Frequency tuning of a double-heterojunction algaas/gaas vertical-cavity surface-emitting laser by a serial integrated modulator diode

Frequency tuning of a vertical-cavity surface-emitting laser (VCSEL) achieved through the monolithical integration of a modulator diode is reported. Current injection into the modulator diode locally changes the refractive index. This in turn leads to a shift of the Fabry-Perot-resonances of the microcavity. The experimental results show a gradient of a frequency blue-shift up to 0.93 GHz/mA by the modulator current. The maximum obtained frequency shift was 14 GHz at 15 mA modulator current. The useful tuning range is at present restricted to approximately 40 mA modulator current due to thermal effects. The onset of these effects leads to a bending over of the frequency shift from a Plasma effect dominated regime to a thermally dominated regime and in turn to a frequency red-shift. A simple theoretical model considering Plasma effect and Joule effect agrees well with the experimental data and predicts a maximum value for the gradient of frequency shift of 1.15 GHz/mA with the given structure.