Optical noise characteristics of quantum dot lasers through external carrier noise reduction

This work theoretically explores the impact of external carrier noise from pump source on the optical noise characteristics of Quantum Dot (QD) lasers. The investigation includes simulations of the effects of a normal pump with a Gaussian carrier distribution and a quiet pump with a sub-Poisson carrier distribution on the spectral linewidth and Relative Intensity Noise (RIN). The results reveal that the spectral linewidth and RIN are significantly reduced when using a quiet pump compared to a normal pump across bias currents ranging from 1.5 to ten times the threshold currents, attributed to the lower carrier noise level of the quiet pump. At six times the threshold current, the spectral linewidth of the quiet pump decreases to 339.8 kHz, approximately half of that observed with normal pump, while the RIN value improves from -142.4 dB/Hz to -169.5 dB/Hz. Moreover, due to the larger external carrier noise of the normal pump at higher currents, this disparity in spectral linewidth and RIN between normal and quiet pump states becomes more pronounced, with the QD laser under normal pump exhibiting a broadening phenomenon that does not occur with the quiet pump. At ten times the threshold current, the spectral linewidth under normal pump broadens to 536.0 kHz, while under quiet pump, the spectral linewidth continues to decrease to 130.8 kHz, and the RIN value decreases from -145.5 dB/Hz to -172.4 dB/Hz. This work thus paves the way for the application of QD lasers in next-generation photonic integrated circuits by effectively reducing both the spectral linewidth and RIN of these optical sources through a straightforward and manageable strategy.