Quantum Dot Lasers
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Joined: Dec 2008
07-04-2009, 11:40 PM
Quantum Dot Lasers can be considered as a quantum leap in the development of lasers. Quantum Dots improve basically the laser emissions. This property of Quantum Dots is well utilized for fiber optic communication, which is now the leading subject under research and development. Quantum Dots are thus very well used in applications fiber optic communication. The remaining major division of the field of quantum electronics deals with the interactions of coherent light with matter and again leads to a wide range of all-optical and optoelectronic devices.
Basically Quantum Dots are made of InGaAs or simply GaAs structures. Also the possibility for extended wave length (>1.1Ã‚Âµm) emission from GaAs based devices is an important characteristic of Quantum Dots. The QDs are formed by an optimized growth approach of alternating sub-monolayer deposition of column III and column V, constituents for optoelectronic device fabrication. Thus there is a large energy separation between states.The infrastructure of the Information Age has to date relied upon advances in microelectronics to produce integrated circuits that continually become smaller, better, and less expensive. The emergence of photonics, where light rather than electricity is manipulated, is posed to further advance the Information Age. Central to the photonic revolution is the development of miniature light sources such as the Quantum dots(QDs).
Today, Quantum Dots manufacturing has been established to serve new datacom and telecom markets. Recent progress in microcavity physics, new materials, and fabrication technologies has enabled a new generation of high performance QDs. This presentation will review commercial QDs and their applications as well as discuss recent research, including new device structures such as composite resonators and photonic crystals Semiconductor lasers are key components in a host of widely used technological products, including compact disk players and laser printers, and they will play critical roles in optical communication schemes. The basis of laser operation depends on the creation of non-equilibrium populations of electrons and holes, and coupling of electrons and holes to an optical field, which will stimulate radiative emission. . Other benefits of quantum dot active layers include further reduction in threshold currents and an increase in differential gain-that is, more efficient laser operation.
Since the 1994 demonstration of a quantum dot (QD) semiconductor laser, the research progress in developing lasers based on QDs has been impressive. Because of their fundamentally different physics that stem from zero-dimensional electronic states, QD lasers now surpass the established planar quantum well laser technology in several respects. These include their minimum threshold current density, the threshold dependence on temperature, and range of wavelengths obtainable in given strained layer material systems. Self-organized QDs are formed from strained-layer epitaxy. Upon reaching such conditions, the growth front can spontaneously reorganize to form 3-dimensional islands. The greater strain relief provided by the 3-dimensionally structured crystal surface prevents the formation of dislocations. When covered with additional epitaxy, the coherently strained islands form the QDs that trap and isolate individual electron-hole pairs to create efficient light emitters.
Optimizing the QD characteristics for use as practical, commercial light sources is based on controlling their density, shape, and uniformity during epitaxy. In particular, the QD's shape plays a large role in determining its dynamic response, as well as the temperature sensitivity of the laser's characteristics. Their density, shape, and uniformity also establish the optical gain of a QD ensemble. All three physical characteristics can be engineered through the precise deposition conditions in which temperature, growth rate, and material composition are carefully controlled.
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