High Occupancy Effects and Condensation Phenomena in Semiconductor Microcavities and Bulk Semiconductors
Semiconductor microcavities are micron scale photonic structures in which quantum wells are embedded within a high finesse Fabry-Perot cavity, the whole structure being prepared by high precision, modern crystal growth techniques [1 ]. In such structures
- PDF / 2,658,077 Bytes
- 17 Pages / 439 x 666 pts Page_size
- 75 Downloads / 172 Views
High Power Quantum Dot Lasers
Christian Ribbat and Roman Sellin
15.1
High Power Laser Diodes
Motivation for and applications of high power diode lasers are briefly summarized, followed by a short description of the main technological approaches to meet the desired application criteria. In 15.2 the quantum dot (QD) growth in respect to laser applications and the heterostructure QD laser design are discussed and key results of high power QD lasers are presented. 15.1.1
Applications of High Power Laser Diodes
High power diode lasers are commonly used as pump sources for either fiber amplifiers like EDFAs (erbium doped fiber amplifiers) or for solid state lasers like Nd:YAG-lasers. However, the economically most relevant application of high power lasers is in telecommunication. Diode lasers at 980 nm are commonly used as optical pump sources for erbium doped fiber amplifiers for long distance optical fiber communication at 1.55/lm. In recent years diode lasers also found applications in direct material processing like welding or metal hardening (carburisation) [1]. Advantages are high efficiency, high optical output power, compactness and modularity of these systems. With the concept of laser bars high optical output powers of several hundred Watt up to kW were demonstrated in continuous-wave operation [2-5]. Due to high wall-plug efficiencies (50%-60%) cooling systems can be kept small. Thus compact modules can be realized. A relevant future application might also be the optical pumping of other fiber amplifiers, like thulium or erbium doped fluoride fiber lasers which emit in the green and blue spectral range [6]. As thulium can be pumped very efficiently at 1120 nm, such a system would be very interesting for future laser display technologies. Nevertheless high power laser diodes beyond 1100 nm, based on standard InGaAs/GaAs quantum well technology, are presently commercially not available. 15.1.2
Requirements for High Power Laser Diodes
High power laser diodes are operated at very high injection currents to reach the required high output powers. To manage the high thermal load generated by high electric and optic power densities within the laser device, good M. Grundmann (ed.), Nano-Optoelectronics © Springer-Verlag Berlin Heidelberg 2002
354
Christian Ribbat and Roman Sellin
thermal stability of threshold current and quantum efficiency is required. A corresponding problem due to the very high optical power density at the front facet is facet degradation. Especially catastrophic optical mirror damage (COD) results in sudden failure of the device. As most applications demand coupling of the emitted radiation into optical fibers, sophisticated approaches are used to increase coupling efficiency, e.g. the use of large optical cavity (LaC) wave-guide structures for optimized far field distribution. High wall-plug efficiency is needed to avoid that the output power of a laser diode is limited by thermal roll-over. This is realized by high internal quantum efficiency, low internal optical loss and an optimize
Data Loading...
