Terahertz Electro-Optics in Semiconductor Nanostructures

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This research focuses on the fabrication and investigation of a novel class of semiconductor electro-optical devices. These devices will enable the study of quantum dynamics of many-body systems driven by strong periodic fields. They also form a cornerstone of a novel approach to utilizing the full 400 Terabit/s communications bandwidth of optical fibers. The devices will use antennas to couple THz fields with frequency f(THz) into a small region containing semiconductor quantum wells or superlattices. Near-Infrared (NIR) radiation with frequency f(NIR), near the semiconductor band-gap, will probe the response of the active region. Absorption, and the emission of sidebands at frequencies f(sideband) = f(NIR) +/- nf(THz), where n=integer, will be monitored. One expects at high THz fields large shifts in interband absorption resonances, and sideband intensities, which oscillate with THz field strength. In doped quantum wells, efficient sideband emission is expected when THz radiation is resonant with the transition between the ground and first excited sub-bands. At higher THz intensities, nonlinear phenomena like period-doubling bifurcations to chaos have been predicted. This research offers graduate and undergraduate students broad training in semiconductor physics, device fabrication, and optics, which will prepare them for future careers in government, industry, or academe.%%%One of today's outstanding technological problems is the rapid communication of digital information. The threads of the Internet are optical fibers, each of which has the potential to carry information at the rate of 40 trillion bits per second. Existing technology is capable of using only 1% of this bandwidth, by sending 10 gigabits per second on several dozen optical frequencies simultaneously. This research focuses on fabricating and testing a new class of nonlinear optical devices, which are capable of selectively shifting information carried on one optical frequency to another one several Terahertz away. The proposed devices are also expected to exhibit a variety of surprising phenomena, which test our understanding of quantum-mechanical systems driven very far from equilibrium. This research offers graduate and undergraduate students broad training in semiconductor physics, device fabrication, and optics, which will prepare them for future careers in government, industry, or academic science.***