest since they are among the most promising light sources for high-speed, long-haul optical transmission system. When designing high-speed lasers, one of the important criteria is to increase the differential gain large enough to overcome the gain saturation because the higher gain saturation is one of the major hurdles limiting the modulation bandwidth of QW lasers [1], [2]. Since the demonstration of the high potential for improving differential gain by the application of strain (both tensile and compressive) [3], extensive studies have been carried out to clarify the effects of strain on the resonance frequency of SL-QW lasers. However, the improvement of the actual modulation bandwidth is not guaranteed at all even if the resonance frequency is increased by the application of strain. This is mainly because the carrier transport, escape and capture processes [4], [5] also play a dominant role in determining the bandwidth as well. To properly evaluate the actual modulation bandwidth, it is necessary to take into account these carrier-transport-related effects as well as the strain effects. In this paper, we analyze the modulation bandwidth of InP-based SL-QW lasers on the basis of the unified formalism which includes both the strain effects and the carrier-transport-related effects. We demonstrate here that both effects compete with each other for determining the modulation bandwidth and that the tensile strain exerts a more pronounced impact on the modulation bandwidth of InP-based SL-QW lasers under the strain-limited situation.