Semiconductor lasers are of great importance to modern communication because of the enormous bandwidth they provide in transmitting information over optical fibers. Quantum dot (QD) lasers (based on small clumps of material) haves significant advantages over the standard technology (which are quantum wells (QWs) based on thin layers of material), including much greater temperature-insensitivity and inherently low chip. However, QD-lasers have not been adopted into commercial laser transmitters largely because no holographically-fabricated, loss-free, single-mode QD-devices at the technologically-important wavelength ranges have yet been demonstrated. The objective is to demonstrate the fabrication of these devices with commercially-feasible techniques.
Intellectual Merit Because the work will be done in direct collaboration with Ortel-Emcore (a semiconductor laser company), successful fabrication of the devices will lead immediately to investigation of their adoption into telecommunications applications. With loss-free devices, the inherent performance and fundamental limits of single-mode QD lasers can be finally evaluated. This proposed mixed-growth method for single mode lasers will be an enabling technology for the widespread adoption of QD material into the telecommunications market.
Broader Impacts The many advantages of QD material suggest applications where it would be superior to quantum well lasers. This technology will drive lower-cost, high-bandwidth optical communications links. The close industrial-academic collaboration, including seminars by Ortel scientists given at Binghamton, seminars by the PI at Ortel and local industries, and on-site work by a graduate student at Ortel-Emcore, are a valuable component to this project and will be excellent experience for the students involved.
Semiconductor lasers are the primary technology which transmits information across optical fiber. Typically, semiconductor lasers are made with quantum wells, thin layers of semiconductor material. Though currently quantum wells are the best material, their properties are strongly affected by the temperature. In addition, the color of the light they emit changes as the device transmits information due to chirp; this limits the length that information that can be transmitted on a fiber to about 100km. Quantum dots are small chunks of semiconductor material, which can also be designed to emit light and are both less sensitive to temperature and have lower theoretical change in emitted color with change in current. For both these reasons, they may potentially be better transmitters than those based on quantum wells. One barrier to adopting quantum dot material into transmitters was the lack of a process to make single-wavelength (or color) devices from quantum dot material in a manufacturable way. In this project, semiconductor lasers that emitted light of only a single color were realized with a process very similar to how quantum well lasers are fabricated. This work was done in collaboration with Emcore, a major laser manufacturer. These lasers are not yet suitable for commercial transmitters, but our collaboration with Emcore is continuing to try to improve their properties. In addition to a fabrication method, we also demonstrated that these devices have a unique property of low thermal conductivity. Heat does not conduct readily through them. This is a somewhat deleterious property for lasers, but suggests that this material may have applications in thermoelectrics, in which energy can be collected from a temperature difference. Other possible applications may result from study of the novel properties of these quantum dot lasers.
