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John Bowers, a academician at the American academy of engineering, has developed a tiny silicon quantum dot laser that can be modulated directly
source :China laser   Time :2017-8-13

       Recently, the optoelectronic research team led by the American Academy of Engineering and Professor John Bowers of the University of California, Santa Barbara developed a directly modulated silicon quantum dot microlaser. The laser is epitaxially grown and integrated on a silicon wafer compatible with CMOS processes. The use of quantum dot-specific substrate defects, sidewall non-radiative recombination effects are reduced, and the buffer layer is optimized to reduce the dislocation density of the interface between the III-V material and the silicon wafer. Excellent laser performance on heterogeneous growth material systems with large differences in reverse domain, lattice mismatch, and thermal expansion coefficient: single mode lasing in the 1.3 μm communication band and high temperature at 103 K characteristic temperature Operating environment stability and low threshold current of 3 mA, 3 dB bandwidth of 6.5 GHz. Related results published in Photonics Research, Volume 2, Issue 20, 2018



       Figure 1 Schematic diagram of the device's epitaxial structure. Illustration: Atomic Force Microscope Topography of Quantum Dots


       Moore's Law predicts that the number of transistors in high-density integrated circuits will roughly double every two years. Correspondingly, the growing demand for miniaturization and large-scale integrated photonic components in large-scale computers and optical communication applications on silicon arrays is also the eternal melody of integrated optoelectronics. Quantum dot lasers have three-dimensional limitations due to the movement of carriers in the quantum dots in the material, with unique substrate defects affecting the reduced performance. This has made quantum dot-based epitaxial growth devices on silicon have made great breakthroughs in recent research. In order to further reduce the energy consumption of optoelectronic devices connected on-chip, the research on small-sized micro-ring lasers with single-mode lasing characteristics has attracted great attention.


       The use of quantum dots for the non-radiative composite effect of sidewalls is reduced. This study is based on the idea of a novel laser architecture that combines microring resonators with quantum dots to epitaxially grow small electrically pumped quantum dot lasers on silicon. And through the complicated process flow, the problem that the electrode metallization is limited by the micro-sized cavity and the optical loss caused by the defects of the whispering-wall mode (WGM) in the process are effectively solved. Compared with the previous experimental results, the results of this study (1) simultaneously achieved high temperature working environment stability (103 K characteristic temperature) and low threshold current (3 mA); (2) reported epitaxial growth of quantum dots on silicon The modulation characteristics of the laser (3 dB bandwidth of 6.5 GHz); (3) The system analyzed the performance degradation of the device with size, and verified the possibility of dense large-scale integration of epitaxially grown quantum dot micro devices on silicon.



       Fig. 2 (a) Schematic diagram of the device structure of the microring quantum dot laser; (b) Scanning electron microscope image; (c) Infrared microscope image of the device under lasing


       Professor John Bowers, deputy director of the Integrated Photonics Manufacturing Innovation Center in the United States, said that this work is an important step in the development of an epitaxial process for directly growing III-V elements on silicon substrates to replace the traditional wafer bonding process. Scale manufacturing while reducing costs, reducing size and reducing power consumption. The first author, Dr. Wan Yating, said that his group will focus on integrating coupled waveguides to effectively derive lasers. At the same time, distributed feedback (DFB) lasers, tunable lasers and other device designs have been completed. The group will combine photonic links with waveguides, modulators, optical switches, detectors and other silicon photonic devices and integrate them into the same material. The platform realizes high-speed, large-capacity on-chip optical communication.