Sony Semiconductor Solutions Corporation and the National Institute of Information and Communications Technology (NICT, Japan) have developed a surface-emitting laser architecture that uses quantum dots as the optical gain medium. According to its developers, the laser, which is designed for use in optical fiber communication systems, is the world's first practical electrically driven VCSEL operating at 1550 nm, the standard wavelength for optical fiber communication, using quantum dots as the optical gain material. NICT completed researchers developed a high-precision crystal growth method for compound semiconductors using molecular beam epitaxy. The developed technology can be used to precisely grow a distributed Bragg reflector (DBR) by strictly controlling the ratio of materials in the crystal growth. Using the method, the team realized a semiconductor DBR with a high reflectivity exceeding 99% even at 1550 nm. Next, strain-compensation techniques were applied to VCSEL production to cancel the internal crystal strain that occurs around the quantum dots, which increases the density of the quantum dots and improves the light-emitting performance. (a) Without a tunnel junction, current flows toward the bottom of the electrode and excites the quantum dot; however, the electrode obstructs light extraction. (b) In the presence of a tunnel junction, the current path can be redirected electrode-free regions, facilitating light extraction. Courtesy of Optics Express. Sony contributed to the second part of the project; the company conceptualized a device design and fabrication process that enables highly efficient current injections using a tunnel junction structure. VCSELs emit light perpendicular to the wafer surface; therefore, even if quantum dots emit light, conventional electrode placement obstructs light extraction. The tunnel junction permitted efficient current flow while facilitating light extraction employing a precise device process. Through the integration of these two technologies, researchers lased VCSELs using quantum dots at 1550 nm as a light-emitting material with a small current of 13 mA. Furthermore, polarization fluctuations were eliminated, resulting in a stable output. VCSELs using quantum dots as optical gain materials maintain temperature stability and exhibit scalable structures that enable mass production. The researchers aim to conduct advanced technical studies on quantum dot-based VCSEL technology to further enhance the capacity and reduce power consumption in optical fiber communication systems beyond the 5G era. The research was published in Optics Express (www.doi.org/10.1364/OE.551300).