Bandwidth enhancement of Fabry-Perot quantum-well lasers by injection-locking

Theory and experiment for dc and small-signal electrical modulation of an injection-locked quantum-well (QW) Fabry-Perot laser are presented. Our experiment is realized by performing side-mode injection locking of a multiple-quantum-well (MQW) InGaAsP Fabry-Perot (FP) laser, which has the advantage of optical wavelength conversion. We first measure the dc characteristics and optical spectra of an injection-locked laser to define its locking range and linewidth enhancement factor. We then show experimentally that the bandwidth of an injection-locked semiconductor laser is 10.5 GHz, which is around twice the free-running electrical modulation bandwidth (5.3 GHz). The relaxation frequency of the injection-locked laser can be 3.5 times greater than the free-running value. Our theoretical model includes mode competition, gain saturation, low frequency roll-off, and optical confinement factor of the QW structure. The theory shows good agreement with our experimental results. We point out that the small-signal modulation of injection-locked lasers still suffers severely from low frequency roll-off, which comes from the carrier transport effect and parasitic effect of the bias circuit. If we can reduce those effects, the modulation bandwidth can be further increased to 15 GHz, which is around 3 times of the free-running value. (c) 2006 Elsevier Ltd. All rights reserved.