Dynamic behavior of injection-locked two-state quantum dot lasers

Abstract

Quantum dot (QD) lasers with excited state (ES) emission exhibit superior characteristics compared with their ground state (GS) emission. Here, we have developed a model that predicts the small-signal modulation response and relative intensity noise (RIN) of a QD laser capable of emitting from both GS and ES resonance energies in free-running and also under optical injection-locking conditions. The GS resonance wavelength in the injection-locked laser benefits a considerable RIN reduction of ∼20 dB/Hz before a lasing threshold of ES emission, while the ES resonance wavelength is promoted more regarding the modulation bandwidth around the lasing threshold, which is almost doubled, especially at very low injection ratios. Contrary to the GS, the injected locked RIN is the poorest property of ES emission, which shows ∼10 dB/Hz enhancement at the lasing threshold and larger injection ratios. It was affirmed that the RIN response of ES emission can be significantly reduced at the cost of setup complexity through simultaneous injection locking of both wavelengths. A 3 dB modulation bandwidth of ∼18 GHz is achieved for ES emission, which is more than twice that of the free-running operation of ES emission.