Tapping into undeveloped frequency bands, a new ultracompact heterogeneous-wavelength laser diode could enable higher-capacity optical data transmission systems. The device combines silicon photonics and quantum-dot (QD) technology and demonstrates wide-range tuning operation around 1230 nm, according to researchers at Tohoku University and the National Institute of Information and Communications Technology (NICT) in Japan. Its optical gain medium is made up of high-quality InAs QDs grown with the sandwiched subnano separator technique. The wavelength-tunable filter was constructed with ring resonators fabricated using silicon photonics techniques. The novel heterogeneous-wavelength tunable laser diode consists of quantum dot and silicon photonics technology. Courtesy of Tomohiro Kita/Tohoku University. Current high-capacity optical transmission systems are based on wavelength-division multiplexing (WDM) systems with dense frequency channels. Frequency channels in the standard C-band (1530 to 1565 nm) are overcrowded, and the frequency utilization efficiency is saturated in such WDM systems, the researchers said. On the other hand, there are extensive and unexploited frequency resources at near-infrared wavelengths (1000 to 1300 nm). The new diode is a promising candidate to realize a compact and broadband light source for this region, the researchers said. Funding came from the Strategic Information and Communications R&D Promotion Program (SCOPE) of Japan's Ministry of Internal Affairs and Communications. The research was published in Applied Physics Express (doi: 10.7567/APEX.8.062701). For more information, visit www.tohoku.ac.jp.