Low Threshold 1.55-μm-Band Si-Photonics-Based Heterogeneous Integrated Quantum Dot Tunable Laser

In recent years, information and communication traffic has exponentially increased in datacenter networks, therefore, research and development of large-capacity transceivers are actively carried out. In particular, compact photonic integrated circuits (PICs) using Si photonics (SiPh) technology are expected to achieve large integration, large capacity, and low power consumption[1]. So far, we have studied quantum dot (QD) and its optical devices [2] because it has the features such as low consumption energy, high temperature stability, high speed response, and so on. In addition, we have also demonstrated heterogeneous integrated tunable laser source with QD reflective semiconductor optical amplifier (RSOA) and SiPh-based PIC and indicated fundamental characteristics of the device [3]. However, it is necessary to further improve the characteristics such as the threshold current, the optical output power, and the wavelength controllability. In this paper, we fabricated a heterogeneous integrated QD tunable laser source emitting in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.55-\mu \mathrm{m}$</tex> band, and demonstrated that the threshold current could be made decreased to 52.2 mA and fine tunability of lasing wavelength by changing the design of SiPh optical device.